Anatomy and Cell Biology 3309 Lecture Notes - Lecture 24: Semicircular Canals, Membranous Labyrinth, Cochlear Duct
15 May 2018
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Lecture 24 – Vestibular System
Anatomy of the ear
- Vestibular system: makes us aware of movements
- Within the inner ear
- Inner ear is embedded in the bone
- Space is perilymph filled (fluid similar to extracellular fluid)
- Suspended in the space within the bone is the membranous labyrinth
Inner ear
- Structure formed by membranes which is suspended within inner ear (opening in bone)
- Collectively called the membranous labyrinth (canals)
- Space within bone is filled with perilymph
- Membranous labyrinth is suspended with perilymph filled space (floats)
- Membranous labyrinth is one continuous system filled with endolymph (like intracellular
fluid – high in K)
- Contains a portion in the cochlea
o Scala media is filled with endolymph
o Organ of Corti sits in scala media on its base on basilar membrane
o Scala media is delimited by basilar membrane and Reissner’s membrane
o Scala media is connected to saccule and utricle, giving rise to semicircular ducts
- There is innervation to different parts of inner ear
o Innervation to organ of Corti which sits on basilar membrane along scala media
▪ This is where the hair cells are and they are innervated by spiral ganglion
cells → pick up signals and form auditory nerve
o Organ of Corti depicts the innervated structure (sensory organ) in scala media
o Saccule and utricle contain innervated structures (hair cells)
▪ Innervated by the same nerve (8th nerve) but it is the vestibular nerve
▪ Vestibular and auditory nerve form the 8th nerve together
▪ Vestibular branch innervates saccule and utricle
o Semicircular ducts within semicircular canals have thickenings called ampulla
▪ Ampulla contains sensory organs (hair cells) innervated by vestibular nerve
as well
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- Vestibular System:
o 2 sacs (utricle and saccule): 90 degree angle to each other (horizontal and vertical)
o 3 semi circular canals (sit perpendicular to each other)
- Auditory System: Cochlea containing the Organ of Corti
- INNERVATION:
o Organ of corti: auditory nerve
o Saccule + utricle (macula): vestibular nerve
o Sensory structures in each of the ampulla (one on each semicircular canal):
vestibular nerve
Membranous labyrinth
- Outer structure does not exist and it is just the opening within the bone that is then filled
with perilymph and suspended within bony structure is membranous labyrinth which is
continuous with scala media, saccule, utricle and 3 semicircular ducts
- Sensory structures:
o Macula in both saccucle and utricle
o Ampulla in every semicircular canal (thickening of the canals)
- Labyrinth is surrounded by space within bone filled with perilymph (blue is perilymph,
purple is endolymph)
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Cochlea
- Scala typani and scala vestibule are perilymph filled spaces and surround the endolymph
filled space (scala media)
- Scala media is part of the membranous labyrinth that is continuous with saccule, utricle and
semicircular ducts
- Oval window: where stapes moves against to move the perilymph
- Perilymph could theoretically move throughout the inner ear but it only moves up the
cochlea and down the scala typani and vestibuli
- Round window is on the other end of the long canal in the cochlea
- Perilymph is continuous between entire inner ear
- Inner ear as a whole contains vestibular and auditory system and is one structure
- Cochlea is continuous with other portions of inner ear that comprise vestibular system
Vestibular system
- Semicircular canals (ducts within canals) x3
o Respond to rotational movement of the head and body
o As the duct rotates, the endolymph lags behind because of inertia and flows through
semicircular duct
▪ Flow of endolymph within duct is picked up by hair cells
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Vestibular system: makes us aware of movements. Space is perilymph filled (fluid similar to extracellular fluid) Suspended in the space within the bone is the membranous labyrinth. Structure formed by membranes which is suspended within inner ear (opening in bone) Membranous labyrinth is suspended with perilymph filled space (floats) Membranous labyrinth is one continuous system filled with endolymph (like intracellular. There is innervation to different parts of inner ear. Vestibular system: 2 sacs (utricle and saccule): 90 degree angle to each other (horizontal and vertical, 3 semi circular canals (sit perpendicular to each other) Innervation: organ of corti: auditory nerve, saccule + utricle (macula): vestibular nerve, sensory structures in each of the ampulla (one on each semicircular canal): vestibular nerve. Sensory structures: macula in both saccucle and utricle, ampulla in every semicircular canal (thickening of the canals) Labyrinth is surrounded by space within bone filled with perilymph (blue is perilymph, purple is endolymph)
