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Personal Injury Anatomy-Nervous System

Fairfax Injury Lawyer Brien Roche Addresses Personal Injury Anatomy-Nervous System

Brien Roche

This posting is an overview of human anatomy and physiology. The source of the information is for the most part a course offered by The Teaching Company and presented by Dr. Anthony Goodman entitled “Understanding The Human Body:An Introduction to Anatomy and Physiology”.

Within the human body there are two different systems of communication. The nervous system is like instant messaging. The other system of communication is the endocrine system or the hormonal system which might be described as being like the U.S. Mail service i.e., relatively slow. We will talk about the nervous system first.

Personal Injury Anatomy-Nervous System Consists of The Central Nervous System and the Peripheral Nervous System

The brain is one of the largest organs in the body. It consists of more than 100 billion cells. It consumes 20% of the body’s blood supply. The brain is surrounded by the skull which consists of two layers of bone separated by air spaces. The largest part of the brain is the cerebrum which is divided into two hemispheres and each hemisphere is then divided into four lobes. The brain is surrounded by three different layers of tissue. The outer layer is the dura. The middle layer is the arachnoid because it is spider-like and the lowest layer is the pia mater which actually sticks to the brain. Within the brain’s open spaces there is cerebral spinal fluid referred to as CSF which covers both the brain and the spinal cord. This CSF provides mechanical protection from injury, chemical protection and also circulates nutrients and eliminates waste. The brain and the rest of the body are separated by what is called the blood-brain barrier. This separation is necessary because the environment of the body is slightly different than the environment of the brain. It is necessary to understand the operation of that blood-brain barrier in terms of administration of drugs because some drugs will not cross the blood-brain barrier .

Sometimes due to a blow to the head or other conditions blood can develop under the dura and that blood becomes known as a subdural hematoma. If that blood deposit is too large it can actually cause the hemispheres to shift which is a dangerous condition. The blood is removed by drilling a hole in the skull and literally sucking the blood out. An epidural hematoma is a collection of blood on the outside of the dura between the dura and the skull. Subarachnoid collections of blood typically involves a tear to the pia mater which is a very dangerous condition .

On each side of the neck there are carotid arteries that carry blood to the brain. At a central location in the brain known as the Circle of Willis, the various arteries that supply blood to the brain join together and literally form a backup system so that if blood is cut off by one artery then the brain can still get the blood it needs from the other arteries.

If there is a momentary loss of blood flow to the brain then there may be a loss of consciousness. Interruption of blood flow for one to two minutes can cause brain damage and typically death results after four minutes.

One of the things that keeps the brain going is the supply of glucose. The brain does not store glucose. As such if there is a drop in the blood glucose level then there is resulting confusion, convulsions, loss of consciousness and eventually death.

One vestigial feature of the brain is what is referred to as the “diving reflex” which cuts off circulation to all parts of the body other than those body parts that absolutely need it when the body is immersed in very cold water. As a result of this there are instances where people have survived drownings in very cold water where they’ve been under water for as much as 30 minutes and yet still not suffer brain damage. This suggests that humans in fact came from the sea since this reflex is a remnant of the primitive brain. The primitive brain is also seen in instances where you put a baby on a glass surface. The baby will show a startle reflex which is driven by a fear of falling. A baby should have no fear of falling since presumably it never has fallen. The primitive reflex however is derived from a fear of falling out of trees and being eaten by snakes and lizards. That fear of snakes and lizards likewise is with all of us at birth even though it is not a learned reaction.

The importance of the brain is seen in the fact that a baby’s brain is essentially fully developed at birth. What is lacking is insulation. Likewise a baby’s eyes are fully developed at birth which is why people frequently comment on the size of the baby’s eyes. The size of the eyes and the size of the head are frequently disproportionate to the rest of the body .

Aside from the cerebrum, the other parts of the brain are the brain stem which is at the base of the brain and right above the spinal cord; the cerebellum which controls a number of functions including complex motor function and the hypothalamus which is the regulator of stability in the body.

The cerebrum is the highest part of the brain and also controls the highest functions performed by the brain. The outermost layer is referred to as the grey matter and below that is the white matter. The two hemispheres consist of folds of brain tissue that give the brain greater surface area. This greater surface area is somewhat similar to the need for surface on an elephant as seen in its large ears. That is, increased surface area promotes cooling .

