Nerve and Muscle Physiology Practice Questions

Q: Group 2 sensory fibres are attached to:

Flower spray ending. ***Flower spray ending*** - **Group II sensory fibers** (also known as Aβ fibers) innervate the **flower spray endings** (secondary endings) of **muscle spindles**. - These endings detect changes in muscle length and contribute to proprioception, responding primarily to static muscle stretch. *Annulospiral ending* - The **annulospiral ending** (primary ending) is innervated by **Group Ia afferent fibers**, not Group II. - These fibers respond to both the rate of change of muscle length (dynamic response) and static muscle length. *Pacinian corpuscle* - **Pacinian corpuscles** are rapidly adapting mechanoreceptors found in subcutaneous tissue and deep fascia, detecting **vibration and deep pressure**. - While they are innervated by Aβ fibers (equivalent to Group II classification), they are **cutaneous mechanoreceptors**, not associated with muscle spindles like the flower spray endings. *Golgi tendon* - The **Golgi tendon organ** is a proprioceptor that detects **muscle tension** and is innervated by **Group Ib afferent fibers**, not Group II. - Its primary role is to monitor tension and provide protective feedback against excessive muscle force.

Q: Nernst potential of Na+ is

+61 mV. ***61*** - The **Nernst potential** (or **equilibrium potential**) for an ion is the electrical potential difference across a cell membrane that exactly counteracts the net diffusion of that ion down its concentration gradient. - For **sodium (Na+)**, with typical extracellular concentrations around 145 mM and intracellular concentrations around 15 mM, the calculated Nernst potential is approximately **+61 mV**. *90* - This value is generally too high for the typical **Nernst potential of Na+** in most physiological contexts. - While the exact potential can vary slightly based on specific intracellular and extracellular concentrations, **+90 mV** is not the standard equilibrium potential for Na+. *-60* - **-60 mV** is closer to the **resting membrane potential** of many cells, which is determined by the permeability to multiple ions, particularly potassium. - The **Nernst potential of Na+** is a positive value because Na+ is more concentrated outside the cell, and its electrochemical gradient would drive a net positive charge into the cell if the membrane were only permeable to Na+. *-80* - **-80 mV** is typically the equilibrium potential for **potassium (K+)**, given its high intracellular and low extracellular concentrations. - It is a negative value because K+ is more concentrated inside the cell, and its electrochemical gradient would drive a net positive charge out of the cell.

Q: Oligodendrocytes are important in:

Myelin formation. ***Myelin formation*** - **Oligodendrocytes** are responsible for producing and maintaining the **myelin sheath** around axons in the **central nervous system (CNS)**. - The myelin sheath acts as an electrical insulator, allowing for the **rapid and efficient transmission of nerve impulses**. *Chemotaxis* - **Chemotaxis** is the movement of a cell or organism in response to a chemical stimulus. - This process is primarily associated with **immune cells** like leukocytes, not oligodendrocytes. *Blood brain barrier* - The **blood-brain barrier (BBB)** is primarily formed by **tight junctions** between **endothelial cells** of cerebral capillaries. - **Astrocytes** also play a crucial role in maintaining the integrity and function of the BBB, but not oligodendrocytes. *Phagocytosis* - **Phagocytosis** is the process by which cells engulf large particles, such as bacteria or dead cells. - This function is primarily carried out by **microglia**, the resident immune cells of the CNS, which clear cellular debris and pathogens.

Q: Which of the following is/are true about nodes of Ranvier? 1. No myelin 2. Rich in sodium channels

Both. ***Both*** - Nodes of Ranvier are **gaps in the myelin sheath** that occur at regular intervals along a myelinated axon, making them areas with **no myelin**. - These nodes are crucially important because they have a **high concentration of voltage-gated sodium channels**, which enables the propagation of action potentials via **saltatory conduction**. - Both statements are **physiologically accurate** descriptions of the nodes of Ranvier, and their unique structure and composition are fundamental to **efficient transmission of nerve impulses**. *None of the options* - This option is incorrect because both statements, "No myelin" and "Rich in sodium channels," are **physiologically accurate** descriptions of the nodes of Ranvier. *No myelin* - While it is true that nodes of Ranvier are **devoid of myelin**, this statement alone does not encompass the full functional importance of these structures. - Their role in nerve impulse conduction also heavily relies on the presence of specific ion channels, which this option does not include. *Rich in sodium channels* - It is accurate that nodes of Ranvier have a **high density of voltage-gated sodium channels**, which is essential for regenerating the action potential. - However, this statement alone omits the key structural feature that they are also **unmyelinated gaps**, which is equally important to their function.

