The Brain and Alzheimer’s | 3D Anatomy Software

by Robert Tallitsch, PhD | March 3, 2022

The Brain and Alzheimer's Disease Explanation and Anato

Video explanation of the Brainstem and Alzheimer's Disease!

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Written by: Robert Tallitsch, PhD

To many, the brain is the most fascinating structure of the human body. Often compared to a computer, the brain is capable of conducting many times more simultaneous functions than any computer constructed thus far. In addition, the brain is able to rewire itself as it learns new facts and functions and - although only to a limited extent - is able to heal itself following illness and/or trauma.

The brain is composed of three basic subdivisions:

  1. Cerebral hemispheres
  2. Cerebellum
  3. Brainstem, which is subdivided into the:
  • Diencephalon
  • Mesencephalon (midbrain)
  • Metencephalon (pons)
  • Myelencephalon (medulla)

Cerebral Hemispheres

Gray Matter of the Hemispheres

The paired cerebral hemispheres, which are partially separated from each other by the longitudinal fissure, are mirror image duplicates. These hemispheres are joined together by the corpus callosum. Each hemisphere is composed of a highly convoluted cortex, consisting of a highly cellular gray matter, an underlying layer of white matter consisting of neuronal processes, and a collection of deeply located nuclear masses termed the basal ganglia.

The surface of each hemisphere is convoluted, being composed of grooves (sulci) and elevations (gyri) that increase the surface area of the cerebrum. In addition, each hemisphere is subdivided into lobes — each of which is named for the bone of the skull superficial to it.

The frontal lobe, which is the largest lobe of the brain, is found deep to the frontal bone. Its posterior boundary is the central sulcus, and its inferior boundary is the lateral sulcus. The primary motor area, premotor area, and prefrontal areas are located within the frontal lobe. The primary motor area, which controls voluntary motor movement, is comprised of the precentral gyrus and the anterior portion of the central sulcus. The prefrontal areas are found rostral to the primary motor area, and are involved in judgement and the setting and achievement of goals.

The parietal lobe houses the primary somesthetic (primary sensory) area and the cortical association areas of the brain. The primary somesthetic area (perception of somesthetic sensory information) is composed of the postcentral gyrus and the posterior portion of the central sulcus. The cortical association areas (understanding and interpretation of somesthetic sensory information) are composed of the inferior parietal lobule of the brain.

The temporal lobe houses the primary auditory cortex (reception of auditory sensory information) and the primary olfactory cortex (reception of olfactory sensory information).

The occipital lobe, which lies deep to the occipital bone, is the location of the visual cortex (reception and understanding of visual information).

The limbic lobe of the cerebral hemisphere is termed an “artificial lobe” or “synthetic lobe” of the brain, in that it consists of large cortical convolutions on the medial aspect of the cerebral hemisphere. The limbic lobe surrounds the rostral portion of the brainstem and the interhemispheric commissure. Simply put, the limbic lobe is responsible for behaviors that are essential to the preservation of the species.

White Matter of the Hemispheres

The white matter forms the medullary core of the hemispheres and consists of three types of neuronal fibers:

  1. Projection fibers convey neuronal information from the cortex to different locations within the central nervous system (CNS).
  2. Association fibers interconnect various cortical regions of the same cerebral hemisphere.
  3. Commissural fibers interconnect cortical regions of the two hemispheres.

Brainstem

Myelencephalon (Medulla)

The medulla, the most caudal portion of the brainstem, extends from the foramen magnum of the skull to the caudal portion of the pons. The medulla is the location of several important physiological centers that serve to regulate the cardiovascular and respiratory systems.

Metencephalon (Pons)

The pons is located between the mesencephalon and the medulla of the brain. The pons is a relay center, being comprised of neuronal processes communicating with the cerebellum, pontine nuclei, tegmentum, and the spinal cord.

Mesencephalon (Midbrain)

The mesencephalon is the smallest and least differentiated portion of the brain. This portion of the brain is composed of the following structures:

  • Tectum, which is composed of the superior and inferior colliculi.
  • The superior colliculi are visual relay centers and are concerned with visual reflexes.
  • The inferior colliculi are auditory relay centers concerned with processing of auditory information and auditory reflexes.
  • Tegmentum, which is a relay center for various brain centers.
  • Crura cerebri, which is a relay center to structures within the spinal cord, pontine nuclei and/or regions within the brainstem.
  • Substantia nigra, which is a relay center and a structure concerned with the regulation of motor function.

