SensorimotorSensorimotor Changes Changes with Agingwith Aging

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ContentsI. I. Neuroanatomical Changes in the CNS:Neuroanatomical Changes in the CNS:

1- Gross Brain Changes.

2-Neurochemical Changes .

II. SENSORY CHANGES WITH AGING SENSORY CHANGES WITH AGING :

1- The Visual System .

2-The Auditory System.

3-The Vestibular System .

4- The Olfactory and Gustatory Systems .

III. Endocrine, Gastrointestinal, and Metabolic Systems.III. Endocrine, Gastrointestinal, and Metabolic Systems.

IV. Respiratory System .IV. Respiratory System .

V. Renal System V. Renal System

Neuroanatomical Changes in the CNS

1-Gross Brain Changes. A linear, age-related decrease in adult brain

weight has been well-documented.

The progressive decrease in brain weight

and volume begins in middle life.

The two most prominent age-related

features are a decline in the physical dimensions

of gyri, known as gyral atrophy, and

ventricular dilation .

Gyral atrophy describes a decrease in the gray or white matter or both.

Ventricular dilatation has been reported to accompany both aging and decreased brain weight .

Age-related decrease in brain weight and dimension is very closely associated with deterioration of myelin and intracellularly lipofuscin accumulation.

Other cellular level features of normal aging are inclusions of phagocytic debris, clumping of mitochondria, and deterioration of neurotransmitter receptors.

Other theories suggested that normal aging of the brain results from general deterioration at the cellular level and decline in the ability of individual cells within a region to work together to produce integrated action.

Some evidence suggests a relationship between a specific area of atrophy and function.

Atrophy of specific brain regions is now being used in the diagnosis of neurodegenerative diseases such as Alzheimer's disease (AD).

Enlargement of the left lateral sulcus (fissure of Sylvius), suggesting loss of cortical tissue, has been correlated with decreased cognitive performance.

2-Neurochemical Changes 2-Neurochemical Changes Morphological changes in the aging brain are

accompanied by significant neurochemical changes. Primary neurotransmitters (NTs) include acetylcholine,

dopamine, norepinephrine, serotonin, and other peptide neurotransmitters.

Aging can affect a variety of steps between synthesis of the NT to the final production of a response in the postsynaptic cell. •Acetylcholine

Acetylcholine (ACh) is essential to the function of the central and peripheral nervous systems and is utilized in both the somatic and autonomic nervous systems.

A primary site for ACh is in the basal forebrain, where the cholinergic system innervates the hippocampus and neocortex or Human Brain, is the most recent area, where we perform high-level thinking and complex integrative tasks.

Since the hippocampus is one of the structures associated with memory and learning, many investigators have tried to establish a link between the presence of ACh and the integrity of short-term memory and learning.

Researches have reported reduced cortical ACh content in the aging human and a profound loss of acetylcholine in specific cortical sites in patients with Alzheimer's disease.

Dopamine :Although dopamine (DA) is widespread in the

CNS, the most frequently studied dopaminergic neurons are those located in the substantia nigra that project to the striatum of the basal ganglia.

The dysfunction of these neurons is directly related to Parkinson's disease. DA is also located in the diencephalon and the medulla.

Changes in the synthesis, inactivation, catabolism, content, and receptors have all been reported with aging.

The amount of DA present and the number of receptors in the striatum of the basal ganglia decrease after the fourth decade.

SENSORY CHANGES SENSORY CHANGES WITH AGING WITH AGING

The Visual System There is a gradual decline in

visual acuity before the sixth decade

followed by a rapid decline in many

patients from 60 to 80 years of age.

By age 40 to 55, visual

correction is necessary in most people

for accurate near vision.

Common ophthalmological

disorders in the older person include

cataracts, glaucoma, and macular

degeneration.

The macula lutea, located in the posterior pole of the human eye, is only about 6 mm in diameter, but it is the most important part of the eye for contrast discrimination because of the high concentration of cone receptors in this area.

1-Age-related maculopathy (ARM) is an age related degenerative disorder of the macula that occurs with a rising prevalence in persons 50 years and older.

2-The small pupil that occurs with aging and the clouding of the lens and its inability to change its shape (accommodation) were the primary targets for visual correction in the older individual.

3-The most common visual problem among older adults is presbyopia, or difficult focusing on near objects.

4-The number of neurons in portions of the primary visual cortex (Brodmann's area 17) is significantly reduced with aging. A loss of one half of the cells that process information has been proposed based on the comparison of neuronal density at age 20 to neuronal density at age 80.

5-Aging also affects the integrity of the visual fields, dark adaptation, and color vision.

6-Color discrimination changes also take place with aging. In particular, older adults have more difficulty identifying blues and greens.

7-Spatial visual sensitivity decreases in the older adult, especially to low spatial frequencies and slow moving targets.

The Auditory SystemPresbycusis age-related decline in auditory function,

is the most common cause of hearing loss in adults.

