Chapter 7.docx

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26 Apr 2012
Chapter 7- Aging and the Regulatory Systems
Sensory System
The sensory system is composed of 5 senses: touch, smell, taste, hearing, and vision
- Sensory organs allow the nervous system to gain info about the external environment
Age-and Disease-Related Changes
The skin is the sense organ for touch
W/ age, these receptors (touch & pressure) decrease both in number and in sensitivity, resulting in a degradation of
the sense of touch, w/ decreases ability to detect, locate or identify objects
Given the importance of smell in the sense of taste, degradations in the ability to smell food may impair an older
person’s appetite
The ability to smell is also important in detecting whether food has gone bad and food-bourne illnesses are a risk for
older adults who have lost much of their sense of smell, as they may be unable to determine whether or not food has
Decrease in the senses of smell may have other safety and behavioural implications like an inability to detect leaking
gas or when one has unacceptable body odours
Most of what we consider is actually a function of smell
The taste buds in the tongue can sense salt, sweet, sour, bitter, fat, and “umami”, which is composed of glutamate
At worst, aging may cause slight decreases in the sensitivity of these neurons, which may be below the sensory
threshold and thus undetectable
Decline in the sense of taste can have serious consequences, as it is one factor that can lead to anorexia in older adults
Age-related changes in the auditory structures affect not only hearing but balance as well
Sound is transmitted through the outer ear via the ear canal into the middle ear through vibrations in the eardrum (Fig
7.1- pg. 166)
The middle ear contains three ossicles, or little bones, that pass vibrations to the oval window, a flexible membrane
that is the beginning of the inner ear
Fluid in the inner ear puts pressure on the cochlea
- This is lined w/ the basilar membrane, which bristles w/ row of 1000’s of neurons that make up the organ of Corti
- These “hair cells” contact nerve fibres that transmit acoustic signals to the CNS
A highly complex structure in the inner ear, called the vestibule allows organisms to sense gravity and head rotation
- The vestibule consists of 2 small, gelatin-filled sacks that have small mineral particles and hairlike sensors
- The minerals press down on the sensors, transmitting info to the brain on the position of the head, and therefore
whether one is upright, upside down or tilted
Many age-related changes can affect hearing and balance
Cells in the ear canal generate earwax, a lubricant that thickens w/ age and can build up, decreasing sensitivity to
Although the eardrum itself can become stiffer and the ossicles a bit arthritic, this does not end to affect hearing
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However, the organ of Corti may be affected by atherosclerotic changes in the capillaries that provide nutrients to it,
by wear and tear, and by ototoxic medications- those that are toxic to the mechanisms of the ear
The structures of the inner ear that sense gravity and head position can also degrade over time, leading to dizziness
and falls
B/c the shorter hair cells that respond to high frequencies are located at the beginning of the cochlea, they receive the
most wear and tear; thus high-pitched sounds are usually lost first
Risk factors included ototoxic drug and occupations w/ high noise exposure, whereas exercise was protective, due to
its positive effect on blood flow
Severe presbycusis can profoundly affect the life of the older person
- E.g. diminished ability to hear car horns, smoke alarms, and barking dogs, negatively affects personal safety
Tinnitus, often defined as a ringing in the ears w/ no discernable cause, is another common problem w/ age
- It has many sources, including ear infections, high blood pressure, diabetes, tumors, atherosclerosis, malnutrition,
medications, and toxic chemicals
- For most people, this is simply annoyance that can be masked by the use of soft music
- It tinnitus becomes severe, however it can be very distracting and interfere w/ sleep and everyday activities
Figure 7.2 (pg. 168)
Light passes through the cornea, a transparent structure that protects the eye and by contracting and dilating, muscles
in the iris regulate the amount of light that enters the eye
At the back of the eye is the retina, which contains photoreceptors( rods and cones)
- The photoreceptors then translate light energy into action potentials in the optic nerve
- Cones are responsible for colour vision, whereas rods only transmit info in black and white, although they are
more sensitive to light
- Cones are must numerous in the macula, which is in the center of gaze in a direct line from the cornea
