Somatic and autonomic nervous systems are two components of the peripheral nervous system of the body. Both nervous systems are involved in controlling the functions of the body based on the internal and external stimuli. The somatic nervous system is composed of spinal and cranial nerves.

The ANS is further divided into the sympathetic nervous system and the parasympathetic nervous system. Both of these systems can stimulate and inhibit effectors.

However, the two systems work in opposition—where one system stimulates an organ, the other inhibits. Working in this fashion, each system prepares the body for a different kind of situation, as follows:.The sympathetic nervous system prepares the body for situations requiring alertness or strength, or situations that arouse fear, anger, excitement, or embarrassment (“fight‐or‐flight” situations). In these kinds of situations, the sympathetic nervous system stimulates cardiac muscles to increase the heart rate, causes dilation of the bronchioles of the lungs (increasing oxygen intake), and causes dilation of blood vessels that supply the heart and skeletal muscles (increasing blood supply). The adrenal medulla is stimulated to release epinephrine (adrenalin) and norepinephrine (noradrenalin), which in turn increases the metabolic rate of cells and stimulates the liver to release glucose into the blood. Sweat glands are stimulated to produce sweat. In addition, the sympathetic nervous system reduces the activity of various “tranquil” body functions, such as digestion and kidney functioning.The parasympathetic nervous system is active during periods of digestion and rest.

It stimulates the production of digestive enzymes and stimulates the processes of digestion, urination, and defecation. It reduces blood pressure and heart and respiratory rates and conserves energy through relaxation and rest.In the SNS, a single motor neuron connects the CNS to its target skeletal muscle.

In the ANS, the connection between the CNS and its effector consists of two neurons—the preganglionic neuron and the postganglionic neuron. The synapse between these two neurons lies outside the CNS, in an autonomic ganglion. The axon (preganglionic axon) of a preganglionic neuron enters the ganglion and forms a synapse with the dendrites of the postganglionic neuron. The axon of the postganglionic neuron emerges from the ganglion and travels to the target organ (see Figure 1). There are three kinds of autonomic ganglia:.The sympathetic trunk, or chain, contains sympathetic ganglia called paravertebral ganglia. There are two trunks, one on either side of the vertebral column along its entire length. Each trunk consists of ganglia connected by fibers, like a string of beads.The prevertebral (collateral) ganglia also consist of sympathetic ganglia.

Preganglionic sympathetic fibers that pass through the sympathetic trunk (without forming a synapse with a postganglionic neuron) synapse here. Prevertebral ganglia lie near the large abdominal arteries, which the preganglionic fibers target.Terminal (intramural) ganglia receive parasympathetic fibers. These ganglia occur near or within the target organ of the respective postganglionic fiber. The target organs of the different nervous systems.A comparison of the sympathetic and parasympathetic pathways follows (see Figure 2):.Sympathetic nervous system. Cell bodies of the preganglionic neurons occur in the lateral horns of gray matter of the 12 thoracic and first 2 lumbar segments of the spinal cord. (For this reason, the sympathetic system is also called the thoracolumbar division.) Preganglionic fibers leave the spinal cord within spinal nerves through the ventral roots (together with the PNS motor neurons).

The preganglionic fibers then branch away from the nerve through white rami (white rami communicantes) that connect with the sympathetic trunk. White rami are white because they contain myelinated fibers. A preganglionic fiber that enters the trunk may synapse in the first ganglion it enters, travel up or down the trunk to synapse with another ganglion, or pass through the trunk and synapse outside the trunk.

Postganglionic fibers that originate in ganglia within the sympathetic trunk leave the trunk through gray rami (gray rami communicantes) and return to the spinal nerve, which is followed until it reaches its target organ. Gray rami are gray because they contain unmyelinated fibers.Parasympathetic nervous system. Cell bodies of the preganglionic neurons occur in the gray matter of sacral segments S 2–S 4 and in the brainstem (with motor neurons of their associated cranial nerves III, VII, IX, and X). (For this reason, the parasympathetic system is also called the craniosacral division, and the fibers arising from this division are called the cranial outflow or the sacral outflow, depending on their origin.) Preganglionic fibers of the cranial outflow accompany the PNS motor neurons of cranial nerves and have terminal ganglia that lie near the target organ. Preganglionic fibers of the sacral outflow accompany the PNS motor neurons of spinal nerves. These nerves emerge through the ventral roots of the spinal cord and have terminal ganglia that lie near the target organ.figure 2.A comparison of the sympathetic and parasympathetic pathways.

IntroductionThe peripheral nervous system is an extension of the central nervous system. Its overall function is to carry information from the central nervous system to other parts of the body to maintain normal body function.

It enables the body to react voluntarily and involuntarily to any stimuli. It is composed of nerve fibers bundles that lie beyond the brain and spinal cord. Some of the nerve fiber bundles proceed to innervate skeletal muscles and sensory receptors. These fibers comprise the somatic nervous system. The remaining nerve fibers innervate visceral organs, smooth muscles, glands and blood vessels.

