Free Neurons and Nerve Impulse MCQs with Answers

• A. dendrites
• B. dendrons
• C. nucleus
• D. axon

Explanation: Each neurone has one long axon that conducts the impulse away towards the next cell, and many short branched dendrites that collect…

• A. the impulse jumps from one node of Ranvier to the next
• B. myelin conducts electricity better than cytoplasm
• C. myelinated axons are always much thinner
• D. myelin increases the number of sodium channels along the whole axon

Explanation: Myelin is an insulator, so ions can cross the membrane only at the gaps between Schwann cells, and depolarisation therefore leaps from…

• A. the free diffusion of sodium into the cell
• B. the sodium potassium pump, which moves three sodium ions out for every two potassium ions in
• C. the opening of voltage gated sodium channels
• D. the release of neurotransmitter at the synapse

Explanation: The pump uses ATP to move more positive charge out than it brings in, and since the membrane is far more permeable to potassium, which…

• A. potassium ions rushing out of the axon
• B. chloride ions entering the axon
• C. sodium ions rushing into the axon through voltage gated channels
• D. the sodium potassium pump reversing direction

Explanation: When the membrane is depolarised to threshold, voltage gated sodium channels open and sodium floods in down both its concentration and its…

• A. a stronger stimulus produces a larger action potential
• B. an impulse can travel in either direction along the axon
• C. every stimulus produces an impulse regardless of its strength
• D. any stimulus at or above threshold produces an action potential of the same size

Explanation: Once threshold is reached the sodium channels open fully, so the size of the spike is fixed by the ion gradients and not by how strong the…

• A. cannot be stimulated again, which keeps the impulse travelling in one direction
• B. conducts impulses at double speed
• C. releases neurotransmitter continuously
• D. reverses its resting potential permanently

Explanation: For a brief interval after an action potential the sodium channels are inactivated and cannot reopen, so the region just passed cannot…

• A. the postsynaptic membrane is thicker
• B. the neurotransmitter is released only from the presynaptic knob and receptors are only on the postsynaptic membrane
• C. the synaptic cleft is too wide for diffusion in the reverse direction
• D. the impulse loses all its energy at the synapse

Explanation: Vesicles of transmitter are stored on one side only and the matching receptors are on the other, so the signal cannot cross backwards even…

• A. +70 mV
• B. -70 mV
• C. 0 mV
• D. -90 mV

Explanation: The resting membrane potential is about -70 mV (inside negative relative to outside), maintained by Na+/K+ pump and K+ leak channels.

• A. The axon is myelinated
• B. Of the refractory period
• C. Of the all-or-none law
• D. Sodium channels are everywhere

Explanation: The refractory period (when Na+ channels are inactivated) prevents backward conduction, ensuring unidirectional propagation.

• A. Increasing axon diameter
• B. Saltatory conduction
• C. Increasing Na+ channels
• D. Decreasing resistance

Explanation: Myelin insulates the axon, allowing action potentials to jump between nodes of Ranvier (saltatory conduction), greatly increasing speed.

• A. Diffusion
• B. Exocytosis
• C. Endocytosis
• D. Osmosis

Explanation: Neurotransmitters are released by exocytosis of synaptic vesicles when Ca2+ enters the presynaptic terminal.

• A. Acetylcholinesterase
• B. Monoamine oxidase
• C. COMT
• D. Peptidase

Explanation: Acetylcholinesterase in the synaptic cleft rapidly breaks down acetylcholine to terminate the signal.

• A. Decreases heart rate
• B. Causes fight-or-flight response
• C. Stimulates digestion
• D. Constricts pupils

Explanation: The sympathetic division mediates fight-or-flight responses: increased heart rate, dilated pupils, inhibited digestion.

• A. Glutamate
• B. GABA
• C. Dopamine
• D. Serotonin

Explanation: GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the CNS, causing Cl- influx and hyperpolarization.

• A. Serotonin
• B. Dopamine
• C. GABA
• D. Acetylcholine

Explanation: Parkinson's disease results from degeneration of dopaminergic neurons in the substantia nigra, causing tremors and rigidity.

• A. Golgi bodies & Smooth ER
• B. Peroxisome & Mitochondria
• C. Lysosome & Vacuole
• D. Ribosome & Rough ER

Explanation: Nissl granules are dense stacks of rough endoplasmic reticulum studded with ribosomes, which is why they stain so darkly and why they are…

• A. Axon ends
• B. Dendrite end
• C. Nissl's granules
• D. Cell body

Explanation: Vesicles of transmitter are stored in the swollen endings of the axon and released into the synaptic cleft when the impulse arrives.

• A. Axon
• B. Dendrites
• C. Myelin sheath
• D. Synaptic knob

Explanation: Dendrites are the short branched processes that carry receptors for neurotransmitter and conduct the resulting signal towards the cell…

• A. Nerve cells
• B. WBC
• C. RBC
• D. Platelets

Explanation: Nissl granules are stacks of rough endoplasmic reticulum in the cell body of a neurone, supporting the heavy protein synthesis a nerve…

• A. Diffusion
• B. Passive transport
• C. Osmosis
• D. Active transport

Explanation: Moving sodium ions from lower to higher concentration requires energy from ATP and is therefore active transport, carried out by membrane…