Neurotransmission in Autonomic Nervous System (ANS)
A nerve consists of lots of neurons and all these neurons are connected with each other with synaptic cleft (space between head of one neuron and tail of another neuron), this called synapse and with effecter organ, this junction called neuroeffect or junction. Chemicals fill this synaptic cleft, which acts as transporter of impulse between neurons forming the junction are called neurotransmitter.
Fig 2.6 Neurotransmission
Two chemical transmitters have been established as neurotransmitter in the ANS. These are acetylcholine and norepinephrine (nor adrenaline). Both the transmitters are synthesized primarily in the nerve endings and stored in the synaptic vesicles and released only when nerve impulse gets arise.
Neurotransmission in the autonomic nervous system occurs at four major sites. Acteylcholine as a neurotransmitter released three sites these are
1. Preganglionic synapse in both parasympathetic and sympathetic ganglia.
2. Parasympathetic postganglionic neuroeffector junctions.
3. All somatic motor end plates on skeletal muscle.
Fig 2.7 Signaling in sympathetic and parasympathetic systems
Norepinephrine as neurotransmitter is released at most sympathetic postganglionic neuroeffector junctions, and the neurons that release this substance are called adrenergic neurons. Its better that always remembers that at postganglionic sympathetic site norepinephrine is the transmitter except in sweat glands and some blood vessels in skeletal muscles and for left places its acetylcholine.
The drugs that mimic the action of actetylcholine are called cholinergic or parasympathomimetic drugs similarly the drugs mimic the action of norepinephrine are called aderenergic or sympathomimetic drugs.