Neurophysiology Practice Questions

Q: Identify the sleep stage marked in the EEG during the sleep-wake cycle?

REM sleep. ***REM sleep*** - The marked EEG pattern shows **low-amplitude, mixed-frequency waves** which are characteristic of REM sleep, often resembling an awake state. - This stage is associated with **rapid eye movements**, vivid dreams, and muscle atonias. *Stage 1 sleep* - Characterized by a transition from alpha waves to **theta waves**, which are slightly slower than alpha waves and have a higher amplitude than the waves shown. - This is the **lightest stage of sleep**, with the person easily aroused. *Stage 2 sleep* - Marked by the presence of **sleep spindles** (bursts of high-frequency waves) and **K-complexes** (large, slow waves), which are not visible in the image. - The background activity consists of **theta waves,** which are slower and higher amplitude than the waves present in the image. *Stage 3 sleep* - This is **deep non-REM sleep**, also known as slow-wave sleep, characterized by **delta waves** (high-amplitude, low-frequency waves). - The waves in the image are much faster and lower amplitude than delta waves characteristic of Stage 3 sleep.

Q: True about decorticate rigidity:

Rigidity is less pronounced than decerebrate rigidity. ***Rigidity is less pronounced than decerebrate rigidity*** - **Decorticate rigidity** indicates damage above the **red nucleus**, disrupting descending inhibitory pathways from the cortex. [1] - While reflecting serious brain injury, it is generally considered a **less severe prognosis** than decerebrate rigidity because the red nucleus and some rubrospinal tract functions remain intact. *Flexion of lower limbs & extension of upper limbs* - **Decorticate rigidity** typically presents with **flexion of the upper limbs** (adduction, internal rotation, elbow flexion, wrist flexion), and **extension of the lower limbs** (adduction, extension, internal rotation) [1]. - This characteristic posture, often described as "mummy baby" or "posture of salvation," is due to uninhibited activity of the **rubrospinal tract** and the absence of cortical input [1]. *Removal of cerebral cortex and basal ganglia* - **Decorticate rigidity** results from lesions that interrupt the descending pathways **above the red nucleus** (e.g., in the cerebral hemispheres or internal capsule) [1]. - This specifically means the **cerebral cortex** is "removed" in terms of its functional input, but the basal ganglia are within the affected region. *None of the options* - This option is incorrect because the statement about decorticate rigidity being **less pronounced than decerebrate rigidity** is accurate. - The other clinical description and neurological basis are distinct from true decorticate rigidity.

Q: What is the rate of CSF formation in children?

0.3 ml/min. ***0.3 ml/min*** - The rate of **cerebrospinal fluid (CSF) formation** is approximately **0.3-0.4 ml/min** in both children and adults. - This rate is relatively **constant across age groups**, although total CSF volume varies (50-60 ml in infants, ~150 ml in adults). - This production rate supports a total CSF volume turnover about **3-4 times per day**. - CSF is primarily produced by the **choroid plexus** in the brain ventricles. *1 ml/min* - This rate is **3 times higher** than the normal physiological CSF production rate. - Such an elevated rate would lead to rapid accumulation of CSF and could result in **hydrocephalus**. - Overproduction of CSF is a rare cause of hydrocephalus (e.g., choroid plexus papilloma). *3 ml/min* - A CSF formation rate of 3 ml/min is **10 times higher** than normal and would be pathologically extreme. - This would result in severe and rapid **hydrocephalus** with significant intracranial pressure elevation. - No normal physiological state is associated with such a high CSF production rate. *20 ml/min* - This rate is **extremely and unrealistically high** (>60 times normal). - Would be incompatible with normal brain function, causing extreme and potentially fatal **hydrocephalus**. - Does not reflect any known physiological or pathological condition of CSF production.

Q: Withdrawal reflex is an example of which of the following?

Polysynaptic reflex. ***Polysynaptic reflex*** - The **withdrawal reflex** involves multiple synapses between sensory neurons, interneurons, and motor neurons. - This complex pathway allows for coordinated muscle contractions (e.g., flexion of a limb) and inhibition of antagonistic muscles to quickly move away from a painful stimulus. *Monosynaptic reflex* - A **monosynaptic reflex** involves only one synapse between a sensory neuron and a motor neuron, such as the **stretch reflex** (e.g., patellar reflex). - It does not involve interneurons, making it a simpler and faster reflex arc. *Both A and B of the above* - The withdrawal reflex is specifically **polysynaptic**, not monosynaptic, because it requires interneurons to integrate the sensory input and coordinate the motor response. - Combining both would imply it can be both at the same time, which is incorrect for this specific reflex. *None of the options* - This option is incorrect because the withdrawal reflex clearly fits the definition and characteristics of a **polysynaptic reflex**. - There is a definitive correct answer provided among the choices.

