neurones

• motor neurones carry electrical impulses from the CNS to effectors
• effectors are all your muscles and glands which respond to nervous impulses
• sensory neurones carry information as electrical impulses from the receptors to the CNS
• receptors are the cells that detect stimuli and send signals to the brain
• in response to nervous impulses muscles contract and glands secrete hormones
• the function of the nervous system is to coordinate the activities of the body and to respond to the environment
• the nervous system is adapted to its function by having a fast response time and a large number of neurones
• nerve cells are adapted to their function by having long bodies to reduce time it takes and having branched connections at either end to receive and carry signals and a myelin sheath to stop messages being lost
• relay neurones are in the CNS and carry impulses from sensory neurones to motor neurones
• the CNS is a coordination centre which receives information and then coordinates a response and the response is carried out by effectors
• a stimulus is a change in the environment which is detected by a receptor eg the eye. impulses from a receptor pass along a sensory neurone to the CNS. Chemical crosses the synapse between a sensory and a relay neurone. Then a chemical crosses between a relay and a motor neurone the motor neurone carries an impulse to an effector which could be a muscle or a gland. And the effector responds
• synapses are the connection 2 neurones where the nerve signal is transferred by chemicals which diffuse across the gap
• synapses short explanation:

  the nerve signal is transferred by chemicals which diffuse across the gap between the nerves. These chemicals then set off a new electrical signal in the next neurone
• synapses long definition:

  an impulse arrives at the end of a pre synaptic neurone and chemicals are released into the synapse and diffuse across the gap. On the other side of the synapse the neurotransmitter binds to the receptor molecule on the membrane of the post synaptic neurone which as the neurotransmitter binds to the receptor a new nerve impulse is stimulated in the post synaptic neurone, finally the chemical messenger diffuses back into the pre-synaptic neurone ready to be reused