NEURONS (NERVE CELLS)
STRUCTURES
NEURONS (NERVE CELLS)
cell body
controls metabolism of nerve cell
dendrite
collects info from other cells
axon
extended to carry info over long distances
myelin sheath
electrical insulation which prevents distortion of the nervous impulse by activities of neighbouring cells
myelinated fibres
insulated fibres which have to cover long distances
unmyelinated fibre
uninsulated fibres which have to cover short distances
schwann cell
fatty individual cells which insulate the axon and form the myelin sheath
nodes of ranvier
allows rapid conduction of impulses by forcing messages to "jump" from one node to the next
functional units of the nervous system
types of neurons
morphological classification (structural types)
multipolar
bipolar
one axon and one dendrite
eg. inter
unipolar
just one axon with cell body to side of axon
eg. sensory
one axon and multiple dendrites extending from cell body
eg. interneurons and motor neurons
synapses
synapse: the junction between the branches of adjacent neurons
action at the synapse:
- nerve impulse reaches end bulb of axon
- vesicles move to end bulb membrane
- neurotransmitters are released into synaptic cleft
- neurotransmitters diffuse across cleft
- neurotransmitters bind to receptor sites on membrane of the dendrites of the next neuron
- binding on causes depolarisation of the next neuron's axon and the impulse travels on
- enzymes break down neurotransmitter after impulse has been transferred
functional types
interneurons
carry messages between motor and sensory neurons
motor neurons
carry messages away from CNS to effectors (muscles and glands) [efferent]
sensory neurons
carry messages from receptors to CNS [afferent]