Nerve and Muscle Physiology Practice Questions

Q: Which of the following neurotransmitters has only inhibitory action?

GABA. ***GABA*** - **Gamma-aminobutyric acid (GABA)** is the primary **inhibitory neurotransmitter** in the central nervous system. - It works by reducing neuronal excitability, often by allowing **chloride ions** into the cell, leading to hyperpolarization. *Glutamine* - **Glutamine** is an **amino acid** that is a precursor to the excitatory neurotransmitter **glutamate** and the inhibitory neurotransmitter GABA, but it is not a neurotransmitter itself. - It plays a crucial role in the **glutamate-GABA cycle**, but its direct action is not neurotransmission. *All of the options* - This option is incorrect because only GABA among the choices has a solely inhibitory action; **glutamine** is a precursor, and **aspartate** is primarily excitatory. - Not all substances listed are neurotransmitters, nor do they all have purely inhibitory actions. *Aspartate* - **Aspartate** is an **excitatory neurotransmitter** and plays a role in synaptic plasticity and learning. - It primarily acts on **NMDA receptors**, similar to glutamate, to depolarize neurons.

Q: The increase in threshold of a receptor when a series of stimuli of subthreshold intensity are applied in succession is called __________.

Accommodation. ***Accommodation*** - This describes the phenomenon where the **threshold of excitability increases** when a nerve or receptor is subjected to **repeated subthreshold stimuli** or a slowly rising stimulus. - As subthreshold stimuli are applied in succession, voltage-gated **sodium channels progressively inactivate** without triggering an action potential. - This inactivation causes the threshold to **increase**, making the receptor or nerve fiber **less excitable** and requiring a stronger stimulus to fire. - This is the **correct answer** as it precisely matches the definition in the question stem. *Adaptation* - This refers to the **decrease in receptor responsiveness** when exposed to a **constant or prolonged stimulus**. - Receptors reduce their firing rate over time even though the stimulus continues (e.g., wearing clothes, background noise). - Adaptation is about **decreased response magnitude**, not an increase in threshold due to subthreshold stimuli. - This is a different phenomenon from what the question describes. *Resistance* - In physiology, resistance typically refers to the **opposition to flow** (e.g., vascular resistance, airway resistance) or the ability to **withstand effects** of drugs or pathogens. - It does not describe changes in **neuronal or receptor threshold** due to stimulation patterns. *Initiation* - This term refers to the **beginning or triggering** of a process, such as the initiation of an action potential or biochemical cascade. - It does not describe the **change in excitability threshold** that occurs with repeated subthreshold stimulation.

Q: 'Lock jaw' indicates

Spasm of masseter muscle. ***Spasm of masseter muscle*** - **\"Lockjaw\"** (or trismus) is a classic symptom referring to the inability to open the mouth fully, primarily caused by **spasm of the masseter muscle**. - This symptom is most notably associated with **tetanus**, where the powerful toxins cause sustained muscle contractions. *Fracture of condyle* - A condylar fracture can cause pain and difficulty in opening the mouth, but it typically presents with **malocclusion** and **deviation of the jaw** towards the fractured side. - While it restricts mouth opening, the primary mechanism is mechanical obstruction and pain, not generalized muscle spasm. *Ankylosis* - **Ankylosis** is the fusion or stiffening of a joint, in this case, the **temporomandibular joint (TMJ)**. - It would lead to chronic and often complete loss of mouth opening, but it's a structural problem rather than an acute muscular spasm. *Inflammatory trismus* - **Inflammatory trismus** can result from infections or inflammation in the oral and maxillofacial regions (e.g., pericoronitis, abscesses). - This type of trismus is caused by inflammation and pain response, leading to reflexive muscle guarding, which is distinct from the sustained, involuntary spasm seen in conditions like tetanus.

Q: Hypokalemia causes:

Hyperpolarisation. ***Hyperpolarisation*** - Hypokalemia leads to an **increased gradient of potassium ions** across the cell membrane, causing more K+ to leave the cell. - This efflux of positive charge makes the **resting membrane potential more negative**, thus hyperpolarizing the cell and making it less excitable. *Increased amplitude of action potential* - Hypokalemia primarily affects the **resting membrane potential** and excitability, not the amplitude of the action potential itself once it's triggered. - The amplitude of an action potential is mainly determined by the **influx of sodium ions** through voltage-gated channels. *Tetany* - **Tetany** is typically associated with **hypocalcemia**, which increases neuronal excitability. - Hypokalemia generally leads to **decreased neuronal and muscle excitability**, causing weakness and paralysis rather than tetany. *Resting membrane potential becomes less negative* - If the resting membrane potential becomes less negative, it's referred to as **depolarization**, which is associated with **hyperkalemia** (reduced potassium gradient, less K+ efflux). - In hypokalemia, the increased potassium gradient causes the membrane to become **more negative** (hyperpolarized).

