sinaps
Download as ppt, pdf0 likes978 views
This document discusses synaptic transmission between neurons. It describes how neurons communicate through synapses, where neurotransmitters are released by the presynaptic neuron and bind to receptors on the postsynaptic neuron. This causes ion channels to open, resulting in an excitatory or inhibitory postsynaptic potential that influences whether an action potential is generated in the postsynaptic cell. The document covers different types of synapses and neurotransmitters, as well as processes like synaptic integration and long-term potentiation that are important for neural communication and functions like learning and memory.
sinaps
- 1. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinaps Bir n旦ron ile dier efekt旦r aras脹ndaki fizyolojik balant脹lard脹r. 聴letim sadece bir y旦nde ger巽ekleir. 1. n旦ron aksonu presinaptik u巽, 2. n旦ronun dendritik ucu ise postsinaptik u巽 olarak adland脹r脹l脹r. Sinaptik iletim kimyasal kap脹l脹 kanallar ile ger巽ekleir. Presinaptik n旦ron ucundan n旦rotransmitter maddeler (NT) sal脹n脹r.
- 2. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. N旦ronal Devreler I
- 3. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. N旦ronal Devreler II
- 4. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Elektriksel Sinapslar Impulses can be regenerated without interruption in adjacent cells. Gap junctions: Adjacent cells electrically coupled through a channel. Each gap junction is composed of 12 connexin proteins. Examples: Smooth and cardiac muscles, brain, and glial cells.
- 5. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kimyasal Sinapslar Terminal bouton is separated from postsynaptic cell by synaptic cleft. NTs are released from synaptic vesicles. Vesicles fuse with axon membrane and NT released by exocytosis. Amount of NTs released depends upon frequency of AP.
- 6. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinaptik Transmission NT release is rapid because many vesicles form fusion-complexes at docking site. AP travels down axon to bouton. VG Ca2+ channels open. Ca2+ enters bouton down concentration gradient. Inward diffusion triggers rapid fusion of synaptic vesicles and release of NTs. Ca2+ activates calmodulin, which activates protein kinase. Protein kinase phosphorylates synapsins. Synapsins aid in the fusion of synaptic vesicles.
- 7. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinaptik Transmission (continued) NTs are released and diffuse across synaptic cleft. NT (ligand) binds to specific receptor proteins in postsynaptic cell membrane. Chemically-regulated gated ion channels open. EPSP: depolarization. IPSP: hyperpolarization. Neurotransmitter inactivated to end transmission.
- 8. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinaptik Transmission (continued)
- 9. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinaptik Transmission (continued)
- 10. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. EPSPs ve IPSPs If the transmitter opens a cation influx, the resulting depolarization is called an Excitatory Post Synaptic Potential (EPSP). These individual potentials are sub-threshold. If the transmitter opens an anion influx, the resulting hyperpolarization is called an Inhibitory Post Synaptic Potential (IPSP All these potentials are additive.
- 11. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. EPSP No threshold. Decreases resting membrane potential. Closer to threshold. Graded in magnitude. Have no refractory period. Can summate.
- 12. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Long-Term Potensilizasyon May favor transmission along frequently used neural pathways. Neuron is stimulated at high frequency, enhancing excitability of synapse. Improves efficacy of synaptic transmission. Neural pathways in hippocampus use glutamate, which activates NMDA receptors. Involved in memory and learning.
- 13. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Electrical Activity of Axons All cells maintain a resting membrane potential (RMP): Potential voltage difference across membrane. Largely the result of negatively charged organic molecules within the cell. Limited diffusion of positively charged inorganic ions. Permeability of cell membrane: Electrochemical gradients of Na+ and K+. Na+ /K+ ATPase pump. Excitability/irritability: Ability to produce and conduct electrical impulses.
- 14. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Synaptic Inhibition Presynaptic inhibition: Amount of excitatory NT released is decreased by effects of second neuron, whose axon makes synapses with first neurons axon. Postsynaptic inhibition (IPSPs): No threshold. Hyperpolarize postsynaptic membrane. Increase membrane potential. Can summate. No refractory period.
- 15. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Synaptic Inhibition
- 16. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sinaptik Integrasyon EPSPs can summate, producing AP. Spatial summation: Numerous boutons converge on a single postsynaptic neuron (distance). Temporal summation: Successive waves of neurotransmitter release (time).
- 17. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Presinaptik fasilitasyon
- 18. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kimyasal Sinapslar EPSP (excitatory postsynaptic potential): Depolarization. IPSP (inhibitory postsynaptic potential): Hyperpolarization.
