Neurophysiology — MCQs

Neurophysiology Indian Medical PG Practice Questions and MCQs

Question 631: Which term describes the representation of the body in the cerebrum?

A. Horizontal
B. Vertical (Correct Answer)
C. Tandem
D. Oblique

Explanation: ### Explanation **Correct Answer: B. Vertical** The representation of the body in the cerebrum (specifically in the primary motor cortex and primary somatosensory cortex) is described as **vertical**. This refers to the **columnar organization** of the cerebral cortex. The cerebral cortex is organized into functional units called **vertical columns** (extending through all six layers of the cortex). Each column serves a discrete sensory or motor function for a specific part of the body. For example, in the somatosensory cortex, all neurons within a single vertical column respond to the same modality of stimulus from the same specific body location. This vertical arrangement ensures efficient processing and integration of information. **Why other options are incorrect:** * **A. Horizontal:** While the cortex has six horizontal layers (laminae), the functional representation and processing units are defined by their vertical orientation across these layers, not by a horizontal spread. * **C. Tandem:** This term refers to things arranged one behind the other. It is not a standard anatomical or physiological term used to describe cortical mapping. * **D. Oblique:** There is no physiological basis for an oblique (slanted) functional organization in the cerebral cortex. **High-Yield NEET-PG Pearls:** * **Homunculus:** The spatial map of the body on the cortex is called the "Homunculus." It is characterized by being **upside down** (inverted), with the exception of the face. * **Cortical Magnification:** The size of the cortical area representing a body part is proportional to the **density of receptors/degree of motor control**, not the physical size of the part (e.g., the thumb and lips have larger representations than the trunk). * **Vernon Mountcastle:** He is the scientist credited with discovering the columnar (vertical) organization of the cerebral cortex.

Question 632: Which of the following is an amino neurotransmitter?

A. Acetylcholine
B. GABA (Correct Answer)
C. Lignocaine
D. Epinephrine

Explanation: Neurotransmitters are chemically classified into three main categories: **Amino acids**, **Amines** (Biogenic amines), and **Neuropeptides**. ### **Explanation of the Correct Answer** **B. GABA (Gamma-Aminobutyric Acid):** This is the correct answer. GABA is a primary inhibitory neurotransmitter in the CNS and is chemically an **amino acid** (specifically, a non-proteinogenic amino acid derived from glutamate). Other examples of amino acid neurotransmitters include **Glutamate** (excitatory), **Glycine** (inhibitory in the spinal cord), and **Aspartate**. ### **Analysis of Incorrect Options** * **A. Acetylcholine:** This belongs to its own distinct chemical class (esters of choline). It is neither an amino acid nor an amine. * **C. Lignocaine:** This is a **local anesthetic** drug (amide-type), not a naturally occurring neurotransmitter. It works by blocking voltage-gated sodium channels. * **D. Epinephrine:** This is a **Biogenic Amine** (specifically a Catecholamine). While amines are derived from amino acids (e.g., Epinephrine is derived from Tyrosine), they are classified separately because they have undergone decarboxylation. ### **High-Yield NEET-PG Pearls** * **Glutamate** is the most common excitatory neurotransmitter in the brain. * **GABA-A receptors** are ionotropic (chloride channels), while **GABA-B receptors** are metabotropic (G-protein coupled). * **Glycine** is unique because it acts as an inhibitory neurotransmitter in the spinal cord but serves as an obligatory co-agonist for the excitatory **NMDA receptor** in the brain. * **Rate-limiting steps:** Tyrosine hydroxylase for Catecholamines; Choline acetyltransferase for Acetylcholine; Glutamic acid decarboxylase (GAD) for GABA.

Question 633: A person with eyes closed and mind wandering will exhibit which of the following brain waves?

A. Alpha waves (Correct Answer)
B. Beta waves
C. Delta waves
D. Theta waves

Explanation: ### Explanation The correct answer is **Alpha waves**. **1. Why Alpha waves are correct:** Alpha waves (8–13 Hz) are the characteristic rhythm of an adult who is **awake but relaxed**, with their **eyes closed** and mind wandering (inattentive). They are most prominent in the occipital cortex. The moment the person opens their eyes or focuses on a specific mental task (like solving a math problem), alpha waves disappear and are replaced by faster, lower-voltage waves—a phenomenon known as **Alpha Block** or **Desynchronization**. **2. Why the other options are incorrect:** * **Beta waves (14–30 Hz):** These are seen when the person is **alert, active, and attentive** with eyes open. They represent a state of mental concentration or sensory stimulation. * **Theta waves (4–7 Hz):** These occur during **Stage 1 NREM sleep** or during periods of emotional stress and frustration in adults. They are also normal in children. * **Delta waves (< 4 Hz):** These are the slowest, highest-amplitude waves. They are characteristic of **deep sleep (Stage 3 NREM)** and are also seen in infants or in cases of organic brain disease. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **EEG Frequency Mnemonic:** **B**eta > **A**lpha > **T**heta > **D**elta (Fastest to Slowest: "**B**at **A**t **T**he **D**oor"). * **Epilepsy:** The classic EEG finding for **Absence Seizures** (Petit mal) is a **3 Hz spike-and-wave pattern**. * **Sleep Spindles & K-complexes:** These are the hallmark EEG features of **Stage 2 NREM sleep**. * **REM Sleep:** The EEG during REM sleep paradoxically resembles the awake state (Beta-like waves), which is why it is called **Paradoxical Sleep**.

