2.6 The Brain

Brain Structure and Functions

The human brain is a remarkable organ in the nervous system, with billions of neurons organized in neural networks to connect the brain's different regions. Part of understanding the ways in which the brain allows us to think, learn, communicate, and coordinate our movements and behaviors, is recognizing the unique functional subdivisions of neural anatomy! 🧠

Image Courtesy of Wikipedia

Our brain can be broken down into a variety of structures, the oldest of which is made up of the brainstem, thalamus, and cerebellum. 

The Brainstem

The brainstem is responsible for controlling many of the body's basic functions. It is composed of three main parts, the midbrain, the pons, and the medulla oblongata:

1. The midbrain is responsible for managing some of the body's reflexes, such as those involved in eye movement and the pupillary light reflex. The midbrain also plays a role in the control of sleep, wakefulness, and alertness, critical functions of consciousness.
2. A bridge-like structure, the pons connects the brainstem to the cerebellum (the part of the brain responsible for balance) and helps with movement coordination as well as the reflexes used in swallowing and coughing.
3. The medulla oblongata, or medulla for short, is the lower part of the brainstem. It is responsible for regulating vital body functions, including heart rate, blood pressure, and breathing. 🫀

Thalamus

The thalamus sits on top of the brainstem and receives and sorts all sensory input (except smell) to other parts of the brain. It plays a crucial role in the processing and relay of sensory information to the appropriate areas of the brain!

Think of the thalamus as a sort of "switchboard operator" for the brain. When you see, hear, taste, or touch something, the information travels to the thalamus first. The thalamus then decides where to send the information next, depending on what the sensory input is. For example, if you see a golden retriever puppy, the thalamus sends the information about the dog to the visual cortex (the part of the brain that processes visual information). If the puppy starts to bark, the thalamus sends the information about the noise to the auditory cortex (the part of the brain that processes sound). 🐾

In this way, the thalamus helps to ensure that the right information is sent to the right part of the brain for processing. Without the thalamus, our senses would be a jumbled mess, and we would have a difficult time interpreting external stimuli in the world around us!

Cerebellum

Lastly, the cerebellum, often referred to as the "little brain," sits at the rear of our brainstem and also processes sensory input, coordinated movement, balance, nonverbal learning, and implicit memory. 

The cerebellum also plays a role in learning new movements and adjusting to changes in the environment. For example, if you are learning to ride a bike, the cerebellum helps to coordinate the movements of the muscles in your legs and arms as you pedal and steer. And if you suddenly stumble or run into a curb, the cerebellum helps to adjust your balance and keep you from falling. 🚴‍♀️

The Limbic System

The limbic system is a group of brain structures that are involved in emotions, drives, and long-term memory. Because of this, the limbic system is called the "emotional brain" due to its role in our expression of and experience with feelings. Structures in the limbic system include the amygdala, hippocampus, and hypothalamus:

Amygdala

As part of the limbic system, the amygdala is the "fear center" of the brain since it is heavily used for emotional processing, particularly aggression and fear. Additionally, the amygdala is associated with the formation of emotionally-charged memories. The amygdala has a direct connection to the hypothalamus, which is a part of the brain that helps regulate the body's stress response, meaning that when the amygdala is activated, it can trigger the release of stress hormones like cortisol to ready the body to respond to danger in an external environment.

Hippocampus

The hippocampus is a small, seahorse-shaped structure located in the limbic system. Primarily, the hippocampus is known for the role it plays in learning and memory, particularly the consolidation of long-term memories. Additionally, the hippocampus is also linked to processes for spatial navigation!

Hypothalamus

Another important structure in the limbic system is the hypothalamus, which is also in the limbic system and deals with maintaining our body’s homeostasis and reward systems, including the "Four F's": Fighting, Fleeing, Feeding, and Mating. 

The hypothalamus is often referred to as the "control center" of the brain because it helps regulate a wide range of bodily functions, including body temperature, thirst, hunger, and fatigue. With the pituitary gland, the hypothalamus is also responsible for controlling the body's endocrine system, which produces the hormones that regulate mood and energy levels. This further connects the hypothalamus to pleasure and motivation in behavior. 

Lobes and Cortices of the Brain

The rest of our brain is made up of lobes and higher-level cortices, and the most important is the cerebral cortex—our ultimate control and processing center. The cerebral cortex is divided into four main lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe. Each of these lobes is responsible for different functions.

1. The frontal lobe deals with problem-solving, decision-making, planning, and judgment.
2. Responsible for processing sensory information, the parietal lobe receives input about touch, temperature, pain, and body position.
3. The temporal lobe processes auditory information and is involved in memory formation.
4. Visual information is handled by the occipital lobe.

Additional cortices of the brain are association areas. Association areas allow us to have higher mental functions, such as learning, remembering, thinking, problem-solving, and speaking by integrating information from other brain regions. 

Hemispheric Lateralization 

Our brain is divided into two hemispheres, and in order for those hemispheres to communicate with one another, we need a bundle of nerve fibers known as the corpus callosum to bridge communication. It allows the two hemispheres to exchange information and coordinate their activities.

For patients with severe epileptic seizures, the corpus callosum may be severed to reduce neural feedback. This results in a “split brain.”  In a split-brain patient, both hemispheres operate independently from one another. For example, a person could be shown a separate image for each of their visual fields. Then, when asked to draw what they have seen, each hand would independently draw a different image, which we can examine in the diagram below:

Image Courtesy of Tutor2u; LVF = left visual field. RVF = right visual field

The left side of the brain corresponds to your right hand and right visual field and vice versa. Everything is the opposite!!

Neuroanatomy Summary

Functional Review

For quick reference and visualization, the following table includes a quick functional review of neuroanatomy:

Vocabulary

🎥 Watch: AP Psychology - Brain and Endocrine System