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THE ROLE OF NEURONS AND NEUROTRANSMITTERS (NEURONS: (AXON TERMINAL: …
THE ROLE OF NEURONS AND NEUROTRANSMITTERS
NEURONS:
SOMA:
the largest part of the neuron.
controls the metabolism and maintenance of the neuron.
in most neurons, the soma receives messages from other neurons
AXON:
the axon is a nerve fibre that extends from the soma and carries information towards the cells that communicate with that neuron.
MYELIN:
The axons of most neurons are covered in myelin sheath.
Myelin sheath is a coating of cells that facilitates the transmission of information to other neurons.
axons with myelin are white.
myelin protects the axon from potential chemical and physical interference to the electrical impulses that travel along it.
The insulation provided by the myelin sheath also enables the information to travel much faster.
AXON TERMINAL:
found at the end of the axon branch and functional to transmit messages to the next neuron.
although they do not touch, axon terminals link with the dendrites of the next neuron.
TERMINAL BUTTONS:
located at the end of each axon terminal.
terminal buttons have sacs that recreate a chemical called neurotransmitter whenever electrical impulses are sent down the axon.
DENDRITES:
dendrites receive information from other neurons, which they carry from he synapse to the soma.
NEUROTRANSMITTERS:
SYNAPTIC TRANSMISSION:
refers to the process of neurons sending information to each other via neurotransmitters.
neurons do not come into contact with each other, rather there is a synapse between them.
LOCK AND KEY PROCESS:
neurotransmitters are contained in small sacs known as synaptic vesicles within the terminal button of each neuron's terminal axon.
Presynaptic neuron fires and synaptic vesicles move towards the presynaptic membrane.
some synaptic vesicles stick to the membrane and break open to release the neurotransmitter into the synaptic cleft.
once in the synaptic cleft, some neurotransmitters will bind with protein molecules known as 'receptors' that are located in the dendrites of the postsynaptic neuron. The receptors act like locks that can only be opened with one neurotransmitter.
when a receptor binds with a neurotransmitter that 'fits' it, the postsynaptic neuron is either activated of inhibited.
INHIBITORY AND EXCITATORY EFFECTS:
in communication between neurons there are either synapses that are excitatory and cause the neuron to fire or synapses that are inhibitory and reduce this likelihood.
how much a neuron 'fires' will depend on the amount of activity of all of the synapses on the dendrites of the neuron, and also how active the soma of the neuron is.
EXCITATORY NEUROTRANSMITTERS:
when an axon of a neuron fires, the terminal buttons of the excitatory synapses release a neurotransmitter that 'excites' the postsynaptic neuron, or causes it to reach its action potential.
this increases the amount of firing of the axon of the postsynaptic neuron.
ACTION POTENTIAL:
the momentary change in the electrical potential of a cell, which allows a nerve cell to transmit a signal or impulse towards another nerve cell.
GLUTAMATE:
an excitatory neurotransmitter the brain involved in learning.
necessary for the changes in synapses that occur with memory formation.
INHIBITORY NEUROTRANSMITTERS:
when inhibitory synapses are activated the 'firing' rate of the postsynaptic neuron is reduced and sometimes it does not fire at all.
GABA (GAMMA-AMINO BUTYRIC ACID):
an inhibitory neurotransmitter
calms nervous activity.
responds to alchohol
deficiency in GABA is related to epilepsy, an increase is known to assist in the treatment of Parkinson's disease.
CHANGES TO NEUROTRANSMITTER FUNCTION:
PARKINSON'S DISEASE:
a progressive neurological condition.
CAUSES:
caused by the degeneration of dopamine-releasing neurons in the substation nigra
the substantial nigra is located in the midbrain, and is responsible for the coordination of movement.
without enough dopamine, the neurons fire uncontrollably, which essentially prevents the sufferer from controlling their own movement.
a drop in dopamine also influences acetylcholine, a neurotransmitter that also affects movement. The striatum requires a balance of dopamine and acetylcholine for effective motor function.
TREATMENT:
researchers have found that the neurons that release dopamine also release GABA, which inhibits or lowers normal neuron activity.
the amount of GABA present in the brain decreases in Parkinson's disease sufferers, possibly contributing to symptoms such as tremors.
a drug can be taken which binds with the GABA receptors and mimics the action of GABA.
there is also evidence that GABA blocks the effect of dopamine, which is already depleted in people with parkinson's disease.
SYMPTOMS:
slowness of movement, rigidity, involuntary movement of the hands, arms etc.
reduced facial expressions, pain, depression, dementia and difficulty sleeping.
symptoms usually develop after an 80% drop in dopamine levels.
