Topic: Cardiovascular Physiology; Subtopic: Cardiac Pacemaker Activity
KEYWORD DEFINITIONS
• Pacemaker potential – Slow diastolic depolarization in nodal tissue
• SA node – Primary pacemaker with highest intrinsic firing rate
• AV node – Secondary pacemaker with slower conduction
• Purkinje fibers – Fastest conduction but slower firing rate
• Action potential – Rapid change in membrane potential enabling impulse propagation
Lead Question – 2015
1. Action potential generates at fastest rate in?
A) SA node
B) AV node
C) Bundle of His
D) Purkinje fibers
Explanation:
The SA node generates action potentials at the fastest intrinsic rate of approximately 60–100 beats per minute, making it the primary pacemaker of the heart. Its steep phase 4 depolarization slope allows rapid spontaneous impulse formation. AV node, Bundle of His, and Purkinje fibers have progressively slower intrinsic rates. Although Purkinje fibers conduct impulses rapidly, their firing rate is slower than that of the SA node. Therefore, the correct answer is **SA node**. Understanding intrinsic pacemaker hierarchy is vital for interpreting arrhythmias and pacemaker activity.
2. Which cardiac tissue has the fastest conduction velocity?
A) SA node
B) Atrial muscle
C) Purkinje fibers
D) AV node
Explanation:
Purkinje fibers exhibit the fastest conduction velocity, approximately 2–4 m/s, ensuring rapid and synchronous ventricular activation. This is essential for efficient ejection of blood during systole. SA and AV nodes conduct impulses slowly due to calcium-dependent depolarization, while atrial muscle conducts at an intermediate speed. Thus, the correct answer is **Purkinje fibers**, which possess large diameter fibers and abundant gap junctions facilitating rapid electrical propagation across the ventricles.
3. A patient presents with complete heart block. Which structure becomes the pacemaker?
A) SA node
B) AV node
C) Purkinje fibers
D) Atrial muscle
Explanation:
In complete heart block, atrial impulses fail to reach the ventricles. As a result, a ventricular escape rhythm develops, typically originating from Purkinje fibers or the Bundle of His. These tissues have an intrinsic rate of about 20–40 beats per minute. Since SA and AV nodes cannot propagate impulses downward, the ventricular conduction system becomes the pacemaker. Therefore, the answer is **Purkinje fibers**, which maintain minimal ventricular activity despite the block.
4. Phase 4 depolarization in SA node is primarily due to which current?
A) Fast sodium current
B) Inward potassium current
C) Funny current (If)
D) Calcium-activated chloride current
Explanation:
SA nodal phase 4 depolarization is dominated by the “funny current” (If), carried mainly by sodium ions. This current activates on hyperpolarization and contributes to gradual diastolic depolarization, allowing spontaneous pacemaker activity. Fast sodium channels are absent in SA nodal cells, and inward potassium currents decrease during phase 4. Thus, the correct answer is **Funny current (If)**, which is crucial for initiating rhythmic impulses.
5. A 65-year-old with bradycardia has a pacemaker set to mimic normal pacemaker firing. What intrinsic rate should it replicate?
A) 20–40 bpm
B) 40–60 bpm
C) 60–100 bpm
D) 100–120 bpm
Explanation:
A normal SA node fires at an intrinsic rate of 60–100 bpm. Artificial pacemakers typically aim to maintain a physiologic resting heart rate within this range unless specific clinical considerations require lower targets. AV node fires more slowly (40–60 bpm) and Purkinje fibers slower still (20–40 bpm). Therefore, the device should replicate **60–100 bpm**, matching the natural sinus rhythm range for optimal hemodynamics.
6. Which cardiac tissue shows the slowest conduction velocity?
A) SA node
B) AV node
C) Ventricular muscle
D) Purkinje fibers
Explanation:
The AV node has the slowest conduction velocity (0.01–0.05 m/s), which allows adequate ventricular filling by delaying impulse transmission from atria to ventricles. SA node conducts marginally faster, while ventricular muscle and especially Purkinje fibers conduct at significantly higher speeds. Thus, the correct answer is **AV node**, whose delay function is vital for synchronized cardiac function.
7. A young athlete experiences occasional ectopic beats originating from the AV node. What is the intrinsic rate of this pacemaker?
A) 20–40 bpm
B) 40–60 bpm
C) 60–100 bpm
D) 120–140 bpm
Explanation:
The AV node has an intrinsic pacemaker rate of 40–60 bpm. Ectopic pacemakers in this region fire at this characteristic speed, slower than the SA node but faster than Purkinje fibers. Such ectopic beats may appear in healthy individuals or with increased vagal tone. Therefore, the correct answer is **40–60 bpm**, reflecting the natural rhythm of this secondary pacemaker.
8. Hyperpolarization-activated cyclic nucleotide–gated (HCN) channels are responsible for?
A) Phase 0 depolarization in Purkinje fibers
B) Phase 4 pacemaker depolarization
C) Plateau phase in ventricular muscle
D) Repolarization in atrial muscle
Explanation:
HCN channels generate the If current that drives phase 4 diastolic depolarization in pacemaker tissues like SA and AV nodes. These channels activate upon hyperpolarization and regulate rhythmic automaticity. They do not contribute to phase 0 depolarization (which in Purkinje fibers is sodium-mediated) nor the plateau phase (calcium-mediated). Therefore, the correct answer is **Phase 4 pacemaker depolarization**, essential for spontaneous impulse initiation.
9. A patient with ischemic injury to the SA node relies on which pacemaker next in hierarchy?
A) Purkinje fibers
B) AV node
C) Atrial muscle
D) Bundle of His
Explanation:
When the SA node fails, the AV node becomes the dominant pacemaker due to its intrinsic firing rate of 40–60 bpm. The Bundle of His and Purkinje fibers fire slower and serve as tertiary pacemakers. Atrial muscle does not possess intrinsic pacemaking capability. Therefore, the correct answer is **AV node**, the natural backup pacemaker in such conditions.
10. Which ion primarily contributes to phase 0 depolarization in SA nodal action potentials?
A) Sodium
B) Chloride
C) Calcium
D) Potassium
Explanation:
SA nodal cells lack fast sodium channels; therefore, phase 0 depolarization is mediated predominantly by L-type calcium channels. This results in slower upstroke velocity compared with ventricular muscle. Thus, the correct answer is **Calcium**, which enables the characteristic slow depolarization seen in nodal tissues and contributes to the controlled pacing of cardiac rhythm.
11. A patient with damaged Purkinje fibers will show which change?
A) Decreased conduction velocity
B) Increased intrinsic firing rate
C) Increased contractility
D) Faster SA nodal activity
Explanation:
Purkinje fibers are the fastest conducting components of the heart. Damage to them reduces conduction velocity, impairing synchronous ventricular contraction. Their intrinsic firing rate is low (20–40 bpm) and does not increase significantly with injury. Contractility and SA nodal activity are not directly influenced by Purkinje damage. Therefore, the correct answer is **Decreased conduction velocity**, which clinically may contribute to arrhythmias and dyssynchrony.
Chapter: Neurophysiology; Topic: Sensory Receptors; Subtopic: Mechanoreceptors
KEYWORD DEFINITIONS
• Mechanoreceptors – Detect mechanical deformation
• Pacinian corpuscle – Responds to vibration and deep pressure
• Meissner corpuscle – Detects light touch
• Merkel disc – Detects pressure and texture
• Ruffini ending – Detects stretch and sustained pressure
Lead Question – 2015
1. Vibration sense is detected by which type of receptor?
A) Merkel's disc
B) Ruffini's end organ
C) Pacinian corpuscle
D) Meissner's corpuscle
Explanation:
Pacinian corpuscles are rapidly adapting mechanoreceptors specialized for detecting high-frequency vibration and deep pressure. Their onion-like lamellar structure allows them to respond quickly to changes in mechanical stimuli. In contrast, Merkel discs detect texture, Meissner corpuscles detect light touch, and Ruffini endings detect skin stretch. Therefore, the correct answer is Pacinian corpuscle. These receptors play an essential role in proprioception and fine manipulation tasks requiring vibration sensing. Damage to deep sensory pathways can reduce vibration sense, making this receptor clinically relevant in neurological examinations.
2. Which receptor adapts the fastest among cutaneous mechanoreceptors?
A) Merkel disc
B) Ruffini ending
C) Pacinian corpuscle
D) Free nerve endings
Explanation:
Pacinian corpuscles show extremely rapid adaptation due to their layered lamellar structure, enabling them to detect high-frequency vibration and abrupt mechanical changes. Merkel discs and Ruffini endings are slowly adapting, while free nerve endings are polymodal and variable in adaptation. Because Pacinian corpuscles stop firing quickly once the stimulus stabilizes, they are ideal for detecting transient mechanical events. Thus, the correct answer is Pacinian corpuscle. Understanding receptor adaptation helps clinicians evaluate sensory deficits related to neuropathy or dorsal column lesions.
