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
- A sensory receptor detects a stimulus
Table of senses and stimuli
Exam Tip
Remember, sensory neurones connect the senses to the CNS