The nervous system is an electrical complex that sends electrical signals through chemical ions. Those signals travel in two directions. Each direction has a separate set of nerves. The nerves are called neurons and most of those neurons are covered with a sheath that essentially acts as insulation. It is much like the insulation on a copper wire. If that insulation is broken then you can have short circuits. Multiple Sclerosis evidences this. Multiple Sclerosis is an autoimmune disease wherein the body attacks itself causing nerves to harden because of the lack of sheathing around them.

In a baby, one way of testing whether or not there are breaks in this insulation is done by scratching the sole of the baby’s foot. The toes should spread apart. In an adult the toes should move towards the center i.e., close. This is called the Babinski reflex and it measures whether or not the insulation is present. Typically in a baby it may not be present but that insulation grows as the baby grows.

The Peripheral Nervous System

The central nervous system is that collection of cells that goes from the brain down the spinal cord. Cells within this system can be several feet long, beginning from the brain going down to the base of the back. There is also a peripheral nervous system, part of which is voluntary and part of which is involuntary. The involuntary nervous system is the system that controls what is called fright, fight and flight. This system releases epinephrine in the event of emergencies. This same component of the nervous system stimulates the digestive tract to promote digestion but it can also shut down that digestive system and blood flow to the GI tract in instances where that energy has to be diverted elsewhere because of an emergency. The voluntary nervous system is what controls the sensation of pain when you touch a hot plate. Some parts of the body are very specialized as far as sensation. For instance the cornea only has nerve endings for touch. If something touches the cornea it feels this and pulls away and also may tear up in order to wash away that foreign invader. Likewise the intestines are not sensitive to cutting or burning but they are sensitive to stretching. The brain itself actually has no pain receptors and as such a surgeon can operate on the brain while the patient is actually awake without anesthesia .

The nerve cells are either wet or floating in fluid. Electrons do not travel through fluids. In order to have electrical communication running along these neurons, that electrical transmission needs to be conducted by electrical charges in the form of ions.

The electrical signals that the neurons carry move as a result of the differences in concentration of charged ions. These charged ions are principally a result of the presence of potassium, sodium and chloride ions. Sodium and chlorine come from salt. Without these charged ions nothing else in the human body works. If you’ve ever been exposed to someone who has had a heat stroke, coincident with attempts to lower the body temperature, electrolytes must be restored to the system through salt tablets or other means to get the body functioning properly.

Sodium and potassium also have a major role in keeping blood pressure normal. Good sources of sodium include such things as salt, dill pickles, pretzels and bread. Good sources of potassium include sweet potatoes, plain nonfat yogurt, yellow fin tuna, non-cured pork chops, cantaloupe, bananas, leafy green vegetables, root vegetables and fruit from the vine. For most Americans a primary source of sodium is from processed food. Generally processed foods should be avoided in favor of more fresh food. The easy way to think of processed food is to think of how many different times it’s handled with either things being added to it or commingled with it.

People that are exerting themselves in hot weather or that are engaging in strenuous exercise need to be especially sensitive to sodium and potassium levels. Excessive salt losses during exercise are a frequent cause of cramping. Excessive water consumption can be a cause of salt in your body being diluted. Frequently during strenuous activities your body may sweat excessively. If after exercise you notice a white salt on the armpits of your clothing, that tends to mean that you are a salty sweater and are emitting a large amount of salt. You need to be sensitive to salt replacement which can come through salt tablets or sports drinks that have these electrolytes added to them.

Electrical charges cannot pass through the synapses which are the attachment points between neurons. As such there are chemicals known as neurotransmitters that receive the electrical signal at one synapse and translate it into a chemical signal to be transmitted to an adjoining synapse. These chemicals may be of a type that promotes certain types of activities or may be ones that inhibit certain activities. Pharmacology over the years has been able to work wonders in terms of altering these chemicals so as to either promote certain activities or retard certain activities. For instance anti-psychotic drugs can block dopamine and thereby lessen symptoms of schizophrenia. Dopamine is a chemical that makes a person feel pleasure. The release of that chemical in the brain can promote certain behavior. Likewise tranquilizers can help control anxiety by controlling the amount of certain chemicals in the brain that determine the level of anxiety.

Improving the level of communication at the synapses can also have a direct impact on learning. That is, the better those channels of communication are working then the more likely it is that productive learning will take place.

The brain consists not only of neurons but also what are called networks of neurons that work together. For instance a piece of information is not necessarily contained in a single neuron but may be contained in a network of neurons that interact. Memory is retained in such networks. Illnesses such as dementia and Alzheimer’s don’t necessarily destroy memory. What they do is they simply make it more difficult for these networks to work together so as to retrieve memory. People that are highly creative have broader networks of neurons than do most other people, resulting in their ability to make quicker and more insightful analyses.

