hello and welcome to the review of chapter 57 of guyton hall's medical physiology textbook in this chapter we go over the role of the cerebellum in addition to the basal ganglia and being able to control muscle movements or at least fine-tune them if you like the video please don't forget to give it a like and subscribe to the channel so to begin with just to overview what we're going to go over the cerebellum and the basal ganglia they don't actually control muscle function itself rather they are more fine-tuning our actions so they're smoother the cerebellum
is responsible for making sure that our motor activities are rapid and there's a smooth progression between each movement and then our basal ganglia help to plan and control these complex muscle patterns such as writing a letter or writing letters in general and helps to allow us to do successive movements that are complicated it is known as the silent area of the brain because electrical excitation doesn't actually cause any outward change in the body however removing the cerebellum causes some very abnormal body movements and this is primarily due to a lack of coordination so the cerebrum
primarily compares to what the actual movement is in the body to what the plan was and then fine-tunes it so then you're able to actually do the movement that we're planning to do it so it is a subconscious corrective signal from the cerebellum that helps us do smooth movements when it comes to the anatomy we have these three primary lobes of the cerebellum so we have the flocculonodular lobe which is more associated with your vestibular apparatus we have the posterior lobe and then the anterior lobe now if we look at this from the top on
view then we end up with this picture here and as you can see the flocculo nodular lobe is down the bottom here and then we have the anterior lobe with the posterior lobe in this primary portion here now we have a vermis which is the central line that's kind of indented and the vermis helps to control muscle movements of the axial body for trying to maintain posture then either side of the vermis we have intermediate zones which help to control the distal portions of the upper and lower limbs so your hands and feet primarily and
you can see that in this picture over here focus 57 3 which shows the topographical representations of the body where you can see that the axial muscles are in the middle here and then the peripheral limbs are on the outside here in the intermediate zones and then that leaves us one last zone which is the lateral zone so this these zones on the lateral aspects of the cerebellum the lateral zones don't actually go out to the periphery rather they have extensive communication with the actual cerebral cortex to help plan sequential motor movements now figure 57
4 here goes over their primary efferent afferent with an a meaning that these are all signals coming into the cerebellum and you can see there are quite a number of different tracks here each coming from different portions of the body and the way to really understand where it's coming from is that the first part of the name is where it's coming from and then the second part is where it's going to so cerebro pontile tract means that it's coming from the cerebrum to the pontine nucleus the ponto cerebellar tract is going from the pontine nucleus
over to the cerebellum and so forth we then also have the two primary afferent signals coming from the body itself the dorsal and ventral spino cerebellar tracts and the dorsal spinal cerebellar tract is mainly taking all those signals from our muscle spindles remember they are the ones that are telling us the position of each our muscle and the length and change in length of our muscles and then we also have our golgi tendon organs which are sensing the tension and rate of tension change in our actual tendons covered in previous chapters all those signals go
in the dorso spinal cerebellar tract to go into the cerebellum which then processes exactly where those movements actually are and compares it to what the brain has wanted it to do and that's how it primarily does its effects it's receives the signals from the brain for the planned motor action it receives the signals from the actual muscles and tendons themselves to see what motor action is actually occurring and then is able to fine-tune it and send out their appropriate signals to either continue the movement or stop the movement depending on what is going on in
the body and then when it comes to efferent pathways efferents with an e which is after a an alphabet so you know it's a signal going away from the cerebellum we've got three primary pathways more relating to that anatomy of the cerebellum that we've already talked about so we have the one coming from the vermis which is going to the brain stem because it's related to the positional muscles you know axial muscles and it's helping to analyze which movements need to occur to maintain our posture we have the pathway coming from the intermediate zone of
the cerebellum which is helping to control our peripheral lumps and that is going up with an eventual final destination of the red nucleus to help control our hands and our feet and then from the lateral cerebellum which primarily just goes right up to the thalamus and cerebral cortex to help to control sequential motor activities or these more complex motor activities if we dive deeper into the actual cell layers then we come up with this diagram here figure 577 so coming from the outer side in outer side we have the molecular layer down into the purkinje
