Neurohumoral transmission

Nervous System

·         Network of nerve cells and fibres which transmits nerve impulse between parts of the body.

 

Classification of nervous system 

Motor: carry neuronal impulse away from CNS to different parts.

Sensory: Carry impulse from sensory stimuli towards the CNS and Brain.

Sympathetic

Parasympathetic

·         Fight or flight condition.

·         Increase BP, HR, Glucose, perfusion to skeletal muscle, mydriasis, Bronchodilator.

·         Rest and digest

·         Miosis

·         Decrease HR, BP, Bronchial secretion, Insulin release, Digestion, excretion

Introduction to Autonomic Nervous System Drugs

Neurohumoral transmission

·         Neurohumoral transmission implies that nerves transmit their message across synapses and neuroeffector junctions by the release of humoral (Chemical) message.

 

Steps in Neurohumoral transmission 

1.      Impulse conduction

·         Resting transmembrane potential -70mv (inside) (High concentration K+ ion).

·         Electrical impulse causes increase in Na+ conductance so depolarization occur.

·         Now the voltage become +20mv.

·         K+ ion then move out in the direction of their concentration and repolarization achieved.

·         The ionic distribution is normalized during the refractory period by activation of Na+ K+ pump.

·         The action potential thus generated set of local circuit currents which active ionic channel at the next excitable part of the membrane.

2.      Impulse release

·         Transmitted stored pre-junctional nerve ending with synaptic cleft.

·         Entry of Ca2+: all contents of the vesicle are extruded.

3.      Transmitter action on post-junctional member

·         Release transmitter combine with specific receptor on post junctional membrane and depending on its nature induce an excitatory postsynaptic potential (EPSP) or inhibitory post-synaptic potential (IPSP.)

EPSP

·         Increase permeability of cations, so that Na+ Ca2+ influx

IPSP

·         Increase permeability of anions (Cl ion move inside)

·         Increase in permeability to K+ ions, which moves out carrying positive charges.

4.      Post junctional activity

·         EPSP: propagated post junctional AP results nerve impulse secretions.

·         IPSP: stabilize the post junctional membrane. It resist depolarization stimuli.

5.      Termination of transmitter action

·         The transmitter locally degraded or partly taken back into pre-junctional neuron (e.g. Ach).

·          Specific carrier protein e.g. NET (Norepinephrine transporter), DAT (Dopamine transporter), SERT (Serotonin transporter), Amino acid transporter, Enkephalins, VIP (Vasoactive intestinal peptides), NPY (Neuropeptide-y).

6.      Co-transmission

·         The co-transmitter is stored in the pre-junctional nerve terminal along with primary but in separate vesicle.

·         Nerve impulse releases both the transmission concurrently.

 

·         It may also act on pre-junctional receptors and modulate release of the transmitters.

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