Autonomic nervous system sympathetic branch

The somatic nervous system is composed of sensory afferents and motor efferents and serves to perceive external states and to modulate appropriate body responses. The autonomic nervous system (ANS), together with the endocrine system, controls the milieu interieur. It adjusts internal organ functions to the changing needs of the organism. The ANS operates largely autonomously, beyond voluntary control, at the subconscious level. Its central components reside in the hypothalamus, brain stem, and spinal cord. The ANS has sympathetic and parasympathetic branches. Both are made up of afferent, mainly in the vagus nerve, and efferent fibers. 

A low level of tonic activity of the sympathetic nerves to vascular smooth muscle adrenergic receptors exists so that withdrawal of sympathetic vasomotor tone results in vasodilatation and reduced pressure. Conversely, enhancement of sympathetic vasomotor tone augments the level of vasoconstriction leading to elevated pressure. While the parasympathetic branch of the autonomic nervous system innervates some blood vessels, it does not generally play a role in regulating peripheral resistance. 

Stress and anxiety conditions affect both physical and mental health and are also associated with a modern lifestyle and its demands. Everyone experiences stress - some is normal and essential. But to be subject to stress over a long period can be very harmful. Stress is thought to exacerbate all other clinical conditions as it acts on the sympathetic branch of the autonomic nervous system. This system is responsible for the fight or flight reactions in the body. It may cause changes to normal digestion, respiratory and cardiovascular system, poor immunity and exhaustion. Mentally it may be... 

The afferent neurons of the autonomic nervous system are important in the reflex regulation, for example, by sensing pressure in the carotid sinus and aortic arch and signaling the CNS to influence the efferent branch of the system to respond. Conditions such as trauma, fear, hypoglycemia, cold, or exercise activate the sympathetic neurons. Both sympathetic and parasympathetic neurons emerge from the brain stem or spinal cord. Blood pressure is regulated largely by sympathetic control of vascular tone. 

Norepinephrine Mostly excitatory, but inhibitory in some areas. Secreted by neurons in the locus ceruleus (subcortical area) to widespread areas of the brain, controlling wakefulness, overall activity, and mood. Also diffusely secreted in the sympathetic nervous system. Diffuse and widespread symptoms, including depression, changes in blood pressure, heart rate, and diffuse physiological responses, among many others. An important transmitter in the sympathetic branch of the autonomic nervous system. Diffusely affected by many medications. Several antidepressants work specifically on this neurotransmitter and its receptor sites. Many medications for general medical conditions affect this neurotransmitter as well. 

The other branch of the autonomic nervous system is the parasympathetic branch, which in general balances the actions of the sympathetic branch by exerting opposite effects. Parasympathetic activity reduces heart rate, bkxxl pressure, and so on. In contrast to sympathetic neurons, parasympathetic synapses arc primarily cholinergic. 

The autonomic nervous system is divided into two branches. The sympathetic branch produces the physiological effects that accompany emotional arousal, and the parasympathetic branch controls the body when at rest. 

Stimulants are classic examples of sympathomimetic drugs that is, they act to stimulate or mimic activity in the sympathetic branch of the autonomic nervous system. Thus, many of their physiological effects arc the same as those seen during emotional arousal heart rate is up, blood pressure is up, respiratory rate is up, and sweating increases meanwhile, blood flow decreases to the internal organs and extremities but increases to the large muscle groups and the brain. Finally, body temperature is elevated and pupils arc dilated. 

Autonomic nervous system (ANS) Part of the PNS has two branches sympathetic and parasympathetic (Chapter 3). 

Norepinephrine ( no r- e-pa- ne-fran) A ncurotransmittcr in the brain that is involved in activity of the sympathetic branch of the autonomic nervous system (Chapter 3). 

The sympathetic branch of the autonomic nervous system (see 15.1 The Nervous System) stimulates cells using the neurotransmitter norepinephrine. Adrenergics (sympathomimetics) mimic actions (Table 15.1) of the sympathetic nervous system. These are referred to as adrenergic agonists because it starts a response at the adrenergic receptor sites. 

In the peripheral nervous system, norepinephrine is an important neurotransmitter in the sympathetic branch of the autonomic system. Sympathetic nerve transmission operates below the level of consciousness in controlling physiological function of many organs and tissues of the body. The sympathetic system plays a particularly important role in regulating cardiovascular function in response to postural, exertional, thermal, and mental stress. With sympathetic activation, the heart rate is increased, peripheral arterioles are constricted, skeletal arterioles are dilated, and the blood pressure is elevated. In addition, sympathetic nerve stimulation dilates pupils inhibits smooth muscles of the intestines, bronchi, and bladder and closes the sphincters. Sympathetic signals work in balance with the parasympathetic portion of the autonomic nervous system to maintain a stable internal environment. 

As compared to the known alkaloids of the ergot group which possess an action on the uterus and on the sympathetic branch of the vegetative or autonomic nervous system the new alkaloid prepared according to the present process has a specific action in very small doses of 20—50 ug. on the central nervous system. 

Stimulation of the parasympathetic and sympathetic branches in the autonomic nervous system results in a wide array of symptoms, depending on which system is more stimulated (Table 4-2). The chemical, route of exposure, and dose determine the symptoms. 

Previously in this chapter you learned that the autonomic nervous system has two branches. These are the sympathetic branch and parasympathetic branch. Both branches act on the same organ cells but in an opposite way. The sympathetic branch stimulates a response and the parasympathetic branch depresses a response by the organ cell. Together, they keep the organ in balance (homeostasis). 

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