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: 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: 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: 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: CSF pressure is increased in all except -

Forced inspiration. ***Forced inspiration*** - During forced inspiration, the **intrathoracic pressure** decreases, which can lead to a slight **reduction** in CSF pressure rather than an increase, by increasing venous return from the head. - This creates a negative pressure gradient that facilitates blood flow from the cranial venous sinuses into the thoracic cavity. *Coughing* - Coughing significantly increases **intrathoracic pressure** and **intra-abdominal pressure**, which in turn impede venous return from the head and increase **intracranial venous pressure**, thereby raising CSF pressure. - This pressure transmission causes a transient but marked surge in CSF pressure. *Valsalva manoeuvre* - The **Valsalva manoeuvre** involves forced expiration against a closed glottis, leading to a significant increase in **intrathoracic** and **intra-abdominal pressures**. - This impedes **venous return** to the heart, causing a rise in **central venous pressure** and subsequently **intracranial venous pressure**, which increases CSF pressure. *Crying* - Crying, particularly vigorous crying, involves sustained **muscle contractions** in the face, neck, and chest, leading to an increase in **intrathoracic pressure** and **venous congestion**. - This rise in venous pressure within the head can cause a temporary increase in **CSF pressure**.

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.

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

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

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 4

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 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

CSF pressure is increased in all except -

Accepted Answer

Forced inspiration

Answer

Valsalva manoeuvre

Answer

Crying

Answer

Coughing

Question 8

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

Question 9

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 10

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

Accepted Answer

Glutamate

Answer

GABA

Answer

Glycine

Answer

Aspartate

Neurophysiology — MCQs

Neurophysiology — MCQs

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