Muscles And Nerves
The function of the muscles is to contract so that their two ends are drawn together, and a movement is thus produced which by various systems of levers can be converted into the particular form of motion required. For example, the contraction of the muscles of the calf draws the heel upward, and in this way causes the whole body to be elevated on the toes.
In order to bring about a muscular contraction the muscle must first be stimulated. The way in which the muscle is normally stimulated is through its nerve, which conducts the nerve impulses from the central nervous system to the muscle fibres. Arriving at the latter, the nerve impulses bring about the complex chemical changes upon which the contraction of the muscle depends. When the nerve impulses cease, the muscle relaxes again.
Brain And Nerves
The nerve system is collection of nervous tissues set apart as special apparatus for the reception and transmission of nerve-impulses. The apparatus consists of the brain, and the spinal cord which is attached to the brain. Many nerve trunks emerge from both and go to all parts of the body and eventually terminate in nerve-endings. The nerve-fibres are in connection with aggregations of nerve-tissue called nerve-ganglia. A ganglion is a small collection of cellbodies connected by means of nerve-fibres and dendtrites with other ganglia and with the central nervous system. The whole nervous system itself is made up of tiny microscopic elements called neurons.
The brain and the spinal cord constitute the central nervous system. The brain is placed in the cranial cavity. The spinal cord extends from the brain, runs along the vertebral canal of the vertebral bones or the spinal column. There are 31 pairs of spinal nerves.
The brain is the most complex and the largest mass of nervous tissues in the body. It is contained in the cranial cavity. It is made up of white and grey matter. It is divided into four principal parts, viz., the cerebrum, the cerebellum or ‘little brain,’ the pons varolii and the medulla oblongata.
The medulla oblongata is the seat of several important or vital centers. It contains the respiratory centers for regulating the functions of respiration ; the cardiac centers which control the rate and force of the heart’s action; the vasomotor center to regulate the size of the small arteries or blood vessels in any part of the body at any particular time, thus controlling the amount of blood furnished to that part; other centers, such as the vomiting centre, heat controlling centre etc. if the medulla is seriously injured, death will result immediately.
The cranial nerves, twelve in number on each side, arise from the base of the brain and medulla oblongata and pass out through openings in the base of the skull. They are (I) Olfactory (sensory); (2) Optic (sensory); (3) Oculomotor (motor); (4) trochlear (motor); (5) Trifacial or trigemina (mixed, but mainly sensory); (6) Abducens (motor) (7) Facial (motor); (8) Auditory (sensory); (9) Glosso pharyngeal (mixed); (10) Pneumogastric or vagus (mixed); (11) Spinal accessory (motor); (12) Hypoglossal (motor).
The olfactory is the special nerve of the sense of smell. The optic nerve is the special nerve of the sense of sight. The oculo-motor nerve supplies all the muscles of the eye except the superior oblique and external rectus. The trochlear nerve supplies only the superior oblique muscle of the eye. The trifacial is the largest of the cranial nerves. The ophthalmic, the superior maxillary and the inferior maxillary are the three branches of the trifacial nerve. The The abducens nerve supplies the external rectus muscle of the eye. The facial nerve is the motor nerve of all the muscles of expression in the face.
The auditory nerve is the special nerve of the sense of hearing. The glosso-pharyngeal nerve is distributed to the tongue and the pharynx being the nerve of sensation belonging to the mucous membrane of the pharynx, conveys motion to the muscles of the pharynx and is the special nerve of taste belonging to a part of the tongue.
The pneumogastric nerve has a more extensive distribution than any other cranial nerves. It passes through the neck and thorax to the upper part of the abdomen. It contains bother motor and sensory fibers. It supplies the organs of voice production and respiration with motor and sensory filaments and the pharynx, oesophagus, stomach and heart with motor fibres. (Cardiac inhibitory).
The spinal accessory nerve consists of two parts, one the spinal portion and the other the accessory portion of the tenth nerve. It is a motor nerve. It supplies certain muscles of the neck, and arises from the spinal cord. The hypoglossal nerve is the motor nerve belonging to the tongue.
