*still working on this*


CHANGES IN OUR NERVOUS SYSTEM AS WE AGE

INTRODUCTION

Nobody is sure as to why humans age. There are contributing factors to aging which might include a person's genetics, lifestyle patterns (such as how often one exercises and what a person eats), and environmental factors (such as where a person lives and how they live economically). As we age, our DNA mutations and errors begin to build up until DNA is no longer functional. Also, as a person ages free radicals build up in their body, their functional hormones start to decrease, the immune system starts to decrease in function, it becomes easier to get sick and cells start to program death. So, when we age all of our body's systems are affected. This includes our skeletal/muscular, digestive, integumentary, circulatory, respiratory, immune, endocrine and nervous systems.
The nervous system is of great concern to us today when it comes to its aging. Problems with our aging nervous system seem to be increasing as time goes by so it is a very important topic of study to scientists today. One of the greatest health threats to the nervous system as we age happens to be cognitive decline and more and more people are beginning to develop different forms of dementia as they age (Bishop 2010). Other neurological issues as a person ages can include movement problems, slower responsive times, loss of senses over time and things like losing appetite due to the loss of senses.

logo.gif
(http://www.medschool.lsuhsc.edu/aging_center/)

BASIC ANATOMY OF THE NERVOUS SYSTEM

Brain

brain_diagram.GIF
(http://www.osovo.com/diagram/braindiagram.htm)

Our brain is divided into two main cerebral hemispheres. The two hemispheres are connected by a large C-shaped fiber bundle called the corpus callosum. There is a fissure which seperates the cerebral hemispheres from the cerebellum (also referred to as the "little brain").
The cerebrum's outer layer is the cortex. The cortex is made up of neurons and other supporting cells. It is gray in color and is made up of what is called "gray matter". Gray matter is unmyelinated. Under the gray matter comes the "white matter" which is made up of myelinated descending and ascending fibers. White matter appears white in color. Subcortical neurons are found deep within the white matter.
The surface of the cerebral cortex has folds which are called gyri and elongated grooves called sulci.
The cerebral cortex is highly organized. It is divided up into different sections linked to different functions. Some of these specific areas in the cortex include the primary sensory areas, primary motor area, premotor area, supplementary motor area, associateion area and visual area.

The cerebrum is divided up furthermore into six lobes ( frontal, temporal, parietal, occipital, insular and limbic). Most of these are named according to their location in relation to the human skull. Each lobe is related to different functions.

The brainstem is divided up into the midbrain, pons and medulla.

(Neuroscience Online 2011)



Spinal cord
spinal-cord-anatomy.jpg
(http://dla-by411.blogspot.com/2011/04/neuroanatomy-post-3-development-spinal.html)

The spinal cord is the very important structure in our body which helps to connect the brain to the rest of our body.
It starts out in the foramen magnum of the skull and finishes at the lumbar vertebrae. It is 50-60 cm in length and 1-1.5 cm in diameter.
Two consecutive nerve roots emerge on each side of the spinal cord. Those nerve roots join distally and form the 31 pairs of spinal nerves.
The spinal cord is made up of nervous tissue which consists of both white and gray matter.

The spinal cord regions from top to bottom are:
Cervical
Thoracic
Lumbar
Sacral

The gray matter of the spinal cord consists of the neuron and glial cell bodies and is divided into four columns:
dorsal horn
intermediate column
lateral horn
ventral horn

White matter surrounds the gray matter. As said before, white matter contains myelinated nerve fibers. The white matter fibers conduct information up (ascending) or down (descending) the spinal cord.
The white matter divides into the dorsal, lateral and ventral columns. The dorsal column is also referred to as the posterior or funiculus column and the ventral column can also be referred to as the anterior column.
Ascending tracts are found in all of the columns and descending tracts are found in the lateral and anterior column.


(Neuroscience Online 2011)


Nerves, neurons

motorneurone.jpg
sensoryneurone.jpg
relayneurone.jpg
(http://www.biologymad.com/nervoussystem/nervoussystemintro.htm)

^ These are the three types of neurons seen in humans. Interneurons work by synapsing with other neurons, motor neurons are responsible for movement and sensory neurons are responsible for sensory signals.


