INSIDE THE BRAIN (part 1): Human Brain Anatomy, Lobes and Functions
- Marcela Emilia Silva do Valle Pereira Ma Emilia
- 14 de abr.
- 12 min de leitura
🧠 Inside the Brain
There is something almost paradoxical about the human brain: it is the organ that allows us to understand the world and, at the same time, the very organ we are trying to understand.
Everything we call the “self” passes through it.
The memory that sustains our history, the emotion that colours our experiences, the language that organises thoughts, the ability to imagine the future, change our mind, build relationships, recognise danger, make decisions or simply exist consciously depends on a biologically delicate, electrically active and chemically precise tissue.
What is most fascinating is that all of this emerges from an organ with a gelatinous texture, extremely vascularised, dependent on glucose, oxygen, sleep and neurochemical balance.
✨ Want something even more fascinating? Although the brain is intensely vascularised and depends on a continuous flow of oxygen and glucose, the brain tissue itself does not have pain receptors.
This means that the brain does not “feel” pain in the way we feel it in the skin, muscles or viscera.
A headache, for example, does not arise from the brain parenchyma itself, but from adjacent structures that sustain and protect it, such as blood vessels, meninges, muscles, cranial nerves and other supporting structures.
✨ It is almost paradoxical: the organ that allows us to perceive pain is not capable of feeling it directly. How crazy is that!
And perhaps this is yet another reminder of how the brain is, at the same time, sophisticated, vulnerable and biologically singular.
In other words: what sustains our identity is also, paradoxically, profoundly vulnerable.
And perhaps it is precisely this contrast that makes the brain so extraordinary.
🧠 More than parts: a living architecture of human experience
When we talk about the parts of the brain, it is common to imagine isolated regions, almost like separate pieces of a machine.
But the real brain does not function in rigid compartments.
It operates as a living architecture of networks, circuits and integrated systems, in which different regions communicate continuously to transform stimuli into meaning, meaning into behaviour and behaviour into experience.
In order to explore the internal part of the brain, it is first necessary to understand the anatomical part of the Central Nervous System, which includes knowing how to observe the brain from its planes and directions and, also, how the brain is organised on a large scale.
📍 Planes and Directions in the Central Nervous System (CNS)
Any study or description of the brain or CNS follows a universal system of planes and directions for the understanding and correct establishment of the regions and areas to be described.
This universal approach allows not only the exact spatial anatomical position of the nervous structure to be described, but also demonstrates the relationships between the parts. These sections (literally or virtually) make the brain easier to visualise.
It is considered that there are three series of planes, and each is at a right angle in relation to the other. They are:
Coronal Plane: (or frontal) It is the plane parallel to the front of the face and is the one that divides the body into an anterior portion (front) and a posterior portion (back).
Sagittal Plane: It is arranged parallel to the median plane and is the plane that divides the body into two sides, left and right.
Axial Plane: (or horizontal, or transverse) It is perpendicular to the other planes and divides the brain into upper and lower portions.
In addition to the planes, the CNS can also be oriented through directions according to which the region is closest:
Rostral: the structure or region closest to the head. Opposite of caudal.
Caudal: the structure or region closest to the tail/feet. Opposite of rostral.
Dorsal: the structure or region closest to the back. Opposite of ventral.
Ventral: the structure or region closest to the belly/front. Opposite of dorsal.
The distribution into directions is a little more complex, since in addition to the traditional directions there are still other sub-directions to designate the point of view.
Distal: structure or region further away from the point of origin. Opposite of proximal.
Proximal: structure or region closer to the point of origin. Opposite of distal.
Median: Plane/direction that divides the body into two identical symmetrical halves.
Lateral: structure or region that is further away from the median plane. From the median outwards. Opposite of medial.
Medial: structure or region closer from the outside towards the median. Opposite of lateral.
Intermediate: Which lies between two structures, one medial and one lateral.
Ipsilateral: structure or region that is on the same side of the body. Opposite of contralateral.
Contralateral: structure or region that is on the opposite side of the body. Opposite of ipsilateral.
