CHAPTER FIFTEEN: HEARING AND EQUILIBRIUM Flashcards
LABEL THE FOLLOWING STRUCTURES ON A DIAGRAM OF AN EAR: EXTERNAL EAR, MIDDLE EAR, INNER EAR, PINNA, EXTERNAL AUDITORY MEATUS, TYMPANIC MEMBRANE, MALLEUS, INCUS, STAPES, PHARYNGOTYMPANIC TUBE, COCHLEA, OVAL WINDOW, ROUND WINDOW, SEMICIRCULAR CANALS, VESTIBULE, UTRICLE, SACCULE. DESCRIBE THE FUNCTIONS OF EACH.
→ outer ear
Pinna: collects sound and transmits into the external auditory meatus
External auditory meatus: carries sound to the tympanic membrane, also contains ear wax
→ middle ear
Tympanic membrane: vibrates sound coming from the external auditory meatus and transfers it to the ossicles.
Ossicles: malleus, incus, stapes: transmits the vibrations from the tympanic membrane onto the oval window.
Oval window: transmits sound from the oval window into the fluid filled cochlea
Round window
Pharyngotympanic tube: connects the ear to the nasopharynx, allows for equalized pressure between the outer and middle ear, if pressure is not equal it can result in impaired hearing. The tube is opened by chewing and opening of the mouth.
→ inner ear
Cochlea: is responsible for hearing, it extends from the oval window via the scala vestibuli. Houses the spiral organ (organ of corti) which is the receptor of hearing. Scala tympani terminates at the round window.
Semicircular canals: is responsible for equilibrium and balance. More specifically, dynamic equilibrium.
Utricle: is continuous with semicircular canals.
Saccule: is continuous with cochlear ducts
LABEL THE FOLLOWING STRUCTURES ON A DIAGRAM OF THE COCHLEA: SCALA VESTIBULI, SCALA TYMPANI, COCHLEAR DUCTS, SPIRAL ORGAN, HAIR CELLS, TECTORIAL MEMBRANE, VESTIBULAR MEMBRANE, BASILAR MEMBRANE, ROUND WINDOW, OVAL WINDOW, HELICOTREMA. DESCRIBE FUNCTIONS OF EACH.
→ scala vestibuli: is part of the bony labyrinth and contains perilymph, is a continuous of the vestibule.
→ scala tympani: is also part of the bony labyrinth and contains perilymph, terminates at the round window.
→ scala media: is part of the membranous labyrinth and contains endolymph. Is the cochlear duct.
→ cochlear ducts: houses the spiral organ and is the scala media.
→ spiral organ: the main hearing organ of the ear, or hearing receptor.
→ hair cells: there are outer and inner hair cells that are sandwiched between the basilar and tectorial membranes. They convert mechanical energy from the vibration in the fluid into electrical energy to send to the central nervous system.
→ tectorial membrane: is stiff like gell and supports hearing by altering the ionic environment around stereocilia.
→ vestibular membrane: acts like a “roof” and separates the scala media and scala vestibuli.
→ basilar membrane: is the floor of the cochlear ducts and supports hearing.
→ oval window: is one of the 2 openings from the inner and middle ear, is the more superior opening. It also transmits vibration from the ossicles into the inner ear.
→ round window: is another one of the 2 openings from the middle to inner ear, is the more inferior opening.
→ helicotrema: apex of the cochlea.
LIST IN DETAIL THE SEQUENCE OF EVENTS THAT OCCUR BETWEEN THE ENTRY OF A SOUND WAVE IN THE EXTERNAL AUDITORY MEATUS, AND FIRING OF AN ACTION POTENTIAL IN THE COCHLEAR NERVE.
Sound coming in from the external auditory meatus will hit against the tympanic membrane, this causes it to vibrate.
Vibrations from the tympanic membrane are amplified by the ossicles (malleus → incus → stapes). The stapes will hit on the oval window, causing the vibrations to be projected into the scala vestibuli.
The perilymph in the scala vestibuli will begin to move in forward and back motions, a pressure wave is sent to the basal end of the helicotrema.
– now there are 2 pathways the sound can take depending on its frequency
→ helicotrema path: sound that is below the range of hearing will take the long path through the cochlear duct → to the scala tympani → and then to the round window. The spiral organ (organ of corti) is not activated and thus you will not hear the sound.
→ basilar membrane path: sound that is within the range of hearing will take a shortcut through the cochlear ducts to the round window. The sound hits the basilar membrane at a specific location depending on its frequency. The vibrations will trigger the hair cells that convert mechanical energy into electrical energy which triggers an action potential in the cochlear nerve. The action potential will then travel to the temporal lobe of the brain.
DESCRIBE HOW DISCRIMINATION OF PITCH AND LOUDNESS OCCUR.
→ pitch: different frequency’s (number of waves or amplitudes in a wave at a given time) will hit the basilar membrane at different locations. The brain interprets this as different pitches.
→ loudness: loudness is determined by increased or decreased deflections from hair cells, in turn causing more or less action potentials. This determines loudness.
DESCRIBE THE FUNCTIONS AND MECHANISMS OF ACTION OF THE SACCULE, UTRICLE, AND SEMICIRCULAR CANALS.
→ the utricle and saccule monitor static equilibrium
Contain maculae, which is also a sensory receptor organ (that has hair cells)
The “hairs” of the hair cells are coated in a gel like substance which also contains little rocks called otoliths. These otoliths increase weight and inertia, cousin greater resistance to motion
Motion triggers waves in the jelly substance, this causes mechanoreceptors to be triggered.
There are maculae in each saccule wall and one in each utricle wall. They Are important for posture.
Utricle = horizontal hair cells that monitor change in the horizontal plane
saccule= vertical hair cells that monitor the changes in the vertical plane
→ the semicircular canals monitor dynamic equilibrium
Instead of maculae, the semicircular canals have their own type of sensory receptor organ (still hair cells) that contain hair cells bundles up into a gell mass called ampullary cupula
Angular motions trigger the endolymph around the cupula, this triggers mechanoreceptors to open which increases receptor potential for neurotransmitter release onto dendrites on the vestibular nerve.
