Question 1

What is the difference between a sensory neurone and a motor neurone?

Accepted Answer

Sensory neurones carry impulses from sensory receptors (e.g., in skin) to the central nervous system (CNS). They have a long dendron and a short axon. Motor neurones carry impulses from the CNS to effectors (muscles or glands). They have a long axon and short dendrites. Relay neurones connect sensory and motor neurones within the CNS.

Question 2

How does the sodium-potassium pump maintain the resting potential?

Accepted Answer

The sodium-potassium pump actively transports 3 Na+ ions out of the neurone and 2 K+ ions in, using ATP. This creates a higher concentration of Na+ outside and K+ inside. The pump is electrogenic, contributing a small negative charge inside. Additionally, K+ leak channels allow K+ to diffuse out, making the inside more negative, establishing the resting potential of about -70 mV.

Question 3

Why does the action potential only travel in one direction?

Accepted Answer

After an action potential passes, the region behind it enters the refractory period, during which voltage-gated Na+ channels are inactivated and cannot reopen. This prevents the action potential from propagating backwards. The region ahead is at resting potential and can be depolarised, ensuring unidirectional transmission.

Question 4

What is the role of calcium ions in synaptic transmission?

Accepted Answer

When an action potential reaches the presynaptic knob, it opens voltage-gated Ca2+ channels. Ca2+ ions enter the knob, causing synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft. Without Ca2+ influx, neurotransmitter release cannot occur.

Question 5

How do inhibitory neurotransmitters affect the postsynaptic membrane?

Accepted Answer

Inhibitory neurotransmitters (e.g., GABA) bind to receptors that open Cl- channels or K+ channels. Cl- enters or K+ leaves, making the inside of the postsynaptic neurone more negative (hyperpolarisation). This generates an inhibitory postsynaptic potential (IPSP), making it harder for the neurone to reach threshold and fire an action potential.

Question 6

What is the difference between temporal and spatial summation?

Accepted Answer

Temporal summation occurs when a single presynaptic neurone releases neurotransmitter repeatedly in quick succession, producing multiple EPSPs that add up over time to reach threshold. Spatial summation occurs when multiple presynaptic neurones release neurotransmitter simultaneously, their EPSPs adding up at the postsynaptic membrane to reach threshold. Both allow integration of signals.

Neuronal communication

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