Neurophysiology Practice Questions

Q: Which of the following is an amino neurotransmitter?

GABA. 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.

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

Spinal cord. ### 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**.

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

Medulla. **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.

Q: Which of the following is the afferent limb of the corneal reflex?

Trigeminal nerve. ***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.

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

Alpha waves. ### **Explanation** The correct answer is **Alpha waves**. #### **1. Why Alpha Waves are Correct** * **Alpha waves (8–13 Hz)** are the characteristic rhythm of a **relaxed, awake adult** with **eyes closed**. They are most prominent in the **parieto-occipital** regions. * The phenomenon described in the question is known as **Alpha Block** or **Desynchronization**. When the person opens their eyes or engages in focused mental activity (like solving a math problem), the synchronized alpha rhythm is replaced by fast, irregular, low-voltage activity. This happens because visual input "breaks" the synchronized firing of cortical neurons. #### **2. Why Other Options are Incorrect** * **Beta waves (13–30 Hz):** These are seen during **active thinking**, alertness, or tension. Opening the eyes usually *increases* beta activity rather than reducing it. * **Theta waves (4–7 Hz):** These are normal in **children** or during **Stage N1 sleep** in adults. In an awake adult, they may indicate emotional stress or certain brain disorders. * **Delta waves (<4 Hz):** These are the slowest waves with the highest amplitude. They are characteristic of **deep sleep (Stage N3)** or infancy. Their presence in an awake adult signifies serious organic brain disease. #### **3. High-Yield Clinical Pearls for INI-CET** * **Mnemonic for EEG Frequencies:** **D**on't **T**ouch **A**ll **B**uttons (**D**elta < **T**heta 2 microvolts is recorded.

Q: Which wave is seen in the given EEG recording?

Delta waves. ***Delta waves*** - The highlighted EEG activity shows **large amplitude, low-frequency waves** (typically 0.5-4 Hz), which are characteristic of delta waves. - Delta waves are normally associated with **deep sleep** (NREM stage 3) or **pathological conditions** in awake adults, indicating significant brain dysfunction. *Alpha waves* - Alpha waves have a frequency range of **8-13 Hz** and typically appear when an individual is in a relaxed, awake state with eyes closed. - The waves in the image are much slower and higher in amplitude than typical alpha waves. *Beta waves* - Beta waves are characterized by a higher frequency range of **14-30 Hz** and are associated with active thinking, alertness, and concentration. - The observed activity is significantly slower and higher in amplitude than beta waves. *Epsilon wave* - The term "epsilon wave" is not a standard classification for EEG brain waves in the context of normal or common pathological activity, unlike alpha, beta, theta, and delta waves. - In cardiology, "epsilon wave" refers to a specific finding on an ECG in **Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)**, not an EEG.

Q: Name the interneuron marked X in colour purple involved in tetanus. (Recent NEET Pattern 2016-17)

Renshaw cell. ***Renshaw cell*** - The image depicts a **Renshaw cell (X)**, which is an **inhibitory interneuron** in the spinal cord, regulating motor neuron activity. - In tetanus, the toxin **tetanospasmin** inhibits the release of neurotransmitters (glycine and GABA) from Renshaw cells, leading to **uncontrolled muscle spasms**. *Basket cell* - **Basket cells** are found in the **cerebellar cortex** and hippocampus, playing a role in inhibiting Purkinje cell activity. - They are not located in the spinal cord gray matter in the position marked X. *Purkinje cell* - **Purkinje cells** are large, distinctive neurons found exclusively in the **cerebellar cortex**, crucial for motor coordination. - They are not present in the spinal cord and are not interneurons in the context of spinal reflexes. *Anterior horn cell* - **Anterior horn cells** are **motor neurons** whose cell bodies reside in the anterior horn of the spinal cord and directly innervate skeletal muscles. - They are not interneurons; rather, they are the target of regulation by interneurons like Renshaw cells.

Q: In the image shown below, which of the marked area is involved in relieving pain in response to massage?

Area A. ***A*** - Area A points to the **dorsal columns** (specifically the fasciculus gracilis and cuneatus) of the spinal cord, which carry **mechanoreceptive** and proprioceptive information. - Massage activates large diameter afferent fibers which transmit signals via the dorsal columns, inhibiting pain transmission through the **gate control theory of pain**. *B* - Area B points to the **dorsal horn** (specifically lamina I, II, and V), which is primarily involved in receiving and processing **nociceptive input**. - While integration of pain occurs here, it is not the primary pathway for the **modulatory effects of touch/pressure** from massage for pain relief. *C* - Area C indicates the **ventral horn** of the spinal cord, which contains **motor neurons** that control skeletal muscle activity. - It is involved in motor output, not directly in the sensory processing or modulation of pain signals from massage. *D* - Area D points to the **lateral white matter**, which contains various ascending and descending tracts, including the **spinothalamic tract** (primary pain pathway) and corticospinal tract. - While the spinothalamic tract carries pain signals, the direct pain-relieving effect of massage primarily involves activation of mechanoreceptors whose signals ascend via the dorsal columns.

