Presentation on theme: "SYNAPTIC TRANSMISSION"— Presentation transcript:
1 SYNAPTIC TRANSMISSION “We are blessed with the tools, let us carve ourselves … …”SYNAPTIC TRANSMISSIONDr. B. M. Palan, M.D., D.Clin.Hypno. (USA)INSTITUTE F0R MIND-BODY HEALING, HEALTHY LIVING & REALIZING HUMAN POTENTIALShrenik Park Char Rasta, Productivity Road, VadodaraPhone: (0265)
2 Electrical and Conjoint S Y N A P S EThe junction where the axon of one neuron (Presynaptic neuron) terminates on the dendrites, soma or axon of another neuron (Postsynaptic neuron)Types of SynapsesChemicalElectrical and ConjointThrough NeurotransmittersAlmost all synapses in human C.N.S.Around 40 transmittersThrough Gap junctionsOnly a fewIn 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: 1Ca++ influx32Synthesis of transmitter in the soma and its transport to the terminal knob.Storage of transmitter in vessicles.Arrival of impulse causing Ca++ influx.4654. 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 ConductionPresynaptic to postsynaptic neurons. Transmitter is present only in presynaptic terminals.Convergence & DivergenceTerminals 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 InhibitionDirect inhibition due to IPSP through inhibitory transmi.4. Presynaptic InhibitionThrough axo-axonal synapses reduce release of excitatory transmitter.
8 ‘C’ stimulated repeatedly, ‘Y’ and ‘Z’ both will discharge. 5. SummationIf ‘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.AOcclusion‘B’ stimulated repeatedly, ‘X’ and ‘Y’ both will discharge due to Temporal summation.‘C’ stimulated repeatedly, ‘Y’ and ‘Z’ both will discharge.XBYCZ‘B’ & ‘C’ stimulated repeatedly simultaneously, ‘X’, ‘Y’ & ‘Z’ (only three) will discharge (and not four).
9 8. FatigueUpon 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 Neuropeptide, Slowly Acting Small-Molecule Rapidly ActingNeuropeptide, Slowly ActingCause 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.