Neurophysiology Practice Questions

Q: Substance P belongs to the tachykinin family of peptides. Which of the following peripheral tissues contain substance P?

Nerve terminal. Substance P is a potent neuropeptide belonging to the tachykinin family. It primarily functions as a neurotransmitter and neuromodulator. Why Nerve Terminals are Correct: Substance P is synthesized in the cell bodies of first-order sensory neurons (located in the dorsal root ganglia) and is transported to both central and peripheral nerve terminals [1]. In the periphery, it is released from the terminals of non-myelinated C-fibers. Its primary role is the transmission of pain signals (nociception) and the mediation of neurogenic inflammation, where its release causes vasodilation and increased vascular permeability [2]. Why Other Options are Incorrect: * Plasma Cells & Mast Cells: While these cells have receptors for Substance P (NK1 receptors) and are activated by it during inflammatory responses (causing mast cell degranulation), they do not synthesize or "contain" the peptide as a primary source [2]. * Vascular Endothelium: The endothelium is a target tissue for Substance P. When Substance P binds to endothelial receptors, it triggers the release of nitric oxide, leading to vasodilation. It is not the site of production or storage. NEET-PG High-Yield Pearls: * Receptor: Substance P acts primarily via the NK1 (Neurokinin-1) receptor, which is a G-protein coupled receptor. * Antagonist: Aprepitant is a clinically significant NK1 receptor antagonist used as an antiemetic in chemotherapy. * Capsaicin: Found in chili peppers, capsaicin causes the depletion of Substance P from sensory nerve endings, which is the basis for its use in topical analgesic creams for post-herpetic neuralgia. * Co-localization: In the spinal cord (dorsal horn), Substance P is often co-released with Glutamate to enhance pain transmission [2].

Q: Which afferent fibers are included in the stretch reflex?

Ia and II fibers. The **Stretch Reflex** (Myotatic Reflex) is a monosynaptic reflex triggered by the stretching of a muscle, which is detected by specialized sensory receptors called **Muscle Spindles**. ### Why Option B is Correct: Muscle spindles contain two types of sensory afferents that mediate the stretch reflex: 1. **Type Ia (Primary) Afferents:** These originate from the annulospiral endings. they are large, myelinated, and fast-conducting. They respond to the **rate of change** in muscle length (dynamic response). 2. **Type II (Secondary) Afferents:** These originate from flower-spray endings (primarily on nuclear chain fibers). They respond to the **static length** of the muscle (static response). Together, these fibers provide the CNS with information regarding both the velocity and the degree of the stretch. ### Why Other Options are Incorrect: * **Type Ib fibers (Options A & C):** These fibers are associated with the **Golgi Tendon Organ (GTO)**. They mediate the *Inverse Stretch Reflex* (autogenic inhibition), which causes muscle relaxation in response to excessive tension to prevent injury. * **Golgi Tendon Organ (Option D):** This is a receptor, not an afferent fiber. It monitors muscle tension rather than muscle length and is not part of the excitatory stretch reflex. ### High-Yield Clinical Pearls for NEET-PG: * **Monosynaptic Nature:** The stretch reflex is the only monosynaptic reflex in the human body (e.g., Knee jerk). * **Gamma Motor Neurons:** These regulate the sensitivity of the muscle spindle. Co-activation of alpha and gamma motor neurons ensures the spindle remains sensitive even during muscle contraction. * **Reciprocal Inhibition:** While the stretch reflex is monosynaptic for the agonist muscle, it involves an inhibitory interneuron to relax the antagonist muscle (polysynaptic component). * **Jendrassik Maneuver:** Used to reinforce sluggish deep tendon reflexes by increasing upper motor neuron excitability.

Q: Which stage of sleep is characterized by the presence of delta waves on an EEG recording?

Deep sleep (Stage N3 NREM sleep). **Explanation:** Sleep is divided into two main types: **Non-Rapid Eye Movement (NREM)** and **Rapid Eye Movement (REM)** sleep. NREM sleep is further subdivided into three stages (N1, N2, and N3) based on EEG frequency and amplitude. **Why Stage N3 is correct:** Stage N3, also known as **Slow Wave Sleep (SWS)** or Deep Sleep, is characterized by **Delta waves**. These are high-amplitude, low-frequency (0.5–4 Hz) waves. For a sleep stage to be classified as N3, delta waves must occupy at least 20% of the epoch. This stage is associated with physical restoration, growth hormone secretion, and the highest arousal threshold. **Analysis of Incorrect Options:** * **REM Sleep:** Characterized by "paradoxical" EEG activity—low-voltage, high-frequency waves (Beta/Theta) that resemble an awake state. It features rapid eye movements and muscle atonia. * **Stage N1 (Light Sleep):** The transition from wakefulness to sleep. The EEG shows a disappearance of Alpha waves and the emergence of **Theta waves** (4–7 Hz). * **Stage N2:** This is the longest stage of sleep. It is characterized by specific EEG markers: **Sleep Spindles** (bursts of 12–14 Hz activity) and **K-complexes** (large biphasic waves). **NEET-PG High-Yield Pearls:** * **Bruxism** (teeth grinding) occurs mostly in Stage N2. * **Parasomnias** like Sleepwalking (Somnambulism), Sleep Terrors, and Bedwetting (Enuresis) typically occur during **Stage N3**. * **Dreaming** occurs primarily in REM sleep (vivid/narrative) but can occur in NREM (abstract). * **PGO spikes** (Ponto-Geniculo-Occipital) are the earliest sign of REM sleep.