3. A patient with posterior column lesion loses vibration sense. Which fiber type carries this sensation?
A) A-delta fibers
B) C fibers
C) A-beta fibers
D) B fibers
Explanation:
Vibration sense is transmitted via large-diameter, heavily myelinated A-beta fibers that rapidly conduct mechanosensory information from receptors such as Pacinian and Meissner corpuscles. These fibers ascend in the dorsal columns to the medulla. A-delta fibers carry fast pain, C fibers carry slow pain and temperature, and B fibers are autonomic. Therefore, the correct answer is A-beta fibers. Loss of vibration sense is a classical feature of dorsal column dysfunction, as seen in vitamin B12 deficiency or tabes dorsalis.
4. Which receptor is primarily responsible for detecting skin stretch during grasping movements?
A) Meissner corpuscle
B) Ruffini ending
C) Pacinian corpuscle
D) Hair follicle receptor
Explanation:
Ruffini endings are slowly adapting mechanoreceptors sensitive to skin stretch and joint movement. They provide critical feedback during handgrip control, helping maintain steady pressure. Meissner corpuscles detect light touch, Pacinian corpuscles detect vibration, and hair follicle receptors detect hair movement. Thus, the correct answer is Ruffini ending. These receptors contribute significantly to proprioception and are often assessed indirectly during neurological examinations of deep sensory functions.
5. A diabetic patient presents with reduced vibration sense in the feet. Which pathway is compromised?
A) Spinothalamic tract
B) Corticospinal tract
C) Dorsal column–medial lemniscal pathway
D) Reticulospinal tract
Explanation:
The dorsal column–medial lemniscal pathway carries fine touch, vibration, and proprioception using large myelinated fibers. In diabetic neuropathy, early damage to these fibers leads to reduced vibration perception. The spinothalamic tract carries pain and temperature, while corticospinal and reticulospinal tracts are motor pathways. Therefore, the correct answer is Dorsal column–medial lemniscal pathway. Assessing vibration sense using a tuning fork is a key clinical test in diabetic neuropathy evaluation.
6. Which receptor is MOST sensitive to low-frequency vibration (e.g., 30–50 Hz)?
A) Pacinian corpuscle
B) Meissner corpuscle
C) Merkel disc
D) Ruffini ending
Explanation:
Meissner corpuscles are rapidly adapting receptors responsible for detecting low-frequency vibration and light touch, especially in glabrous skin. Pacinian corpuscles detect high-frequency vibration, Merkel discs detect sustained pressure, and Ruffini endings detect stretch. Thus, the correct answer is Meissner corpuscle. These receptors are abundant in fingertips and play a major role in tactile discrimination and grip control.
7. A 40-year-old presents with impaired proprioception and vibration sense. Which vitamin deficiency is most likely?
A) Vitamin A
B) Vitamin B12
C) Vitamin D
D) Vitamin K
Explanation:
Vitamin B12 deficiency leads to demyelination of the dorsal columns, causing loss of vibration sense, proprioception, and gait disturbances. Vitamins A, D, and K do not typically affect dorsal column pathways. Therefore, the correct answer is Vitamin B12. Early detection is essential because neurological deficits can become irreversible if treatment is delayed.
8. Merkel discs are best known for detecting which sensation?
A) Vibration
B) Skin stretch
C) Deep pressure
D) Texture and form
Explanation:
Merkel discs are slowly adapting mechanoreceptors specialized for detecting texture, shape, and fine spatial details, enabling high-resolution tactile discrimination. They respond to sustained pressure but not to vibration. Thus, the correct answer is Texture and form. Their dysfunction can impair fine touch perception, affecting tasks requiring precision such as reading Braille.
9. A patient reports inability to detect vibration but retains crude touch. Which spinal tract is intact?
A) Dorsal column
B) Spinothalamic tract
C) Spinoreticular tract
D) Dorsal spinocerebellar tract
Explanation:
Crude touch is carried by the spinothalamic tract, while vibration sense is transmitted via the dorsal columns. Loss of vibration with preserved crude touch suggests dorsal column dysfunction with intact spinothalamic function. Therefore, the correct answer is Spinothalamic tract. This distinction is clinically valuable in assessing sensory loss patterns in spinal cord lesions.
10. Which receptor is MOST abundant in the fingertips and essential for fine tactile discrimination?
A) Pacinian corpuscle
B) Meissner corpuscle
C) Ruffini ending
D) Free nerve endings
Explanation:
Meissner corpuscles are concentrated in glabrous skin, especially fingertips, where they detect light touch and fine tactile detail. Pacinian corpuscles detect vibration, Ruffini endings detect stretch, and free nerve endings detect pain and temperature. Thus, the correct answer is Meissner corpuscle. Their density makes fingertips the most sensitive region for performing delicate tactile tasks.
11. A patient cannot perceive high-frequency vibration applied to the skin. Which receptor is dysfunctional?
A) Merkel disc
B) Meissner corpuscle
C) Pacinian corpuscle
D) Hair follicle receptor
Explanation:
High-frequency vibration (around 250 Hz) is detected primarily by Pacinian corpuscles, which are rapidly adapting deep mechanoreceptors. Meissner corpuscles detect low-frequency vibration, Merkel discs detect pressure, and hair follicle receptors detect hair movement. Therefore, the correct answer is Pacinian corpuscle. Their loss signals dysfunction in deep mechanoreceptor pathways, often associated with peripheral neuropathy.
Chapter: Neurophysiology; Topic: Sensory Receptors; Subtopic: Mechanoreceptors – Vibration Sensation
KEYWORD DEFINITIONS
• Mechanoreceptors – Detect mechanical deformation
• Deep receptors – Located in deeper tissues; detect vibration and pressure
• Pacinian corpuscle – Primary receptor for vibration
• Meissner corpuscle – Detects light touch and low-frequency vibration
• Posterior column pathway – Carries vibration and proprioception
Lead Question – 2015
1. Vibration sense is detected by?
A) Nociceptors
B) Deep receptors
C) Superficial receptors
D) None of the above
Explanation:
Vibration sense is primarily detected by deep receptors, especially Pacinian corpuscles located in deeper layers of the skin, joints, and fascia. These receptors are rapidly adapting mechanoreceptors sensitive to high-frequency vibration. Nociceptors detect pain, not vibration, while superficial receptors detect touch and texture rather than vibration. Therefore, the correct answer is Deep receptors. In clinical practice, vibration sense assessment helps evaluate the integrity of the dorsal column–medial lemniscal pathway, which is often impaired in conditions such as diabetic neuropathy and vitamin B12 deficiency.
2. Which receptor is MOST responsible for high-frequency vibration detection?
A) Merkel disc
B) Ruffini ending
C) Pacinian corpuscle
D) Free nerve endings
Explanation:
Pacinian corpuscles are deep, rapidly adapting mechanoreceptors specifically tuned to detect high-frequency vibration around 200–300 Hz. Their onion-like capsule structure enables rapid response to changes in mechanical pressure. Merkel discs detect texture, Ruffini endings detect stretch, and free nerve endings detect pain and temperature. Thus, the correct answer is Pacinian corpuscle. This receptor plays a key clinical role in assessing vibration sense during neurological examination using a tuning fork, especially in neuropathies and dorsal column lesions.
3. A patient with posterior column damage loses vibration sense. Which tract is affected?
A) Spinothalamic tract
B) Spinocerebellar tract
C) Dorsal column–medial lemniscal pathway
D) Reticulospinal tract
Explanation:
The dorsal column–medial lemniscal pathway carries vibration, fine touch, and proprioception. Damage to this pathway leads to loss of vibration sense, gait imbalance, and impaired position sense. Spinothalamic tract carries pain and temperature, spinocerebellar tract carries unconscious proprioception, and reticulospinal tract mediates motor modulation. Therefore, the correct answer is Dorsal column–medial lemniscal pathway. This distinction is vital in diagnosing neurological disorders such as tabes dorsalis or B12 deficiency.
4. Low-frequency vibration (30–50 Hz) is best detected by?
A) Pacinian corpuscle
B) Meissner corpuscle
C) Ruffini ending
D) Merkel disc
Explanation:
Meissner corpuscles are rapidly adapting superficial mechanoreceptors highly sensitive to low-frequency vibration and light touch. They are abundant in fingertips and glabrous skin, enabling tactile discrimination. Pacinian corpuscles detect high-frequency vibration, Ruffini endings detect stretch, and Merkel discs detect sustained pressure and texture. Thus, the correct answer is Meissner corpuscle. These receptors play a central role in fine motor tasks and early detection of surface changes.
