Tag: nervous system of man

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. 

Esophageal peristalsis and sphincter function are controlled by the autonomic nervous system. Swallowing is a complex mechanism using both skeletal muscle (tongue) and smooth muscles of the pharynx and esophagus. The autonomic nervous system (ANS) coordinates this process in the pharyngeal and esophageal phases. Knee jerk is a sudden kicking of the lower leg after the tendon below knee cap has been tapped. The pupillary reflex is also controlled by autonomic nervous system.

The acetylcholine is the neurotransmitter that is released by the presynaptic nerve fibres into the synaptic cleft which is received by the receptors on the post-synaptic nerves. It allows the transfer of the information from the presynaptic neuron to the post-synaptic neurons. The preganglionic and the post-ganglionic parasympathetic nerves are cholinergic because they secrete the acetylcholine. The preganglionic nerve fibres of the sympathetic nervous system are also cholinergic.

Auerbach plexus is the interwoven network of the vagus nerve in the inner circular and outer longitudinal muscles of the muscularis layer of the visceral organs.