3.6.2.1 Nerve impulses

What is the primary function of myelin in a motor neurone?

• To increase the speed of nerve impulse transmission

• To decrease the speed of nerve impulse transmission

• To provide nutrients to the neurone

• To protect the neurone from damage

Answer explanation

The primary function of myelin in a motor neurone is to increase the speed of nerve impulse transmission. Myelin acts as an insulating layer, allowing impulses to jump between nodes, which enhances conduction velocity.

Which ions are primarily involved in establishing the resting potential of a neurone?

• Calcium and chloride ions

• Sodium and potassium ions

• Magnesium and phosphate ions

• Hydrogen and hydroxide ions

Answer explanation

The resting potential of a neurone is primarily established by the movement of sodium (Na+) and potassium (K+) ions across the cell membrane, with potassium ions playing a key role in maintaining the negative charge inside the cell.

What is the term used to describe the rapid change in membrane potential that occurs during an action potential?

• Hyperpolarisation

• Depolarisation

• Repolarisation

• Stabilisation

Answer explanation

The rapid change in membrane potential during an action potential is called depolarisation. This phase involves the influx of sodium ions, causing the membrane potential to become more positive.

What principle states that an action potential either occurs fully or not at all?

• Graded response principle

• All-or-nothing principle

• Threshold principle

• Summation principle

Answer explanation

The all-or-nothing principle states that an action potential will either fully occur or not at all, meaning it does not vary in strength. This distinguishes it from graded responses, which can vary in magnitude.

How does the refractory period affect nerve impulse transmission?

• It allows continuous impulses

• It produces discrete impulses

• It increases the frequency of impulses

• It has no effect on impulse transmission

Answer explanation

The refractory period prevents the immediate reactivation of a neuron after an impulse, ensuring that impulses are discrete rather than continuous. This allows for clear signaling and prevents overlapping signals.

Which factor does NOT affect the speed of conductance in a neurone?

• Myelination

• Axon diameter

• Temperature

• Neurone length

Answer explanation

Neurone length does not significantly affect the speed of conductance. In contrast, myelination, axon diameter, and temperature all enhance the speed of nerve impulse transmission.

What is saltatory conduction?

• The continuous conduction of impulses along an axon

• The jumping of action potentials from one node of Ranvier to the next

• The slow movement of ions across the membrane

• The diffusion of neurotransmitters across a synapse

Answer explanation

Saltatory conduction refers to the process where action potentials jump from one node of Ranvier to the next along a myelinated axon, allowing for faster signal transmission compared to continuous conduction.

What happens to the membrane potential during depolarisation?

• It becomes more negative

• It becomes more positive

• It remains unchanged

• It fluctuates randomly

Answer explanation

During depolarisation, the membrane potential becomes more positive as sodium ions enter the cell, reducing the negative charge inside relative to the outside. This shift is crucial for initiating action potentials.

Which of the following is a characteristic of non-myelinated axons?

• Faster impulse transmission

• Slower impulse transmission

• Impulse transmission is unaffected by myelination

• Impulse transmission is random

Answer explanation

Non-myelinated axons transmit impulses more slowly than myelinated ones because they lack the insulating myelin sheath, which facilitates faster conduction through saltatory propagation.

What is the role of potassium ions during the repolarisation phase of an action potential?

• They enter the cell

• They leave the cell

• They remain stationary

• They are not involved

Answer explanation

During the repolarisation phase of an action potential, potassium ions (K+) leave the cell. This efflux of K+ helps restore the negative membrane potential after depolarisation, making 'They leave the cell' the correct answer.