5. A diabetic patient presents with impaired vibration sense. Which structure is most likely damaged?
A) Spinothalamic tract fibers
B) A-beta fibers
C) A-delta fibers
D) C fibers
Explanation:
A-beta fibers are large, myelinated sensory fibers responsible for transmitting vibration and fine touch sensation from mechanoreceptors such as Pacinian and Meissner corpuscles. These fibers are highly vulnerable in diabetic neuropathy, leading to early loss of vibration sense. Spinothalamic fibers carry pain and temperature, A-delta fibers carry fast pain, and C fibers carry slow pain. Therefore, the correct answer is A-beta fibers. Assessment using a tuning fork is a crucial clinical tool for early neuropathy detection.
6. Which receptor detects sustained pressure and contributes to proprioception?
A) Pacinian corpuscle
B) Ruffini ending
C) Meissner corpuscle
D) Hair follicle receptor
Explanation:
Ruffini endings are slowly adapting receptors that detect skin stretch and sustained pressure. They provide continuous feedback regarding finger position and grip modulation. Pacinian corpuscles detect vibration, Meissner corpuscles detect light touch and low-frequency vibration, and hair follicle receptors detect hair movement. Thus, the correct answer is Ruffini ending. These receptors are essential for proprioceptive accuracy during tasks requiring hand stability.
7. A 55-year-old alcoholic patient has loss of vibration and position sense. What deficiency is most likely?
A) Folate
B) Vitamin A
C) Vitamin B12
D) Vitamin C
Explanation:
Vitamin B12 deficiency causes demyelination of the dorsal columns, resulting in loss of vibration sense, proprioceptive deficits, and ataxic gait. Folate deficiency affects red cell production but not dorsal columns, while vitamins A and C do not cause such neurological deficits. Hence, the correct answer is Vitamin B12. Early diagnosis is essential because prolonged deficiency leads to irreversible neurological damage.
8. Which receptor is responsible for detecting texture and form discrimination?
A) Merkel disc
B) Pacinian corpuscle
C) Ruffini ending
D) Meissner corpuscle
Explanation:
Merkel discs are slowly adapting mechanoreceptors specialized for fine touch and texture discrimination. Located in the basal epidermis, they respond to sustained pressure and help identify object shape. Pacinian corpuscles detect vibration, Ruffini endings detect skin stretch, and Meissner corpuscles detect light touch. Thus, the correct answer is Merkel disc. These receptors are essential for reading Braille and performing detailed tactile tasks.
9. A patient cannot detect vibration but has intact pain and temperature. Which tract remains functional?
A) Dorsal column pathway
B) Corticospinal tract
C) Spinothalamic tract
D) Vestibulospinal tract
Explanation:
Pain and temperature sensations are carried by the spinothalamic tract, whereas vibration and proprioception are carried by the dorsal column pathway. If vibration sense is absent but pain and temperature remain intact, the spinothalamic tract is functioning. Therefore, the correct answer is Spinothalamic tract. This sensory dissociation helps localize lesions within the spinal cord.
10. Which receptor is primarily responsible for detecting high-frequency vibration applied to joints and deep tissues?
A) Meissner corpuscle
B) Pacinian corpuscle
C) Ruffini ending
D) Free nerve endings
Explanation:
Pacinian corpuscles are deep mechanoreceptors located in ligaments, joints, and subcutaneous tissues, making them ideal for detecting high-frequency vibration. Their rapid adaptation allows them to respond immediately to mechanical changes. Meissner corpuscles detect low-frequency vibration, Ruffini endings detect stretch, and free nerve endings detect pain and temperature. Thus, the correct answer is Pacinian corpuscle. These receptors are essential in proprioceptive feedback and vibration sense testing.
11. Which receptor is most affected when high-frequency vibration (e.g., tuning fork) cannot be perceived on examination?
A) Meissner corpuscle
B) Merkel disc
C) Pacinian corpuscle
D) Ruffini ending
Explanation:
High-frequency vibration is detected by Pacinian corpuscles, which are located deep within tissues and respond rapidly to mechanical changes. Meissner corpuscles detect low-frequency vibration, Merkel discs detect pressure and texture, and Ruffini endings detect stretch. Therefore, the correct answer is Pacinian corpuscle. In clinical practice, loss of vibration sense indicates dorsal column or peripheral nerve pathology, making this receptor highly relevant in neurological assessment.
Chapter: Neurophysiology; Topic: Sensory Receptors; Subtopic: Adaptation & Vibration Receptor Physiology
KEYWORD DEFINITIONS
• Mechanoreceptors – Sensory receptors responding to mechanical deformation
• Rapidly adapting receptors – Respond quickly to stimulus onset; detect vibration
• Slowly adapting receptors – Detect sustained pressure and stretch
• Pacinian corpuscle – Deep, rapidly adapting receptor for high-frequency vibration
• Meissner corpuscle – Rapidly adapting receptor for low-frequency vibration
Lead Question – 2015
1. Vibrations are detected by which types of receptors?
A) Slowly adapting
B) Rapidly adapting
C) Non-adapting
D) None of the above
Explanation:
Vibration is detected by rapidly adapting mechanoreceptors, primarily Pacinian and Meissner corpuscles. These receptors respond quickly at the start and end of a stimulus, making them ideal for sensing vibratory frequencies. Slowly adapting receptors detect sustained pressure and stretch, while non-adapting receptors are not typical in the somatosensory system. Therefore, the correct answer is Rapidly adapting. Clinically, vibration testing using a tuning fork evaluates large-fiber dorsal column integrity, which is crucial in diagnosing neuropathies and posterior column disorders such as tabes dorsalis and vitamin B12 deficiency.
2. Which receptor detects high-frequency vibration (≈250 Hz)?
A) Merkel disc
B) Ruffini ending
C) Pacinian corpuscle
D) Free nerve endings
Explanation:
Pacinian corpuscles are deep, rapidly adapting mechanoreceptors specialized for detecting high-frequency vibration around 200–300 Hz. Their lamellated structure permits rapid response to transient mechanical stimuli. Merkel discs detect pressure and texture, Ruffini endings detect skin stretch, and free nerve endings respond to pain and temperature. Therefore, the correct answer is Pacinian corpuscle. High-frequency vibration assessment is vital in early detection of peripheral neuropathies, especially diabetic neuropathy.
3. A patient with dorsal column damage will MOST likely lose which sensation first?
A) Pain
B) Temperature
C) Vibration
D) Crude touch
Explanation:
The dorsal column–medial lemniscal pathway carries fine touch, vibration, and proprioception. Among these, vibration sense is often the earliest to be impaired, especially in neuropathies or spinal cord lesions. Pain and temperature are carried by the spinothalamic tract and remain intact initially. Crude touch can also be preserved due to overlapping pathways. Thus, the correct answer is Vibration. Testing with a 128 Hz tuning fork is a crucial bedside neurological examination tool.
4. Low-frequency vibration (30–50 Hz) is detected by which receptor?
A) Pacinian corpuscle
B) Merkel disc
C) Meissner corpuscle
D) Ruffini ending
Explanation:
Meissner corpuscles are rapidly adapting receptors located in glabrous skin, particularly fingertips, and are sensitive to low-frequency vibration and light touch. Pacinian corpuscles detect high-frequency vibration, Merkel discs detect texture and sustained pressure, and Ruffini endings detect skin stretch. Therefore, the correct answer is Meissner corpuscle. These receptors are essential for tasks involving fine tactile discrimination and grip modulation.
5. A diabetic patient presents with decreased vibration sense. Which fibers are most likely affected?
A) C fibers
B) A-delta fibers
C) A-beta fibers
D) B fibers
Explanation:
A-beta fibers are large, myelinated sensory fibers that transmit vibration and fine touch from mechanoreceptors such as Pacinian and Meissner corpuscles. In diabetic neuropathy, these fibers are affected early, causing loss of vibration sense before pain and temperature deficits appear. C fibers and A-delta fibers carry nociceptive and thermal sensations, while B fibers belong to the autonomic system. The correct answer is A-beta fibers. Vibration sense testing helps detect early large-fiber neuropathy.
6. Which type of receptor exhibits very rapid adaptation and is ideal for detecting sudden mechanical changes?
A) Slowly adapting receptor
B) Non-adapting receptor
C) Rapidly adapting receptor
D) Thermoreceptors
Explanation:
Rapidly adapting receptors discharge quickly at the onset and offset of a stimulus, making them highly effective for detecting dynamic changes such as vibration and movement. Pacinian corpuscles and Meissner corpuscles fall into this category. Slowly adapting receptors detect sustained pressure, while thermoreceptors respond to temperature. Non-adapting receptors are not typical in somatosensory physiology. Therefore, the correct answer is Rapidly adapting receptor. Their function is essential in evaluating dorsal column sensory integrity.
