synaptic transmission.pptx AND ACTION POTENTIAL
- 1. SYNAPTIC TRANSMISSION SPEAKER:- Dr. VIDISHA ROUT PGT2 MODERATOR:- Dr. SOUMYA MISHRA
- 2. CONTENT • DEFINATION • HISTORY • TYPES OF SYNAPSE • ANATOMY OF SYNAPSE • STEPS OF SYNAPTIC TRANSMISSION • SYNAPTIC POTENTIAL • PROPERTIES OF SYNAPSES • APPLIED ASPECT
- 3. DEFINATION • Synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to. the target effector cell • They are the fundamental unit of Intercellular communication in nervous systems.
- 4. HISTORY • Santiago Ramón Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine. • The word "synapse" was introduced in 1897 by the English neurophysiologist Charles Sherrington in Michael Foster's Textbook of Physiology.
- 5. TYPES • There are different types of synapse depending on 1. Anatomical types :- Axodendritic, Axosomatic, Axoaxonic synapse 2. Physiological types:- Chemical, Electrical & Conjoint synapse
- 11. STRUCTURE OF SYNAPSE • The presynaptic axon terminal, postsynaptic membrane & synaptic cleft form the SYNAPSE
- 12. A. SYNAPTIC KNOB :- The axon of neuron on reaching synapse lose the myeline sheath & divides into number of fine branches with small swelling. • Each synaptic knob contains synaptic vesicles(which contains NT) & mitochondria. • There are 3 synaptic vesicles a. Small clear vesicles containing Ach, Glycine & GABA b. Small vesicles with dense core containing catecholamines c. Large vesicles with dense core containing neuropeptides
- 13. • B. PRESYNAPTIC MEMBRANE :- It’s the axonal membrane lining the synaptic knobs • C. SYNAPTIC CLEFT :- It’s a gap b/w pre & post synaptic membranes which is filled with ECF containing glycoproteins • D. POSTSYNAPTIC MEMBRANE:- It’s the membrane lining the postsynaptic process & it has large number of receptor proteins (Ion channel receptor proteins & enzymatic receptor proteins)
- 15. NEUREXINS It’s a protein attached to presynaptic membrane which binds with neurexin receptors located in postsynaptic membrane . It provide structural stability to synaptic architecture.
- 16. MEMBRANE PROTEIN A/W SYNAPTIC TRANSMISSION
- 18. STEPS OF SYNAPTIC TRANSMISSION
- 19. SYNAPTIC POTENTIAL (EPSP & IPSP) EPSP IPSP Occurs due to depolarization of postsynaptic membrane produced by excitatory neurotransmitters Occurs due to hyperpolarization of postsynaptic membrane produced by inhibitory neurotransmitters Neurotransmitter is GLUTAMATE Neurotransmitter is GLYCINE & GABA Ions basis is Na+ influx & Ca2+ influx Ions basis is K+ efflux & Cl- influx
- 21. INHIBITION AT SYNAPSE • 4 types of inhibition occurs at synapse in CNS :- • Postsynaptic inhibition(Direct inhibition) • Presynaptic inhibition(Indirect inhibition) • Feedback inhibition • Feed-forward inhibition
- 22. FEEDBACK INHIBITION • The feedback inhibition is also know as Renshaw cell inhibition which occur in spinal alpha motor neuron. • In feedback inhibition a neuron inhibits those neuron that excite it.
- 23. FEED-FORWARD INHIBITION • This inhibition is basically seen in cerebellum • In this type the neuron is connected through 2 pathways :- one excitatory & other inhibitory.
- 24. PROPERTIES OF SYNAPTIC TRANSMISSION 1. One way conduction 2. Synaptic Delay 3. Summation 4. Convergence & Divergence 5. Occlusion Phenomenon 6. Subliminal Fringe Effect 7. Synaptic facilitation 8. Synaptic Fatigue 9. Synaptic Plasticity 10. Reciprocal Inhibition
- 25. 1.ONE WAY CONDUCTION :- The chemical synapse travel from pre synaptic membrane to post & never opposite direction called as LAW OF DYNAMIC POLARITY or BELL-MAGENDIE LAW 2.SYNAPTIC DELAY :- refers to time lapse which occurs between arrival of nerve impulse at presynaptic terminal & its passage to postsynaptic membrane
- 26. SUMMATION • The EPSP is a graded response hence its doesn’t follow all-or-none law & its shows Temporal & Spatial Summation
- 28. CONVERGENCE & DIVERGENCE • Convergence:- Termination of signals from many sources • Divergence:- One presynaptic neuron terminate on many postsynaptic neuron
- 29. OCCLUSION • Response to stimulation of two presynaptic neurons is less than sum of total of response obtained when they are stimulated separately
- 30. SYNAPTIC FACILITATION This is the process by which transmission through a synaptic is increased which is caused due to increase in the transmitter release from presynaptic terminal hence called presynaptic facilitation
- 31. SUBLIMINAL FRINGE EFFECT • When an afferent neuron is stimulated the efferent(postsynaptic) neuron that has many presynaptic terminals is excited to threshold level & AP is fired & others in peripheral zone(fringe area) are excited to subthreshold level and AP not fired
- 32. SYNAPTIC FATIGUE On stimulating the presynaptic neuron the rate of impulse in postsynaptic is initially high but decreases within few seconds & finally disappears :- HABITUATION/Synaptic fatigue
- 33. SYNAPTIC PLASTICITY Plasticity refers to capability of being easily moulded or changed • Plasticity changes in synaptic transmission known as:- a) Post -tetanic potentiation b) Long term potentiation
- 34. RECIPROCAL INHIBITION • It refers to a phenomenon in which an afferent signal activates an excitatory neuron to a group of muscle simultaneously activates the inhibitory signals to other usually antagonist muscle
- 35. APPLIED ASPECT • BOTULINUM TOXINS:- act on synaptobrevin that in turn prevent fusion of vesicles with membrane that blocks release of NT from presynaptic terminal • Used in low dose in Achalasia cardia to relax the lower sphincter & in decreasing facial wrinkle by relaxing facial muscle
