Cerebrum - The Definitive Guide | (original) (raw)

Definition

The cerebrum of the central nervous system is the uppermost part of the brain. It is composed of the basal ganglia, cerebral cortex, and olfactory cortex. The cerebrum is divided into a left and right hemisphere on either side of a central fissure. As the largest part of the brain, the cerebrum sits in front and on top of the brainstem. It receives sensory information, processes it, regulates motor and conscious activity, and is responsible for a broad range of cognitive processes.

cerebrum

What Is The Cerebrum?

The cerebrum is the largest part of the brain. Its outer surface is covered by the cerebral cortex spread over five paired lobes: frontal lobe, parietal lobe, temporal lobe, occipital lobe, and (to a lesser degree) limbic lobe.

brain lobes cerebrum parietal lobe occipital limbic frontal temporal

Cerebral lobes of the brain

The brain in its entirety is, together with the spinal cord, part of the central nervous system. It can be divided into eight anatomical structures, a few of which overlap. These are the:

forebrain midbrain hindbrain neural tube brain development cerebrum cerebellum brainstem

Different parts of the brain evolve from the fetal neural tube

In the above list, the cerebrum is part of the prosencephalon (forebrain). The prosencephalon is divided into two main structures – the diencephalon and the telencephalon. The cerebrum is a subcategory of the telencephalon. These develop from the fetal brain (neural tube), as seen in the above image.

Telencephalon

The telencephalon is the most developed and largest part of the forebrain. Each hemisphere is divided by the longitudinal fissure and lateral ventricle but is well-connected to its opposite partner. Specific sides can be dominant for certain functions. For example, a specialized region of brain tissue called Broca’s area (see below) is most commonly located at the side of the left frontal lobe when the left-hand side of the brain is dominant for communication.

broca's area

Important language-processing areas of the brain

The telencephalon is divided into seven main structures:

The cerebral cortex is covered with gray matter which gives the brain its distinguishable color. The neocortex of high primates and humans covers white matter made of concentrated neuron soma (bodies). In the average human cerebral cortex, there are approximately ten billion neurons.

cerebral cortex neocortex cerebrum

Functional areas of the cerebral cortex

Cerebrum

The primary three parts of the cerebrum are the basal ganglia, cerebral cortex, and olfactory cortex (not the olfactory bulb). In terms of cerebrum vs cerebral cortex, the latter is part of the former; they are not the same structures.

basal ganglia limbic system lobe hippocampus amygdala

Location of the basal ganglia

Basal ganglia refer to a group of specialized neurons that form part of the extrapyramidal system of the central nervous system. This tract of nerve fibers starts in the brainstem and brings motor stimuli to the spinal cord, controlling muscle tone, balance, and movement. The basal ganglia are composed of the:

The cerebral cortex is the second main area of the cerebrum and is present in four paired lobes of the brain: frontal, temporal, parietal, and occipital. It is, therefore, involved in all of the sensory and motor actions associated with each lobe. Other parts of the cerebral cortex are:

hippocampus limbic system cerebrum

Location of the paired hippocampus

The third and final area of the cerebrum is the olfactory cortex responsible for processing our sense of smell. As this is close to the areas of the brain that regulate emotion and memory, it is understandable why a certain scent can affect our emotions. The olfactory cortex is composed of four main structures:

deep brain stimulation dbs basal forebrain cerebrum

Deep brain stimulation of the basal forebrain might slow down neurodegeneration

It is, therefore, apparent that the cerebrum controls in at least some aspect every nerve pathway in the central nervous system. If you are asked, “What does the cerebrum do?”, it is important to include the collection, processing, and regulation of sensory and motor stimuli from the four paired lobes, involvement in cognitive function in terms of memory, reward, and learning, and its role in consciousness, balance, and our senses of smell and taste in your answer.

Cerebrum Location

Cerebrum location should always include the cerebral cortex, basal ganglia, and olfactory cortex. Drawing a line around these structures is not as clear-cut as it may seem, especially as the limbic and olfactory systems cross between different regions of the telencephalon.

The cerebrum is located in the superior part of the cranial cavity inside the skull. It is divided by the longitudinal fissure (easily recognized when looking at the top surface of the brain) with each hemisphere linked by the corpus callosum (the white structure in the below image).

longitudinal fissure sheep brain

The longitudinal fissure of a sheep brain

Within the brain, this location is less apparent. The basal ganglia lie deep inside the cerebral cortex close to the midline and around the corpus callosum. The olfactory cortex sits under the basal ganglia.

Cerebrum vs Cerebellum

In cerebrum versus cerebellum, the cerebrum is a subcategory of the brain telencephalon that is part of the forebrain. The cerebellum is a subcategory of the rhombencephalon or hindbrain. These are fetal brain forms that eventually develop into multiple complex structures.

cerebellum slice brain anatomy

The tree-like form of the cerebellum

Cerebrum functions have been discussed in basic detail above. We can compare these functions with that of the cerebellum and note the differences between both structures.

The first obvious difference is size; the cerebrum is much larger than the cerebellum. This, however, disguises the fact that the cerebellum contains more neurons than the cerebrum. It only makes up 10% of total brain mass but contains over 50% of the total neurons of the brain.

If we look at the reptilian brain, it is easier to have a better indication of cerebrum vs cerebellum. This is because the cerebellum is most developed in mammals – especially humans – and reptiles have brains composed of brainstem and cerebellum but not cerebrum. Most theories agree that early forms of the brain evolved from reptilian-like structures to include first a limbic system and, finally, a neocortex. The more intelligent the animal the greater the volume of the neocortex.

reptilian brain mammalian primate neocortex brainstem cerebellum limbic system

From cerebellum and brainstem to neocortex – brain evolution

The reptilian brain controls the vital functions of the body and is, therefore, part of the autonomic (involuntary) nervous system. Our heart rate, respiration, body temperature, movement, and balance are controlled here. Reptiles act in the same way and learning is the result of repetition and conditioning.

Over time, mammals involved: The earliest of these had brains consisting of the brainstem, cerebellum, and limbic system – or emotions and memory. Only when the neocortex of the cerebellum evolved in mammals did functions such as decision making, communication, imagination, and thought become possible.

classroom teacher student learning memory neocortical

Our highly-developed neocortex puts us on another level

Even so, all of these evolving structures work closely together. For example, the human cerebellum is also involved in decision-making and working memory.

Together, the cerebrum, brainstem, and cerebellum make up the mammalian brain. The brain and spinal cord form the central nervous system. All parts are interconnected, making mammals the most intelligent creatures on earth. The human brain has the largest cerebrum, separating us from animals through our ability to carry out conscious thought and communicate at an extremely high level.

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