7. A 65-year-old presents with inability to perceive vibration on toes but intact pain sensation. Which pathway is preserved?
A) Dorsal column pathway
B) Spinocerebellar pathway
C) Spinothalamic pathway
D) Vestibulospinal pathway
Explanation:
Pain and temperature sensations remain intact through the spinothalamic pathway. Loss of vibration sense indicates dorsal column involvement. Since pain sensation is preserved, the spinothalamic tract must be intact. Therefore, the correct answer is Spinothalamic pathway. This dissociation is clinically useful in diagnosing neuropathies and spinal cord lesions affecting selective sensory modalities.
8. Which receptor detects texture discrimination and form recognition?
A) Pacinian corpuscle
B) Meissner corpuscle
C) Merkel disc
D) Ruffini ending
Explanation:
Merkel discs are slowly adapting receptors specialized for detecting texture, form, and fine spatial details. They respond to sustained pressure rather than vibration. Meissner corpuscles detect low-frequency vibration, Pacinian corpuscles detect high-frequency vibration, and Ruffini endings detect stretch. Hence, the correct answer is Merkel disc. These receptors are vital for tactile precision tasks such as Braille reading.
9. A patient cannot detect high-frequency vibration on the ankle. Which receptor is most likely impaired?
A) Meissner corpuscle
B) Ruffini ending
C) Pacinian corpuscle
D) Free nerve ending
Explanation:
Pacinian corpuscles are located deep in subcutaneous tissues, joints, and fascia and are responsible for detecting high-frequency vibration. Meissner corpuscles detect low-frequency vibration, Ruffini endings detect stretch, and free nerve endings detect pain and temperature. Therefore, the correct answer is Pacinian corpuscle. Clinically, reduced vibration over bony prominences indicates large-fiber neuropathy.
10. Which receptor type is MOST closely associated with grip modulation and tactile feedback during object handling?
A) Ruffini ending
B) Merkel disc
C) Meissner corpuscle
D) Pacinian corpuscle
Explanation:
Meissner corpuscles provide rapid feedback during grip adjustments because of their sensitivity to low-frequency vibration and slip detection. They are crucial for maintaining precise hand control. Ruffini endings detect stretch, Merkel discs detect form and texture, and Pacinian corpuscles detect deep high-frequency vibration. Therefore, the correct answer is Meissner corpuscle. Dysfunction of these receptors compromises fine motor control.
11. A patient with severe B12 deficiency shows complete loss of vibration sense. Which anatomical pathway is affected?
A) Spinothalamic tract
B) Dorsal column–medial lemniscal pathway
C) Reticulospinal tract
D) Corticospinal tract
Explanation:
Vitamin B12 deficiency leads to subacute combined degeneration, affecting the dorsal columns, which carry vibration, proprioception, and fine touch. Spinothalamic pathway carries pain and temperature, while reticulospinal and corticospinal tracts are motor pathways. Therefore, the correct answer is Dorsal column–medial lemniscal pathway. Loss of vibration sense is an early and sensitive sign of dorsal column dysfunction in B12 deficiency.
Chapter: Neurophysiology; Topic: Sensory Receptors; Subtopic: Slowly Adapting Cutaneous Receptors
KEYWORD DEFINITIONS
• Mechanoreceptors – Receptors responding to mechanical deformation
• Slowly adapting receptors – Detect sustained pressure and continuous stimuli
• Ruffini endings – Slowly adapting receptors sensing stretch and sustained pressure
• Merkel discs – Slowly adapting receptors sensing texture and steady pressure
• Meissner & Pacinian corpuscles – Rapidly adapting receptors for light touch/vibration
Lead Question – 2015
1. Which of the following receptor is stimulated by sustained pressure?
A) Ruffini's end organ
B) Merkel's disc
C) Hair cells
D) Meissner Corpuscles
Explanation:
Ruffini’s end organs are slowly adapting mechanoreceptors that respond to sustained pressure and skin stretch. They continue firing as long as the stimulus persists, unlike rapidly adapting receptors such as Meissner and Pacinian corpuscles, which respond mainly at stimulus onset and offset. Merkel discs also respond to steady pressure but are more involved in texture discrimination. Hair cells function in hearing and balance rather than somatosensation. Therefore, the correct answer is Ruffini’s end organ. These receptors play an important role in proprioception and grip modulation during sustained mechanical loading.
2. Which receptor is MOST sensitive to low-frequency vibration?
A) Ruffini ending
B) Meissner corpuscle
C) Merkel disc
D) Pacinian corpuscle
Explanation:
Meissner corpuscles are rapidly adapting receptors sensitive to low-frequency vibration (30–50 Hz) and light touch. They are abundant in glabrous skin such as fingertips and are essential for grip control and tactile discrimination. Pacinian corpuscles detect high-frequency vibration, Merkel discs detect texture and steady pressure, and Ruffini endings detect stretch. Thus, the correct answer is Meissner corpuscle. Clinical testing of vibration sense using a tuning fork helps identify dorsal column or peripheral nerve dysfunction.
3. A patient with posterior column lesion presents with impaired vibration sense. Which receptor’s input is mainly affected?
A) Meissner corpuscle
B) Pacinian corpuscle
C) Ruffini ending
D) Free nerve endings
Explanation:
Pacinian corpuscles provide high-frequency vibration sensation and transmit signals through large A-beta fibers into the dorsal column–medial lemniscal pathway. Damage to this pathway results in loss of vibration, proprioception, and fine touch. Meissner corpuscles also contribute but mainly to low-frequency vibration. Free nerve endings transmit pain and temperature, not vibration. Thus, the correct answer is Pacinian corpuscle. Posterior column pathology is characteristic in conditions like tabes dorsalis and vitamin B12 deficiency.
4. Which receptor detects fine texture and detailed form discrimination?
A) Merkel disc
B) Ruffini ending
C) Meissner corpuscle
D) Pacinian corpuscle
Explanation:
Merkel discs are slowly adapting receptors specialized for detecting texture, shape, and fine spatial details. They respond to sustained pressure and are located in the basal epidermis. Meissner corpuscles detect low-frequency vibration, Pacinian corpuscles detect high-frequency vibration, and Ruffini endings detect stretch. Hence, the correct answer is Merkel disc. These receptors are crucial for reading Braille and recognizing object surfaces during tactile exploration.
5. A diabetic patient shows early loss of vibration sense. Which fibers are damaged first?
A) A-delta fibers
B) C fibers
C) A-beta fibers
D) B fibers
Explanation:
A-beta fibers are large, myelinated sensory fibers that carry vibration and fine touch information from mechanoreceptors such as Pacinian and Meissner corpuscles. These fibers are commonly affected early in diabetic neuropathy, leading to diminished vibration perception. A-delta fibers carry fast pain, C fibers carry slow pain and temperature, and B fibers are autonomic. Therefore, the correct answer is A-beta fibers. Tuning fork testing is a sensitive way to detect early large-fiber neuropathy.
6. Which type of receptor is MOST likely to show rapid adaptation during continuous stimulation?
A) Merkel disc
B) Ruffini ending
C) Pacinian corpuscle
D) Nociceptor
Explanation:
Pacinian corpuscles exhibit extremely rapid adaptation, responding only to the onset and offset of mechanical stimuli. This feature allows them to detect transient changes such as vibration. Merkel discs and Ruffini endings are slowly adapting, maintaining continuous firing during sustained stimulation, while nociceptors respond to painful stimuli rather than vibration or pressure. Thus, the correct answer is Pacinian corpuscle. Rapidly adapting receptors are essential in motion detection and discriminating dynamic mechanical changes.
7. A patient with difficulty perceiving object slippage in the hand likely has dysfunction of which receptor?
A) Pacinian corpuscle
B) Meissner corpuscle
C) Merkel disc
D) Ruffini ending
Explanation:
Meissner corpuscles are rapidly adapting receptors that detect low-frequency vibration and slip sensations, providing crucial feedback for grip modulation. Dysfunction impairs the ability to adjust finger pressure, leading to poor handling of objects. Pacinian corpuscles detect high-frequency vibration, Merkel discs detect texture, and Ruffini endings detect stretch. Therefore, the correct answer is Meissner corpuscle. Damage to these receptors significantly affects hand dexterity.
8. Which receptor primarily detects stretching of skin and joints?
A) Merkel disc
B) Ruffini ending
C) Meissner corpuscle
D) Pacinian corpuscle
Explanation:
Ruffini endings are slowly adapting mechanoreceptors that respond to sustained stretch of the skin and joint capsules. They provide important proprioceptive information regarding finger position and hand configuration. Merkel discs detect steady pressure, Meissner corpuscles detect light touch and low-frequency vibration, and Pacinian corpuscles detect high-frequency vibration. The correct answer is Ruffini ending. These receptors are essential in maintaining grip force and coordinated movement.
