Autonomic Nervous System: Sympathetic vs Parasympathetic, Animation

The autonomic nervous system, or ANS, is the part  of the nervous system that regulates activities of   internal organs. The ANS is largely autonomous,  acting independently of the body’s consciousness   and voluntary control. It has two main divisions:  sympathetic, SNS, and parasympathetic, PSNS.  In situations that require alertness and  energy, such as facing danger or doing physical   activities, the ANS activates its sympathetic  division to mobilize the body for action. This   division increases cardiac output, accelerates  respiratory rate, releases stored energy,   and dilates pupils. At the same time, it also  inhibits body processes that are less important   in emergencies, such as digestion and urination. On the other hand, during ordinary situations,   the parasympathetic division conserves  and restores. It slows heartbeats,   decreases respiratory rate, stimulates  digestion, removes waste and stores energy.  The sympathetic division is therefore  known as the “fight or flight” response,   while the parasympathetic division is  associated with the “rest and digest” state.  Despite having opposite effects on  the same organ, the SNS and PSNS are   not mutually exclusive. In most organs,  both systems are simultaneously active,   producing a background rate of activity  called the “autonomic tone” - a balance   between sympathetic and parasympathetic inputs.  This balance shifts, one way or the other,   in response to the body’s changing needs. Some organs, however, receive inputs from   only one system. For example, the smooth muscles  of blood vessels only receive sympathetic fibers,   which keep them partially constricted and thus  maintaining normal blood pressure. An increase   in sympathetic firing rate causes further  constriction and increases blood pressure,   while a decrease in firing rate dilates  blood vessels, lowering blood pressure.  The autonomic nerve pathways, from the  control centers in the central nervous   system to the target organs, are composed  of 2 neurons, which meet and synapse in an   autonomic ganglion. Accordingly, these neurons  are called preganglionic and postganglionic.  In the SNS, the preganglionic neurons arise from  the thoracic and lumbar regions of the spinal   cord; their fibers exit by way of spinal nerves  to the nearby sympathetic chain of ganglia. Once   in the chain, preganglionic fibers may follow any  of 3 routes: some fibers synapse immediately with   postganglionic neurons; some travel up or  down the chain before synapsing; some pass   through the chain without synapsing - this third  group continues as splanchnic nerves to nearby   collateral ganglia for synapsing instead. From the  ganglia, long postganglionic fibers run all the   way to target organs. The SNS has a high degree  of neuronal divergence: one preganglionic fiber   can synapse with up to 20 postganglionic neurons.  Thus, effects of the SNS tend to be widespread.  In the PSNS, the preganglionic neurons arise from  the brainstem and sacral region of the spinal   cord. Preganglionic fibers exit the brainstem  via several cranial nerves and exit the spinal   cord via spinal nerves before forming the  pelvic splanchnic nerves. Parasympathetic   ganglia are located near or within target organs,  so postganglionic fibers are relatively short. The   degree of neuronal divergence in the PSNS  is much lower than that of the SNS. Thus,   the PSNS produces more specific,  localized responses compared to the SNS.

Channel: Alila Medical Media

Views: 766,237

Rating: 4.9309239 out of 5

Keywords: yt:quality=high, anatomy, animated, animation, ans, autonomic tone, autonomous, biology, brain, cns, cranial nerves, fight or flight response, ganglia, ganglion, glands, heartbeat, homeostasis, medical, medicine, nervous system, neural pathway, neurology, neuronal divergence, neuroscience, parasympathetic, pathways, postganglionic neuron, preganglionic neuron, psns, rest and digest, science, sensory, smooth muscle, sns, stimulation, sympathetic system, vagus nerve, vasomotor tone, viscera, visceral reflex

Id: D96mSg2_h0c

Length: 4min 22sec (262 seconds)

Published: Tue Mar 06 2018