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NERVOUS TISSUE The Synapse

NERVOUS TISSUE The Synapse. The Synapse. Area of contact between two neurons or between a neuron and a sensor or an effector Two types: Electrical (rare) and chemical synapses. Signal transduction Can be excitatory or inhibitory. Synapses. Signal transduction.

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NERVOUS TISSUE The Synapse

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  1. NERVOUS TISSUEThe Synapse

  2. The Synapse • Area of contact between two neurons or between a neuron and a sensor or an effector • Two types: Electrical (rare) and chemical synapses

  3. Signal transduction Can be excitatory or inhibitory Synapses

  4. Signal transduction • An electrical signal coming from the pre-synaptic neuron is transformed in a chemical signal on the post synaptic neuron

  5. Action potential Voltage-gated Ca channels open Calcium triggers exocytosis NT diffuses and binds to receptor Response in cell Response terminated by removing neurotransmitter from synaptic cleft Degradation Reuptake Diffusion Signal transduction

  6. Cell response to the signal • The response will depend on the type of channel that is binding the neurotransmitter • If the neurotransmitter is binding to a sodium channel (or Ca++), an EPSP is triggered • If the neurotransmitter binds to a potassium channel, an IPSP is triggered

  7. What will happen if the neurotransmitter binds to a chloride channel?

  8. The neurotransmitters • Chemical messengers of the brain • Location and action vary with the neurotransmitter • Classification: - Acetylcholine - Biogenic amines - Amino acids - Peptides - Others

  9. Acetylcholine • Found in PNS and CNS, most abundant neurotransmitter in PNS • Neurotransmitter present at the synapse between motor neurons and skeletal muscle fibers • Excitatory or inhibitory • Synthesized in cytosol of axon terminal: • Acetyl CoA + choline  acetylcholine + CoA • Degradation occurs in synaptic cleft by acetylcholinesterase (AChE)

  10. Fast acting Poisoned by nicotine Nicotinic cholinergic receptors

  11. Muscarinic cholinergic receptors • Slow acting • Poisoned by muscarine from a mushroom

  12. Acetylcholine - Pathology

  13. Monoamines -- Catecholamines (derived from tyrosine) - Epinephrine and norepinephrine (=adrenaline and noradrenaline) - Dopamine -- Serotonin from tryptophan -- Histamine from histidine

  14. Monoamines • Present in various areas of the brain • Functions vary with area • Mostly excitatory, linked with emotions (pleasure) • Eliminated by 1) reuptake into the synaptic axon and 2) with enzymatic degradation by monoamine oxidase (MAO) and catechol-o-methyltransferase (COMT)

  15. Adrenergic receptors • Alpha adrenergic receptors • Alpha1 • Alpha2 • Beta adrenergic receptors • Beta1 • Beta2 • Beta3

  16. Serotonin • CNS neurotransmitter (brainstem) • Functions • Regulating sleep • Emotions - LSD mimics serotonin - Antidepressants like prozac, paxil, zoloft inhibit reuptake

  17. Other neurotransmittors • Amino acids: - Excitatory (glutamic acid) - Inhibitory (glycine, GABA) • Polypeptides - Substance P (mediates pain) - Endogenous opiods (endorphins, enkephalins) - Neuropeptide Y (abundant, increase appetite) • Gases - Nitrous oxide = NO = laughing gas

  18. Cocaine blocks the reuptake of norepinephrine and dopamine. • Which effects do you expect?

  19. Amphetamines stimulate the release of norepinephrine and dopamine at the synapse. • What will be the consequences?

  20. Axonal transport • Anterograde and retrograde • It is the transport of substances within the axon • NOT to be confused with AP

  21. Anterograge axonal transport • Substances are carried from the body of the neuron toward the terminal vesicles in the axon • Substances: mitochondria, proteins, neurotransmitters…

  22. Retrograde axonal transport • Substances are transported from the terminal vesicles of the axon toward the body • Examples: neurotransmitters, viruses (rabies, herpes), toxin (tetanus)

  23. Nerve injury (Wallerian degeneration)

  24. Readings: • Chp. 9: p. 217-251 • Chp. 11: p. 303-321 • Not expected to be known: • sleep, p. 243-246, memory, p.247-248 • Autonomic neuroeffector junctions p. 310

  25. Helpful web sites: • outreach.mcb.harvard.edu/teachers/Summer05/RaymondBroadhead/Synapses_and_Drugs.ppt • http://www.sumanasinc.com/webcontent/animations/neurobiology.html

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