- 36. • TETANUS TOXIN:- acts on synaptobrevin & prevents its attachment with syntaxis preventing release of NT from vesicles at different synapse in CNS which produce spastic paralysis
Editor's Notes
- #5: Axodendriti:- Axon of presynaptic neuron connect with dendrite of postsynaptoic neuron , axosomatic:- axon of presynaptic neuron synapse with cell body of post synaptic neuron , axoaxonic :- axon of presynaptic synapse with axon of post synaptic neuron
- #11: The neuron from which the information passes through the sypanse is the presynaptic neuron. The neuron which receives the information is the postsynaptic neuron. Presynaptic axon terminal forming the synapse is called presynaptic membrane & postsynapctic neuron is caleed postsynaptic membrane The space between pre & post synaptic membrane is the synaptic cleft
- #14: Step 1:- NT molecules are packaged into synaptic vesicles & specific proteins in membrane use the energy of H+ to uptake NT in vesicles synaptic vessels released content through small hole & then reseal membrane so the main vesicles remain inside cell this phenomemon is called KISS & RUN DISCAHRGE Step 2:- AP is generated which involves voltage gated Na+ & K+ channels arrives at presynaptic nerve terminal Step 3:- Depolarization opens voltage gated ca2+ channels which allow Ca2+ to enter presynaptic membrane Step 4:- Increaes in ca2+ cause fusion of synaptic vesicles with presynaptic membrane leading to release of transmitter mol into synaptic cleft (usually only 1 type of NT is released from single neuron & its called DALE’S PHENOMENON Step 5:- Transmitters molecules diffuse across synaptic cleft & binds to specific receptors on membrane of postsynaptic cells Step 6:- binding of transmitter activates receptor which in turn activates postsynaptic cell Step 7 :- Process is terminated by :- 1. Hydrolysis of Ach by actylecholinesterase 2. Uptake of transmitter into the presynaptic nerve terminal by Na+ dependent transport system ‘
- #16: Vesicles membrane gets coated with clathrin & takes up endocytosis into presynaptic terminal where reutilized for NT Fusion of Synaptic vesicle with cell membrane is facilitated by Synaptobrevin , a v snare protein present in vesicular membrane & syntaxin a t snare protein present in cell membrane Combination of synaptobrevin with synaptotaxin causes docking and priming of vesicles Other synaptic proteins SNAP 25 connect with syntaxin & alpha/g SNAPs connect with synaptobrevin A multiproein complex regulated by small GTPase like Rab3
- #21: Postsynaptic inhibition(Direct inhibition):- when synaptic inhibition occurs through formation of ipsp on postsynaptic neuron , e.g. :- Inhibition of anterior horn cell by descending inhibitory fibres in spinal cord Presynaptic inhibition(Indirect inhibition):- occurs due to decrese release of NT from presynaptic nerve terminal it has 2 mechanism :- a. activation of presynaptic recptors facilitate Cl- which decrease magnitude of AP decrease Ca2+ entry b. Activation of voltage gated K+ channels causes K+ efflux & reduces Ca2+ influx
- #22: Neuron is inhibited by its own output , firing of AP by a motor neuron of spinal cord is followed by phase of hyperpolarization feedback inhibition is basically a postsynaptic inhibition but is classified separately because the inhibition of Renshaw cells are activated by a collateral of ventral horn cell rather than afferent neurons
- #23: In the cerebellum the Grc(granular cells) excites the Purkinje cells(PC) which is inhibited by Basket cells(BC) The basket cell has excited by the granular cells
- #24: One way conduction :- The chemical synapse travel from pre synaptic membrane to post & never opposite direction called as LAW OF DYNAMIC POLARITY or BELL-MAGENDIE LAW(This happens as presynaptic membrane had NT 7 post has receptors) Synaptic delay :- refers to time lapse which occurs between arrival of nerve impulse at presynaptic terminal & its passage to postsynaptic membrane (due to time taken for release of NT & diffusion of NT from synaptic cleft to post synaptic membrane)
- #25: 1.(This happens as presynaptic membrane had NT 7 post has receptors) 2.(due to time taken for release of NT & diffusion of NT from synaptic cleft to post synaptic membrane)
- #30: Due to prolonged at AP presynaptic ending helps voltage gated Ca2+ channel to remain open fo a longer duration which ensure more Ca2+ influx that in turn increase transmitter release from presynaptic ending
- #31: The postsynaptic which has fired is called:- discharge zone & the one not fired is the :- subliminal fringe Stimulation of 2 presynaptic neurons is greater than sum total response obtained when they are stimulated separately (EXACTLY OPPOSITE OF OCCLUSION)
- #32: Its caused due to exhaustion of NT , accumulation of waste products
- #33: Post -tetanic potentiation:- When presynaptic neuron is stimulated with single stimulus followed by stimulation with a volley of stimuli then again with single stimulus the second stimuli evokes a larger postsynaptic respone than the first stimuli Long term potentiation:- when post tetanic potentiation gets prolonged & last for days which occur due to increase in inyracellular Ca2+ in postsynaptic rather than presynaptic neuron Seen in HIPPOCAMPUS
- #34: Example :- During flexion of joint the afferent stimulus causes excitation of neuron suppling flexor muscle of the joint & at same time excites the inhibitatory interneuron supplying extensor muscle of joints