- Rods are typically found in the more peripheral regions of the retina
The lens focuses on the image on the retina, adjusting for the distance of the object
The whole structure is supported by gel-like substances called humors in the chambers in the eye
- Aqueous humor not only provides support but also transports nutrients and wastes, whereas the more gel-like
vitreous humor protects the eye against shock
The conjunctiva, a clear mucus membrane inside the eyelids also provides protection
The complexity and sensitivity of the eye make it quite vulnerable to aging effects
The cornea, lens, and vitreous humor all diminish in transparency, reducing the amount of light entering the eye and
also scattering the light that does come in, making the eye more sensitive to glare
- Yellowing of the lens also decrease its transparency and makes it difficult to differentiate blues, greens, and violets
- The lens loses elasticity w/ age, making it more difficult to focus on near objects- called presbyopia and is most
common age-related visual problems
The muscles in the iris decrease in number and strength w/ age, and its collagen stiffens, reducing the ability of the
pupil to enlarge
The lacrimal (tear) gland and conjunctiva produce less of their protective fluids, which can result in inflammation and
- The rate at which aqueous humor is generated also declines, and there might not be enough to properly maintain
the shape of the cornea
- Vitreous humor also decreases in size and becomes more liquid- as it moves about, it can create tension on the
retina, causing flashes; too much tension can cause the retina to detach, causing blindness
Rods in the older person’s retina may become irregular, further decreasing the ability to see in dim light and optic
nerve fibres are also lost, decreasing the quality of vision
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The 4 most common serious diseases of the eye in late life are cataracts, macular degeneration, glaucoma, and
diabetic retinopathy
Characterized by cloudiness or opacity of the lens; this can occur at any age but if found more frequently in later years
Although painless, w/ time it can interfere w/ vision, particularly at night or in bright sun-light
The main risk factors for developing cataracts, besides age, are exposure to UV-B light and environmental pollutants,
topical or internal steroids, diabetes, smoking and low levels of antioxidants
The leading cause of blindness in adults over the age of 50 and can be present for many years w/o any symptoms
Caused by an increasing build-up of aqueous humor in the eye, which results in an increase in intraocular pressure and
damage to the retina and optic nerve
Macular degeneration (AMD)
There are two types, known informally as wet (or exudative) and dry (atrophic) AMD
- Dry AMD has a gradual onset where as wet AMD can be sudden resulting in precipitous visual decline
- Although the dry form is the more common type, the wet form is responsible for most cases in which there is
severe vision less
- Exposure to UV rays and smoking are probably the major risk factors, but there is some evidence that the
ingestion of vegetable fats also increases the risk of AMD
Promoting Optimal Aging
Avoid smoking which affects taste buds and is a risk factor for cataracts and may accelerate hearing loss
Maintain good health through diet (avoid diets high in fat and get sufficient levels o vitamin A and antioxidants) and
Use sunglasses to avoid ultraviolet light b/c it decelerates age-related changes in vision
Nervous System
Basic Anatomy and Physiology
It monitors and provides communication b/w all the systems and regulates homeostasis
Also permits voluntary movement and underlies all cognitive processes, like sensation, attention and language
The CNS consists of the brain and the spinal cord; the PNS consists of sensory and motor neurons
The ANS is responsible for all regulatory functions, like monitoring and controlling blood pressure, digestion etc; it
includes components of both the CNS and PNS
- Further divided into the sympathetic (SNS) and parasympathetic nervous system, which act in consort to stimulate
and inhibit their target organs in order to respond adequately to environmental challenges and then return to
baseline functioning
There are several types of neuronal cells, but each consists of a cell body or soma, an axon, and dendrites
- Each nerve cell has a single axons which can extend for far distances, but many spiky dendrites, which branch out
from the soma
- Neurons communicate w/ each other across interneuronal junctions called synapses
- Communication across synapses is primarily chemical but can be electrical, especially outside the brain
- Communication across a particular synapse is always unidirectional, and can be inhibitory or excitatory
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