Question

Describe the relationship between the two motor neurons in the ANS pathways. How do they differ for sympathetic and parasympathetic pathways? Which neurotransmitter (ACh or NE) is being released by the pre- and postganglionic neurons for the sympathetic and parasympathetic pathways?

Answer 1

The autonomic nervous system controls involuntary activities of the body such as the activities of smooth muscle, cardiac muscle and glands.

The afferent component is identical to the somatic nervous system. The efferent component differs in a manner that somatic nervous system contains only one efferent (motor neuron). ANS contains two efferents, one arising from the CNS (first order neuron) and second neuron arising from autonomic ganglia (second order neuron). The first and second order neurons are autonomic efferent pathway and are called preganglionic and postganglionic neurons respectively.

The preganglionic neurons relay their fibres in an autonomic ganglion. This ganglia are located close to the target organs in parasympathetic system and ganglia of sympathetic system are present near the spinal cord. Therefore preganglionic neurons are longer in parasympathetic and shorter in sympathetic. Accordingly, postganglionic neurons are shorter in parasympathetic and longer in sympathetic.

Neurotransmitters: Both sympathetic and parasympathetic use Acetylcholine (ACh) as their neurotransmitter for preganglionic neurons.

Parasympathetic use ACh for postganglionic also.

Sympathetic use Norepinephrine and ACh according to the organ involved.