Although the brain is generally thought of as the center of the nervous system, there are instances where the brain is bypassed. For instance if you touch a hot plate, the reflex reaction will immediately cause your hand to pull away. That series of sensory signals bypassed the brain even though the brain may have eventually learned of it.

The spinal cord consists of the vertebrae of the neck, the mid back, the lower back and the sacral area which is a fused set of bones. The spinal cord itself is curved in two directions much like a spring might be curved and it is designed to provide shock absorber capability. The coverings of the spinal cord are the same as what you see in the brain. Likewise surrounding the spinal cord is CSF. A spinal tap is literally a tap into the spinal cord area to extract CSF for analysis which gives information about both the brain and the spinal cord. These types of taps are called lumbar punctures and the physician performing them must be careful not to extract too much fluid otherwise the brain and the cord can literally sag. Anesthesia can also be introduced into the spinal sac to anesthetize certain areas below the point of injection. The effect this anesthesia has however is controlled by the position of the body and the law of gravity .

There are several conditions that can damage the central nervous system. Polio is no longer as much of a threat as it used to be. Polio is an oral fecal disease which passes from feces to the mouth. It is called the rich man’s disease because when it emerged, poor people tended to be immunized from it because of their exposure whereas the wealthier people were not immunized to it because they maintained better bathroom hygiene. When they had a lapse of good bathroom hygiene and low resistance to the virus, it then caused its damage. Lou Gehrig’s disease involves a degeneration of the actual neurons themselves and can be fatal. The breakdown of the fat pads between the vertebrae in the spinal column causes nerve impingement and can cause paralysis. As part of the aging process these disc pads recede thereby allowing the growth of bone spurs which can also cause problems.

The reflexes within the body are part of the nervous system. Tapping below the knee cap may seem like a simple test and indeed it is but it tests the functionality of the nerves that travel along the thigh to the spinal cord and then back down to the thigh muscles. This tap below the knee cap also tests the ham string muscles which have a function of inhibiting so that the thigh muscle can do its job. If this reflex and other reflexes in the body are not normal then that signals that the neurons are not receiving the proper messages .

One miraculous feature of the nervous system is that nerves to some extent have the ability to regenerate at the rate of approximately 1 mm. per day.

The Eye

The eye is part of the nervous system. An important feature of vision is distance. That binocular vision is a function of both eyes focusing on an object in the distance. Think of the two eyes as being the base of a triangle. The line of sight of each eye to the object are the long arms of that triangle. As those long arms form a smaller angle at the base, the object is closer. As those long arms form a larger angle at the base, the object is more distant. If only one eye is operating then that ability to conduct this type of triangulation is lost .

The outer surface of the eye is called the conjunctiva which is a very thin layer. Below that is the cornea which is the fibrous layer that covers the eye. The cornea can help the eye focus and as a result is a site of surgery wherein the cornea literally is shaved in order to improve vision. Because of the curved nature of the cornea it can help focus the light. Corneas also can be transplanted. The white of the eye is what gives shape to the globe which contains the iris which is the colored part of the eye. The pupil literally is the hole in the donut. The lens is controlled by muscles that change its shape and thereby change the refraction of light. The retina is at the back of the eye and can be thought of as the film in a camera. The retina contains 120 million rods which are the receptors which principally are sensitive to movement and shapes. There are also 6 million cone shaped receptors in the retina that allow for colored vision where there is light. If there is no light then there is no color vision. Instead everything is either grey or black. That’s why at night the best vision is peripheral vision. If you’re a hunter you know that if you are hunting at night, it’s best to look at your prey through your peripheral vision.

By looking at the retina a physician can tell a great deal about the patient. In particular, diabetes can be diagnosed through retinal damage.

On the exterior of the eye there are eyelids which serve as windshield wipers. There are also tear ducts that generate fluid in order to clear particles away from the eye. Those tear ducts drain into the nose and this explains that when you cry you get a runny nose .

If you’ve ever experienced sea sickness then you know that your eyes and your brain don’t like an unstable horizon. To some extent your eyes can rotate within your head in order to keep the horizon relatively flat. When that movement becomes so great that the eyes can’t rotate then the brain reacts. The brain wants to see a flat horizon. When it’s not seeing that, the result may be sea sickness.

The eyes also like to focus on single objects as opposed to focusing on multiple moving objects. If you are on a train passing a series of fixed objects, the eyes will fix on a point in that landscape and follow it until it disappears and then pick another one.

