Third lectureThird lecture

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

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)

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 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

Classification of nerve fibersClassification of nerve fibers::

• Histologically (myelinated & non myelinated).

• Functionally (meter-sensory).

• Chemically (cholinergic-adrenergic).

• According to diameter & conduction velocity.

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.

• 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 stimulusThe stimulus::

• It is a change in the surrounding environment.

• stimuli can be divided into:

• 1- Electrical stimuli

• a) Galvanic current

• b) Faradic current

The stimulusThe stimulus

2- Chemical stimuli:• Chemical transmiters (acetylcholine,

noradrenalin and adrenalin).

• Hormones.

• Drugs.

• Ions (Na+, K+, Ca++ … etc).

• Gases (O2 and CO2).

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.

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.

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.