Hi everyone, Dr Mike here. In this video we're going to take a look at the frontal lobe. Now, to orientate ourselves, let's look at the other lobes of the brain.
We know that we've got the frontal lobe here, the parietal lobe, the occipital lobe and the temporal lobe. And if you were to pull that away, you would see the insula underneath. We're focusing in this mini lecture on the frontal lobe. Now, a couple of things. We need to know some of the anatomical divisions.
So how do we know that the frontal lobe sits here? What sits under it being the temporal and parietal behind it? How do we delineate between those particular lobes?
So first thing is with the frontal lobe what you're going to find is that there is a dip down that we call a sulcus and then there's a bump up called a gyrus and then another dip down called a sulcus. So if I've got a sulcus here there's always going to be a gyrus the bump up right next to it and then there's going to be another sulcus for example. What you're going to find is that there is a sulcus sitting pretty much in the middle of the brain going straight down like that.
and we call this the central sulcus. Now the central sulcus, the central sulcus is actually the delineating marker anatomically that separates the frontal lobe from the parietal lobe. Now inferiorly, we've got this fissure that sits here called the sylvanian fissure or called the lateral sulcus and that separates the frontal lobe from that of the temporal lobe.
So central sulcus separates the frontal from the parietal. and the lateral sulcus separates the frontal from the temporal lobe. So now that we've identified the anatomical barriers, lateral sulcus, write that down, what we can now talk about are the functional divisions of the frontal lobe.
Now, functionally they're not as defined as, you know, here's a sulcus and this is where this function starts and ends. But I can tell you whereabouts these functions predominantly sit. Now, as you can see, there's five different functions I want to go through that basically make up what the frontal lobe does.
But the way I want you to think about is this, the frontal lobe is the action lobe. We want something done, we recruit the frontal lobe. It may be motor movement, it may be talking, it may be some sort of emotional behavior that we need to demonstrate.
It all needs to come from the frontal lobe. So what we're going to do is we're going to start centrally and move anteriorly. And we're going to start with, we've got the central sulcus.
which means there must be a gyrus in front of it which we can see here, which we call the precentral gyrus. So that's this area here, precentral gyrus. This is actually the site of the primary motor cortex. Now the primary motor cortex is important. It is the area in which we initiate voluntary movement.
The area that we initiate voluntary movement. So that's worth writing down. Initiate Voluntary or conscious movement.
Now if I want to move my mouth for example, it needs to be initiated from here. If I want to move my arm again, the signal needs to start from here and so forth. So how does it know to move my arm or move my mouth or move my feet?
Well importantly, there's actually a map of all the muscles of the body. or at least all the voluntary or consciously moved muscles, so skeletal muscles, there's a map of the skeletal muscular system on the brain, specifically on this motor cortex. And if I were to cut down the central sulcus and have a look in, this is what we would see, right? And this is how the map works. So I'll just wipe this off here.
So what you'll find is that the muscles of the foot are mapped here. Then the muscles of the leg are mapped here, and the muscles of the bum, and the back, and the arm, and the hand, and the neck, and the face, and the eyes, and the mouth, and the pharynx, larynx, and tongue. This is how we map the muscles, skeletal muscles of the body, onto the primary motor cortex.
This is called our motor homunculus. And as you can see, some muscles have not much area of the primary motor cortex dedicated to it, and some have a lot. So for example, our back doesn't have much area dedicated to it, but the hand and the face does.
Why is this? Well, it's because muscles that require a lot of fine skill or fine motor movement. So for example, our hand, if I were to pick up a pen, it requires a lot of fine motor movement.
Same with our lips for speech, for example, and our face. So what that means is those areas have a larger part of the brain dedicated to it. Because you need more neurons to allow for a nice pattern sequence of firing so that you can articulate that movement better.
