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198 / JAIN STUDIES AND SCIENCE
In addition, thirty one pairs of spinal nerves originate and ramify from the spine to reach every part of the body. One part of these nerve pairs is called motor root and another sensory root. The motor root innervates muscles to produce movement, whereas the sensory root gathers information from the peripheral receptors like skin, joints, etc. and transmits it to the brain.
2.1. Autonomic Nervous System (ANS)
All our spontaneous internal body mechanisms like, digestion, heart-beat, hormone secretion etc. are governed by ANS. The part of brain-hypothalamus has shouldered this responsibility. From here the information passes through spinal cord via the brain stem.
The actions of the autonomic nervous system are largely involuntary (in contrast to those of the sensory-somatic system). It also differs from the sensorysomatic system in using two groups of motor neurons to stimulate the effectors instead of one.
The first, the preganglionic neurons, arise in the CNS and run to a ganglion in the body where they synapse with postganglionic neurons, which run to the effector organ (a muscle or a gland).
The autonomic nervous system has two subdivisions -
Sympathetic nervous system • Parasympathetic nervous system. 2.1.1. The Sympathetic Nervous System
The preganglionic motor neurons of the sympathetic system arise in the spinal cord. They pass into sympathetic ganglia which are organized into two chains that run parallel to and on either side of the spinal cord.
The neurotransmitter of the preganglionic sympathetic neurons is acetylcholine (ACh). It stimulates action in the postganglionic neurons which in turn release noradrenalin. The action of noradrenaline on a particular gland or muscle is excitatory is some cases and inhibitory in others. The release of noradrenalin has following effects -
increases heartbeat raises blood pressure dilates the pupils dilates the trachea and bronchi
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