The Autonomic Nervous System

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The Autonomic Nervous System

Many of the body's activities are controlled automatically.

Actions such as breathing and digestion occur without us thinking about them.

Each organ is provided with two sets of nerves that work in opposing ways. These are known as sympathetic and parasympathetic nerves.

The sympathetic neurons accelerate such activity as the heart rate by the release of adrenaline into the bloodstream. The parasympathetic neurones slow activity down by the release of acetylcholine.

All this occurs in the absence of conscious knowledge or control.

The Autonomic Nervous System
The Autonomic Nervous System

There are two types of reflex responses:

There are reflex actions that are rapid responses to a stimulus by one or more organs. An example of this can be seen when we touch something hot - there is a rapid response to move from the hot surface.

There are also conditioned reflexes.

This will have initially involved a learning of a skill such as riding a bicycle. At some point during the learning conscious thought was required to keep the bike balanced, going in the correct direction and peddling as well as a host of other things. Eventually we develop a number of conditioned reflexes that we don't have to think about like turning the handle bars, ringing the bell or peddling.

The major difference between reflex actions and consciously thought out actions is the speed of the action.

Conscious thought requires time for the brain to consider the options work out the action and send the appropriate messages to the motor organs for example the arms or legs.

This takes a relatively long time and during that time the appropriate response can be too late.

A reflex response bi-passes the brain and goes via the central nervous system, the spinal cord. The response time is infinitely faster and therefore the appropriate response can be made in time.

A reflex arc

The Autonomic Nervous System