Humans have 31 pairs of spinal nerves and 12 pairs of cranial nerves. (Neuroscience online 2011)



NERVOUS SYSTEM FUNCTIONS

brain-diagram2.JPG
(http://www.osovo.com/diagram/braindiagram.htm)

nervoussystem.jpg
(http://www.biologymad.com/nervoussystem/nervoussystemintro.htm)


WHEN A PERSON AGES

Basic Overview

When people age, their nervous system begins to change.
The brain and spinal cord lose cells and weight. Also, nerve cells start to decrease their productivity- they begin to transmit signals at a slower rate. Waste products begin to build up more and more in the brain, and this can lead to plaque and tangle build-up. Lipofuscin, which is a fatty-brown pigment can also build up in the nervous system tissue.
As a person begins to lose nerve cells and nerve cells start to break down everything controlled by the nervous system can start to decrease in function. One thing that depends on nerve cells (sensory neurons specifically) is sensation. Loss of sensation can lead to problems with movement, tasting, smelling, feeling, touching, etc.
Thought processes, memory and thinking can slow down as a person ages. An abnormal change in these things is a problem and usually means a person may have developed dementia. Dementia is not part of the normal aging process.
(UMMC 2011)

Senses

The stimulus needed to produce a reaction with senses as we age increases. We need a lot more of a certain stimulus in order to get the signal in our neurons to fire.
The reason we need a stronger sensory input as we age has a lot to do with our body parts and how they change when we age.

-Hearing (+Balance)
Our ears have two roles- to help with hearing and to also help with maintaining balance.
The way hearing works is our ear picks up a sound (stimulus), that signal then travels through our ear and forms vibrations in the ear drum then ends up in the inner ear. The sound stimulus is changed into a nerve impulse and carried to the brain out of the ear by the auditory nerve.
Structures within our ear are responsible for the maintenance of balance. There are fluid and hairs in the semicircular canal which respond to sudden head movements and a signal is sent out a nerve to the brain. These structures in our ear are important role players in the vestibular system which is responsible for maintaining balance and posture in our bodies.
When a person ages, their ear structure begins to change. The ear drum begins to thicken. Also, inner ear bones and surrounding bones may be affected by the ear drum changes. Maintaining balance and hearing become a problem as we age because the ear changes. Most people develop some sort of a hearing loss when they age. People who have been exposed to lots of noise when they were younger are more likely to develop a hearing loss as they age. Age related hearing loss is called presbycusis. About 30 percent of the population over 65 is estimated to have some significant hearing impairment.
Also, the sharpness of hearing may start to decline at about age 50- this maybe be caused by changes in the auditory nerve. Due to changes in the auditory nerve, the brain may have difficulties with translating sound into something meaningful and processing it correctly. Also, a build up of a lot of ear wax may be another factor that impairs hearing and the older we get, the more ear wax build up we find in our ears. Ear wax may be cleaned at the doctor's office.
Other hearing loss problems occur in aging people and most of them are solved by usage of a hearing aid.
(UMMC 2011)



-Vision
Eye changes might begin as early as a person's 30's. As the eye ages, things begin to change of course, just like every other part in your body when you age. An aging eye begins to produce less tears. Less tears mean that the eye can become very dry, which might become irritable to a person. The eye structures become to change. The cornea (which is the outside part of the eye where light hits) becomes less sensitive. This means that injuries may become unnoticed. When you turn 60 years old, the pupils have decreased in size (about 1/3rd the size they were when you are 20 years old). Also, the pupil's reaction rate to light and darkness becomes slower. The lens changes also. It starts to become more yellow in color, less flexible and a little cloudy. The fat that surrounds the eye for cushioning starts to shrink so the eye sinks back into the socket. Also, the eye muscles start to change and they become less able to complete their function, which is to rotate the eye horizontally and vertically.
Your vision worsens as you age due to all of the changes in the eye. Most people get contact lenses, or glasses in order to correct their vision.

-Others
As far as taste and smell- those two senses go together often. Smell is picked up by receptors in the nose and taste is picked up by your taste buds on the tongue. As a person ages, they start to have a decrease in the amount of taste buds. Taste buds begin to show atrophy. So, tasting food begins harder and distinguishing different flavors is more difficult. Another change that happens in the mouth as you age is that saliva production is greatly decreased. Less saliva means that old people always experience a dry mouth feeling. That can make swallowing more difficult and also make the digestive process less efficient.
The sensitivity towards the different tastes does not start to diminish until after age 60. Smelling starts to decrease after age 70. The reason smelling becomes more difficult is thought to be due to loss of nerve endings in the nose as a person ages.

(UMMC 2011)

Movement and touch

Touch related sensations about pain, temperature, position, texture, vibration and pressure (whether it is from joint receptors or cutaneous receptors) may decrease as a person ages.
The thing with these changes is that it is not figured out yet whether they occur due to our bodies aging, or due to certain disorders that older people tend to have. A reason we see a change in touch related sensations as people age may be due to a decrease of blood flow to the touch receptors or to the brain and spinal cord. Also, a person's diet may also be the source for the changes (an example being a decrease of Vitamin B1).
Another thing that can happen is people's sensitivities might increase as they age. Some people become more sensitive to touches, since their skin tends to become thinner. Also, a lot of old people become more sensitive to hot and cold.

