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“We are blessed with the tools, let us carve ourselves … …”

“We are blessed with the tools, let us carve ourselves … …”. SYNAPTIC TRANSMISSION. Dr. B. M. Palan, M.D., D.Clin.Hypno . (USA). INSTITUTE F0R MIND-BODY HEALING, HEALTHY LIVING & REALIZING HUMAN POTENTIAL Shrenik Park Char Rasta, Productivity Road, Vadodara 390 020

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“We are blessed with the tools, let us carve ourselves … …”

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  1. “We are blessed with the tools, let us carve ourselves … …” SYNAPTIC TRANSMISSION Dr. B. M. Palan, M.D., D.Clin.Hypno. (USA) INSTITUTE F0R MIND-BODY HEALING, HEALTHY LIVING & REALIZING HUMAN POTENTIAL Shrenik Park Char Rasta, Productivity Road, Vadodara 390 020 Phone: (0265) 233 58 54 E-mail: drpalan@gmail.com www.drpalan.com

  2. S Y N A P S E • The junction where the axon of one neuron (Presynaptic neuron) terminates on the dendrites, soma or axon of another neuron (Postsynaptic neuron) Types of Synapses Chemical Electrical and Conjoint • Through Neurotransmitters • Almost all synapses in human C.N.S. • Around 40 transmitters • Through Gap junctions • Only a few • In smooth & cardiac muscles.

  3. Functional Anatomy: • Ends of presynaptic terminals form terminal buttons / synaptic knobs. • Knobs contain many mitochondria and vesicles. • Vesicles contain packets of neurotransmitter. • Types: (1) Axodendritic, (2) Axo-axonal and (3) Axo-somatic. • Synaptic cleft – 30 to 50 nm wide. • Postsynaptic membrane contains excitatory or inhibitory receptors. • In human CNS, about 10ⁿ (n=14) synapses.

  4. Synaptic Transmission: 1 Ca++ influx 3 Synthesis of transmitter in the soma and its transport to the terminal knob. Storage of transmitter in vessicles. Arrival of impulse causing Ca++ influx. 2 4 6 5 4. Release of transmitter by exocytosis. 5. Excitatory or Inhibitory Postsynaptic Potentials. 6. Reuptake of neurotransmitter.

  5. Electrical Events at Synapse: • Studied in spinal motor neurone. • Excitatory Postsynaptic Potentials (EPSP) – - Single stimulus of one synaptic knob >After a synaptic delay of 0.5 ms > Opening of voltage-gated Na+ channels > A local and graded depolarizing potential produced in postsynaptic membrane > excitability to other stimuli is increased. - EPSPš are summated to produce Action Potential (AP). - Spatial summation: Activities in many synaptic knobs at the same time. - Temporal summation: Repeated afferents in a single knob causing new EPSP before the decay of previous EPSP.

  6. Electrical Events at Synapse: (contd.) • Inhibitory Postsynaptic Potentials: (IPSP) - Single stimulation of some presynaptic fibers > Opening of Clˉ channels > Influx of Clˉ> Local hyperpolarizing potential > Decreased excitability to other stimuli. - Spatial and Temporal summation of IPSPš > Postsynaptic inhibition. • When the algebraic sum of EPSPš and IPSPš reach 10–15 mV, firing level, a propagated and ‘all or none’ type of Action Potential results at the Axon Hillock.

  7. Properties of Synaptic Transmission: • One-Way Conduction • Presynaptic to postsynaptic neurons. Transmitter is present only in presynaptic terminals. • Convergence & Divergence • Terminals from around 100 neurons converge on one postsynaptic neuron and a single neuron diverges its information to around 100 postsynaptic neurons. Form basis for several properties of synapse. • 3.Postsynaptic Inhibition • Direct inhibition due to IPSP through inhibitory transmi. • 4. Presynaptic Inhibition • Through axo-axonal synapses reduce release of excitatory transmitter.

  8. 5. Summation • If ‘A’ & ‘B’ are stimulated at the same time > ‘X’ develop EPSP at two places > Spatial summation. • Subliminal Fringe • ‘Y’ do not fire but its excitability is increased. It is in subliminal fringe zone. A • Occlusion • ‘B’ stimulated repeatedly, ‘X’ and ‘Y’ both will discharge due to Temporal summation. • ‘C’ stimulated repeatedly, ‘Y’ and ‘Z’ both will discharge. X B Y C Z • ‘B’ & ‘C’ stimulated repeatedly simultaneously, ‘X’, ‘Y’ & ‘Z’ (only three) will discharge (and not four).

  9. 8. Fatigue • Upon repetitive stimulation of excitatory synapses at a rapid rate, the discharge rate by postsynaptic neuron becomes progressively less. • Fatigue is mainly due to exhaustion of transmitter substance.

  10. SYNAPTIC TRANSMITTERS Small-Molecule Rapidly Acting Neuropeptide, Slowly Acting • Cause acute responses: Transmission of sensory or motor impulses. • Cause more prolonged actions: Long-term changes in numbers of receptors, long-term opening or closure of ion channels, changes in number of synapses. • Synthesized in the cytosol of presynaptic terminal. • Synthesized in the neuronal cell body by ribosomes. • Vesicles recycled. • Vesicles autolyzed.

  11. Small-Molecule Rapidly Acting Transmitters: Class II Norepinephrine Epinephrine Dopamine Serotonin Histamine Class I Acetylcholine Class III Gama-aminobutyric acid Glycine Glutamate Aspartate Class IV Nitric Oxide (NO)

  12. Neuropeptide, Slowly Acting Transmitters: • Peptides acting on Gut & Brain • Leucine enkephalin Methionine enkephalin Substance P Gastrin Cholecystokinin Vasoactive intestinal polypept. Nerve growth factor Neurotensin Insulin Glucagon • Hypothalamic R. H. • T.R.H. L.H.R.H. Somatostatin • Pituitary peptides • A.C.T.H. ß-Endorphin ά-M.S.H. Thyrotrophin G.H. Vasopressin Oxytocin • From other tissues • Angiotensin II Bradykinin Calcitonin

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