The way that the retina works is that light strikes the retina, the rods and cones are activated and that light energy is then converted into chemical energy. The chemical energy is vitamin A dependent and that is why you should eat your carrots. That chemical energy is converted into electrical energy which eventually reaches the optic nerve and essentially creates a digital message put together by the brain resulting in a picture. It’s much the same as the creation of a picture by a camera .

There are a number of things that can go wrong with the eye. Glaucoma is the result of increased pressure that damages the retina. Cataracts are a very common loss of vision. Cataracts consist of the lens becoming clouded. This can be a result of simply the aging process, diabetes, smoking or a host of other things. Looking at the sun can cause this although typically looking at the sun is not an activity that your eyes will allow especially on a bright day. What is more dangerous is looking up towards the sun on a cloudy day.

Hearing and Balance

The ears are another organ of the nervous system. The ear actually fulfills functions of both hearing and balance. The ear consists of the external ear, the eardrum, the middle ear and then the area that is called the labyrinth or the inner ear. Sound waves are simply the movement of air. This explains why there is no sound in outer space i.e., there is no atmosphere. Those airwaves hit the eardrum also known as the tympanic membrane and cause the eardrum to vibrate at the same pitch and amplitude of those airwaves. Pitch is frequency. That is, the number of sound waves that are passing a fixed point over a fixed period of time. Amplitude is the size of the wave. That is, the intensity or loudness of the wave. The movement of the eardrum in turn causes movement of three bones that are inside the middle ear. The sound waves transmitted on those bones are then picked up by fluid containing small hairs which wave with the motion of that fluid and transmit those waves to a nerve which then transmits that signal to the brain.

There is a tube known as the eustachian tube that connects the middle ear to the nose and mouth cavity. This tube is designed to equalize pressure. It’s more efficient at releasing air from the inner ear than it is at drawing air back into the inner ear. When you’re in an airplane that is landing, the external pressure at that point increases putting pressure on the inner ear. The best way to equalize that pressure is to swallow in order to allow air to enter the inner ear through the eustachian tube.

Helen Keller was reportedly asked which of the two senses that she had lost was the most important i.e., sight or hearing. She responded without hesitation that hearing was far and away the most important because it is through hearing that emotion is conveyed.

Hearing loss is an increasing worry because of the prevalence of earphones and earbuds. These types of devices can cause damage to the nerves in the ear. That type of damage is not reversible.

Another important function within the ear is that of balance. Balance becomes important not only when you’re standing still and/or moving but also when you’re moving at uniform motion i.e., at constant speed in the same direction. Your sense of balance can detect what is called static equilibrium (where the body is stationery) and can detect dynamic equilibrium where there is a change in motion. What it cannot detect is uniform motion i.e., where there is a constant speed in a constant direction.

There are three small canals in the inner ear that are at right angles to each other which detect dynamic motion. One of those canals is horizontal, one is vertical and one travels from the front to the back of the body. This provides three axes in order to sense motion. The body of fluid that transmits sound waves to the nerves also is the fluid that produces the nerve impulses that are sent to the brain to tell the brain where the head is. Proprioception is a series of sensors all over the body that tell the brain where the body is. If your body spins around in a circular motion and then stops spinning the fluid in the inner ear for some period of time continues spinning, telling the brain that there is ongoing movement even though the body is actually stopped.

Memory

Another important component of the nervous system is memory. Insanity is defined by some as making the same mistake over and over again and expecting a different result. In fact insanity is probably a bit broader than that. Loss of memory may be a component of insanity.

The entire brain is involved in the memory process. It is this system of networking discussed previously that allows one to maintain memory of events. A baby’s brain is for the most part fully developed at birth. That means that at birth you have almost all of the neurons that you need. Life experiences don’t expand the number of neurons but rather they simply fill those networks of neurons with memories. Memory can be broken down into immediate memory which is that which occurred within few seconds of the event, short-term memory which covers the timeframe of a few seconds to a few minutes and long-term memory which then goes beyond that. Only about one percent of conscious information is stored in long-term memory.

Amnesia is the loss of memory. Typically amnesia that is associated with some traumatic event is referred to as “circumscribed amnesia” which means that the memory is lost directly before the event and to the extent there is a loss of consciousness, after the event. If the memory returns then the oldest memories return first followed by the newer ones. Complete amnesia involving a loss of all memory is very rare.

Also within the brain is the limbic system which controls emotions. Only mammals have complex emotions.

For more information about the nervous system see the pages on Wikipedia.

