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
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.
Organisms need to be able to
respond to stimuli from changes in their environment, primarily to
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:
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.
peripheral nervous system
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
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
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
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.