The Nervous System - Structure (OCR Gateway GCSE Biology: Combined Science)

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Key Terms in the Nervous System

  • The human nervous system consists of the central and peripheral nervous system as seen in the image below
  • The nervous system enables humans to react to their surroundings and to coordinate their behaviour
  • Information is sent through the nervous system as electrical impulses – electrical signals that pass along nerve cells known as neurones
  • A bundle of neurones is known as a nerve
The human nervous system

The nervous system is made up of the CNS and the PNS
  • There are many key terms associated with the nervous system topic
  • Some of the most important terms and their definitions include
    • Stimulus: A detectable change in the internal or external environment of an organism e.g. light, sound or temperature
    • Receptor: A cell or organ which detects a stimulus
    • Neurone: A nerve cell, specially adapted to carry electrical charges, called nerve impulses from one part of the body to another
    • Sensory neurone: A neurone which carries nerve impulses from receptors to the central nervous system
    • Motor neurone: A neurone which carries nerve impulses from the central nervous system to effectors
    • Relay neurone: A neurone that acts as a coordinator, transmitting impulses from the sensory to the motor neurone in the spinal cord
    • Effector: A cell, tissue, organ or organ system that responds to a stimulus
    • Voluntary response: A nerve pathway which produces a conscious response to a stimulus
    • Reflex response: A nerve pathway which produces an automatic response to a stimulus
    • Synapse: A gap between two neurones
    • Axon: A single long fibre within a neurone which carries a nervous impulse away from the cell body
    • Electrical impulse: A signal which is passed through the nervous system as electrical charge to instigate a response
    • Central nervous system (CNS) – The part of the nervous system which includes brain and spinal cord
    • Peripheral nervous system (PNS) – All of the nerves in the body which extend from the CNS

The Central Nervous System

  • The central nervous system (CNS) consists of the brain and spinal cord
  • It is responsible for coordinating the response by directing the electrical impulse to the correct effector
    • Voluntary responses move through the nervous system via the brain
    • Automatic responses move through the unconscious part of the brain or the spinal cord
  • The neurones that are found in the CNS are relay neurones

The Peripheral Nervous System

  • Peripheral nervous system (PNS) is made up of all of the nerves in the body that extend from the CNS
  • It also includes sensory receptors which detect stimuli from the surroundings
  • The pathway of the electrical impulse is as follows:
    • A sensory receptor detects a stimulus
      • This might include changes in light, sound, smell, temperature or pressure
    • The receptor transmits the information as an electrical impulse along the sensory neurone to the relay neurones in the CNS
    • The CNS coordinates the response and sends the electrical impulse along a motor neurone to the effector
      • The effector may be a muscle or a gland
    • The effector initiates the response
      • This response may be a muscle contraction or secretion of a hormone from a gland
Table of senses and stimuli

Sense Organs table

Exam Tip

Remember, sensory neurones connect the senses to the CNS

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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.