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Personal Injury Anatomy-Nervous System

Fairfax Injury Lawyer Brien Roche Addresses Personal Injury Anatomy-Nervous System

Brien Roche

This posting is an overview of human anatomy and physiology. The source of the information is for the most part a course offered by The Teaching Company and presented by Dr. Anthony Goodman entitled “Understanding The Human Body:An Introduction to Anatomy and Physiology”.

Within the human body there are two different systems of communication. The nervous system is like instant messaging. The other system of communication is the endocrine system or the hormonal system which might be described as being like the U.S. Mail service i.e., relatively slow. We will talk about the nervous system first.

Personal Injury Anatomy-Nervous System Consists of The Central Nervous System and the Peripheral Nervous System

The brain is one of the largest organs in the body. It consists of more than 100 billion cells. It consumes 20% of the body’s blood supply. The brain is surrounded by the skull which consists of two layers of bone separated by air spaces. The largest part of the brain is the cerebrum which is divided into two hemispheres and each hemisphere is then divided into four lobes. The brain is surrounded by three different layers of tissue. The outer layer is the dura. The middle layer is the arachnoid because it is spider-like and the lowest layer is the pia mater which actually sticks to the brain. Within the brain’s open spaces there is cerebral spinal fluid referred to as CSF which covers both the brain and the spinal cord. This CSF provides mechanical protection from injury, chemical protection and also circulates nutrients and eliminates waste. The brain and the rest of the body are separated by what is called the blood-brain barrier. This separation is necessary because the environment of the body is slightly different than the environment of the brain. It is necessary to understand the operation of that blood-brain barrier in terms of administration of drugs because some drugs will not cross the blood-brain barrier .

Sometimes due to a blow to the head or other conditions blood can develop under the dura and that blood becomes known as a subdural hematoma. If that blood deposit is too large it can actually cause the hemispheres to shift which is a dangerous condition. The blood is removed by drilling a hole in the skull and literally sucking the blood out. An epidural hematoma is a collection of blood on the outside of the dura between the dura and the skull. Subarachnoid collections of blood typically involves a tear to the pia mater which is a very dangerous condition .

On each side of the neck there are carotid arteries that carry blood to the brain. At a central location in the brain known as the Circle of Willis, the various arteries that supply blood to the brain join together and literally form a backup system so that if blood is cut off by one artery then the brain can still get the blood it needs from the other arteries.

If there is a momentary loss of blood flow to the brain then there may be a loss of consciousness. Interruption of blood flow for one to two minutes can cause brain damage and typically death results after four minutes.

One of the things that keeps the brain going is the supply of glucose. The brain does not store glucose. As such if there is a drop in the blood glucose level then there is resulting confusion, convulsions, loss of consciousness and eventually death.

One vestigial feature of the brain is what is referred to as the “diving reflex” which cuts off circulation to all parts of the body other than those body parts that absolutely need it when the body is immersed in very cold water. As a result of this there are instances where people have survived drownings in very cold water where they’ve been under water for as much as 30 minutes and yet still not suffer brain damage. This suggests that humans in fact came from the sea since this reflex is a remnant of the primitive brain. The primitive brain is also seen in instances where you put a baby on a glass surface. The baby will show a startle reflex which is driven by a fear of falling. A baby should have no fear of falling since presumably it never has fallen. The primitive reflex however is derived from a fear of falling out of trees and being eaten by snakes and lizards. That fear of snakes and lizards likewise is with all of us at birth even though it is not a learned reaction.

The importance of the brain is seen in the fact that a baby’s brain is essentially fully developed at birth. What is lacking is insulation. Likewise a baby’s eyes are fully developed at birth which is why people frequently comment on the size of the baby’s eyes. The size of the eyes and the size of the head are frequently disproportionate to the rest of the body .

Aside from the cerebrum, the other parts of the brain are the brain stem which is at the base of the brain and right above the spinal cord; the cerebellum which controls a number of functions including complex motor function and the hypothalamus which is the regulator of stability in the body.

The cerebrum is the highest part of the brain and also controls the highest functions performed by the brain. The outermost layer is referred to as the grey matter and below that is the white matter. The two hemispheres consist of folds of brain tissue that give the brain greater surface area. This greater surface area is somewhat similar to the need for surface on an elephant as seen in its large ears. That is, increased surface area promotes cooling .

