Nerve Fibre Types and Conduction Practice Questions
20 free Nerve Fibre Types and Conduction practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following nerve fiber types has the fastest conduction velocity?
- A Type A-alpha
- B Type A-beta
- C Type B
- D Type C
Correct answer: Type A-alpha
Type A-alpha fibers are the largest in diameter and are heavily myelinated. Conduction velocity is directly proportional to fiber diameter and the presence of myelin, making these fibers the fastest in the body.
The sensation of 'slow' or 'second' pain is primarily mediated by which fiber type?
- A Type A-delta
- B Type A-gamma
- C Type B
- D Type C
Correct answer: Type C
Type C fibers are small, unmyelinated fibers with slow conduction velocities. They are responsible for transmitting dull, aching, or burning pain sensations, often referred to as second pain.
According to the Erlanger-Gasser classification, which fibers are preganglionic autonomic fibers?
- A Type A-alpha
- B Type A-beta
- C Type B
- D Type C
Correct answer: Type B
Type B fibers are myelinated small-diameter fibers that function as preganglionic autonomic neurons. They have a slower conduction velocity than Type A fibers but are faster than Type C fibers.
Which factor is the primary determinant of the length constant (lambda) of a nerve fiber?
- A The frequency of the electrical stimulation applied
- B The ratio of membrane resistance to axial resistance
- C The duration of the absolute refractory period
- D The concentration of extracellular magnesium ions
Correct answer: The ratio of membrane resistance to axial resistance
The length constant represents the distance over which a graded potential decays to 37% of its original value. It is calculated as the square root of the membrane resistance divided by the axial resistance.
Saltatory conduction occurs specifically at which anatomical location?
- A The internodes
- B The myelin sheath
- C The Nodes of Ranvier
- D The synaptic cleft
Correct answer: The Nodes of Ranvier
In myelinated fibers, voltage-gated sodium channels are highly concentrated at the Nodes of Ranvier. The action potential 'jumps' from one node to the next, which significantly increases the speed of conduction.
Which nerve fiber type is most sensitive to local anesthetics like lidocaine?
- A Type A-alpha
- B Type A-beta
- C Type B
- D Type C
Correct answer: Type C
Small-diameter, unmyelinated Type C fibers and small myelinated Type B fibers are typically blocked more easily than large Type A fibers. This allows for the clinical block of pain and autonomic function before motor function.
What happens to the conduction velocity of a nerve fiber if the temperature decreases?
- A It decreases
- B It increases
- C It remains unchanged
- D It increases for myelinated but decreases for unmyelinated
Correct answer: It decreases
Low temperatures decrease the kinetic energy of ions and slow the opening/closing kinetics of voltage-gated channels. This results in a significant reduction in the speed of action potential propagation.
In the Lloyd-Hunt classification of sensory fibers, Group Ia fibers correspond to which Erlanger-Gasser type?
- A Type A-alpha
- B Type A-beta
- C Type A-delta
- D Type C
Correct answer: Type A-alpha
Group Ia sensory fibers, which carry information from primary muscle spindle endings, are large and myelinated. They are functionally and structurally equivalent to Type A-alpha motor fibers.
Which of the following provides the myelin sheath for neurons in the Peripheral Nervous System (PNS)?
- A Oligodendrocytes
- B Astrocytes
- C Microglia
- D Schwann cells
Correct answer: Schwann cells
Schwann cells wrap around axons in the peripheral nervous system to form the myelin sheath. In contrast, oligodendrocytes serve this function within the central nervous system.
What is the primary effect of demyelination, such as in Multiple Sclerosis, on nerve conduction?
- A Accelerated impulse conduction velocity
- B Decreased resting membrane capacitance
- C Increased axonal length constant
- D Current leakage and conduction block
Correct answer: Current leakage and conduction block
Myelin acts as an insulator that reduces membrane capacitance and increases resistance. Loss of myelin allows current to leak out across the membrane, preventing the threshold from being reached at the next Node of Ranvier.