Question 634: What is the lowest level of integration for the stretch reflex?

A. Cerebral cortex
B. Lower medulla
C. Spinal cord (Correct Answer)
D. All of the above

Explanation: ### Explanation **1. Why the Spinal Cord is Correct:** The stretch reflex (myotatic reflex) is a **monosynaptic reflex**, meaning it involves only one synapse between the sensory (afferent) neuron and the motor (efferent) neuron. The anatomical pathway consists of: * **Receptor:** Muscle spindle. * **Afferent:** Type Ia nerve fibers. * **Center:** The **Spinal Cord** (specifically the anterior horn cells). * **Efferent:** Alpha motor neurons. Because the entire reflex arc is completed within a single spinal segment without requiring input from higher brain centers, the spinal cord is the **lowest and primary level of integration**. **2. Why Other Options are Incorrect:** * **Cerebral Cortex:** This is the highest level of motor control. While it modulates reflexes via descending pathways (like the corticospinal tract), it is not required for the basic execution of the stretch reflex. * **Lower Medulla:** This region contains centers for vital autonomic functions (respiration, vasomotor) and cranial nerve nuclei, but it does not serve as the integration center for peripheral spinal stretch reflexes. * **All of the Above:** Since the reflex can function perfectly in a "spinal animal" (where the spinal cord is transected from the brain), higher centers are not part of the basic integration level. **3. NEET-PG High-Yield Pearls:** * **Monosynaptic Nature:** The stretch reflex is the *only* monosynaptic reflex in the human body. * **Reciprocal Inhibition:** While the stretch reflex is monosynaptic, the inhibition of the antagonist muscle is **polysynaptic** (via inhibitory interneurons). * **Clinical Correlation:** Testing Deep Tendon Reflexes (DTRs) assesses the integrity of specific spinal segments (e.g., Knee jerk = L2-L4). * **Upper vs. Lower Motor Neuron:** Lesions above the spinal cord level (UMN) lead to **hyperreflexia** due to loss of descending inhibition, while lesions at the spinal level (LMN) lead to **areflexia**.

Question 635: What is the rhythm per second of Buerger waves (alpha waves) on an EEG?

A. 0-4 Hz
B. 4-7 Hz
C. 7-13 Hz (Correct Answer)
D. 13-30 Hz

Explanation: **Explanation:** The correct answer is **C (7-13 Hz)**. **Alpha waves**, also known as **Buerger waves**, are the characteristic EEG rhythm of an awake, relaxed individual with their eyes closed. They are most prominent in the occipital and parietal regions. The frequency typically ranges from **8 to 13 Hz** (standardized as 7-13 Hz in many texts). The defining physiological feature of alpha waves is **Alpha Blockade** (or desynchronization): when the subject opens their eyes or focuses on a mental task, the high-amplitude alpha waves are replaced by low-amplitude, high-frequency beta waves. **Analysis of Incorrect Options:** * **A. 0-4 Hz (Delta waves):** These are the slowest, highest-amplitude waves. They are normal during deep sleep (Stage N3 NREM) and in infants, but pathological in awake adults (indicating brain injury or coma). * **B. 4-7 Hz (Theta waves):** These occur during light sleep (Stage N1 NREM) and are common in children. In awake adults, they may indicate emotional stress or frustration. * **D. 13-30 Hz (Beta waves):** These are fast, low-voltage waves seen during active mental concentration, alertness, or REM sleep. **High-Yield Clinical Pearls for NEET-PG:** * **Gamma waves (30-100 Hz):** Associated with higher mental activity and "binding" of different sensory inputs. * **Order of frequency (Highest to Lowest):** Gamma > Beta > Alpha > Theta > Delta (**Mnemonic:** **G**o **B**e **A** **T**rue **D**octor). * **EEG in Hepatic Encephalopathy:** Characterized by **Triphasic waves** (usually in the theta/delta range). * **Absence Seizures:** Classically show **3 Hz spike-and-wave** discharges.

Question 636: What does the nerve impulse leading to smooth muscle contraction initiate?