9. A patient retains pain and temperature sensation but loses vibration and joint position sense. Which tract is intact?
A) Dorsal column
B) Spinothalamic tract
C) Spinocerebellar tract
D) Corticospinal tract
Explanation:
The spinothalamic tract carries pain and temperature sensations. Because these sensations are preserved while vibration and proprioception are lost, the dorsal column pathway is affected while the spinothalamic tract remains intact. Spinocerebellar and corticospinal tracts carry proprioceptive and motor signals respectively. Thus, the correct answer is Spinothalamic tract. This sensory dissociation helps localize spinal lesions clinically.
10. Which receptor responds best to high-frequency vibration applied over bony prominences?
A) Merkel disc
B) Meissner corpuscle
C) Pacinian corpuscle
D) Free nerve ending
Explanation:
Pacinian corpuscles detect high-frequency vibration (200–300 Hz) and are located deep in fascia, joints, and subcutaneous tissues, making them ideal for vibration detection near bones. Meissner corpuscles detect low-frequency vibration, Merkel discs detect texture, and free nerve endings detect pain/temperature. Therefore, the correct answer is Pacinian corpuscle. Clinical tuning fork tests mainly assess Pacinian-mediated pathways.
11. A 70-year-old with B12 deficiency shows severe loss of vibration sense. Which pathway is damaged?
A) Spinothalamic tract
B) Reticulospinal tract
C) Dorsal column–medial lemniscal pathway
D) Vestibulospinal tract
Explanation:
The dorsal column–medial lemniscal pathway carries proprioception, fine touch, and vibration. Vitamin B12 deficiency causes demyelination of this pathway, producing deficits like vibration loss, ataxia, and impaired joint position sense. Spinothalamic tract carries pain and temperature, vestibulospinal modulates posture, and reticulospinal influences muscle tone. Therefore, the correct answer is Dorsal column–medial lemniscal pathway. Early detection is essential to prevent irreversible neurological damage.
Chapter: Neurophysiology; Topic: Higher Cortical Functions; Subtopic: Visual Association Cortex – Face Recognition
KEYWORD DEFINITIONS
• Prosopagnosia – Inability to recognize familiar faces
• Visual association cortex – Processes complex visual information
• Fusiform gyrus – Brain region responsible for face perception
• Agnosia – Failure to recognize despite intact sensory function
• Temporal lobe – Critical for memory and recognition functions
Lead Question – 2015
1. "Prosopagnosia" is characterized by:
A) Inability to read
B) Inability to identify faces
C) Inability to write
D) Inability to speak
Explanation:
Prosopagnosia is characterized by the inability to recognize familiar faces despite intact vision and intellectual abilities. The condition results from damage to the fusiform face area in the temporal lobe, especially on the right side. It is a form of visual agnosia specific to facial identity, not general object recognition. Reading, writing, and speech are not primarily impaired. Therefore, the correct answer is Inability to identify faces. Clinically, patients may identify others using secondary cues like voice or gait, highlighting the selective nature of this deficit.
2. Damage to the fusiform face area results in:
A) Pure alexia
B) Prosopagnosia
C) Agraphia
D) Anomia
Explanation:
The fusiform face area, located in the inferior temporal cortex, specializes in processing facial recognition. Lesions here cause prosopagnosia, a selective inability to recognize familiar faces. Pure alexia arises from left occipitotemporal lesions, agraphia involves parietal lobe damage, and anomia results from disruptions in language areas. Thus, the correct answer is Prosopagnosia. Clinically, these patients can still recognize individuals using auditory or contextual cues, confirming the specificity of the deficit.
3. A patient recognizes objects but not faces. This condition is called:
A) Aphasia
B) Agnosia
C) Prosopagnosia
D) Apraxia
Explanation:
Prosopagnosia is a subtype of visual agnosia where facial recognition alone is impaired, while recognition of objects remains intact. Aphasia affects language, apraxia affects motor planning, and general agnosia involves broader recognition deficits. Therefore, the correct answer is Prosopagnosia. This condition commonly results from bilateral temporal-occipital damage and may be seen in stroke, trauma, or degenerative diseases.
4. A 60-year-old stroke patient cannot recognize family members by face but can identify their voices. Most likely lesion?
A) Wernicke’s area
B) Fusiform gyrus
C) Precentral gyrus
D) Postcentral gyrus
Explanation:
The fusiform gyrus in the temporal lobe specialized for face recognition is the primary site affected in prosopagnosia. Voices are processed separately, therefore remain intact in these patients. Wernicke’s area affects language comprehension, while precentral and postcentral gyri manage motor and sensory functions respectively. Thus, the correct answer is Fusiform gyrus. Recognition of individuals through non-visual cues helps distinguish this disorder from more global cognitive deficits.
5. Inability to identify familiar faces despite normal vision is called:
A) Visual agnosia
B) Prosopagnosia
C) Agraphesthesia
D) Autotopagnosia
Explanation:
Prosopagnosia represents a specialized form of visual agnosia affecting face perception. Visual acuity and fields remain intact. Agraphesthesia involves inability to recognize symbols traced on skin, while autotopagnosia refers to inability to localize body parts. The correct answer is Prosopagnosia. This deficit can be congenital or acquired, with acquired cases often following posterior cerebral artery strokes.
6. Which lobe is primarily involved in facial recognition?
A) Frontal
B) Temporal
C) Parietal
D) Occipital
Explanation:
The temporal lobe, particularly the inferior temporal cortex and fusiform gyrus, plays a central role in facial recognition. While the occipital lobe handles initial visual processing, detailed identification occurs in temporal association areas. Frontal and parietal lobes contribute to higher cognitive and sensory processing, but not specifically facial identity. Therefore, the correct answer is Temporal. Lesions here cause prosopagnosia, highlighting its functional importance.
7. A patient with right temporal lobe damage may show:
A) Difficulty reading
B) Prosopagnosia
C) Difficulty writing
D) Aphasia
Explanation:
Right temporal lobe lesions often lead to deficits in face recognition due to involvement of the right fusiform face area. Left temporal lesions more commonly cause language disturbances like aphasia. Reading and writing are mainly parietal–occipitotemporal functions. Thus, the correct answer is Prosopagnosia. Patients often rely on voice or contextual clues to identify known individuals.
8. Prosopagnosia is best classified as:
A) Motor disorder
B) Language disorder
C) Visual agnosia
D) Attention deficit
Explanation:
Prosopagnosia is a selective visual agnosia in which patients cannot recognize faces despite intact basic visual function. It is not related to motor or language deficits, nor is it an attention deficit disorder. It specifically reflects impaired higher-order processing in the temporo-occipital association cortex. Thus, the correct answer is Visual agnosia. Patients may still identify individuals using other sensory cues.
9. A patient identifies objects but cannot recognize his own reflection. This is due to damage in:
A) Prefrontal cortex
B) Primary visual cortex
C) Inferior temporal cortex
D) Angular gyrus
Explanation:
The inferior temporal cortex, particularly the fusiform face area, is essential for recognizing faces including one’s own. Primary visual cortex damage causes blindness, angular gyrus injury produces reading/writing disorders, and prefrontal lesions affect executive functions. Therefore, the correct answer is Inferior temporal cortex. This condition illustrates precise cortical localization of complex recognition functions.
10. Prosopagnosia is commonly associated with infarction of which artery?
A) Anterior cerebral artery
B) Middle cerebral artery
C) Posterior cerebral artery
D) Basilar artery
Explanation:
The posterior cerebral artery supplies the occipital and inferotemporal regions including the fusiform gyrus. Infarction here can impair facial recognition and produce prosopagnosia. MCA strokes affect language and motor areas, while ACA strokes affect medial frontal lobes. Basilar artery strokes produce brainstem deficits. Therefore, the correct answer is Posterior cerebral artery. Diagnosis is supported by neuroimaging and neuropsychological testing.
11. A patient with degenerative dementia shows progressive facial recognition impairment. Most likely diagnosis?
A) Alzheimer’s disease
B) Parkinson’s disease
C) Huntington’s disease
D) ALS
Explanation:
Alzheimer’s disease frequently affects temporo-parietal association cortices, including areas related to visual recognition such as the fusiform gyrus. As degeneration progresses, patients may develop prosopagnosia. Parkinson’s and Huntington’s primarily affect motor circuits, and ALS affects motor neurons. Thus, the correct answer is Alzheimer’s disease. Prosopagnosia in dementia highlights involvement of higher-order visual processing circuits.
