Parasympathetic and Sympathetic Nervous Systems

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Table of Contents

Action Potential
Functions of SNS
The Functions of PNS
CV System
Definition of terms
Physiological effects of Angiotensin II
List of Structures that Air passes through to alveoli

Action Potential

Action potential is simply a communication function in the nervous system. It takes across ion charged plasma membranes and is characterised by very fast reversals of voltage exchange. This is possible by the presence of voltage gated ionic channels that are found along the axon hence enable conduction of the action potential. It can be explained in five phases as of resting potential, threshold, rising phase, falling phase and the recovery phase. The resting potential phase is characterised by small movements of K+ ions in and out in order to maintain the membrane potential constant for safeguarding the cell. In this phase, the neuron is said to be at the rest. Threshold potential is signaled by the arrival of Na+ ions as they enter the neuron hence depolarising the membrane and, at the same time, increasing negativity.

If the stimulus causes depolarisation to reach the threshold potential, more Na+ ions quickly are allowed to pass by the sodium channels hence this triggers voltage change of the membrane resulting in positive values. This signals the peak of the action potential where the sodium channels start to close and potassium channels open hence letting positive charges leave the cell. This leads to the membrane potential to revert to its original resting potential state. At this state, the K+ channels are fully opened and activated resulting in beyond depolarisation of the resting membrane. High levels of K+ ions leave the cell and this causes closure of the potassium channels in order to restore the membranes resting potential. The steady state is achieved by normal opening of the Potassium channels hence the return to the membrane resting state.

Functions of SNS

The Sympathetic Nervous System originates from the spinal column and extends towards the middle parts of the spinal cord.

It is traceable from the thoracic section to the third lumber section. It belongs to the autonomic nervous system whose primary function is monitoring and regulation.

The SNS and PNS together form the Autonomic Nervous system. The biggest function of the SNS is reflected from this background although its major work is in preparation for fight-flight response. It is responsible for up and down sympathetic chains that aid in homeostatic mechanisms regulation in living organisms. The SNS is meant to prepare the body for stressful situations which require regulated and well maintained pH and temperature. In its criteria of functions, it works to counteract the parasympathetic nervous system. The SNS innervates a high number of organs in order to effectively perform its regulatory functions.

It is assigned the role of control of internal body organs like the heart, lungs, eyes, blood vessels, sweat glands, digestive system, kidney as well as others. In this process, the release of acetylcholine and noradrenaline serve as the most important processes for the SNS to be effective. The messaging in SNS is bidirectional with the presence of both efferent and afferent messages which help in speedy functions needed for this preparation of body organs like in the case of fight or flight response. In essence, the SNS is associated with accelerated heart rate, dilation of bronchial and tracheal systems, dilation of pupils stimulation of glycogenolysis as well as vaso-constriction of the blood vessels, increased blood pressure as well as other involuntary functions in the body. This list is long and these regulation mechanisms are triggered by the release of noradrenaline. This results in sensations of cold, heat or pain and hence helps the body in protection against any adversary or weather vagaries. The SNS works together with systems in the nervous system and therefore coordination with networks like sino-atrial nodes and atrio-ventricular nodes contributes to the overall picture of its functions.

The Functions of PNS

This nervous system works together with the sympathetic nervous system but in the opposite directions. Where SNS raises the blood pressure, PNS lowers it, acceleration of her rate by SNS, PNS decelerates the rate. The most important function of the PNS helps in reverting the body organs to their normal levels after the fight-flight response effects from SNS. The SNS regulates automatic reflexes as well as autonomic activities through innervating the body muscles like cardiac muscles. It consists of four cranial nerves that originate from the brainstem where all its activities are initiated up to the sacral region. The most useful nerve is the vagus nerve which functions in resting digestion after the SNS activity.

CV System

Right atrium, tricuspid or right atrio-ventricular valve Right ventricle, lungs, pulmonary artery, pulmonary semilunar valve, Pulmonary vein, heart, left atrium, Bicuspid or Mitral valve, left ventricle, Aortic semilunar valve, aorta, arteries, body, capillaries, veins, Venacava.

Definition of terms

Filtration: It takes place in the glomerulus and involves blood pressure forcing plasma, dissolved substances and small proteins out of the glomeruli into the Bowmans capsule which is now referred to as renal filtrate. The high pressure of the blood results in this process.
Reabsorption- It is the process that follows after filtration. By active transport using ATP energy, useful materials are reabsorbed back through renal tubules and they include glucose, amino acids, vitamins and positive ions. Other negative ions like chloride would be absorbed through passive transport to balance the positive ions. Water is reabsorbed through Osmosis and this happens in the proximal Convoluted Tubule section. This process allows the regulation of glucose levels and inorganic ions in the blood hence the kidneys role of homeostasis is achieved.
Secretion- It is a process of active secretion of waste products, ammonia, creatinine and other metabolic products from the body are eliminated to the collecting duct as urine. In the process, Hydrogen ions are secreted into the tubule cells in order to regulate the body blood pH.

Simple Diagrams of Negative feedback Mechanism of Up regulation of CO and TPR.

Simple diagram of feedback mechanism for ADH.

Physiological effects of Angiotensin II

Angiotensin II is a hormone effector of the renin-angiotensin system. Its most visible and quick physiological effects include vasoconstriction and blood pressure regulation. It is also affiliated to endothelial dysfunction, atherosclerosis, inflammation as well as heart failure. Its effects depend on whether it is chronic or acute.

List of Structures that Air passes through to alveoli

Nose, nasal cavity, mouth cavity, the pharynx, trachea, epiglottis, the Larynx, Bronchi, bronchioles and alveoli.

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