there are 100billionnerve cells (neurones) in the human nervous system, 80% of which are located in the brain. by transmitting signals electrically and chemically, these provide the nervous system with its primary means of communication.
what are the three types of neurons?
motor neurons, sensory neurons and relay neurons.
what is the role of motor neurons?
connect the CNS to effectors such as muscles and glands. they have short dendrites and long axons.
what is the role of sensory neurons?
carry messages from the PNS to the CNS. they have long dendrites and short axons.
what is the role of relay neurons?
connect sensory neurons to motor or other relay neurons. they have short dendrites and short axons.
what are the basic structural elements of neurons?
cell body (or soma), dendrites, axon and terminalbuttons.
cell body (or soma)
includes a nucleus which contains the genetic material of the cell.
dendrites
branch-like structures that protrude from the cell body. these carry nerveimpulses from neighbouring neurons towards the cell body.
axon
carries the electrical impulse away from the cell body down the length of the neuron
covered in a fatty layer of myelin sheath that protects the axon.
gaps in the axon called nodes of ranvierspeed up the transmission of the impulse.
terminal buttons
found at the end of the axon.communicate with the next neuron in the chain across the synapse.
electric transmission- the firing of a neuron
when a neuron is in a resting state the inside of the cell is negatively charged compared to the outside. when a neuron is activated, the inside of the cell becomes positively charged for a split second causing an action potential to occur. this creates an electrical impulse that travels down the axon towards the end of the neuron.