The peripheral nervous system consists of three systems of nerves.
i) Cranial nerves
Cranial nerves travel between brain and various organs without passing
through the spinal cord. They are sensory, motor or mixed nerves. They
are associate with responses.
ii) The Sympathetic nerves
They form autonomic nervous system. They prepare the body for
emergency situation.
iii) Parasympathetic nerves
They form autonomic nervous system. They involve in eating, sexual
activity and urination etc.
Autonomic nervous system therefore regulates involuntary systems of the body
automatically.
Reflex Arcs: -
Reflax arc is regarded as the functional unit of nervous system. A reflex is an
automatic response to stimuli. A nervous pathway which operates without having
to wait for directions of brain is a reflex arc. These reflexes increase the efficiency of
nervous system. For example if our hand touches with a very hot thing it pulls back
ward without any further delay.
Importance of Reflexes: -
i) Reflexes are mechanism for maintaining appropriate posture.
ii) Reflexes are responsible to regulate blood pressure.
iii) They keep the body as per environmental condition.
Involuntary Actions: -
i) Involuntary action is an action, which is performed without any conscious
effort.
ii) These actions have adaptive values because these actions required to
produce at once.
iii) For example when a person touches something very hot the hand is
automatically withdrawn.
Voluntary Actions: -
i) Voluntary Action is an action, which is performed on the will of an
organism e.g. walking, talking, playing etc.
ii) In these actions stimuli may be conveyed to brain or spinal cord.
iii) The brain or spinal cord then analyze the information and send motor
impulses to effectors.