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Neurons and Synaptic transmission - Coggle Diagram
Neurons and Synaptic transmission
The Structure and Function of Neurons.
there's 100 billion neurons in human NS - 80% are located in brain.
by transmitting signals electrically & chemically, these neurones provide NS with it's primary means of communication
3 types of neurones:
(1)
sensory neurones
= carry messages from PNS to CNS. they have long dendrites & short axons
(2)
relay neurone
= connect sensory neurons to motor & other relay neurons. they have short dendrites & short axons.
motor neuron
= connect CNS to effectors such as muscles & glands. they have short dendrites & long axons.
cell body
of neuron contains a
nucleus
which contains
genetic material
of the cell.
branchlike structure called
dendrites
protrude from the cell body. they carry nerve impulses from neighbouring neurons towards the cell body.
the
axon
carries impulses away from cell body & down length of neuron. axon is covered in fatty layer of
myelin sheath*
which protects axon & speeds up electrical transmission of the impulse.
if myelin sheath was continuous this would have reverse effect & slow down the electrical impulse. as result myelin sheath is separated in to sections called
nodes of ranvier
- these speed up transmission of impulse by forcing it to 'jump' across gaps along the axon.
finally at end of axon are
terminal buttons
which communicate with the next neuron in the chain across a gap known as the
synapse
location of neurons
cell body of motor neurone may be in CNS but they have long axons which form part of PNS.
sensory neurons are located outside CNS in PNS in clusters known as
ganglia
relay neurones make up 97% of all neurons & most are found in the brain & visual system.
electrical transmission - the firing of a neuron
when neuron is in resting state the inside of the cell is negatively charged compared to outside. when neuron is activated by stimulus, inside of cell becomes positively charged for split second causing
action of potential
to occur = creates electrical impulse that travels down axon towards end of neuron
Synaptic transmission
Chemical transmission
neurons communicate with each other within groups known as
neural networks
.
neurons are separated from each other by extremely tiny gap called synapse.
signals within neurons are transmitted electrically between neurons are transmitted chemically across the synapse.
when electrical impulse meets end of neuron (
presynaptic terminal
) it triggers the release of
neurotransmitter from tiny sacs called
synaptic vesicles**
neurotransmitters
excitation & inhibition