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CNS (SYNAPSE). Synapse. At the end of this lecture you should be able to ; Synapse and its types Properties of Synapses. The Synapse. Junctional point between two neurons that transmits impulse from first to the second Neuron. Classification.
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CNS (SYNAPSE)
Synapse • At the end of this lecture you should be able to ; • Synapse and its types • Properties of Synapses
The Synapse • Junctional point between two neurons that transmits impulse from first to the second Neuron.
Classification • Anatomical Classification • (on the Basis of Communication ) • 1. Axo-Dendritic • 2. Axo-Somatic • 3. Axo-Axonic • 4. Dendro-dendritic (amacrine cells in Eye) PHYSIOLOGICAL Classification: (According to Nature) 1. Electrical 2. Chemical
Physiological Anatomy Components 1. Presynaptic terminal 3. Postsynaptic membrane 2. SynapticCleft Typical Anterior Motor Neuron
Mechanism of Action of Neuro-transmitter on the Post-synaptic Membrane • Receptor Proteinshave Two Components: • Binding Component • Ionophore Component Anionic channel a. Ion Channels { Cationic channel b. Second Messenger Activator
Second Messenger System in the Postsynaptic Neuron • G-Proteins; is Attached to Receptor Protein on its inner surface. • Three components of G-Protein. 1. Alpha - Activator 2. Beta & Gamma - attached to alpha component On activation, ά-Component separates from β & γ components - is Free to perform the function specific for that particular Neuron.
Functions Which Can be Performed By α-Component • Opening of specific Ion channel in the Postsynaptic Membrane. • Activation of Cyclic AMP • Activation of intracellular Enzymes. • Activation of Gene Transcription
Rapidly Acting Transmitters(Small Molecules) • Class-I. - Acetylcholine Class-II.(Amines) Adrenalin (Epinephrine) Nor-adrenaline (Nor-Epinephrine) Dopamin Serotinin Histamine CLASS-III. ( Amino Acids) Gamma Amino Butyric Acid (GABA) Glutamate Glycin Aspartate Class-IV-Nitrous Oxide Class-V- Neuropeptides. Substance-P, Enkephalin, Endorphins
Neurotransmitter Removal Monoamine Oxidase
Properties of Synapses orSynaptic Transmission 1. One Way Conduction 2. Synaptic Delay. minimum 0.5 m.sec 3. Excitation (EPSP) Presynaptic 4. Inhibition-{ Postsynaptic
Excitation & Inhibition Excitation:is carried out by: 1. Opening of Sodium Channels 2. Decreased conduction through K+ or Cl- Channels. 3. Various changes in the metabolism of Postsynaptic Neuron Inhibtion: Pre & Post Synaptic Inhibition 1. Opening of chloride Channels 2. Increase in K+ ion efflux by opening K+ Channels 3. activation of Enzymes which inhibit metabolism. > By producing Hyperpolarization
Negative feedback inhibition of Spinal Motor Neuron via Inhibitory interneuron (Renshaw Cell) in the spinal cord Renshaw Cell
Properties of Synapses 5. Synaptic fatigue: Partially due to exhaustion of stores of neurotransmitter & Probable two other factors include; 1. Progressive inactivation of postsynaptic receptors 2. Slow development of abnormal concentration of ions inside the postsynaptic neuronal cell. Significance: Stabilization of Nervous system
Properties of Synapses Spatial summation ( > one Neuron) 6. Summation { Temporal summation (Only One N repetitively)
Properties of Synapses 7. Facilitation
Properties of Synapses 8.Occlusion – Net Response < than the individualPresynaptic N & Subliminal Fringe Subliminal fringe is due to spatial summation. Occlusion is due to Overlapping of the fibers.
Occlusion • The decrease in expected response due to pre synaptic fibers sharing post synaptic neurons is called occlusion
Properties of Synapses 9.Convergence e.g on ά-motor N CNS correlates ,summates and sort different types of Information. 10.Divergence Amplifing type Cortico spinal pathway
Properties of Synapses 11.Recruitment. involving more & more neurons as the stimulus becomes stronger 11. After discharge.-Prolonged out put discharge after the incoming signal is over. Mechanism: a. Synaptic after discharge (parallel Collaterals) b. Reverberatory circuits
Properties of Synapses . 13.Posttetanic Potentiation; Production of enhanced postsynaptic potentials in response to stimulation. Due to accumulation of Ca++ in the Presynaptic Neuron. 14. Habituation; Gradual Disappearance of response to a repeated benign stimulus is called Habituation. > Decrease Release of Ach > Decrease Intracellular Ca++. .
Properties of Synapses • Effect of Acidosis & Alkalosis: Acidosis: Greatly depresses neuronal activity Fall in pH from 7.4 to 7.0 > Comma ( Diabetic or Uremic ) Alkalosis: Greatly Increase Neuron Excitability Hypoxia: > unconsciousness Within 3-7 seconds. Drugslike Caffeine, theophyline & theobromine > Increase Excitability Decrease in ca++ > Increased Excitability & Vice versa Anesthetics > Increase in threshold for excitation