Chapter 13 - Coordination and response

COORDINATION IN ANIMALS

• stimuli= changes in an orgnism's environment
• Stimuli are sensed by specialised cells called receptors.
• The organism responds using effectors (e.g. muscles, salivary glands). 
• Most animals have two methods of sending information from receptors to effectors:
  • the fastest way is by means of nerves. The receptors and nerves make up the animals nervous system. 
  • A slower method, but still important, is by means of chemicals called hormones. Hormones are part of the endocrine system. 

THE HUMAN NERVOUS SYSTEM

• The human nervous system is made up of special cells called neurones. 
• An axon is the longest fibre in a neurone. 
• The dendrites pick up nerve impulses from other neurones lying nearby. 
• Some of the nerve fibres of active animals like mammals are wrapped in a layer of myelin (fat and protein). 
• A myelin fibre carries nerve impulses faster than a fibre without any myelin can. 

• The CNS (central nervous system) is made up of the brain and spinal cord.
• The peripheral nervous system is made up of nerves and receptors. 
• Relay neurones relay the impulse on to other neurones. They also pass the impulse to the brain and can pass it on to an effector.
• The pathway along which the nerve impulse passes - the sensory neurone, relay neurones and motor neurones - is called a reflex arc. 
• involuntary actions= actions which are not under our conscious control (e.g. reflex actions).
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