Despite the myth of using just 10% of their total capacity, humans use nearly 100% of their brains every day. Nevertheless, the human brain is most likely one of the most complicated things on the planet. We wouldn't be able to think, feel emotions, or revel in joyful memories if we didn't have them. We'd be unable to walk, talk, see, hear, or touch. But how much do we truly know about it?
- We are going to discuss the brain and what makes up the human brain.
- First, we will provide an overview of the brain, highlighting the major components and the ventricles of the brain.
- Then, we will delve into the different parts of the brain, exploring the lobes of the brain and their functions.
- Finally, we will cover the cerebellum and the brain stem, exploring their role within the brain, and how fluid in the brain affects cognition.
The Brain: An Overview
The brain is a complex organ (containing around 86 billion neurons alone²) consisting of two hemispheres, the right and the left, connected by nerve fibres known as the corpus callosum. These fibres allow the exchange of information between the hemispheres. The brain can be divided in multiple ways. Three standard regions include the forebrain, the midbrain, and the hindbrain.
| Brain division | Brain regions |
| Forebrain | - Cerebrum
- Thalamus
- Hypothalamus
- Pituitary gland
- Limbic system (importantly the hippocampus and the amygdala)
- Olfactory bulb
|
| Midbrain | - Colliculi
- Tegmentum
- Cerebral peduncles
|
| Hindbrain | - Pons
- Cerebellum
- Medulla oblongata
|
Table 1. Main divisions of the brain and their components.The brain has four different lobes, and each lobe is responsible for specific functions. The lobes of the brain are usually divided into four sections, the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe.
Functions of the brain differ depending on the hemisphere. The two hemispheres of the brain control the opposite sides of the body; the brain works contralaterally.
Fig. 1 - The brain is composed of four lobes, amongst three general regions.
Ventricles of the Brain
Cerebrospinal fluid (CSF) is a clear, colourless liquid that encircles the brain and spinal cord. It is produced by the choroid plexus in the ventricles of the brain and is constantly replenished. CSF plays several important roles, including cushioning the brain and spinal cord, removing waste products, and delivering nutrients and hormones to the central nervous system. It also helps to maintain a stable environment for the brain by regulating the pressure around it.
Brain ventricles are interconnected, fluid-filled cavities in the brain related to the production and circulation of CSF.
Cerebrospinal fluid fills the brain's ventricles, and there are four ventricles within the brain:
- The lateral ventricles are extensive chambers, one in each half of the brain.
- The third ventricle shares the walls of the thalamus and hypothalamus, located in the diencephalon.
- The fourth ventricle is a cavity located within the hindbrain, beneath the cerebellum.
Fig. 2 - Cerebrospinal fluid fills the ventricular system of the brain¹.
Parts of the Brain
The brain, as per its intricate nature, is composed of different parts. Some of the important parts include the cerebrum and cerebral cortex.
Cerebrum
The cerebrum is the largest part of the brain, composed of grey matter (the outer layer, composed of the cell bodies and dendrites of the neurons) and white matter (the inner layer, composed of the axons and myelin sheaths of the neurons). The cerebrum consists of the cerebral hemispheres we discussed above, of which there are two.
The distribution of grey and white matter is not constant throughout the central nervous system. Even though in the brain grey matter constitutes the outer layer of brain tissue, in the spinal cord it is the inner layer. The opposite is true for white matter: it is the interior layer of the brain, and the outer layer in the spinal cord.
Grey and white matter get their names from how they appear to the naked eye. Grey matter is composed of nerve cell bodies, which give it its characteristic grey colour, whereas white matter contains mostly nerve processes, such as axons. As they are covered in myelin, a pale substance, this portion of the brain appears whiter.
Understandably, the cerebrum is involved in many functions including movement coordination, language, and thinking and reasoning.