cell layer down into the granular cell layer and then eventually our deep nuclei which is sending out output signals essentially input comes in via either the mossy fiber or the climbing fiber which will automatically send an excitatory signal to the deep nuclei to send out another output but both of these fibers will also send a signal out into our molecular layer which will eventually also excite a kinji cell and the purkinje cell is primarily inhibitory on that deep nuclear cell so we get an instantaneous excitation of our output cell with a delay and eventual inhibition
of that same output cell so we get an initial impulse that's then stopped this on and off switch that occurs shortly after itself now a primary difference between our climbing fiber which comes from our inferior olivary nucleus of the medulla that sends a primary just complex spike that goes straight up into our purkinje cells whereas our mossy fiber and as you can imagine it's more like moss has a lot of little arms to it with a lot of synapses and you require a lot of signals which are weaker to actually result in stimulation and that
results in a simple spike in addition to these major cells here we also have two other types of cells within the molecular layer called stellate cells and basket cells and they are responsible for lateral inhibition as we've talked about as a concept very frequently in the last couple chapters this helps to sharpen the signal so they were able to send that signal where we want it to the appropriate purkinje cell to then inhibit the appropriate deep nuclear cell so this on and off switch of the cerebellum helps to really turn on the agonistic muscle that
we need for the primary movement but at the same time stop that excitational signal and stop the contraction of that muscle when it's deemed appropriate and that is the same with the antagonistic muscle as well so it's able to stop the antagonistic muscle from contracting and then help to contract it to stop the movement altogether so the primary function of the cerebellum is really to help to finally control when we contract and when we stop contracting our muscles and this can become a learned function as well and that occurs within the purkinje cells themselves so
the purkinje cells which is the inhibitory signal which is the off portion of the cerebellum when you first perform a particular movement if you slightly overshoot it and you don't quite turn off that signal fast enough that will be learned within the cerebellum so the next time you go to do that function you will turn off the excitatory signal a little bit earlier if you do it too early then the same thing that will be learned and eventually the pikenji cell will know when to actually inhibit that signal from occurring so whenever you go to
do a movement you don't overshoot it which is the overall role of the cerebellum when it comes to separating out these different functions to three separate levels we have these three primary control functions so the vestibulo cerebellum function which involves a floccular nodular lobe that sits just underneath the cerebellum this is responsible for the body's equilibrium movements and really helps to keep us stable during rapid motions so helps to make sure that our postural muscles are able to respond to rapid movement so we don't actually fall over and there's a large anticipatory correction in the
postural motor signals because as you could imagine if you're turning you need to know how fast you're turning and in which direction and preemptively contract certain muscles to stop you from falling over if you do it after the fact you will fall over regardless of knowing that you are turning in in which direction so it needs to be a preemptive role the second major function of the cerebellum involves the spino cerebellum and that involves the spermus and the adjacent intermediate zones remember that helps to control our posture and in our distal portions of our limbs
so that's really involved with general voluntary movement in a sense and helping to fine-tune the muscles of the body and then lastly here our third control function is the cerebral cerebellum coming from the lateral zones which don't actually send any outputs to the periphery of the body instead it receives its inputs from the cerebral motor cortex and then sends its signals back to the cerebral motor cortex and it's helping to create this mode of imagery and then helping to actually plan voluntary movements without actually fine-tuning current voluntary movement so it's planning how to perform a
complex action so going into more detail about these three areas the vestibulo cerebellum we've kind of already touched on everything here we're really helping to control our posture in the face of rapid changing and direction whereas the spino cerebellum this system which is helping to control the axial and also our distal limb movements we receive the information from the cerebral cortex for exactly what the movement we want to do and then we also receive information from the peripheral parts of our body from those proprioceptive receptors from the actual movements so this is the part of
the cerebellum that's receiving both the planned action from the brain and the actual action from the muscles and then correcting the actual movement to perform the movement that was planned in the beginning so helps so smooth and helps to create a coordinated movement without this function we can end up with tremors or intention tremors because we are going to tend to overshoot everything and although this cerebellum isn't there to process this information that input for overshooting a certain movement will be processed within the actual brain itself but it's a lot slower so it realizes oh
