question_answer 73)

        What constitutes the central and peripheral nervous systems? How are the components of central nervous system protected?

Answer:

                    The central nervous system consists of the brain and the spinal cord (i) Brain It is the main coordinating centre in the body It is lodged in the brain box or cranium which protects it. It is covered by membranes called meanings, which also help to protect it. The space between the membranes and the brain is filled with a cerebrospinal fluid which protect the brain from mechanical shock. The brain is broadly divided into three regions fore-brain, mid-brain and hind-brain. (ii)Spinal cord It is a long cylindrical structure. It begins from the medulla oblongata and extends downwards. It is enclosed in a bony cage called Verebral column that protects it. It is also surrounded by meninges. It is concered with spinal reflex actions and conduction of nerve impulses to and from the brain. Peripheral Nervous System (PNS) It includes the following (i)Cranial nerves 12 pairs that emerge from the brain. (ii)Spinal nerves 31 pairs that arise from the spinal cord and spread throughout the body. (iii)Visceral nerves They are special kind of nerves mostly arise from the spinal cord and are connected to the internal organs of the body. They carry both sensory and motor neurons. The PNS works according to our will, i.e., it is related to voluntary acts.