Right? So this is how we map those skeletal muscles onto the primary motor cortex. So if I were to translate this onto Here for example, what you're going to find is that the foot's going to be a little bit around the corner, but then we're going to have the leg, then we're going to have the bum, back, arm, hand, neck, face. eyes, mouth, pharynx, larynx, tongue. And so this is moving around like that, and so it's moving around like that.
So the way that this primary motor cortex works, if I just want to move the mouth, contract those muscles, that gets activated. Move the arm, contract those muscles. this area gets activated.
But we don't just move those muscles in isolation, we usually move them because we want some sort of planned, patterned and sequenced motor activity. So for example, if I need to write, it needs to be a planned patterned, sequenced motor activity. If I want to juggle or play the piano, the same thing.
So we need to recruit another part of the frontal cortex to help this area. We need a part of the brain that says, okay, fire this muscle at this time, and then this muscle at this time, and then this muscle at this time. So it plans and sequences that motor firing and this is what we now call the motor association cortex.
This sits just in front of this primary motor cortex in this area here, just immediately in front of it and it's made up of the pre-motor cortex and the supplementary motor cortex. We're going to talk about them together. And what happens is this, if I want to grab a pen and start writing, I need to tell certain muscles to contract in a certain sequence.
It needs to be planned and sequenced like I said. And this is going to begin here at this motor association cortex. Now, where are the muscles or where's the area of the primary motor cortex for the muscles of the hand? It's all here.
So, the motor association cortex for hand skills are going to be here. It could be playing the piano or juggling or whatever it may be. So, we've got hand skills here.
And again, that's going to fire off and then tell the Primary motor cortex what to fire at what moment. If I want to turn or move my head for example It's gonna fire here. There's gonna be head tilt or head turning. If I want to speak produce language Articulate words or sounds that come out of my mouth.
This is going to happen in this area here. Language production But this language production area actually has a name. It's called Broca's area. B-R-O-C-A-S area. And this is actually important enough to have its own function.
So Broca's area is actually there for language production, language and speech production, to be able to speak. Now importantly, again this motor association cortex here, it's there for planned, sequenced motor skills. That's what that motor association cortex does. And again that's the same with language because it's planned, it's sequenced, it's a motor skill but specifically it's for language production and it's called Broca's area. If you have damage to Broca's area, what do you think you have?
Aphasia. Inability speaks with Broca's aphasia, inability to produce words. Now we're going to talk about the frontal eye field and the frontal eye field sits around about here. And the frontal eye field is important for following objects.
So if you see an object jump into your vision and you can follow it and track it, this is the frontal eye field. It's important also for rapid eye movement. So let's write this down. Tracking, objects and rapid eye movement. Alright, the last part I want to talk about makes up most of the frontal lobe and it's called the prefrontal cortex.
Prefrontal cortex. And again, I said that the whole frontal lobe is the action lobe, right? So the prefrontal cortex is about demonstrating these actions in regards to emotions and behaviors and understanding and cognition. Alright, so for example, this is why I like it because the prefrontal cortex has a whole bunch of stuff.
But the way I like to think about it is like this. How do you know how to behave in a particular scenario? How do you know what to say in this context as opposed to this context? What you say in a job interview may not be what you say to your friends and family, for example.
How do you know not to walk up and just slap somebody in the face or yell profanities at them? It's because you can cognitively understand and process a situation. and then behave appropriately in that situation all because of the prefrontal cortex.
And we know this because, for example, individuals who have damage to the prefrontal cortex, their behaviors change, their emotions change, their processing of how to behave in context change. An individual called Phineas Gage, back in the 1800s, working on the railway, an explosion put a metal spike through his prefrontal cortex and his behavior totally changed. He went from being this calm and placid person to quite a crude and crass person in social contexts.
So that's the prefrontal cortex. So again, it's important when it comes to cognition, behavior, emotion, but also things like language as well, processing and so forth. So what you can see here is the frontal lobe, the action and the way we've divided it anatomically and functionally.