Unit 1 study cards (inner ear) Flashcards
Inner Ear
part of the ear where mechanical energy is TRANSDUCED into neural signals.
Structures of the inner ear are encased within the petrous temporal bone
Two components of the Inner ear:
1. Cochlea - for hearing
—Three chambers/Scala (3 fluid filled spaces)
2. Vestibular system - (semi-circular canals, utricle and saccule in vestible) - balance
—Tube within a Tube (2 fluid filled spaces)
Bony Labyrinth
The space within the temporal bone that encases the inner ear-cavities which contain fluids and and the membranous labyrinth.
Perilymph is between the Bony and Membranous Labyrinth but I am putting it on this flashcard for ease.
Membranous Labyrinth
the inner core of the inner ear, encased in membranes (sort of like having a hose inside of a hose).
contains Endolymph
characteristics of the COCHLEA
Makes 2 3/4 turns
It is 35mm long from the base to the apex
about 6.8 mm high
What does the Cochlea do? It converts mechanical movements of the middle ear Ossicular chain into firings of the fibers of CN VIII (Vestibulocochlear nerve).
Functions: Filtering, Distribution, Transduction
Entirely enclosed in petrous temporal bone (otic capsule)
There are three chambers of the cochlea
1. Scala Vestibuli
2. Scala Media
3. Scala Tympani
Chambers/Scala of the COCHLEA
- Scala Vestibuli
- Scala Media
- Scala Tympani
Endolymph Fluid
-High in potassium ions (K+)
-found ONLY in the Scala Media
-unique composition similar to saliva
-about 2.7 microliters in humans
Perilymph Fluid
-between bony and membranous labyrinth
-High in sodium ions (Na+)
-found in Scala Tympani and Scala Vestibuli
-Similar to CSF
-about 16-23 microliters in humans
Scala Vestibuli
-Perilymph filled (sodium fluid is between bony labyrinth and membranous labyrinth)
-superior to the Scala Media
-oval window membrane is at the entrance and pushes on this scala
Scala Media
-Endolymph filled (potassium fluid is within the membranous labyrinth) - bounded by membranous labyrinth
-action in terms of hearing sensation takes place here inside of the organ of corti.
-the BASILAR MEMBRANE makes up part of the floor of the scala media
-runs 33MM
Scala Tympani
-Perilymph filled (sodium fluid is between bony labyrinth and membranous labyrinth)
- inferior to the scala media
-this is where the entrance of the round window (membrane) sits and it bulges out as the stapes pushes in and vice versa
Osseous Spiral Lamina
It is a bony spiral plate and projection from the bony core at the center of the cochlea (Modiolus). It is shaped like a spiral ramp.
It makes up the floor of the SCALA MEDIA by connecting to the basilar membrane which makes up the rest of the floor.
called a habenula perforata (hole for the nerve fibers).
Modiolus
The core of temporal bone at the center of the cochlea. The 8th nerve fibers run though the hollow core and exit through openings in the Osseous Spiral Lamina to innervate the entire length of the Cochlea.
Spiral Ganglion
Cell bodies of the fibers of the 8th nerve form a spiral ganglion because of the very special arrangement of the neurons of the 8th nerve (they run up through the modular core and fan out all the way along the spiral lamina).
Helicotrema
The Helicotrema is the narrow passageway that connects the Scala Tympani and the Scala Vestibuli and allows the fluids to communicate.
organ of corti
has the receptor cells and runs the entire length of the cochlea (35 mm long).
It is kind of like a long strip.
only 1 row of inner hair cells along the organ of corti.
shaped like a twizzler.
There is either a separate fluid known as cortylimph or it’s perilymph leaking up through the basilar membrane.
sits on top of the basilar membrane.
the reticular lamina covers it.
Reissner’s membrane
Reisner’s membrane separates the SCALA MEDIA from the SCALA VESTIBULI. It is also known as the Vestibular Membrane.
Recticular Lamina
It is the covering of the organ of corti and it’s water tight. It prevents the perilymph fluid from mingling in a toxic way with the endolymph fluid in the Scala Media.
Tunnel of Corti
What is in it? It is filled with Endolymph fluid
What supports it? It is supported by pillars of protein that separate the inner and outer hair cells.
Fluid can flow through the tunnel. supported by deiter, hensen and claudious cells.
Stria Vascularis
It is on the lateral wall of the Scala Media (outside edge).
It helps to provide the BATTERY that is necessary for ion flow to take place and neural firing to occur for transduction.
it provides electrical activity within the Cochlea
One can think of the cochlea as a water baloon encased in cement. The oval window pushes on this balloon, but the movements are not powerful enough to compress the fluids of the cochlea. What additional structures makes it possible for cochlear fluids to move when the oval window moves?
The additional structure making it possible for cochlear fluids to move when the oval window moves is the STAPES bone. The stapes bone presses against the oval window which moves vibrations from the middle to the inner ear causing fluids to move with it.
Inner Hair cells
Closer to the modiolus within the organ of corti are the ones that provide the PRIMARY AFFERENT information to the auditory nervous system.
They respond to the velocity of the basilar membrane because that determines how fast the fluids are moving and that will cause them to bend.
-They are flask shaped.
- 40 stereocilia per inner hair cell
- U pattern of stereocilia
-1 row in the organ of corti
They provide the primary afferent (sensory) information for the brain.
Outer hair cells
they are mostly involved in MOTOR control of the inner ear. They have efferent pathways as well as afferent and there is an inner ear reflex that they are involved in.
They ossilate in response to sound and change in length giving us the ability to tell frequencies apart. embedded in the tectorial membrane so they bend in response to the displacement of the basilar membrane.
-There are 3 rows in the Organ of Corti (they run the entire length of the cochlea)
-They are tubular in shape.
-humans have 12,000 per ear
-20 micrometers at the base
-50 micrometers at the apex
-cell organelles are consistent with a high metabolic rate and muscle like capabilities.
-150 stereocilia per outer hair cell
-V pattern
stereocilia
IMPORTANT BECAUSE it is the movement of the stereocilia that allows ion channels to open and allows ions to flow into the cells which causes them to release neurotransmitters to the nerve fibers causing hearing.
What interconnects the stereocilia?
–>They are connected by fibers called cross-links made of proteins.
What is the Basal body of the Kinocilium?
It is a remnant of the more primitive kinocilium. The basal body is on the more lateral side of each bunle of stereocilia, towards the wall of the cochlea.