Chapter: Neurophysiology; Topic: Higher Cortical Functions; Subtopic: Language Areas – Motor Speech
KEYWORD DEFINITIONS
• Broca’s area – Motor speech area responsible for word formation
• Wernicke’s area – Comprehension of spoken and written language
• Arcuate fasciculus – Connects Broca’s and Wernicke’s areas for repetition
• Aphasia – Impairment of language production or comprehension
• Dominant hemisphere – Usually left hemisphere controlling language functions
Lead Question – 2015
1. Broca's area is concerned with:
A) Word formation
B) Comprehension
C) Repetition
D) Reading
Explanation:
Broca’s area, located in the dominant frontal lobe (usually left), is the motor speech area responsible for word formation and articulation. It coordinates the movements required for verbal expression. Damage to this region results in Broca’s aphasia, characterized by slow, effortful speech with preserved comprehension. Wernicke’s area manages comprehension, while repetition requires the arcuate fasciculus. Reading involves multiple visual and language centers. Thus, the correct answer is Word formation. Clinically, Broca’s aphasia patients understand language but cannot produce fluent speech.
2. Damage to Broca’s area causes which condition?
A) Fluent aphasia
B) Broca’s aphasia
C) Conduction aphasia
D) Global aphasia
Explanation:
Lesions in Broca’s area lead to Broca’s aphasia, a non-fluent type of aphasia in which comprehension remains relatively intact but speech output becomes slow, effortful, and fragmented. Fluent aphasia occurs in Wernicke’s lesions, conduction aphasia in arcuate fasciculus damage, and global aphasia in extensive perisylvian lesions. Therefore, the correct answer is Broca’s aphasia. Patients struggle with forming words but often retain awareness of their deficits.
3. A patient speaks with slow, effortful speech but comprehension is intact. Most likely lesion?
A) Wernicke’s area
B) Angular gyrus
C) Broca’s area
D) Primary auditory cortex
Explanation:
Slow, effortful, and non-fluent speech with preserved comprehension is the hallmark of Broca’s aphasia, resulting from damage to Broca’s area in the inferior frontal gyrus. Wernicke’s area lesions impair comprehension, angular gyrus lesions impair reading and writing, and primary auditory cortex lesions impair sound perception. Thus, the correct answer is Broca’s area. These patients produce telegraphic speech but retain the ability to understand spoken language.
4. Repetition is specifically impaired in which type of aphasia?
A) Broca’s aphasia
B) Conduction aphasia
C) Wernicke’s aphasia
D) Transcortical motor aphasia
Explanation:
Conduction aphasia is characterized by disproportionately impaired repetition despite preserved comprehension and relatively fluent speech. It arises from damage to the arcuate fasciculus, which links Broca’s and Wernicke’s areas. In Broca’s aphasia speech is non-fluent, in Wernicke’s aphasia comprehension is impaired, and repetition is preserved in transcortical aphasias. Therefore, the answer is Conduction aphasia. Patients often make phonemic errors and struggle to repeat even simple phrases.
5. Which artery supplies Broca’s area?
A) Anterior cerebral artery
B) Middle cerebral artery
C) Posterior cerebral artery
D) Basilar artery
Explanation:
Broca’s area is supplied by the superior division of the middle cerebral artery (MCA). Infarction in this region produces non-fluent aphasia. The anterior cerebral artery supplies medial frontal regions, while the posterior cerebral artery supplies occipital and inferotemporal lobes. Basilar artery involvement affects brainstem structures. Therefore, the correct answer is Middle cerebral artery. MCA strokes are among the most common causes of cortical language deficits.
6. A patient understands language but cannot speak fluently. This describes:
A) Wernicke’s aphasia
B) Broca’s aphasia
C) Global aphasia
D) Dysarthria
Explanation:
Patients with Broca’s aphasia have intact comprehension but reduced fluency due to impaired language motor planning. Wernicke’s aphasia features fluent but nonsensical speech with poor comprehension. Global aphasia affects all language modalities, and dysarthria results from motor weakness rather than language planning deficits. Therefore, the correct answer is Broca’s aphasia. Awareness of the deficit often leads to patient frustration during communication attempts.
7. A right-handed patient with a left inferior frontal gyrus lesion will MOST likely present with:
A) Fluent speech with poor comprehension
B) Impaired repetition only
C) Slow, non-fluent speech
D) Impaired naming with intact fluency
Explanation:
Left inferior frontal gyrus lesions (Broca’s area) cause slow, non-fluent, effortful speech with intact comprehension. Wernicke’s lesions cause fluent speech with poor comprehension, arcuate fasciculus lesions impair repetition, and naming deficits with fluency suggest anomic aphasia. The correct answer is Slow, non-fluent speech. This highlights the role of Broca’s area in expressive language.
8. Which cortical area is primarily involved in language comprehension?
A) Broca’s area
B) Wernicke’s area
C) Prefrontal cortex
D) Supplementary motor area
Explanation:
Wernicke’s area, located in the superior temporal gyrus of the dominant hemisphere, is crucial for understanding spoken and written language. Broca’s area handles speech production, the prefrontal cortex manages executive functions, and the supplementary motor area coordinates motor planning. Therefore, the answer is Wernicke’s area. Lesions here cause fluent but meaningless speech with impaired comprehension.
9. Inability to read despite normal vision is called:
A) Alexia
B) Apraxia
C) Dysarthria
D) Prosopagnosia
Explanation:
Alexia, often called word blindness, results from lesions in the left occipitotemporal region, disrupting visual–language integration. Prosopagnosia affects face recognition, apraxia affects motor planning, and dysarthria affects articulation due to motor weakness. Therefore, the correct answer is Alexia. Patients can see text but cannot interpret printed words, indicating higher-order processing deficits.
10. A patient cannot repeat simple phrases but has intact comprehension and fluent speech. Diagnosis?
A) Wernicke’s aphasia
B) Conduction aphasia
C) Broca’s aphasia
D) Transcortical sensory aphasia
Explanation:
Conduction aphasia is caused by damage to the arcuate fasciculus, disrupting communication between Broca’s and Wernicke’s areas. As a result, repetition is disproportionately impaired while fluency and comprehension remain largely intact. Wernicke’s aphasia impairs comprehension, Broca’s impairs fluency, and transcortical sensory aphasia preserves repetition. Thus, the correct answer is Conduction aphasia. Patients often substitute similar-sounding words during speech.
11. A patient with global aphasia has lesions affecting:
A) Broca’s and Wernicke’s areas
B) Only Broca’s area
C) Only Wernicke’s area
D) Arcuate fasciculus only
Explanation:
Global aphasia occurs when both Broca’s and Wernicke’s areas, along with surrounding perisylvian cortex, are damaged—most commonly due to extensive MCA infarction. All language functions are severely impaired including fluency, comprehension, and repetition. Damage to one area alone does not produce this profound deficit. Therefore, the correct answer is Broca’s and Wernicke’s areas. This is the most severe form of aphasia and has a poor prognosis.
Chapter: Neurophysiology; Topic: Higher Cortical Functions; Subtopic: Brodmann Areas – Motor Speech Area
KEYWORD DEFINITIONS
• Brodmann areas – Cortical regions mapped based on cytoarchitecture
• Broca’s area – Motor speech area responsible for word formation
• Area 44/45 – Inferior frontal gyrus regions involved in speech output
• Wernicke’s area – Language comprehension region
• Arcuate fasciculus – Connects Broca’s and Wernicke’s areas for repetition
Lead Question – 2015
1. Broadman's area for motor speech?
A) Area 1,2,3
B) Area 4,6
C) Area 28,29
D) Area 44
Explanation:
Broca’s area, the motor speech area responsible for word formation and articulation, corresponds mainly to Brodmann area 44 and partly area 45 in the dominant hemisphere. It coordinates motor planning for expressive speech. Areas 1,2,3 form the primary somatosensory cortex, area 4 and 6 belong to the motor and premotor cortex, and areas 28/29 belong to the limbic cortex. Therefore, the correct answer is Area 44. Damage to this region results in Broca’s aphasia, characterized by non-fluent, effortful speech with preserved comprehension.
2. Which Brodmann area is associated with language comprehension?
A) Area 44
B) Area 6
C) Area 22
D) Area 17
Explanation:
Wernicke’s area, responsible for comprehension of spoken and written language, corresponds to Brodmann area 22 in the dominant hemisphere. Broca’s area (44/45) manages speech production, area 6 is premotor cortex, and area 17 is the primary visual cortex. Thus, the correct answer is Area 22. Lesions to this area lead to fluent but nonsensical speech, characteristic of Wernicke’s aphasia, where comprehension is severely impaired.
3. A patient presents with fluent speech but poor comprehension. Which region is most likely damaged?
A) Area 4
B) Area 22
C) Area 44
D) Area 7
Explanation:
Fluent but meaningless speech with impaired comprehension is the hallmark of Wernicke’s aphasia, caused by lesions in Brodmann area 22. Area 4 handles voluntary motor control, area 44 controls motor speech, and area 7 is involved in visuospatial processing. Therefore, the correct answer is Area 22. Such patients often produce “word salad” and are unaware of their deficits, unlike Broca’s aphasia patients.