A. Opening of calcium channels, leading to increased intracellular Ca+2 concentration. (Correct Answer)
B. Depolarization of both the plasma membrane and T-tubules.
C. Inhibition of Na+ entry into the sarcomere.
D. Binding of acetylcholine to receptors in the sarcoplasmic reticulum.

Explanation: **Explanation:** The fundamental mechanism of smooth muscle contraction is the increase in cytosolic calcium ($Ca^{2+}$). Unlike skeletal muscle, smooth muscle contraction is primarily triggered by the influx of extracellular $Ca^{2+}$ through voltage-gated or ligand-gated calcium channels and its release from the sarcoplasmic reticulum. Once intracellular $Ca^{2+}$ rises, it binds to **Calmodulin**. This complex activates **Myosin Light Chain Kinase (MLCK)**, which phosphorylates the myosin head, allowing it to bind to actin and initiate contraction. **Analysis of Incorrect Options:** * **Option B:** While depolarization occurs, smooth muscles **lack a well-developed T-tubule system**. Instead, they have rudimentary indentations called **caveolae**. T-tubules are characteristic of skeletal and cardiac muscles. * **Option C:** Inhibition of $Na^+$ entry would typically lead to hyperpolarization or prevent depolarization, which would inhibit rather than initiate contraction. * **Option D:** Acetylcholine (ACh) binds to **muscarinic receptors** (like $M_3$) on the **sarcolemma** (plasma membrane), not the sarcoplasmic reticulum. This binding triggers a second messenger cascade ($IP_3$ pathway) to release $Ca^{2+}$. **High-Yield NEET-PG Pearls:** * **Regulatory Protein:** Smooth muscle uses **Calmodulin**; skeletal/cardiac muscle uses **Troponin C**. * **L-type Calcium Channels:** These are the primary targets for Calcium Channel Blockers (CCBs) used in treating hypertension. * **Latch-bridge Mechanism:** A unique feature of smooth muscle allowing it to maintain prolonged tension with minimal ATP consumption. * **Multi-unit vs. Unitary:** Unitary (visceral) smooth muscle acts as a syncytium via **gap junctions** (e.g., GI tract, uterus).

Question 637: The tonic neck reflex is lost in a lesion of which part of the central nervous system?

A. Cerebral cortex
B. Midbrain
C. Medulla (Correct Answer)
D. Spinal cord

Explanation: **Explanation:** The **Tonic Neck Reflex (TNR)** is a primitive postural reflex mediated by the **Medulla Oblongata**. It is triggered by the stimulation of proprioceptors in the cervical muscles and joint capsules when the head is turned or tilted. **1. Why Medulla is Correct:** Postural reflexes are organized hierarchically within the CNS. The Medulla is the primary integration center for static postural reflexes, including the Tonic Neck Reflex and the Tonic Labyrinthine Reflex. In a **decerebrate animal** (where the brainstem is transected at the midbrain level, leaving the medulla intact), these reflexes are exaggerated and clearly demonstrable. Therefore, a lesion involving the medulla or structures below it results in the loss of this reflex. **2. Analysis of Incorrect Options:** * **Cerebral Cortex:** Lesions here (decorticate state) actually release the lower brainstem centers from cortical inhibition, making the tonic neck reflex more prominent rather than losing it. * **Midbrain:** The midbrain is the center for **Righting Reflexes** (which allow the animal to restore its normal position). A lesion at the midbrain level results in a decerebrate state where tonic neck reflexes (medullary) are still present and hyperactive. * **Spinal Cord:** While the spinal cord mediates basic stretch reflexes, it lacks the integrative circuitry required for the complex coordination of the tonic neck reflex. **High-Yield Clinical Pearls for NEET-PG:** * **Integration Levels:** * Spinal Cord: Stretch reflexes. * Medulla: Tonic Neck & Tonic Labyrinthine reflexes. * Midbrain: Righting reflexes. * Cerebral Cortex: Hopping & Placing reactions. * **Clinical Significance:** In infants, the "Asymmetric Tonic Neck Reflex" (Fencing posture) is normal but should disappear by **6 months**. Persistence suggests upper motor neuron lesions or cerebral palsy.

Question 638: Which intracranial structure is sensitive to pain?