we've overshot that movement we need to move in the other direction so now let's say your arm was moving in one direction and you have overshot that direction the brain realizes that after the fact and then makes you move the your arm in the other direction but once again it overshoots it because it's not receiving those signals from the proprioceptive receptors fast enough since you've overshotted in the other other direction now you then perform the same movement originally and overshoot it once again so you end up going back and forth in this oscillating fashion which
is seen as a tremor now another function of the spino cerebellum is this ballistic movements and this involves a movement which you just want to rapidly occur and then stop without receiving any input during the action of the actual movement because it's happening so rapid for instance typing you want your finger to go down and hit a key and you don't need to know whether or not you're going in the right direction you just need to go and hit it really quickly and move on to the next one and you'll realize after the fact if
it's wrong that is a ballistic movement and without the cerebellum then you end up having a very slow initiation of this ballistic movement the force developed is very weak and it's also very slow to turn off as well so instead of being able to quickly type you just have to slowly think about where you're positioning your finger each time with a weak slow movement and then lastly here we have that cerebral cerebellum coming from the lateral zone to control these complex and help to plan these complex movements and without these lateral zones we end up
with extreme coordination of complex movements of our hands our feet our fingers and our speech apparatus so it helps to plan these sequential movements and also the timing of when it occurs it also allows us to quickly progress smoothly from one movement to the next because it has been pre-planned so you're able to jump from one action to the next action as it's been processed within the cerebellum in the cerebral cortex in this little gray box here we go into some abnormalities when the cerebellum is no longer functional for instance when the lateral cerebral cortex
is dysfunctional we can still have motor functions which are pre-planned but they're just a lot slower so the cerebellum helps to speed up actions do it faster do it smoother we can end up with ataxia because we don't know where the position of our limbs are and relative to space because we have lost that proprioceptive input so now your walking ability may seem really wobbly because you don't exactly know where you are as you're doing a movement and then past pointing meaning that we've lost that signal which is turning off an action so we end
up pointing past or moving past where our intended movement was to go towards and then we have various other disorders here as well so the inability to actually perform rapid alternating movements failure to actually progress in talking and tension tremors and then tremor of the eyeballs as well all of these functions which are meant to be able to stabilize the movement and then help to move to another movement altogether so next up we're going to talk about the basal ganglia which essentially is another accessory motor system like the cerebellum it doesn't initiate movements but it
helps to process them and make them smooth its location is surrounding the thalamus which is located here and we have several basal ganglia mainly most of the sensory and motor nerve fibers that connect to the cerebral cortex and spinal cord they have to pass through the space through what's called the internal capsule and within this internal capsule we have these two primary areas called the chordate nucleus and the putamen which is what we're going to focus on now so the putamen circuit is described or shown up here if you need to know this entire pathway
then by all means rote learn it but the purpose of the circuit is to actually control complex patterns of modem activity and this involves all skilled movements which almost seem subconscious so cutting paper hammering nails performing skilled activities in sports such as shooting a basketball passing a football kicking a football passing a baseball etcetera so these skilled almost subconscious movements involve these circuits involving the putamen portion of the basal ganglia and it receives its inputs from the primary motor cortex and eventually that ends up back at the primary motor cortex it also describes a couple
of abnormalities here of issues with this putamen circuit the most notable of which is parkinson's disease which involves the substantia and we'll get into more details very shortly about parkinson's disease later on in this chapter now the other main circuit in the basal ganglia is the chordate circuit and the chordate circuit is more involved with cognition control of motor activity and remember cognition is this thinking process of the brain using both sensory inputs and also stored memory input as well so it's more the process of actually thinking about your motor activity and that's where the
chordate circuit comes into play and that receives a lot of its inputs from the association areas of the cerebral cortex and then sends it back to the prefrontal premolder and supplementary modal areas of the cerebral cortex it doesn't really involve the primary motor cortex itself now to really summarize the overall function of the basal ganglia is that it is able to control how rapid a movement is performed and how large the movement will be so people with dysfunction in the basal ganglia the timing and the scaling of functions is poor now gives an example here
