Nervous System
The human nervous system consists of:
The nervous system composed of nerve cells, or neurones:
Motor Neurone:
Sensory Neurone:
Intermediate (relay neurone):
Receptors to effectors
The diagram summarises how information flows from receptors to effectors in the nervous system.
Receptors
Receptors are groups of specialised cells. They can detect a change in the environment (stimulus) and produce electrical impulses in response. Sense organs contain groups of receptors that respond to specific stimuli.
Sense organ vs Stimulus
Skin
Touch, temperature
Tongue
Chemicals (in food and drink, for example)
Nose
Chemicals (in the air, for example)
Eye
Light
Ear
Sound
Effectors
Effectors are parts of the body - such as muscles and glands - that produce a response to a detected stimulus. For example:
Reflex actions
A reflex action is a way for the body to automatically and rapidly respond to a stimulus to minimise any further damage to the body. It follows this general sequence and does not involve the brain:
stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response
The nerve pathway followed by a reflex action is called a reflex arc. For example, a simple reflex arc happens if we accidentally touch something hot.
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The human nervous system consists of:
- the central nervous system (CNS) – the brain and spinal cord
- the peripheral nervous system – nerve cells that carry information to or from the CNS
The nervous system composed of nerve cells, or neurones:
Motor Neurone:
- Efferent Neuron – Moving toward a central organ or point
- Relays messages from the brain or spinal cord to the muscles and organs
Sensory Neurone:
- Afferent Neuron – Moving away from a central organ or point
- Relays messages from receptors to the brain or spinal cord
Intermediate (relay neurone):
- Relays message from sensory neurone to motor neurone
- Make up the brain and spinal cord
Receptors to effectors
The diagram summarises how information flows from receptors to effectors in the nervous system.
Receptors
Receptors are groups of specialised cells. They can detect a change in the environment (stimulus) and produce electrical impulses in response. Sense organs contain groups of receptors that respond to specific stimuli.
Sense organ vs Stimulus
Skin
Touch, temperature
Tongue
Chemicals (in food and drink, for example)
Nose
Chemicals (in the air, for example)
Eye
Light
Ear
Sound
Effectors
Effectors are parts of the body - such as muscles and glands - that produce a response to a detected stimulus. For example:
- a muscle contracting to move an arm
- muscle squeezing saliva from the salivary gland
- a gland releasing a hormone into the blood
Reflex actions
A reflex action is a way for the body to automatically and rapidly respond to a stimulus to minimise any further damage to the body. It follows this general sequence and does not involve the brain:
stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response
The nerve pathway followed by a reflex action is called a reflex arc. For example, a simple reflex arc happens if we accidentally touch something hot.
- Receptor in the skin detects a stimulus (the change in temperature).
- Sensory neurone sends impulses to relay neurone.
- Motor neurone sends impulses to effector.
- Effector produces a response (muscle contracts to move hand away).
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