Q: Sensory nerve action potential in nerve conduction velocity (NCV) studies is used to calculate:

Sensory conduction. ***Sensory conduction*** - The **sensory nerve action potential (SNAP)** directly measures the electrical activity of **sensory nerve fibers**. - This allows for the calculation of **sensory nerve conduction velocity** and amplitude, assessing the function of these specific nerve pathways. *Conduction velocity* - This is a general term and does not specify whether referring to **sensory** or **motor nerve conduction velocity**. - While SNAPs contribute to conduction velocity calculations, this option is too broad and not as precise as "Sensory conduction." *Motor conduction* - **Motor nerve conduction** is measured using **compound muscle action potentials (CMAPs)**, which reflect the activity of motor nerve fibers and the muscle itself. - SNAPs specifically assess sensory nerves and are not used to calculate motor conduction parameters. *Muscular contraction* - **Muscular contraction** is the physiological response to nerve stimulation, but it is not directly calculated using the **sensory nerve action potential**. - Muscle contraction is more directly assessed through **electromyography (EMG)** and motor nerve conduction studies.

Q: Sensory fiber with least conduction velocity:

C- fiber. ***C- fiber*** - **C-fibers** are **unmyelinated** and have a very small diameter, leading to the **slowest conduction velocity** among all nerve fiber types. - They transmit **slow, dull pain**, temperature, and crude touch sensations. - Conduction velocity: **0.5-2 m/s** *Beta fiber* - **Beta fibers** (Aβ fibers) are **myelinated sensory fibers**, have a medium-to-large diameter, and conduct impulses at a faster rate than C-fibers. - They transmit touch, pressure, vibration, and proprioception. - Conduction velocity: **30-70 m/s** *A-delta fiber* - **A-delta fibers** (Aδ fibers) are **thinly myelinated sensory fibers** that conduct faster than C-fibers but slower than A-beta fibers. - They transmit **sharp, acute pain**, cold temperature, and pressure sensations. - Conduction velocity: **12-30 m/s** *Alpha fiber* - **Alpha fibers** (Aα fibers) are the **largest diameter**, most heavily **myelinated** nerve fibers, resulting in the **fastest conduction velocity**. - They include alpha motor neurons for **skeletal muscle contraction** and Ia/Ib sensory afferents for proprioception. - Conduction velocity: **70-120 m/s**

Q: Calcium does not bind to

Tropomyosin. ***Tropomyosin*** - **Tropomyosin** is a protein that winds around **actin filaments** and, in relaxed muscle, blocks the **myosin-binding sites** on actin, preventing contraction. - Calcium does **not directly bind** to tropomyosin; rather, its binding to **troponin** causes a conformational change that moves tropomyosin away from the binding sites. - **This is the correct answer** because tropomyosin lacks calcium-binding sites. *Incorrect: Troponin* - **Troponin** is a complex of three proteins (**troponin I, T, and C**) that is crucial for muscle contraction. - **Troponin C** is the specific subunit that **binds calcium ions**, initiating the cascade of events leading to muscle contraction. - This option is incorrect because troponin DOES bind calcium. *Incorrect: Calmodulin* - **Calmodulin** is a ubiquitous **calcium-binding messenger protein** expressed in all eukaryotic cells. - It mediates many crucial cellular processes by interacting with and regulating various protein targets (e.g., kinases, phosphatases) when it **binds to calcium ions**. - This option is incorrect because calmodulin DOES bind calcium. *Incorrect: None of the options* - This option would suggest that all the listed proteins bind calcium. - Since **tropomyosin does NOT bind calcium**, this option is incorrect.

Q: A pole vaulter had a fall during pole vaulting and had paralysis of the arm . Which of the following investigations gives the best recovery prognosis -

Electromyography. Electromyography - **Electromyography (EMG)** can help assess the extent of nerve damage and reinnervation, providing insights into the potential for recovery [1]. - The presence of **spontaneous activity** (fibrillations, positive sharp waves) indicates denervation, while the appearance of **motor unit action potentials (MUAPs)** suggests reinnervation [1]. *Creatine phosphokinase levels* - **Creatine phosphokinase (CPK)** levels primarily indicate **muscle damage**, not the extent of nerve injury or recovery potential. - While muscle damage can occur with nerve injury, CPK does not provide specific prognostic information for nerve regeneration. *Strength Duration Curve* - The **strength duration curve** assesses the excitability of a nerve or muscle to electrical stimulation. - While it can differentiate between **nerve and muscle damage**, it provides less comprehensive prognostic information compared to EMG regarding the status of nerve regeneration. *Muscle biopsy* - A **muscle biopsy** would directly evaluate muscle pathology, such as atrophy or regeneration. - However, it is an **invasive procedure** and provides less direct information about nerve recovery compared to EMG, which directly assesses nerve and muscle electrical activity.