Q: Intracranial pressure is not raised during

Hyperventilation. ***Hyperventilation*** - **Hyperventilation** reduces **PaCO2**, leading to cerebral vasoconstriction and decreased cerebral blood flow, thereby lowering **intracranial pressure (ICP)**. - This is a common maneuver used to temporarily reduce acutely elevated ICP in emergency settings. *Status epilepticus* - **Status epilepticus** significantly increases **cerebral metabolic demand**, leading to increased cerebral blood flow and volume, which can raise **ICP**. - Prolonged seizures can also cause **cerebral edema** due to metabolic disturbances, further contributing to elevated ICP. *Head injury* - **Head injury** frequently causes **brain swelling** (cerebral edema), hematoma formation (extradural, subdural, intraparenchymal), or hydrocephalus, all of which expand intracranial contents and increase **ICP**. - The direct trauma can disrupt the **blood-brain barrier**, leading to vasogenic edema and increased brain volume. *Subdural hematoma* - A **subdural hematoma** is a collection of blood between the dura mater and the arachnoid mater, which acts as a mass lesion within the rigid cranial vault. - This added volume directly increases **intracranial pressure** by occupying space and compressing brain tissue.

Q: 'C' fibers carry sensations through which pathway?

Lateral spinothalamic tract. ***Lateral spinothalamic tract*** - **C fibers** are unmyelinated nerve fibers that transmit **slow, dull, burning, or aching pain**, as well as **temperature** sensations. - The **lateral spinothalamic tract** is the primary ascending pathway responsible for conveying these **pain and temperature** sensations from the spinal cord to the brain. *Posterior column* - The **posterior column-medial lemniscus pathway** is primarily responsible for transmitting **fine touch, vibration, conscious proprioception, and two-point discrimination**. - It consists of thickly myelinated A-beta fibers, which are distinct from the unmyelinated C fibers involved in pain transmission. *Anterior spinothalamic tract* - The **anterior spinothalamic tract** mainly carries crude touch and pressure sensations. - While it is a part of the anterolateral system, it does not primarily transmit the pain and temperature signals carried by C fibers. *All of the options* - This option is incorrect because C fibers specifically transmit sensations through the **lateral spinothalamic tract**, not all the listed pathways. - Each pathway has distinct roles in sensory transmission, and C fibers are not associated with the posterior column or exclusively with the anterior spinothalamic tract for their primary functions.

Q: What is the maximum duration of time spent in the NREM sleep stage N2?

20-40 minutes. ***20-40 minutes*** - **NREM stage N2** can last up to 20-40 minutes in a single sleep cycle, particularly in the later cycles of the night when N2 episodes become more prolonged. - This stage is characterized by **sleep spindles** and **K-complexes** on EEG, representing consolidated sleep that is deeper than N1 but lighter than N3. - While N2 comprises 45-55% of total sleep time across the entire night, the question asks about maximum duration in a single episode, not cumulative time. *45-60 minutes* - This duration would encompass most of an entire sleep cycle (90-110 minutes), leaving insufficient time for N3 and REM stages. - This likely confuses the **percentage of total sleep time** (45-55%) with the **duration per cycle**. - No single NREM stage typically lasts 45-60 minutes continuously in a normal sleep cycle. *5-10 minutes* - This duration is typical for **NREM stage N1**, the lightest stage of sleep and the transition from wakefulness to sleep. - N1 accounts for only about 5% of total sleep time and is characterized by theta wave activity on EEG. *1-5 minutes* - This represents the **initial entry into sleep (NREM stage N1)** or very brief arousals during the night. - This is far too short to represent the maximum duration of N2, which is a more substantial and prolonged sleep stage.

Q: Which of the following is the primary excitatory neurotransmitter in the central nervous system?

Glutamate. ***Glutamate*** - **Glutamate** is the primary **excitatory neurotransmitter** in the central nervous system - It acts on ionotropic receptors (AMPA, NMDA, kainate) and metabotropic receptors to **depolarize** the postsynaptic membrane - Increases the likelihood of postsynaptic neuron firing by opening ligand-gated ion channels - Plays a crucial role in **synaptic plasticity**, learning, and memory *GABA* - **GABA (gamma-aminobutyric acid)** is the primary **inhibitory neurotransmitter** in the CNS - Hyperpolarizes the postsynaptic membrane by opening chloride channels - Reduces neuronal excitability throughout the brain *Glycine* - **Glycine** is the primary **inhibitory neurotransmitter** in the spinal cord and brainstem - Acts via glycine receptors (chloride channels) leading to hyperpolarization - Important for motor and sensory processing in the spinal cord *Aspartate* - **Aspartate** is also an **excitatory neurotransmitter** acting on NMDA receptors - However, it is **much less abundant** and less important than glutamate - Glutamate is considered the main excitatory neurotransmitter due to its widespread distribution and predominant role

Q: Which of the following is a primary function of the cerebellum?

