Today I'm going to talk about the human brain, its structure and function. The brain and nervous system was one of my favorite systems second only to the cardiac system. The brain is the human version of the computers CPU. It's the organ responsible for who we are. It's extremely complex and the limits to its complexities is beyond the mind-no pun intended.
Study it so next time we get together, we can talk about it. 😃😃
Please remember, structure is what it's made up of, and function is what it does. We sometimes refer to this as anatomy (structure or anatomy) and physiology (function or physiology). The cool thing is that we're going to go through seventeen different structures in the brain, laying out its basic plan. But you're also using your brain to process this! If you do a good job, by the end, when I review all the parts, you should be able to tell me both their structure and function.
So, what type of organisms have brains? Animals. Animals use nerves and muscles to move around, so they need a brain to organize that movement. If we look at the two basic body plans of animals, some are radially symmetrical—in other words, built around something like a tire. Others are bilaterally symmetrical—for instance, a lion, where you could draw a line down the middle, creating a clear right and left side, as well as a clear front and back. As we became bilaterally symmetrical, we had to organize that movement.
This is a simple animal body plan. As the animal moves, it takes in sensory information using neurons. For example, you're currently taking in sensory information from your eyes and ears. Inside your brain, you're integrating this information—making sense of it—before figuring out how to act. This forms a loop: sensory neurons bring information in, and motor neurons send information out. This basic loop is also important for understanding how our brain works.
If we look at primitive brains, we see a consistent structure: four "humps." These are the spinal cord, the hindbrain, the midbrain, and the forebrain. This structure is found in all animals. For instance, a shark’s brain still resembles this primitive plan. The spinal cord brings in information, while the hindbrain, midbrain, and forebrain manage other functions. The closer we are to the spinal cord, the more basic the functions. For example, the hindbrain keeps the heart beating and controls digestion, while the forebrain governs emotional responses, like when a shark decides to attack.
When you were an embryo, your brain also followed this primitive plan. Over time, however, it grew and developed into the complex adult brain. While the spinal cord, hindbrain, and midbrain remain, the forebrain has expanded significantly, housing emotions, memories, and higher-level thinking.
Now, let's explore the anatomy of the brain. There are 17 parts to review, and for each, you should ask: What is the structure? Where is it? What is its function?
Basic Brain Plan
The brain can be divided into four main components:
1. Brainstem
2. Cerebellum (located at the back of the brain)
3. Thalamus and Hypothalamus
4. Cerebrum (the dominant, upper portion of the brain)
Brainstem
The brainstem has three parts:
- Medulla oblongata
- Pons
- Midbrain
Its functions include managing basic life functions like breathing, circulation, digestion, and swallowing. It also routes sensory and motor information.
Cerebellum
The cerebellum is responsible for motor control and motor memory. It coordinates actions like riding a bike or playing sports.
Thalamus and Hypothalamus
- Thalamus: Acts as a data router, sorting and directing information.
- Hypothalamus: Manages homeostasis, including body temperature, osmolarity, and circadian rhythms. It also oversees hormone release via the posterior pituitary gland, which secretes antidiuretic hormone (water balance) and oxytocin.
Cerebrum
The cerebrum integrates sensory data, with billions of neurons and synapses processing information. It's divided into two hemispheres, connected by the corpus callosum. Each hemisphere specializes in different functions, though these are plastic (changeable).
Below the cerebral cortex is the basal ganglia, a group of nuclei responsible for motor control. Dysfunction here, as in Parkinson’s disease, disrupts movement.
Four Lobes of the Cerebrum
1. Frontal Lobe: Governor's executive functions, emotional control, and decision-making.
2. Parietal Lobe: Processes sensory input and environmental interactions.
3. Occipital Lobe: Manages vision.
4. Temporal Lobe: Handles language, hearing, and memory.
Specialized Areas
- Somatosensory Cortex: Processes sensory input.
- Motor Cortex: Direct motor output.
The brain dedicates more neurons to sensitive areas like the fingers or lips than to less sensitive areas like the back.
Functional MRIs are helping us map the brain's activity, allowing us to uncover more about its structures and functions down to the neuronal level.