The parasympathetic division is one of the divisions of the autonomic nervous system that is concerned with digestion, urination and defecation. It has a different effect from that of the sympathetic division because this division involves the body in a state of rest. Unlike the sympathetic, the parasympathetic decreases respiration and heart rate; hence, it conserves and stores energy instead of using it. This action allows the body to replenish itself and be ready for any sympathetic action that may ensue during perceived threats or emergencies.
It cannot function properly, though, without these essential related parts. Axons are found in preganglionic neurons to form a connection between spinal and cranial nerves, all the way to the terminal ganglia. The preganglions are cell bodies located in the oculomotor nerve, brainstem, vagus nerve, facial nerve, glossopharyngeal nerve, and in the spinal cord. The terminal ganglia are found in the walls of the target organs at the pelvis, thorax and abdomen or in the head.
Preganglionic neurons are produced in the spinal column and the brain. Majority of the neurons in the parasympathetic division originate from the midbrain, the pons and the medulla oblongata. The effects of the action of the parasympathetic division are opposite to that of sympathetic, and the process is “rest and digest” instead of “fight or flight.”
An innervation is the stimulation of nerves or muscles in the body to affect specified responses. Aside from the sympathetic division, the parasympathetic division is also involved in various innervations. There are two general innervations involved, and these are the cranial preganglionic innervation and the sacral preganglionic innervation. The preganglionic innervation involves the facial nerves like the nerves of the eyes, salivary and lacrimal. The sacral preganglionic innervation innervates the nerves in the bladder, lower portion of the colon, the rectum, and the reproductive organs.
Receptors are substances that “receive’ the “message” from the neurotransmitters. These receptors in the effector organs combine with the neurotransmitters. The combination will trigger biochemical or physiological reactions, like muscle contraction and relaxation, increased secretion of hormones in endocrine glands, release of these hormones, and similar activities.
Specific receptors of toxic substances like nicotine and muscarine are also present. Nicotine is found in tobacco or cigarettes and muscarine in toadstools. These two receptors, nicotinic and muscarinic, when triggered, can cause side effects that are detrimental to the body’s proper function.
The ganglionic cells of the parasympathetic division have fewer dendrites as compared to that of the sympathetic division. Its preganglionic axons are also few or one for each ganglion. The parasympathetic ganglia are innervated by the cranial and sacral preganglionic cells.
Based on the facts presented, the parasympathetic division is therefore a vital part of the autonomic nervous system. It brings balance and homeostasis to the body because it induces relaxation and a restful state. You can just imagine if only the sympathetic division is responsible for body processes, we would always be on the go with no time to rejuvenate our tired and weary bodies.