The nervous system is an electrical complex that sends electrical signals through chemical ions. Those signals travel in two directions. Each direction has a separate set of nerves. The nerves are called neurons and most of those neurons are covered with a sheath that essentially acts as insulation. It is much like the insulation on a copper wire. If that insulation is broken then you can have short circuits. Multiple Sclerosis evidences this. Multiple Sclerosis is an autoimmune disease wherein the body attacks itself causing nerves to harden because of the lack of sheathing around them.

In a baby, one way of testing whether or not there are breaks in this insulation is done by scratching the sole of the baby’s foot. The toes should spread apart. In an adult the toes should move towards the center i.e., close. This is called the Babinski reflex and it measures whether or not the insulation is present. Typically in a baby it may not be present but that insulation grows as the baby grows.

The Peripheral Nervous System

The central nervous system is that collection of cells that goes from the brain down the spinal cord. Cells within this system can be several feet long, beginning from the brain going down to the base of the back. There is also a peripheral nervous system, part of which is voluntary and part of which is involuntary. The involuntary nervous system is the system that controls what is called fright, fight and flight. This system releases epinephrine in the event of emergencies. This same component of the nervous system stimulates the digestive tract to promote digestion but it can also shut down that digestive system and blood flow to the GI tract in instances where that energy has to be diverted elsewhere because of an emergency. The voluntary nervous system is what controls the sensation of pain when you touch a hot plate. Some parts of the body are very specialized as far as sensation. For instance the cornea only has nerve endings for touch. If something touches the cornea it feels this and pulls away and also may tear up in order to wash away that foreign invader. Likewise the intestines are not sensitive to cutting or burning but they are sensitive to stretching. The brain itself actually has no pain receptors and as such a surgeon can operate on the brain while the patient is actually awake without anesthesia .

The nerve cells are either wet or floating in fluid. Electrons do not travel through fluids. In order to have electrical communication running along these neurons, that electrical transmission needs to be conducted by electrical charges in the form of ions.

The electrical signals that the neurons carry move as a result of the differences in concentration of charged ions. These charged ions are principally a result of the presence of potassium, sodium and chloride ions. Sodium and chlorine come from salt. Without these charged ions nothing else in the human body works. If you’ve ever been exposed to someone who has had a heat stroke, coincident with attempts to lower the body temperature, electrolytes must be restored to the system through salt tablets or other means to get the body functioning properly.

Sodium and potassium also have a major role in keeping blood pressure normal. Good sources of sodium include such things as salt, dill pickles, pretzels and bread. Good sources of potassium include sweet potatoes, plain nonfat yogurt, yellow fin tuna, non-cured pork chops, cantaloupe, bananas, leafy green vegetables, root vegetables and fruit from the vine. For most Americans a primary source of sodium is from processed food. Generally processed foods should be avoided in favor of more fresh food. The easy way to think of processed food is to think of how many different times it’s handled with either things being added to it or commingled with it.

People that are exerting themselves in hot weather or that are engaging in strenuous exercise need to be especially sensitive to sodium and potassium levels. Excessive salt losses during exercise are a frequent cause of cramping. Excessive water consumption can be a cause of salt in your body being diluted. Frequently during strenuous activities your body may sweat excessively. If after exercise you notice a white salt on the armpits of your clothing, that tends to mean that you are a salty sweater and are emitting a large amount of salt. You need to be sensitive to salt replacement which can come through salt tablets or sports drinks that have these electrolytes added to them.

Electrical charges cannot pass through the synapses which are the attachment points between neurons. As such there are chemicals known as neurotransmitters that receive the electrical signal at one synapse and translate it into a chemical signal to be transmitted to an adjoining synapse. These chemicals may be of a type that promotes certain types of activities or may be ones that inhibit certain activities. Pharmacology over the years has been able to work wonders in terms of altering these chemicals so as to either promote certain activities or retard certain activities. For instance anti-psychotic drugs can block dopamine and thereby lessen symptoms of schizophrenia. Dopamine is a chemical that makes a person feel pleasure. The release of that chemical in the brain can promote certain behavior. Likewise tranquilizers can help control anxiety by controlling the amount of certain chemicals in the brain that determine the level of anxiety.

Improving the level of communication at the synapses can also have a direct impact on learning. That is, the better those channels of communication are working then the more likely it is that productive learning will take place.

The brain consists not only of neurons but also what are called networks of neurons that work together. For instance a piece of information is not necessarily contained in a single neuron but may be contained in a network of neurons that interact. Memory is retained in such networks. Illnesses such as dementia and Alzheimer’s don’t necessarily destroy memory. What they do is they simply make it more difficult for these networks to work together so as to retrieve memory. People that are highly creative have broader networks of neurons than do most other people, resulting in their ability to make quicker and more insightful analyses.

