so that white matter now on the outside is basically a ferrant and efferent nerve fiber tracts and it's white because it's myelinated so it's got this fat little wrapping around it the FM ones are the sensory ones they're right here they are blue in this chart and tapering information into the brain and the descending ones the efferent or motor pathways carrying tracts and they go out of the central nervous system praying to the body when we look at their naming we named them according to their origin and their destination so that's kind of cool because that way you can kind of figure out as you see the name where that stuff is going and you don't have to memorize everything just some of it when we look at neural pathways within those tracts they're all sensory or motor and the sensory ones or tracks that have three neurons or pathways that have three neurons so what happens is when you feel like let's say this is a touch receptor right here so you like get a press somebody presses and you feel a touch the first neuron goes in right here to the spinal cord level and then it goes up the spine and it actually then synapses goes to a different neuron and it goes as a second neuron up the spine to that place that we call the thalamus remember that place from last chapter and then from the thalamus it projects to the cerebral cortex for conscious integration so that's three neurons so they call that pathway a three new ROM pathway first order second order third or the motor pathways the bonds that go down have only two runs so they come down from well this is you from the pituitary gland but we'll call them from the cortex they come down and while neuron goes down to the spinal cord and at the spinal cord level that's where we have a synapse and then we go to the effector organ riches as we said before a muscle and other nerve or gland most of the tracks decussate and that means they cross over to the other side the sensor tracked a lot of them cross over at the spinal cord level and the motor tracks a lot of them cross over at the medulla oblongata level internally the tracks are very precisely organized and reflect an orderly map of the body you could see that you can see how we can organize everything up here we see where the sacral segments go through the lumbar and so forth they call that so mado topi that arrangement ability it's like a map topographical map so let's talk about a few tracks so first we go look at the ACE anyones the sensory bones I got a few here that I that I outlined one is known as the spinocerebellar tract those send info about muscle and tension stretch and they go through the cerebellum so they're unconscious so you see here spine I mean spine and the cerebellar cerebellar means cerebellum so you know they send stuff to the cerebellum and then the cerebellum process is what goes on this is like when you fall down into the pothole and you have to balance that's where that stuff goes over and then we got some that carry discriminative torch and proprioceptive impulses to travel through here so that's sort of funiculus they call them while sometimes tracks they call them funiculus - which means rope actually and either one that we want to know here so this one is not really named after the origin and destination those of that one you would just have to memorize but most of them are look at this one spinothalamic tract that's a cool one that's the one right here that's conscious sensation of pain temperature and course torch that goes through this tract up the spine this is the brainstem here upwards to the thalamus as we said before multiple times and from there it gets relayed to the appropriate region of the postcentral gyrus which is where the somatosensory cortex lies so that's where we can have conscious perception perception of the stimulus that comes in when we look at a sending pathway small a lot of them control skeletal muscles so we call that tract one of the names is cortical spinal tract so you see cortical that means cortex in the brain right here cortical that means the cortex in the brain and NEC spinal that's the spine so you know it goes from the cortex to the spine therefore you know it's a motor pathway the other name for that tract is the pyramidal pyramidal tract that's because these neurons cell bodies up there look like upside down little pyramids or triangles and so that's why they named it that way we saw that pyramidal tract in the front of the medulla oblongata as it travels from the brain to the spinal cord which is were that tract crosses over that's the decussation see that medullary pyramid that's where that is and then as we get down to the bottom at the spinal cord level where we need to go to to then exit the body into the muscle that's where we have a synapse and we get to a second order new Rome so in the motor tract we call the first order neuron on top they call that an upper motor neuron they also call that and then below from the spinal cord to the muscle we have what they call a lower motor neuron and of course if we want to go turn on a light switch we have this involuntary muscle movement to do we gonna have a few things happening number one we want to walk and we don't have to want to think about putting one leg in front of the other all the time so we have these automated Friedmann ocean patterns