Audition: Sense of Hearing (Nursing)

00:01 The last two of our special senses are hearing and equilibrium.

00:06 The transduction of sound vibrations by the ear sensory receptors into electrical signals is a thousand times faster than the response to the light by one's eye photoreceptors.

00:18 Also, while the ear is responsible for hearing, it also contains receptors for equilibrium.

00:27 So starting with hearing, we noticed that the ear is divided into three regions, we have the external ear, the middle ear and the internal ear.

00:40 The external ear is going to contain the auricle which is where sound is going to be captured.

00:48 From there, it goes to the external auditory canal which is then going to transmit sound to the eardrum or the tympanic membrane.

00:59 The tympanic membrane and the external auditory canal are protected by a substance known as cerumen which is a secretion of our ceruminous glands, and what we refer to as earwax.

01:14 Next we have the middle ear.

01:17 The middle ear is going to contain three very small bones, actually the smallest bones in our body known as the auditory ossicles.

01:26 This includes the malleus, incus and stapes.

01:32 Sound vibrations are transmitted from the eardrum through these bones and to the oval window which is going to now connect the outside world to our inner ear.

01:46 The auditory tube is a tube that extends from the middle ear into the nasopharynx and works to regulate air pressure in the middle ear.

01:57 This is also sometimes referred to as our eustachian tube.

02:01 On the pharyngeal end of this tube, it is normally closed but it opens when we yawn or when we swallow and allows air to enter and leave the middle ear thus equalising the pressure in the middle ear This is why sometimes our ears pop when we're yawning.

02:21 This pathway is also an important pathway for ear infections as it is usually the route that pathogens take to get to the inner ear.

02:34 The internal ear or the labyrinth is going to contain cochlea which are going to translate vibrations into neural impulses that the brain can then interpret as sound.

02:47 Also in the internal ear, we have semicircular canals that are gonna work with the cerebellum for balance and equilibrium.

02:56 Forces look at how the inner ear is going to transmit sound to the brain.

03:03 Here, we see the location and orientation of the structures of the ear including the cochlea as well as the semicircular ducts.

03:15 Vibrations are transmitted from the stapes through the oval window to the cochlea and fluid pressure waves are going to be transmitted into the perilymph of the scala vestibuli This begins at the oval window of the cochlea.

03:36 From here, pressure waves are going to travel to the scala tympani and then to the round window which bulges back into the middle ear.

03:48 Between the scala vestibuli and the scala tympani, you have the cochlear duct.

03:55 This is a membranous duct filled with endolymphs and containing the spiral organ or the organ of Corti The membrane that separates this duct from the scala vestibuli is referred to as the vestibular membrane.

04:12 The membrane that separates this duct from from the scala tympani is referred to as the basilar membrane.

04:19 Atop the basilar membrane, the spiral organ is a coiled sheet of epithelial cells that contain thousands of hair cells.

04:30 At the tip of these hair cells are stereocilia which extend into the endolymph found inside of this duct.

04:39 On the top of the hair cells sits a gelatinous structure known as the tectorial membrane.

04:46 The hair cells of the spiral organ are going to synapse with both sensory and motor neurons of the cochlear branch of the vestibulocochlear nerve.

04:59 Pressure waves travel from the scala vestibuli to the vestibular membrane to the endolymph of the cochlear duct.

05:10 The basilar membrane then vibrates and this move those hair cells of the spiral organ against the tectorial membrane.

05:21 These cells are then going to generate a nerve impulse in the cochlear nerve fibres of the vestibulocochlear nerve.

05:31 Putting it all together, sound waves in the form of vibrations are going to enter through the external auditory canal From there, these sound vibrations are going to push up against the tympanic membrane be transmitted through the ossicles, the malleus, incus and stapes and then transmitted to the oval window of the cochlea.

06:02 As the states vibrates against the oval window that separates the middle ear from the inner ear, these vibrations are transmitted through the perilymph found in the scala vestibuli.

06:15 Vibrations are also being transmitted through the membrane of the cochlear duct.

06:22 Vibrations travel from the scala vestibuli and through the apex of the cochlea also referred to as the helicotrema.

06:32 From there, these vibrations go to the scala tympani.

06:37 And at the end, these vibrations are going to go to the round window that then bulges into the middle ear.

06:47 The cochlear nerves are going to form a branch of the vestibulocochlear nerve.

06:53 The axons are gonna synapse with neurons in this cochlear nuclei in the medulla oblongata.

07:01 From there, impulses are gonna travel to the medial geniculate nuclei of the thalamus and in the primary auditory area of the cerebral cortex in the temporal lobe of the brain.