Unit 3.4

A complex network of nerve cells (neurons) which recieve and transmit electrical signals (nerve impluses) and glial cells which support and maintain the neurons.

• Dendrites: branched nerve fibres which receives nerve impulses and pass them towards a cell body. • Axon: single nerve fibres that carry nerve impulses away from the body. Insulated by myelin. • Cell Body: contains nucleus and DNA which codes for neurotransmitters.

Dendrites —> Cell Body —> Axon

The fatty protective coating that surrounds and insulates the axon.

Myelin increases the speed of impulse conduction.

The process if myelin developing around the axon fibres.

In the first 2 years of life as myelination is not complete at birth making responses to stimuli not as rapid or coordinated of those as an adult.

Glial cells.

Whilst glial cells do not transmit nerve impulses, they maintain homeostatis, for myelin and provide support and protection for neurons.

By phagocytosis.

Multiple sclerosis (MS)

The synaptic cleft.

The small gap where 2 neurons meet.

Before: pre-synaptic neuron After: post-synaptic neuron

Neurotransmitters are chemicals which relay messages from neuron to neuron within and out with the brain. • Acetylcholine • Noradrenaline

In the vesicles in the axon endings of the PRE-synaptic neuron.

Electrical signals which diffuse across the cleft further binding to receptors.

• An electrical nerve impulse travels along the axon of the first neuron (presynaptic neuron). • When the impulse reaches the end of the axon, chemical messengers called neurotransmitters are released. • These chemicals diffuse across the synaptic cleft. The chemicals bind with receptor molecules on the membrane of the second neuron (postsynaptic neuron). • The receptor molecules on the second neuron can only bind to specific neurotransmitters released from the first neuron. • The binding of neurotransmitter to the receptors stimulates the second neurons to transmit an electrical impulse along its axon. The signal therefore has been carried from one neuron to the next.

• Excitatory: causes an increase in action e.g. muscles to contract. • Inhibitory: causes a decrease in action e.g. slow heart rate.

Re-uptake: The neurotransmitter is reabsorbed back into the presynaptic neuron and restored inside a vesicle ready to be used again. E.g. noradrenaline. Enzyme degradation: Neurotransmitter is broken down by an enzyme into smaller inactive product before being reabsorbed by the presynaptic neuron and resynthesised into the active neurotransmitter.

Only once there are enough neurotransmitters released to have an effect on the receptors on the post-synaptic membrane (stimuli threshold). A series of weak stimuli can combine, increasing the amount of neurotransmitters that is released resulting in enough neurotransmitter being diffused across the synaptic cleft to trigger the impulse in the post-synaptic neuron.

• Severe injury • Prolonged and continuous exercise • Stress • Certain foods

Dopamine which can bring about responses of • Euphoria • Appetite regulation • Release of sex hormones

Chemicals that mimics the action of neurotransmitters. Agonists bind to and stimulate receptors, triggering the same response as the neurotransmitter.