The Human Nervous System

1
The Human Nervous System

• A simple reflex arc is the simplest response to a
  stimuli. There whole arc only involves 3 sections
  of a nerve pathway. The the response is automatic
  and very rapid, the reason that it is so fast is
  because the information does not have to travel
  or be processed by the brain. The three neurons
  which normally make up the pathway are
• (1) sensory neuron
• (2) relay neuron
• (3) motor neuron

This is how it works
Stimulus sensor coordinator
effector response
Touch pain receptor CNS
muscle movement
2
ANS The 2 Divisions

• The roles of the sympathetic and parasympathetic
  nervous system are opposing. Generally the
  sympathetic nervous system has a stimulatory
  affect and prepare the body for action while the
  parasympathetic system returns the body functions
  to normal.

3
The autonomic nervous system and the pupil

• To operate well in different light conditions the
  eye must be able to control the amount of light
  entering the eye it does this by changing the
  diameter of the pupil. The changes in the size of
  the pupil are brought about by a reflex arc so it
  involves no conscious thought. The light
  receptors in the retina detect the intensity of
  the light (sensor). E.g too weak or too strong
  this information is then sent to the brain via
  the optic nerve(Sensory Neuron). Then impulses
  from the brain are transmitted to the iris
  muscles by the nerve fibres.

4
Emptying of the bladder

• The human bladder can hold up to 800 cm3 of urine
  but what happens when its full? Stretch receptors
  in the bladder wall send a impulse to the CNS
  alerting it to the urgency the rely neuron send
  an impulse to the motor neuron which sends an
  impulse to the sphincter muscles to relax and we
  urinate. But not always as we humans have learnt
  hoe to control our sphincter muscles (potty
  training) so we can go when and where convenient.