What Is Sympathetic Nervous System And Parasympathetic Nervous System – Home Quizzes & Games History & Social Sciences & Tech Biography Animals & Nature Geography & Travel Arts & Culture Money Videos

The autonomic nervous system is a part of the peripheral nervous system that regulates basic intestinal processes necessary for the maintenance of normal bodily functions. It functions independently of voluntary control, although some events, such as stress, fear, sexual arousal, and changes in the sleep-wake cycle, alter the level of autonomic activity.

What Is Sympathetic Nervous System And Parasympathetic Nervous System

The autonomic system is generally defined as the motor system that innervates three main types of tissue: cardiac muscle, smooth muscle, and glands. However, it also relays visceral sensory information to the central nervous system and processes it to modify the activity of specific autonomic motor outflows, such as those that control the heart, blood vessels, and other visceral organs. It also stimulates the release of certain hormones involved in energy metabolism (eg, insulin, glucagon, and epinephrine [also called adrenaline]) or cardiovascular functions (eg, renin and vasopressin). These coordinated responses maintain the normal internal environment of the body in a state of equilibrium called homeostasis.

Autonomic Nervous System Poster

The autonomic system consists of two main divisions: the sympathetic nervous system and the parasympathetic nervous system. This often works in the opposite way. The motor outflow of both systems is formed by two serially connected sets of neurons. The first group, called preganglionic neurons, originate in the brain stem or spinal cord, and the second group, called ganglion cells or postganglionic neurons, lie outside the central nervous system in collections of nerve cells called autonomic ganglia. Parasympathetic ganglia reside near or within their neurons that reside within organs or tissues, while sympathetic ganglia are located at locations more distant from their target organs. Both systems involve sensory fibers that send feedback to the central nervous system regarding the functional status of target tissues.

The third division of the autonomic system, the enteric nervous system, consists of a collection of neurons embedded within the wall of the gastrointestinal tract and its derivatives. This system regulates gastrointestinal motility and secretion.

The sympathetic nervous system normally functions to produce local adjustments (such as sweating in response to an increase in temperature) and reflex adjustments of the cardiovascular system. In stressful situations, however, the entire sympathetic nervous system is activated, producing an immediate, widespread response called the fight-or-flight response. This response is characterized by the release of large amounts of epinephrine from the adrenal gland, increased heart rate, increased cardiac output, skeletal muscle vasodilation, skin and gastrointestinal vasoconstriction, pupillary dilation, bronchial dilation, and pyloerection. The overall effect is to prepare the individual for imminent danger.

Sympathetic preganglionic neurons originate in the lateral horns of the 12 thoracic and the first 2 or 3 lumbar segments of the spinal cord. (For this reason the sympathetic system is sometimes referred to as the thoracolumbar outflow.) The axons of these neurons exit the spinal cord at ventral roots and then synapse on specialized cells of the adrenal gland called sympathetic ganglion cells or chromaffin cells.

Autonomic Nervous System: Parts, Organization And Functions

Sympathetic ganglia can be divided into two main groups, paravertebral and prevertebral (or preaortic), based on their location in the body. Paravertebral ganglia are usually located on each side of the spinal cord and are connected to form the sympathetic chain or trunk. There are usually 21 or 22 pairs of these ganglia—3 in the cervical region, 10 or 11 in the thoracic region, 4 in the lumbar region, and 4 in the sacral region—and a single unpaired ganglion lies in front of the coccyx, called the ganglion impar. The three cervical sympathetic ganglia are the cervical ganglion, the middle cervical ganglion, and the cervicothoracic ganglion (also called the stellate ganglion). The superior ganglion innervates the viscera of the head, and the middle and stellate ganglia innervate the neck, chest (i.e., trachea and heart), and viscera of the upper limbs. Thoracic sympathetic ganglia innervate the trunk region, and lumbar and sacral sympathetic ganglia innervate the pelvic floor and lower limbs. All paravertebral ganglia provide sympathetic innervation to muscles and blood vessels of the skin, erector pili muscles attached to hair, and sweat glands.

The three preaortic ganglia are the celiac, superior mesenteric, and inferior mesenteric. Lying on the anterior surface of the aorta, the preaortic ganglia provide axons that distribute along the three major gastrointestinal arteries arising from the aorta. Thus, the celiac ganglion is the first part of the stomach, liver, pancreas, and duodenum, the small intestine; The superior mesenteric ganglion enters the small intestine; And the inferior mesenteric ganglion innervates the descending colon, sigmoid colon, rectum, urinary bladder, and sexual organs.