Q: Which is NOT a function of muscles?

Absorb nutrients. ***Absorb nutrients*** - Muscles are primarily involved in **movement**, **posture**, and **heat generation**, not direct nutrient absorption. - **Nutrient absorption** mainly occurs in the **gastrointestinal tract**, with specialized cells designed for this function. *Cause movement* - **Skeletal muscles** contract to pull on bones, generating the forces necessary for **locomotion** and other body movements. - **Smooth and cardiac muscles** are responsible for involuntary movements like **peristalsis** and **heart pumping**. *Maintain posture* - **Skeletal muscles** continuously contract to oppose gravity and maintain the body's **erect position** and stability. - This sustained, low-level contraction is known as **muscle tone**. *Produce heat* - **Muscle contraction** is an inefficient process, with a significant portion of the energy converted into **heat**. - This heat production is crucial for maintaining **body temperature**, especially during exercise or in cold environments.

Q: Annulospiral endings are present on:

Both. ***Both*** - **Annulospiral endings** are the primary sensory afferents (Type Ia) that innervate the central, non-contractile region of both **nuclear bag fibers** and **nuclear chain fibers** within the muscle spindle. - These endings respond to changes in **muscle length** and the **rate of change of muscle length**, playing a crucial role in the stretch reflex. *Nuclear bag fibers* - These are intrafusal muscle fibers that have their nuclei clustered in a central "bag-like" region. They primarily detect the **rate of change of muscle length (dynamic response)**. - While they are innervated by annulospiral endings, so are nuclear chain fibers. *Nuclear chain fibers* - These intrafusal fibers have their nuclei arranged in a single row or "chain." They primarily detect **static changes in muscle length**. - They are also innervated by annulospiral endings, indicating that the annulospiral endings are not exclusive to nuclear bag fibers. *None of the options* - This option is incorrect because annulospiral endings are definitively present on both nuclear bag and nuclear chain fibers.

Q: The effect seen due to decreased serum calcium concentration is

Excitability of muscle. ***Excitability of the muscle*** - A decrease in serum calcium concentration (**hypocalcemia**) reduces the threshold potential for sodium channels, making nerve and muscle cells **more excitable**. - This increased excitability can lead to symptoms like **tetany**, muscle spasms, and even convulsions. *Depression of Nervous system* - This is typically seen with **hypercalcemia** (increased serum calcium), where elevated calcium levels stabilize nerve membranes, making them less excitable. - **Hypocalcemia**, conversely, leads to neuronal hyperexcitability, not depression. *Increase the renal absorption* - Renal calcium reabsorption is primarily regulated by **parathyroid hormone (PTH)**. Low serum calcium stimulates PTH release, which *increases* renal calcium reabsorption to restore calcium levels. - This is a *physiological response* to hypocalcemia, not an *effect* of hypocalcemia on neural or muscular function. *Relaxation of muscle* - Muscle relaxation requires ATP and the re-sequestration of calcium into the sarcoplasmic reticulum, and is not a direct consequence of low extracellular calcium. - Instead, **hypocalcemia** causes increased muscle **contraction** and spasms due to enhanced neuromuscular excitability.

Q: Nernst equilibrium potential for Cl– is

–70mV. ***–70mV*** - The **Nernst equilibrium potential** for an ion represents the membrane potential at which there is no net movement of that ion across the membrane, as the **electrical gradient** exactly balances the **chemical (concentration) gradient**. - For Cl⁻, the extracellular concentration is **higher than intracellular**, creating a **chemical gradient that drives Cl⁻ inward**. - At **–70mV** (negative inside), the **electrical gradient repels Cl⁻ outward** (negative ions repelled by negative charge), balancing the inward chemical drive and achieving equilibrium. - This is the typical value in **most neurons**. *–90mV* - A potential of **–90mV** is typically the **equilibrium potential for potassium (K⁺)** in neurons, reflecting K⁺'s high intracellular concentration. - In **skeletal muscle**, ECl can approach –90mV, but in neurons it is typically less negative (around –70mV). *+80mV* - At a **positive membrane potential**, the electrical gradient would **attract Cl⁻ into the cell** (negative ion attracted to positive charge). - This would **reinforce** the inward chemical gradient, causing net Cl⁻ influx, not equilibrium. - This value does not represent the equilibrium potential for any major physiological ion. *+60mV* - At **+60mV**, Cl⁻ would experience both electrical attraction inward and chemical drive inward, causing **strong net influx**, not equilibrium. - This value approximates the **equilibrium potential for sodium (Na⁺)**, which has high extracellular concentration and reaches equilibrium at positive potentials.

