adrenal medulla sympathetic nervous system
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The autonomic nervous system (ANS or visceral nervous system) is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition (urination), and sexual arousal. Whereas most of its actions are involuntary, some, such as breathing, work in tandem with the conscious mind.
It is classically divided into two subsystems: the parasympathetic nervous system and sympathetic nervous system. Relatively recently, a third subsystem of neurons that have been named 'non-adrenergic and non-cholinergic' neurons (because they use nitric oxide as a neurotransmitter) have been described and found to be integral in autonomic function, particularly in the gut and the lungs.
With regard to function, the ANS is usually divided into sensory (afferent) and motor (efferent) subsystems. Within these systems, however, there are inhibitory and excitatorysynapses between neurons.
The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.
ANS innervation is divided into sympathetic nervous system and parasympathetic nervous system divisions. The sympathetic division has thoracolumbar â€œoutflowâ€�, meaning that the neurons begin at the thoracic and lumbar (T1-L2) portions of the spinal cord. The parasympathetic division has craniosacral â€œoutflowâ€�, meaning that the neurons begin at the cranial nerves (CN 3, CN7, CN 9, CN10) and sacral (S2-S4) spinal cord.
The ANS is unique in that it requires a sequential two-neuron efferent pathway; the preganglionic neuron must first synapse onto a postganglionic neuron before innervating the target organ. The preganglionic, or first, neuron will begin at the â€œoutflowâ€� and will synapse at the postganglionic, or second, neuronâ€™s cell body. The post ganglionic neuron will then synapse at the target organ.
The sympathetic division (thoracolumbar outflow) consists of cell bodies in the lateral horn of spinal cord (intermediolateral cell columns) of the spinal cord from T1 to L2. These cell bodies are GVE neurons (general visceral efferent), and are the preganglionic neurons. There are several locations upon which preganglionic neurons can synapse for their postganglionic neurons:
- Paravertebral ganglia of the sympathetic chain (these run on either side of the vertebral bodies)
- Prevertebral ganglia (celiac ganglia, superior mesenteric ganglia, inferior mesenteric ganglia)
- Chromaffin cells of adrenal medulla (this is the one exception to the two-neuron pathway rule: synapse is direct onto cell bodies)
These ganglia provide the postganglionic neurons from which innervation of target organs follows. Examples of splanchnic (visceral) nerves are:
- Cervical cardiac nerves & thoracic visceral nerves which synapse in the sympathetic chain
- Thoracic splanchnic nerves (greater, lesser, least) which synapse in the prevertebral ganglion
- Lumbar splanchnic nerves which synapse in the prevertebral ganglion
- Sacral splanchnic nerves which synapse in the inferior hypogastric plexus
These all contain afferent (sensory) nerves as well, also known as GVA neurons (general visceral afferent).
The parasympathetic division (craniosacral outflow) consists of cell bodies from one of two locations: brainstem (Cranial Nerves 3, 7, 9, 10) or sacral spinal cord (S2, S3, S4). These are the preganglionic neurons, which synapse with postganglionic neurons in these locations:
- Parasympathetic ganglia of the head (Ciliary (CN3), Submandibular (CN7), Pterygopalatine (CN7), Otic (CN9))
- In or near wall of organ innervated by Vagus (CN10), Sacral nerves (S2, S3, S4))
These ganglia provide the postganglionic neurons from which innervations of target organs follows. Examples are:
- The preganglionic parasympathetic splanchnic (visceral) nerves
- Vagus nerve, which wanders through the thorax and abdominal regions innervating, among other organs, the heart, lungs, liver and stomach
The sensory arm is made of â€œprimary visceral sensory neuronsâ€� found in the peripheral nervous system (PNS), in â€œcranial sensory gangliaâ€�: the geniculate, petrosal and nodose ganglia, appended respectively to cranial nerves VII, IX and X. These sensory neurons monitor the levels of carbon dioxide, oxygen and sugar in the blood, arterial pressure and the chemical composition of the stomach and gut content. (They also convey the sense of taste, a conscious perception). Blood oxygen and carbon dioxide are in fact directly sensed by the carotid body, a small collection of chemosensors at the bifurcation of the carotid artery, innervated by the petrosal (IXth) ganglion. Primary sensory neurons project (synapse) onto â€œsecond orderâ€� or relay visceral sensory neurons located in the medulla oblongata, forming the nucleus of the solitary tract (nTS), that integrates all visceral information. The nTS also receives input from a nearby chemosensory center, the area postrema, that detects toxins in the blood and the cerebrospinal fluid and is essential for chemically induced vomiting or conditional taste aversion (the memory that ensures that an animal which has been poisoned by a food never touches it again). All these visceral sensory informations constantly and unconsciously modulate the activity of the motor neurons of the ANS
Motor neurons of the ANS are also located in ganglia of the PNS, called â€œautonomic gangliaâ€�. They belong to
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Answers:True. The adrenal medulla is innervated by preganglionic sympathetic neurons. The adrenal medulla consists of cells that are essentially postganglionic neurons, but they are clustered in the middle of the adrenal tissue and do not have axons. When stimulated, they release norepinephrine and epinephrine.
Answers:I think the answer is easier than you are making it. You don't seem to have a problem with knowing HOW the SNS and PNS are working, but are basically asking WHY evolution hasn't made this system better by making the preganglionic fibers of the SNS longer than the the slower postganglionic fibers to increase the speed of the signal. We have to look at the different functions of the SNS and PNS, and see how they are reflected their structure and composition. One of the big differences between them is that the signals or the SNS are extremely widespread rather than specific to one organ or muscle sheet, as in the case of the PNS. For this reson it makes sense to have the SNS ganglions close to the vertbral column, as opposed to all the way to each organ/muscle.
Answers:the answer is C. increasing GI motility is the function of the parasympathetic system
Answers:In a normal situation, yes. But all these systems are interrelated. The medulla oblongata acts to control the pulse by sympathetic and parasympathetic impulses. Baroreceptors in the aorta and carotid sinuses alter the cardiac output via the glossopharyngeal nerve and the vagus nerve. Overall the parasympathetic system has a greater influence on rate in the basal rate, but those things can fluctuate as need be.