Upon reaching their target organs by traveling along the blood vessels that supply them, sympathetic fibers terminate as a series of swellings near the end organ. Because of this anatomical arrangement, autonomic transmission occurs at junctions rather than synapses. “Presynaptic” sites can be recognized because they contain synaptic vesicles and membrane thickening; The postjunctional membrane, on the other hand, is rarely characterized morphologically, but contains specific receptors for various neurotransmitters. The distance between the pre- and postsynaptic elements can be quite large compared to normal synapses. For example, the distance between cell membranes of a typical chemical synapse is 30–50 nanometers, while the distance in blood vessels is often more than 100 nanometers or, in some cases, 1–2 micrometers (1,000–2,000 nanometers). Because of this relatively large distance between autonomic nerve terminals and their effector cells, neurotransmitters act slowly; They also gradually become inactive. To compensate for this inefficiency, many effector cells, such as those in smooth and cardiac muscles, are connected by low-resistance pathways that allow for electrotonic coupling of the cells. Thus, if only one cell is activated, multiple cells will respond and act as a group.

At first glance, chemical transmission in the sympathetic system appears simple: preganglionic neurons use acetylcholine as a neurotransmitter, while most postganglionic neurons use norepinephrine (noradrenaline)—the major exception being that postganglionic neurons use the inner line. However, upon closer inspection, neurotransmission is found to be more complex, as multiple chemicals are released, and each acts as a specific chemical code affecting different receptors on the target cell. Furthermore, these chemical codes are self-regulatory, in that they act on presynaptic receptors located on their own axon terminals.

Moods And Emotions In Our Social Lives

Chemical codes are specific to specific tissues. For example, most sympathetic neurons that innervate blood vessels secrete both norepinephrine and neuropeptide Y; Sympathetic neurons innervating the submucosal neural plexus of the gut contain both norepinephrine and somatostatin; And sympathetic neurons that innervate sweat glands contain calcitonin gene-related peptide, vasoactive intestinal polypeptide, and acetylcholine. In addition, other chemicals besides the neuropeptides mentioned above are released from autonomic neurons along with the so-called classical neurotransmitters, norepinephrine and acetylcholine. For example, some neurons synthesize the gas, nitric oxide, which acts as a neuronal messenger molecule. Thus, neural transmission in the autonomic nervous system involves the release of combinations of various neuroactive agents that affect both pre- and postsynaptic receptors.

Neurotransmitters released from nerve terminals bind to specific receptors, which are specialized macromolecules embedded in the cell membrane. The binding action initiates a series of specific biochemical reactions in the target cell that produce a physiological response. In the sympathetic nervous system, for example, there are five types of adrenergic receptors (receptors that bind epinephrine): α

Autoreceptors (receptors located at sympathetic presynaptic nerve endings) act to inhibit the release of norepinephrine. Other types of tissues have unique adrenoceptors. Heart rate and myocardial contractility, for example, are regulated by β

Cholinergic receptors (receptors that bind acetylcholine) are also found in the sympathetic system (as well as the parasympathetic system). Nicotinic cholinergic receptors stimulate sympathetic postganglionic neurons, adrenal chromaffin cells, and parasympathetic postganglionic neurons to release their chemicals. Muscarinic receptors are primarily involved in parasympathetic functions and are located in peripheral tissues (eg glands and smooth muscle). Peptidergic receptors also exist in target cells.

Nervous System 6: The Autonomic Nervous System

The length of time each type of chemical acts on its target cell is variable. As a rule, peptides develop slowly, causing long-lasting effects (a minute or more), while classical transmitters produce short-term effects (about 25 milliseconds). At our core, we are made up of nervous systems with primary nervous systems. There is a central and peripheral nervous system (see Figure 1).

The central nervous system is made up of the brain and spinal cord, it is part of our thinking. While the peripheral nervous system is made up of the somatic and autonomic nervous systems, without us thinking about it, the somatic and autonomic nervous systems control the body’s basic functions, muscles and senses.

The autonomic nervous system has two branches, the parasympathetic and the sympathetic. The parasympathetic branch calms us down, while the sympathetic branch, often referred to as the “fight or flight” nervous system, is about our personal survival: it responds immediately, automatically, and physiologically to environmental stressors (Figure see 2).

Before going any further, I need to let you in on a little secret about it

Human Nervous System

What is the difference between sympathetic and parasympathetic nervous system, sympathetic versus parasympathetic nervous system, sympathetic parasympathetic nervous system, parasympathetic nervous system vs sympathetic, peripheral nervous system sympathetic and parasympathetic, central nervous system sympathetic and parasympathetic, function of sympathetic and parasympathetic nervous system, sympathetic and parasympathetic nervous system difference, compare sympathetic and parasympathetic nervous system, what is sympathetic and parasympathetic nervous system, sympathetic nervous system and parasympathetic, functions of parasympathetic and sympathetic nervous system