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biology 0610printed 180 · PDF 180
328 pagesrevision 46933
printed 180 · PDF 180
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Synapses
● There are small gaps between neurons which are called synaptic gaps.
● The ends of the two neurons plus the gap is together known as a synapse.
● In one of the neuron ends there are small vesicles or tiny vacuoles. These
contain huge numbers of molecules of a chemical called neurotransmitters.
● When an electrical impulse arrives along the axon of the neuron it causes
these vesicles to move to the cell membrane. They fuse with the membrane
and empty their contents in the gap.
● The neurotransmitters quickly diffuse to the other side and attach to the
receptor proteins in the cell membrane of the other neuron end. The shape
of the receptor proteins are complementary to the shape of the
neurotransmitters.
● This binding triggers an electrical impulse in the other neuron.
● Synapses act as one way valves. Receptor proteins are found on only one of
the neuron’s ends. This makes sure electrical impulses move in one desired
direction only.
Sense Organs
● Sense organs are the ones that have receptors which are specialised cells to
detect stimuli.