Sympathetic Nervous System

Sympathetic Nervous System & All About It

 

The sympathetic nervous system belongs to autonomic nervous system along with parasympathetic nervous system. The sympathetic nerves starts from the spinal column running towards the middle part of spinal cord in the lateral horn. It originates at the spinal cord’s first thoracic segment and extends to third lumbar segment. This nervous system is considered to have thoracolumbar outflow since the cells of these nerves originates in the lumbar and thoracic regions. The primary function of this nervous system is mobilization of the body’s nervous system due to fight or flight response. 

This is done by mediating hormonal and neuronal stress response. This nervous system is continuously active to maintain stability, temperature, and pH of the body. Primarily, this nervous system counteracts parasympathetic nervous system. This system also helps in controlling the internal organs of the body such as eyes, heart, lungs, blood vessels, sweat glands, digestive system, kidney, and penis. Dilation of pupils, rate and force of contraction, dilation of bronchioles, constriction of blood vessels, activation of sweat secretion, inhibition of peristalsis, promotion of renin secretion, and promotion of ejaculation in men are all aided by this nervous system. Since the messages through this system travels in a bidirectional flow, both afferent and efferent messages help in various functions of the body such as acceleration of heart rate, widening of bronchial passages to give increased oxygen, decreased movement of large intestine, piloerection, and perspiration.

It also helps in feeling sensations like cold, heat, and pain. The stress response of this system is also known as sympathoadrenal response since the preganglionic fibers of this nervous system activates secretion of adrenaline and noradrenaline which are commonly called epinephrine and norepinephrine. Since these fibers end in the medullar part of the adrenal gland, it secretes acetylcholine which also helps in activation. Sometimes this nervous system is affected by various causes. Some of the causes are diseases such as parkinson’s disease and alzheimer’s disease due to the damage caused to the transmission system with degeneration of sympathetic nerves, autoimmune disorders, excessive alcohol consumption, traumatic brain injury, brain infection in addition to spinal cord infection such as meningitis and encephalitis, structural defects such as birth defects, problems of the immune system, benign or malignant tumors of the brain, and stroke due to the interruption in supply of blood to the brain. The common symptoms of SNS disorders are slurred speech, loss of muscle strength, hypertension, headache, loss of memory, seizures, tremors, cardiovascular diseases, erectile dysfunction, breathing problems, and trouble with swallowing. 

The major disorders of the sympathetic nervous system are sympathicotonia, fibromyalgia, complex regional pain syndrome or reflex sympathetic dystrophy syndrome, diabetic neuropathy, and Parkinson’s disease. Sympathicotonia is a condition where the nervous system is stimulated leading to hypertension, goose bumps, and vascular spasm. Fibromyalgia is a painful condition which is also caused due to hyperactivity of this nervous system. Reflex sympathetic dystrophy syndrome is caused by immune response of SNS which causes pain, swelling, and redness. Diabetic neuropathy is a condition where the blood vessels are damaged due to diabetic injury. Parkinson’s disease occurs due to widespread damage to this nervous system leading to trembling, akinesia, and postural instability. This major part of the autonomic nervous system helps the body in performing various functions.

sympathetic nervous system definition

The nervous systems in humans and indeed in all mammals have so many subdivisions. It is, therefore, important that individuals should get a clear sympathetic nervous system definition in order to make individuals understand the role that each division of the nervous system works. The CNS is the most commonly known by all and it controls the entire nervous system in the body. However, the autonomous nervous system is also very essential in the body. It is important also to keep in mind that one cannot offer a clear sympathetic nervous system definition if the person does not understand the mechanics of the autonomous nervous system.

The functions of sympathetic nervous system definition must include accelerating heart rate, constriction of blood vessels, increasing blood pressure and so many other involuntary functions in the body. It should be noted that these are merely the functions of sympathetic nervous system and they should not be mistaken, or even be considered to offer sympathetic nervous system definition. In fact, the closest that these functions can be used in the definition of the system is stating that sympathetic nervous system is the part of the nervous system that performs and controls involuntary actions.

