Understanding Alzheimer's Disease

This assignment focuses on understanding Alzheimer's disease. It examines various aspects including the causes, symptoms, and available treatments. The provided resources cover brain anatomy, behavioral risk factors associated with aging, and therapies for prevention and treatment of Alzheimer's. The document also highlights research findings on neurodegeneration in the context of Alzheimer's.

Running Head: NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
Neurological Basis of Alzheimer’s Disease
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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
Neurological Basis of Alzheimer’s Disease
The human brain is an intricate modular structured organ, responsible for the
entire nervous system of the body (Lewis, 2016). It consists of about hundred billion
nerves, and is organized into distinct cortical areas for sensation, perception, and
information, maintained through trillions of connections called synapses (Hoffman,
2017). Though the brain’s cortical areas act individually (Fukushima et al., 2015),
they may malfunction due to injuries, degeneration, and genetic flaws, thereby
affecting the neurobiological mechanisms to cause behavioral disorders (Hoffman,
2017). Alzheimer's disease is one such neurological disorder that originates from
genetic, environmental, and lifestyle factors that influence the brain in due course,
leading to cognitive decline and memory loss (MacGill, 2016). Considering its
increasing incidence in the aging people, this essay analyzes the neurological basis of
Alzheimer’s disease and the underlying biological bases of behavior.
Alzheimer’s disease
Alzheimer’s disease is a type of dementia that develops from the disruptions in
the neurological functions of the human brain. It affects nearly 80% of people over 65
years old, creating problems in their memory, communication, emotion control,
reasoning, decision making, concentration, and perception. Biologically, Alzheimer’s
occurs when the proteins and fibers accumulated in the brain, tend to destroy the nerve
cells, blocking the nerve signals (Bernstein, 2016). Neurologically, it involves several
processes in the brain, and before delving deep into them, it is necessary to illustrate the
anatomy of the human brain and its functions deriving sensation, perception, and
processing of information.
Anatomy of human brain

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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
The human brain is larger in size than the other brains, and is the command
and control center of the human nervous system. The brain and the spinal cord make
the central nervous system, while the neural structure extensions act as the peripheral
nervous system, having somatic and autonomic divisions (Rughani & Penar, 2015).
The brain has three parts, namely the forebrain, the midbrain, and the hindbrain. The
cerebrum is developed from the forebrain, while the midbrain becomes a portion of
the brainstem. The cerebellum and the remaining part of the brainstem build the entire
hindbrain (Lewis, 2016).
The cerebrum consists of two hemispheres and the brainstem lies underneath
it. Behind the brainstem is the cerebellum. The cerebral cortex on its outermost layer
includes frontal, parietal, temporal, and occipital lobes, and is made up of the gray
matter (Lewis, 2016, Rughani & Penar, 2015). The long myelin coated axon fibers,
called the white matter, lie below the cortex, connecting the neurons for increasing the
signal’s conduction speed. The central sulcus separates the parietal lobe from the
frontal lobe, and the lateral sulcus divides the temporal lobe from them. On the
medial surface, the parieto-occipital sulcus keeps apart the occipital lobe from the
parietal lobe. The cortex, the subcortical fibers, and the basal nuclei include the
telencephalon of the cerebrum. The diencephalon section of the cerebrum has
thalamus and hypothalamus (Rughani & Penar, 2015).
The brainstem, consisting of the medulla oblongata, pons, and midbrain, relays
information between the brain and the body. The cranial nerves extending to the face
and head are supplied by the brainstem, and at the same time, it regulates the
functions of the heart, breathing and consciousness. The thalamus and hypothalamus
sit between the cerebrum and brainstem. It is the thalamus that transmits the sensory
and motor signals to the cortex and is responsible for controlling consciousness, sleep