Q: Midbrain is the centre for the integration of which of the following reflexes?

Vestibular righting reflex. **Explanation:** The integration of posture and equilibrium involves various levels of the Central Nervous System (CNS). The **Midbrain** (specifically the red nucleus and superior colliculus) serves as the primary integration center for **Righting Reflexes**, which function to restore the head and body to their normal upright position when displaced. 1. **Why Option A is Correct:** The **Vestibular Righting Reflex** (and the Neck Righting Reflex) is integrated in the **midbrain**. When the body is tilted, vestibular impulses (from the otolith organs) trigger the neck muscles to rotate the head back to a level position. This is a classic midbrain-level reflex. 2. **Why Other Options are Incorrect:** * **B. Optical Righting Reflex:** While this also helps maintain the head's position, it requires the **Visual Cortex** for integration. Therefore, it is a **cortical reflex**, not a midbrain reflex. * **C. Magnet Reaction:** This is a "positive supporting reaction" where the limbs extend to support weight. It is integrated at the **spinal cord/medulla** level. * **D. Hopping and Placing Reactions:** These are complex postural adjustments that allow an animal to stay upright when pushed or placed on a surface. These are **cortical reflexes** and are lost if the cerebral cortex is removed. **High-Yield NEET-PG Pearls:** * **Spinal Level:** Integration of stretch reflexes and basic withdrawal reflexes. * **Medullary Level:** Integration of Tonic Neck and Tonic Labyrinthine reflexes (static postural reflexes). * **Midbrain Level:** Integration of all Righting Reflexes (except Optical). * **Cortical Level:** Integration of Hopping, Placing, and Optical Righting reflexes. * **Decerebrate Rigidity:** Occurs due to a transection between the superior and inferior colliculi (midbrain), leading to overactivity of the pontine reticulospinal tract.

Q: Which cranial nerve contributes 75% to the parasympathetic nervous system?

Vagus. ### Explanation The parasympathetic nervous system (craniosacral outflow) is primarily mediated by four cranial nerves: CN III, VII, IX, and X [1]. Among these, the **Vagus nerve (CN X)** is the most significant, contributing approximately **75% of all parasympathetic outflow** in the body. **Why Vagus is the Correct Answer:** While other cranial nerves are restricted to the head and neck, the Vagus nerve has an extensive distribution. It provides preganglionic parasympathetic fibers to the thoracic and abdominal viscera, extending from the esophagus and heart down to the splenic flexure of the large intestine [1]. Its massive territory and high density of autonomic fibers account for its dominant percentage in the system. **Analysis of Incorrect Options:** * **A. Oculomotor (CN III):** Supplies the ciliary muscle and sphincter pupillae (constriction of the pupil) [1]. Its reach is limited strictly to the intraocular muscles. * **B. Facial (CN VII):** Supplies the lacrimal, submandibular, and sublingual glands, as well as glands of the nasal and palatine mucosa [1]. * **C. Glossopharyngeal (CN IX):** Provides parasympathetic innervation specifically to the parotid gland via the otic ganglion [1]. **High-Yield NEET-PG Pearls:** * **Nucleus Origin:** The parasympathetic fibers of the Vagus nerve originate in the **Dorsal Nucleus of the Vagus** (located in the medulla). * **Sacral Outflow:** The remaining parasympathetic supply (for pelvic organs and the distal colon) comes from the **S2–S4 spinal segments** (Pelvic splanchnic nerves) [1]. * **Vagal Reflexes:** The Vagus nerve is the afferent limb for the aortic arch baroreceptor reflex and the efferent limb for the carotid sinus reflex (slowing heart rate). * **Vagotomy:** Highly selective vagotomy is a surgical procedure used to treat peptic ulcers by reducing gastric acid secretion without affecting gastric emptying.

Q: Posture is maintained by which reflex mechanism?

