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May 16, 2013

The Peripheral Nervous System



We make all movements, handle things, run, sit and kneel etc with the help of “peripheral nerves “. Dropping of a notebook from our hand and picking it up is the movement which involves a bundle of fibres, the peripheral nerves both sensory and motor type of peripheral nerves are the major functionaries in the system. One kind of peripheral nerve, the sensory nerves transmit information from our body (eyes, or other sense organ or part of the body) to our brain. On receiving that information, the other kind, our motor nerves, transmit information from our brain to the concerned muscles (telling the arms and the hand to pick up the notebook). Motor nerves are part of either the somatic or the autonomic nervous system, the two subdivisions of the peripheral nervous system.

The Somatic Nervous System: It is the system that controls reflexes which direct muscles and organs to actions such as picking up the notebook or looking back, are parts of the somatic nervous system. These nerves control the striped or striated muscles of the body. They appear as striped when seen under a microscope. Our movements are accomplished through the way our muscles are attached to our bones, our skin and the muscles. This is applicable to all movements, large ones like running and jumping and small ones like subtle changes in facial expression. Muscles work together, sometimes in antagonistic (opposing) pains.

For example, when we raise our forearm we contract our biceps muscle. The muscle antagonistic to that one, the triceps relaxes. In certain other movements other muscles work together in synergistic or cooperative ways. When we lift a bar bell, the biceps work together with finger muscles that maintain posture, and with leg muscles that either straighten or bend our knees. Some muscles that work as synergistic in one movement will act as antagonistic ones in another. Different patterns of muscular contractions will produce different types of movements and all these patterns are coordinated in the nervous system.

How do we hold our head while lifting a heavy weight? ‘What about muscles controlling facial express ions, arm, finger, leg and back movements and other body exercises? The answer is that all these movements are controlled by somatic motor neurons located in the spinal cord and in the brain stem. The motor nerves in the brain stem (the cranial nerves, we may say) control muscles in the face, the neck and the head, while those in the spinal cord control muscles in the rest of the body. Each motor neuron contacts only one muscle but each muscle receives contacts from many different motor neurons. The strength of a contraction depends on two factors, the number of active motor neurons and the frequency of the impulses they send. These, impulses are sent to synaptic transmission and the neurotransmitter involved in such muscles movements in acetylcholine (Ach).

The Autonomy Nervous System: Side by side with lifting a heavy barbell our body functions in many other ways too. Our heart is beating, we are breathing and our digestive system is active. These activities are being conducted by two other kinds of muscles the cardiac (or heart) muscles and the smooth muscles that control the throat, the viscera (internal organs such as stomach and intestines) the diaphragm (which controls breathing), and other organs. The endocrine and the nervous system both control the cardiac and the smooth muscles. How these functions, of involuntary and life - support nature are controlled by the autonomic nervous system? This system has Iwo parts - the sympathetic and the parasympathetic divisions which operate quite differently and have often op1osing effects in many parts of the body.

The autonomic nervous system’s smooth muscles of viscera and heart never relax totally but always generate sonic contractions. The striped muscles of the somatic system contract only when they receive the neural messages. This is why heart muscles can continue to pulsate even after it has been removed from the body. To relax heart and visceral muscles, then, the muscles themselves must be inhibited. The sympathetic and the parasympathetic divisions work on concert in the autonomic system. One division stimulates a muscle and the other inhibits it. Both systems change roles and arc capable of triggering contraction or relaxation depending on the target organ.

John S Lam is an IT Instructor at Examskey. He is VCP510 Certified Professional. Take the benefit of our 200-120 material and assure your success. Check out our free demo of all certifications Exams.

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