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Date May 2019 Marks available 3 Reference code 19M.3.SL.TZ1.5
Level Standard level Paper Paper 3 Time zone Time zone 1
Command term Explain Question number 5 Adapted from N/A

Question

Explain the neural control of swallowing.

[3]
a.

Neurons are initially produced by differentiation in the neural tube. Outline the mechanisms of axon and synapse development that follow the initial creation of neurons.

[4]
b.

Markscheme

a. voluntary passage of food through the mouth ✔

b. «bolus of» food touches the walls of the pharynx ✔

c. nerve sends message/impulse to brain ✔

d. swallowing centre in the medulla «oblongata» ✔

e. now involuntary/unconscious/autonomic responses/reflexes ✔

f. triggers closing of epiglottis «to prevent choking» ✔

g. leading to contraction of muscles/peristalsis «in the pharynx and esophagus» ✔

a.

a. axons are extensions of the neuron cell body ✔ 

b. some axons grow out of the neural tube and connect to other parts of the developing embryo ✔

c. chemical stimuli affect axon growth ✔

d. more dendrites form ✔

e. axon reaches the target cell ✔

f. forms single/multiple synapse«s» ✔

g. neural pruning involves the loss of neurons/synapses ✔

Do not accept migration of neurons

b.

Examiners report

Very few candidates recognized the voluntary aspect of swallowing. The role of the medulla and consequent involuntary action were most often described, although answers were frequently quite muddled.

a.

The question was often not read properly, with answers describing formation and migration of neurons, and chronological steps were rarely seen. Most answers receiving credit involved synapse formation and neural pruning.

b.

Syllabus sections

Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Core topics) » A.2 The human brain
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Option A: Neurobiology and behaviour » Option A: Neurobiology and behaviour (Core topics)
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