When it comes to movement, as a person ages, their bones and muscles being to lose mass. A lot of problems arise with this. Movement becomes slower, and limited. Strength decreases as people age, but endurance might increase or decrease depending on the person's athletic status.
Elderly people might have reduced reflexes, which is due to changes in their muscles and tendons as they age. It is not so much due to the nerves, but more to the muscle and tendon. Usually, the knee jerk and ankle jerk reflex decrease. An example of a change of reflex that is not a normal part of aging would be a positive Babinski's reflex. The best way to prevent movement problems as we age is to keep good shape from healthy exercise and to have a good diet.

(UMMC 2011)



NEUROLOGICAL DISORDERS AND PROBLEMS RELATED TO AGING
-Alzheimer's disease
-Delirium
-Hearing loss
-Vertigo
-muscle atrophy or contractions (lead to problems in movement)-skeletalmuscular and nervous system related
-vision problems- cataracts, glaucoma, senile macular degeneration and diabetic and hypertensive retinopathy
-pressure ulcers (due to a decrease in being able to feel pressure)
-fall risks (due to your body not being able to sense your position as well)



RESEARCH AND IMPORTANCE

The field of geriatrics is a growing one and it is a very wide one. There is research being done on Alzheimer's, other forms of dementia, loss in all of the senses, change in movement, and a lot more interesting things (such as the effects of certain central nervous system drugs on the aging population- I read an article that talked about the relationship between CNS drugs and fall risks in the elderly). Speaking of falls, when it comes to movement the aging nervous system is very important to study. As the elderly population rises, more people enter nursing homes and it is important to study changes in movement in the elderly so better techniques get developed for preventing falls and things like pressure ulcers (due to not changing positions and moving around as much). Another interesting field of research is nutrition. Nutritionists are interested in finding out about the different senses of smell and taste as a person ages, and also their movement of their mouth. Due to aging changes in the taste and smell senses old people begin to lose their appetites so this is why there is lots of nutrition research being done on the aging population.

As our country's aging population starts to rapidly increase in the upcoming years this is a good field to do research in. We have to remember that aging is a normal process of life and it cannot be reverted, however research should be done to increase prevention and hopefully more treatments for abnormal aging, especially in relation to the nervous system.


GLOSSARY

knee jerk reflex- a reflex extension of the leg due to a sharp tap on the patellar tendon
glaucoma- a condition of increased pressure in the eye causing gradual loss of sight
senile macular degeneration- age related, affects the older population. results in loss of vision in the center of the visual field because of damage to the retina.
cataracts- a medical condition in which the lens of the eye becomes progressively opaque which results in blurry vision
CNS- central nervous system
PNS- peripheral nervous system
Babinski's reflex- also known as plantar reflex. stimulated by stroking a pointed object against a person's foot. If toes curl down this is a negative reflex and indicates normal motor cortex function. If toes curl up this is a positive reflex and means there must be some brain damage.
Alzheimer's disease- plaque and tangle build up in the brain, uncurable brain disease as people age. not normal, people still not sure what the cause of it- could be a person's lifestyle, or genetics, or randomness.
vertigo- a sensation of whirling and loss of balance, associated particularly with looking down from a great height, or caused by disease affecting the inner ear or the vestibular nerve
muscle atrophy- muscle begins to break down
muscle contraction- muscle is stuck in a position

QUIZ

-questions
T/F:
1.) Alzheimer's is a normal part of the aging process.
2.) Taste buds do not break down and decrease in amount as we age
3.) Scientists are not sure whether touch-related problems are due to the aging process or to other problems that just occur in the aging population
4.) Aging problems in the eye can start as early as a person's 30's
5.) The brainstem consists of only the pons and midbrain

-answers
1. F
2. F
3. T
4. T
5. F


RESOURCES

Alzheimer's association. 2009 Alzheimer's facts and figures. 2009. Alzheimer's and Dementia Journal of the Alzheimer's Association. 5: 234-270

Bishop, Nicholas A., Lu, Tao and Yanker, Bruce A. Neural Mechanisms of ageing and cognitive decline. 2010. Nature. 464: 529-535

Neuroscience online website- various chapters

http://www.umm.edu/ency/article/004023.htm

http://www.umm.edu/ency/article/004013.htm