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Cells of the Nervous System; Neurotransmitters at Synapses - Coggle Diagram
Cells of the Nervous System; Neurotransmitters at Synapses
Neurons carry electrical impulses
Neuron Structure:
Axon: carries nerve impulses away from a cell body which is insulated by myelin
Dendrites: receive nerve impulses and pass them toward a cell body
A myelin sheath increases the speed of the nerve impulses along the neuron
Certain diseases, like polio, cause the myelin sheath to be destroyed which damages motor neurons
Myelin sheath is produced by glial cells
Glial cells maintain homeostasis, for myelin, provide support and protection for neurons and remove debris by phagocytosis
Synapses
A synapse is a small gap where two neurons meet
Each neuron's membrane is separated by a narrow space called a 'synaptic celft'
Transmission of nerve impulses
3
. Neurotransmitters diffuse across the synaptic cleft and bind with receptor molecules on the membrane of the second neuron
4
. Receptors bind to specific neurotransmitters
2
. When the nerve impulse reaches the dendrites, neurotransmitters are released
5
. Neurotransmitter binding to receptors stimulates second neuron to transmit an electrical impulse along its axon.
1
. Nerve impulse travels along the axon
Neurotransmitters are stored inside vesicles, found in the presynaptic neuron
During impulses transmitter molecules are rapidly removed from the synaptic cleft
Re-uptake - neurotransmitter is reabsorbed
Enzyme degradation - broken down and resynthesised as neurotransmitter
Excitatory and Inhibitory Signals
excitatory increases contraction of muscle fibres
Inhibitory decreases contraction of muscles fibres
Synapses can filter out weak stimuli arising from insufficient secretion of neurotransmitters
Neurotransmitter Effects on Mood & Behaviour
Endorphins
Stimulate neurons involved in reducing the intensity of pain
Increased levels are involved with feelings of pleasure (prolonged exercise, eating, sex, etc)
Endorphin production increases in response to severe injury, prolonged and continuous exercise, stress & certain foods
Dopamine induces feelings of pleasure and reinforced particular behaviour in the reward pathway
Neurotransmitter-related Disorders / Treatment
Alzheimer's disease is related to levels of acetlycholine
Parkinson's disease consists of low dopamine levels which the part of the brain controlling movement
Treatments:
Agonist
Mimic neurotransmitter effect where they bind to and stimulate receptors (e.g. morphine)
Antagonist
Block neurotransmitters from binding to and stimulating receptors (e.g. antihistamines)
Other drugs inhibit the enzymes which degrade neurotransmitters or inhibit re-uptake
Recreational Drugs
Mode of Action
Can mimic neurotransmitters
Changes in neurochemistry, like alter mood, cognition, perception and behaviour
Many affect neurotransmission in the reward circuit in the brain
Drug Addiction / Tolerance
Sensitisation is the increase in number and sensitivity of
neurotransmitter receptors - anagonsits - addiction
Desensitisation is the decrease in sensitivity and neurotransmitter receptors - agonist - tolerance