Coordination of voluntary movements. ***Coordination of voluntary movements*** - The cerebellum plays a crucial role in **coordinating voluntary movements**, ensuring they are smooth, precise, and fluid. - It receives sensory input from the body and motor commands from the cortex, integrating this information to **adjust ongoing movements** for accuracy. - This is considered the **most prominent and primary function** of the cerebellum in clinical and physiological contexts. *Regulation of muscle tone* - The cerebellum **does regulate muscle tone** and is part of the classical triad of cerebellar functions (coordination, equilibrium, and muscle tone). - However, when compared to coordination of voluntary movements, this is considered a **secondary or supporting function**. - Cerebellar lesions typically cause **hypotonia** (reduced muscle tone), demonstrating its role in tone regulation. - In the context of "primary function," coordination takes precedence over tone regulation. *Planning and initiation of movement* - **Planning and initiation of movement** are primarily functions of the **cerebral cortex**, particularly the supplementary motor area and premotor cortex, along with the basal ganglia. - The cerebellum contributes to motor planning but does not initiate the movement itself. *None of the options* - This option is incorrect because the cerebellum has a clear and primary function as described in the correct option.

Q: What is the total volume of cerebrospinal fluid (CSF) in an adult human?

150 ml. ***150 ml*** - The total volume of **cerebrospinal fluid (CSF)** in an adult human is approximately 150 ml, distributed within the brain's ventricles, subarachnoid space, and spinal canal. - This volume is constantly replenished; about 500 ml of CSF are produced daily, meaning the entire volume is replaced several times a day. *500 ml* - While 500 ml is the approximate **daily production rate** of CSF, it is not the total static volume present in the central nervous system at any given time. - The CSF is continually produced and reabsorbed, maintaining a circulating volume of about 150 ml. *50 ml* - 50 ml is significantly **lower** than the actual total volume of CSF found in an adult human. - Such a low volume would likely be insufficient to provide adequate **cushioning** and metabolic support for the brain and spinal cord. *800 ml* - 800 ml is an **excessively large** volume for the total CSF in an adult human and would indicate a severe condition of **hydrocephalus**. - This volume is far beyond the normal physiological capacity for circulating CSF.

Question 1

Identify the sleep stage marked in the EEG during the sleep-wake cycle?

Accepted Answer

REM sleep

Answer

Stage 1 sleep

Answer

Stage 2 sleep

Answer

Stage 3 sleep

Question 2

True about decorticate rigidity:

Accepted Answer

Rigidity is less pronounced than decerebrate rigidity

Answer

Flexion of lower limbs & extension of upper limbs

Answer

Removal of cerebral cortex and basal ganglia

Answer

None of the options

Question 3

What is the rate of CSF formation in children?

Accepted Answer

0.3 ml/min

Answer

1 ml/min

Answer

3 ml/min

Answer

20 ml/min

Question 4

Withdrawal reflex is an example of which of the following?

Accepted Answer

Polysynaptic reflex

Answer

Monosynaptic reflex

Answer

Both A and B of the above

Answer

None of the options

Question 5

Intracranial pressure is not raised during

Accepted Answer

Hyperventilation

Answer

Status epilepticus

Answer

Head injury

Answer

Subdural hematoma

Question 6

'C' fibers carry sensations through which pathway?

Accepted Answer

Lateral spinothalamic tract

Answer

Posterior column

Answer

Anterior spinothalamic tract

Answer

All of the options

Question 7

What is the maximum duration of time spent in the NREM sleep stage N2?

Accepted Answer

20-40 minutes

Answer

5-10 minutes

Answer

45-60 minutes

Answer

1-5 minutes

Question 8

Which of the following is the primary excitatory neurotransmitter in the central nervous system?

Accepted Answer

Glutamate

Answer

GABA

Answer

Glycine

Answer

Aspartate

Question 9

Which of the following is a primary function of the cerebellum?

Accepted Answer

Coordination of voluntary movements

Answer

None of the options

Answer

Regulation of muscle tone

Answer

Planning and initiation of movement

Question 10

What is the total volume of cerebrospinal fluid (CSF) in an adult human?

Accepted Answer

150 ml

Answer

500 ml

Answer

50 ml

Answer

800 ml

Neurophysiology — MCQs

Neurophysiology — MCQs

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