Nervous co-ordination

The nervous and endocrine systems work together to co ordinate the actions withing the body.

Nervous system:
info is passed as electrical impulses along nerve fibres and chemically over synapses.
Transmission is relatively rapid with a short response time. however it is short lived.
the response is very local as 1 nerve fibre supplies a group of effector cells.

endocrine systems:
info is passed as chemical substances in the bloodstream/plasma.
transmission is relatively slow and the response time is long, the response may carry on for a long time.
the response can be widespread and cells in different parts of the body can respond to the chemical.
cell body: contains the nucleus and mitochondria. providing atp for sodium/ potassium pump.
dendrites: increase the surface areas many synapses can be made with other neighboring neurones.
axon: transmit electrical impulses away from the cell body, they are long so there are fewer synapses to slow it down.
myelin: enclcoses the axon, fatty sheath. insulates, speeds up conduction and prevents action potentials being formed.
Nodes of ranvier: gap in the myelin sheath where action potentials can form.
synaptic bulbs: end of the branch the axon contains vesicles of neurotransmitters.

3 types of neurones:
1) sensory neurones- conduct nerve impulses away from a receptor toward the central nervous system.
2) relay neurones- conduct impulses from the sensory neurones to a motor neurone.
3)motor(effector) neurones conduct nerve impulses from a relay neurone in the spinal cord to an effector e.g a muscle.

myelination and schwann cells
schwann cells produce the fatty myelin surrounding the axon. the schwann cell wraps around the axon, covering it.
The action potentials move from each node of ranvier to the next.(saltatory conduction)
as the schwaan cell grows around the axon it twists many times and myelin is formed from the layers of schwaan cell membrane pressed together.

The Nerve Impulse:
potential differences are caused by uneven distribution of positively charged ions, on either side of the nerve cell membranes.
A resting potential exists when there is no nerve impulse.

outiside there is high Na+ and low k+
overall more positive outside = resting potential of -60mV
inside low Na= and high K
there is more k channel than na channels and 3na ions move out and 2 k move in .

Synapse:
in most synapses the gap is too large for electrical impulses to jump across and instead the impulse triggers the release of the chemical transmitter.

mechanisms for synaptic transmission
1) the action potential reaches the bulb of the presynaptic membrane, calcium channels open and calcium diffuses in.
2) calcium simulates the movement of vesicles to the membrane.
3) the vesicles fuse with the membrane and release their transmitter by exocytosis into the synaptic cleft.
4) the transmitter diffuses across and binds to receptors on the postsynaptic membrane, this causes ion channels to open.
5) the movement of ions results in the generation of a postsynaptic potential.
6) the transmitter substance is quickly broken down by enzymes.