Neurophysiology Practice Questions

Q: Which Brodmann areas correspond to the motor cortex?

4 and 6. The motor cortex is located in the frontal lobe, anterior to the central sulcus. It is primarily composed of **Brodmann Area 4** (Primary Motor Cortex) and **Brodmann Area 6** (Premotor and Supplementary Motor Areas). ### **Why Option A is Correct:** * **Brodmann Area 4 (Primary Motor Cortex):** Located in the precentral gyrus. It contains the giant pyramidal cells of Betz and is responsible for the execution of voluntary movements. * **Brodmann Area 6:** Located anterior to area 4. It includes the **Premotor Cortex** (planning complex movements) and the **Supplementary Motor Area** (coordination of bilateral movements and mental rehearsal of tasks). ### **Analysis of Incorrect Options:** * **Option B (1, 2, and 3):** These correspond to the **Primary Somatosensory Cortex** located in the postcentral gyrus of the parietal lobe. They process tactile and proprioceptive information. * **Option C (5 and 7):** These represent the **Sensory Association Cortex** in the superior parietal lobule. They are involved in spatial orientation and integrating sensory inputs. * **Option D (17 and 18):** These are the **Visual Cortex** areas (Area 17 is primary; Area 18 is secondary) located in the occipital lobe. ### **NEET-PG High-Yield Pearls:** * **Motor Homunculus:** A map representing the body parts in the motor cortex; the face and hands have disproportionately large representations due to the complexity of their movements. * **Lesion of Area 4:** Results in contralateral hemiparesis/paralysis (Upper Motor Neuron lesion signs). * **Lesion of Area 6:** Can lead to **Apraxia** (inability to perform complex learned movements despite normal muscle strength). * **Broca’s Area:** Located in Brodmann areas **44 and 45** (motor speech area) in the dominant hemisphere.

Q: What is the primary neurotransmitter in the striatal pathway?

Dopamine. **Explanation:** The **Nigrostriatal pathway** is one of the major dopaminergic pathways in the brain, connecting the substantia nigra pars compacta (SNc) in the midbrain to the striatum (caudate nucleus and putamen). **Dopamine** is the primary neurotransmitter released by these neurons. It plays a critical role in the modulation of the basal ganglia’s direct and indirect pathways, facilitating smooth, coordinated voluntary movement. **Analysis of Options:** * **Dopamine (Correct):** It acts on D1 receptors (excitatory) and D2 receptors (inhibitory) within the striatum to balance motor output. * **Glutamine (Incorrect):** This is a non-essential amino acid and a precursor to glutamate. While **Glutamate** is the primary excitatory neurotransmitter of the *corticostriatal* pathway, glutamine itself is not a primary signaling neurotransmitter. * **Glycine (Incorrect):** This is the major inhibitory neurotransmitter in the **spinal cord** and brainstem, not the striatum. * **Serotonin (Incorrect):** While serotonergic fibers from the raphe nuclei project to the striatum, it is a modulatory neurotransmitter rather than the primary driver of the nigrostriatal system. **High-Yield Clinical Pearls for NEET-PG:** * **Parkinson’s Disease:** Caused by the degeneration of dopaminergic neurons in the substantia nigra, leading to a depletion of dopamine in the striatum (Clinical triad: Tremor, Rigidity, Bradykinesia). * **GABA:** While dopamine is the primary *input* transmitter from the SNc, **GABA** is the primary *output* neurotransmitter of the striatum (striatonigral/striatopallidal pathways). * **MPTP:** A neurotoxin that specifically destroys dopaminergic neurons in the nigrostriatal pathway, inducing permanent Parkinsonian symptoms.

Q: The cyclical flexion and extension motions of a leg during walking result from activity at which level of the nervous system?

Spinal cord. **Explanation:** The correct answer is **Spinal Cord**. This is based on the concept of **Central Pattern Generators (CPGs)**. **1. Why the Spinal Cord is correct:** The basic rhythmic patterns for locomotion, such as the cyclical flexion and extension of the limbs during walking, are generated by neuronal circuits located entirely within the **spinal cord**. These CPGs can produce coordinated stepping movements even in the absence of sensory feedback or descending commands from the brain. While the brain initiates and modulates walking, the "hard-wired" rhythmic execution is a spinal function. **2. Why the other options are incorrect:** * **Cerebral Cortex:** It is responsible for the **initiation** of voluntary movement and navigating complex terrain, but it does not generate the basic rhythmic cycle. * **Cerebellum:** It acts as a comparator. It coordinates movement, maintains equilibrium, and ensures **smoothness and precision** by comparing intended movement with actual performance, but it is not the primary generator of the rhythm. * **Globus Pallidus (Basal Ganglia):** It is involved in the **planning and regulation** of muscle tone and scaling the amplitude of movements. Dysfunction here (e.g., Parkinson’s) leads to difficulty initiating gait, but the rhythmic circuitry itself resides lower. **3. High-Yield Clinical Pearls for NEET-PG:** * **Spinal Animal Model:** A "spinal" cat (with a transected spinal cord) can still perform rhythmic walking movements on a treadmill, proving the spinal cord's autonomous rhythmic capability. * **Reflex Stepping:** This is seen in neonates; when held upright with feet touching a surface, they perform stepping motions—a manifestation of spinal CPGs before cortical inhibition matures. * **Descending Control:** The **Mesencephalic Locomotor Region (MLR)** in the midbrain is the primary "on-switch" that activates these spinal CPGs.

