Nerve and Muscle Physiology Practice Questions

Q: Which of the following statements is NOT true regarding red muscle fibers?

Increased muscle fiber length. ***Increased muscle fiber length*** - The length of muscle fibers is generally determined by the muscle's anatomical structure and function, not by whether they are red or white fibers. - While red muscle fibers (slow-twitch) are optimized for **endurance** and **sustained contractions**, this optimization does not involve an inherent increase in the length of individual muscle fibers. *Decreased glycolytic enzymes* - Red muscle fibers, also known as slow-oxidative fibers, primarily rely on **aerobic metabolism** for ATP production. - They have a lower content of glycolytic enzymes compared to white muscle fibers, which are specialized for **anaerobic glycolysis**. *Increased blood flow* - Red muscle fibers have a rich capillary supply, leading to **increased blood flow**, which is essential for delivering oxygen and nutrients for sustained aerobic activity. - This extensive vascularization contributes to their characteristic red appearance and their ability to resist fatigue. *Used for aerobic activity* - Red muscle fibers are well-suited for prolonged, low-intensity activities due to their high concentration of **mitochondria**, myoglobin, and oxidative enzymes. - They are primarily responsible for maintaining posture and performing **endurance activities** such as long-distance running.

Q: Which of the following proteins is primarily responsible for muscle relaxation?

SERCA (Sarcoplasmic Reticulum Ca2+ ATPase). ***SERCA (Sarcoplasmic Reticulum Ca2+ ATPase)*** - **SERCA** pumps calcium ions from the **cytosol** back into the **sarcoplasmic reticulum**, reducing cytosolic calcium levels and allowing muscle relaxation. - This active transport of **Ca2+** away from the contractile proteins (actin and myosin) is essential for stopping muscle contraction. *Both Actin and SERCA* - While **SERCA** is critical for relaxation, **actin** is a structural component of the thin filament involved in muscle contraction, not relaxation. - **Actin** interacts with myosin during the cross-bridge cycle to shorten the sarcomere, a process reversed by **Ca2+** removal. *Actin* - **Actin** is a primary component of the **thin filaments** and is directly involved in muscle **contraction** when bound by myosin. - It does not play a direct role in the active process of muscle relaxation; its interaction with myosin ceases when **calcium** is removed. *None of the options* - This option is incorrect because **SERCA** is a specific protein with a well-defined role in muscle relaxation by actively sequestering **calcium**. - The other options either include incorrect proteins or misattribute functionality for muscle relaxation.

Q: What is the second messenger responsible for smooth muscle relaxation mediated by nitric oxide (NO)?

Cyclic GMP. ***Cyclic GMP*** - **Nitric oxide (NO)** activates **guanylyl cyclase**, an enzyme that converts **GTP to cGMP**. - Elevated **cGMP** levels activate **protein kinase G (PKG)**, leading to smooth muscle relaxation through various mechanisms, including reduced intracellular calcium and altered sensitivity of contractile proteins. *Calcium* - **Calcium** is primarily a key second messenger for **smooth muscle contraction**, not relaxation. - An increase in intracellular **calcium** promotes the binding of **calcium to calmodulin**, activating myosin light chain kinase and leading to contraction. *Cyclic AMP* - While **cyclic AMP (cAMP)** can cause smooth muscle relaxation (e.g., via beta-2 adrenergic stimulation), it is not the direct second messenger for **nitric oxide (NO)**-mediated relaxation. - **cAMP** is produced by **adenylyl cyclase** and primarily activates **protein kinase A (PKA)**. *Magnesium* - **Magnesium** is an important cofactor for many enzymes and can influence muscle contraction and relaxation, but it does not serve as a primary second messenger for **nitric oxide (NO)**. - High concentrations of **magnesium** can directly induce muscle relaxation by competing with **calcium** and modulating various channels and enzymes.

Q: Excitatory postsynaptic potentials are due to

Na+ movement into the cell. ***Na+ movement into the cell*** - **Excitatory postsynaptic potentials (EPSPs)** are caused by the **depolarization** of the postsynaptic membrane. - This depolarization primarily occurs when **neurotransmitters** open **ligand-gated ion channels** that allow a net influx of **positively charged sodium (Na+) ions** into the cell. *K+ movement into the cell* - **K+ influx** would make the inside of the cell more positive, but the resting membrane potential is already close to the **equilibrium potential for K+**; its movement into the cell under normal circumstances does not cause the characteristic depolarization of an EPSP. - While **Na+/K+ ATPase** pumps K+ into the cell, this process is responsible for maintaining the resting potential, not generating rapid EPSP depolarization. *Na+ movement out of the cell* - **Na+ movement out of the cell** would lead to **hyperpolarization** or repolarization, making the inside of the cell more negative, which is characteristic of an inhibitory postsynaptic potential (IPSP) or the repolarization phase of an action potential. - The **Na+/K+ ATPase** pumps Na+ out of the cell, but this is a metabolic pump, not the ion channel mechanism responsible for EPSP generation. *Ca++ movement into the cell* - While **Ca++ influx** can also be excitatory and lead to depolarization, especially in certain types of neurons or during specific synaptic events (e.g., neurotransmitter release), it is not the primary mechanism responsible for most fast **EPSPs** in the central nervous system. - The influx of **Ca++** is more commonly associated with signaling pathways, muscle contraction, and sustained depolarization rather than the rapid, transient depolarization seen in typical EPSPs from ionotropic receptors.

