2.83 - 2.85

2.83 recall that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves

The nervous system controls your actions. It coordinates different parts of your body so that they work together and are able to bring about the correct responses.
The nervous system consists of the brain and the spinal cord - both are made up of delicate nervous tissue.
The central nervous system is connected by different parts of the body by nerves which are made up of lots of neurons.
Sense organs are our receptors and the instructions are sent along sensory neurons to the central nervous system.

2.84 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses

The messages that nerves carry are called nerve impulses - they are electrical signals. They pass very quickly along the axon of the neuron. Some of the axons have a fatty sheath around them that insulates the axon and makes the impulse travel along faster. The motor neuron carries signals from the central nervous system to the muscles and this controls the response. Sensory neurons carries signals into the central nervous system.
The electrical nerve impulses are very fast enabling a fast response and therefore known as 'rapid responses'

2.85 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object

A reflex is a type of response that are there to protect you where it happens very quickly without thinking. You do this automatically.

The flowchart of co-ordination in a reflex system is:

stimulus (hot flame) ---> receptor (in this case, fingertip - it has a pain sensor) ---> sensory neuron ---> coordinator (Central Nervous System) ---> Motor neuron ---> effector (muscles) ---> response

The stimulus is the hot flame, the receptor is the heat sensor in the skin. The impulse travels to the spinal cord along the sensory neuron and in the spinal cord, the impulse is passed on to the relay neuron. From this, the impulse then goes to the motor neuron and then into a muscles in the arm. The muscle is the effector and it contracts to remove the hand from the hot object. This action is known as the response.