- 19. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acetylcholine (ACh) as NT ACh is both an excitatory and inhibitory NT, depending on organ involved. Causes the opening of chemical gated ion channels. Nicotinic ACh receptors: Found in autonomic ganglia and skeletal muscle fibers. Muscarinic ACh receptors: Found in the plasma membrane of smooth and cardiac muscle cells, and in cells of particular glands.
- 20. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ligand-Operated ACh Channels Most direct mechanism. Ion channel runs through receptor. Receptor has 5 polypeptide subunits that enclose ion channel. 2 subunits contain ACh binding sites. Channel opens when both sites bind to ACh. Permits diffusion of Na+ into and K+ out of postsynaptic cell. Inward flow of Na+ dominates . Produces EPSPs.
- 21. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G Protein-Operated ACh Channel Only 1 subunit. Ion channels are separate proteins located away from the receptors. Binding of ACh activates alpha G-protein subunit. Alpha subunit dissociates. Alpha subunit or the beta- gamma complex diffuses through membrane until it binds to ion channel, opening it.
- 22. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Asetilkolinesteraz (AChE) Enzyme that inactivates ACh. Present on postsynaptic membrane or immediately outside the membrane. Prevents continued stimulation.
- 23. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ACh in CNS Cholinergic neurons: Use ACh as NT. Axon bouton synapses with dendrites or cell body of another neuron. First VG channels are located at axon hillock. EPSPs spread by cable properties to initial segment of axon. Gradations in strength of EPSPs above threshold determine frequency of APs produced at axon hillock.
- 24. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ACh in PNS Somatic motor neurons synapse with skeletal muscle fibers. Release ACh from boutons. Produces end-plate potential (EPSPs). Depolarization opens VG channels adjacent to end plate.
- 25. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Monoamines as NT Monoamine NTs: Epinephrine. Norepinephrine. Serotonin. Dopamine. Released by exocytosis from presynaptic vesicles. Diffuse across the synaptic cleft. Interact with specific receptors in postsynaptic membrane.
- 26. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inhibition of Monoamines as NT Reuptake of monoamines into presynaptic membrane. Enzymatic degradation of monoamines in presynaptic membrane by MAO. Enzymatic degradation of catecholamines in postsynaptic membrane by COMT.
- 27. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanism of Action Monoamine NT do not directly open ion channels. Act through second messenger, such as cAMP. Binding of norepinephrine stimulates dissociation of G- protein alpha subunit. Alpha subunit binds to adenylate cyclase, converting ATP to cAMP. cAMP activates protein kinase, phosphorylating other proteins. Open ion channels.
- 28. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Serotonin as NT NT (derived from L-tryptophan) for neurons with cell bodies in raphe nuclei. Regulation of mood, behavior, appetite, and cerebral circulation. SSRIs (serotonin-specific reuptake inhibitors): Inhibit reuptake and destruction of serotonin, prolonging the action of NT. Used as an antidepressant. Reduces appetite, treatment for anxiety, treatment for migraine headaches.
- 29. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dopamine an NT NT for neurons with cell bodies in midbrain. Axons project into: Nigrostriatal dopamine system: Nuerons in substantia nigra send fibers to corpus straitum. Initiation of skeletal muscle movement. Parkinsons disease: degeneration of neurons in substantia nigra. Mesolimbic dopamine system: Neurons originate in midbrain, send axons to limbic system. Involved in behavior and reward. Addictive drugs: Promote activity in nucleus accumbens.
- 30. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Norepinephrine (NE) as NT NT in both PNS and CNS. PNS: Smooth muscles, cardiac muscle and glands. Increase in blood pressure, constriction of arteries. CNS: General behavior.
- 31. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Amino Acids as NT Glutamic acid and aspartic acid: Major excitatory NTs in CNS. Glutamic acid: NMDA receptor involved in memory storage. Glycine: Inhibitory, produces IPSPs. Opening of Cl- channels in postsynaptic membrane. Hyperpolarization. Helps control skeletal movements. GABA (gamma-aminobutyric acid): Most prevalent NT in brain. Inhibitory, produces IPSPs. Hyperpolarizes postsynaptic membrane. Motor functions in cerebellum.
- 32. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Polypeptides as NT CCK: Promote satiety following meals. Substance P: Major NT in sensations of pain. Synaptic plasticity (neuromodulating effects): Neurons can release classical NT or the polypeptide NT.
- 33. Copyright 息 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Polypeptides as NT Endogenous opiods: Brain produces its own analgesic endogenous morphine-like compounds, blocking the release of substance P. Beta-endorphin, enkephalins, dynorphin. Neuropeptide Y: Most abundant neuropeptide in brain. Inhibits glutamate in hippocampus. Powerful stimulator of appetite. NO: Exerts its effects by stimulation of cGMP. Macrophages release NO to helps kill bacteria. Involved in memory and learning. Smooth muscle relaxation.