The Anatomy of the Brain

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Introduction to the Brain - The Cerebral Cortex

Brain arteries
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The human brain is not only one of the most important organs in the human body; it is also the most complex. In the following tour, you will learn about the basic structures that make up the brain as well as how the brain works. This is not an in-depth look at all of the research on the brain (such a resource would fill stacks of books). Instead, the goal of this brain tour is to familiarize you with major brain structures and their functions.

The cerebral cortex is the part of the brain that functions to make human beings unique. Distinctly human traits including higher thought, language and human consciousness as well as the ability to think, reason and imagine all originate in the cerebral cortex.

The cerebral cortex is what we see when we look at the brain. It is the outermost portion that can be divided into the four lobes of the brain. Each bump on the surface of the brain is known as a gyrus, while each groove is known as a sulcus.

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The Four Lobes

Lobes of the Brain
The brain can be divided into four sections, known as lobes. Image by John A Beal, Louisiana State University Health Sciences Center Shreveport

The cerebral cortex can be divided into four sections, which are known as lobes (see image above). The frontal lobe, parietal lobe, occipital lobe, and temporal lobe have been associated with different functions ranging from reasoning to auditory perception.

  • The frontal lobe is located at the front of the brain and is associated with reasoning, motor skills, higher level cognition, and expressive language. At the back of the frontal lobe, near the central sulcus, lies the motor cortex. This area of the brain receives information from various lobes of the brain and utilizes this information to carry out body movements. Damage to the frontal lobe can lead to changes in sexual habits, socialization, and attention as well as increased risk-taking.
  • The parietal lobe is located in the middle section of the brain and is associated with processing tactile sensory information such as pressure, touch, and pain. A portion of the brain known as the somatosensory cortex is located in this lobe and is essential to the processing of the body's senses. Damage to the parietal lobe can result in problems with verbal memory, an impaired ability to control eye gaze and problems with language.
  • The temporal lobe is located on the bottom section of the brain. This lobe is also the location of the primary auditory cortex, which is important for interpreting sounds and the language we hear. The hippocampus is also located in the temporal lobe, which is why this portion of the brain is also heavily associated with the formation of memories. Damage to the temporal lobe can lead to problems with memory, speech perception, and language skills.
  • The occipital lobe is located at the back portion of the brain and is associated with interpreting visual stimuli and information. The primary visual cortex, which receives and interprets information from the retinas of the eyes, is located in the occipital lobe. Damage to this lobe can cause visual problems such as difficulty recognizing objects, an inability to identify colors, and trouble recognizing words.

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The Brain Stem

The brain stem is comprised of the hindbrain and midbrain. The hindbrain contains structures including medulla, the pons and the reticular formation.

The Hindbrain

The hindbrain is the structure that connects the spinal cord to the brain.

  • The medulla is located directly above the spinal cord and controls many vital autonomic functions such as heart rate, breathing and blood pressure.
  • The pons connects the medulla to the cerebellum and helps coordinate movement on each side of the body.
  • The reticular formation is a neural network located in the medulla that helps control functions such as sleep and attention.

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The Midbrain

Midbrain

The midbrain is the smallest region of the brain that acts as a sort of relay station for auditory and visual information.

The midbrain controls many important functions such as the visual and auditory systems as well as eye movement. Portions of the midbrain called the red nucleus and the substantia nigra are involved in the control of body movement. The darkly pigmented substantia nigra contains a large number of dopamine-producing neurons are located. The degeneration of neurons in the substantia nigra is associated with Parkinson’s disease.

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The Cerebellum

Cerebellum
Image by Ministry of Education, Culture, Sports, and Technology(MEXT) Integrated Database Project

Sometimes referred to as the "little brain," the cerebellum lies on top of the pons behind the brain stem. The cerebellum is comprised of small lobes and receives information from the balance system of the inner ear, sensory nerves, and the auditory and visual systems. It is involved in the coordination of motor movements as well as basic facets of memory and learning.

The cerebellum makes up approximately 10 percent of the brain's total size, but it accounts for more than 50 percent of the total number of neurons located in the entire brain. This structure is associated with motor movement and control, but this is not because the motor commands originate here. Instead, the cerebellum serves to modify these signals and make motor movements accurate and useful.

For example, the cerebellum helps control posture, balance, and the coordination of voluntary movements. This allows different muscle groups in the body to act together and produce coordinated, fluid movement.

In addition to playing an essential role in motor control, the cerebellum is also important in certain cognitive functions including language.

Reference: Knierim, J. (1997). Chapter 5: Cerebellum. Neuroscience Online. The University of Texas Medical School. Retrieved from http://neuroscience.uth.tmc.edu/s3/chapter05.html

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The Thalamus

The thalamus helps relay sensory information.
The thalamus is located above the brain stem. Image by Ministry of Education, Culture, Sports, and Technology(MEXT) Integrated Database Project

Located above the brainstem, the thalamus processes and transmits movement and sensory information. It is essentially a relay station, taking in sensory information and then passing it on to the cerebral cortex. The cerebral cortex also sends information to the thalamus, which then sends this information to other systems.

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The Hypothalamus

Hypothalamus
Image by Ministry of Education, Culture, Sports, and Technology(MEXT) Integrated Database Project

The hypothalamus is a grouping of nuclei that lie along the base of the brain near the pituitary gland. The hypothalamus connects with many other regions of the brain and is responsible for controlling hunger, thirst, emotions, body temperature regulation, and circadian rhythms. The hypothalamus also controls the pituitary gland by secreting hormones, which gives the hypothalamus a great deal of control over many body functions.

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The Limbic System

The amygdala is one of the major structures found in the limbic system. Image by Ministry of Education, Culture, Sports, and Technology(MEXT) Integrated Database Project

The limbic system is comprised of four main structures: the amygdala, the hippocampus, regions of the limbic cortex and the septal area. These structures form connections between the limbic system and the hypothalamus, thalamus and cerebral cortex. The hippocampus is important in memory and learning, while the limbic system itself is central in the control of emotional responses.

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The Basal Ganglia

Basal Ganglia and related structures
Image from the Wikimedia Commons

The basal ganglia are a group of large nuclei that partially surround the thalamus. These nuclei are important in the control of movement. The red nucleus and substantia nigra of the midbrain have connections with the basal ganglia.

References:

Thompson, R.F. (2000). The Brain: A Neuroscience Primer. New York: Worth Publishers.

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