So, the biggest portion of the brain is our cerebrum and the cerebral cortex or the outermost portion
which is composed of gray matter is going to contain billions, billions with a B of neurons.
The cerebrum is composed of a bunch of gyri, fissures and sulci and they can be identified on the cortex.
So, when you look at a picture of the brain, all those different folds and dips are not random.
Each of them has a specific purpose. Deep to the cortex, we have the white matter.
This is composed of tracts of neurons that connect parts of the brain to each other as well as to the spinal cord.
A bundle of white matter tracts are called the corpus callosum
and it also connects the right and left hemispheres of the cerebrum.
So, now, let's take a closer look at the details of the cerebral cortex.
As you can see, the cerebral cortex is divided into two hemispheres, the left hemisphere and the right hemisphere.
As well, the cerebral cortex is divided into different lobes, you have the frontal lobe, the parietal lobe,
the temporal lobe, and the occipital lobe.
Notice that the lobes correspond with the names of the cranial bones where the lobes are found.
Separating the left and the right hemisphere, you have a deep groove known as the longitudinal fissure.
As well, we have a precentral gyrus and postcentral gyrus that are across a shallower groove known as the central sulcus.
So, just to recap these vocabulary words, a gyrus are the folds of the brain,
a sulcus is the shallower grooves between gyri, and a fissure is a very deep groove between the folds
and the most common of the fissures is going to be our longitudinal fissure.
So, on the end side of the cerebrum, we have our cerebral white matter tracts.
Recall that the outer cortex of the cerebrum is gray matter and the inner portion is white matter.
In these tracts, we have association tracts
which are going to conduct nerve impulses between gyri in the same hemisphere of the cerebrum.
As well, we have commissural and projection tracts.
The commissural tracts include the anterior commissure and the corpus callosum,
as well as the posterior commissure which we cannot see in this image.
These are going to conduct nerve impulses from gyri to the corresponding gyri on the opposing cerebral hemisphere.
For our projection tracts, these are going to be able to conduct nerve impulses from the cerebrum
to the lower parts of the central nervous system, such as the thalamus, the brainstem, and the spinal cord.
These tracts go in both directions.
So, they go from the cerebrum to the lower parts, as well as, from the lower parts back to the cerebrum.