Afferent 6- Hearing


– HEARING, OKAY, SO NOW WE’RE FACED WITH
ANOTHER MECHANICAL STIMULUS. AND WE TALKED A LITTLE BIT
ABOUT THIS IN THE BEGINNING. SOUND WAVES ARE MECHANICAL
DISRUPTIONS OF AIR MOLECULES. AND WE PROBABLY SHOULD
DO A LITTLE TINY BIT OF REVIEW OF EAR ANATOMY JUST
TO BE COMFORTABLE WITH THIS, SO ESSENTIALLY THE PINNA IS
THE OUTER PART OF YOUR EAR THAT YOU CAN SEE AND YOU
HAVE THE EXTERNAL AUDITORY CANAL THAT BASICALLY THE PINNA TAKES
THE SOUND WAVES AND CHANNELS THEM INTO THE EXTERNAL
AUDITORY CANAL, BUT ALL THAT’S BEING CHANNELED
IN HERE LITERALLY ARE WAVES AND YOU CAN FEEL IT
IF YOU TURN UP THE VOLUME ON YOUR COMPUTER RIGHT NOW,
AND I START YELLING AT YOU, LIKE YOU CAN FEEL
THE VIBRATIONS OF THE SOUND AND WHEN IT GETS TOO CRAZY,
YOU’RE LIKE DUDE, JUST STOP BUT KEEP GOING
BECAUSE THIS IS A PHYSIO AND WE HAVE WORK TO DO. WHEN THOSE SOUND WAVES HIT
THE TYMPANIC MEMBRANE, WHICH IS YOUR EAR DRUM,
THAT’S THIS THING RIGHT HERE, TYMPANIC MEMBRANE IT CAUSES
THE TYMPANIC MEMBRANE TO WIGGLE. AND THEN YOU HAVE A SERIES
OF THREE LITTLE INNER EAR BONES, MIDDLE EAR BONES,
I DO IT EVERY TIME, THIS IS YOUR OUTER EAR,
THIS IS YOUR MIDDLE EAR. THE MIDDLE
EAR IS FILLED WITH AIR AND THE TYMPANIC
MEMBRANE VIBRATES THANKS TO THE SOUND WAVES. AND IT WIGGLES THE BONES OF
THE MIDDLE EAR AND THE WIGGLING OF THOSE BONES BASICALLY
AMPLIFIES THE STIMULUS, AMPLIFIES THE WIGGLE 22 TIMES. SO IF YOU DIDN’T
HAVE THOSE BONES IN THERE AND YOU JUST RELIED
ON YOUR SOUND WAVES TO WIGGLE YOUR COCHLEA AND THIS IS YOUR
ULTIMATE RECEPTOR ORGAN, THIS IS THE COCHLEA,
YOU WOULD HEAR, YOU WOULD HAVE TO TALK
22 TIMES LOUDER TO BE HEARD AT THE SAME
LEVEL WHICH, YOU KNOW, GO AHEAD AND GIVE ME
A CHALLENGE I’M HAPPY TO TRY TO TALK 22 TIMES LOUDER,
MIGHT BE ENTERTAINING. THE COCHLEA IS FOUND
IN THE INNER EAR AND IT’S FILLED WITH FLUID. SO WHEN THE INNER, MIDDLE EAR BONES WIGGLE
BECAUSE OF THE SOUND WAVES, THEY ARE CONTACTING
ANOTHER LIKE A TYMPANIC MEMBRANE BUT IT’S CALLED THE OVAL WINDOW. AND THAT, IT’S JUST
ANOTHER MEMBRANE, SO BASICALLY,
WHOA THAT SAYS OVAL WINDOW, THE TYMPANIC MEMBRANE
AND THE OVAL WINDOW BOTH WIGGLE THE OVAL WINDOW IS
GOING TO WIGGLE 22 TIMES BIGGER THAN THE TYMPANIC
MEMBRANE WIGGLED FROM THE ORIGINAL SOUND WAVES. AND THE OVAL WINDOW WIGGLING
MAKES WAVES IN THE FLUID. OKAY, SO NOW YOU’VE GOT WAVES INSIDE THIS SNAIL
SHAPED STRUCTURE AND, OF COURSE, THE WAVES LIKE I HOPE BY THIS POINT YOU’RE THINKING
