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Third lecture
Synapses:
• 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
Chemical 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)
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).
Nerve 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
Classification of nerve fibers:
• Histologically (myelinated & non
myelinated).
• Functionally (meter-sensory).
• Chemically (cholinergic-adrenergic).
• According to diameter & conduction
velocity.
Chemical composition of
nervous 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.
• 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
The stimulus:
• It is a change in the surrounding
•
•
•
•
environment.
stimuli can be divided into:
1- Electrical stimuli
a) Galvanic current
b) Faradic current
The stimulus
2- Chemical stimuli:
• Chemical transmiters (acetylcholine,
noradrenalin and adrenalin).
• Hormones.
• Drugs.
• Ions (Na+, K+, Ca++ … etc).
• Gases (O2 and CO2).
The 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.
The 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.
The 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.