NERVOUS SYSTEM

The nervous system is a very complex system made up of;

·        CNS – Central Nervous System – brain and spinal cord

·        ANS – Autonomic Nervous System- activates involuntary responses

·        PNS – Peripherial Nervous System – controls sensory and effector neurones

The functions of theses are;

·        Collects information of the internal and external environment

·        Processes and integrates information usually in past experiences

·        Acts upon the information by co-ordinating the bodies activities

There are three types of cells;

·       Motor Neurones – found in the brain and spinal cord, they conduct impulses from the CNS to effector or tissues.

·       Sensory Nerve Cell – takes information from internal environment which has been processed from external comes in from connections (communicates with other knobs on the nerve cells) detector. Comes from receptors which take information up to the brain / spinal cord, which sums up a response by motor neurones. (Known as afferent nerve cells).

·       Sheaf – helps to transport nerve impulse away from cell body, affector takes information away from brain and spinal cord.

REFLEX ACTION (ARC)

A reflex action is a response to a stimulus, (sort of impulse). This is an automatic protected response. Information travels to the spinal cord, it may not have to travel all the way to the brain. If kept on the source of pain though information would travel to the brain. Information shoots up the arm from the receptor in the skin, and passed on by neurones sent via nerve fibres to the spinal cord. If a reflex response occurs here, the impulse is transported via motor nerves.

If there was a reflex in the hand the response would be;

Hand, receptors, sensory nerve to spinal cord.

A nerve impulse travels away from the cell body down the axons to the synapses, and where one cell ends another begins.  A nerve impulse is a charged particle = ion (reflexes) which is the flow of energy in solution.

Axon – an axon is semi-permiable, and has an influx of sodium ions, (movement) through nerve.

Synapse – this is a junction between two neurones. Electrical impulses at this junction stimulate chemicals causing the movement of impulses.

Anything that interferes with reaction can affect your ability. Various chemicals can effect the transmission of nerve cells across a synapse and responses. Alcohol can also affect the membranes of cells and make them unstable. If sheaf’s are damaged, sensory nerves will not function. We do however lose nerve cells everyday.

Transmission of nerve impulses

When nerve impulses are at rest there are fewer sodium ions present -70mv, this is before a nerve is stimulated. There is a balance of negative charge, then an influx of sodium ions. This is a movement that takes time, a bit like dominoes (part of the axon) falling down one by one, it all flows one way. The membrane is repolarised, outside is positive and inside is negative. The sodium pump expels sodium ions = +40.  the membrane is depolarised; inside becomes positive, outside becomes negative, sodium ions enters the axon. Membrane polarised outside positive, inside negative, sodium ions expelled by sodium pump mechanism. Just like the dominoes they all go back up ready for action again. The action potential is depolarised, called absolute refractory period.