An introduction to body and mind
The human body – even when a mere seven weeks after conception is a highly complex machine, an apparatus of intricate, vital processes take place. But despite this complexity its mechanism function with inimitable efficiency and precision, and its basic structure is relatively unaccomplished.
The interaction of body and mind
While our knowledge of how the body and the mind work mechanically is reasonably advanced, the way in which they interact to produce “the-person” remains an unsolved puzzle. That the two are not separate and are related to obvious from what we know now of the psychosomatic diseases. These are psychological disorders such as hypertension and ulcers that are, in part, caused by psychological factors. We are also aware that attitudes of mind affect the body’s susceptibility to attack by diseases. But we are far from unraveling the extent and complexity of the relationship of body and mind – indeed almost all current research points to the fact that it would seem impossible to draw a line clearly between the two. Too little is known for the way in which they relate to be controlled or influenced with any degree of success.
What is now better understood is the way in which the brain controls the body and how changes in body function are achieved to maintain optimum working efficiency. Two main systems are involved. The first of these consists of nerve pathways carrying controlling impulses from the brain to the organs themselves. This type of control includes the regulation of breathing and heart rate. Centers in the brain constantly monitor the body’s performance and alter breathing and heart rates accordingly.
The second great system, the endocrine system, is chemical and makes use of the bloodstream. The pituitary gland at the base of the brain is its coordinator and also provides the link between it and the brain. In response either to impulses from the brain or to changes in body chemistry, it secretes hormones into the bloodstream. The hormones flow around the body and cause changes in its organs. Many of these changes, such as the control of urine secretion, the regulation of digestion and metabolism, the secretion by the adrenal gland of hormones to combat stress, are important in maintaining life.
The Nervous System
The nervous system is the circuit that brings our bodies alive. It allows us to perceive the world outside and monitor the world within. Through its efficiency we can respond and react to changes in the environment around us by moving our muscles and coordinating the actions of our various organs. Without it survival would be impossible.
The structure of the nervous system
The nervous system can be thought of as a number of separate but integrated sections that monitor the environment and instigate and coordinate the bodies multiple activities. The central nervous system (CNS) consists of the brain and spinal cord. Connected to it and running throughout the body is the peripheral nervous system which has two main parts – the somatic or voluntary nervous system and the autonomic or involuntary nervous system which deals with the unconscious control of the human organs. The somatic is related largely with the awareness of sensation and the voluntary control of muscle activity. Information is fed into it through the sensory nerves from the eyes and ears, taste buds, balance organs and the millions of contact, temperature, pressure and pain receptors in the skin which together make up the sense of touch. There are also receptors for sensing the degree of tension in muscles and tendons and for monitoring blood pressure and the levels of oxygen, glucose and carbon dioxide in the blood. Motor nerves, originating in the CNS, carry information to the muscles and in the way initiate movement.
The cells or neurons that make up the nervous system consist of a cell body, which contains the nucleus, and a long tail or extension called the axon. On the cell body at the end of the axon are short branches called dendrites. Contact between nerve cells, from the axon of one to the cell body of the next, is established via these dendrites but takes places across a small gap called a synapse. The nerves of the peripheral system consist mainly of axons that run the whole length of the nerve, while those of the CNS consist mainly of cell bodies with short tracts or bundles of axons. Where cell bodies occur outside the CNS, as with sensory and automatic nerves, they are collected together in groups called ganglia.
How nerves send their messages
Although nerves can be thought of as wires of telegraph cables carrying messages in the form of bursts of electricity, in fact a nerve impulse is more complicated than a surge of electrons traveling along a copper wire. The transmission of an impulse through a living cell involves the movement of electricity charged particles – ions – across, not along, a membrane, in this case the wall of the axon.
At rest a nerve cell is polarized. In other words the outside of its membrane bears a different electrical charge from the inside. This is because of the different concentrations of sodium and potassium ions within the membrane and outside it. Inside is a high concentration of potassium and a low concentration of the sodium while the reverse is true outside. When a nerve is stimulated, the arrangement of the molecules in the membrane is altered, allowing potassium ions to leak out and sodium to leak in. At this moment, the nerve membrane becomes depolarized and the electrical change causes an alteration in the molecular structure of the next section of membranes, which in turn becomes depolarized. In this way an impulse travels rapidly along the nerve fibre.
Nerve cells are remarkable because they can “communicate” with each other. A stimulated neuron sends messages, in the form of the tiny rapid pulses of the electrical activity described, along its axon, the synapses, but the signal is passed by causing the release of a chemical transmitter substance that makes the surface of the next neuron develop in impulse.
The role of the nervous system
Everything we do requires the meditation of the nervous system, from the simplest flick of a finger to highly coordinated, sophisticated activities. Some simple responses use only particular parts of the nervous system. If someone touches something hot, he pulls his hand away quickly. This simple but essential response is called a spinal reflex, since impulses from the sensory nerve endings in the skin need reach only the spinal cord to be acted upon. Impulses generated within motor cells in the spinal cord pass back down the motor neurons of the arm and activate the muscles that move the hand. The reflex is automatic and is unlearned: a baby behaves identically.
The behavior of very simple animals is made up entirely of reflex movements but higher animals and man have greater freedom of action and can respond in a variety of ways to most situations. Reflexes continue to be important in emergencies and for such vital activities as breathing and bowel movements. But most human behavior falls into another category – it is voluntary, learned and non-reflex. This kind of behavior is made possible because the nervous system can learn from experience and direct its own activities. Since no two people have the same range of experiences, and no two brains are exactly alike, every nervous system behaves in a unique way.
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