Cerebral Cortex
The cerebral cortex is the outer layer of the brain's cerebrum. It is the brain's grey matter and consists of cell bodies, as we mentioned above, which gives it its grey colouring. The cerebral cortex is highly folded and therefore has a large surface area.
More surface area means more neurons and more neurons means more brain power.
The folds are separated into the gyri and sulci – the gyri are the ridges (bumps), and the sulci are the furrows (dips). The longitudinal fissure, for instance, is what separates the brain into the two hemispheres.
The cerebral cortex is responsible for many different functions overall – it encompasses many areas of the brain and is widely interconnected. It plays a significant role in:
- consciousness,
- Memory,
- language,
- thoughts, and
- perceptions (the highest order of processing occurring here).
Cerebellum and Brain Stem
The cerebellum is located at the base of the skull under the cerebrum and is one of the largest parts of the hindbrain. It is responsible for:
- Coordinating voluntary movements, e.g., moving a limb with dexterity.
- Balance and equilibrium, so that you do not fall over and lose your balance.
- Memory and reflex motor arcs².
The brain stem leads to the spinal cord, comprising the midbrain, pons, and medulla oblongata, and is responsible for some of the more basic processes, such as:
- Reflexes (such as breathing, swallowing, and heart rate).
- Sweating, blood pressure, and all types of automatic responses that are not controlled voluntarily.
- Ability to sleep.
Overall, any damage to the different parts of the brain can cause many problems.
Fig. 3 - The cerebellum is entirely involved in motor functions.
Lobes of the brain
There are four lobes of the brain: frontal, parietal, occipital, and temporal lobe. The frontal lobe is located at the anterior region (towards the front) of the cerebral hemispheres. The parietal lobe is located towards the posterior (towards the back) of the central sulcus, with the occipital lobe occupying the most posterior section of the brain. The temporal lobe is located near the parietal and occipital lobes, lying below the Sylvian fissure.
Fig. 4 - The brain has four lobes, the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe.
The frontal lobe
The frontal lobe is responsible for:
- Voluntary movements (such as moving a hand).
- Expressive language (putting thoughts into words).
- Managing complex or high-level executive functions (e.g., forming long-term memory, awareness, making judgements about the self and others).
- Impulse control.
- Social behaviour (this includes talking to others and initiating conversations, assessing others and the situation, and overall sexual behaviour).²
Phineas Gage had an accident where a metal rod went through his frontal lobe. His personality was severely affected, according to his friends. He became a more aggressive, rude, and temperamental man, compared to his previous demeanour of a quiet, reserved man.
Considering how the frontal lobe is implicated in personality, damage to the frontal lobe coincides well with personality changes.
It contains crucial areas such as:
- The primary motor cortex. The highest levels of voluntary control of movement occur here.
- The prefrontal cortex. Social behaviour is monitored here.
- Broca's area in the left frontal lobe. Broca's area is involved in speech production.
The parietal lobe
The parietal lobe is responsible for:
- Sensory perception and integration with other brain areas (interpretation of sound, touch, taste, vision and hearing, the brain is highly interconnected).
- Spatial awareness, which perceives and helps map the world around us. As a result, you can walk from one end of the room to the other without bumping into everything².
It contains essential areas such as:
- The primary somatosensory cortex, a region that interprets information from different areas of the body.
The occipital lobe
The occipital lobe is responsible for:
- Vision, the visual processing centre or visual cortex. It relays processed information to other parts of the brain for interpretation and processing.
- Mapping the visual world (vital for spatial understanding and memory, it places objects so you can orient and remember them after scanning visual space)². It is responsible for or plays a hand in, depth perception, recognising of faces, and memory formation.
It contains essential areas such as:
- The primary visual cortex.
- Brodmann's area 17 (primary visual cortex), which is involved in depth perception and image placement.
The temporal lobe
The temporal lobe is responsible for:
- Hearing through perceiving, processing and interpreting sounds. The temporal lobe is heavily implicated in language production and comprehension, as a result.
