Describe the shape of a motor neurone.

A motor neurone has a cell body in the grey matter of the central nervous system with many short dendrites radiating from it, and one very long axon running out to the effector.

How does the position of the cell body in a sensory neurone differ from that in a motor neurone?

In a sensory neurone the cell body sits in a side branch part way along the fibre, in the dorsal root ganglion, whereas in a motor neurone it lies at one end within the central nervous system.

Which organelles are abundant in a neurone cell body, and why?

The cell body is packed with rough endoplasmic reticulum and mitochondria, because large amounts of protein and neurotransmitter must be made and a great deal of ATP is needed.

OCR A-Level Biology B H422

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The Nervous System and the Identification and Consequences of Damage

The structure of motor, sensory and relay neurones

3 things to know
Components 01, 02 and 03

Overview

Recall questions on dendrites, dendrons and axons, the structure of motor, sensory and relay neurones, organelles in the cell body, Schwann cells, myelin and nodes of Ranvier, the axon membrane, synaptic knobs, and what electron micrographs of neurones reveal.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is the function of the dendrites of a neurone?

Key term

Distinguish between a dendron and an axon.

Key term

Where are relay neurones found, and how does their length compare with the other two types?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the function of the dendrites of a neurone?
Model answer
Dendrites receive signals from other neurones or from receptors and carry the resulting depolarisation towards the cell body.
2
Distinguish between a dendron and an axon.
Model answer
A dendron carries impulses towards the cell body, whereas an axon carries impulses away from the cell body.
3
Describe the shape of a motor neurone.
Model answer
A motor neurone has a cell body in the grey matter of the central nervous system with many short dendrites radiating from it, and one very long axon running out to the effector.
4
How does the position of the cell body in a sensory neurone differ from that in a motor neurone?
Model answer
In a sensory neurone the cell body sits in a side branch part way along the fibre, in the dorsal root ganglion, whereas in a motor neurone it lies at one end within the central nervous system.
5
Where are relay neurones found, and how does their length compare with the other two types?
Model answer
Relay neurones lie entirely within the central nervous system and are short, with many short dendrites and a short axon.
6
Which organelles are abundant in a neurone cell body, and why?
Model answer
The cell body is packed with rough endoplasmic reticulum and mitochondria, because large amounts of protein and neurotransmitter must be made and a great deal of ATP is needed.

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