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.