Neuroanatomy S3 E1: Balance #neuroanatomy #ubcmedicine

[Music] from atomic particles to celestial bodies all objects in the universe are in a perpetual state of motion just like the planet we stand on we human beings are constantly moving through time and space [Music] our journey through the world is chaotic and tumbling through it by all means it should feel like chaos so why doesn't it if everything is moving how do we human beings still feel grounded how do we find stability amongst the constant confusion of motion how do we ever manage to land on our feet [Music] our eyes relentlessly scan our environment for cues as to where we are in relation to the objects around us while proprioceptors continuously sample the position of our limbs in space but there's one piece of this puzzle still missing and that is the acceleration of our body through space movement is chaotic and our bodies must be able to make sense of it each element of this chaos needs to be isolated within a confined space the structure that confined the chaos that senses acceleration that allows the brain to understand movement it's tiny it's smaller than a fingernail it's called the vestibulum and it's the organ of balance oh and we have two of them [Music] the tiny vestibulum sits within a labyrinth of canals within the petrous part of the temporal bone the vestibulum helps us sense movement by breaking it down into its component parts linear acceleration or forward backward side to side up-down movement on three axes X why and said and angular acceleration otherwise known as rotation around these same axes X Y and said the unique architecture of the vestibular system isolates these movements shaped like a snail's shell this is the cochlea it contains the sensory apparatus for hearing connected to the cochlea or the vestibule and the three semicircular canals and within the vestibule are the utricle and the saccule let's have a closer look at these structures starting with the semicircular canals which we've modeled on this person here this is the horizontally now here is the anterior canal and here is the posterior canal notice that the semicircular canals are positioned at right angles to each other this helps them to isolate rotations around the x y and z axis the horizontal canal is oriented in the horizontal plane and it's architecture will allow for the detection of angular acceleration around the y axis in order to detect angular acceleration around the x and z axis things get a little bit more complicated now remember that we have two of these vestibular organs of course you do they're on either side of the head they're mirror images of each other and rotated at 45 degrees this means that the anterior canal in one ear is in the same plane as the posterior canal in the other ear the anterior and posterior canals work together angular acceleration around the x axis is detected by both the anterior and posterior canals an acceleration around the z axis is detected by an opposite activation of the anterior and posterior canals isolating angular acceleration within the three canals allows the brain to interpret the body's rotation let's look in some more detail at rotation or angular acceleration and to keep things simple we'll focus on the horizontal canal remember it detects angular acceleration around the y axis it helps this dancer during a pirouette this diagram shows a cross-section through the horizontal canal this space here is filled with fluid called endolymph when we turn our head the bony labyrinth this part of the diagram moves with us of course it does it's part of our head but the fluid inside the labyrinth is lazy and stays behind we call this inertia the net effect is that the fluid moves in the opposite direction of the bone and our head this part here the cupula is where the hair cells are located they're the receptor cells that will signal to the brain each hair cell has the stereocilia braided in size from longest called the kinocilium to shortest and all hair cells on the cupula are oriented in the same way now when the fluid pushes on them they all get deflected either towards the kinocilium or away from it depending on the direction of the acceleration when the stereocilia get pushed towards the kinocilium ion channels open and the hair cells are depolarized they signal when the stereocilia get pushed away from the kinocilium all iron child's clothes and the cells hyperpolarize we're shutting down even the baseline firing rate now let's look at linear acceleration and stick with me here because it's complicated [Music] linear acceleration will be detected by otolithic organs along horizontal and vertical planes the saccule is oriented vertically and detects up-and-down movement along the y axis the utricle is oriented horizontally and detects linear acceleration in that plane or along the x axis linear acceleration along the z axis is detected by both the utricle and the saccule let's have a closer look at the architecture of these organize a sensory membrane called macula contains hair cells within a gelatinous membrane and crystals called oh da cunha which sit on top of the gelatin this shifts the center of gravity of the macula to the top the o da cunha make the whole thing top-heavy and now when we move the macula by simply moving our head the gelatin will deflect remember the inertia of the fluid we talked about earlier here we use a similar principle as the head moves forward the ODA Konya lag behind and pulled the gelatinous membrane backwards now when we stop moving the Oder Konya still have momentum and they continue moving forward but what happens when we tilt our head again we take advantage of the greater mass of the ODA Konya and the high center of gravity the ODA Konya will pull the top of the membrane down in a tilt these deflections will pull on the cilia of the hair cells and these will then move either towards the kinocilium causing activation or way causing deactivation so this helps us understand linear acceleration along the x y and z axes but we don't just move strictly along these axes our movements are fluid and somewhat chaotic and yet the otolithic organs can make sense of it but how ok we'll have to go back to the architecture of the macula remember we have our hair cells within a gelatin with odor Konya on top the key to analyze in the chaos of our linear accelerations is the arrangement of the hair cells within the macula this curved line called the stree Allah is the reference for the orientation of the hair cells through this no acceleration goes undetected for each possible direction different populations of cells are activated and deactivated in summary the system contains and deconstructs are complex chaotic movements into these tiny spaces this deconstruction allows us to respond to single elements of a complex movement adjust our posture our eye movements and maintain our balance the interplay between sensing processing and adjusting position allows us to navigate and interact with the world around us it puts some order into the chaos it keeps us balanced and grounded [Music] you

Channel: UBC Medicine - Educational Media

Views: 174,746

Keywords: neuroanatomy, balance, vestibulum, cochlea, semi-circular canals, dance, UBC, inner ear, anatomy

Id: RLYAnFgu-YI

Length: 12min 14sec (734 seconds)

Published: Mon Mar 19 2018