WHAT DO THOSE WAVES DO? HOW IS, HOW IS A WAVE TRANSLATED
INTO AN ACTION POTENTIAL? WELL SINCE YOU ASKED, I GUESS ONLY JUST BECAUSE YOU
ASKED, LET’S GO LOOK. DUDE, WHERE DID IT GO? THIS WAY, BUT OF COURSE THIS IS
MY SENSORY RECEPTOR CELL. THIS IS CALLED A HAIR CELL. AND HAIR CELLS ARE EMBEDDED
IN THE WALL OF THE COCHLEA. SO THIS IS THE FLUID
INSIDE THE COCHLEA AND YOU CAN IMAGINE
THAT THIS IS COCHLEA WALL LIKE THE SNAIL SHELL
OF THE COCHLEA. AND THESE HAIR CELLS,
NOW LOOK AT THIS, THIS IS A HAIR CELL RIGHT THERE. THIS IS A NEURON. AND MY HAIR CELL IS
ESSENTIALLY GOING TO, I LOVE THIS, THIS IS FANTASTIC. AND YOU HAVE TO TAKE
A DEEP BREATH BECAUSE IT’S A LITTLE BIT WEIRD. WHEN THE WAVE COMES,
HERE COMES THE WAVE, AND WAVES LIKE MOVE THINGS. SO THE WAVE WIGGLES THE HAIR
ON THIS HAIR CELL. AND THE WIGGLING HAIR, TAKE A DEEP BREATH
‘CAUSE THIS IS SO WEIRD, THE WIGGLING HAIR,
THERE’S MY STIMULUS, THE RESULT IS
THAT CALCIUM CHANNELS OPEN AND THAT CAUSES
AN ACTION POTENTIAL. THAT CAUSES DEPOLARIZATION AND
AN ACTION POTENTIAL IS CREATED AND A MESSAGE IS SENT. NOW DOES ANYBODY GO LIKE DUDE, BULL CRAP BECAUSE THERE’S NO WAY THAT OPENING POTASSIUM CHANNELS
CAUSES AN ACTION POTENTIAL. WE KNOW FROM OUR
OTHER EXPERIENCES WITH ACTION POTENTIALS THAT NO,
IT ACTUALLY WOULD INHIBIT THE CREATION
OF AN ACTION POTENTIAL. THIS IS YOUR FIRST EXAMPLE
OF DUDE THERE ARE EXCEPTIONS TO EVERY RULE
AND THIS EXCEPTION IS POSSIBLE BECAUSE THE MAKE UP OF
THE FLUIDS IS DIFFERENT. THE RESTING POTENTIAL
OF A HAIR CELL IS DIFFERENT. THE EXTRA CELLULAR FLUID
IN A HAIR CELL IS DIFFERENT THAN THE EXTRA CELLULAR
FLUIDS SURROUNDING MOST NEURONS. SO WE SET UP A DIFFERENT
SCENARIO WHERE NOW IF WE OPEN POTASSIUM CHANNELS, THAT’S WHAT’S GOING TO GENERATE
THE ACTION POTENTIAL. THE ACTION POTENTIAL GETS
GENERATED, THE MESSAGE GETS SENT THROUGH THE CRANIAL NERVE EIGHT,
AWESOME. THE VESTIBULAR COCHLEAR, AND THE MESSAGE GETS SENT
TO YOUR BRAIN AND YOU HEAR SOUND.
WHAT? ALSO IN YOUR EAR YOU
HAVE THE SEMI CIRCULAR CANALS ANOTHER FANTASTIC MECHANISM. DON’T YOU WISH WE
HAD LIKE A YEAR TO SPEND JUST ON SENSORY
MECHANISMS ‘CAUSE IT REALLY IS INTERESTING TO COMPARE
ALL THESE DIFFERENT WAYS THAT STIMULUS GETS TURNED
INTO AN ACTION POTENTIAL. THE LAST THING WE’RE GOING
TO TALK ABOUT IS SIGHT

2 Comments

Add a Comment

Your email address will not be published. Required fields are marked *