The nervous system & eye

• Any change in the internal or external environment is called a stimulus
• Receptors detect stimuli and send signals to the CNS.
• Receptors in the sense organs (the eyes, ears, nose tongue and skin) are groups of cells that detect external stimuli
• Receptors communicate with effectors via the nervous system, the hormonal system or sometimes both
• Effectors are cells that bring about a response to stimuli. They include muscle cells and cells found in glands e.g the pancreas
• Effectors respond in different ways, muscle cells contract, whereas glands secrete hormones
• The nervous system is made up of all the neurones in your body. the three main types of neurone:

  • motor
  • relay
  • sensory
• The central nervous system (CNS) consists of the brain and spinal cord only