A level Biology exam revision resources written by A level Examiners





 

The cells that the nervous system is made up of are called neurones. The neurones that make up the different parts of the nervous system have some features in common, but also some differences.

Table 3
Branch of nervous system, Afferent (Input to CNS), CNS, Efferent (Output from CNS), Features of neurones, Sensory neurones: these cells have long axons and the nucleus, which is within the cell body, is often located part way down the axon, Interneurones (also called relay neurones): these cells are small cells with many interconnections, Motor neurones: these cells have long axons and the nucleus, which is within the cell body, is often located at the beginning of the axon.

At A level the details of nerve cell structure are usually only required for the motor neurone. These are shown in figure 5 below.

Figure 5 : Nerve Cell structure
Figure 1 : Nerve Cell structure

The motor neurone shown in figure 5 would be called a myelinated neurone. This is because the axon is surrounded by Schwann cells which contain the fatty substance myelin. The myelin enables nerve impulses to be passed down this type of neurone very rapidly, see section on propagation of the action potential  click to make the link.



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