What is a motor neurone?

A neurone that carries impulses from the central nervous system to an effector.

What is a relay neurone?

A neurone within the CNS that links sensory neurones to motor neurones.

Where is the cell body of a sensory neurone?

To one side of the axon, in the dorsal root ganglion outside the spinal cord.

Where is the cell body of a motor neurone?

At one end of the neurone, in the grey matter of the spinal cord.

What do Schwann cells do?

They wrap around axons many times to form the myelin sheath.

Why is myelin an insulator?

It is rich in lipid, so ions cannot cross the membrane where it is present.

What are nodes of Ranvier?

Gaps in the myelin sheath between neighbouring Schwann cells.

What does grey matter contain?

Cell bodies of neurones and synapses.

What does white matter contain?

Mainly myelinated axons running along the spinal cord.

List the parts of a reflex arc in order.

Stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response.

Give two features of a reflex.

Rapid and involuntary; protective, with few synapses.

What are the two kinds of effector?

Muscles (which contract) and glands (which secrete).

Neurones and the reflex arcEdexcel International A Level Biology: Flashcards

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What is a sensory neurone?

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What is a sensory neurone?: A neurone that carries impulses from a receptor to the central nervous system.
What is a motor neurone?: A neurone that carries impulses from the central nervous system to an effector.
What is a relay neurone?: A neurone within the CNS that links sensory neurones to motor neurones.
Where is the cell body of a sensory neurone?: To one side of the axon, in the dorsal root ganglion outside the spinal cord.
Where is the cell body of a motor neurone?: At one end of the neurone, in the grey matter of the spinal cord.
What do Schwann cells do?: They wrap around axons many times to form the myelin sheath.
Why is myelin an insulator?: It is rich in lipid, so ions cannot cross the membrane where it is present.
What are nodes of Ranvier?: Gaps in the myelin sheath between neighbouring Schwann cells.
What does grey matter contain?: Cell bodies of neurones and synapses.
What does white matter contain?: Mainly myelinated axons running along the spinal cord.
Through which root do sensory neurones enter the spinal cord?: The dorsal root.
Through which root do motor neurones leave the spinal cord?: The ventral root.
List the parts of a reflex arc in order.: Stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response.
Give two features of a reflex.: Rapid and involuntary; protective, with few synapses.
What are the two kinds of effector?: Muscles (which contract) and glands (which secrete).

Exam questions on Neurones and the reflex arc

A person touches a hot saucepan handle and pulls their hand away before they feel any pain. The withdrawal is a spinal reflex.
Explain why the withdrawal reflex is faster than a conscious, voluntary response.2 marks
A neurobiologist examines a transverse section through a human spinal cord and a longitudinal section through a motor neurone with its myelin sheath.
Describe how Schwann cells form a myelin sheath and explain why the sheath insulates the axon.2 marks
A child steps on a sharp drawing pin and lifts her foot straight away. A student describes the pathway. A receptor in the skin detects the pin. A neurone carries the impulse into the spinal cord through the dorsal root, and the cell body of this neurone lies in a swelling outside the cord. In the spinal cord the impulse passes across a synapse to a short neurone, then across a second synapse to a neurone that leaves the cord through the ventral root and reaches a muscle in the leg.
Describe the pathway of the impulse in this reflex, from the receptor to the response, naming the types of neurone involved.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).