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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
and alertness. The function of the hypothalamus is to connect the nervous system to
the hormone producing endocrine system, through the pituitary gland. The cerebellum
lying below the cerebrum performs the motor control, such as coordination and
balance, as well as some cognitive functions (Lewis, 2016).
Limbic system
The limbic system, which is formed of cortical and subcortical structures, such
as the amygdala, hippocampus, mammillary bodies, fornix, cingulate gyrus, and the
parahippocampal gyrus, engage in intricate interactions between them. The signals
produced by the hippocampus are transmitted to the mammillary bodies through the
fornix, and from there, they are sent by means of the mammillothalamic tract to the
thalamus anterior nucleus. The ensuing thalamocingulate radiation signals project to
the cingulate gyrus and are sent back to the hippocampus for completing the circuit.
Thus, the hippocampus becomes the primary output component of the limbic system
that is involved in the memory and emotional response production (Rughani & Penar,
2015).
When the amygdala receives multiple sensory information modes as inputs,
the outputs that originate from the amygdala output structures, such as the
hypothalamus, thalamus, hippocampus, brainstem, and the cortex, pass through the
stria terminalis and the ventral amygdalofugal path, to mediate the emotional parts of
memory and fear responses. The hippocampus is crucial in the formation of
declarative memory, which provides the ability to remember the past life events
(Rughani & Penar, 2015).
The complex thought processes of humans are thus seated in the cerebral
cortex, and the visual processes take place in the occipital lobe at the back of the
skull. The temporal lobe accounts for sound and language, while the hippocampus

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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
regulates the memory and the amygdala controls the emotion part. The parietal lobe
coordinates all the signals received from the different senses and manages the spatial
orientation and navigation (Lewis, 2016). Historically, cerebellum was considered to
carry out the ‘non-thinking’ functions, like balance, motor control, and muscular
coordination, making the cerebral cortex as the seat of cognitive functions, like
social intelligence, linguistics, logic, creativity, and many more activities.
Notwithstanding, the cerebellum controls several cognitive functions, including
emotional interactions (Bergland, 2016).
The basal nuclei
The basal nuclei possess the caudate nucleus, globus pallidus, putamen,
substantia nigra, and subthalamic nucleus. While the lentiform nuclei are formed out
of putamen and globus pallidus, the putamen and caudate nucleus combine to form
the striatum. The basal nuclei integrate with the thalamus motor nuclei, motor cortex,
and premotor cortex to modulate body movements. The primary motor cortex and
premotor cortex give input to the basal nuclei, consisting of pyramidal cells in the
cortical layer V, leading to the striatum, which also receive input from the substantia
nigra’s dopaminergic cells. Subsequently, the striatum releases inhibitory projections
to the interna and globus pallidus externa, which send the inhibitory projections to the
subthalamic nucleus. The subthalamic nucleus will then send the excitatory
projections to the globus pallidus interna, which in turn projects them to the thalamus
ventral anterior and lateral nuclei (Rughani & Penar, 2015).
Each of the left and right portions of the thalamus is separated by the internal
medullary lamina into anterior, ventrolateral, and medial nuclei, out of which the
anterior thalamic nuclei function with the limbic system to elicit reciprocal
connections between the mammillary bodies and cingulate gyrus, while the medial

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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
nuclei project reciprocal connectivity to the frontal and premotor cortex. The divisions
of the ventrolateral nuclei work as the sensory transmissions in the body and face.
The other thalamic structures, like the medial and lateral geniculate bodies, regulate
the auditory and visual information in the brain. The pulvinar provides reciprocal
connectivity with the parietal and occipital cortex. All the while, the intralaminar
nuclei of the internal medullary lamina collect input from the thalamic nuclei and
project it to the basal nuclei and other thalamic nuclei. The centromedian nucleus, as a
part of the reticular activating system, maintains cortical arousal (Rughani & Penar,
2015).
Biological processes in the brain
The neurons are made up of three different parts, such as the cell body,
multiple dendrites, and axon. The cell body involves the nucleus, which possesses the
genetic trait that controls the activities of the cell. The dendrites are structures that
protrude from the cell body and gather information from the other neurons.
The axon is similar to a cable at the cell endings, positioned against the dendrites for
relaying messages to the neuron counterparts. The functions of the neurons depend on
the different biological processes, such as communication, metabolism, and repair,
remodeling, and regeneration (National Institute of Aging, 2017).
Communication
The neurons are in constant touch with the adjacent cells, and when an
individual neuron gets signals from its counterparts, it generates an electrical charge.
This charge journeys through the axon and emits certain neurotransmitter chemicals
along a tiny gap, known as a synapse. Subsequently, each neurotransmitter molecule
connects to a specific dendrite receptor of an adjacent neuron, triggering chemical or
electrical signals for stimulating the signal-receiving-neuron’s activity. This

