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biology 0610printed 179 · PDF 179
328 pagesrevision 46933
printed 179 · PDF 179
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● They have thin fibres of cytoplasm stretching out from their body.
● The longest fibre is called axon.
● The shortest fibres are called dendrites.
● The dendrites pick up signals from other neurons lying nearby. These are
called nerve impulses. These then pass through the axon which passes it on
to other neurons.
The Central Nervous System
● All mammals have a central nervous system and a peripheral nervous
system.
● The CNS is made up of the spinal cord and the brain.
● Its role is to coordinate the electrical impulses travelling through the nervous
system.
● The PNS is made out of nerves that spread out of the CNS.
● Receptors in our sense organs are also included in the PNS.
● When a stimulus is detected the signals are sent from the receptor to the
brain or spinal cord which then sends it to the effector for response.
Reflex Arcs
● In a reflex arc there are three types of neurons involved.
● When a receptor detects a stimulus it starts off an electrical impulse which
travels to the spinal cord. This cell is called the sensory neuron.
● In the spinal cord the neuron passes the electrical impulse to many other
neurons. These neurons are called relay neurons.
● The relay neurons pass the impulse to the brain and then onwards to the
motor neuron which delivers it to the effector.
● The pathway along which the nerve impulses pass is called the reflex arc.
● All three neurons have different shapes.
● The reaction that happens after an impulse has sped around the reflex arc is
called reflex action.