Q: Demyelination is the major feature of Multiple Sclerosis. Which of the following cells forms myelin in the central nervous system?

Oligodendrocytes. ***Oligodendrocytes*** - **Oligodendrocytes** are glial cells exclusively found in the **central nervous system (CNS)** that produce and maintain the **myelin sheath**. - The myelin sheath, formed by these cells, insulates axons and allows for rapid, efficient **saltatory conduction** of action potentials. *Astrocytes* - **Astrocytes** are star-shaped glial cells that provide structural and metabolic support for neurons, regulate the **blood-brain barrier**, and maintain the extracellular environment. - They do not form myelin; instead, they play roles in **neurotransmission** and response to injury. *Ependymal cells* - **Ependymal cells** line the ventricles of the brain and the central canal of the spinal cord, forming an interface between the neural tissue and **cerebrospinal fluid (CSF)**. - They are involved in **CSF production** and circulation, having no role in myelination. *Microglia* - **Microglia** are the resident immune cells of the CNS, functioning as **macrophages** to remove cellular debris, pathogens, and damaged neurons. - They are crucial for immune surveillance and inflammatory responses but do not produce myelin.

Q: The protein responsible for elasticity of the muscle is:

Titin. ***Titin*** - **Titin** is a giant protein that functions as a molecular spring within the sarcomere, providing **passive elasticity** to muscle. - It helps anchor **myosin filaments** and contributes to the muscle's ability to **stretch and recoil**. *Myosin* - **Myosin** is primarily responsible for generating force and muscle contraction through its interaction with **actin**, not for elasticity. - It forms the thick filaments and uses **ATP hydrolysis** to power the cross-bridge cycle. *Actin* - **Actin** forms the thin filaments and serves as the binding site for myosin heads during muscle contraction. - While essential for contraction, it does not provide the primary elastic properties of muscle. *Tropomyosin* - **Tropomyosin** is a regulatory protein that wraps around actin filaments and blocks myosin-binding sites in the relaxed state. - It plays a role in **muscle contraction regulation**, not in providing elasticity.

Question 1

Which of the following neurotransmitters has only inhibitory action?

Accepted Answer

GABA

Answer

Glutamine

Answer

All of the options

Answer

Aspartate

Question 2

The increase in threshold of a receptor when a series of stimuli of subthreshold intensity are applied in succession is called __________.

Accepted Answer

Accommodation

Answer

Resistance

Answer

Initiation

Answer

Adaptation

Question 3

'Lock jaw' indicates

Accepted Answer

Spasm of masseter muscle

Answer

Fracture of condyle

Answer

Ankylosis

Answer

Inflammatory trismus

Question 4

Hypokalemia causes:

Accepted Answer

Hyperpolarisation

Answer

Increased amplitude of action potential

Answer

Tetany

Answer

Resting membrane potential becomes less negative

Question 5

Sensory nerve action potential in nerve conduction velocity (NCV) studies is used to calculate:

Accepted Answer

Sensory conduction

Answer

Conduction velocity

Answer

Motor conduction

Answer

Muscular contraction

Question 6

Sensory fiber with least conduction velocity:

Accepted Answer

C- fiber

Answer

beta fiber

Answer

A-delta fiber

Answer

Alpha fiber

Question 7

Calcium does not bind to

Accepted Answer

Tropomyosin

Answer

Troponin

Answer

Calmodulin

Answer

None of the options

Question 8

A pole vaulter had a fall during pole vaulting and had paralysis of the arm . Which of the following investigations gives the best recovery prognosis -

Accepted Answer

Electromyography

Answer

Strength Duration Curve

Answer

Creatine phosphokinase levels

Answer

Muscle biopsy

Question 9

Demyelination is the major feature of Multiple Sclerosis. Which of the following cells forms myelin in the central nervous system?

Accepted Answer

Oligodendrocytes

Answer

Astrocytes

Answer

Ependymal cells

Answer

Microglia

Question 10

The protein responsible for elasticity of the muscle is:

Accepted Answer

Titin

Answer

Myosin

Answer

Actin

Answer

Tropomyosin

Nerve and Muscle Physiology — MCQs

Nerve and Muscle Physiology — MCQs

On this page

Practice by Chapter

Want unlimited practice?