Sympathetic Nervous System

nerve-cell-145909_1280The sympathetic nervous system is the part of the autonomic nervous system which also includes parasympathetic nervous system. It is the involuntary portion of the nervous system which controls our body in a stressful and unpredictable situations. It will also affect any involuntary act in your body such as digestion, heart rate, breathing, etc. If you’ve ever been in a situation where you started sweating, your heart pumped like crazy or you’ve had some difficulty in breathing, it is due to the sympathetic nervous system. It controls how you respond in emergency situations. It controls the main reaction which is called fight-or-flight which expresses in an event which can be crucial and life-threatening.

What Is The Sympathetic Nervous System?

The sympathetic nervous system acts as a part of an autonomic nervous system which is the part of the central nervous system or the brain itself. The central nervous system has a second part which is called somatic nervous system. It controls the voluntary actions such as walking, talking, and also a reflex arcs needed for the reflex impulse to get to the brain and back to the reacting muscle or organ. The sympathetic nervous system is the part capable of making you stronger than you think you are and making you do the unthinkable. It controls the actions you cannot control. It does so by secreting specific hormones that act on the receptors and on the rest of the body.

The Structure Of The Sympathetic Nervous System

There are a lot of connections with the peripheral nervous system through ganglia, where it joins the peripheral sympathetic neurons. The main cell in the nervous system is called neuron. It has two types of the nerve cells. The first one is called the preganglionic neuron and the second one is called postganglionic neurons. They differ by their structure and function. Preganglionic neurons go from the central nervous system or the spinal cord to the ganglia and it makes a connection with the post neurons. It connects by a chemical synapse which has the ability to respond to a stimulus or the impulse. As a response, noradrenaline is being secreted. It binds to the adrenergic receptors and results in effects which you can see in a fight-or-flight reaction.

There are two differences where the postganglionic neurons act differently in sweat glands and chromaffin cells in the adrenal gland. The sweat glands have the postganglionic neurons which release the acetylcholine. It activates different receptors called muscarinic receptors which cause the sweat secretion. These receptors are absent in the sole area of the feet, palms of hands. The adrenal gland has the chromaffin cells in its medulla. They act as postganglionic neurons which connect with the preganglionic neurons and release epinephrine and norepinephrine.

Hormones Associated With Sympathetic Nervous System

There are two hormones which are released as an impulse reaction. They are epinephrine and norepinephrine. When there is a sudden activation of the sympathetic nervous system such as in a stressful situation where it needs to act quickly, the hormone norepinephrine is being secreted. When this happens, your body will be awake and prepared to respond to any of the outside influences. It the situation is not a sudden one, but a chronical or a prolonged one, the nervous system acts in a way where it releases the second hormone, epinephrine. It acts as an amplifier and an additional hormone which will adjust the body’s response.

The Action Of The Sympathetic Nervous System

When you’re in such situation where your body acts on its own, without your will and knowledge, know that your sympathetic nervous system is working. Here are some of the effects:

  • Increased Heart Rate. When the sympathetic nervous system gets activated, it secretes the hormones which bind to the receptors and make your heart pump faster which will increase the oxygen delivery to your brain and skeletomuscular system which are main in fight-or-flight action.
  • High Glucose Level. There are other hormones which are being secreted in stressful situations such as cortisol, ACTH, growth hormone and T3, T4 besides adrenaline (noradrenaline) and norepinephrine. They act at a cell membrane level and release the glucose from the cells, giving the brain and the muscles the food for the stressful situations.
  • Tachypnea. It is the term for a high breathing rate. Your airways dilate for the extra oxygen to get inside which will serve for your body at a time.
  • Widen Pupils. This is the reaction of the eye accommodation where your pupils widen for you to be more cautious. Your eye will have a better sight at a dark place and you will be prepared for any actions.
  • Slow Down The Digestive System. Although the sympathetic nervous system acts as a booster for the rest of the body, it slows down the digestive tract making it more prepare for the sudden events. When your body stops with digestion process, it will have enough blood supply to the brain and the muscles. It redirects the energy for the vital organs which react in this situation.

When the stressful and alarming situation calms down, your body will function again at a slower pace, where the parasympathetic nervous system will take some of the lead. You heart rate will slow down as well as your breathing. Your digestive system will work again at a normal frequency.