When talking about directions, the terminology created originates from Latin and Greek, evolving from comparative anatomy to describe the orientations of vertebrates. However, these terminologies, without any authorship to be attributed, were created from a four-legged animal, and therefore the rostrocaudal axis is seen as a straight line, but in the human being, who assumes a bipedal posture, the axis bends and the encephalon lies at a ninety-degree angle in relation to the spinal cord.
🧬 From anatomy to functional evolution
The cerebral formation in animals follows a pattern of organisation regarding the location of the general anatomy of the nervous system. However, aspects of phylogeny (evolution) and ontogeny (embryology) of the CNS of each animal species meant that some anatomical parts of the brain are not shared by all throughout the animal kingdom.
Evolution itself happens in populations and not only in individuals. Since evolution is the summation of the potential of certain biological and adaptive neurobehavioural characteristics acquired and shared over time by a community of other living beings.
When looking at the brain, it is no different. Phylogeny was not something exclusive to a single being from which all living beings descend:
EVERY CHARACTERISTIC THAT EXISTS TODAY IS AN ADAPTATION THAT SERVES A PURPOSE, SOLVES A PROBLEM, FULFILS A FUNCTION
(Herculano-Houzel, Suzana)
That is to say, the evolution of the brain came to make a difference in something, solve a problem and fulfil a certain function of a community and not just of a single being.
🧠 And one interesting thing is that, by definition, the brain loves solving problems.
And it was the development of technologies and the brain’s ability to solve problems that allowed the human species the development of the brain.
Indeed, the Theory of the Microgenesis of the Human Brain, by Paul McLean, that the brain results from three brains is still very popular around the globe. Even though this example is an excessive simplification of what brain evolution truly is, it is a useful and easy starting point to understand the three major systems into which our brain is divided on a large scale.
In McLean’s theory, the three major systems were called the “Reptilian Brain”, Limbic System and the Neocortex. (Even though the latter two still keep the same names, the “Reptilian Brain” is today referred to as the Brainstem.)
🦎 The “Reptilian Brain” was so named by McLean because it was a brain area observed in both mammals and reptiles. It represents the oldest structures from the point of view of the evolutionary history of the brain, as it is linked to automatic survival behaviours such as defensive responses, territoriality, motor automatisation, vigilance and vegetative functional processes.
In the Brainstem, located immediately rostral to the spinal cord, it is divided into the medulla, pons and midbrain, and these related structures are basic motor circuits and deep nuclei that sustain more automatic patterns.
❤️ The Limbic System, in turn, was only observed in mammals and also represents the grey matter arranged in the brain. But this term is the collective for the limbic structures of the brain such as the amygdala, hippocampus, hypothalamus and parts of the cingulate gyrus, which amplify and participate in emotional experience, memory, attribution of relevance, stress response, motivation, learning and social behaviour.
✨ It is with this system that life experiences cease to be merely information and begin to carry affective meaning.
🧠 The Neocortex, on the other hand, is a structure that is almost exclusive to mammals, but it is only observed and particularly developed in its total size in the human being. In fact, because this area is enlarged, this part of the brain is prominently folded onto itself, with three prominent sulci (central, lateral and parieto-occipital) and a series of gyri (sulci and gyri — the scientific name for those curves and little grooves in the brain).
Moreover, these sulci and gyri are similar from one brain to another and they are used as reference points to divide each hemisphere into the brain lobes between frontal, temporal, parietal, limbic and occipital.
Yes, in humans it is directly associated with higher cognitive functions such as language, traditional and abstract reasoning, planning, imagination, creativity, inhibitory control, prediction, reflective consciousness, among many others.
We can add to this list that it is this structure that allows the brain not only to react to the world, but to simulate possibilities by constructing predictive internal narratives based on past and present experiences, while at the same time reorganising behaviour itself.
The fascination, however, lies in realising that these divisions do not function as “separate brains”.
The real human brain is a deeply integrated network, in which automatic, emotional and cognitive processes coexist all the time.
An apparently rational decision may be modulated by emotional memory. An instinctive reaction may be reinterpreted by the prefrontal cortex. A simple sensory stimulus may simultaneously activate vegetative, affective and cognitive circuits.
🧠 It is precisely this integration between survival, emotion and abstraction that makes the brain so extraordinary — and, at the same time, so vulnerable to small changes at different levels of organisation.