Q: The following electrical recording is known as:

Visual evoked potential (VEP). ***Visual evoked potential (VEP)*** - The image displays a checkerboard pattern stimulus and recordings from electrodes placed on the scalp, which are characteristic components of a **visual evoked potential** test. - The graph shows a "Normal recording" and a "Multiple sclerosis recording," indicating how demyelination affects the conduction time of visual pathways, a key application of VEP studies. *Electroencephalogram (EEG)* - An EEG records the brain's **spontaneous electrical activity** over time, typically showing rhythms like alpha, beta, theta, and delta waves. - While it uses scalp electrodes, it does not involve specific sensory stimulation like a checkerboard pattern to evoke a response. *Electromyogram (EMG)* - An EMG measures the electrical activity of **muscles** in response to nerve stimulation or during voluntary contraction. - It involves needle electrodes inserted into muscles and is used to diagnose muscle and nerve disorders, not visual pathway integrity. *Nerve conduction study (NCS)* - An NCS measures how fast electrical signals travel along **nerves** in the limbs to assess their function. - It typically involves stimulating a peripheral nerve and recording the response from a muscle or nerve further along the pathway, which is distinct from the visual pathway assessment shown.

Q: A polysomnography is performed on a patient. Based on the provided EEG, EOG, and EMG findings, which stage of sleep is indicated? (Image: img-182.jpeg)

NREM 2. ***NREM 2*** - This stage is characterized by the presence of **sleep spindles** (bursts of brain activity) and **K-complexes** (large, slow waves) on the EEG. - The EOG typically shows **no significant eye movement**, and the EMG registers **lower muscle tension** compared to wakefulness or NREM 1. *NREM 1* - This initial stage of sleep is marked by the appearance of **theta waves** on the EEG and a reduction in alpha wave activity. - The EOG often shows **slow, rolling eye movements**, and the EMG indicates slightly **reduced muscle tone** compared to the wake state. *NREM 3* - Often referred to as **deep sleep** or slow-wave sleep, this stage is characterized by a significant presence of **delta waves** (high amplitude, low frequency) on the EEG, comprising 20-50% of the epoch. - Eye movements are **minimal or absent** on EOG, and muscle tension on EMG is **lower** than in NREM 2 but still present. *REM* - This stage is distinguished by **rapid eye movements** (REMs) observed on the EOG and a characteristic **sawtooth pattern** or low-voltage, mixed-frequency activity on the EEG. - A key feature of REM sleep is **atonia** (paralysis of skeletal muscles), resulting in the **lowest muscle tone** on the EMG, often appearing as a flat line.

Question 1

Which of the following is an amino neurotransmitter?

Accepted Answer

GABA

Answer

Acetylcholine

Answer

Lignocaine

Answer

Epinephrine

Question 2

What is the lowest level of integration for the stretch reflex?

Accepted Answer

Spinal cord

Answer

Cerebral cortex

Answer

Lower medulla

Answer

All of the above

Question 3

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

Accepted Answer

Medulla

Answer

Cerebral cortex

Answer

Midbrain

Answer

Spinal cord

Question 4

Which of the following is the afferent limb of the corneal reflex?

Accepted Answer

Trigeminal nerve

Answer

Facial nerve

Answer

Trochlear nerve

Answer

Optic nerve

Question 5

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

Accepted Answer

Alpha waves

Answer

Theta waves

Answer

Beta waves

Answer

Delta waves

Question 6

Which wave is seen in the given EEG recording?

Accepted Answer

Delta waves

Answer

Alpha waves

Answer

Beta waves

Answer

Epsilon wave

Question 7

Name the interneuron marked X in colour purple involved in tetanus. (Recent NEET Pattern 2016-17)

Accepted Answer

Renshaw cell

Answer

Basket cell

Answer

Purkinje cell

Answer

Anterior horn cell

Question 8

In the image shown below, which of the marked area is involved in relieving pain in response to massage?

Accepted Answer

Area A

Answer

Area B

Answer

Area C

Answer

Area D

Question 9

The following electrical recording is known as:

Accepted Answer

Visual evoked potential (VEP)

Answer

Electroencephalogram (EEG)

Answer

Electromyogram (EMG)

Answer

Nerve conduction study (NCS)

Question 10

A polysomnography is performed on a patient. Based on the provided EEG, EOG, and EMG findings, which stage of sleep is indicated? (Image: img-182.jpeg)

Accepted Answer

NREM 2

Answer

NREM 1

Answer

NREM 3

Answer

REM

Neurophysiology — MCQs

Neurophysiology — MCQs

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