The Ear

This is the remarkable human ear An amazing outcome of evolution. What began in our aquatic ancestors, adapted over time to capture sound through air - As well as gravity and acceleration, along with balance and inertial precision. To convert the sounds around us The MIDDLE EAR contains three tiny little structures The malleus, Incus and stapes This chain of bones transmit sound from a vibrating membrane - the ear drum - to a circular coil of special liquid called peri-lymph Within the tympanic vestibule - These three bones are surrounded by a bubble of moist air In which just two muscles - The tensor tympani and stapedius - both work to protect us from loud noises The outer ear is a funnel for sound made of cartilage and skin that both reflect and concentrate vibrations With only our eye into the external canal, all you can see Is the foot of the malleus and some of the ear drum With an endoscope The canal is slightly windey. And looking through the ear drum Is the oval window and stapes With the corda tympani nerve Between the malleus and incus below the stapes - is the round window And the Eustachian canal Turning we see the tympanic attic and mastoid canal And below it the malleolar foot Past which we return to the outside world From most accessible let’s see our most inaccessible Deep past the Middle Ear - nearest our brain stem two major data input units - Connect the physical world - and feed raw data to our inner world The Vestibule detects our head’s position in space and the direction we move through it The utricle detects linear movement in the horizontal plane and the semi circular canals tell us which way our heads are rotationally turning - in x, y and z planes… The saccule tells us our up and down linear movement… like riding an elevator The Vestibular System has Two Interconnected Mechanisms The first are patches of ciliated (hairy) cells located in special areas of the vestibule - influenced by calcite crystals. When the head accelerates, these crystals shift, stimulating the hair cells to detect balance changes. They also respond to sound vibrations. This process depends on endolymph, produced in the endolymphatic sac - a potassium-rich, sodium-poor fluid with almost no calcium Endolymph is also used in the cochlear canal, allowing the detection of sound. Thus, hearing and balance share the same specialized fluid to process movement and sound together 5:02 For physical sound to be converted to neural data The main data processing unit is found in the scala media - To receive sound vibrations - the endolymph found in the cochlear duct - is surrounded by a double coil of perilymph fluid The main vibration coil by which the Scala media receives sound- lies to the front of the coil - it is called the scala vestibuli. On the underside - is the return coil - the scala tympani So here is where sound transfer starts - with the stapes - vibrating atop a column of perilymph liquid Coiling towards the Helicotrema - with a knot of a connection between the two coils 5:58 So the sound wave starts at the oval window And sound energy returns at the round window And the fluid enters these tubes from the perilymphatic duct, where it first formed from the cerebro spinal fluid surrounding the brain The vestibulo cochlear nerve transports signals to the brain The cochlear nerve is spiral And intimately follows the endolymph of the cochlear duct The vestibular nerve has two distinct branches and ganglia 06:47 Lying nearby is the facial nerve With its geniculate ganglion near its sharp knee-like bend The Facial Nerve wraps around the middle ear, where it gives off the chorda tympani - and which passes through the middle ear and on towards the tongue 7:08 The entire middle ear lies directly against the brain’s cerebellum The nerves enter underneath the pons And have travelled via the cerebello-pontine angle from the inner ear You can see the endo and perl-lymph organs where they lie against the cerebellum 7:34 The effective reception of sound energy—closely connected to balance and movement—has evolved to shape distinct human behaviors, including speech, complex tool use, and bipedal locomotion. This is the remarkable human ear And if you enjoyed this video, please subscribe or like, or share or comment 8:02 M 8:03 And YouTube will tell you when my next video is here On the Remarkable Human Jaw Joint Thank you for watching