Neurohemoral transmission Autonomic nervous System.pptx

Neurohemoral transmission in Autonomic nervous system

1. Neurohemoral transmission Autonomic Nervous System By-Dixhu Raj Dixit M.Pharm pharmacology 2 nd sem, Assam down town university, Guwahati

2. Neurohumoral transmission Nerves transmit their message across synapses and neuroeffector junctions by release of humoral chemical messengers. The transfer of nerve impulse from pre-synaptic to post synaptic neuron by means of humoral agent ex- biogenic amine,an amino acid or a peptide.

3. STEPS IN NEUROHUMORAL TRANSMISSION Impulse conduction Transmitter release Action on the postjunctional membrane Postjunctional activity Termination of transmitter action

4. 1.IMPULSE CONDUCTION Refers to passage of an impulse along nerve fibre . A supra threshold stimulus initiates a localized change in permeability of the axonal membrane. Action potential =Depolarization-------Influx of Na+, Repolarization ----------------Efflux of K+

5. 2. TRANSMITTER RELEASE The arrival of action potential at the terminal intiates a series of events that triggers transmission of an excitatory and inhgibitory impulse across the neuroeffector junction. The release occuring through exocytosdis involving Ca++ The transmitters in ANS ------- Acetylcholine and Norepinephrine . SNS------------Acetylcholine

6. 3. ACTION ON THE POST – JUNCTIONAL MEMBRANE And Post Junctional Activity When EPSP is generated ,initiates a propagated nerve vaction potential in the post junctional nerve. When an IPSP is initiated ,it oppose the stimultaneous excitatory potentials at the post junctional site. IOPSP>EPSP-------- INHIBITION IPSP<EPSP----------STIMULATION

7. TERMINATION OF TRANSMITTER ACTION The neurotransmitter termination can occur in three ways,reuptake by astreocytes or presynaptic terminal where the neurotransmitter is stored or destroyed by enzyme. Second degradation by enzymes in the synaptic cleft such as acetylcholinesterase .

8. Acetylcholine (Ach) is a major neurohumoral transmitter at autonomic, somatic as well as central sites. Choline is actively taken up by the axonal membrane by a Na+: choline cotransporter and acetylated with the help of ATP and coenzyme- A by the enzyme choline acetyl transferase present in the axoplasm . Hemicholinium (HC3) blocks choline uptake (the rate limiting step in Ach synthesis) and depletes Ach. Most of the Ach is stored in ionic solution within small synaptic vesicles, but some free Ach is also present in the cytoplasm of cholinergic terminals. Active transport of Ach into synaptic vesicles is effected by another carrier which is blocked by vesamicol . Release of Ach from nerve terminals occurs in small quanta—amount contained in individual vesicles is extruded by exocytosis .

9. Epinephrine (adrenaline) is a potent stimulant of both a and b adrenergic receptors, and its effects on target organs are thus complex. Most of the responses are seen after injection of epinephrine, although the occurrence of sweating, piloerection, and mydriasis depends on the physiological state of the subject. Particularly prominent are the actions on the heart and on vascular and other smooth muscle.