DESCRIBE THE STRUCTURE OF THE ANS SYSTEM AND DISCUSS THE EFFECTS IT HAS SHOWN TO HAVE ON PHSIOLOGICAL AND BEHAVIOURAL FUNCTIONS?
The ANS is a purely motor system, meaning that it transmits impulses out of the CNS to various motor or effect or organs of the body. These include the smooth muscle of the blood vessels and the gastro intestinal system, heart muscle, and several glands such as the pancreas, the adrenal medulla and the salivary glands. The ANS first function is to regulate internal bodily processes. It does this by sending information to and from the CNS. Although the ANS is very important it is the CNS that is in control.
The ANS operates as an independent or autonomous control system. Although we learn as we mature in age to control our autonomic functions, such as urination and defecation, these would occur in the absence of control of them. These bodily processes and many others are controlled by the ANS without requiring conscious effort. To enable the ANS to perform its functions it has two branches. The sympathetic branch that produces a pattern of arousal in the body, with heart rate and blood pressure increased, adrenaline released and from the adrenal gland. The parasympathetic branch run to the same organs, but their activation leads to opposite effects. Heart rate and blood pressure are reduced, adrenaline secretion falls, and digestive activity increases.
The sympathetic branch or ganglia of neurons comprising the sympathetic branch are interconnected so that they form a long chain on each side of the spinal cord. The sympathetic branch originates in the two middle portions of the spinal cord; the interconnections between the neurons allow the sympathetic branch to act as a unit. It is important because the sympathetic branch prepares the body to extend energy. As well as the effects show in the diagram below
It also increases blood pressure, releases sugar from the liver into the blood and increases the blood flow to the muscles used in physical action. Further, it tells the endocrine system to release hormones into the bloodstream to strengthen these responses.
Walter Cannon 1972 suggested that the major function of the sympathetic branch was to mobilise the body of an emergency, he called this the fight – or –flight response since physiological changes that occur are designed to help us defend ourselves or flee from a threatening situation.
The parasympathetic ganglia are much more widely distributed than the sympathetic branch ganglia. Drawn in the diagram previously, the nerve fibres originate at either end of the spinal cord, near the organs they affect. However, because the fibres are less interconnected than those of the sympathetic branch, the parasympathetic branch acts less as a unit and more on individual organs. The diagram previously shows that the parasympathetic branch operates in the opposite direction to the sympathetic branch and stimulates processes that serve to restore or conserve energy. The parasympathetic also carries out the bodies “maintenance needs”. As well as digestion it provides for the exclusion of waste products and directs tissue repairs. Parasympathetic activity is mostly in the use when we are relaxed or inactive. There is a balance between the two branches of the ANS; therefore our internal environment is kept balanced.
One of the glands affected by the ANS is the adrenal medulla. When stimulated, the medulla releases two closely related hormones into the bloodstream – adrenaline and nor adrenaline. These are carried around the body where they act as sympathomimetics, meaning their actions are similar to the sympathetic branch of the ANS. The adrenaline and the nor adrenaline can be seen as part of the ANS, as nor adrenaline is the synaptic transmitter at the synapses between the ANS sympathetic neurons and their target structures.
A key feature of the ANS is that this regulation of our internal physiological systems, or metabolism is largely automatic and proceeds outside our conscious awareness. The ANS also has an important role in the form of homeostasis that is the maintenance of a constant internal environment. E.g. the control of our body temperature.