Stretch reflex. **Explanation:** The maintenance of posture and muscle tone is primarily mediated by the **Stretch Reflex (Myotatic Reflex)**. When gravity causes a slight displacement of a joint, the associated muscles are stretched. This activates **Muscle Spindles** (the sensory receptors), which send impulses via Type Ia afferent fibers to the spinal cord. These fibers synapse directly with alpha motor neurons, causing the stretched muscle to contract, thereby resisting the displacement and maintaining an upright posture. This is a monosynaptic reflex and is the only reflex that is continuously active to counteract gravity. **Analysis of Incorrect Options:** * **A. Crossed Extensor Reflex:** This is a polysynaptic withdrawal reflex. When one limb encounters a painful stimulus and withdraws (flexion), the opposite limb extends to support the body weight. While it helps in balance during sudden movements, it is not the primary mechanism for steady-state posture. * **C. Golgi Tendon Reflex (Inverse Stretch Reflex):** This is a protective disynaptic reflex mediated by Golgi Tendon Organs (GTOs). It causes muscle **relaxation** in response to excessive tension to prevent tendon avulsion. It acts as a "safety valve" rather than a postural mechanism. **High-Yield NEET-PG Pearls:** * **Muscle Spindle:** Detects change in muscle **length** (Static and Dynamic). * **Golgi Tendon Organ:** Detects change in muscle **tension**. * **Gamma Motor Neurons:** Regulate the sensitivity of the muscle spindle; they are crucial for maintaining the "stretch reflex" during voluntary contraction (Alpha-Gamma Co-activation). * **Supraspinal Control:** The Pontine Reticulospinal and Lateral Vestibulospinal tracts are the primary excitatory pathways to the gamma motor neurons that maintain postural tone.

Q: What is the receptor for Brain-Derived Neurotrophic Factor (BDNF)?

Trk-B. **Explanation:** **Brain-Derived Neurotrophic Factor (BDNF)** is a key member of the neurotrophin family, essential for the survival, growth, and plasticity of neurons in the central and peripheral nervous systems. 1. **Why Option B is Correct:** Neurotrophins exert their effects by binding to specific high-affinity transmembrane tyrosine kinase receptors known as **Trk (Tropomyosin receptor kinase) receptors**. BDNF specifically binds to and activates **TrkB**. Upon binding, TrkB undergoes dimerization and autophosphorylation, triggering intracellular signaling pathways (like MAPK and PI3K) that promote neuronal survival and long-term potentiation (LTP). 2. **Why Other Options are Incorrect:** * **TrkA:** This is the primary receptor for **Nerve Growth Factor (NGF)**. * **TrkC:** This is the primary receptor for **Neurotrophin-3 (NT-3)**. * *Note:* All neurotrophins (NGF, BDNF, NT-3, and NT-4/5) can also bind to a low-affinity receptor called **p75NTR**, which belongs to the tumor necrosis factor receptor family and often mediates apoptosis. 3. **High-Yield Clinical Pearls for NEET-PG:** * **BDNF & Memory:** BDNF is crucial for **Long-Term Potentiation (LTP)** in the hippocampus, making it vital for memory formation. * **Depression Link:** The "Neurotrophic Hypothesis of Depression" suggests that decreased levels of BDNF contribute to hippocampal atrophy in clinical depression; many antidepressants work by increasing BDNF expression. * **Val66Met Polymorphism:** A common genetic variation in the BDNF gene is associated with altered memory function and susceptibility to neuropsychiatric disorders. * **Exercise:** Physical activity is one of the most potent physiological stimulators of BDNF production in the brain.

Q: Injection of hypertonic saline into which region of the hypothalamus produces intense thirst?

Preoptic nucleus. **Explanation:** The regulation of thirst and water intake is primarily governed by **osmoreceptors** located in the **Anteroventral Third Ventricle (AV3V) region** of the hypothalamus. This region includes the **Preoptic nucleus** (specifically the median preoptic nucleus) and the organum vasculosum of the lamina terminalis (OVLT). 1. **Why Preoptic Nucleus is Correct:** The neurons in the preoptic area act as osmoreceptors. When hypertonic saline is injected, it increases the osmolarity of the extracellular fluid. This causes water to move out of these osmoreceptor cells by osmosis, causing them to shrink. This physical shrinkage triggers nerve impulses that project to the cerebral cortex to create the conscious sensation of **thirst** and to the supraoptic/paraventricular nuclei to release ADH. 2. **Why other options are incorrect:** * **Posterior region:** This area is primarily involved in thermoregulation (response to cold) and arousal; it is not a primary center for thirst. * **Supraoptic and Paraventricular nuclei:** While these nuclei are the sites of **synthesis** for Antidiuretic Hormone (ADH/Vasopressin) in response to osmotic changes, they are the *effectors* of water conservation rather than the primary sensory trigger for the *sensation* of thirst. **High-Yield Clinical Pearls for NEET-PG:** * **Thirst Center:** Located in the lateral hypothalamus and the preoptic area. * **Osmoreceptors:** Lack a blood-brain barrier, allowing them to sense plasma osmolarity directly. * **Stimuli for Thirst:** Increased plasma osmolarity (most potent), decreased ECF volume (via Angiotensin II), and dry mouth. * **Adipsia:** Damage to the anterior hypothalamus can lead to a total loss of thirst, even in the presence of severe dehydration.