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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
communication happens in all the network of brain cells (National Institute of Aging,
2017).
Metabolism, Repair, remodeling, and regeneration
Metabolism is crucial in the healthy functioning of the cell and also in its
survival. To facilitate this, the cells need energy in the form of oxygen and glucose
from the blood circulating in the brain. Since neurons need self maintenance, they
remodel their synaptic connections, according to the stimulation received from the
other neurons. Adult brains exhibit neurogenesis, characterized by the generation of
the new neurons. The remodeling of synaptic associations and neurogenesis are
critical in learning, memory, and brain repairs. The glial cells in the forms of
microglia, astrocytes, and oligodendrocytes support the neurons to remain healthy.
The glial cells protect the neurons from physical and chemical damages, as well as
the disposal of alien substances and cellular debris from the brain (National Institute
of Aging, 2017).
Causes of Alzheimer’s disease
Alzheimer's disease is a neurodegenerative disease, caused by the death of
brain cells (MacGill, 2016). It is distinguished by the loss of cognitive function and
development of several behavioral problems, having severe consequences (Rouch &
Dorey et al., 2014). The disease is characterized by the blood-brain barrier disruption,
mitochondrial impairment, oxidative stress, neuroinflammation, and hypometabolism.
Alzheimer’s disorder is more associated with the accumulation of amyloid-β peptide
accumulation tau hyperphosphorylation, along with the reduction in the levels of
acetylcholine and cerebral blood flow (Mendiola-Precoma et al., 2016). As a result,
the size of the brain shrinks, leaving the nerve cells and connections reduced over
time (MacGill, 2016). The people with Alzheimer's disease has fewer neurons,

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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
because of Necroptosis, causing cells to explode from the inside and die (Arizona
State University, 2017).
Though the living brain seldom reveals the disease, an autopsy will display
minute forms of dying cells called plaques and tangles. The plaques are formed out of
the protein called beta-amyloid, whereas the tangles develop from the disintegration
of a protein called tau (MacGill, 2016). The neuropathological characteristics of the
different forms of Alzheimer’s disease can be identified as the abnormal extracellular
accrual of amyloid-β peptide (Aβ) in the amyloid plaques and tau protein that are
accumulated in the intracellular neurofibrillary tangles (NFTs) (Mendiola-Precoma et
al., 2016). However, recent researches demonstrate that if the microglia cells of the
brain lack enough TDP-43 protein, they will remove Alzheimer's plaques and
synapses, causing the neurodegeneration in Alzheimer's patients (University of
Zurich, 2017).
Conclusion
Alzheimer’s disease (AD), which is associated with the progressive
neurodegenerative disorder, affects 44 million people, globally in 2015, and is
estimated to double within the next 3 decades (Rouch & Dorey et al., 2014). The
symptoms of Alzheimer's include problems with memory, judgment, and thinking
process. A healthy human brain has billions of neurons, having the ability to process
and relay information through electrical and chemical signals, between the brain and
other organs of the body. Alzheimer’s disease devastates these communication
provisions among the neurons, causing loss of cell activity and death (National
Institute of Aging, 2017). The main contributing elements of this disease are genetic,
environmental, and lifestyle factors, and their impact in the mid-life can make the
later life troublesome (Lafortune et al., 2016). The strategies for preventing the

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NEUROLOGICAL BASIS OF ALZHEIMER’S DISEASE
occurrence of Alzheimer’s disease include lifestyle interventions, like physical
activities, healthy diet, mental challenges, and socialization (Mendiola-Precoma et al.,
2016). Though there is no strong evidence of preventing Alzheimer’s disease, the
cognitive training and the use of drugs that thwart the brain clogging plaques, can
delay the memory loss and other behavioral problems in the affected people (Fox,
2017).

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