Sympathetic And Parasympathetic Nervous System example essay topic

The Structure & function of the Autonomic Nervous System Introduction: The organs of our body are controlled by many systems in order to function correctly and efficiently in order to survive within the environment we live in. These include the heart, stomach and intestines and other vital organs and body systems. All of the systems in our body are regulated by a part of the nervous system called the autonomic nervous system (ANS). The ANS is part of the peripheral nervous system and it controls many organs and muscles within the body. Rather bizarrely we are unable to determine or feel its presence in our bodies as it is working involuntary, as a reflexive manner. A common example of this involuntary action is best understood when you think about your circulatory system.

We do not notice when blood vessels change size or when our heart beats faster, unless of course the change is shockingly dramatic. But otherwise it's an internal change to your bodies internal environment that you do not have any mental or physical control upon. However, it is known that, some people can train themselves to control some functions of the ANS such as heart rate or blood pressure. Deep sea diving with out the use of underwater breathing equipment, is an efficient use for this technique as it allows you to reduce your heart rate. This then allows the bodies oxygen consumption rate to be reduced, resulting in an overall increase in the ability to hold your breath to dive deeper depths (up to 60 ft has been recorded).

But don't be mislead, this is not an ability that anyone could simply undertake on the family holiday. It requires strict self-control and powerful meditational skills. The Sympathetic and parasympathetic Nervous System: The ANS is divided into two parts, the Sympathetic Nervous System and the Parasympathetic Nervous System. These have opposite (antagonistic) effects on the organs, which they supply. Generally, the sympathetic system prepares the body for stressful / emergency situations and the Para-sympathetic system reduces stress. The responses of the ANS are co-ordinated by two subconscious brain regions, the medulla oblong ata and the hypothalamus.

The sympathetic nervous system plays a major role in our reactions and responses to the environment surrounding us, these are important when making responsive life saving decisions. This particular subsystem is commonly known as a flight of fight response, a quick example of this is your ability to run away in the sight of life endangerment. Take notice of figure. 1 in the illustrated diagram that the sympathetic nervous system originates in the spinal cord. Specifically, the cell bodies of the first neuron are located in the thoracic and lumbar spinal cord.

Axons from these neurons project to a chain of ganglia located near the spinal cord. In most cases, this neuron makes a synapse with another post ganglionic neuron in the ganglion. A few pre ganglionic neurons go to other ganglia outside of the sympathetic chain and synapse there. The post ganglionic neuron then projects to the 'target' - either a muscle or a gland. Two more facts about the sympathetic nervous system are the synapse in the sympathetic ganglion, uses acetylcholine as a neurotransmitter.

The synapse of the post ganglionic neuron with the target organ uses the neurotransmitter called norepinephrine. There is one exception to this, the sympathetic post ganglionic neuron that terminates on the sweat glands uses acetylcholine. The Parasympathetic nervous system is an antagonist to the sympathetic nervous system. Its primary function is to give you the ability to rest and relax, in times when you are tired or stressed. The parasympathetic nervous system works to save energy and allow your blood pressure to also decrease. Your heartbeat reduces becoming much slower, and digestion can start.

Notice again in figure 1 on the left, that the cell bodies of the parasympathetic nervous system are located in the spinal cord (sacral region) and in the medulla. In the medulla, the cranial nerves, VII, IX and X form the pre ganglionic parasympathetic fibres. The pre ganglionic fibre from the medulla or spinal cord projects to ganglia very close to the target organ and makes a synapse. This synapse uses the neurotransmitter called acetylcholine. From this ganglion, the post ganglionic neuron projects to the target organ and uses acetylcholine again at its terminal.

Figure. 1: Autonomic nervous system Para-sympathetic and sympathetic differences: The sympathetic and parasympathetic nervous system generally have opposing effects on organs they supply, and this enables the body to make rapid and precise adjustments of involuntary activities in order to maintain a steady state. An example is an increase in heart rate due to the release of noradrenalin by sympathetic neurones, this is then compensated for by, the release of acetylcholine by parasympathetic neurones. This prevents heart rate from increasing beyond its working capabilities and allows it to reduce and settle back to its resting state. The effects of sympathetic and parasympathetic stimulation are tabulated below in figure. 2.

Notice that the effects are generally in opposition to each other, in relation to each organ affected by a particular reflex. Feature Sympathetic Parasympathetic Origin of Neurones Emerge from cranial, thoracic and lumbar regions of CNS Emerge from cranial and sacral regions of CNS Position of Ganglion Close to spinal cord Close to effector Length of Fibres Short pre ganglionic fibres Long post ganglionic fibres Long pre ganglionic fibres Short post ganglionic fibres Number of Fibres Numerous post ganglionic fibres Few post ganglionic fibres Distribution of Fibres Preganglionic fibres cover a wide area Preganglionic fibres cover a restricted region Area of Influence Effects diffuse Effects localised Transmitter Substance Noradrenaline released at effector Acetylcholine released at effector General Effects Increases metabolic level e.g. blood sugar Increases metabolic rate Increases rhythmic activities e.g. heart rate Raises sensory awareness Decreases metabolite levels, e.g. blood sugarNoneDecreases rhythmic activities, e.g. heart rate Restores sensory awareness to normal levels Overall Effect Excitatory homeostatic effect Inhibitory homeostatic effect Conditions when Active Dominating during danger, stress and activity, controls reactions to stress Dominant during rest Controls routine body activities Figure 2: Tabulated difference between the Para / Sympathetic nervous systems The significance: If we need to evaluate any evidence about the importance of the autonomic nervous system in life, we need only witness the disabling nature of autonomic disorders. Patients with severe autonomic failure are unable to stand but for few seconds, before syncope ensue due to hypotension. The autonomic nervous system modulates the function of virtually all organ systems. These patients also suffer a variety of other symptoms. In most cases of autonomic failure is very noticeable the actions are progressively slow due to neuro degenerative processes or systemic illnesses.

In its severest forms, previously normal individuals can develop complete autonomic failure and be bedridden within a few days. Without this highly evolved and advance system, we would not be able to control and co-ordinate our bodies both internally and externally. The ability to breath, exercise and enjoy our lives, involving ourselves in the recreational activities we most enjoy, would become impossible to achieve and do. It is only when you think about the significance of this responsive system and appreciate just how important it actually is, to our survival. You will only begin to realise how much we actually take our every day-to-day functioning for granted. Listed

Bibliography

Books, - Biological Science 2: third edition - D.J. Taylor, N.P.O. Green, G.W. Stout- Life The Science of Biology: Seventh edition - Purves, Sada va, Organs, Heller Web, - Journal of Neurophysiology: web W, Gerber S, Orr-Urt reger A, Armstrong D, Lewis RA, Ou CN, Patrick J, Role L, De Bias i M, and Beau det AL. Megacystis, mydriasis, and ion channel defect in mice lacking the alpha 3 neuronal acetylcholine receptor. Proc Natl Acad Sci USA 96: 5746-5751, 1999- web web.