The autonomous nervous system was considered a part of the nervous system that is functionally independent of the brain although this has been discredited since all impulses rely on the brain for execution and transmission. It is worth mentioning that sympathetic nervous system is only one part of the autonomic nervous system besides the parasympathetic nervous system. The two systems work by generation of electric impulses that are conducted to the muscles of the heart, which in turn trigger action. Sympathetic nervous system definition cannot be complete if the definition does not offer an insight into the mechanisms by which sympathetic nervous system works to control the involuntary nervous functions. One thing that cannot be left behind during the definition is that the system works in conjunction of other networks such as the sinoatrial nodde and atrioventricular nodes that together form what is referred to as the cardiac conduction system. Additionally, it would be unjust to fail in mentioning that the sinoatrial node is the natural pacemaker of the human heart which is quite essential to the organism. It is thus easy to deduce from the functions of the system that sympathetic nervous system definition relies on the functions and modes of actions of the nervous system.

The nervous system is what determines the reactions of the body to any changes in the environment. Sympathetic nervous system is more responsible for the reactions that come from unexpected changes in the body and the environment. These changes are usually the fight and flight responses and includes those involuntary activities mentioned above. Sympathetic nervous system definition must therefore reflect these activities if it has to be complete and true to the letter. Most people do not know the human anatomy and physiology and may not realize how important sympathetic nervous system is in life. However, this should not be misconstrued to indicate the superiority of the system in the entire nervous system.

The Parasympathetic Nervous System

The sympathetic and parasympathetic nervous system is a division of the human autonomic nervous system (ANS). Autonomic nervous system innervates the smooth muscle and glands and cardiac muscle and regulates the automatic reflexes and autonomic activities. The function of the ANS is to prepare the body for stress and recover the body from stress. This is where the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) stems from. SNS and PSNS are anatomically separate and different from one another. These 2 divisions antagonize one another by working against one another. The sympathetic nervous system acts as our fight or flight and parasympathetic nervous system function while on rest or digest action. The sympathetic nervous system connects the internal organs to the brain via the spinal nerve. When stimulated, these nerves provides essential control of many tissues by increasing heart rate, dilating the pupil, inhibiting digestion, nasal secretions and production of saliva. It inhibits liver, kidneys and gall bladder and dilates the bronchioles.

 

It also stimulates sweating. The parasympathetic nervous system is composed of 4 cranial nerves that originate from the brainstem. The PNS activity begins in the head to the sacral region this reason why this is called activity that is called cranio-sacral in nature while the SNS is thoraco-lumbar in nature. The most involved nerve in a PNS activity is the vagus nerve. It works by transmitting information between the posterior hypothalamus, the brainstem of the central nervous system and vital organs as well as the glands. Sympathetic nervous system does the fight and flight functions, while the parasympathetic nervous system performs the rest and digests response. PNS works by antagonizing the action of SNS by lowering heart rate, decreasing blood pressure, constricting pupils and increasing intestinal motility. It increases the release of endorphins a hormone that is called “feel good” so we can recover from the actions from sympathetic nervous system stimulation. 

While both of these 2 ANS divisions work in an opposite manner. Take note that both activities take place in the same organs. This is called dual innervations wherein they work by complementing each other through innervating the exact same organs. An example of this action is presented in cases of exposure to stress. When you are stressed, your heart rate increases, the pupils get dilated and so on. The SNS gets activated and as you recover from stress, the PNS will take control as it slows down the heart rate, contracts the pupil, and stimulates the liver, bladder and kidneys and so on. 

Knowing what happens in our sympathetic and parasympathetic nervous system during an activity gives us a clear idea how our reaction to things is being manifested and acted upon by our own physiologic functions. In a way, somehow, we would understand what is happening inside our body. The moment we reacted to situations and the moment we recover from that event are clearly explained in this occurrence. The body is so designed to respond to different stimulus as well as cope up so it can recover from any danger that could possibly happen should the situation become worse.