It will be observed that of the 12 pairs of cranial nerves, four and a part of the fifth are distributed to the eye, viz., the optic, motor oculi, trochlear, abducens and the ophthalmic branch of the fifth. The ear has one special nerve, the auditory, and is sparingly supplied with motor and sensory fibres from other nerves. The nose also has one special nerve, the olfactory, and is more abundantly supplied than the ear with motor and sensory fibres from other nerves. The tongue has two special branch nerves of taste – the lingual, a branch of fifth, and the glossal, a branch of the ninth; it has also its own motor nerve, the hypoglossal.
It is difficult to answer what the nature of the nerve impulse is. The nerve-fibre serves as a conveyor of nerve impulses. The speed at which an impulse travels along an efferent nerve-fibre is about 140feet per second. An afferent impulse travels somewhat slower, 110 feet per second. Efferent nerves carry the nerve impulses from the nerve-cell to the nerve-endings, i.e., from the brain towards the skin. Those in which the impulses travel in the reverse direction from the skin towards the brain are called the afferent nerves. It is the afferent nerve that carries the sensation of pain from the finger to the brain when a scorpion stings the finger! It is the efferent nerve that carries the impulse from the brain towards the finger which makes us take the finger away from the scorpion. Everything is done in the fraction of a second. The afferent impulse goes to the spinal cord from the skin and from the spinal cord it is transmitted to the brain. The efferent impulse comes from the brain to the spinal cord and from the spinal cord it is transmitted to the skin. The spinal cord is thus the via media between the brain and the skin.
Other sets of nerves carry on the function of digestion, circulation, etc. They perform their work independently. You need not think about them at all. They go on with their work whether you are asleep or awake. These are the self-governing nerves that belong to the sympathetic nervous system. The sympathetic system sends motor impulses to the involuntary muscles, conveys sensations from the different organs, controls the vasomotor system, the heart’s action and secretion.
The brain is divided into two halves by a fissure or groove in the middle. The left side of the brain transmits messages to the right side of the body and vice versa. The main nerves of the central nervous system control all coluntary movements of the body. Through the play of these nerves we move our limbs, walk, run, jump etc. All the nerves are in direct communication with the sympathetic nervous system which controls the involuntary functions, such as digestion, circulation of blood, etc. The two nervous systems are inter-dependent. The sympathetic depends for its energy and efficient working on the central nervous system. The central nervous system is sustained and built up by the blood manufactured and circulated through the agency of the sympathetic. Lowering the vitality of the sympathetic system will react on the central nervous system.
The sympathetic system is made up of a chain of nerve fibres which run down each side of the spine. Just in front of it, there is a ganglion in each fibre. All these nerve fibres form the ‘solar-plexus’ which governs the functions of the digestive organs, the liver, kidneys, etc. If there is any disorder in the sympathetic system ganglia or the ‘solar-plexus’ you will suffer from torpidity of the liver. The kidneys will not perform their function efficiently. You will experience some congestion here, a pain or irritation there, a little swelling in the feet or the cheeks, a little burning in the stomach and so on.
The sympathetic and the para-sympathetic constitute the automatic system which is to some extent independent of the central nervous system. The action of the sympathetic fibres is antagonistic to the action of the fibres of the parasympathetic. The sympathetic nerves accelerate the heart’s action, while the para-sympathetic nerves accelerate the heart’s action, while the para-sympathetic system retards the action of the heart. The sympathetic chain is a system of a ganglia vertically arranged on both sides of the spinal column. The major part of the para-sympathetic system is made up by the vagus.
A Yogi can control the automatic nervous system. By suppressing all voluntary and involuntary actions he can bring the working of the human machine to a standstill. In the year 1926 under the auspices of the Bombay Medical Union, Deshbandhu demonstrated certain Yogic feats, such as the stopping of the radial and the temporal pulse on both sides at will. He stopped the beatings of the heart for a few seconds. Through the practice of Kechari Mudra and Pranayama, Yogis have buried themselves for days and even months.