Central & Peripheral Nervous System (Edexcel International A Level (IAL) Biology): Revision Note

Central & Peripheral Nervous System

• 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 $\to$ receptor $\to$ sensory neurone $\to$ CNS $\to$motor neurone $\to$effector

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