TUT4: Physio PDF

TUT4: Physio Integration of sympathetic and parasympathetic functions Integration of sympathetic functions o Sympathetic nervous system is an emergency system that prepare the body to face stresses (e.g. fear, fight, flight, muscular exercise and exposure to cold …..). o It is usua...

TUT4: Physio Integration of sympathetic and parasympathetic functions Integration of sympathetic functions o Sympathetic nervous system is an emergency system that prepare the body to face stresses (e.g. fear, fight, flight, muscular exercise and exposure to cold …..). o It is usually discharge as one unit (mass discharge) leads to widespread response all over the body. o Its functions are integrated with each other. This integration occurs as follows: Eyes Increased visual field by dilation of the eye pupil and exophthalmos. Cardiovascular system Increased heart rate and force of contraction to increase the arterial pressure and blood flow to the tissues. Respiratory system Dilation of the respiratory passages better ventilation and more oxygenation to the tissues. Blood vessels V.D of blood vessels of the skeletal and cardiac muscles and V.C to other areas. This help in shifting the blood to these active areas. Skin Increased sweating so helping the body to loss heat Spleen Contraction of the splenic capsule adds more blood to the circulation. Liver Supplying the body by energy through glycogenolysis in the liver and lipolysis in adipose tissues increasing blood glucose & free fatty acids. Other functions of minor importance are temporarily inhibited e.g. gastrointestinal motility. 1|Page  TUT4: Physio Integration of parasympathetic functions o Parasympathetic system is anabolic system (preserving energy), This occurs through : 1) ⬇️⬇️Heart rate and force of contraction, so the heart is at rest and excess energy is stored. 2)⬆️⬆️GIT functions increasing secretion of its hormones and enzymes to digest the food and supply the tissues with food stuff which store the energy for the time of need. o Parasympathetic functions continue during sleep and rest Sympathetic and parasympathetic tone o As the sympathetic and parasympathetic systems are continually active. During rest one system is dominant to some organs giving tone (mild continuous activity during rest). o The value of tone is that it allows a single nervous system to increase or to decrease the activity of a stimulated organ. Sympathetic tone Parasympathetic tone Sympathetic tone keeps most blood vessels partially Parasympathetic tone maintains smooth constricted (approximately half of their maximum muscle tone in the intestines and holds diameter) and this maintains ABP. resting heart rate down to about 70-80 beats/minute in order to decrease the high inherited rhythm of SAN (vagal Loss of sympathetic tone can cause rapid drop in tone). ABP thus a person goes into shock If the parasympathetic vagus nerves to the heart are cut, the heart beats by its own intrinsic rate of about 100 beats/minute. 2|Page  TUT4: Physio Control of autonomic nervous system The lateral horn cells and brain stem nuclei from which the autonomic preganglionic neurons arise are controlled both reflexly (i.e. by impulses arriving along afferent neurons) as well as by descending impulses from certain high centers in the nervous system. a) Reflex control of autonomic functions. b) Higher control of autonomic functions. 1) Reflex control of autonomic functions a) Spinal autonomic reflexes: These produce responses by stimulating the spinal autonomic centers (the lateral horn cells). E.g. The micturition and defecation reflexes; distention of the urinary bladder or rectum, stimulate certain receptors in these organs, which discharge impulses along afferent nerves to the sacral region of the spinal cord, resulting in micturition or defecation via the sacral parasympathetic outflow. B) brain stem autonomic reflexes: These produce responses by stimulating the cranial parasympathetic centers in the brain stem. 1) Reflex salivary, gastric and pancreatic secretion Introduction of food in the mouth stimulates the taste and other receptors in the buccal cavity which discharge impulses along afferent nerves to the brain stem where they stimulate the salivary and dorsal vagus nuclei resulting in reflex salivary, gastric and pancreatic secretion (unconditioned reflexes). 3|Page  TUT4: Physio 2) Reflex pupilloconstriction On exposing the eyes to light, the photoreceptors in the retina are stimulated leading to discharge of impulses in afferent fibers of optic nerve which stimulate the Edinger Westphal nucleus in the midbrain resulting in miosis (light reflex). 2)Higher control of autonomic functions 1) Reticular formation o The reticular formation in the brain stem contains many centers that control autonomic functions, e.g. the vasomotor and cardio-inhibitory centers in the medulla oblongata that control cardiovascular functions. If the arterial blood pressure is lowered (as in severe hemorrhage) the vasomotor centre is activated and the descending impulses stimulate the sympathetic lateral horn cells leading to generalized V.C in the body as well as heart acceleration, and such responses result in elevation of the arterial blood pressure towards the normal level. 2) The hypothalamus o The anterior hypothalamic nuclei control parasympathetic functions while the posterior hypothalamic nuclei control sympathetic functions. o The hypothalamus exerts its effects through affecting the centers located in the reticular formation e.g. in certain emotions, impulses are discharged from the hypothalamus to the medulla oblongata where they stimulate the vasomotor centre leading to generalized V.C and tachycardia through stimulating the sympathetic nervous system. 3) The cerebral cortex: o This controls the autonomic centers in both the hypothalamus and articular formation: o Prolonged mental work stimulates the vasomotor centre and frequently leads to chromic hypertension. o Thinking of food induces salivation as well as gastric and punctuates accretion by cortical signals that stimulate the salivary and vagal nuclei in the brain stem (conditioned reflexes). 4|Page