Q: Nuclear bag fibre detects

Sense dynamic length of muscle. ***Sense dynamic length of muscle*** - **Nuclear bag fibres** are a type of intrafusal muscle fibre found in **muscle spindles** that are sensitive to the **rate of change of muscle length (dynamic stretch)**. - They transmit this information via **primary (annulospiral) afferent fibres** (Ia afferents) to the central nervous system, contributing to reflexes and proprioception. *Involved in reciprocal innervations* - **Reciprocal inhibition** involves the relaxation of an antagonist muscle when the agonist contracts, a function coordinated by interneurons in the spinal cord, not directly detected by nuclear bag fibers. - While muscle spindles contribute to the overall reflex arc, reciprocal innervation is a broader reflex phenomenon, not a primary detection function of nuclear bag fibres themselves. *Alpha motor neuron stimulation* - **Alpha motor neurons** innervate **extrafusal muscle fibres** causing muscle contraction, and they are not directly detected by nuclear bag fibres. - **Gamma motor neurons** innervate the intrafusal fibres (including nuclear bag fibres) to maintain their sensitivity during muscle contraction, but this is an efferent control, not a detection function. *Senses muscle tension* - **Muscle tension** is primarily detected by **Golgi tendon organs (GTOs)**, which are located in the tendons and respond to changes in tension during muscle contraction. - While nuclear bag fibres detect muscle stretch, their primary role is related to length and rate of change of length, not directly tension.

Q: The most significant immediate result of lowered serum calcium is

Hyperirritability of nerves and muscles. ***Hyperirritability of nerves and muscles*** - Lowered serum calcium (hypocalcemia) decreases the threshold potential of excitable cells, leading to **increased neuronal and muscular excitability**. - This can manifest as **tetany**, muscle cramps, paresthesias, and in severe cases, seizures. *Decalcification of bones* - **Chronic hypocalcemia** can lead to secondary hyperparathyroidism, which may eventually cause bone decalcification. - This is a **long-term effect**, not an immediate significant result of acutely lowered serum calcium. *Decalcification of teeth* - Tooth decalcification is primarily associated with **fluoride deficiency**, poor oral hygiene, or acidic erosion, not directly with acute systemic hypocalcemia. - The calcium in teeth is **highly stable** and less readily mobilized than bone calcium in response to acute serum calcium changes. *Weakened heart action* - While severe **hypocalcemia can impair myocardial contractility** and lead to a weakened heart action, it is often preceded or accompanied by significant neuromuscular symptoms. - **Hyperkalemia** is more classically associated with immediate life-threatening cardiac dysfunction, while hypocalcemia primarily affects nerve and muscle excitability first.

Question 1

Group 2 sensory fibres are attached to:

Accepted Answer

Flower spray ending

Answer

Annulospiral ending

Answer

Pacinian corpuscle

Answer

Golgi tendon

Question 2

Nernst potential of Na+ is

Accepted Answer

+61 mV

Answer

+90 mV

Answer

-60 mV

Answer

-80 mV

Question 3

Oligodendrocytes are important in:

Accepted Answer

Myelin formation

Answer

Chemotaxis

Answer

Blood brain barrier

Answer

Phagocytosis

Question 4

Which of the following is/are true about nodes of Ranvier?
1. No myelin
2. Rich in sodium channels

Accepted Answer

Both

Answer

None of the options

Answer

No myelin

Answer

Rich in sodium channels

Question 5

Which is NOT a function of muscles?

Accepted Answer

Absorb nutrients

Answer

Cause movement

Answer

Maintain posture

Answer

Produce heat

Question 6

Annulospiral endings are present on:

Accepted Answer

Both

Answer

Nuclear bag fibers

Answer

Nuclear chain fibers

Answer

None of the options

Question 7

The effect seen due to decreased serum calcium concentration is

Accepted Answer

Excitability of muscle

Answer

Depression of nervous system

Answer

Increased renal absorption

Answer

Relaxation of muscle

Question 8

Nernst equilibrium potential for Cl– is

Accepted Answer

–70mV

Answer

–90mV

Answer

+80mV

Answer

+60mV

Question 9

Nuclear bag fibre detects

Accepted Answer

Sense dynamic length of muscle

Answer

Involved in reciprocal innervations

Answer

Alpha motor neuron stimulation

Answer

Senses muscle tension

Question 10

The most significant immediate result of lowered serum calcium is

Accepted Answer

Hyperirritability of nerves and muscles

Answer

Decalcification of bones

Answer

Decalcification of teeth

Answer

Weakened heart action

Nerve and Muscle Physiology — MCQs

Nerve and Muscle Physiology — MCQs

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