Tag: autonomic nervous system

The sympathetic nervous system (SNS) is part of the autonomic nervous system (ANS), which also includes the parasympathetic nervous system (PNS).

Parasympathetic stimulation causes: slowing down of the heartbeat; lowering of blood pressure; constriction of the pupils; increased blood flow to the skin and viscera; salivation increase; peristalsis of the GI tract.

During the initial activation of the sympathetic system, norepinephrine gets released first as a preparatory hormone. This gets the body ready for the first stages of the emergency event. 

Parasympathetic nerve fibres arise from the central nervous system with the $S _2$, $S _3$, and $S _4$ spinal nerves and from the third, seventh, ninth, and tenth cranial nerves. 

Corpus callosum is a broad band of nervous tissue that connects two cerebral hemispheres. It consists of $300$ million fibres and is present only in mammals.

The sympathetic nervous system is involved in the stimulation of activities that prepare the body for action, such as increasing the heart rate, increasing the release of sugar from the liver into the blood, and other generally considered as fight-or-flight responses (responses that serve to fight off or retreat from danger). 

The autonomic nervous system is made up of sympathetic nervous system and para-sympathetic nervous system. The sympathetic nervous system made up of sympathetic fibers is responsible for the body's flight or fight response The sympathetic nerves or fibers increases heart rate and helps enhancing the blood flow, while inhibiting digestion and peristalsis.

Ramus communicans is the branch which connects the spinal nerve and the sympathetic trunk.  There are two forms of ramus communicans. They are gray ramus communicans and white ramus communicans. They are responsible for conduction of signals in the sympathetic nervous system. The white rami communicans are the preganglionic sympathetic outflow from the spinal cord. The gray rami communicans contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons.

Parasympathetic nerve fibres arise from the central nervous system with the $S _2$, $S _3$, and $S _4$ spinal nerves and from the third, seventh, ninth, and tenth cranial nerves. Because of its location, the parasympathetic system is commonly referred to as having craniosacral outflow.

The autonomous nervous system control the heart beat rate via cardio regulatory centre in medulla oblongata. The emergency conditions activate the sympathetic motor nerve and make the adrenal medulla to release epinephrine and nor-epinephrine which in turn increase the heart beat rate.  Thus, the correct answer is C. The central nervous system (Central NS) includes brain and spinal cord. It integrates and stores the sensory information from external and internal sense organs and commands different organs to respond accordingly. Peripheral nervous system (PNS) lies outside the central nervous system and is further divided into somatic and autonomic nervous system. It serves to carry the sensory information from external sensory receptors to CNS and motor signals from CNS to skeletal muscles via its somatic division (the voluntary actions). The autonomic division of peripheral nervous system controls the cardiac and smooth muscles and glands, thereby the functioning of internal organs, without our conscious control (the involuntary actions). On the other hand, vagus nerve conducts the parasympathetic motor impulses which in turn slow down the hearth beat rate by effect of acetylcholine; a neurotransmitter released by parasympathetic nervous system.