🧠 Lobes of the Cerebral Hemisphere
The cerebral cortex is a layer of grey matter divided into two symmetrical hemispheres, measuring, in humans, a total area of around 2200 to 2400 cm², but because it is folded, it occupies only one third of this space.
It is within it that the three parts mentioned in the previous section are fitted, however, for the purpose of its study, the cortex is usually divided by functional properties that can be distinguished from one another by anatomical morphological differences such as sulci and gyri.
These anatomical classifications are called lobes and take the name of the bone that overlies them. In this case, there are four main divisions — frontal, parietal, temporal and occipital — and the fifth, the limbic system, also considered the limbic lobe, although it is not overlaid by any bone.
The central sulcus then divides the frontal lobe from the parietal lobe, which in turn has the Sylvian fissure (or lateral fissure) that interposes these two parts of the lateral lobe. The occipital lobe, in turn, is delimited from the parietal and lateral lobes by the parieto-occipital sulcus.
🧠 Frontal Lobe
The most anterior part of the cortex, the frontal lobe is a highly relevant region for cognitive development and one that differentiated human beings from other animals.
It is crucial for higher cognitive functions, personality, decision-making, planning and voluntary movements. Consequently, it controls social behaviours, such as speech (Broca’s area) and working memory (short-term memories).
✨ Interesting Features:
It contains the primary motor cortex, responsible for voluntary movements on the opposite side of the body.
Planning, reasoning, problem-solving and attention.
It is one of the last brain areas to fully mature, a process that may extend until close to 25 years of age.
Because it is such an important region in social and cognitive functioning, lesions or diseases in this region (such as tumours or stroke) may result in drastic behavioural changes, impulsivity, loss of motivation (abulia), executive difficulties and speech alterations.
🧠 Parietal Lobe
It is the uppermost region of the head, specialised in somatosensory information.
As one of the main divisions of the brain, located behind the central sulcus and above the temporal lobe, it is responsible for processing sensory information (touch, pain, temperature), proprioception (body position), spatial orientation, mathematical calculations and language comprehension.
✨ Interesting Features:
It is the Postcentral Gyrus that processes somatic sensations such as touch, pain, temperature and vibration from the whole body.
The dominant hemisphere (left for right-handed people and vice versa) is crucial for mathematical skills, writing and language comprehension.
It helps with spatial attention, particularly the non-dominant hemisphere (right for right-handed people and vice versa), which manages recognition of the opposite side of the body and environment.
The parietal lobe is extremely important for location, sensitivity and orientation. Lesions in this brain region may cause severe damage that can affect a person’s life without them even realising it, as in the case of hemispatial neglect.
Other serious consequences include agraphia, acalculia, finger agnosia and right-left disorientation, when in the dominant side. In the non-dominant hemisphere it may then generate hemispatial neglect (ignoring the left/right side of the body/environment) and apraxia (difficulty performing learned motor tasks).
🎧 Temporal Lobe (Lateral)
A region divided from the frontal and parietal lobe by the Sylvian Sulcus (lateral fissure), located laterally in the skull, it is the only lobe that is bilateral and in which both sides perform the same function.
They are essential for hearing, language, memory and emotion. This is because it is in this region that the insula is found, the cerebral part responsible for managing emotional responses, and Wernicke’s area, which performs all auditory processing and comprehension of the language being transmitted.
✨ Interesting Features:
It is irrigated by the middle cerebral artery.
The insula is located deeply within the lateral sulcus (Sylvian fissure). It is not externally visible, being covered by the operculum (parts of the frontal, parietal and temporal lobes).
The parietal lobe is extremely interconnected with the lateral lobe by managing sensation, touch, temperature and spatial perception, reconciling them with lateral areas important for coordination.
The reverse is also true: the lateral areas are essential for the integration of sensory information, with the left hemisphere frequently dominant for language and the right for spatial attention.
The main lesions and dysfunctions that originate from the temporal lobe are epileptic seizures, and when untreated they may cause speech difficulty, memory changes, auditory or olfactory hallucinations, déjà vu, intense fear or involuntary movements.