Presbycusis is characterized by the gradual,

progressive onset of bilateral hearing loss of high-

frequency tones first and later involving loss across the

entire spectrum.

Presbycusis can occur for at least two distinct reasons;

(1) Changes in the peripheral sensory organ; the outer,

middle and inner ear; or changes in the central pathway.

(2) Changes in the auditory portions of the cerebral cortex.

The peripheral structures are related to hearing

sensitivity, whereas the central systems are related to

understanding speech, especially under difficult listening

conditions. .

The Vestibular System Complaints of dizziness

and disequilibrium are common in older persons.

The vestibular end organs are responsible for transforming the forces associated with head acceleration into action potentials, producing awareness of head position in space (orientation), and motor reflexes for postural and ocular stability.

The utricles and saccule sense linear acceleration, and the semicircular canals monitor angular acceleration.

Presbyastasis is the term to describe age-related

disequilibrium when no other pathological condition is

noted.

Studies of the vestibular system indicate an age-

related 20% decline in hair cells of the saccule and

utricle and a 40% reduction in hair cells in the

semicircular canals.

Age-related changes in the morphology of the

vestibular system correspond to changes in vestibular

function using caloric testing, i.e., bathing the auditory

canal with warm or cold water and examining ocular

responses.

Young patients respond with involuntary eye

movements of high frequency and large amplitude

when warm or cold water is placed in the auditory canal

compared with persons older than 60 years.

Presbyastasis must be distinguished from

pathology of the vestibular system in older individuals.

Vertigo, nystagmus, and postural imbalance may

be symptoms of age-related decline if underlying

vestibular pathology is ruled out.

The Olfactory and Gustatory Systems Hyposmia, a diminished sensitivity to smell, and

hypogeusia, a diminished sensitivity to taste, are both

reported as age-dependent changes in the olfactory and

gustatory systems, respectively.

The mechanisms that account for the age-related

changes in the two systems remain equivocal.

The current hypothesis for age-related hypogeusia is a

change in the taste cell membranes with altered functioning

of ion channels rather than a decreased number of taste buds.

Such deficits can alter food choices and intake of

food, leading to exacerbation of disease states, impaired

nutritional status, and weight loss that interferes with

functional capacity.

Endocrine, Gastrointestinal, and Metabolic Systems

Aging results in a decrease in the amount of total body water and total body fat.

There is no clear evidence of a decline in metabolic activity, but the total number of body cells decreases.

There is deterioration of the structures in the mouth. Periodontal disease can cause loss of gum tissue and subsequent tooth loss.

There is also a decrease in salivary flow from degeneration of the salivary glands.

The smooth muscle contractions of the esophagus decrease and the opening between the esophagus and stomach loses tone.

Smooth muscle contractions throughout the rest in the intestinal tract are slowed. Therefore, it takes much longer for food to move through the system.

The lining of the intestinal tract degenerates and fewer nutrients are absorbed. This contributes to malnutrition.

The smooth muscle contractions of the large intestine are also diminished. This often leads to fecal impaction and constipation.

In some cases, degeneration of the rectal sphincter occurs and can cause loss of bowel control.

The liver decreases in size, weight, and function, which decreases liver enzymes. This causes a loss in the liver's ability to aid in digestion and to metabolize certain drugs.

Respiratory System From 30 to 80 years of age there are changes in the

respiratory system. These changes occur mainly as a result of alterations in the respiratory muscles and in the normal elasticity and recoil of the thorax.

There is a decrease in the size and strength of the muscles used for respiration, and calcium deposits begin to form where the ribs join the sternum, causing the rib cage to become less pliable.

The diffusion of oxygen and carbon dioxide across the alveolar membrane also decreases as more and more alveolar surfaces degenerate.

Finally, the body becomes less sensitive to hypoxia or increased levels of carbon dioxide in the blood and tissues.

Elderly patient's lungs also have a diminished ability to inhibit or resist disease and infection.

The cough and gag reflexes also decrease, thus preventing adequate clearing of substances from the airway and allowing respiratory infections to develop more often.

Furthermore, elderly patients often suffer from dehydration which increases the tendency for respiratory infections.

The net effect of these respiratory system changes seen in the elderly is that less air enters and exits the lungs, less gas exchange occurs, the lung tissue loses its elasticity, and many of the muscles involved with breathing lose their strength and coordination.

Renal System In the renal system of the elderly patient there is a

decline in kidney function. The number of functioning nephrons (functional units

of the kidneys) may decrease 30-40 percent.Renal blood flow decreases which:

1) Increased the amount of waste product in the blood. 2) Contributes to a decrease in the kidneys responsiveness to hormones that regulate fluid and electrolyte balance.

These changes may cause fluid and electrolyte imbalances.

Since the kidneys filter out many drugs (including antibiotics), it is common for the elderly to suffer from drug toxicity.

In the elderly male patient, the prostate often becomes enlarged (benign prostatic hypertrophy), causing difficulty urinating or urinary retention.