Central & Peripheral Nervous System (Edexcel International A Level Biology)

• The human nervous system consists of
  • Central nervous system (CNS) – the brain and spinal cord
  • Peripheral nervous system (PNS) – the parts of the nervous system that are not within the central nervous system and that extend to the rest of the body
• The nervous system allows detection of stimuli in the surroundings and the coordination of the body's responses to the stimuli
  • Stimuli are detected by cells called receptor cells
    • Receptor cells are gathered together in the sense organs, e.g.
      • Photoreceptors that are stimulated by light are found in the eye
      • Chemoreceptors that are stimulated by chemicals are found on the tongue
      • Pressure receptors that are stimulated by pressure are found on the skin and inside the blood vessels
  • The parts of the body that respond to stimuli are known as the effectors
    • Effectors can be muscles or glands
• Information is sent through the nervous system in the form of electrical impulses that pass along nerve cells known as neurones 
  • A bundle of neurones is known as a nerve
  • There are different types of neurones including sensory neurones, relay neurones, and motor neurones
• The PNS connects the receptor cells in the sense organs with the CNS, and connects the CNS with effectors
  • The CNS acts as a central coordinating centre for the impulses that come in from, and are sent out to, any part of the body
• Nerve impulses pass through the nervous system along the following pathway

stimulus  receptor  sensory neurone  CNS motor neurone effector

The nervous system consists of the central nervous system and the peripheral nervous system