Overview of the Central Nervous System (CNS)

hi everybody dr mike here in this video i want to introduce to you the various parts of the central nervous system so to begin with you need to understand that the central nervous system is made up of the brain and the spinal cord and it's central anatomically because it sits in the middle of the body but it's also central functionally because it's the site of information integration it's where we make sense of all the signals that are coming into us from the environment whether that's the external or internal environment we make a decision we understand

what's going on and then we send a signal out to the various muscles tissues or glands of the body in order to have some sort of reaction to those stimuli that are coming in now if we look at the brain itself first thing i want to begin with is the fact that the brain sits within a skull casing that bony structure that we call the skull but above the brain but below the scale there's actually three protective layers on of the brain that we termed the meninges or meningeal layers so these three layers if i

were to draw them up for you very quickly the first layer is the layer that's most adherent to the brain itself and this layer is termed the pia mater and pr means soft mater means mother it's the soft mother basically it's like tissue paper that's stuck to the brain itself on top of the pia mater we've got another layer that has these projections down to the pia mata that look a little bit like a spider's web and this is called the arachnoid mata or spider mother interestingly below the arachnoid layer but above the pia mater

is where the cerebral spinal fluid floats through now on top of the arachnoid mater we've got a very tough layer called the jura mata which means tough mother and it's like a paper bag consistency very tough on top of the duramata is where we have our skull and again cumulatively these three layers are called our meninges or meningeal layers and if they have some sort of infection or inflammation associated with them that's called meningitis so let's take the brain move it down have a look at the various parts of the brain first we've got the

actual brain itself that we call the cerebrum which is made up of multiple lobes so we've got the cerebrum here then we've got the little cerebrum which we term the cerebellum and cerebellum actually does mean little cerebrum and then we've got the brain stem and obviously below the brain stem that's where we've got the spinal cord so the brain stem first thing i want to look at is the cerebrum so remember if you were to cut into the brain itself and have a look you'd find that some aspects we call gray matter some aspects we

call white matter why is that what is the difference well if i were to draw a neuron up a very basic neuron with a cell body an axon and the axon terminal and so for example this neuron may be speaking to another neuron right now what you find is that these cell bodies when you have a collection of these neuron cell bodies they make up the gray matter and the axons actually make up the white matter now why is this the case it's because the axons all they do is send information they need to send

information really quickly so they're surrounded by insulation which is fat and fat looks white and that's why the axons are white matter and the cell bodies relative to the axons are grey matter the other important point is that wherever you find gray matter it means there's obviously a lot of cell bodies this is where information is being made sense of this is the site of integration this is where all the thought and behavior and processes occur the axons or the white matter they're just highways that's all they are sending information back and forth now both

the brain and the spinal cord have gray and white matter associated with them now if we look at the cerebrum it's broken up into various lobes or cortices now the cortex is simply the few millimeters of the outside of the cerebrum made up of gray matter so it's the place where we make sense of stuff and we become consciously aware and we can break these cortices or lobes up into what we've got as the frontal lobe we've got the frontal lobe we've got the temporal lobe we've got the parietal lobe and we've got the occipital

lobe and what you'll find is that the bones of the skull that overlay them have the same particular names so what do these particular lobes do well they all play very important roles and functions within the body and there's a lot of overlap in those functions but some important roles that we can designate to particular areas include the following so the frontal lobe is the site of the motor cortex motor cortex now what that means is this is the area in which if you want to consciously initiate movement so to talk to move to run

jump sing dance whatever it may be it must begin at the motor cortex which is located at the frontal lobe the parietal lobe is the location of what we call the somato sensory cortex and the somat so somato means body sensory is picking up sensation so anytime you become consciously aware of sensation whether it be touch pressure pain whatever it may be it must go to the parietal lobe in order for you to understand it and make sense of it the occipital lobe is where we have the visual cortex again anytime you see something in

order for you to understand it and be aware of it it must go to the occipital lobe and the temporal lobe is the site of the auditory cortex this is where we understand and make sense of sound now there's obviously other various roles but this is a very quick intro to some of the important roles of the various lobes now let's go to the cerebellum the small brain or the small cerebrum three important roles here that you should be aware of first of which is it plays a role in maintaining tone and posture and balance

they're the three important roles you should be aware of what this means is an example i like to use is if somebody said can you help me move house sure help me move those boxes that's a heavy box be careful mike make sure you bend with your knees not with your back and you get down you tense those muscles up ready to pick it up and then you realize it's an empty box and they pointed at the wrong box now what's stopping you from flipping backwards because you're prepared to pick up something very heavy it's

the cerebellum it receives input coming in from your muscles and where you are in your own space and how bent or flexed the particular joint is and it fine-tunes it and so it fine-tunes that tone so how contracted a muscle is your posture and your balance that's the important roles of the cerebellum now what about the brain stem well the brain stems made up of three parts we've got the first part here sitting immediately underneath the cerebrum second part here and third part here underneath that third part that's where we've got the spinal cord so

what are these three parts well the first part is what we call the midbrain second part is what we call the pons and the third part is what we call the medulla oblongata also just known as the medulla now what does the brain stem do well firstly it is the house of most of what we call the cranial nerves these are the nerves that play important roles in the head and neck so basically being able to touch being able to see being able to talk and move and all those particular functions of the head and

neck their cell bodies most of them are located in that brain stem but the brain stems important for a number of other reasons for example it's extremely important when it comes to respiratory and cardiovascular rhythms so that's breathing rhythms and heart rate really important here at the brain stem and the brain stem is extremely important when it comes to various types of reflexes so remember reflexes bypass our conscious understanding and it's reflexive and it's usually there to protect us so some of the important reflexes at the brain stem include the blink reflex so if something

were to touch your eye and you would close your eyes reflexively it is if you see a particular shape or sound or something happening in your periphery and your eyes dart to that position that reflex is happening at the brain stem it's also the cough reflex the vomiting reflex the jaw jerk reflex for example so a number of really important reflexes that's the brain stem all right now i want to move over to the spinal cord and when we have a look at the spinal cord it's going to be separated into various divisions or regions

now the spinal cord has axons or neurons that shoot out in a way and back into it and various areas so for example you've got the cervical you've got the thoracic the lumbar the sacral and the coccygeal these are the various regions of our spinal cord and there's neurons that shoot at away and back in from the cervical which just means neck or cervical thoracic lumbar sacral coccygeal and they've got peripheral nerves associated with them and there's actually 31 pairs of peripheral nerves that sit throughout the spinal cord now the spinal cord also plays an

important role for reflexes as well now a reflex like i said it bypasses go into the conscious area so the cortices of the brain and it can be something where i touch a hot plate and my arm reflexively moves back for example or if i'm walking and i step on some glass it allows for that leg to move back and for the other leg to plant so these reflexes actually occur at the spinal cord itself so what we've done is a quick run-through introduction to the various parts and functions of the central nervous system