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Neurons are nerves cells which transmit nerve impulses The three types of neurons are: sensory, inter and motor All neurons are made up of a cell body, one axon and several dendrites The cell body of a neuron contains the nucleus and most of the cytoplasm The cell body is the control centre of the cell’s metabolism and contains ribosomes The axon is a single nerve fibre that carries nerve impulses away from the cell body to the next neuron The direction of a nerve impulse is always dendrites cell body axon Axons are surrounded by a myelin sheath which insulates it Gaps in the myelin sheath are called nodes The presence of the myelin sheath increases the speed impulses can be transmitted Myelination continues from birth to adolescence Diseases that destroy the myelin sheath include Polio, Multiple Sclerosis, Tay-Sachs disease Glial cells physically support neurons and produce the myelin sheath A synapse is a tiny region between the axon of one neuron and the dendrite of another Pre-synaptic neuron is the nerve cell before the synaptic cleft Neurons connect with other neurons, at a synaptic cleft muscle fibres and endocrine glands Neurotransmitters are chemical messages relayed across synaptic clefts from neuron to neuron Examples of neurotransmitters are Acetylcholine and Norepinephrine Neurotranmitters are stored in vesicles before their release Neurotranmitters bind to receptors on the nerve endings once they have diffused across the cleft Acetylcholine released between a motor neuron and a skeletal muscle fibre Acetylcholine released between a motor neuron and a heart muscle fibre Neurotransmitters can be removed binds to receptors that have an excitatory effect on the muscle, making it contract binds to receptors which have an inhibitory effect, reducing rate and strength of the muscle contraction. by enzyme degradation and re-uptake Summation is when a series of weak stimuli trigger enough neurotransmitter to fire an impulse Converging neural pathways increase sensitivity to excitatory and inhibitory signals by Diverging neural pathways influence several neurons impulses from several sources meeting at a common point at the same time by branching out from a common point Reverberating pathway neurons later synapse with earlier ones, sending the in the pathway impulse back through the circuit Plasticity of response is Plasticity occurs when the brain cells’ ability to become altered as a result of new environmental experiences new neural pathways are developed Endorphins are neurotransmitters that act as natural pain killers Endorphin production increases in response to severe injury, prolonged exercise, physical and emotional stress and certain food stuff feelings of euphoria, regulate appetite and release sex hormones Increased levels of endorphins may bring about Dopamine induces the Neurotranmitter related disorders feeling of pleasure and rewards particular behaviour in the reward pathway include Alzheimer’s and Parkinson’s diseases Neurotransmitter-related disorders can be treated by agonists, antagonists and inhibitors Agonists bind to and stimulate receptors mimicking the neurotransmitter Antagonists bind to specific receptors blocking the action of the neurotransmitter Inhibitors inhibit the enzymes which degrade the neurotransmitters or inhibit re-uptake Alzheimer’s disease is treated using cholinesterase inhibitors Parkinson’s disease is treated by using L-dopa, agonists that mimic dopamine Recreational drugs affect the transmission of nerve impulses in the reward circuit of the brain. Drug tolerance is said to have built up reaction to a drug has decreased when intensity even though the drug’s concentration remains the same Sensitisation leads to addiction Desensitisation leads to drug tolerance