Nerve and Muscle Physiology Practice Questions

Q: Which of the following nerve fibers are responsible for conduction of fast pain (first pain) impulses?

Delta. ***Delta*** - **Aδ (A-delta) fibers** are responsible for transmitting **fast, sharp, localized pain** (first pain). - These fibers are **thinly myelinated**, allowing for rapid conduction of pain signals (12-30 m/s). - They mediate the initial sharp pain sensation when tissue is injured. *gamma* - **Gamma motor neurons** innervate intrafusal muscle fibers within muscle spindles, playing a role in **muscle tone and proprioception**, not pain conduction. - They are efferent (motor) fibers, not afferent (sensory) fibers. *Alpha* - **Alpha motor neurons** innervate extrafusal muscle fibers and are responsible for **muscle contraction** (motor function). - **Aα fibers** conduct proprioception from muscle spindles, and **Aβ fibers** transmit touch and pressure sensations, but neither are involved in pain transmission. *beta* - **Aβ fibers** transmit information related to **touch, pressure, and vibration**, not pain. - They are large, heavily myelinated fibers that conduct impulses faster than pain fibers. - **Note:** C fibers (unmyelinated) conduct slow, burning pain (second pain), but Aδ fibers specifically conduct fast pain.

Q: Which of the following is true regarding Na+ (sodium) ions?

Responsible for depolarization. ***Responsible for depolarization*** - The rapid influx of **Na+ ions** into the cell through voltage-gated sodium channels is the primary event that causes **depolarization** during an action potential. - This influx makes the inside of the cell more positive, shifting the membrane potential from negative toward positive values. *Sodium ion is responsible for Donnan effect* - The **Donnan effect** describes the unequal distribution of permeable ions across a semi-permeable membrane due to the presence of impermeant charged molecules (e.g., proteins). - **Na+ ions are small, permeable ions** - they do not create the Donnan effect. The effect is caused by large, non-diffusible charged molecules like proteins, not by sodium ions. *Does not help other ions in transport* - The **sodium-potassium pump (Na+/K+-ATPase)** actively transports Na+ out of the cell and K+ into the cell, maintaining their concentration gradients. - These Na+ gradients are crucial for **secondary active transport**, where the energy from Na+ moving down its electrochemical gradient is used to move other ions (e.g., in Na+-glucose cotransport) or molecules against their gradients. *Responsible for the resting membrane potential* - The **resting membrane potential** is primarily established by the differential permeability of the membrane to K+ ions and the activity of the Na+/K+-ATPase. - While Na+ leaking into the cell contributes slightly, the dominant factor is the efflux of **K+ ions** through leak channels, as the membrane is much more permeable to K+ than to Na+ at rest.

Q: Type I muscle fibers are

Red. ***Red*** - Type I muscle fibers are also known as **slow-twitch oxidative fibers**, characterized by their **high myoglobin content** which gives them a red appearance. - They are rich in **mitochondria** and have a large supply of capillaries, making them highly efficient at **aerobic metabolism**. *Glycolytic* - **Glycolytic fibers** (Type IIb, or fast-twitch glycolytic) primarily rely on **anaerobic glycolysis** for energy. - These fibers are generally **white** due to lower myoglobin content and fewer mitochondria. *Anaerobic* - **Anaerobic metabolism** is characteristic of **Type II (fast-twitch)** muscle fibers, which are suited for short bursts of high-intensity activity. - Type I fibers primarily use **aerobic metabolism** and are fatigue-resistant, suited for sustained activity. *Large* - **Type II (fast-twitch)** muscle fibers tend to be **larger in diameter** than Type I fibers, allowing them to generate greater force. - Type I fibers are generally **smaller** and produce less tension but are more resistant to fatigue.

Q: Pressure sensation is carried by

Aβ fibres. ***Aβ fibres*** - **Aβ fibres** are large, myelinated nerve fibres responsible for transmitting touch, vibration, and **pressure sensations**. - Their significant myelination allows for rapid conduction of these **discriminative sensory inputs**. *Aγ fibres* - **Aγ fibres** are motor efferent fibres that innervate the **intrafusal muscle fibres** of muscle spindles, regulating their sensitivity. - They are not involved in the direct transmission of **sensory information** like pressure. *Aα fibres* - **Aα fibres** are the largest and fastest conducting nerve fibres, primarily responsible for **proprioception** (muscle stretch) and **motor efferents** to skeletal muscles (extrafusal fibres). - While they carry some sensory information, they are not the primary carriers of **pressure sensation**. *Aδ fibres* - **Aδ fibres** are lightly myelinated and transmit sensations of **fast pain**, cold temperature, and crude touch. - They conduct more slowly than Aβ fibres and are not primarily responsible for **pressure sensation**.

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.

Question 1

Which of the following nerve fibers are responsible for conduction of fast pain (first pain) impulses?

Accepted Answer

Delta

Answer

gamma

Answer

Alpha

Answer

beta

Question 2

Which of the following is true regarding Na+ (sodium) ions?

Accepted Answer

Responsible for depolarization

Answer

Does not help other ions in transport

Answer

Responsible for the resting membrane potential

Answer

Sodium ion is responsible for Donnan effect

Question 3

Type I muscle fibers are

Accepted Answer

Red

Answer

Glycolytic

Answer

Anaerobic

Answer

Large

Question 4

Pressure sensation is carried by

Accepted Answer

Aβ fibres

Answer

Aγ fibres

Answer

Aα fibres

Answer

Aδ fibres

Question 5

Group 2 sensory fibres are attached to:

Accepted Answer

Flower spray ending

Answer

Annulospiral ending

Answer

Pacinian corpuscle

Answer

Golgi tendon

Question 6

Nernst potential of Na+ is

Accepted Answer

+61 mV

Answer

+90 mV

Answer

-60 mV

Answer

-80 mV

Question 7

Oligodendrocytes are important in:

Accepted Answer

Myelin formation

Answer

Chemotaxis

Answer

Blood brain barrier

Answer

Phagocytosis

Question 8

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 9

Which is NOT a function of muscles?

Accepted Answer

Absorb nutrients

Answer

Cause movement

Answer

Maintain posture

Answer

Produce heat

Question 10

Annulospiral endings are present on:

Accepted Answer

Both

Answer

Nuclear bag fibers

Answer

Nuclear chain fibers

Answer

None of the options

Nerve and Muscle Physiology — MCQs

Nerve and Muscle Physiology — MCQs

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