Page 32 - Biology_Form_3

Biology for Secondary Schools

Synaptic ending Nucleus Receptor in the skin

Axon Cell body
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Schwan cell
CNS
Dendron

Direction of Node of Myelin sheath
impulses Ranvier

Figure 2.4: Structure of sensory neurone

Motor neurones
Motor neurones are also called efferent neurones. They have short dendrites and a long
axon as shown in Figure 2.5. Their dendrites and cell bodies are located in the CNS and
the end part of the axon is located in an effector organ. Motor neurones transmit nerve
impulses from the CNS to the effector organs such as muscles or glands. The cell body
collects impulses from other neurones through hundreds of tiny fibres called dendrites.
A long, single axon carries these impulses from the cell body to a muscle fibre or gland.
At the point where an axon of a motor neurone enters a muscle fibre, there is a structure
called a motor end plate. When impulses reach the motor end plate, they set off chemical
reactions that result in muscular contraction.

Node of ranvier
Nucleus Cell body Myelin sheath

CNS Axon

Direction of impulses
Node of Ranvier

Dendrites Schwan cell Motor end plates of muscles fibre
Figure 2.5: Structure of motor neurone

25 Student’s Book - Form Three

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