UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 20/05/2023 [SEARCH]

Nervous system: 1. Introduction to the nervous system

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INDEX of biology notes on the nervous system

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(1) Introduction to the nervous system

The nervous system and hormones enable us to respond to external changes - external stimuli.

The nervous system and hormones also help us to control conditions inside our bodies.

A nerve impulse as an electrical signal that passes along specialised nerve cells called neurones

Nerve cells (neurones) are those that communicate with each other in complex systems that include information messaging to all the structures of the body like organs, glands ad muscles etc.

Infancy and childhood are critical periods when most of these vital nerve cell connections are made and they are crucial to our physical and mental development and general wellbeing.

A 'simple' single celled organism can only respond to its immediate environment, but the cells of multicellular organisms must be able to communicate with each other before responding to any internal or external changes.

Therefore complex multicellular systems have evolved nervous and hormonal 'messaging' systems.

The nervous system enables humans to detect changes in their situation, react to their surroundings and coordinate their behaviour responses - which may be deliberate from the conscious mind or autonomic, meaning an automatic response of the nervous system like the reflex arc (described in detail later).

Organisms need to be able to respond to stimuli from changes in their environment, primarily to survive!

Any change in your surroundings eg temperature, visual, sound etc. is potentially a detectable stimulus to one of you sensory organs eg skin, eyes, ears etc. The stimulus might be chemical, light, pain, position, pressure, sound, temperature, touch etc.

You have five different sense organs ears, eyes, nose, skin and tongue which contain receptors (groups of cells) that are sensitive to particular stimuli.

In the receptor cells the stimulus input is converted into an electrical nerve signal - an electrical impulse which is sent to the central nervous system (CNS)

Although complex, the nervous system has two main groups of nerve cell connections:

(i) The central nervous system (CNS) for vertebrates (animals with backbones) consists of the brain and spinal cord.

The CNS is effectively the control centre for the whole body.

(ii) The peripheral nervous system (PNS) consists of all the rest of the nerve cells (neurones) that connect to all the rest of the parts of the body.

All of these peripheral nerve connections lead to and from the brain and spinal cord, so all the messaging from anywhere in the body must occur by way of the CNS.

The CNS receives signals via the sensory neurones from receptor cells e.g. of touch, light, temperature.

Motor neurons send electrical signals from the CNS to effector cells e.g. in the muscles to effect movement of a part of your body.

Effector cells are found in all your muscles and glands and respond to impulses from the CNS.

Both of which are involved with the coordination and regulation of bodily functions.

The reflex actions that can happen by virtue of our central nervous system help prevent injury from various sources in potentially dangerous situations - details later.

With our varied receptor cells, we as humans can react to our surroundings and coordinate our behaviour to our best advantage - throughout millions of years all animals exhibit survival adaptations.

Note on types of 'action'

Voluntary action - When an action is produced with the involvement of thoughts, they are called voluntary action e.g. walking, eating, jumping and running. You consciously produce these actions. Both the spinal cord and brain of the CNS are involved and these coordinate with the PNS to generate necessary movements.

Involuntary action (reflex actions) - Actions which take place without consciousness or willingness of an individual are called the involuntary actions e.g. digestion, heart beating, sneezing are all autonomic 'unconscious' actions and tend to happen relatively fast e.g. the reflex arc effect.

BUT,  both involuntary and voluntary actions are controlled by the same parts of the brain.


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