The Nervous System

• Organisms need to respond to stimuli in order to survive
• Stimuli

  changes in the environment
• A single-celled organism can just respond to its environment, but the cells of multicellular organisms need to communicate with each other first
• As multicellular organisms evolved, they developed nervous and hormonal communication systems
• The nervous system is made up of:

  • the central nervous system (CNS)
  • sensory neurones
  • motor neurones
  • effectors
• Central nervous system (CNS)

  • in vertebrates (animals with backbones) this consists of the brain and spinal cord only
  • In mammals, the CNS is connected to the body by sensory neurones and motor neurones
• Sensory neurones

  the neurones that carry information as electrical impulses from the receptors to the CNS
• Motor neurones

  the neurones that carry electrical impulses from the CNS to effectors
• Effectors

  all your muscles and glands, which respond to nervous impulses
• Receptors

  cells that detect stimuli
• There are many different types of receptors, such as taste receptors on the tongue and sound receptors in the ears
• Receptors can form part of larger, complex organs, e.g. the retina of the eye is covered in light receptor cells
• Effectors respond to nervous impulses and bring about a change
• Effectors:

  • muscles contract in response to a nervous impulse
  • glands secrete hormones is response to a nervous impulse
• The CNS is a coordination centre - it receives information from the receptors and then coordinates a response which is carried out by the effectors
• The nervous system:

  1. stimulus
  2. receptor
  3. sensory neurone
  4. central nervous system
  5. motor neurone
  6. effector
  7. response
• Synapse

  the connection between two neurones
• In a synapse, the nerve signal is transferred by chemicals which diffuse across the gap, which then set off a new electrical signal in the next neurone