Neurohumoral Transmission

Neurohumoral transmission is the process where nerve impulses release chemical messengers to transmit signals.

Definition:

• Neurohumoral transmission refers to the process by which a nerve impulse leads to the release of a chemical substance (neurotransmitter), which then acts on a target cell (neuron, muscle, or gland) to produce a specific physiological response.

Steps of Neurohumoral Transmission:

1. Impulse conduction: Electrical signal travels down the axon of a neuron.
2. Calcium influx: At the axon terminal, the action potential opens voltage-gated Ca²⁺ channels.
3. Vesicle fusion: Calcium triggers the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane.
4. Neurotransmitter release: Neurotransmitters are released into the synaptic cleft.
5. Receptor binding: Neurotransmitters bind to specific receptors on the postsynaptic membrane.
6. Response generation: Receptor activation causes ion channel opening or second messenger activation → Excitatory or inhibitory response.
7. Termination: Neurotransmitter action is stopped by:
   • Reuptake into the presynaptic neuron
   • Enzymatic degradation
   • Diffusion away from the synaptic cleft

Sites:

• Neuro-neuronal (between neurons)
• Neuro-effector (between neuron and muscle/gland)

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