These fibers comprise the autonomic nervous system. Somatic Nervous SystemThe somatic nervous system is composed of nerves that originate from the spinal cord. Nerves that supply muscles on the head originate from the brain. It is comprised of motor neurons that supply skeletal muscles to allow movement.

Its axon is continuous from the spinal cord to the skeletal muscle, forming the neuromuscular junction. The neuromuscular junction is an important structure for neurotransmission to stimulate muscular contraction. Inhibition of locomotion occurs through inhibitory pathways coming from the central nervous system. Transmitters and R eceptorsThe space between the and the skeletal muscle is called a synaptic cleft. The axon terminal of motor neurons releases the neurotransmitter, acetylcholine, which is the only neurotransmitter for the somatic nervous system.

Acetylcholine is stored within vesicles located on the knob-like terminal end of the nerve fiber, called a terminal button. The terminal button contains calcium channels. When calcium is sufficiently released, this triggers the release of acetylcholine from the vesicles into the synaptic cleft. Acetylcholine binds to nicotinic cholinergic receptors, which activates a series of chemical reactions that changes the ionic composition of the motor endplate. Effector Organs and FunctionThe release of acetylcholine stimulates the opening of ionic channels for sodium and potassium. Ionic particles carry an electrical charge and concentration gradient. This reaction generally moves sodium inward and potassium outward causing a depolarization of the motor end plate.

This allows electrical current to flow from the depolarized motor end plate and adjacent areas triggering the opening of voltage-gated sodium channels. This propagates an action potential throughout the effector organ, which is the skeletal muscle. The initiated electrical potential activity spreads within the entire muscle allowing contraction of the skeletal muscle fiber. The aforementioned chain of events enables voluntary control of muscle groups that is essential for locomotion. Autonomic Nervous SystemThe autonomic nervous is system is composed of nerves that originate from the. It is also known as the visceral nervous system because its nerve bundles proceed to supply visceral organs and other internal structures.

Its axon is discontinuous and is separated by a ganglion, forming a two-neuron chain. The autonomic nervous system has two functionally different subdivisions. The sympathetic division enables the human body to involuntary respond to emergency situations, creating a “fight or flight” response. The parasympathetic division enables normal visceral functions by allowing storage of energy to conserve body reserves. Transmitters and R eceptorsThe autonomic nervous system preganglionic neurons release acetylcholine at the synaptic area, which binds to nicotinic cholinergic receptors at the postsynaptic membrane. In parasympathetic nervous system, post-ganglionic neurons also release acetylcholine, which binds to muscarinic receptors located in salivary glands, stomach, heart, smooth muscles and other glandular structures.

In sympathetic nervous system, post-ganglionic neurons release norepinephrine, which binds to alpha-1 receptors in smooth muscles, beta-1 receptors in the heart muscle, beta-2 in smooth muscles and alpha-2 adrenergic receptors. Effector Organs and FunctionBoth the sympathetic and parasympathetic nerve fibers are present in all visceral organs. The principal effector organs that are the skin, liver, pancreas, lungs, heart, blood vessels and kidneys. Nerve fibers from the sympathetic and parasympathetic subdivisions are complementary in function to allow involuntary mechanisms that preserve the internal homeostatic mechanisms. The skin serves to regulate the body’s core temperature by preserving or conserving water loss from sweat glands. The liver and the pancreas regulate the metabolism of glucose and lipids. The lungs regulate the concentration of oxygen and acidic particles in the blood by allowing oxygen inhalation and carbon dioxide exhalation.

The heart and blood vessels regulate blood pressure through cardiac rhythmic nodes and blood vessel wall diameter changes. The kidneys regulate the excretion of toxins in the body. It also works synergistically with the lungs to maintain normal blood pH levels. Assault android cactus wikipedia 1. SummaryThe somatic and autonomic nervous systems have salient anatomic and structural differences that give rise to different functions. Somatic nerves predominantly come from the spinal cord and are composed of motor neurons that travel to the skeletal muscle. It releases acetylcholine, which stimulates the voluntary contraction of skeletal muscles. Its function is controlled by central nervous system structures such as the motor cortex, basal ganglia, cerebellum, brainstem and the spinal cord.

On the other hand, autonomic nerves come from both the spinal cord and the brain that travels to various internal organs, smooth muscles, glands and blood vessels. It is comprised of a two-neuron chain with a preganglionic area that releases acetylcholine, and a post-ganglionic area that releases acetylcholine for parasympathetic terminals and norepinephrine for sympathetic terminals.

Neurotransmitter release allows involuntary control of visceral organs by stimulation or inhibition. This is regulated by central nervous system structures such as the prefrontal cortex, hypothalamus, medulla and spinal cord. References:0Berne, R. M., Koeppen, B. M., & Stanton, B.

Berne & Levy physiology. Philadelphia, PA: Mosby/Elsevier.1Preston, R. R., & Wilson, T. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.2Sherwood, L. Fundamentals of Human Physiology.

Belmont, CA: Brooks/Cole Cengage Learning.3Snell, R. Clinical Neuroanatomy. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.4Weiten, W. Psychology: Themes and Variations. Belmont, CA: Cengage/Wadsworth.5on DifferenceBetween.net are general information, and are not intended to substitute for professional advice.

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