The nervous system is essential to the body in several ways. It allows us to detect changes in the surroundings but additionally the ability to react to it. The nervous system is categorised into two main sections:

1. The central nervous system – The spinal chord and the brain

2. The peripheral nervous system – All the other neurons that connect to the central nervous system

Specialist cells called receptors are used by the body to sense stimuli (changes in the environment) and send information down nerves. Receptors are most commonly located at specific sensory organs, such as:

Eye: Receptors here are able to detect changes in light

Skin: Receptors here are sense changes in pressure and temperature

Tongue: Receptors here are sensitive to chemicals in food

Ears: Receptors here are sensitive to sound and changes in position (so we can keep our balance)

Nose: Receptors here are responsible for changes in chemicals in the air

When a receptor detects some form of stimulus it sends the information as an electrical signal down nerves (neurons). The brain is then able to gather information about changes in the environment and co-ordinate a response. This response is more rapid and often involves effectors.


Effectors are glands or muscles that the brain sends commands to via nerves. Any mobile body part of the body is an effector as are internal glands: a muscle used to lift your leg up is an effector; a muscle that controls the eye lid is an effector; a gland that releases a hormone into the cardiovascular system is an effector.


Generally when a receptor detects stimuli causing an electrical Synapse xt message to travel down the sensory nerve to the central nervous system. Here the brain organises a reaction (thinking time) and another electrical impulse is sent down down the motor neuron.This in turn sends an electrical signal to an effector and the effector produces a response:

Stimuli->Receptor->Sensory neuron->CNS->Motor neuron->Effector->Response

skips out the CNS to speed up the action: a receptor detects a stimulus and an electrical impulse travels down the sensory neuron. Here it sends an electrical signal down a relay neuron which skips out the brain and communicates directly with a motor neuron which causes an effector to produce an action:

Stimuli->Receptor->Sensory neuron->Relay neuron->Motor neuron-Effector->Response

Though a relay neuron is part of the CNS, this is more rapidly as it skips out the thinking time.

Nerve Structure

Neurons are a type of cell that is capable of transmitting electrical impulses. Neurons are involved in the whole system. Without them we would not be able to think or move! There are 3 main types of neuron:

1.Sensory neurons
2.Relay neurons
3.Motor neurons

Despite these different neurons having different places within the nervous system, they have some central anatomical features:

Axon: This is what an electrical message travels down

Myelin Sheathe: This insulates the Axon and speeds up the electrical impulse.

Dendrites: These overlap with other neuron dendrites at junctions called synapses. This is where nerves communicate with each other.

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