Q: Which part of the brain gets activated first to initiate skilled movements?

Neocortex. **Explanation:** The initiation of a skilled, voluntary movement begins in the **Neocortex**, specifically within the **Association Areas** (such as the prefrontal and posterior parietal cortex). These areas conceptualize the "idea" of movement. This information is then relayed to the **Premotor and Supplementary Motor Areas** to create a motor plan, and finally to the **Primary Motor Cortex (Brodmann area 4)** to execute the command via the pyramidal tracts. **Why other options are incorrect:** * **Basal Ganglia:** These nuclei are involved in the **planning and programming** of movement. They receive input from the cortex and provide feedback to smooth out movements and regulate muscle tone, but they do not "initiate" the original intent. * **Cerebellum:** Known as the "silent area" of the brain, it acts as a **comparator**. It coordinates movement, maintains equilibrium, and ensures timing and precision by comparing the cortical intent with peripheral sensory feedback. It functions during and after the initiation phase. * **Pons:** This is a part of the brainstem that serves primarily as a relay station for signals between the forebrain and cerebellum and contains nuclei for cranial nerves. It does not initiate voluntary motor activity. **Clinical Pearls for NEET-PG:** * **Hierarchy of Movement:** Ideation (Association Cortex) → Programming (Basal Ganglia/Cerebellum) → Execution (Primary Motor Cortex). * **Lesion Localization:** A lesion in the Neocortex (Motor Area) leads to **spastic paralysis**, while a lesion in the Basal Ganglia leads to **involuntary movements** (e.g., tremors, chorea) or rigidity. * **Readiness Potential (Bereitschaftspotential):** An EEG recording shows electrical activity in the supplementary motor area nearly 800ms *before* a voluntary movement occurs.

Q: In the length-tension relationship of skeletal muscle, what is the length at which active tension is maximum?

Sarcomere length 2.25 micrometers. **Explanation:** The length-tension relationship in skeletal muscle is governed by the **Sliding Filament Theory**. Active tension is directly proportional to the number of **cross-bridge formations** between actin (thin) and myosin (thick) filaments. **1. Why Option D is Correct:** The maximum active tension is achieved at the **optimal sarcomere length ($L_0$)**, which ranges between **2.0 and 2.25 $\mu$m**. At 2.25 $\mu$m, there is an ideal overlap between actin and myosin, allowing the maximum number of cross-bridges to form. This results in the peak of the length-tension curve. **2. Why Other Options are Incorrect:** * **Option B (3.65 $\mu$m):** This is the point of **zero active tension**. At this length, the sarcomere is stretched so far that actin and myosin filaments do not overlap at all; hence, no cross-bridges can form. * **Option C (1.65 $\mu$m):** At this shortened length, the actin filaments from opposite ends of the sarcomere begin to overlap and collide (interference), and the thick myosin filaments hit the Z-discs. This physical crowding significantly reduces tension. * **Option A (2.0 $\mu$m):** While 2.0 $\mu$m is the lower limit of the "plateau" of maximum tension, 2.25 $\mu$m is the standard physiological value cited for the peak of the length-tension relationship in most medical textbooks (like Guyton). **High-Yield Facts for NEET-PG:** * **Total Tension:** The sum of Active Tension (cross-bridge cycling) and Passive Tension (elastic recoil of titin and connective tissue). * **Frank-Starling Law:** This is the cardiac application of the length-tension relationship, though cardiac muscle operates on the ascending limb of the curve to prevent overstretching. * **Titin:** The protein responsible for the **passive tension** in a muscle fiber.

Q: Which of the following functions is primarily associated with the frontal lobe?

