Mod7-Obj2: Structures of the ear relating to hearing and balance Flashcards
Structure of the ear: Hearing and balance
Three major areas of the ear
- ) External (outer) ear
- hearing only - ) Middle ear (tympanic activity)
- hearing only - ) Internal (inner) ear
- hearing and balance
- Activated independently, respond seperately
Structure of the Ear: External ear
- ) Auricle (pinna)
- elastic cartilage - ) External acoustic meatus
- Auditory canal extends to the eardrum
- Earwax secreting glands - ) Tympanic membrane (eardrum)
- Thin translucent membrane
- Vibrates in response to sound
Role of the external ear
Auricle funnels sound waves into the external acoustic meatus
-Earwax traps foreign particles
External ear: sound waves
Sound waves entering external acoustic meatus vibrate tympanic membrane which then transfers sound energy to bones of the middle ear
Structure of the ear: Middle Ear (tympanic cavity)
-Air-filled cavity in the temporal bone
-Flanked
+Laterally by eardrum
+Medially by bony wall containing:
*Oval window
*Round window
-Auditory ossicles
-Pharyngotympanic tube (eustachian tube)
Pharyngotympanic tube
Connects middle ear to nasopharynx
-Equalises air pressure in the middle ear cavity with external air pressure
Auditory ossicles
1.) Malleus-hammer
2.) Incus-anvil
3.) Staples-stirrup
The role of the auditory ossicles is to transmit and amplify the vibration motion of the eardrum to the oval window
Structure of the ear: Internal Ear
(Located in the temporal lobe)
1.) Bony labyrinth
1.) Bony labyrinth: tunnels in the temporal bone subdivided into…
-Vestibule
-Semicircular canals
-Cochlea
filled with perilymph
Structure of the ear: Internal Ear
2.) Membranous labyrinth
Series of interconnecting sacs and ducts with the bony tunnels
-filled with endolymph
Cochlea
Spiral, bony chamber
- Extends from the vestibule
- Coils around like a snail shell
- Contains cochlear duct (houses spiral organ of corti, the receptor organ for hearing)
Cochlea
Cavity of cochlea divided into 3 chambers
- Middle chamber is the cochlear duct that contains endolymph
- Other 2 chambers contain perilymph (top chamber=oval window, bottom chamber=round window)
Spiral organ of corti
Cochlear hair cells-auditory receptors (mechanoreceptors)
- Sound waves traveling through the cochlea induce movement of the basilar membrane. This movement causes the cilia of the hairs to move or bend against the tectorial membrane, initiating a depolarisation
- Impulses generated in hair cells transmit fibres 9sensory neurons) in the vestibulocochlear nerve (CNVIII)
Pathway of sound waves through the ear
Tympanic membrane to Ossicles (Auditory) to Oval window to Cochlea (perilymph) to Spiral Organ of Corti to Round window
Sound 4 stages: stage 1
Sound waves vibrate the tympanic membrane
Sound 4 stage: Stage 2
Auditory ossicles vibrate. Pressure is amplified
Sound 4 stages: Stage 3
Pressure wave created by stapes pushing on the oval window, move through perilymph
Sound 4 stages: Stage 4:
Pressure waves of the perilymph vibrate the basilar membrane and bend receptor hair cells that are embedded in overlaying tectorial membrane. Generation of impulse in cochlear nerve
Balance or equilibrium
Is the response felt by the vestibule and semicircular canals to various head movements (receptors are found here)
Role of equilibrium
Provides information about the location of our head we need to know how rapid the movement and in which direction or involved in acceleration or deceleration
Equilibrium depends on
Inputs from the internal ear as well as vision and information from stretch receptors of muscles and tendons
2 types of equilibrium
- ) Static equilibrium
2. ) Dynamic equilibrium
Static equilibrium
Evaluating the position of the head relative to gravity. It is requited when the head is motionless, or moving in straight line-detected by hair cells in the vestibule (saccule and utricle)
Dynamic equilibrium
Required when the head is rotating, or moving in an angular direction-detected by hair cells in the semicircular canals
Equilibrium receptors
Mechanoreceptors: hair cells
- Hair cells are distorted in response to a stimulus
- Distorted hair cells depolarise and an impulse generated
- Impulses travel via the vestibulocochlear nerve to the reflex centres of the brainstem, cerebellum and vestibular cortex
Equilibrium receptors: Linear movement
Linear movement for hair cells in vestibule
Equilibrium receptors:
Rotational movement
Rotational movement for hair cells in semicircular canals
Vestibule: Contain 2 membranous sacs
Contain equilibrium receptors
- ) Saccule is continuous with cochlear duct
- ) Utricle is continuous with semicircular canals
Static equilibrium: Vestibule
Utricle & saccule contains hair cells that are embedded in jellylike substance
- Tiny stones are embedded in the surface of the jelly. When head position is changed, gravity pulls on the stones and distorts the jelly and hair cells
- Distortion of the hair cells is the stimulus for their depolarisation and the transmission of impulses to underlying sensory neurons
Semicircular canals
3 fluid filled canals that lies in three planes of space
-Equilibrium receptors that respond to rotational movement of the head
Dynamic equilibrium: Semicircular canals
Contains hair cells surrounded by endolymph
- Angular movement moves endolymph
- Hair cells are distorted and depolarised
