The Nervous System

The Nervous System

1. Sense organs

   • Detect stimuli
     • Change in environment which you may need to react to
   • Eyes
     • Light receptors
       • Cells have a nucleus, cytoplasm and cell membrane
   • Ears
     • Sound receptor
     • Balance receptors - sensitive to changes in position
   • Nose
     • Smell receptors - sensitive to chemical stimuli
   • Tongue
     • Taste receptors
       • Sensitive to bitter, salt, sweet, sour and savoury - chemical stimuli
   • Skin
     • Sensitive to touch, pressure, pain and temperature change

2. Central nervous system

   • Sensory neurones
     • Nerve cells carry signals as electrical impulses from the receptors in the sense organs to the CNS
   • Motor neurone
     • Nerve cells carry signals from the CNS to the effector muscles or glands
   • Relay neurones
     • Nerve cells carry signals from sensory neurones to motor neurones
   • Effector
     • Muscles and glands
       • Muscles contract in response to a nerve impulse
       • Glands secrete hormones
   • Where all the information from sense organs are sent and where reflexes and actions are coordinated
     • Neurones transmit information as electrical impulses quickly to and from the CNS
       • Instructions from CNS are sent to effectors which respond
   • Brain and spinal cord only

3. Synapses

   • Connection between two neurones
     • Nerve signal is transferred by chemicals which diffuse across the gap

4. Reflexes

   • Prevent injury
   • Automatic responses to certain stimuli
     • Eg. bright lights make your pupils automatically get smaller for less light to enter

5. Reflex arc

   • Stimulus is detected by receptors, impulses are sent along a sensory neurone to the CNS
     • When impulses reach a synapse between the sensory and a relay, they trigger chemicals to be released - these cause impusles to be sent along the relay
       • When impulses reach a synapse between the relay and motor, chemicals are released and impulses are sent along the motor
         • Impulses travel along the motor to the effector
           • Muscle then contracts