Diencephalon

This is the most rostral portion of the brainstem, and it is composed of four parts:

  1. Epithalamus
  2. Thalamus
  3. Hypothalamus
  4. Subthalamus

Cerebellum

The cerebellum overlies the posterior portions of the pons and medulla, and fills the greater portion of the posterior cranial fossa. It is composed of two hemispheres that are connected via a midline vermis.

Structurally the cerebellum, like the cerebrum, has a convoluted surface, and a medullary core of white matter. The folds of the cerebellum are termed the folia cerebelli.

Alzheimer’s Disease

Alzheimer’s disease has perplexed researchers for decades. One of the few things that researchers are able to agree upon is that the damage to the brain caused by Alzheimer’s disease begins at least a decade before alterations in memory or other cognitive functions appear in the patient.

The timing of the first symptoms of Alzheimer’s, as well as the symptoms themselves,  varies from person to person. Symptoms of early-onset Alzheimer’s typically manifest in an individual between the age of 30 and the mid-60s, while symptoms of late-onset Alzheimer’s typically manifest in the mid-60s or beyond. Although it varies from person to person, one of the first signs of cognitive impairment from Alzheimer’s disease is a progressive loss of memory. Other signs may involve (in no specific order) the inability to find the appropriate word to use in a sentence (loss of word finding), visual and/or spatial issues, impaired reasoning or judgement, decline in the ability to make reasonable decisions and judgements, and the inability to perform familiar tasks.

Medications may temporarily improve or slow the progress of Alzheimer’s, but there is no cure nor lasting treatment for Alzheimer’s.

Although there is no definitive known cause for Alzheimer’s, it appears to be linked to the degradation of brain proteins, resulting in the inability of brain neurons to function properly. As a result, neurons are damaged, lose connections to other neurons within the brain, and ultimately die.

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This Brain Builder video and activity focuses on the brainstem. You can see our other Brain Builder that covers the Brain and Dementia by clicking here. 

Key Terms: 

Brainstem - Division of the brain composed of the diencephalon, mesencephalon (midbrain), metencephalon (pons), and myelencephalon (midbrain).

Myelencephalon (Medulla) - The most caudal portion of the brainstem and location of physiological centers that regulate the cardiovascular and respiratory systems.

Metencephalon (Pons) - Relay center communicating with the cerebellum, pontine nuclei, tegmentum, and spinal cord.

Mesencephalon (Midbrain) - Smallest portion of the brainstem composed of the tectum, tegmentum, crura cerebri, and substantia nigra.

Tectum - A portion of the mesencephalon containing the superior and inferior colliculi.

Superior colliculi - Visual relay centers concerned with visual reflexes.

Inferior colliculi - Auditory relay centers concerned with processing of auditory information and auditory reflexes.

Diencephalon - The most rostral portion of the brainstem composed of the epithalamus, thalamus, hypothalamus, and subthalamus.

Alzheimer's disease - Progressive brain disorder that kills neurons and affects memory, thinking, and behavior.

Questions:

  1. What are the three subdivisions of the brain?
    A: Cerebrum, brainstem, and cerebellum.
     
  2. What is the smallest subdivision of the brainstem?
    A: Mesencephalon or midbrain

  3. Which subdivision of the brainstem is involved in the regulation of the cardiovascular and respiratory systems?
    A: Myelencephalon or medulla

  4. What is the function of the substantia nigra?
    A: The substantia nigra is a relay center and a structure concerned with the regulation of motor function.

  5. The substantia nigra is located within what subdivision of the brain?
    A: Mesencephalon

  6. What are the four structures that make up the diencephalon?
    A: Thalamus, epithalamus, hypothalamus, subthalamus.

  7. What is usually the first sign or symptom of Alzheimer’s disease?
    A: Progressive loss of memory

  8. When does the damage to the brain caused by Alzheimer’s occur?
    A: At least a decade before the alterations in memory or other cognitive functions affect the patient.

  9. Early-onset Alzheimer’s begins within what age range?
    A: Between the mid-30s and mid-60s.
     
  10. What happens to neurons affected by Alzheimer’s disease?
    A: The neurons are not able to function properly and as a result are damaged, lose connections to other neurons, and eventually die.

 

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