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SBI4U Neurotransmitters

SBI4U Neurotransmitters. Neurotransmitter Properties:. 1) Synthesized in the presynaptic neuron 2) Stored in vesicles in the presynaptic neuron 3) Released when an Action Potential stimulates the neuron

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SBI4U Neurotransmitters

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  1. SBI4U Neurotransmitters

  2. Neurotransmitter Properties: 1) Synthesized in the presynapticneuron 2) Stored in vesicles in the presynaptic neuron 3) Released when an Action Potential stimulates the neuron 4) Rapidly removed from the Synaptic Cleft by reuptake (reuse) or degradation (recycle) 5) Attach to a Receptor on the post-synaptic neuron. 6) Binding to the receptor elicits a new Action Potential

  3. Two Categories: EXCITATORY Acetylcholine Serotonin Dopamine Norepinephrine Epinephrine Histamine *Glutamate *Aspartate INHIBITORY GABA *Glycine (Gamma Aminobutyric Acid!)

  4. Presynaptic Neuron Synaptic Vesicle Postsynaptic Neuron Mitochondrion Neurotransmitter molecules Postsynaptic Membrane Synaptic cleft

  5. Example: Action of Acetylcholine • Action potential arrives at end of axon (synaptic knob), causing influx of Ca2+ • Synaptic vesicles fuse to membrane, releasing Acetylcholine into Synaptic Cleft • Acetylcholine binds to receptors on post-synaptic neuron; stimulates new A.P. • Acetylcholine is then released from receptors, and ‘cleaned up’ by the enzyme Acetylcholinesterase.

  6. Structure of Acetylcholinesterase • Acetylcholinesterase (AchE) hydrolyses acetylcholine. • The active site of AChE ismade up oftwo subsites, both of which are critical to the breakdown of ACh: Acetylcholine + H2O  Choline + H+ Acetate

  7. The Catecholamines: Dopamine, Norepinephrine & Epinephrine • All Formed from the amino acid Tyrosine. • Four-part reaction: • Decarboxylation to Dopamine • Hydroxylation to Norepinephrine • Methylation to Adrenaline.

  8. The Catecholamines: Dopamine, Norepinephrine & Epinephrine Norepinephrine • Epinephrine & Norepinephrine keep us alert & feeling energetic • They’re part of many responses: anger, fear, stress • Dopamine is part of our reward & motivation responses • Imbalances of Dopamine are involved in Epilepsy, Parkinson’s Disease. Epinephrine Dopamine

  9. Serotonin • Serotonin is synthesized from the amino acid Tryptophan. • The synthesis of serotonin involve two reactions: Hydroxylation & Decarboxylation • Serotonin is our ‘feel good’ hormone: calming, quieting effect in the CNS • Repetitive actions have been shown to increase Serotonin release

  10. Serotonin, Mood & Depression: • Serotonin levels are altered in mood disorders & depression • With Norepinephrine & Dopamine, many aspects of mood & mental function are regulated.

  11. Serotonin, Mood & Depression: • SSRI’s = Specific Serotonin Reuptake Inhibitors • They stop reuptake of Serotonin • Excess Serotonin in the Synaptic Cleft continues to stimulate the post-synaptic neuron • Serotonin build-up makes up for the low serotonin levels found in depression • Used as Anti-Depressants

  12. Endorphins • From “endogenous morphine”… naturally occuring opioids • Produced only in brain; hypothalamus/pituitary • Mimic opium, morphine • Released during exercise, excitement, pain, orgasm & eating spicy foods. • Contribute to habits?

  13. GABA • The main inhibitory NT • Regulates nerve function in CNS; our ‘brakes’ • Also has a role of stopping some nerve responses in PNS • Contributes to muscle tone • Imbalances have a role in Epilepsy, Muscle spasms, Cerebral Palsy

  14. Neurotransmitters & Addiction: • Many addictive substances mimic neurotransmitters, or influence their actions • They act on brain neurons involved in perception, alertness, satiation and reward pathways.

  15. Neurotransmitters & Addiction:

  16. Neurotransmitter Molecule Derived From Site of Synthesis Acetylcholine Choline CNS, parasympathetic nerves Serotonin5-Hydroxytryptamine (5-HT) Tryptophan CNS, chromaffin cells of the gut, enteric cells GABA Glutamate CNS Histamine Histidine hypothalamus Epinephrine synthesis pathway Tyrosine adrenal medulla, some CNS cells Norpinephrine synthesis pathway Tyrosine CNS, sympathetic nerves Dopamine synthesis pathway Tyrosine CNS Nitric oxide, NO Arginine CNS, gastrointestinal tract Summary:

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