Chapter 1. Brain Development: Late Adulthood

Synopsis

Human Development Video Activity

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You must read each slide, and complete any questions on the slide, in sequence.

Alzheimer’s disease

A terminal, degenerative brain disease characterized by gradual loss of memory, intellectual capacity, conversational skills, and eventually basic physical functions. Alzheimer’s is the most common cause of dementia.

axon

Long, slender nerve fiber that extends from the neuron's cell body. Axons create the transmission lines of the nervous system as they rapidly conduct electrical impulses from one neuron cell body to the dendrites of adjacent neurons.

cerebral cortex

The folded outer layers of the brain covering the cerebrum that are critically involved in many complex functions, such as memory, attention, perceptual awareness, thought, language, and consciousness.

dendrite

Slender projections of the nerve cell body that receive electrical impulses from adjacent neurons.

dementia

Dementia is not a disease itself but a term for mental decline that interferes with daily life and normal functioning. While common, dementia is not a normal part of aging. Alzheimer’s is the most common cause of dementia.

neuron

A nerve cell that receives and communicates information throughout the body as part of the central nervous system.

neurotransmitter

A chemical messenger that acts to transmit signals from one neuron to another. When the neuronal signal reaches the axon terminal, neurotransmitters cross the synaptic gap transporting the signal to the dendrites of adjacent neuron or neurons.

Parkinson’s disease

A degenerative brain disease in which cells that produce dopamine (a neurotransmitter) are damaged leading to muscle tremors and muscle rigidity. As these symptoms progress, they can result in difficulty walking, tendency to fall, and trouble writing. While not a curable disease, there are treatments available.

senescence

The state of being old or growing old. Biological aging.

synapses

The microscopic gap across which the axon of a neuron can transfer an electrical impulse to the dendrites of an adjacent neuron.

vascular dementia

Mental decline that is caused by a reduction in blow flow to brain cells. Cells that do not receive adequate oxygen and nutrients via the blood can wither and die. After Alzheimer’s disease, vascular dementia is the second most common cause of dementia.

axons

The long threadlike part of a nerve cell along which impulses are conducted from the cell body to other cells.

neurons

A specialized cell transmitting nerve impulses; a nerve cell.

Brain Development: Late Adulthood

Author

S. Stavros Valenti, Hofstra University

Synopsis

In this activity, you will observe animated illustrations of brain development in late adulthood. To demonstrate the normal aging processes, the animation will show the decrease in brain tissue accompanied by an enlargement of the ventricles as well as a microscopic view of the loss of gray matter and white matter. To show an impaired brain of older adults, you will see views that present changes in the brain of someone with Alzheimer’s disease, multi-infarct dementia, and Parkinson’s disease.

Normal Aging

In most cases, late adulthood is a time of continued connection to family, friends, vocations, and leisure activities for many people. Bodies and brains change with age, and some functions typically decline as part of a process known as senescence. However, you will see how these typical brain changes probably have little effect on the everyday behavior of people in good health after the age of 65.

Continued Thinning of Gray and White Matter

As the amount of brain tissue gradually diminishes during normal aging, there is a compensatory increase in the volume of cerebrospinal fluid, which results in an enlargement of the ventricles.

Note: video has no audio.

Starting in the early 20s and continuing through late adulthood, there is a gradual loss of brain volume as the gyri (“hills”) of the cerebral cortex become narrower and the sulci (“valleys”) become wider. The loss of brain volume coincides with an increase in the size of the ventricles, the inner chambers of the brain that are filled with cerebrospinal fluid.

As a first sign that the brain is aging, thinning appears in the gray matter layer, where neurons are concentrated. This is usually detectable in the brain of a person’s in his/her early 20s, but this thinning may start even earlier. In contrast to the thinning of the gray matter, the white matter, which includes myelinated axons and support cells, increases until about age 40 after which its volume decreases throughout the rest of a person’s life.

Play the animation to view the loss of brain volume in the adult years.

Microscopic Brain Changes

As a general rule, normal aging is associated with a loss of gray matter, but the rate of loss varies considerably in different areas of the brain.

Note: video has no audio.

While observing changes of the older adult brain under the microscope, the thinning of the gray matter seems to be mainly due to a loss of neurons and a reduction in the number of synapses. White matter loss seems to be due to a loss of axons and their myelin sheaths as well as to a loss of glial (support) cells.

Play the animation to view brain changes of gray and white matter during the adult and late adult years.

Brain Slowdown and Compensation

You might think that the loss of neurons and their connections would directly result in problems in thinking and everyday behavior in older adults, but this is not the case in most instances. When neurons die, other neurons routinely take over their function, and dendrites continue to grow over time.

Other brain changes are clearly related to a “brain slowdown” during late adulthood that includes the typical decrease in reaction time and in the speed of information processing. These changes in brain function are related to the reduction in the production of neurotransmitters, in the total volume of neural fluid, in the speed of cerebral blood flow, and in the pace of activation in various parts of the brain.

Interestingly, brain slowdown may not have much effect on thinking in everyday contexts where expertise, rather than not speed, is required. Expertise can compensate for slowdown, and it gives older adults the clear advantage over teens and younger adults in many situations.