Type A-delta fibers are primarily associated with which sensory modality?
- A Fast, sharp pain and temperature
- B Proprioception
- C Pre-ganglionic sympathetic outflow
- D Vibration and touch
Correct answer: Fast, sharp pain and temperature
Type A-delta fibers are small, myelinated fibers that conduct faster than C fibers. They carry 'fast pain' signals and cold temperature sensations to the central nervous system.
The 'safety factor' for transmission in a nerve fiber refers to the ratio of:
- A Sodium ion influx to potassium ion efflux
- B Myelin sheath thickness to axon diameter
- C Internal resistance to external resistance
- D Action potential size to firing threshold
Correct answer: Action potential size to firing threshold
The safety factor is the ratio of the current generated by an action potential to the minimum current required to trigger an action potential in the next segment. A high safety factor ensures reliable conduction even under mild stress.
Which of these nerve fibers is most susceptible to hypoxia (pressure/ischemia)?
- A Type A
- B Type B
- C Type C
- D All are equally susceptible
Correct answer: Type A
Large myelinated Type A fibers are the most sensitive to mechanical pressure and ischemia. Type C fibers are the least sensitive to pressure but the most sensitive to local anesthetics.
Which ion channel is primarily responsible for the regenerative nature of the action potential along the axon?
- A Voltage-gated Sodium channels
- B Voltage-gated Potassium channels
- C Ligand-gated Chloride channels
- D Calcium-activated Potassium channels
Correct answer: Voltage-gated Sodium channels
The rapid influx of sodium through voltage-gated channels creates a positive feedback loop (Hodgkin cycle). This ensures that the action potential is propagated without decrement along the length of the nerve.
In a compound action potential (CAP), which peak appears first on the oscilloscope?
- A Alpha peak
- B Beta peak
- C Gamma peak
- D Delta peak
Correct answer: Alpha peak
A compound action potential represents the sum of signals from fibers with different speeds. The Alpha peak (from A-alpha fibers) arrives at the recording electrode first because it has the highest conduction velocity.
What is the approximate conduction velocity of a Type C fiber?
- A 70 - 120 m/s
- B 30 - 70 m/s
- C 3 - 15 m/s
- D 0.5 - 2.0 m/s
Correct answer: 0.5 - 2.0 m/s
Type C fibers are the slowest conducting fibers in the human body, typically ranging from 0.5 to 2 meters per second. This slow speed is due to their small diameter and lack of myelination.
The time constant (tau) of a nerve membrane is determined by:
- A Axon length
- B Membrane resistance and membrane capacitance
- C The number of Nodes of Ranvier
- D The concentration of sodium ions outside the cell membrane
Correct answer: Membrane resistance and membrane capacitance
The time constant is the product of membrane resistance (Rm) and capacitance (Cm). It represents the time it takes for the membrane potential to reach 63% of its final value following a stimulus.
Which nerve fiber type innervates the intrafusal fibers of the muscle spindle (motor)?
- A A-alpha
- B A-beta
- C A-gamma
- D A-delta
Correct answer: A-gamma
Type A-gamma motor neurons innervate the contractile ends of intrafusal muscle fibers. They regulate the sensitivity of the muscle spindle to stretch by maintaining tension on the spindle.
What is the effect of increasing axon diameter on internal (axial) resistance?
- A Internal resistance increases
- B Internal resistance decreases
- C Internal resistance remains the same
- D Internal resistance becomes infinite
Correct answer: Internal resistance decreases
As the diameter of the axon increases, the cross-sectional area increases, which provides more space for ion flow. This reduces the axial resistance, allowing current to spread further and faster.
Postganglionic autonomic fibers belong to which classification?
- A Type A-beta
- B Type B
- C Type C
- D Type A-delta
Correct answer: Type C
Postganglionic sympathetic and parasympathetic fibers are unmyelinated and small in diameter. Therefore, they are classified as Type C fibers according to the Erlanger-Gasser system.