Q: The reflex originating from the Golgi tendon organ to relax the responding muscle is a

Disynaptic reflex. ***Disynaptic reflex*** - The reflex arc originating from the **Golgi tendon organ** involves an afferent neuron synapsing with an inhibitory interneuron, which then synapses with the alpha motor neuron. - This two-synapse pathway (Golgi tendon organ sensory neuron to interneuron, then interneuron to alpha motor neuron) makes it a **disynaptic reflex**. *Monosynaptic reflex* - This type of reflex involves only **one synapse** between the afferent sensory neuron and the efferent motor neuron, such as the **stretch reflex**. - The Golgi tendon reflex requires an **interneuron** to inhibit the motor neuron, thus making it more complex than monosynaptic. *Polysynaptic reflex* - This term describes reflexes involving **multiple interneurons** and more than two synapses. - While the Golgi tendon reflex involves an interneuron, the primary direct inhibition of the motor neuron is achieved through a **single inhibitory interneuron**, making disynaptic a more precise description. *Reflex with center in medulla oblongata* - Reflexes centered in the **medulla oblongata** typically regulate vital functions such as breathing, heart rate, and blood pressure. - The **Golgi tendon reflex** is a spinal reflex with its neural circuitry located within the spinal cord segments associated with the involved muscle.

Q: A person is able to sense fast, sharp pain and temperature normally. Which type of nerve fiber is primarily involved in carrying these fast pain and temperature sensations?

A-delta. ***A-delta*** - **A-delta fibers** are **myelinated**, medium-diameter fibers responsible for transmitting **fast, sharp pain** and **cold temperature** sensations. - Their myelination allows for **rapid conduction** of nerve impulses, leading to the immediate perception of acute pain. *A-beta* - **A-beta fibers** are large-diameter, highly myelinated fibers primarily involved in transmitting **touch** and **pressure** sensations. - While they can transmit some non-painful signals from the skin, they are not the primary carriers of sharp pain or temperature. *C fibers* - **C fibers** are **unmyelinated**, small-diameter fibers that transmit **slow, dull, burning pain** and **warm temperature** sensations. - Their lack of myelination results in **slower conduction velocity**, which is why the duller pain is perceived after the sharp pain. *A-alpha* - **A-alpha fibers** are the **largest diameter**, most heavily myelinated fibers in the periphery. - They are primarily responsible for **proprioception** (sense of body position) and **motor control** to skeletal muscles, not pain or temperature.

Q: Which of the following statements about smooth muscles is true?

Presence of Caveolae. ***Presence of Caveolae*** - **Caveolae** are small invaginations of the plasma membrane in smooth muscle cells that function in **calcium handling** and cell signaling. - They increase the surface area and contain receptors and ion channels crucial for smooth muscle contraction. *Ca2+ binds to troponin C* - In **smooth muscle**, calcium ions (Ca2+) bind to **calmodulin**, not troponin C. - **Troponin C** is the calcium-binding protein found in **striated muscle** (skeletal and cardiac muscle). *The anchorage for actin filaments is given by Z-lines* - In **smooth muscle**, **dense bodies** serve as the anchor points for **actin filaments**, analogous to Z-lines in striated muscle. - **Z-lines** are characteristic structures of **sarcomeres** in skeletal and cardiac muscle. *Voltage-gated L-type Ca2+ channels are present in T-tubules* - While L-type Ca2+ channels are present in some smooth muscle cells, their distribution in **T-tubules** is primarily characteristic of **cardiac muscle**. - **Smooth muscle** generally lacks **T-tubules**, and Ca2+ entry occurs mainly through channels on the plasma membrane or from the sarcoplasmic reticulum.

Q: Which of the following types of nerve fibers are primarily responsible for transmitting slow, dull, and chronic pain sensations?

