Originally Posted by shakeel ghori

Q:3-Write down the structure and function of CNS and PNS? (20 Marks)


1--Introduction..
Nervous system is consist of interconnected organ system that co-ordinates actions. It is responsible for controlling behaviour and adjusting organisms with their respective environments. Since humans at their most basic level are biological beings, many psychologists believe that the true knowledge of human behaviour cannot be had without having full understanding of nervous system. In view of this fact, the primary concern of almost every psychologist is same: to study the basis of brain and other parts of nervous system.

2--Structure and function of nervous system..

For the sake of better understanding the whole nervous system has been divided into three parts: neurons, central nervous system, and the peripheral nervous system. Although they are interconnected with each other--and perhaps different names of the same system-- for exclusively elaborating their functions and structure they are separately mentioned:

@Neurons.
Neurons are the fundamental elements of nervous system. They are the communicator of different messages in body. Basically, they are cells but the function which they play is essentially different from other cells. They have an ability of communicating with each other. As mentioned, they carry electrochemical messages within body; so in simple, we can say that they connect the all organs of body with brain. Each neuron is made up of axon, dendrite and cell body. The axon is a rod like structure through which electrical messages pass. The dendrites are the first site of receiving message from the neighbouring neuron which conveys it to the axon. the cell body is the part which plays essential role in keeping neurons alive: metabolism, protection from pathogenic invasion and so forth.
As soon as any change occurs in any part of the body, neurons carry signals to the brain which subsequently sends messages for appropriate response. However, one thing should be noted that they alone are not responsible for communication within body. Endocrine system which releases harmones has also the same function of carrying messages from body to brain and vice versa..

Nervous system has been divided into two parts: central nervous system and peripheral nervous system.

@Central nervous system.
Central nervous system consists of brain and spinal cord. We shall disucss them separately.

Brain.
Brain is the command centre of entire body. As far as its basic structure and functions are concerned, it would not be wrong to say that nothing may be more miraculous in this world than brain. It consists of billions of neurons. Although, it has happened very recently that the scientists are able to understand the basic structure and chemistry of brain through modern equipments, the functions brain plays in our life are in our knowledge for a long time. It helps the body to respond to the information it receives from senses and other parts of body. On the basis of its functions brain is divided into several parts each of which plays a specific role. For example, hypothalamus regulates hunger and thirst. At the same time, it also helps body to maintain its temperature within suitable limits. Limbic system, another part of brain, is responsible for various emotional responses and consolidation of memory. In short, every specific area of brain has a particular function in regulating our behaviour. For elaborating more the role of brain in our life we can take an example. When a light of specific colour strikes with our eye, we cannot see it. Thereafter it reaches to our retina, we still cannot see it. Light passes through nerve cells, and even at that stage we don't see the light. It is only when it reaches to the brain which interprets it and gives us concious signal, that we are able to see it. Our every move, action, emotion, thought, sensation, perception depends on the co-ordination of brain.

Spinal cord.
Second part of central nervous system is spinal cord. It is a bundle of neurons that stems (leaves) from brain and runs down the length of the back. The primary function of spinal cord is that it serves as a channel between brain and the rest of the body. It connects all the body parts with brain except the parts above the neck. Messages from various organs first reach to the spinal cord which then transport those messages to the brain. The brain decides a particular response and then sends that signal to the concerned part of the body through spinal cord. The proof of this fact can be ascertained when in certain accidents spinal cord gets injured which results in the inactivity of lower part of the body to function (to move). It happens simply because owing to injury spinal cord becomes unable to serve as a connector between brain and specific body part.
However, the spinal cord is not just a communication channel. It also controls some simple behaviours on its own, without any help from the brain. In such cases, an immediate response is required so it does act on its own without taking any help from brain. For example, when we unintentionally touch a hot object, the sudden act of pulling back the hand is govern by spinal cord. Such responses are known reflex actions. While concluding the discussion about spinal cord, it is appropriate to keep in mind that after brain it is most important part of nervous system.

@Peripheral nervous system.
The peripheral nervous system consists of all the parts of nervous system other than brain and spinal cord. Peripheral nervous system connects the sense organs, muscles, glands and other organs with central nervous system (i.e with brain and spinal cord). The major role in peripheral system is of neurons which communicates signals to the spinal cord, or in few instances directly to the brain. These neurons are of two kinds. Those which sends messages from body to brain are sensory neurons(also called afferent). Those neurons which carry commands of brain to specific body parts are motor neurons (efferent). The peripheral nervous system is divided into somatic and autonomic divisions. somatic division involves in the control of voluntary movements such as muscle contraction, eye movements, and so forth. The autonomic division controls the organs which function involuntary without our awareness and are responsible to keep us alive such as heart, lungs, kidneys, blood vessels, glands and other likewise organs. The autonmic system is furthr divided into sympathetic and parasympathetic.
For making a distinguish between the two, it is adequate if we see that how the autonomic division of peripheral nervous system works in emergencies. When we encounter any threat or emergency situation, the very first response is of sympthetic division of autonomic nervous system. Its activation increases the heart beat, expands vessels, accelerates blood flow, enlarges the size of pupil (thus makes us more watchful) etc. These are the changes whcih are brought about by the activation of sympathetic division. These changes help us a lot to deal with emergency situations. When the negative situation passes away, the parasympthetic division starts its function. It sends signals to the excited body organs to come into their original state. From the last statement we can conclude that the parasympathetic division of autonomic division remains in play when the situations are ordinary. It overseas the various body fucntions which comes under its purview. Only in the emergencies the sympathetic division comes into play to enable us to deal with the emergency situation.

3--Conclusion.
From the above discussion, the role of nervous system in regulating our various body functions is almost clear. It does not only control those body functions which keep us alive, but also responsible for our emotions, thoughts, actions, hopes and aspirations. The branch of science which studies the basic elements of nervous system and their connection with human behaviour is known as neuroscience. With the help of modern equipment, the psychologist are now more able to understand the basic structure of nervous system and thus have produced many drugs to cure various psychological disorders having biological causes. The neuroscientists are making rapid progress in understandig human brain. But we know that much is still remaining to uncover, for the human brain is most complex and astonishing object of the world.

All respected members are requested to assess my attempt.