Nervous system

• Automatic control systems include receptors, coordination centres and effectors
• Receptors are cells that detect change in an organisms internal or external environment, these changes are known as stimuli
• The brain, spinal cord and pancreas are examples of coordination centres
• Coordination centres receive and process information from receptors
• effectors receive information from coordination centre then respond to restore conditions back to the optimum
• Effectors can be muscles, which respond by contracting muscles, or glands which respond by releasing hormones
• Cells called neurones receive info and carry it around body as electrical impulses
• The central nervous system is made up of the brain and spinal cord
• what are the three types of neurones

  Sensory neurones

  relay neurones

  motor neurones
• Sensory neurones carry impulses from receptors to the CNS
• Relay neurones carry impulses within the CNS
• Motor neurones carry impulses from the CNS to effectors
• Neurones have long fibre ( an axon) so they can carry electrical impulses across long distances
• The axon is insulated by a fatty material called myelin so information isn lost
• Neurones have tiny branches called dendrons which allow them to receive impulses from other neurones
• A synapse is a gap between neurones
• Electrical impulses can’t cross synapses but chemicals can
• When an electrical impulse reaches a synapse it causes chemicals to be released

  the chemicals diffuse across then bind to receptors on the other neurons stimulating an electrical impulse in the other neurone
• A reflex action is a rapid automatic response to a stimulus
• Reaction time is a measure of how quickly an organism can respond to a particular stimulus
• reflex actions involve a special nerve pathway called a reflex arc
• The reflex arc starts when a receptor detects a stimulus.

  The receptor sends an electrical impulsethrough a sensory neurone.

  The impulse reaches a synapse.

  Chemicals cross the synapse and generate an impulse in a relay neurone.

  The impulse reaches another synapse and more chemicals are released.

  This generates an impulse in a motor neurone.

  The motor neurone carries the impulse to an effector, usually a muscle.

  The muscle contracts, in our example above to move the hand away from the painful stimulus.