The Nervous System - Structure (OCR GCSE Biology A (Gateway))

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 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