Sympathetic nervous system

The sympathetic nervous system is one of the divisions of the autonomic nervous system. It involuntarily regulates numerous actions, including the contraction of smooth muscles and the secretion of many glands. Its effects are generally opposite to those of the parasympathetic nervous system. The most important neurotransmitters of the sympathetic system are adrenaline and norepinephrine. Its main action is related to a fight or flight response to external stimuli that may endanger the body, for this reason it increases the frequency and strength of the heartbeat, dilates the lung bronchi, dilates the pupil, increases blood pressure. arterial, dilates the blood vessels that supply blood to skeletal muscles throughout the body and stimulates the production of sweat by the sweat glands. This set of actions can be considered as a preparation for fight or flight, but they are triggered automatically by any intense stimulus such as a startle, a sharp pain or an anxiety-generating situation.

Structure

The sympathetic nervous system is structured through preganglionic neurons whose bodies are found in the brain or spinal cord and postganglionic neurons located in the sympathetic ganglia. The preganglionic neurons transmit nerve impulses through the cranial or spinal nerves to the postganglionic neurons, from where the nerve fibers that retransmit these nerve signals to the different viscera and effector organs depart. The preganglionic sympathetic nerve fibers emerge from the anterior roots of the spinal cord, they continue through the white communicating rami to the chain of sympathetic ganglia in which the postganglionic neurons are found.

Sympathetic ganglia are divided into two main groups: paravertebral and prevertebral.

• Paravertebral nodes are located on both sides of the spine, from the cervical spine to the coxis and inerve the organs of the upper half of the body, i.e. those located above the diaphragm.
• The anticipated vertebral nodes are in front of the spine and emit nerve fibers that mainly inert the organs in the abdomen and under the diaphragm. Three of them stand out: celiac node, upper mesential node and lower mesential node.

Function

Puppy dilated by activation of the sympathetic nervous system.

The sympathetic nervous system acts on numerous organs and systems:

• Cardiovascular system: Increases the frequency and strength of the heart contractions, so this organ is able to pump more blood per minute. It increases blood pressure by decreasing the caliber of small arteries that carry blood to the skin and other organs, however it spreads the arteries that bring blood to the skeletal muscles with which they receive more oxygen and can perform more intense work.
• Respiratory aparatus: Dilates the lung bronchus, thus making it easier for the inspired air to reach the lung alveolos more easily than the place where gaseous blood exchange occurs.
• Eye. It produces the dilation of the pupil (midriasis).
• Digestive device: Decreasing the contraction of the smooth muscles that are found on the wall of the digestive tract. This action decreases peristalism and makes the digestion process slower. At the same time the tone of the sphincters increases, among them the anal sphincter.
• Pancreas: inhibition of activity.
• Adrenal gland: It stimulates the production of adrenaline by the adrenal glands. The adrenaline thus released acts in turn on the remaining organs.
• Sweat glands: Sweat production stimula for sweat glands.

In most organs the sympathetic nervous system has an action contrary to that of the parasympathetic nervous system.

Recipients

Noradrenaline.

Adrenaline.

Endings of the sympathetic nervous system release norepinephrine and adrenaline that bind to specific receptors located in tissues. There are different types of receptors:

• Alpha receivers. They can be divided into 2 major types called alpha 1 and alpha 2.
• Beta receivers. They are classified into beta 1, beta 2 and beta 3.

Mass activation

It takes place due to certain very intense emotional or painful stimuli that produce, through the hypothalamus, an activation of the sympathetic system throughout the organism. In this way, the body prepares itself for significant muscular activity, blood pressure rises, blood flow to the muscles increases and blood flow decreases to other non-vital organs, the heart rate rises in preparation for strenuous physical activity, and the cell metabolism and glucose production.

Pharmacology

Medications that act on the sympathetic nervous system can be divided into two groups:

• Simpaticomimetics. They stimulate the sympathetic action, for example adrenaline, noradrenaline and dopamine. They can act on alpha delta or beta adrenergic receptors.
• Nice. These medicines inhibit the sympathetic response. When alpha receptors are blocked, they are called alpha-blockers, for example prazosin, and when they block beta receptors are beta-blockers like propanolol.

Pathology

Diseases that affect this part of the nervous system are rare. Diabetic patients sometimes have diabetic autonomic neuropathy, a complication of diabetes in which the sympathetic nervous system performs its function poorly, causing a multitude of symptoms that affect different organs, including heart rate changes, poor adaptation to physical exercise, constipation, sexual impotence and urinary incontinence.

Sympathectomy

Sympathectomy is a surgical intervention that consists of removing or destroying certain sympathetic ganglia for some therapeutic purpose. It is used in cases of excessive sweating on the hands (hyperhidrosis).