C fibers. ***C fibers*** - These are **unmyelinated**, small-diameter nerve fibers that conduct impulses slowly (0.5-2 m/s). - They are primarily responsible for transmitting **slow, dull, burning, or aching pain** (second pain or chronic pain), as well as temperature sensations and itch. - Their slow conduction velocity results in the delayed, poorly localized pain sensation that persists after initial injury. *A-alpha fibers* - These are the **largest and fastest-conducting** myelinated nerve fibers (70-120 m/s). - They are primarily involved in transmitting **proprioception** (sense of body position) and **motor information** to skeletal muscles. - They do **not transmit pain** signals. *A-beta fibers* - These are **large, myelinated** fibers with a fast conduction velocity (30-70 m/s). - They primarily transmit **touch and pressure sensations**, and can modulate pain perception through the gate control theory. - They are **not nociceptors** and do not directly transmit pain. *A-delta fibers* - These are **small, myelinated** nerve fibers that conduct impulses at 12-30 m/s. - They transmit **fast, sharp, well-localized pain** (first pain or acute pain) and cold sensations. - While they do transmit pain, they are responsible for the **initial sharp pain**, not the slow, dull, chronic pain that defines C fiber function.

Q: Which among the following is a feature of denervation of smooth muscle?

Increased sensitivity to chemical mediators. ***Increased sensitivity to chemical mediators*** - Denervation of smooth muscle leads to **denervation supersensitivity**, meaning the muscle becomes more reactive to agonists due to an increase in receptor numbers or changes in post-receptor signaling pathways. - This increased sensitivity specifically applies to circulating or locally released chemical mediators, even at low concentrations. *Atrophy of the muscle.* - While denervation of **skeletal muscle** often leads to significant atrophy, **smooth muscle cells** are less prone to severe atrophy following denervation. - Smooth muscle tone is significantly influenced by both nervous and intrinsic myogenic activity, so loss of innervation alone does not typically cause complete incapacitation or severe atrophy. *No change in the number of receptors for neurotransmitters.* - Denervation often leads to an **increase in the number of receptors** on the smooth muscle cell surface, a phenomenon known as **upregulation**, contributing to denervation supersensitivity. - This adaptive change helps the muscle respond more strongly to any available neurotransmitters or circulating hormones. *Decreased neurotransmitter release At NMJ* - This option describes a potential cause of denervation (e.g., nerve damage leading to reduced release) rather than a feature of the denervated smooth muscle itself. - Denervation refers to the state where the nerve supply to the muscle is lost, not a change in neurotransmitter release from the now-absent nerve endings.

Question 1

Which of the following statements is NOT true regarding red muscle fibers?

Accepted Answer

Increased muscle fiber length

Answer

Decreased glycolytic enzymes

Answer

Used for aerobic activity

Answer

Increased blood flow

Question 2

Which of the following proteins is primarily responsible for muscle relaxation?

Accepted Answer

SERCA (Sarcoplasmic Reticulum Ca2+ ATPase)

Answer

Both Actin and SERCA

Answer

Actin

Answer

None of the options

Question 3

What is the second messenger responsible for smooth muscle relaxation mediated by nitric oxide (NO)?

Accepted Answer

Cyclic GMP

Answer

Calcium

Answer

Cyclic AMP

Answer

Magnesium

Question 4

Excitatory postsynaptic potentials are due to

Accepted Answer

Na+ movement into the cell

Answer

K+ movement into the cell

Answer

Na+ movement out of the cell

Answer

Ca++ movement into the cell

Question 5

The reflex originating from the Golgi tendon organ to relax the responding muscle is a

Accepted Answer

Disynaptic reflex

Answer

Polysynaptic reflex

Answer

Reflex with center in medulla oblongata

Answer

Monosynaptic reflex

Question 6

A person is able to sense fast, sharp pain and temperature normally. Which type of nerve fiber is primarily involved in carrying these fast pain and temperature sensations?

Accepted Answer

A-delta

Answer

C fibers

Answer

A-beta

Answer

A-alpha

Question 7

Which of the following statements about smooth muscles is true?

Accepted Answer

Presence of Caveolae

Answer

Ca2+ binds to troponin C

Answer

The anchorage for actin filaments is given by Z-lines

Answer

Voltage-gated L-type Ca2+ channels are present in T-tubules

Question 8

Which of the following types of nerve fibers are primarily responsible for transmitting slow, dull, and chronic pain sensations?

Accepted Answer

C fibers

Answer

A-alpha fibers

Answer

A-beta fibers

Answer

A-delta fibers

Question 9

Which among the following is a feature of denervation of smooth muscle?

Accepted Answer

Increased sensitivity to chemical mediators

Answer

Atrophy of the muscle

Answer

Decreased neurotransmitter release at NMJ

Answer

No change in the number of receptors for neurotransmitters

Question 10

What is the primary reason for the unidirectional nature of neuronal synaptic conduction?

Accepted Answer

Chemical mediators are released from the presynaptic terminal.

Answer

Dendrites can be depolarized and repolarized.

Answer

An area can be depolarized again after repolarization.

Answer

Antidromic impulses are less effective than orthodromic impulses.

Nerve and Muscle Physiology — MCQs

Nerve and Muscle Physiology — MCQs

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