4. Broca’s aphasia typically occurs due to a lesion in which cerebral artery territory?
A) ACA
B) PCA
C) MCA – superior division
D) MCA – inferior division
Explanation:
Broca’s area is supplied predominantly by the superior division of the middle cerebral artery (MCA). Infarction here results in non-fluent aphasia with preserved comprehension. The inferior division of MCA supplies Wernicke’s area, PCA supplies occipital lobe and inferotemporal regions, and ACA supplies medial frontal areas. Therefore, the correct answer is MCA – superior division. Speech becomes effortful and telegraphic, but understanding remains intact.
5. Which Brodmann area corresponds to primary motor cortex?
A) Area 1
B) Area 6
C) Area 4
D) Area 44
Explanation:
The primary motor cortex is located in Brodmann area 4, situated in the precentral gyrus. It is responsible for voluntary motor control. Area 6 is the premotor cortex, area 1 is part of the sensory cortex, and area 44 corresponds to Broca’s area. Therefore, the correct answer is Area 4. Damage here leads to contralateral weakness or paralysis, demonstrating strict somatotopic organization.
6. A patient understands speech but struggles severely with articulation. Most likely defect?
A) Area 22 lesion
B) Area 4 lesion
C) Area 44 lesion
D) Area 17 lesion
Explanation:
Intact comprehension with difficulty in articulation strongly suggests Broca’s aphasia, caused by damage to Brodmann area 44. Area 22 lesions impair comprehension, area 4 lesions impair motor control of limbs, and area 17 lesions affect vision. Therefore, the correct answer is Area 44. Speech becomes non-fluent and effortful, but patients retain insight and attempt to correct their mistakes.
7. Which area connects Broca’s and Wernicke’s regions for repetition?
A) Angular gyrus
B) Arcuate fasciculus
C) Uncinate fasciculus
D) Corpus callosum
Explanation:
The arcuate fasciculus is the white matter tract that links Broca’s and Wernicke’s areas, enabling repetition of spoken words. Damage causes conduction aphasia, characterized by impaired repetition with preserved comprehension and fluency. Angular gyrus is involved in reading/writing, uncinate fasciculus connects frontal–temporal poles, and corpus callosum coordinates interhemispheric exchange. Thus, the answer is Arcuate fasciculus.
8. The region responsible for converting written language into spoken form is:
A) Area 17
B) Angular gyrus
C) Area 44
D) Area 4
Explanation:
The angular gyrus integrates visual information (letters/words) and converts it into linguistic form, enabling reading comprehension. Area 17 is primary visual cortex, area 44 handles speech production, and area 4 controls motor output. Therefore, the correct answer is Angular gyrus. Damage leads to alexia with agraphia, where reading and writing abilities are lost.
9. A patient cannot repeat words but speaks fluently with preserved comprehension. Diagnosis?
A) Broca’s aphasia
B) Wernicke’s aphasia
C) Conduction aphasia
D) Global aphasia
Explanation:
Conduction aphasia is caused by damage to the arcuate fasciculus connecting Broca’s and Wernicke’s areas. This results in selective impairment of repetition while fluency and comprehension remain intact. Broca’s aphasia affects speech production, Wernicke’s affects comprehension, and global aphasia affects all aspects. Hence, the correct answer is Conduction aphasia. Patients often produce phonemic substitution errors.
10. Brodmann area 45 is primarily associated with:
A) Motor planning
B) Speech articulation
C) Auditory comprehension
D) Visual processing
Explanation:
Area 45, along with area 44, forms Broca’s complex and plays an essential role in speech planning and articulation. It works with motor cortex to orchestrate expressive language. Comprehension occurs in area 22, motor planning in area 6, and vision in area 17. Thus, the correct answer is Speech articulation. Lesions here contribute to expressive aphasia and impaired verbal fluency.
11. Global aphasia results from damage to:
A) Area 22 exclusively
B) Area 44 exclusively
C) Perisylvian cortex
D) Occipital cortex
Explanation:
Global aphasia occurs when both Broca’s and Wernicke’s areas, along with surrounding perisylvian cortex, are damaged—usually due to extensive MCA infarction. This causes profound impairment in fluency, comprehension, naming, and repetition. Damage to area 22 or 44 alone cannot produce global aphasia. Therefore, the correct answer is Perisylvian cortex. This represents the most severe form of aphasia with widespread cortical involvement.
Chapter: Neurophysiology; Topic: Proprioception; Subtopic: Muscle Spindles – Distribution & Function
KEYWORD DEFINITIONS
• Muscle spindle – Stretch receptor sensing muscle length and rate of stretch
• Intrafusal fibers – Specialized fibers inside muscle spindles
• Gamma motor neurons – Regulate spindle sensitivity
• Proprioception – Awareness of body position
• Fine motor muscles – Muscles requiring precise control, having high spindle density
Lead Question – 2015
1. Maximum density of muscle spindle is found in?
A) Calf muscle
B) Lumbricals
C) Quadriceps muscle
D) Triceps
Explanation:
Muscle spindles are most densely distributed in muscles requiring fine, precise movements. Lumbricals of the hand perform delicate actions such as finger flexion–extension balance, making them rich in muscle spindles. Large postural muscles like calf, quadriceps, and triceps have fewer spindles per gram, as they focus more on power than precision. Therefore, the correct answer is Lumbricals. High spindle density ensures accurate proprioceptive feedback essential for coordinated hand movements and fine motor tasks.
2. Muscle spindle primarily detects:
A) Muscle tension
B) Muscle length
C) Vibration
D) Temperature
Explanation:
Muscle spindles respond to changes in muscle length and the rate of lengthening. They contain intrafusal fibers innervated by gamma motor neurons, allowing dynamic regulation. Golgi tendon organs detect tension, Pacinian corpuscles detect vibration, and temperature is sensed by thermoreceptors. Therefore, the correct answer is Muscle length. This mechanism plays a crucial role in stretch reflexes, posture maintenance, and coordinated movement.
3. A patient loses proprioception in the lower limb. Which structure is most likely affected?
A) Golgi tendon organ
B) Pacinian corpuscle
C) Muscle spindle
D) Free nerve endings
Explanation:
Proprioception depends largely on muscle spindles, which monitor muscle length and movement. Damage to these structures impairs the ability to sense limb position, leading to ataxic gait. Golgi tendon organs detect muscle tension, Pacinian corpuscles detect vibration, and free nerve endings mediate pain and temperature. Therefore, the answer is Muscle spindle. Clinical tests include joint position sense and Romberg’s sign evaluation.
4. Gamma motor neurons regulate which function?
A) Muscle contraction strength
B) Spindle sensitivity
C) Tendon tension
D) Skin stretch
Explanation:
Gamma motor neurons adjust intrafusal fiber tension, thereby regulating muscle spindle sensitivity. This ensures spindles remain responsive during both contraction and relaxation. Alpha motor neurons drive muscle contraction, Golgi tendon organs monitor tension, and Ruffini endings detect skin stretch. Therefore, the correct answer is Spindle sensitivity. Gamma activation is essential for fine motor coordination and maintaining posture.
5. Which muscle type has the highest muscle spindle-to-muscle fiber ratio?
A) Postural muscles
B) Fine control muscles
C) Power muscles
D) Respiratory muscles
Explanation:
Fine control muscles, such as extraocular muscles and lumbricals, require precise regulation of movement and thus have the highest density of muscle spindles. Postural muscles have moderate numbers, while power muscles prioritize force over precision. Respiratory muscles rely more on central drive. Therefore, the correct answer is Fine control muscles. High spindle ratio ensures accurate proprioceptive signaling during delicate motor tasks.
6. A 55-year-old diabetic patient shows impaired position sense in toes. Which pathway is likely affected?
A) Spinothalamic tract
B) Dorsal column pathway
C) Corticospinal tract
D) Vestibulospinal tract
Explanation:
The dorsal column–medial lemniscal pathway transmits proprioception, vibration, and fine touch from muscle spindles and mechanoreceptors. Diabetic neuropathy commonly damages large myelinated fibers, leading to proprioceptive loss. Spinothalamic tract carries pain and temperature, corticospinal tract mediates voluntary motor control, and vestibulospinal tract maintains balance. Hence, the answer is Dorsal column pathway. Testing includes vibration sense and joint position assessment.
