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In the human species, various activities of the nervous system are conscious and under the control of the will.
Thinking, moving an arm, or changing facial expression are examples of voluntary activities. Many other actions, however, are autonomous or involuntary, that is, they occur independently of our will. Examples of involuntary activities are heartbeat, digestion process, excretion etc.At voluntary actions result from the contraction of skeletal striated muscles, which are under the control of the voluntary or somatic peripheral nervous system. Already the involuntary actions result from contraction of the smooth and cardiac muscles controlled by the autonomic peripheral nervous system, also called involuntary or visceral.
The voluntary or somatic SNP has the function of react to stimuli from the external environment. It consists of motor fibers that drive impulses from the central nervous system to skeletal muscles. The cellular body of a voluntary SNP motor fiber is located within the central nervous system and the axon goes directly from the brain or spinal cord to the innervating organ.
The autonomic or visceral SNP has as its function regulate the internal environment of the body, controlling the activity of the digestive, cardiovascular, excretory and endocrine systems. He contains motor fibers that drive impulses from the central nervous system to the smooth muscles of the viscera and the musculature of the heart.
An autonomic SNP motor nerve differs from a voluntary SNP motor nerve in that it contains two types of neurons, one preganglionic neuron and another post-ganglion. The cell body of the pre-ganglion neuron is located within the central nervous system and its axon goes to a ganglion, where a nerve impulse is synaptically transmitted to the post-ganglion neuron. The neuron's cell body lies within the nerve ganglion and its axon conducts the nerve stimulus to the effector organ, which may be a smooth or cardiac muscle.
Sympathetic autonomic SNP and parasympathetic autonomic SNP
Autonomous SNP (SNPA) is divided into two branches: nice and parasympathetic, which are distinguished by both structure and function. As for structure, the sympathetic and parasympathetic SNPA branches differ by the location of the ganglion in the nervous pathway. While the sympathetic pathway ganglia are located beside the spinal cord, distant from the effector organ, the parasympathetic pathway ganglia are far from the central nervous system and close to or even within the effector organ.
The sympathetic and parasympathetic nerve fibers innervate the same organs, but work in opposition. While one branch stimulates a certain organ, the other inhibits. This antagonistic situation maintains the balanced functioning of the internal organs.
O Sympathetic SNPAThey generally stimulate actions that mobilize energy, allowing the body to respond to stressful situations. For example, the sympathetic system is responsible for accelerating the heartbeat, increasing blood pressure, increasing blood sugar concentration and activating the body's general metabolism.
Already the Parasympathetic SNPA, mainly stimulates relaxing activities, such as reductions in heart rate and blood pressure among others.