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.