of one of the portions of the cerebral cortex that it functions in close association with so the posterior parietal cortex and this is the ability to perceive objects through normal sensory mechanisms and a dysfunction is in that is agnosia and the people which have let's say dysfunction in one side so let's say the right's posterior parietal cortex if there's dysfunction there then often we end up with this kind of result in figure 573 where they almost ignore or don't even acknowledge the left side of vision and body so people who draw this drawing end up
just drawing primarily everything that they see on the right side and they can even ignore the left side of their body altogether but getting back to the actual basal ganglia just a summary of the neurotransmitters that work in this region include dopamine which is primarily inhibitory gaba which is always inhibitory acetylcholine which is usually excitatory and then also multiple other pathways that can involve norepinephrine serotonin and encephalin so if we start to talk about primarily the action of the dopamine side of things then we end up with parkinson's disease where there is actually a destruction
in the portion of the substantia which actually sends out dopamine signals which is remember inhibitory so since we lose that inhibitory effect we result in rigidity of the musculature because there is no inhibitory signal telling those muscles to actually relax we can get involuntary tremors difficulty in initiating a movement called akinesia postural instability so frequent falling over and then other motor symptoms as well like dysphagia which is a difficulty in swallowing speech disorders gait disturbances and fatigue now there are some treatments for parkinson's disease that involves these two drugs so l-dopa which is the precursor
for dopamine you can't give dopamine itself because it can't cross the blood-brain barrier so giving l-dopa helps to provide the substrate for the brain to produce dopamine which is not being produced in this disease and then our depranol and this drug helps to actually inhibit monoamine oxidase and monoamine oxidase is actually responsible for breaking down dopamine so by inhibiting it you actually helped it dopamine from staying longer in the body they have also tried some surgical options and then also trying to actually implant fetal dopamine cells but they don't live for longer than a few
months now the other primary disease that they talk about here is huntington's disease which is an autosomal dominant heritage disorder meaning that it will get passed on to your children and this disease typically actually presents itself when you're roughly 30 to 40 years of age and it starts off with these flickering movements and individual muscles to eventually result in distortional movements of the entire body and also severe dementia the actual muscle tremors and distortional movements is due to a loss of gaba secreting neurons so this inhibitory neuron which is meant to be inhibiting those signals
and then the dementia is believed to come from a loss of acetylcholine neurons which is helping in the thinking areas of the cerebral cortex so that is the cerebellum and the basal ganglia control of the motor system now there is this portion here in this chapter going over a summary of everything that we've gone over so far which is quite nice so the spinal cord level we go over local patterns of muscle movements remember these are the rhythmical motions and they can be controlled by higher levels of the body and that also is involved with
those rapid reflexes where if you touch something hot automatically your muscles are eventually going to receive a signal to pull away hind brain or brain stem these are mainly for maintaining axial tone in the body so we can stand and then also information from the vestibular apparatus so then we're able to not fall over and maintain body equilibrium when it comes to the motor cortex it's mainly helping to activate motor signals in the spinal cord to perform a movement whether it's a basic movement or typically a more complex movement and cortical patterns are learned whereas
spinal cord movements are hardwired so those reflexes so it's more of a complex learned patterns and it more activates the spinal cord movements if we dive deeper into each component we have the cerebellum as we've talked about which helps with rapid movements and also smooth coordinated activities so then we're able to easily transition from one movement to the next and not overshoot our movements so then everything actually occurs as we've planned it to occur as we receive all the signals from the body the cerebellum is able to tell exactly where all our muscles and tendons
are and know that we need to adjust a certain movement for a particular planned movement and then the basal ganglia which once again helps to helps the cerebral cortex about learned patterns of movements and then also helps to transition from one pattern of movement to the next to actually perform a task and then this last little paragraph here talks about what it arouses us from an activity and that is really the limbic system and we will get into the limbic system on chapter 59 but for now that is everything and i just want to mention
lastly here if you'd like to support the channel and get access to downloadable audio files you can do so in the description where there is a link to become a patreon otherwise i hope you enjoyed this video feel free to leave a comment and we'll see you in the next chapter
