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Synapse
II. The synapse- junction between two communication neurons
ie. Presynaptic neuron  synaptic cleft  post synaptic neuron
Synaptic transmission
A. Synaptic vesicles- membranes sacs in the synapse that contain neurotransmitters
B. Neurotransmitters- 50 types produced in synaptic knobs
1. Acetylcholine- stimulate skeletal muscle
2. Monoamines- epinephrine, norepinephrine [very strong], dopamine etc.
3. Amino acids – anyone can act or be combined to act as neurotransmitters
4. Peptids
5. Monoamine oxidase [enzyme]
C. Cholinesterase – decomposes some neurotransmitters
D. Actions of neurotransmitters
1. Excitatory- increases pot synaptic membrane permeability to Na+ to trigger
nerve impulses (acetylcholine and norepinephrine)
2. Inhibitory- decreases the membrane permeability to NA+ thus casing threshold
to raise (dopamine and amino acids)
3. Combination of both – releases together. One in greater concentration has the
effect
E. Neuronal Pools- varying numbers of neurons in the CNS which receive and transmit
impulses into branched systems consisting of hundreds of synapses
1. Facilitation – when one neuron in a neuronal pool becomes more excitable and
triggers as a result of various neurotransmitters
2. Convergence- when two nerves in a pool transmit their impulse to one nerve in
the pool
3. Divergence – when one nerve impulse leaves a nerve fiber and sends that
impulse to 3 other nerves in the pool, this amplifies the impulse
III. Types of neurons- classified by structure, size, shape and function
A. Size
1. Multipolar- many nerve fibers only one is an axon the rest are dendrites (CNS nerves)
2. Bipolar- only 2 fibers 1 axon and 1 dendrite found in the eyes, nose and ears
3. Unipolar- one branched dendrite and one axon leading to CNS(spinal cord)
4. Ganglion- masses of unipolar nerve cells outside brain and spinal cord
B. Function
1. Sensory – collect and carry sensory impulses o the brain receptors
2. Interneurons- transmit impulse to brain from one part to another. Direct impulses to
proper locations.
3. Motor neurons- bring about muscle movement or glandular excretion