Although the brain is generally thought of as the center of the nervous system, there are instances where the brain is bypassed. For instance if you touch a hot plate, the reflex reaction will immediately cause your hand to pull away. That series of sensory signals bypassed the brain even though the brain may have eventually learned of it.

The spinal cord consists of the vertebrae of the neck, the mid back, the lower back and the sacral area which is a fused set of bones. The spinal cord itself is curved in two directions much like a spring might be curved and it is designed to provide shock absorber capability. The coverings of the spinal cord are the same as what you see in the brain. Likewise surrounding the spinal cord is CSF. A spinal tap is literally a tap into the spinal cord area to extract CSF for analysis which gives information about both the brain and the spinal cord. These types of taps are called lumbar punctures and the physician performing them must be careful not to extract too much fluid otherwise the brain and the cord can literally sag. Anesthesia can also be introduced into the spinal sac to anesthetize certain areas below the point of injection. The effect this anesthesia has however is controlled by the position of the body and the law of gravity .

There are several conditions that can damage the central nervous system. Polio is no longer as much of a threat as it used to be. Polio is an oral fecal disease which passes from feces to the mouth. It is called the rich man’s disease because when it emerged, poor people tended to be immunized from it because of their exposure whereas the wealthier people were not immunized to it because they maintained better bathroom hygiene. When they had a lapse of good bathroom hygiene and low resistance to the virus, it then caused its damage. Lou Gehrig’s disease involves a degeneration of the actual neurons themselves and can be fatal. The breakdown of the fat pads between the vertebrae in the spinal column causes nerve impingement and can cause paralysis. As part of the aging process these disc pads recede thereby allowing the growth of bone spurs which can also cause problems.

The reflexes within the body are part of the nervous system. Tapping below the knee cap may seem like a simple test and indeed it is but it tests the functionality of the nerves that travel along the thigh to the spinal cord and then back down to the thigh muscles. This tap below the knee cap also tests the ham string muscles which have a function of inhibiting so that the thigh muscle can do its job. If this reflex and other reflexes in the body are not normal then that signals that the neurons are not receiving the proper messages .

One miraculous feature of the nervous system is that nerves to some extent have the ability to regenerate at the rate of approximately 1 mm. per day.

The Eye

The eye is part of the nervous system. An important feature of vision is distance. That binocular vision is a function of both eyes focusing on an object in the distance. Think of the two eyes as being the base of a triangle. The line of sight of each eye to the object are the long arms of that triangle. As those long arms form a smaller angle at the base, the object is closer. As those long arms form a larger angle at the base, the object is more distant. If only one eye is operating then that ability to conduct this type of triangulation is lost .

The outer surface of the eye is called the conjunctiva which is a very thin layer. Below that is the cornea which is the fibrous layer that covers the eye. The cornea can help the eye focus and as a result is a site of surgery wherein the cornea literally is shaved in order to improve vision. Because of the curved nature of the cornea it can help focus the light. Corneas also can be transplanted. The white of the eye is what gives shape to the globe which contains the iris which is the colored part of the eye. The pupil literally is the hole in the donut. The lens is controlled by muscles that change its shape and thereby change the refraction of light. The retina is at the back of the eye and can be thought of as the film in a camera. The retina contains 120 million rods which are the receptors which principally are sensitive to movement and shapes. There are also 6 million cone shaped receptors in the retina that allow for colored vision where there is light. If there is no light then there is no color vision. Instead everything is either grey or black. That’s why at night the best vision is peripheral vision. If you’re a hunter you know that if you are hunting at night, it’s best to look at your prey through your peripheral vision.

By looking at the retina a physician can tell a great deal about the patient. In particular, diabetes can be diagnosed through retinal damage.

On the exterior of the eye there are eyelids which serve as windshield wipers. There are also tear ducts that generate fluid in order to clear particles away from the eye. Those tear ducts drain into the nose and this explains that when you cry you get a runny nose .

If you’ve ever experienced sea sickness then you know that your eyes and your brain don’t like an unstable horizon. To some extent your eyes can rotate within your head in order to keep the horizon relatively flat. When that movement becomes so great that the eyes can’t rotate then the brain reacts. The brain wants to see a flat horizon. When it’s not seeing that, the result may be sea sickness.

The eyes also like to focus on single objects as opposed to focusing on multiple moving objects. If you are on a train passing a series of fixed objects, the eyes will fix on a point in that landscape and follow it until it disappears and then pick another one.