- Memory acquisition, formation of memories and their embedding.
- Object recognition.
It contains essential areas such as:
- The primary auditory cortex.
- Wernicke's area, which deals is responsible for understanding speech and converting pitches and different frequencies into intelligible pieces of information. It is responsible for the fluency of speech and ensures that it makes sense and is coherent.
| Lobe of the brain | Location | Main functions | Important regions |
| Frontal lobe | Anterior region of the brain. | - Voluntary movements
- Expressive language
- Complex or high-level executive functions
- Impulse control
- Social behaviour
| - The primary motor cortex (voluntary movement).
- The prefrontal cortex (social behaviour).
- Broca's area (speech production).
|
| Parietal lobe | Posterior to the central sulcus. | - Sensory perception and integration
- Spatial awareness
| - The primary somatosensory cortex (sensory processing).
|
| Occipital lobe | Most posterior section of the brain. | - Vision and mapping the visual world
| - The primary visual cortex/Brodmann's area 17 (depth perception and image placement).
|
| Temporal lobe | Below the Sylvian fissure. | - Hearing
- Memory acquisition,
- Object recognition.
| - The primary auditory cortex (hearing).
- Wernicke's area, (speech understanding).
|
Table 2. Lobes of the brain: location, function and most important areas.
Fluid on the Brain
Fluid on the brain can indicate a range of issues occurring, depending on the fluid present. Cerebrospinal fluid accumulation can have different meanings to blood, for instance.
Hydrocephalus (sometimes referred to as water on the brain) is where cerebrospinal fluid has accumulated in the brain's ventricles and it can cause a rise in pressure that affects brain function.
Increased pressure can affect vision, cause headaches and migraines, and can even be fatal if left untreated.
Blood on the brain, however, can indicate trauma has occurred, the person has suffered a stroke, a tumour is present, or infection is damaging brain tissue.
Lesions on the brain
Brain lesions are damages to brain tissue that can be detected as abnormalities with certain brain imaging techniques. Brain lesions can be caused by numerous factors, like:
- infections
- vasculature issues (stroke, blood clots)
- trauma to the head
- tumours
- neurodegenerative diseases
Brain lesions can also vary in size and severity. Some can be discovered in the brain by chance, while the doctor is looking for other things or during a laboratory experiment, because they have no clinical symptoms. Others can cause severe damage to the brain and significant symptoms for the patient, including death.
Depending on the type and severity of the brain lesion, the doctor might recommend different treatment options like antibiotics, radiotherapy, surgery, or other options.
The Brain - Key takeaways
- The brain is a complex organ consisting of two hemispheres, the right and the left, connected by nerve fibres called the corpus callosum.
- The brain is composed of three general regions known as the forebrain, midbrain, and hindbrain.
- It is also divided into different lobes, called the frontal lobe, parietal lobe, occipital lobe, and temporal lobe.
- Each lobe has specific functions associated with its structure.
- The cerebellum is located at the base of the skull, and the brain stem leads to the spinal cord. Both have their functions.
References
- Azevedo, F. A., Carvalho, L. R., Grinberg, L. T., Farfel, J. M., Ferretti, R. E., Leite, R. E., Jacob Filho, W., Lent, R., & Herculano-Houzel, S. (2009). Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. The Journal of comparative neurology, 513(5), 532–541.
- Robert P. Lehr Jr., Brain Function, Centre for Neuro Skills, 28 September 2021
- Fig. 2: The ventricular system of the brain by BodyParts3D[1] by DBCLS., CC BY-SA 2.1 JP https://creativecommons.org/licenses/by-sa/2.1/jp/deed.en, via Wikimedia Commons
- Fig. 4: The cerebellum by BodyParts3D is generated by DBCLS, CC BY-SA 2.1 JP https://creativecommons.org/licenses/by-sa/2.1/jp/deed.en, via Wikimedia Commons
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