<span> <span>The PNS is divided into a)
somatic and b) autonomic nervous system, and c) the enteric nervous system.
Somatic nerves mediate voluntary movement. The </span>autonomic nervous
system<span>) is the one that
influences the function of </span><span>internal organs,
it</span> <span>is further
subdivided into the </span>sympathetic<span> <span>and the </span></span>parasympathetic<span> <span>nervous systems. The sympathetic nervous system is activated in cases of
emergencies to mobilize energy, while the parasympathetic nervous system is
activated when organisms are in a relaxed state. The </span></span>enteric nervous
system<span> <span>functions to control the </span></span>gastrointestinal<span> <span>system. Both autonomic and enteric nervous systems function
involuntarily. Nerves that exit from the cranium are called </span></span>cranial nerves<span> <span>while those exiting from the spinal cord are called </span></span>spinal nerves<span>.</span></span>
Diffusion is the random movement of molecules or particles from a region of high concentration to a region of low concentration bringing a natural flow in the system. Diffusion ensures that there is a state of equilibrium in the number of molecules in the system.
The defecation reflex involves two postive feedback loops. these loops are the stretch receptors in the rectal walls and the sacral parasympathetic system. Defecation reflex empties the rectum by peristaltic movements push fecal matter from the sigmoid colon into the rectum. Then this distension of the rectal walls stimulates stretch receptors which results in defecation.