The way that the retina works is that light strikes the retina, the rods and cones are activated and that light energy is then converted into chemical energy. The chemical energy is vitamin A dependent and that is why you should eat your carrots. That chemical energy is converted into electrical energy which eventually reaches the optic nerve and essentially creates a digital message put together by the brain resulting in a picture. It’s much the same as the creation of a picture by a camera .

There are a number of things that can go wrong with the eye. Glaucoma is the result of increased pressure that damages the retina. Cataracts are a very common loss of vision. Cataracts consist of the lens becoming clouded. This can be a result of simply the aging process, diabetes, smoking or a host of other things. Looking at the sun can cause this although typically looking at the sun is not an activity that your eyes will allow especially on a bright day. What is more dangerous is looking up towards the sun on a cloudy day.

Hearing and Balance

The ears are another organ of the nervous system. The ear actually fulfills functions of both hearing and balance. The ear consists of the external ear, the eardrum, the middle ear and then the area that is called the labyrinth or the inner ear. Sound waves are simply the movement of air. This explains why there is no sound in outer space i.e., there is no atmosphere. Those airwaves hit the eardrum also known as the tympanic membrane and cause the eardrum to vibrate at the same pitch and amplitude of those airwaves. Pitch is frequency. That is, the number of sound waves that are passing a fixed point over a fixed period of time. Amplitude is the size of the wave. That is, the intensity or loudness of the wave. The movement of the eardrum in turn causes movement of three bones that are inside the middle ear. The sound waves transmitted on those bones are then picked up by fluid containing small hairs which wave with the motion of that fluid and transmit those waves to a nerve which then transmits that signal to the brain.

There is a tube known as the eustachian tube that connects the middle ear to the nose and mouth cavity. This tube is designed to equalize pressure. It’s more efficient at releasing air from the inner ear than it is at drawing air back into the inner ear. When you’re in an airplane that is landing, the external pressure at that point increases putting pressure on the inner ear. The best way to equalize that pressure is to swallow in order to allow air to enter the inner ear through the eustachian tube.

Helen Keller was reportedly asked which of the two senses that she had lost was the most important i.e., sight or hearing. She responded without hesitation that hearing was far and away the most important because it is through hearing that emotion is conveyed.

Hearing loss is an increasing worry because of the prevalence of earphones and earbuds. These types of devices can cause damage to the nerves in the ear. That type of damage is not reversible.

Another important function within the ear is that of balance. Balance becomes important not only when you’re standing still and/or moving but also when you’re moving at uniform motion i.e., at constant speed in the same direction. Your sense of balance can detect what is called static equilibrium (where the body is stationery) and can detect dynamic equilibrium where there is a change in motion. What it cannot detect is uniform motion i.e., where there is a constant speed in a constant direction.

There are three small canals in the inner ear that are at right angles to each other which detect dynamic motion. One of those canals is horizontal, one is vertical and one travels from the front to the back of the body. This provides three axes in order to sense motion. The body of fluid that transmits sound waves to the nerves also is the fluid that produces the nerve impulses that are sent to the brain to tell the brain where the head is. Proprioception is a series of sensors all over the body that tell the brain where the body is. If your body spins around in a circular motion and then stops spinning the fluid in the inner ear for some period of time continues spinning, telling the brain that there is ongoing movement even though the body is actually stopped.

Memory

Another important component of the nervous system is memory. Insanity is defined by some as making the same mistake over and over again and expecting a different result. In fact insanity is probably a bit broader than that. Loss of memory may be a component of insanity.

The entire brain is involved in the memory process. It is this system of networking discussed previously that allows one to maintain memory of events. A baby’s brain is for the most part fully developed at birth. That means that at birth you have almost all of the neurons that you need. Life experiences don’t expand the number of neurons but rather they simply fill those networks of neurons with memories. Memory can be broken down into immediate memory which is that which occurred within few seconds of the event, short-term memory which covers the timeframe of a few seconds to a few minutes and long-term memory which then goes beyond that. Only about one percent of conscious information is stored in long-term memory.

Amnesia is the loss of memory. Typically amnesia that is associated with some traumatic event is referred to as “circumscribed amnesia” which means that the memory is lost directly before the event and to the extent there is a loss of consciousness, after the event. If the memory returns then the oldest memories return first followed by the newer ones. Complete amnesia involving a loss of all memory is very rare.

Also within the brain is the limbic system which controls emotions. Only mammals have complex emotions.

For more information about the nervous system see the pages on Wikipedia.

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