Q: Slow wave sleep predominates in the first one-third of the night's sleep. Which phase of sleep is characterized by this?

NREM stages 3 and 4. **Explanation:** Sleep is divided into two main types: **NREM (Non-Rapid Eye Movement)** and **REM (Rapid Eye Movement)**. NREM sleep is further subdivided into stages 1 through 4 (in traditional classification). **Why NREM Stages 3 and 4 are correct:** Slow Wave Sleep (SWS), also known as **Deep Sleep**, specifically refers to NREM stages 3 and 4. It is characterized by high-amplitude, low-frequency **Delta waves** (0.5–4 Hz) on EEG. SWS is most prominent during the **first one-third of the night**, as the body prioritizes physical restoration and growth hormone secretion early in the sleep cycle. As the night progresses, SWS duration decreases while REM sleep duration increases. **Analysis of Incorrect Options:** * **NREM Stages 1 and 2:** These are "Light Sleep" phases. Stage 1 is a transition from wakefulness (Theta waves), and Stage 2 is characterized by **Sleep Spindles** and **K-complexes**. They occur throughout the night but do not constitute "Slow Wave Sleep." * **REM Sleep:** Also called "Paradoxical Sleep," it is characterized by high brain activity (Beta-like waves) and muscle atonia. REM sleep predominates in the **last one-third** of the night. **High-Yield Clinical Pearls for NEET-PG:** * **EEG Waves:** Remember the mnemonic **BATS Drink Blood** (Beta, Alpha, Theta, Spindles/K-complex, Delta, Beta) for the sequence of EEG waves from wakefulness to deep sleep and REM. * **Parasomnias:** Sleepwalking (Somnambulism), Sleep Terrors, and Bedwetting (Enuresis) typically occur during **Stage 4 NREM** (SWS). * **Growth Hormone:** Peak secretion occurs during NREM stages 3 and 4. * **Bruxism (Teeth grinding):** Occurs predominantly in Stage 2 NREM.

Question 1

Substance P belongs to the tachykinin family of peptides. Which of the following peripheral tissues contain substance P?

Accepted Answer

Nerve terminal

Answer

Plasma cell

Answer

Mast cell

Answer

Vascular endothelium

Question 2

Which afferent fibers are included in the stretch reflex?

Accepted Answer

Ia and II fibers

Answer

Ia and Ib fibers

Answer

Ib and II fibers

Answer

Golgi tendon organ

Question 3

Which stage of sleep is characterized by the presence of delta waves on an EEG recording?

Accepted Answer

Deep sleep (Stage N3 NREM sleep)

Answer

REM sleep

Answer

Stage N1 NREM sleep

Answer

Stage N2 NREM sleep

Question 4

Midbrain is the centre for the integration of which of the following reflexes?

Accepted Answer

Vestibular righting reflex

Answer

Optical righting reflex

Answer

Magnet reaction

Answer

Hopping and placing reaction

Question 5

Which cranial nerve contributes 75% to the parasympathetic nervous system?

Accepted Answer

Vagus

Answer

Oculomotor

Answer

Facial

Answer

Glossopharyngeal

Question 6

Which of the following is NOT seen in Kluver-Bucy syndrome?

Accepted Answer

Seizures

Answer

Hypersexuality

Answer

Metamorphopsia

Answer

Visual agnosia

Question 7

Posture is maintained by which reflex mechanism?

Accepted Answer

Stretch reflex

Answer

Crossed extensor reflex

Answer

Golgi tendon reflex

Answer

None of the above

Question 8

What is the receptor for Brain-Derived Neurotrophic Factor (BDNF)?

Accepted Answer

Trk-B

Answer

TrkB

Answer

Trk-C

Answer

None of the above

Question 9

Injection of hypertonic saline into which region of the hypothalamus produces intense thirst?

Accepted Answer

Preoptic nucleus

Answer

Posterior region

Answer

Paraventricular nucleus

Answer

Supraoptic nucleus

Question 10

Slow wave sleep predominates in the first one-third of the night's sleep. Which phase of sleep is characterized by this?

Accepted Answer

NREM stages 3 and 4

Answer

NREM stages 1 and 2

Answer

NREM stage 1

Answer

REM sleep

Neurophysiology — MCQs

Neurophysiology — MCQs

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