This can result either from an infection, irritation, or injury, among other things. Any part of the body can be potentially inflamed. If the name of a body part ends in -itis, then we are talking about the pathology of inflammation of that part: tendonitis, tonsillitis, appendicitis, arthritis (arthro = joint), men- ingitis (menin = the covering of the brain), carditis (cardi = heart), and so on.
The intensity of the inflammation and the degree of involvement of body parts determines how impaired the pilot will be.
Although inflammation is the most common general pathology, there are oth- ers, of course, and they will be defined with the specific body system.
The brain is divided into three main parts, the largest being the forebrain, orcerebrum. This contains much of our “gray matter,” or thinking cells. The forebrain is further divided into two hemispheres, right and left. The surface of these hemispheres is called the cerebral cortex. Each hemisphere is further divided into four lobes, each supplying its own functions.
The frontal lobes are responsible for complex thoughts, decisions, and judgments. From these lobes, signals or “messages” are transmitted via nerves to muscles, telling them what to do. Next are the parietal lobes where some of the senses send information for processing. The tempo- ral lobes are where the speech center is located and where the brain computes information and data and assists in written and spoken com- munications. The occipital lobes are where information from the eyes is processed.
The second part of the brain is the midbrain. It contains the hypothalamus, which produces hormones that affect temperature, growth, and other physi- ological activities. The hindbrain, which is the third part of the brain, is the center of regulation of many of the body’s basic functions, including breath- ing, blood pressure, heart rate, and many others.
All these parts, as well as others, define how we think, learn, process sensory information, and consciously act. Our mind is the “computer” that describes our abilities, personality and intelligence. Like computers, our mind can do wondrous things—or terrible things. And this mental “factory” can be affected by everything discussed in this text.
Various parts of the brain can become infected or inflamed by afflictions such as meningitis and encephalitis, which can result in permanent damage to brain tissue. The same is true of injury. Because the brain is in a closed container (the skull), any impact to the skull can cause torn blood vessels, bruised brain cells, or swelling of the brain itself. To explain how the brain is damaged when the head is hit, some have used the descriptive analogy of what happens to a fresh tomato that just fits inside a jar, and then someone drops the jar. The tomato “bounces” back and forth (a rebound effect) within the jar with unpredictable physical results. A human would have multiple areas of injury to all parts of the brain; therefore, any closed-head injury is considered serious.
A concussion, by definition, is any period of unconsciousness caused by a blow to the head. If one experiences any kind of loss of consciousness (LOC) for any reason, there is usually short- or long-term brain damage or some other underlying problem. This brain damage is a potential risk for problems, especially in flight. Such problems range from a simple headache to convulsions. Hypoxia is known to trigger serious symptoms in someone with a history of any brain pathology, whether from injury, tumor, surgery, burst blood vessel (stroke), or infection; therefore, any brain pathology is a potential risk to flying until it can be medically proven that there is little chance of a problem developing in flight as a result of the unique conditions of flight.
The nervous system 15
16 Basic human anatomy
The spinal cord
Signals from the various parts of the brain are transmitted to the rest of the body by a bundle of nerves called the spinal cord, located in the bony protec- tion of the spine. This is the link between the central nervous system (the brain) and the peripheral nervous system, becoming the direct linkage to muscles, internal organs, and our sensory organs. All nerves to everything in the body come from this cord; for example, we experience a pain in the foot as it is transmitted to the brain from nerves that leave the spinal cord at the end of the spine, which is in the lower back, and extend to the foot.
In addition, the spinal cord brings back signals from “end organs” (organs that process and execute the body’s functional activities) as a form of feed- back, which the brain processes with other data needed for overall function.
For example, the brain will tell the pilot to turn the ignition on with his fin- gers, and when the sound of the engine starting reaches the ear, that signal is transmitted back to the brain to tell the pilot to release the ignition switch, all via the spinal cord.
Any pathology in the spinal cord will interfere with these critical transmis- sions. Injury to the cord results in total loss of neurological control to any part of the body that is connected to nerves distant from the brain and closest to the injury. The same is true if there is a tumor pressing on the cord or an infection or inflammation affecting even a small portion of the cord. It’s simi- lar to cutting a telephone or computer cable, except the “human cable” usu- ally can’t be replaced and probably can’t be repaired, nor will it likely grow back; however, current surgical and medical technologies are accomplishing remarkable results of nerve regeneration and repair.
The peripheral nervous system
The signals to and from the brain are transmitted to the various organs, cells, and parts of the body via the series of smaller single nerves in the peripheral nervous system. Each muscle and organ has one or more nerves controlling its functions. Comparing again to a telephone cable, just as every house has its own telephone line, every part of the body, including selected cells, has its own nerve.
Control of body functions is more complex than just a single nerve telling an organ or body part what to do when the person or the brain decides what action it wants to take. Breathing, digestion, heart rate, blood pressure, internal temperature control, and many more functions are automatic and do not require conscious effort to initiate action. The feedback system from various organs, like an air conditioning thermostat, tells the brain what it needs and then the brain responds without our awareness. This process is often called the autonomic or sympathetic nervous system.
This is also true in the “fight-or-flight” situation. When one is suddenly alarmed, scared, facing a dangerous activity, or in a situation requiring quick response, the brain senses the urgency and, in addition to sending electrical signals, also releases chemicals and hormones (commonly adrenaline), all
of which increase the body’s metabolism to be able to respond to the emer- gency. Many times this is instantaneous. Everyone has experienced the rush of adrenaline with the associated rapid heart rate, tingling sensation, and other symptoms in a potentially dangerous situation, like a near-collision in your car. The body instinctively responds without your intervention, usually with the brain processing data many times faster.
Control of our senses is also automatic. We see, hear, taste, smell, and feel without having to consciously ask the brain to begin. The switch is always on, and we are continuously receiving cues from our sensory organs. What we do once we begin processing these signals now becomes a conscious activity.
Pain is a good example. We can reach for a hot pan on the stove and pick it up through conscious commands. If it’s too hot, we automatically and instinc- tively let go very quickly and pull our hand back, probably also dropping the pan. This happens so suddenly that we are usually unable to intercede and hang onto the pan before dropping it. What we do next to recover from that reflex requires a conscious effort.
Training could, in effect, allow us to overcome the reflex so as to hold on to the pan even though it is hot. The same holds true in flying. Many actions and functions of flight are contrary to what the body thinks it ought to do without our input, such as hypoxia, disorientation, and G forces. The brain tries to protect us from this perceived threat. This is why it is so important to be familiar with those flight conditions not usually tolerated by the body and to train and practice until the body computer, or “thermostat,” can be reset to accommodate the flight environment. Lack of currency in flying skills in instrument conditions is a good example of slipping back into unsafe old habits and conditioned fight or flight responses.
The peripheral nervous system must also be intact to transmit the various signals to and from the brain. A nerve can be infected and inflamed like any other body part. Add itis to neuro (nerve) and you have neuritis. The symp- toms of neuritis depend on what body part or organ the nerve is serving. If it works on the skin, there is a tingling or painful symptom. If it goes to the muscle, there could be twitching. Injury to the nerve, like to the spinal cord, cuts off any input to or output from the organ, making that organ useless.
Cut the nerve to a finger, and the finger goes limp. Peripheral nerves do have the property of growing back over a long period of time (months) if they are injured and then heal properly. This is another area where surgery, specifi- cally microsurgery, is accomplishing incredible results with sewing nerves back together, as well as regeneration.