The part of the peripheral nervous system which receives sensory information from the sensory organs and that controls movements of the skeletal muscles __ is called the somatic nervous system. The other branch of the peripheral nervous system ---- the autonomic nervous system (ANS) is concerned with regulation of smooth muscles, cardiac muscles and glands. (Autonomic means “self-governing”). Smooth muscles is found in the skin (associated with hair follicles), in blood vessels, in the eyes (controlling pupil size and accommodation of the lens), and in the walls and sphincters of the gut, gallbladder and urinary bladder. Thus the autonomic nervous system is involved in controlling blood pressure, body temperature, digestive functions and other physiological functions. The ANS consists of two anatomically separate systems the Sympathetic division and the Parasympathetic division. With few exceptions organs of the body are innervated by both of these subdivisions and each has a different effect.
Sympathetic Division of the ANS
The sympathetic division is most involved in activities associated with expenditure of energy from reserves that are stored in the body. F.E when an organism is excited, the sympathetic nervous system increase blood flow to skeletal muscles, stimulates the secretion of epinephrine (a harmone that increase heart rate and raises blood sugar level), and causes piloerection __erection of four in mammals that have it and production of “goose bumps” in humans.
The cell bodies of sympathetic motor neurons are located in the gray matter of the thoracic and lumbar regions of the spinal cord (hence the sympathetic nervous system is also known as the Thoracolumbar system). The axons of these neurons exit via the ventral roots. After joining the spinal nerves the axons branch off and pass into spinal sympathetic ganglia (not to be confused with the dorsal root ganglia). The axons that leave the spinal cord through the ventral root are part of the Preganglionic neurons. The neurons with which they form synapses are called Postganglionic neurons.
Parasympathetic Division of the ANS
The parasympathetic division of the ANS supports activities that are involved with increase in the body’s supply of stored energy. These activities include salivation, gastric and intestinal motility, secretion of digestive juices and increased blood flow to the gastrointestinal system.
Cell bodies that give rise to Preganglionic axons in the parasympathetic nervous system are located in two regions: the nuclei of some of the cranial nerves (especially the Vagus nerve) and the gray mater in the sacral region of the spinal cord. T parasympathetic division of the ANS has often been referred to as the Craniosacral system. The terminal buttons of both Preganglionic and postganglionic neurons in the parasympathetic nervous system secrete Acetylcholine.
0 comments:
Post a Comment