Brain Slowdown and Compensation (continued)

Question 1.1

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In your response, please cite an instance when an older adult acted as a guide or teacher in a particular skill or in a philosophy toward an aspect of life. Be sure to explain how the experience and expertise of the older adult were particularly involved in this example.

Alzheimer’s Disease: Accelerated Loss of Brain Tissue

The majority of older adults can expect reasonably good health if they eat well, exercise, and stay active. Unfortunately, some people in late adulthood will develop dementia, a severe impairment of judgment, memory, or problem-solving caused by organic brain damage or disease.

A common form of dementia is Alzheimer’s disease, a disorder characterized by a loss of brain tissue that is greater than that which normally occurs in aging. This degeneration causes the gyri to become thinner, the sulci to become wider, and the fluid-filled ventricles to become larger.

Play the animation to compare a brain that has aged normally with the brain of a person who has Alzheimer’s disease.

Alzheimer’s Disease: Plaques

^{Microscopic abnormalities, such as the formation of multiple areas called neuritic plaques, occur. The plaques consist of a protein called B-amyloid, which is derived from degenerating neurons.}

Another characteristic of Alzheimer’s disease is the accumulation of plaques that form outside the brain cells from a protein called B-amyloid. This same protein can also accumulate inside the blood vessels of the brain and may cause a cerebral hemorrhage (rupture).

Play the animation to follow the changes that occur in the brains of people who have Alzheimer’s disease.

Alzheimer’s Disease: Neurofibrillary Tangles

^{Microtubules of a neuron collapse due to an abnormal form of tau protein. Neurofibrillary tangles develop within the neurons while neuritic plaques develop outside of the neurons.}

Microtubules make up the complex system of tiny tubes that serve to transport various substances within neurons. In Alzheimer’s disease, an abnormal form of tau protein accumulates within the neurons causing the microtubules to collapse, and this collapse interferes with their functioning.

Play the animation to see a close-up of a neuron of someone with Alzheimer’s disease.

Multi-infarct Dementia

^{This brain shows a mild reduction in size as infarcts occur.}

A second major cause of dementia in late adulthood is the blockage of blood vessels in the brain. This vascular dementia can be produced by a number of disease processes.

The most common of these is multi-infarct dementia, a condition in which a blockage or blockages of arteries in various parts of the brain occur. Over time, a person with these types of blockages may acquire multiple areas of brain damage. People with multi-infarct dementia usually show a progression of their condition in marked steps in contrast to those with Alzheimer’s disease whose symptoms are steadily progressive.

Play the animation to observe multi-infarct dementia, a form of vascular dementia.

Parkinson’s Disease

^{Parkinson’s disease: the substantia nigra of the midbrain}

In contrast to the more widespread changes that occur in a brain with Alzheimer’s disease or vascular dementia, a brain suffering from Parkinson’s disease shows a degeneration of a specific group of neurons in the midbrain. These neurons are part of an important control circuit for movement, balance, speech, and other functions.

These neurons communicate with other neurons in the circuit by releasing the chemical neurotransmitterdopamine from their axon terminals. When large numbers of these neurons die, the circuit malfunctions, and the symptoms and signs of Parkinson’s disease, such as stiffness, slowness and tremor, emerge.

Play the animation to observe the brain changes and motor symptoms of Parkinson’s disease.

Some Thoughts About Late Adulthood and the Brain

There are normal changes that occur in every person’s brain during late adulthood. Reaction times and information processing are slower than in early and middle adulthood, but in many everyday settings, this slowdown does not matter that much. Expertise, good judgment, a healthy lifestyle, and strong social bonds allow most adults to enjoy old age.

Assessment: Check Your Understanding

Question 1.2

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Correct! Loss of white matter is mainly due to a loss of axons and their myelin sheaths as well as a loss of glial cells, which are support cells for neurons.

Sorry. Loss of white matter is mainly due to a loss of axons and their myelin sheaths as well as a loss of glial cells, which are support cells for neurons.

Assessment: Check Your Understanding

Question 1.3

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Correct! In late adulthood, neurons may die, but dendrites continue to grow.

Sorry. In late adulthood, neurons may die, but dendrites continue to grow.

Assessment: Check Your Understanding

Question 1.4

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Correct! Expertise can compensate for “brain slowdown.”

Sorry. Expertise can compensate for “brain slowdown.”

Assessment: Check Your Understanding

Question 1.5

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Correct! Blocked brain arteries cause multi-infarct dementia. The death of certain kinds of neurons that release the neurotransmitter, dopamine, causes Parkinson’s disease resulting in problems with movement, speech, and other functions.

Sorry. Blocked brain arteries cause multi-infarct dementia. The death of certain kinds of neurons that release the neurotransmitter, dopamine, causes Parkinson’s disease resulting in problems with movement, speech, and other functions.

Assessment: Check Your Understanding

Question 1.6

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The Alzheimer’s brain shows an accumulation of plaques that form outside the brain cells from a protein called B-amyloid. This same protein can also accumulate inside the blood vessels of the brain causing a cerebral hemorrhage (rupture). Additionally, an abnormal form of tau protein accumulates within the neurons causing the microtubules to collapse, and this collapsing interferes with neuronal functioning.

Congratulations! You have completed this activity.Total Score: x out of x points (x%) You have received a provisional score for your essay answers, which have been submitted to your instructor.