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Neurotransmitters
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- 4. INTRODUCTION Neurotransmittersare chemical messengersthat transmit signals from a neuron to a target cell across a synapse. Target cell may be a neuron or some other kind of cell like a muscle or gland cell. Necessary for rapid communication in synapse. Neurotransmitters are packaged into synapticvesicles - presynaptic side of a synapse.
- 5. Illustration of themajor elements in chemical synaptic transmission.
- 6. Axon Vesicles (containing neurotransmitters) Synaptic cleft Receptors Receivingneuron Pre synaptic knob Post synaptic knob A schematic representation of a chemical synapse
- 7. PROPERTIES OF NEUROTRANSMITTERS 1) Synthesizedin the presynaptic neuron 2) Localized to vesicles in the presynaptic neuron 3) Released from the presynaptic neuron under physiological condition 4) Rapidly removed from the synaptic cleft by uptake or degradation 5) Presence of receptor on the post-synaptic neuron. 6) Binding to the receptor elicits a biologicalresponse
- 8. TYPES OF NEUROTRANSMITTERS BOTH Acetylcholine Norepinephrine EXCITATORY Glutamate Aspartate Nitric oxide INHIBITORY Glycine GABA Serotonin Dopamine
- 10. ACETYLCHOLINE (ACh) Acetylcholine wasthe first neurotransmitter to be discovered. Isolated in 1921 by a German biologist named OttoLoewi. Uses choline as a precursor - cholinergicneurotransmitter. Used by the Autonomic Nervous System, such as smooth muscles of the heart, as an inhibitory neurotransmitter. Responsible for stimulation of muscles, including the muscles of the gastro-intestinal system. Used everywhere in the brain. Related to Alzheimer'sDisease.
- 11. DOPAMINE Is synthesized inthree steps from the amino acidtyrosine. Associated with reward mechanisms inbrain. Generally involved in regulatory motor activity, in mood, motivation and attention. Schizophrenicshave too much dopamine. Patients with Parkinson'sDiseasehave too little dopamine. Dopamine
- 12. NOREPINEPHRINE (noradrenaline) Synthesizeddirectly fromdopamine. Direct precursor to epinepherine. It is synthesized in four steps from tyrosine. Synthesized within vesicles. Norepinephrine is strongly associated with bringing our nervous systems into "high alert." It increases our heart rate and our blood pressure. It is also important for forming memories. Norepinephrine
- 13. GLUTAMATE It is anamino acid It the most commonly found excitatory neurotransmitter in the brain. It is involved in most aspects of normal brain function including cognition, memory and learning. Glutamate is formed from α –ketoglutarate, an intermediate of Kreb’s cycle.
- 14. γ-AMINO BUTYRIC ACID(GABA) Synthesized directly from glutamate. GABAis the most important inhibitory neurotransmitter Present in high concentrations in the CNS,preventing the brain from becoming overexcited. IfGABAis lacking in certain parts of the brain, epilepsy results. GABA
- 15. SEROTONIN (5-HT) Synthesized intwo steps from the aminoacid tryptophan Regulates attention and other complex cognitive functions, such as sleep (dreaming), eating,mood, pain regulation. Too little serotonin has been shown to lead to depression, anger control etc.
- 17. 1.Neurotransmitters are synthesized fromprecursors under the influence of enzymes 2.Stored in vesicles 3.Neurotransmitter molecules that leak from their vesicles are destroyed by enzymes 4.Action potential cause vesicle to fuse with synapse and release neurotransmitters 5.Some of it binds with auto receptor and inhibit subsequent neurotransmitter release 6.Rest of it bind to post synaptic receptors. 7.Released neurotransmitters are deactivated either by re uptake or enzyme degradation.
- 18. Steps in neurotransmitterprocessing are: Synthesis: Neurotransmitters are synthesized by the enzymatic transformation of precursors. Storage: They are packaged inside synaptic vesicles. Release: They are released from presynaptic terminal by exocytosis when calcium enters axon terminal during an action potential Diffuse across the synaptic cleft to the postsynaptic membrane. Binding: They bind to receptor proteins. Inactivation: The neurotransmitter is degraded either by being broken down enzymatically, or reused by active reuptake.
- 20. MODE OF ACTIONOF ACETYLCHOLINE Release • When nerve impulse reaches pre synaptic knob Ca channels open. • Increased Ca ions fusion of vesicle to presynaptic membrane and release of ACh into cleft. Binding • ACh bind to receptors in post synaptic membrane. • Ion channels open inflow of Na and K ions • Depolarisation and formation of action potential. • Propogation of action potential & contraction of fibres. Deactivation • ACh is hydrolysed by acetyl cholinesterase. • Choline taken back to presynaptic domain for resynthesis of Ach.
- 21. ALCOHOL & NEUROTRANSMITTERS Itbindsdirectlytoreceptors for ACh, serotonin, GABA and glutamate. It enhancestheeffects ofthe GABA, which is an inhibitory neurotransmitter. ◦ Enhancing an inhibitor make things sluggish. ◦ The neuron activity is diminished- sedative effectsof alcohol. Alcohol inhibitsglutamatereceptor function. ◦ This causes discoordination, slurred speech, staggering, memory disruption, and blackout. Alcohol raisesdopamine levels. ◦ This leads to excitement, pleasure and later addiction.
- 22. NICOTINE & NEUROTRANSMITTERS Nicotine imitatestheaction of ACh& binds to ACh receptor. Like acetylcholine, nicotine leads to a burst of receptor activity. Nicotine activatescholinergic neuronsin many different regions throughout your brain simultaneously. This stimulation leads to: ◦ Increased release of glutamate. ◦ Stimulation of cholinergic neurons promotes the release of dopamine.The production of dopamine causes feelings of reward and pleasure.
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- 24. REFERENCES Knut Schmidt Nielsen,Animal Physiology – Adaptation and environment, 4th edition, Cambridge University Press, U.K http://www.sciencedaily.com/releases/2011/12/111205 165907.htm http://www.columbia.edu/cu/psychology/courses/1010 /mangels/neuro/transmission/transmission.html http://www.chemistryexplained.com/NeNu/Neurotransmitters .html#b