Personality. **Explanation:** The **Frontal Lobe** is the largest lobe of the brain and is considered the "executive center." It is responsible for higher-order cognitive functions, including **personality**, social behavior, emotional regulation, and decision-making. Specifically, the **Prefrontal Cortex (PFC)** serves as the seat of personality; damage to this area (as famously seen in the case of Phineas Gage) leads to profound changes in character, loss of social inhibitions, and irritability. **Analysis of Options:** * **B. Memory:** While the frontal lobe handles "working memory," the primary center for long-term memory consolidation is the **Hippocampus** (located in the **Temporal Lobe**). * **C. Vision:** Visual processing is the primary function of the **Occipital Lobe** (Primary Visual Cortex, Brodmann area 17). * **D. Calculation:** Mathematical abilities and spatial orientation are primarily localized to the **Parietal Lobe** (specifically the dominant angular gyrus). **High-Yield Clinical Pearls for NEET-PG:** * **Broca’s Area:** Located in the inferior frontal gyrus (Brodmann areas 44, 45) of the dominant hemisphere; damage causes **motor (expressive) aphasia**. * **Micturition Center:** The frontal lobe inhibits the voiding reflex; lesions here can lead to **precipitant urgency** or incontinence. * **Primitive Reflexes:** Frontal lobe lesions can cause the reappearance of "frontal release signs" like the **Grasp, Snout, and Rooting reflexes**. * **Foster Kennedy Syndrome:** A frontal lobe tumor causing ipsilateral optic atrophy and contralateral papilledema.

Q: What is the resting membrane potential of a neuron?

-70mV. **Explanation:** The **Resting Membrane Potential (RMP)** is the electrical potential difference across the plasma membrane when a cell is in a non-excited state. In a typical large neuron, this value is **-70 mV**, indicating that the inside of the cell is negative relative to the outside. **Why -70mV is correct:** The RMP is primarily determined by two factors: 1. **Selective Permeability:** The resting membrane is significantly more permeable to Potassium ($K^+$) than to Sodium ($Na^+$) due to "leak channels." 2. **Ionic Gradients:** The $Na^+$-$K^+$ ATPase pump maintains high intracellular $K^+$ and high extracellular $Na^+$. While the equilibrium potential for $K^+$ is approx. -90 mV, the slight inward leak of $Na^+$ (equilibrium potential +60 mV) pulls the final RMP to **-70 mV**. **Analysis of Incorrect Options:** * **-9 mV:** This is the RMP of **Red Blood Cells (RBCs)**. * **-50 mV:** This is close to the **threshold potential** (usually -55 mV) required to trigger an action potential, but not the resting state. * **-100 mV:** This is more negative than the equilibrium potential of $K^+$, representing extreme hyperpolarization rarely seen under physiological conditions. **NEET-PG High-Yield Pearls:** * **Goldman-Hodgkin-Katz Equation:** Used to calculate RMP considering all permeable ions. * **Skeletal Muscle RMP:** -90 mV (similar to the $K^+$ equilibrium potential). * **SA Node RMP:** -55 to -60 mV (unstable, showing prepotential). * **Main Contributor:** The diffusion of $K^+$ out of the cell is the most important factor in establishing RMP, while the $Na^+$-$K^+$ pump is electrogenic and contributes only about -4 to -5 mV directly.

Question 1

Which Brodmann areas correspond to the motor cortex?

Accepted Answer

4 and 6

Answer

1, 2, and 3

Answer

5 and 7

Answer

16 and 18

Question 2

In Kluver-Bucy syndrome, which brain structure is typically lesioned?

Accepted Answer

Amygdala

Answer

Prefrontal cortex

Answer

Corpus callosum

Answer

Pituitary gland

Question 3

What is the primary neurotransmitter in the striatal pathway?

Accepted Answer

Dopamine

Answer

Glutamine

Answer

Glycine

Answer

Serotonin

Question 4

The cyclical flexion and extension motions of a leg during walking result from activity at which level of the nervous system?

Accepted Answer

Spinal cord

Answer

Cerebral cortex

Answer

Cerebellum

Answer

Globus pallidus

Question 5

The vestibulo-ocular reflex is primarily concerned with which part of the cerebellum?

Accepted Answer

Flocculonodular lobe

Answer

Archicerebellum

Answer

Neocerebellum

Answer

Occipital lobe

Question 6

Which part of the brain gets activated first to initiate skilled movements?

Accepted Answer

Neocortex

Answer

Pons

Answer

Basal ganglia

Answer

Cerebellum

Question 7

In the length-tension relationship of skeletal muscle, what is the length at which active tension is maximum?

Accepted Answer

Sarcomere length 2.25 micrometers

Answer

Sarcomere length 2.0 micrometers

Answer

Sarcomere length 3.65 micrometers

Answer

Sarcomere length 1.65 micrometers

Question 8

Which of the following functions is primarily associated with the frontal lobe?

Accepted Answer

Personality

Answer

Memory

Answer

Vision

Answer

Calculation

Question 9

Which one of the following forms the Blood Brain Barrier?

Accepted Answer

Astrocytes and endothelial cells

Answer

Choroidal cells

Answer

Oligodendrocytes

Answer

Endothelial cells exclusively

Question 10

What is the resting membrane potential of a neuron?

Accepted Answer

-70mV

Answer

-9mV

Answer

-50mV

Answer

-100mV

Neurophysiology — MCQs

Neurophysiology — MCQs

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