The brain is one of the most complex systems in existence. When people talk about the strength and power of the brain, we should clarify that the brain is not a muscle – it is sometimes mistaken to be a muscle, but it is in fact an organ (like our lungs, liver, and kidneys). Although it is not a muscle, we can still “train” our brains. In fact, one of the most impressive properties of the brain is its plasticity, which refers to the capacity to “re-wire” its own connections [1]. Since the brain is able to strengthen, weaken, and modify connections between its neurons (the main type of cells in the nervous system), this leads to the basis of learning and memory.
From an anatomical perspective, the brain is part of the nervous system. The nervous system can be subdivided into two broad categories: Central Nervous System (CNS) or Peripheral Nervous System (PNS). The CNS mainly contains the brain and the spinal cord. The PNS includes the nerves that connect the CNS with the rest of our bodies. These can be classified as afferent nerves* or efferent nerves**. Through these nervous connections, the CNS can receive sensory perceptions and send motor signals to our body. For example, when the doctor checks your knee reflexes, your body first perceives the pressure of the doctor tapping your knee, this signal travels through your afferent nerves to the spinal cord, and then the spinal cord sends a signal through the efferent nerves, causing a muscle contraction.
Figure 1. Categories of the nervous system.
There are different classifications of brain parts. One of the most important is based on the embryological origin. By analyzing how brains develop when we are embryos inside the womb, scientists have identified three main vesicles (regions): hindbrain, midbrain, and forebrain. These parts will then subdivide into five: the hindbrain becomes the metencephalon and myelencephalon, the midbrain is now known as the mesencephalon, and the forebrain splits into the diencephalon and telencephalon [2,3].
Based on those embryonic segments, different structures of the brain will be developed. In an image of the brain, there are three visually distinct sections [3]:
The largest part is called the cerebrum [4], which is split into two hemispheres that are interconnected by a group of fibers called corpus callosum. Interestingly, these hemispheres are not identical (for example, some language abilities are typically more related to the left hemisphere). Each hemisphere receives and sends signals from the opposite side of the body [5]. For example, the right hemisphere controls the motion of the left arm whereas the left hemisphere controls the motion of the right arm. In the outer layer of our cerebrum, we can find the cortex, which is one of the most important structures. This cortex contains the cell bodies responsible for many different processes: vision, motor control, sensory perception, among others.
Below the cerebrum and near the back of the skull appears the cerebellum. This structure has multiple roles but several of them are involved in voluntary motion and motor coordination [2].
Finally, the brain stem connects the brain to the spinal cord, and it can be divided into three structures: the midbrain (involved in some sensory and motor processes, as well as eye pupil reflexes [6]), the pons (which serves as one of the important “relay” stations for many signals [2]), and the medulla oblongata (crucial for functions like breathing and heart rate) [2].
Figure 2. Parts of the brain.
In summary, our nervous system is composed of the CNS and PNS. The CNS includes the spinal cord and the brain, which in turn can be subdivided into multiple other structures (such as the cerebrum, brain stem, and cerebellum). The enhanced development of the brain in humans has given us many advantages. Stay tuned for future posts where we will discuss split brains!
*Afferent: the sensory signal is going from the periphery towards the CNS.
**Efferent: the motor signal is going from the CNS towards the periphery.
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Written by: Nicole
Edited by: Natasha
Figure created by: Sahar
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References:
Mateos-Aparicio, P., and Rodríguez-Moreno, A. (2019). “The Impact of Studying Brain Plasticity”. Frontiers in cellular neuroscience, 13, 66. Available at: https://www.frontiersin.org/articles/10.3389/fncel.2019.00066/full
Thau L, Reddy V, Singh P. Anatomy, Central Nervous System. (2022). “Anatomy, Central Nervious System”, StatPearls Publishing. Available at: https://www.ncbi.nlm.nih.gov/books/NBK542179/
Brain Anatomy Introduction Lab (2013). University of Minessota – Fletcher, T.F. Available at: http://vanat.cvm.umn.edu/neurLab3/divisions.html (Accessed: 15 August 2023).
Cerebrum: what to know (2022). Web MD - Venkat, S.R. Available at: https://www.webmd.com/brain/cerebrum-what-to-know (Accessed: 15 August 2023).
Brain Basics: Know your Brain (2023). National Institute of Neurological Disorders and Stroke - NIH. Available at: https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-know-your-brain#:~:text=The%20brain%20can%20be%20divided,as%20respiration%20and%20heart%20rate (Accessed: 15 August 2023).
Caminero, F. and Cascella, M. (2022) "Neuroanatomy, Mesencephalon Midbrain", StatPearls Publishing. Available at: https://www.ncbi.nlm.nih.gov/books/NBK551509/ [Updated 2022 Oct 24]
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