B1b

average reaction time =                 total time

                                       number of people in the group

Synapses - when there is a small gap between each pair of neurones. This is called a synapse.

When an impulse arrives at the end of the neurone a chemical transmitter or neurotransmitter is released from tiny structures, called vesicles.

The mitrochondria provide energy to make the chemicals.

Special receptor cells in the membrane of the next neurone pick up the chemical transmitter.

They can start a new electrical impulse.

Synapses are also found where neurones join muscles. These are called motor end plates. The muscle contracts when the chemical transmitter crosses the synapse.

There are several conditions that can affect the brain.

Parkinson's disease - causes trembling of the rms and legs, stiffness of the muscles and slowness of movement. It is caused when neurones in the part of the brain that coordinates movement die and stop producing a chemical transmitter calles dopamine.

A stroke -  is caused when part of the brain is deprived of oxygen, usually by a blood clot. This causes some brain cells to die and can affect movement and speech.

Brain Tumours -  due to abnormal growth of neurones. One effect of a brain tumour can be to cause epilepsy.

Epilepsy - due to abnormal electrical activity in the brain. This can cause convulsions when impulses are simultaneously sent to many different muscles. A grand mal is a serious epileptic fit. A grand mal seizure can cause loss of conciousness and convulsions.

Synapses helps to ensure that the nervous system works properly.

They only allow impulses to travel in one direction as only one side of the synapse can make the chemical transmitter and only the other side can respond to it.

They ensure that the nervous system does not send out impulses to readily. A neurone needs to recieve the chemical transmitter from several impulses before it produces a new impulse. This could be several impulses from the same neurone or from a few different neurones.

Synapses can be used to send impulses to several different effectors at a time.