👁️ Occipital Lobe
The smallest lobe of the cerebral cortex, yet still one of the most important. Located in the most posterior part of the brain, it rests on the tentorium cerebelli, separated from the parietal and temporal lobes by the parieto-occipital sulcus, and is the region responsible for all visual processing.
The occipital lobe is essential for the interpretation of images, recognition of colours, shapes, depth and movement.
✨ Interesting Features:
• Visual processing in the occipital lobe occurs in two parts: first, the primary visual cortex (V1/Area 17) receives information from the eyes, while the association areas (V2-V5/Areas 18 and 19) interpret this information.
The main consequences and lesions associated with this region are cortical blindness (amaurosis), visual agnosia and visual hallucinations, such as distorted perception of colours, sizes and shapes.
❤️ Limbic Lobe
Although not necessarily considered a lobe, but rather a more specific cerebral anatomical region located on the medial face of the cerebral hemisphere, it is situated on the medial surface of the cerebral hemispheres, surrounding the corpus callosum.
It is ring-shaped, composed mainly of the cingulate and parahippocampal gyri, thus acting as a central part of the limbic system, being essential for the processing of emotions, behaviour, memory and olfaction.
✨ Interesting Features:
It includes three gyri in its ring: the cingulate gyrus, parahippocampal gyrus and dentate gyrus.
It integrates with the limbic system to generate emotional responses, form long-term memories and regulate behaviour, known as the “emotional brain”.
It actively participates in the Papez Circuit, linking conscious feeling to emotional expression.
The main dysfunctions and lesions in this area may cause personality changes, epilepsy, memory problems and abnormal behaviours.
🧠 Although the classification by lobes is functional, it is very broad and makes the real localisation of the countless functional parts of the cerebral cortex difficult.
And because of this, there are also other ways of classifying the brain in a more detailed way, such as the cytoarchitectural classification, of which the best known is the Brodmann classification, which divides the cortex into fifty-two different regions.
There is also classification by phylogenetic aspects and by physiological/functional classification, being divided according to sensory afferents, that is, those that originate or receive projection fibres.
🌍 Conclusion
By exploring the brain through its planes, directions, evolutionary history, major systems and lobes, it becomes increasingly evident that it is far from being merely an organ divided into anatomical parts.
Each sulcus, each gyrus, each lobe and each circuit reveal a deeply integrated biological logic, in which movement, sensation, memory, emotion, language and behaviour coexist to sustain what we call the human experience.
🧠 The fascination lies precisely in realising that what seems so abstract — personality, creativity, language, perception, identity — depends on a cerebral geography that is extremely organised and, at the same time, vulnerable.
Small changes in a single lobe can transform speech, memory, attention, visual perception, social behaviour and even the relationship we have with our own body.
And perhaps this is one of the greatest lessons of neuroscience:
✨ the more we understand the anatomy of the brain, the more we understand the delicacy of what makes us human.
In the next part, we will leave anatomical geography behind and enter something even more fascinating: as the why of the size of human brain, the mystery behind the electricity in our brain and how the brain sustains life.
📚 Scientific Foundations and Core Readings
Nolte, J. The Human Brain: An Introduction to Its Functional Anatomy. Translated edition. Elsevier, 2008.
Cosenza, R. M. Fundamentals of Neuroanatomy. 4th ed. Guanabara Koogan, 2021.
Gazzaniga, M. S., Ivry, R. B., & Mangun, G. R. Cognitive Neuroscience: The Biology of the Mind. 2nd ed. W. W. Norton, 2002.
Thompson, R. F. The Brain: A Neuroscience Primer. 3rd ed. Worth Publishers, 2000.
Camazine, S. (n.d.). Brain, fiber tractography image #8 [Photograph]. Pixels. https://pixels.com/featured/8-brain-fiber-tractography-image-scott-camazine.html
The Holistic Register. (2024, January 16). Is the triune brain theory still relevant? The Holistic Register. https://www.holisticregister.com/blog/is-the-triune-brain-theory-still-relevant
Galileo Feynman. (2013, January). Comparative brain anatomy in different animals. Galileo Feynman Blog. http://galileofeynman.blogspot.com/2013/01/comparative-brain-anatomy-in-different.html
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