third lecture synapses: it is the junctional region where one neurone end and the next begin....
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Third lectureThird lecture
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SynapsesSynapses::
• It is the junctional region where one neurone end and the next begin.
• synapse can be classified into: • 1-Axosomatic synapse.• 2-Axodendritic synaps.• 3- Axo-axonic synapse.
– Mechanism of synaptic transmition:• Is the transfer of informormation across a
synaptic junction. It is done by: 1-chemical• 2-electrical • 3-or both
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Chemical nature of transmittersChemical nature of transmitters::
• 1-Acetyl choline• 2- Noradrenaline• 3- Dopamine• 4-5-Hydroxytriptamine• 5- Histamine• 6- Protaglandine• 7- Some amino acids as, alanine, glycine,
aspartic acid, and glutamic acid• 8- Gamma amino butoric acid (GABA)
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Motor end plate and acetyl choline:
Liberation of acetyl choline in the muscle. Acetyl choline as the cause of contraction. Cholinesterase destroy the acetyl choline.Action of anticholinesterase. Action of curare (drug cause paralysis).
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Nerve fiberNerve fiber::
• Each nerve fiber is an axon covered by a myelin sheath and s Schwann sheath. The nerve is surrounded by:
• the epineurium, Bundles of individual nerve fibers, enclosed in perineurium, Inside the bundles, nerve fibers , surrounded by the endoneurium
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Classification of nerve fibersClassification of nerve fibers::
• Histologically (myelinated & non myelinated).
• Functionally (meter-sensory).
• Chemically (cholinergic-adrenergic).
• According to diameter & conduction velocity.
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Chemical composition of Chemical composition of nervous systemnervous system::
• It is highly alkaline during active. It has the high cholesterol and phospholipids. The grey matter contain more water (84%) and less solid (16%) compared with the white matter that have 70% water and 30% solid.
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• Functions of nerve fibers:
• Conduction of nerve impulses.
• Properties of nerve fibers:
• Excitabilility (irritability):
• It is the ability of any living tissue to respond to an adequete stimuli
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The stimulusThe stimulus::
• It is a change in the surrounding environment.
• stimuli can be divided into:
• 1- Electrical stimuli
• a) Galvanic current
• b) Faradic current
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The stimulusThe stimulus
2- Chemical stimuli:• Chemical transmiters (acetylcholine,
noradrenalin and adrenalin).
• Hormones.
• Drugs.
• Ions (Na+, K+, Ca++ … etc).
• Gases (O2 and CO2).
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The stimulusThe stimulus
• 3- Physical stimuli:
• Thermal e.g. cooling or warming.
• Mechanical e.g. stretch, touch, pressure and injury.
• Electromagnetic e.g. light rays affecting the retina of the eye.
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The stimulusThe stimulus
• Electrical stimuli are commonly used for stimulariton in experimental work because they are:– Easily applied.– Accurately controlled as to strength and
duration.– Similar to the physiological process of excitation.– Causes no (or minimal) damage to the tissues,
so they can be repeated.
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The stimulusThe stimulus
• The response of the nerve fibers to a stimulus is determined by two factors:
• 1- the effectiveness of the stimulus
• 2- the excitability of the nerve fibers.