7. Stretch reflex is mediated by:
A) Pacinian corpuscles
B) Golgi tendon organs
C) Muscle spindles
D) Free nerve endings
Explanation:
The stretch reflex is initiated when muscle spindles detect rapid stretch, sending Ia afferent signals to spinal cord motor neurons, causing reflex contraction. Golgi tendon organs mediate inverse stretch reflex, reducing tension. Pacinian corpuscles detect vibration, and free nerve endings detect pain. Therefore, the correct answer is Muscle spindles. This reflex is clinically tested with tendon taps such as knee jerk.
8. Golgi tendon organ differs from muscle spindle by detecting:
A) Joint position
B) Muscle tension
C) Muscle velocity
D) Skin stretch
Explanation:
Golgi tendon organs respond to muscle tension, particularly during strong contractions, preventing damage by inhibiting excessive force. Muscle spindles detect length changes, not tension. Skin stretch is sensed by Ruffini endings, and joint position involves multiple proprioceptors. Therefore, the correct answer is Muscle tension. Golgi-mediated inhibition protects muscles from overload injuries.
9. A patient with posterior column degeneration has difficulty standing with eyes closed. This is due to loss of:
A) Pain sensation
B) Temperature sense
C) Proprioception
D) Touch-pressure sense
Explanation:
Posterior column degeneration, as seen in B12 deficiency or tabes dorsalis, impairs proprioception from muscle spindles. With eyes closed, visual compensation is lost, leading to a positive Romberg’s sign. Pain and temperature are transmitted through spinothalamic pathways and remain intact early. Therefore, the answer is Proprioception. This confirms reliance on spindle-mediated feedback for posture.
10. Muscle spindles are most active during:
A) Muscle contraction only
B) Muscle relaxation only
C) Both contraction and stretch
D) Tendon injury
Explanation:
Muscle spindles remain active during both stretch and contraction due to gamma motor neuron control, maintaining sensitivity across muscle states. They detect dynamic and static length changes. Golgi tendon organs monitor tension during contraction. Tendon injury does not preferentially activate spindles. Therefore, the correct answer is Both contraction and stretch. This dual activity ensures stable posture and coordinated movement.
11. Fine motor muscles like lumbricals have dense spindles primarily to improve:
A) Power generation
B) Precision of movement
C) Endurance
D) Reflex inhibition
Explanation:
High spindle density in fine motor muscles enhances proprioceptive accuracy for delicate movements. These receptors provide continuous feedback about muscle length and position, enabling precise control of finger motion. Power and endurance depend on muscle fiber type, not spindle density. Reflex inhibition is mediated by Golgi tendon organs. Therefore, the correct answer is Precision of movement. This anatomical specialization supports skilled hand functions like writing and typing.
Topic: Autonomic Nervous System; Subtopic: Sympathetic – Fight or Flight Response
KEYWORD DEFINITIONS
• Epinephrine – Adrenal medullary hormone enhancing sympathetic responses
• Norepinephrine – Sympathetic neurotransmitter increasing vascular tone
• Fight-or-flight response – Acute stress reaction increasing perfusion to vital organs
• Vasoconstriction – Narrowing of blood vessels in skin/splanchnic areas
• Bronchodilation – Widening of airways to increase airflow
Lead Question – 2015
1. Function of epinephrine and norepinephrine in fight-or-flight response is?
A) Increased blood flow to skin
B) Increased blood flow to muscles
C) Bronchoconstriction
D) Bradycardia
Explanation:
During the fight-or-flight response, epinephrine and norepinephrine increase blood flow to skeletal muscles through β₂-mediated vasodilation, improving oxygen supply for action. They simultaneously reduce blood flow to the skin and gut via α₁-mediated vasoconstriction. These hormones also cause bronchodilation and increase heart rate and force of contraction. Therefore, the correct answer is Increased blood flow to muscles. This coordinated response enhances physical performance, alertness, and survival during acute stress situations.
2. Which receptor mediates vasoconstriction in skin during stress?
A) β₁ receptor
B) α₁ receptor
C) β₂ receptor
D) M₂ receptor
Explanation:
Norepinephrine activates α₁ receptors in skin and splanchnic vessels, causing vasoconstriction that diverts blood to essential organs such as the heart and skeletal muscles. β₂ receptors mediate vasodilation in skeletal muscles, β₁ affects the heart, and M₂ receptors belong to the parasympathetic system. Thus, the correct answer is α₁ receptor. This mechanism is essential for optimizing perfusion during the fight-or-flight response.
3. A patient experiencing a panic attack shows tachycardia and tremors. Which hormone is responsible?
A) Cortisol
B) Epinephrine
C) Insulin
D) Thyroxine
Explanation:
Epinephrine released from the adrenal medulla stimulates β₁ receptors causing tachycardia and β₂ receptors causing tremors. Cortisol contributes to long-term stress, insulin lowers blood glucose, and thyroxine affects metabolism. Therefore, the correct answer is Epinephrine. This acute surge enhances physical readiness and heightened alertness during stress or panic episodes.
4. Which effect is characteristic of sympathetic activation?
A) Increased gut motility
B) Miosis
C) Bronchodilation
D) Decreased heart rate
Explanation:
The sympathetic system produces bronchodilation through β₂ receptors, preparing the respiratory system for increased oxygen demand. It decreases gut motility, dilates pupils (mydriasis), and increases heart rate (tachycardia). Therefore, the correct answer is Bronchodilation. This change ensures efficient airflow during emergency responses.
5. A trauma patient shows high heart rate and dilated pupils. What is the primary mediator?
A) Serotonin
B) Dopamine
C) Norepinephrine
D) GABA
Explanation:
Norepinephrine is the main neurotransmitter of the sympathetic nervous system, causing tachycardia via β₁ receptors and pupil dilation via α₁ receptors. Serotonin and GABA are CNS neurotransmitters, while dopamine acts centrally and peripherally but not as a primary fight-or-flight mediator. Hence, the answer is Norepinephrine. These changes prepare the body for rapid action under stress.
6. Which effect is NOT produced by epinephrine during stress?
A) Glycogenolysis
B) Lipolysis
C) Increased insulin secretion
D) Increased cardiac output
Explanation:
Epinephrine decreases insulin secretion (via α₂ receptors) while increasing glycogenolysis, lipolysis, and cardiac output. Thus, “increased insulin secretion” is incorrect. Therefore, the correct answer is Increased insulin secretion. The metabolic effects of epinephrine ensure an immediate supply of glucose and fatty acids.
7. A 40-year-old presents with asthma. Which receptor is targeted by rescue inhalers to mimic sympathetic action?
A) α₁ receptor
B) β₂ receptor
C) M₃ receptor
D) D₂ receptor
Explanation:
Rescue inhalers (e.g., salbutamol) activate β₂ receptors causing bronchodilation, similar to epinephrine. α₁ receptors cause vasoconstriction, M₃ induces bronchoconstriction, and D₂ receptors are dopaminergic. Therefore, the correct answer is β₂ receptor. This mechanism relieves bronchospasm during asthma attacks.
8. Which physiological change occurs due to sympathetic stimulation of the heart?
A) Decreased contractility
B) Decreased conduction velocity
C) Increased heart rate
D) Increased refractory period
Explanation:
Sympathetic activation through β₁ receptors increases heart rate, conduction velocity, and contractility. Refractory period typically decreases rather than increases. Thus, the correct answer is Increased heart rate. These changes enhance cardiac output during stress.
9. A patient with pheochromocytoma shows episodic headaches, sweating, and palpitations. Mechanism?
A) Excess GABA
B) Excess epinephrine/norepinephrine
C) Excess dopamine
D) Excess acetylcholine
Explanation:
Pheochromocytoma secretes large amounts of epinephrine and norepinephrine, causing episodic sympathetic surges with hypertension, tremors, sweating, and palpitations. This reflects exaggerated fight-or-flight activation. GABA and acetylcholine do not mediate these symptoms. Therefore, the answer is Excess epinephrine/norepinephrine. Diagnosis is confirmed by elevated metanephrines.
10. Sympathetic activation shifts blood flow to which area?
A) Skin
B) Intestine
C) Skeletal muscle
D) Liver
Explanation:
During fight-or-flight, β₂-mediated vasodilation increases blood flow to skeletal muscles for rapid motor activity. Skin and intestinal flow decrease due to α₁-mediated vasoconstriction. Liver receives moderate redistribution for metabolic support. Therefore, the correct answer is Skeletal muscle. This prioritization ensures physical readiness under stress.
11. Which metabolic effect is produced by sympathetic activation through epinephrine?
A) Decreased blood glucose
B) Increased glycogenolysis
C) Decreased lipolysis
D) Increased insulin release
Explanation:
Epinephrine increases glycogenolysis in muscle and liver, raising blood glucose to meet energy demands. It also increases lipolysis and decreases insulin secretion. Therefore, the correct answer is Increased glycogenolysis. These metabolic adjustments supply immediate fuel during acute stress.