and that's governed in this basal ganglia so the basal ganglia is going to influence that initial motor command that we want to go turn on a light or so like that and then we also brain stem nuclear that we talked about this abstention I grow the red nucleus the influence motions and of course the big one is the cerebellum and that's a balancing and so the way I see that is like when I like walk and I've fall into a pothole and I'm not falling because I'm balancing out that's the cerebellum talking so that's a very very fast reactive system so it's crucial for coordinating this voluntary motion through these corrective commands and what's actually cool about the cerebellum it receives two planned a copy of the planned motion through what's known as the cortical cerebellar tracts again then they make sense on that and then it fine Tunes muscle actions by then assessing also stimuli to come in through stretch receptors in the joints and in the muscles and those are travel through that spinocerebellar tract that we identified on the previous slide so that's kind of neat I think now we talked about this upper motor neuron and modern or motor neuron before on the previous slides the two slides back upper and lower motor neuron so the upper motor neuron is the one from the cortex all the way down to the spinal cord level and then the lower motor neuron goes from the spinal cord level to the muscle and so when we look at lesions this is a place where we can sort of get a clue a bit better of how things work but also we get a clue when we see a person what kind of lesion am i half and so when the motor mint vendor upper motor neuron is leased by like an infarct or by a spinal cord severing or something like that that's bad then what happens down here the lower motor neuron actually is always activated and is rhythmically a reflex itself and so that's kind of interesting because what happens when we don't have the upper motor neuron firing the lower motor neuron just goes haywire and all the muscle spasm oh and it called this purr Alyce's and this look right here where you see that elbow bent really heavily and then the wrist is bent again that's when that happens because when these muscles fire all impeded li and again they're like rhythmically always sort of wanting to fire this is kind of the weird thing that a lot of times in Neurology we think about immoral commands get sent but we can send a modal command also by toning down something that always works or by letting something work and so a lot of these motions in the body are actually reflex driven and then they are altered by whatever the modal commands are I know it gets a little complicated but that's why when the upper motor neuron is broken the lower motor neuron just fires ongoingly and the muscle spasm up in a fashion that the stronger muscles contract more than the weaker muscles and the flexor muscles here the biceps brachii brachialis and all that and the flexor muscles in the forearm are strong or much stronger than the extensor muscles and therefore that's the look that you get so they overpower it but you know you should see that position and you put yourself in that position and hold it real tight for a while you start turning real fast so that helps us understand when we see these people that is you know it's not yeah it's not fun then we have a problem in the lower motor neuron so we just got a cop somewhere here or you know down here we actually break that cycle and we don't have that cycle anymore and then the muscle just goes limp and it doesn't do anything and that's called a flaccid paralysis there you go little pathophysiology right there now that brings me to that ongoing rhythmic motion thing that that the muscles always contract until they're sort of told to shut off a little bit and that's that's why we get to talk about reflexes so reflexes are involuntary hard-wired responses to stimuli it's a lot of reflexes just are ongoing they're rhythmic but we can started the reflex by things like when before example bring a finger and we prickle the finger and it hurts and we get ouch there is a nerve that goes into the system into the spinal cord actually and then this is the integration system in the spinal cord right here and Roger says you know he Rogers that something needs to happen and an impulse is sent to the muscle that then contract and what it does it pulls of course that finger away from the stimulus if that's a prickly needle or if that's a he played or something's and so that's kind of that's kind of neat so when we look at that reflex arc and describe it it's kind of like the negative feedback mechanism it's very similar we got a muscle receptor here it's great I don't know it's red here's a receptor that picks up the muscle stretch for example or a prickly that hurts or he temperature that hurt something like that and it sends this sensory stimulus into the spinal cord and right there at the spinal cord level it's such an automotive situation that the integration happens that it fires right to an efferent lower motor neuron and that just contracts that muscle to pull that arm away so receptor registers change it sends an impulse via an afferent neuron to the spinal cord for processing and then a response is sent via an efferent neuron to the muscle that needs to do the action