Now, let’s take a look at each of these lobes to appreciate more fully the functions that
are associated with them as well as the various subdivisions of each lobe. We can also explore
as we move through each lobe, what might happen if there’s a lesion within a specific area of a lobe.
So here, we’re looking at the primary motor cortex. This is shown right in through here
in green. The primary motor cortex is associated with the gyrus that’s immediately anterior
to the central sulcus. This is the precentral gyrus. We have the famous homunculus
associated with the primary motor cortex. The little man, the homunculus demonstrates the
density of upper motor neurons that are going to control the musculature of various regions
of the body. So, we see a large area here mapped out for the face because a large number
of motor neurons, upper motor neurons are going to control the muscles of the face.
We also have a large area here mapped out for the hand. Again, a large number of motor
neurons are going to control the fine, delicate movements that are associated with this
part of our anatomy. This homunculus does extend over the top of the cerebral cortex,
over the top of that precentral gyrus and continues on the medial aspect. We’ll see that
continuation on the next slide. An important aspect about motor control is that of the motor
neurons on one side. Here, we’re looking at the left precentral gyrus. They’re going to
control the contralateral muscles, those that lie then on the right in this case. What might
happen if there’s a lesion within the precentral gyrus? That will cause contralateral paralysis
or paresis. Because you are damaging and destroying the upper motor neurons, you may
very well see Babinski response depending on the location of the lesion. So, if the lesion is in
this area specifically, you would have contralateral paralysis or paresis of the hand
for example. If we continue our view here on the medial aspect of the precentral gyrus and again,
that’s shown in green, we can see the buttocks lie here on the superior aspect of the precentral
gyrus medially. Then you can start to see the lower extremities continue distally,
so that the feet are approaching the cingulate gyrus that’s along here. If the stroke is in this
area and you have a lesion in this area and you’re unable to have upper motor neuron control
of the distal extremity of the lower extremity then that’s when you can see a Babinski response
as well as a contralateral paralysis or paresis of that associated anatomy. Another area of
interest that I want you to understand is that of the premotor cortex. The premotor cortex lies
anterior to the primary motor cortex. We see it’s a small area here. But it’s essential in the
programming of motor events. So, this programming will then cause these neurons that
reside in this territory to activate prior to the primary motor neurons that are within the
precentral gyrus. A lesion of the premotor cortex is associated with apraxia. Apraxia is a
motor speech disorder. This can be associated with other lesions in the frontal lobe. Our next
area of the frontal lobe is that of the supplemental motor cortex. We see it identified again
anterior to the precentral gyrus. It’s involved in the planning of complex motor movements.
A lesion of this cortical area can cause apraxia as well. Another area within the frontal lobe
is the frontal visual field cortex. This area right in through here. It’s even a bit more anterior
to the other areas that we were describing, that I was just describing for you. It's involved
in the coordination of voluntary movements. A lesion of this small area can result or will
result in paralysis of conjugate gaze to the opposite side. This is discussed in another
presentation, what conjugate gaze is and how that circuitry works. Another important area
within the frontal lobe is this area in blue. This is Broca’s area shown right in through here.
This is the area of the frontal lobe that’s involved in word production or motor speech.
A lesion here results in expressive aphasia or nonfluent aphasia. Lastly, within the frontal
lobe, I want you to understand the prefrontal cortex. We see that area here. This is
the area of the cerebrum that takes some degree of maturation to become fully functional.
This is involved in executive functioning. One of the functions under this heading
would be that of problem solving. It’s also involved in making day to day multiple judgments.
Many times we make very, very good judgments or decisions. These judgments as we mature
tend to make us make the right choice or the right decision. Another aspect of the executive
functioning is that this is the area that allows us to plan. It also drives behavior and emotions.
It’s not the only area but behavior and emotions are modulated by the prefrontal cortex.
Then an area of the prefrontal cortex is involved in olfaction, the olfactory pathway.