Question

In the autonomous motor system there is a 2-step connection (i.e., 2 neurons in series) from the brain to the target muscles. This is different from the somatic motor system (only 1 neuron). Please list and briefly explain which advantage(s) in control this 2-step process provides.

Answer 1

The autonomic nervous system represents the visceral component of the nervous system.

It consists of neurones located within both, the central nervous system and the peripheral nervous system and which are concerned with the control of the internal environment, through innervation of secretory glands, both cardiac and smooth muscle.

The autonomic activities is expressed by regulation of body temperature, blood pressure, cardiorespiratory rate, gastro - intestinal motility and glandular secretion.

Autonomic afferent

Autonomic afferent pathways resemble somatic afferent pathways

The cell bodies of autonomic afferent origin are unipolar neurones located in cranial and dorsal root ganglia. Their peripheral processes are distributed through autonomic ganglia or plexuses or possibly through somatic nerves, without interruption.

Visceral efferent

Autonomic efferent pathways differ from their somatic equivalents in that the former are interrupted by peripheral synapses, there being a sequence of at least two neurones between the CNS and the target structure. These are referred to as preganglionic and post ganglionic.

Autonomic system consists of sympathetic and parasympathetic system

Sympathetic system

In sympathetic system, the preganglionic fibres are short and post ganglionic fibres are long. One preganglionic fibre make synaptic connections with twenty or more postganglionic neurons. Sympathetic system is also called adrenergic system because post ganglionic sympathetic fibres liberate adrenaline. But sympathetic fibres to swaet glands of hairy skin are cholinergic.The entire function of sympathetic is a nerve of emergency and during stress and strain to fight or flight. It is actabolic nerve and works for today. Thoracic and upper two lumbar sympathetic ganglion is connected to corresponding spinal nerve by both white and gray rami communicates.

Parasympathetic system

The preganglionic motor neurons are partly located in the brain stem in connection with cranial nerves. Post ganglionic para- sympathetic neurons consists of collateral and terminal ganglia.

BOth sympathetic and parasympathetic preganglionic fibres liberate acetylcholine.

The preganglionic fibres are longer than post ganglionic fibres. One preganglionic neurons one or two post ganglionic neurons. The action of parasympathetic is localise and accurate. Afferent parasympathetic fibres convey general visceral sensation like hunger, thirst or nausea, distension of bladder etc. The cell bodies are located in the ganglia IX and X cranial nerve and dorsal root ganglia of 2nd to 4th sacral nerves.