Identify the THREE anatomical regions of the ear
1.External ear
2.Middle ear
3.Inner ear
Describe the structures AND functions of the external ear
- Auricle or Pinna - Directs sound waves to the tympanic membrane (eardrum)
- External Auditory Canal - Ceruminous glands produce cerumen (ear wax), cerumen lubricates and protects the external canal.
- Tympanic membrane - sound waves vibrate the tympanic membrane and transfers that energy to ossicles.
Describe the structures AND functions of the middle ear
- Contains the 3 ear ossicles connected by synovial joints (ossicles transmit and amplify sound waves)
- Malleus (attached to tympanic membrane)
- Incus
-Stapes (attached to the oval window) - Auditory tube (eustachian tube) leads to the nasopharynx - helps to equalize pressure on both sides of tympanic membrane
Describe the structures AND functions of the inner ear
- Divided into 3 areas: The vestibule, The cochlea and The semicircular canals
Has two main divisions:
Bony labyrinth - is filled with fluid called perilymph
Membranous labyrinth - is within the bony labyrinth, contains a series of sacs and ducts that filled with fluid called endolymph
- Cochlea - has three channels:
- Scala vestibuli
- Cochlea duct (Scala media)
- Scala tympani
Cochlea duct - resting on the basilar membrane is the spiral organ (organ of Corti), the organ of hearing
Name the cranial nerve (and number) involved in hearing and equilibrium – identify the branches of this nerve AND what each branch is responsible for
Vestibulocochlear (VIII) nerve
Two separate branches:
Vestibular - is responsible for static equilibrium
The cochlear - is responsible for special sensation of hearing
Identify where perilymph and endolymph are found
Perilymph - in the bony labyrinth
Endolymph - in the membranous labyrinth
Describe the passage of a sound wave generated in the air moving through the structure(s) of the ear
- Sound waves vibrate the tympanic membrane
- Vibration of the ossicles transfers and amplifies the vibratory motion to the oval window
- Pressure waves are created in the perilymph of the cochlea
- Pressure waves travel through the perilymph (in the bony labyrinth), pass through the vestibular membrane and into the endolymph (in the membranous labyrinth)
5.Pressure waves in the endolymph cause the basilar membrane to vibrate which moves the hair cells and (if the threshold is met) creates an action potential (nerve impulse)
Describe the path of a nerve impulse starting from the cochlea by including receptors, name of nerve and areas of the brain involved, in sequence
- Cochlea receptors (hair cells) generate the nerve impulse
- Neurons form the cochlear branch of the vestibulocochlear (Vlll) nerve
- Impulses carried to the medulla oblongata where some axons cross over
- Ascends to the midbrain
- Ascends to the thalamus
Ascends to the primary auditory area in temporal lobe
Describe equilibrium
Equilibrium is the state of being balanced and refers to the position of the head in relation to the body
Static equilibrium
Static - Helps maintain the position of the head relative to the force of gravity.
Involves movements of tilting the head and linear acceleration/deceleration.
Receptors are located within vestibule
Dynamic equilibrium
Maintains position of the head during sudden movement of any type of rotation, deceleration or acceleration.
Receptors are located within the semicircular canals
Identify two causes of hearing loss
Tinnitus - ringing in the ear often associated with nerve degeneration, infection, side effect or some medications eg. Gentamycin, Quinine
Vestibular imbalance - occurs more frequently in the elderly due to loss of receptor cells (hair cells)
Describe Presbycusis and TWO causes of this
Presbycusis = Age-associated progressive loss of hearing in both ears
- Related to damage and loss of hair cells in the spinal organ
- Degeneration of the nerve pathway for hearing
