Age Related Dysfunctions to the Nervous System

Decreased Reflex Responses

A decrease in reflex responses begins around the age of 60 and continues to decline as part of the aging process.  This includes the absence of jerk reflexes of the ankle, knee, bicep muscles, and tricep muscles.

Declining Autonomic Responses

The autonomic nervous system is responsible for regulating body temperature, pulse rate, and the control of anal and urethral sphincters.  As humans age maintaining normal body temperature during periods of extreme hot or cold, returning to a normal pulse rate after exercise, and maintaining control of urine and fecal matter due to a declining autonomic response.

Insomnia

There are two types of sleep: rapid-sys-movement (REM) sleep and slow-wave (non-REM) sleep.  Throughout the sleep cycle REM and non-REM sleep cycle.  It is thought that physiological recuperation occurs during non-REM sleep.  Although the time spent sleeping changes little with age, the ratio between REM and non-REM sleep changes, resulting in fewer periods of restorative non-REM.  Older people also complain of difficulty failing asleep and staying asleep.

Dementia

Dementia is a general term for a group of brain disorders that increase with age and cause memory changes, intellectual defects, behavioral disturbances, and other signs of mental deterioration.

Alzheimer’s disease, otherwise known as senile dementia of the Alzheimer type, is the most common form of dementia.  10% of people over the age 65 are afflicted with this disease while 40% of people over the age of 85 are afflicted with this disease.  The symptoms of Alzheimer’s disease are progressive, and at least three stages of this disease have been defined.

Stage one symptoms include impairments of recent memory, spatial disorientation, and a lessening of spontaneous emotional responses.   By stage two the patient loses higher learning functions, such as the abilities to read, write, and calculate.  The person will become confused, lose track of time, and eventually the person is unable to recognize his or her family.  In the final stage of the disease the person experiences seizures and becomes unable to speak appropriately.  While the exact cause of Alzheimer’s disease is unknown it is know that all people suffering from Alzheimer’s experience an accumulation of proteins in the brain.  It is thought that these proteins, also known as plaques, interfere with normal brain functioning.

Non-Alzheimer dementias the cognitive and behavioral changes resemble Alzheimer’s disease, but differ in that they are not progressive.

Multi-infarction dementia is characterized by multiple mini-strokes which cause damage to many small regions of the brain.  The person suffering from the mini-strokes may not be aware of the strokes or the progressive damage they are causing.  Over time if the strokes are left untreated the person may exhibit Alzheimer’s like symptoms.

Parkinson’s disease is a disorder of the basal nuclei, specifically of the substantia nigra, that demonstrates the effects of the direct and indirect pathways. Parkinson’s disease is the result of neurons in the substantia nigra pars compacta dying. These neurons release dopamine into the striatum. Without that modulatory influence, the basal nuclei are stuck in the indirect pathway, without the direct pathway being activated. The direct pathway is responsible for increasing cortical movement commands. The increased activity of the indirect pathway results in the hypokinetic disorder of Parkinson’s disease. Parkinson’s disease is neurodegenerative, meaning that neurons die that cannot be replaced, so there is no cure for the disorder. Treatments for Parkinson’s disease are aimed at increasing dopamine levels in the striatum. Currently, the most common way of doing that is by providing the amino acid L-DOPA, which is a precursor to the neurotransmitter dopamine and can cross the blood-brain barrier. With levels of the precursor elevated, the remaining cells of the substantia nigra pars compacta can make more neurotransmitter and have a greater effect. Unfortunately, the patient will become less responsive to L-DOPA treatment as time progresses, and it can cause increased dopamine levels elsewhere in the brain, which are associated with psychosis or schizophrenia.

Cerebrovascular accident, or stroke, is a common aging dysfunction that is often considered to be a dementia because it affects the brain.  The disease originates in the cardiovascular system when a blood vessel to the brain is obstructed or ruptures.  This cuts off blood flow to a region of the brain, causing the area to deteriorate and possibly producing permanent brain damage.  Large strokes may cause paralysis, dementia, or even death.  The death rates increase dramatically in individuals 65 years of age or older.