By now we know that our nerve cells send the signals from the organs to the brain. The brain then does all the thinking and it passes the process information back to the organs. So we can say that brain is the main coordinating organ in our body. But what about reflex actions, they are coordinated by spinal cord. So we can say that brain and spinal cord both are very crucial for our nervous system. These brain and spinal cord are one of the most delicate organs of our body and so they are covered by cranial box and vertebral column respectively for the protection. Brain and spinal cord together form the central nervous system or CNS while the remaining part of the nervous system is called peripheral nervous system or PNS. Now this PNS consists of the nerve from brain that is the cranial nerves and nerve from spinal cord that is the spinal nerves and it then connect these cranial and spinal nerves to all the parts of our body. So it can be said that the main function of PNS is to connect the CNS to all the sensory organs. Now let’s see the structure of the brain. The outermost part of the brain is called cranium or skull. It is a bony box which protects the brain from external injuries. It has a fluid in it which also helps in shock absorption of brain. Our brain has three main parts; forebrain, midbrain and hindbrain. So now let’s discuss about all these parts one by one. As the name suggests fore brain is the forward most part of the brain. It is the largest part which consists of hypothalamus and cerebrum. It is in this part that the main thinking of the brain is done. Forebrain receives sensory impulses from different sensory receptors and then process them and send them back. It has separate areas for receiving different sensory impulses like hearing, smelling, seeing etc. It also takes care of more complex sensations in nature. For example it tells us about the sensations of hunger. It tells us when to start or stop eating. Fore brain also has areas where the sensory information from all the receptors is put together and is interpreted. This information is then transferred to the motor area of the forebrain where the main thinking is done. Now we’ll discuss about the midbrain. It is the middle part of the brain. It is involved in activities like sleep, wakefulness, pain, perception etc. It is also involved in changing the size of the pupil when we stand in bright light. Hind brain is the last part of the brain. As you can see in the diagram it consists of three parts; Pons, medulla and cerebellum. It controls the wider functions of our body like breathing, digestion, controlling heartbeat, blood pressur, etc. All these actions like breathing, digestion, maintaining heartbeat, maintaining blood pressure, which are not in control of our will are called involuntary actions; while all the actions like running, speaking, walking which are in control of our will are called voluntary actions. So now can we say that the involuntary actions are also the reflex actions. Of course we can. Now the question arises that how do these nerve tissue cause these actions or movements? We’ve talked about that the brain sends the processed information to the nerve cells which in turn sends them to the muscle tissues in our body which caused these movements. But the question how do these muscle cells move is still unanswered. The notion is that these muscles move because of the change in their shape and this change in their shape is cause by a special protein in them. When these proteins receive electrical impulses from nerves cells, they change their shape and arrangement in the cells and this change in shape and arrangement of proteins present in muscle cells is responsible for muscular movement. Now let’s have a quick recap. We just learn that central nervous system consists of the brain and spinal cord. while peripheral nervous system consists of the nerves cells outside the brain and the spinal cord. We saw that the brain is made up of three main parts; forebrain midbrain and hindbrain. Fore brain controls all the voluntary activities of our body, while midbrain and hindbrain controls all the involuntary or the reflex actions of one body. Next we studied how nervous tissue cause muscular movements. When proteins in the muscle receives electrical impulses from nerves they change their shape and arrangement in the cells as a result the muscles move.