A. Pia mater
B. Pial vessels
C. Dura mater (Correct Answer)
D. Brain matter

Explanation: ### Explanation **Correct Answer: C. Dura mater** The brain's sensitivity to pain is localized to specific structures, as the brain parenchyma itself lacks nociceptors. Pain sensitivity in the cranium is primarily governed by the **trigeminal nerve (CN V)** supratentorially and the **upper cervical nerves** infratentorially. **1. Why Dura Mater is Correct:** The **Dura mater** is highly sensitive to pain, particularly along the course of the dural arteries (like the middle meningeal artery) and the venous sinuses. Stimulation of these areas, whether by stretching, inflammation, or pressure, results in headache. The dural innervation is dense, making it the most clinically significant pain-sensitive intracranial structure. **2. Why the Other Options are Incorrect:** * **Pia mater and Arachnoid mater:** These inner layers of the meninges are generally considered **insensitive** to pain. * **Pial vessels:** While the **proximal segments** of large cerebral arteries (at the base of the brain) are pain-sensitive, the distal pial vessels on the brain surface are largely insensitive to painful stimuli. * **Brain matter:** The brain parenchyma itself is **completely insensitive** to pain. This is why neurosurgeons can perform "awake craniotomies" where they probe or cut brain tissue while the patient is conscious without causing pain. **3. High-Yield Facts for NEET-PG:** * **Pain-Sensitive Structures:** Dura mater, dural arteries (Middle Meningeal), venous sinuses, proximal portions of large cerebral arteries (Circle of Willis), and cranial nerves with sensory components (V, IX, X). * **Pain-Insensitive Structures:** Brain parenchyma, ependyma, choroid plexus, and most of the pia-arachnoid. * **Clinical Correlation:** Headaches often arise from the traction or displacement of dural vessels or inflammation of the dura (meningitis). * **Rule of Thumb:** Structures above the tentorium cerebelli refer pain to the front of the head (CN V), while structures below refer pain to the back of the head/neck (C1-C3).

Question 639: Which of the following is the afferent limb of the corneal reflex?

A. Facial nerve
B. Trigeminal nerve (Correct Answer)
C. Trochlear nerve
D. Optic nerve

Explanation: ***Trigeminal nerve***- The **Trigeminal nerve (CN V)**, specifically its **ophthalmic division (V1)**, detects the tactile sensation on the cornea, making it the sensory input (afferent limb) of the reflex arc.- Sensory impulses travel through the nasociliary nerve (a branch of V1) to the **principal sensory nucleus of CN V** in the pons.*Optic nerve*- The **Optic nerve (CN II)** is crucial for the sense of **vision** and serves as the afferent limb for the **pupillary light reflex**.- It transmits light stimuli, whereas the corneal reflex is triggered by **tactile stimuli** (touch or pain).*Facial nerve*- The **Facial nerve (CN VII)** serves as the **efferent (motor) limb** of the reflex, responsible for causing the blink via innervation of the **orbicularis oculi** muscle.- It carries the motor command *away* from the nucleus to the muscle, contrasting with the afferent nerve which carries sensation *to* the nucleus.*Trochlear nerve*- The **Trochlear nerve (CN IV)** is a motor nerve responsible for innervating the **superior oblique muscle**, which controls eye movement (depression and intorsion).- It has no role in the sensation of the cornea or the motor response (blinking) that characterizes the corneal reflex.

Question 640: In a normal awake person at rest with eyes closed, EEG waves that are reduced on opening the eyes:

A. Theta waves
B. Beta waves
C. Alpha waves (Correct Answer)
D. Delta waves

Explanation: ***Alpha waves*** - These waves (8-13 Hz) are characteristic of the **relaxed wakefulness** state, present chiefly over the occipital areas when the eyes are closed (the **Berger rhythm**). - When the eyes are opened or the person concentrates, the alpha waves are immediately abolished and replaced by fast, low-voltage **Beta waves**, a phenomenon known as **alpha block** or desynchronization. *Beta waves* - These waves (>13 Hz) are associated with **active concentration**, mental alertness, or the act of opening the eyes. - The opening of the eyes causes the brain activity to shift *towards* the Beta rhythm, thus they are increased, not reduced, in this scenario. *Theta waves* - Theta waves (4-7 Hz) are typically observed during **NREM sleep stages 1 and 2** (light sleep) and are usually infrequent in the normal awake, resting adult. - Their presence or absence is not primarily governed by the action of opening or closing the eyes in an awake individual; they reflect stages of sleep or deep emotional arousal. *Delta waves* - Delta waves (<4 Hz) are the slowest waves, typically dominating the EEG during **deep slow-wave sleep (N3)** or indicative of serious brain pathology when seen in an awake adult. - They are absent in the normal awake, resting state, so the act of opening the eyes does not lead to their reduction.

Practice by Chapter

Neurons and Glial Cells

Practice Questions

Synaptic Transmission

Practice Questions

Sensory Processing

Practice Questions

Motor Control Systems

Practice Questions

Autonomic Nervous System

Practice Questions

Hypothalamus and Limbic System

Practice Questions

Cerebral Cortex Functions

Practice Questions

Electroencephalography

Practice Questions

Neuroplasticity

Practice Questions

Sleep and Wakefulness

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free