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11.
The Human Body
Nervous System (Part III)
HOW THE NERVOUS SYSTEM WORKS Life and the hum of electric flow The
function of the nervous system depends on the neurons (nerve cells) present
in the CNS, PNS and ANS.
Each nerve has a long arm (axon) that carries on electric signal to the next
neuron where it is converted into a chemical signal.
The next neuron on receiving the chemical transmitters then conveys the
electric signal to the next cell till it reached the target cells.
It also has short branching arms (dendrites) nerve signal enter through these
short arms.
Nerve Impulse Chemicals - ions and electric charge
This impulse is brought about by the movement of chemical ions either into
or out of a neuron.
- These ions have an electric charge this causes the flow of an electric
current.
- When it reaches a junction between two neurons (synapse). It causes
the release of a neurotransmitters to stimulate the ion movement in
the next neuron.
- This impulse flows at a speed of 320 kilometers per hour.
- This is much slower than the speed of electricity. Thus there is a
delay in reaction or reaction time for every action.
Nerve Facts Speed of Signals
Each neuron has only one axon, but this can be anything from 1mm
long to over 1m long.
Myelinated nerves can transmit nerve signals 200 times faster than
unmyelinated ones.
The faster nerve signals travel at over 120 meters a second
over 250 mph.
After passing a signal, a nerve recovers ready to pass another
signal in less than one hundredth of a second.
There are 100 billion neurons in your brain.
Each neuron is linked to hundreds of other.
Nerve Synapse. Nerve function
Excitement and inhibition
If every nerve signal was passed on by the synapse, we would be
overwhelmed by nerve signals.
So at some
synapses
the receiving cell reacts to the
neurotransmitter by passing on the signal, but others react by
blocking it.
This is called excitation and inhibition.
Some tranquillizing drugs work
by
increasing inhibition. some
stimulants increase excitation.
Neurotransmitters Chemistry of Signals
There are over
40 neurotransmitting chemicals.
Acetylcholine is involved in making muscles contract.
Noradrenaline helps control heartbeat and blood flow.
Dopamine works in parts of the brain that control movement. Poo
response to dopamine may cause Parkinson's disease.
Endorphins are 'neuropeptide' transmitters produced and used by the
brain to control pain.
CNS Nerves
Symptom to remember
- Loss of sensation – numbness
- Tingling }
} sensation in hands and feet
- Burning }
- Weakness of muscle
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