Samenvatting
Summary Chapter 2
Chapter 2 lecture notes Erik Scherder
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Summary chapter 2 + lecturenotes
2 theories central to the aging process: (1) wear and tear (Swaab) and (2) use it or lose it (Drachman).
Wear and tear
The usage of organic tssue leads to release of free radicals that are produced during aerobic
metabolism. Those radicals contribute to accelerated cell aging. The maintenance of a healthy weight
can minimize the release of the free radicals. Also antioxidants (vitamins E and C) reduce the release
of free radicals, so a healthy diet is important as well. Hypothesis: lipofuscin contributes to cell aging
no longer certain if that is true.
Aging coincides with changes in the CNS, making it more vulnerable to neurodegeneratve diseases.
These diseases may lead to an inactve lifestyle which can contribute to changes in various sensory
systems that will in their turn further increase inactvity. By increasing physical actvity levels, this
cycle may be interrupted. Higher levels of physical actvity are related to lower risk levels of cognitve
dysfuncton.
Use it or lose it
Aging is characterized by reducton in brain volume by neuronal death (apoptosis) and neuron
shrinkage (atrophy). Shrunken neurons stll possess some metabolism, so they may be reiactvated
again to reduce the vulnerability for neurodegeneratve processes. In an early phase of AD, sproutng
may help compensate for neuron loss by an increase in dendrites. However, in later phases it may
produce plaques. Stmulaton of neurons may postpone the onset of side efects of the aging process.
This stmulaton can be achieved by providing an enriched environment, manipulaton of trophic
factors, hormones and neurotransmiters. For example stmulaton of excitatory neurotransmiters
such as glutamate may be successful as the neurotransmiter is involved in memory and learning.
Exposure to an enriched environment must occur as early as possible. By stmulatng the brain with
sensory stmuli of various modalites, regeneratve processes may stll occur.
Executve functons (EF) are also vulnerable to the aging process. Especially the prefrontal cortex
(PFC) plays a major role in performing EFs. EFs coordinate and control other cognitve functons. The
PFC works in close relatonship with the hippocampus (atenton and inhibiton in episodic memory).
The reducton in aerobic physical actvity in older individuals is relected in a decline in physical
actvity energy expenditure. This energy expenditure is ofen expressed in metabolic equivalents
(METs). The higher the level of aerobic physical actvity, the lower the ageirelated decline in brain
tssue density of the frontal, parietal and temporal lobes. Noniaerobic physical actvity does not show
these benefts. Especially people with cardiovascular diseases and diabetes have the lowest level of
expended energy, a risk factor for those diseases but also for AD and vascular dementa. Those also
had most difcultes with (I)ADL ((instrumental) actvites of daily life). However, physical aerobic
exercising did not exert a positve inluence on cogniton in those with vascular dementa. An
explanaton might be that the CV risks atenuate the positve efects of physical actvity on cogniton.
The cognitve functon may sufer from physical actvity because the blood supply to the muscles may
occur at the expense of blood supply to various cortcal areas. In those with neurodegeneratve
diseases, it may be true that a decrease in physical actvity further aggravates existng cognitve
deterioraton. For those without a neurodegeneratve disease, physical actvity may postpone the
onset of such a disease. Cognitve impairment coincides with sensorimotor slowing; cognitve and
sensory processes are both required for locomoton. Declines in hand and motor functon may
further reduce the ability to perform ADL that may afect one’s QoL.
, Visual impairments tend to have the greatest impact on cognitve functons. Both hearing problems
and visual impairments inluence the IADL negatvely. Visual problems may increase the risk of
mortality. Also proprioceptve functon declines, seen in declines in statc and dynamic joint positon
sense (JPS), which increase the risks for falling and subsequent injury. Declines in odor identfcaton
have a negatve inluence on appette and food intake. This increases the risk for weight loss /
anorexia. Impaired processing of tactle stmuli further declines food intake. Research shows that
auditory, visual and motor capacites correlate highly with an ageirelated decline in general
intelligence. Partcularly longiterm memory processes appear to be vulnerable to the aging process.
This indicates that changes in central processing mechanisms of sensory stmuli are partly
responsible for declines in cognitve functon. Four hypothesis (see lecture notes). Apparently,
sensory dysfuncton can be predictve of cognitve dysfuncton, although there is no relatonship
between visual and auditory capacity and executve functons.
A loss of appette may reduce nutritonal state and immune system functoning, thereby increasing
the risk for other diseases. Intensifying the taste and smell of food may increase the appette.
However, an increase in salt or sugar is not advised as it may have adverse efects to the general
health of older people. Furthermore, physiological processes may contribute to the decline in
appette. Testosterone levels decrease during aging, causing an increase in leptn secreton which
subsequently reduces food intake and increases the rate of metabolism at rest. Malnutriton is likely
to exacerbate weight loss, reduce muscle mass and decrease muscle strength. Physical actvity
decreases body fat and leptn secretons.
Our sense of propriocepton enables us to understand the relatve positon of our bodies (and its
parts) in space and it plays a large role in helping us to maintain balance. The Joint Positon Sense
(JPS) is the ability to accurately estmate the angle of a jointiangle. A decline in statc JPS in older
people negatvely inluences gait and increases postural instability. It appear to be the muscle
receptors that are compromised. Knee JPS is further reduced by fatgue. Muscle receptors sending
JPS informaton do not functon optmally because of the aging process. Another cycle: quadriceps
strength drops, which also decreases JPS. This in turn decreases postural stability which in turn leads
to decreased IADL. This further decreases strength of the quadriceps. Next to statc JPS there is also
dynamic JPS; estmate a jointiangle while it is in moton. This is primarily facilitated by muscle
spindles. Age appears to have only a small efect on the dynamic positon sense, but may in
combinaton with other sensory disturbances increase the risk for falls. However, the decline in JPS
scores may also be due to a decline in divided atenton.
Phenomenon ‘last in i frst out’ neural circuits that reach structural maturaton latest in
development are the most vulnerable to early neurodegeneraton. Related to this is retrogenesis
the progression of degeneraton follows the course of normal maturaton in reverse order.
In considering gait disturbances, a few key points are important: (1) gait disturbances are not
preserved untl the later stages of dementa, they ofen occur in the earliest stages. (2) the nature of
the disturbances appear to be closely related to the stage of the disease at which assessment takes
place. Certain symptoms may disappear during the course of AD. (3) gait disturbances difer between
the various types of dementa and may therefore contribute to diferental diagnosis. (4) clinicians
are ofen unaware that gait disturbances can be an important clinical feature of dementa. Gait
disorders are classifed at three levels (see lecture notes). Higherilevel gait is closely related to
higherilevel cognitve functoning. A disturbance in higherilevel gait and gaitirelated motor actvity
can decrease the level of physical actvity a person engages in. This coincides with a decline in
cognitve functoning. Women have a more profound decline in posture control than men and appear
to have weaker lower limb extensor strength.
ADL, insttutonalizaton, QoL and mortality can be inluenced by hand motor functon. The
relatonship between cognitve impairment and the performance of functonal tasks in older people
with dementa is understudied.
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