1.3 Special Sense Organs (Ear) Flashcards
What are the 3 distinct regions of the ear and their jobs:
External: sound collection
Middle: sound transmission
Inner: sound reception / Vestibular (balance center
What makes up the external ear:
Pinna and external canal:
Pinna collects sound & funnels it into the external canal ending at the tympanic membrane
What makes up the Middle ear:
The 3 ossicles / bones transmit vibrations across tympanic membrane
What does the Tympanic membrane divide?
middle and outer ear
helps equalize pressure in middle ear
eustachian tube
What makes up the Inner ear:
Membranous labyrinth of fluid chambers (cells can detect sound waves here)
What is the vestibular complex made up of?
- saccules
- Utricules
- 3 semi-circular canals
Explain what this diagram is showing Part 1 of 4:
- Before neuro plate closure, the surface ectoderm is induced to thicken
- This thickening is the Auditory Placode
Explain what this diagram is showing Part 2 of 4:
The auditory placode deepens and invaginates to form the auditory pit
Explain what this diagram is showing Part 3 of 4:
- Auditory pit continues to fold in until the area of ectoderm separates from the surface by ‘pinching off ‘
- This now forms and becomes the auditory vesicle
Explain what this diagram is showing Part 4 of 4:
The Auditory vesicle induces the surrounding mesenchyme to form the cartilaginous ear capsule
Differentiation of Auditory vesicle to form inner ear Part 1:
Dorso-ventral extension (elongation) of the Auditory Vesicle
Differentiation of Auditory vesicle to form inner ear Part 2:
- Finally, the ‘body’ of the auditory vesicle is subdivided
- Forms Utricle and Saccule
The utricle and saccule are important for?
linear movement
External Ear development:
*Within the mesenchyme of the 1st visceral cleft (between the 1st VA and the hyoid arch) focal condensations appear
*These condensations each produce a nodular enlargement either side of the cleft
*Nodular enlargements coalesce and form primordium of the pinna
*Modified by differential outgrowth.
Scutiform Cartilage characteristics:
- Has a boot-like structure
- L shapes before the tympanic membrane
- animals get things stuck in here due to horizontal position
cochlea function & how it detects sound to send to medulla
1) external sound waves travel through external auditory meatus hitting tympanic membrane
2) tympanic vibrates oval window transfering vibrations to ossicles
2) ossicles amplify sound shifting tectorial &basilar membranes against cochlear endolymph hair cells
3) Hair cells displace& bend stimulating organ of corti hair cells to covert sound vibrations into nerve impulses
4) CN VIII sends impulses to brain
An indication that a hematomia has formed near auricular cartilage?
IF:
- hot
- swollen
- painful
- blood
Where does the blood supply come from for the outer ear?
Most of the supply will come from carotid blood vessels and eventually go through ear
what is the bony labyrinth?
vestibule as central chamber, semicircular canals, cochlea all with portion of membranous labyrinth inside them
What could damage to the Chondra tympani cause? What nerve branch is this?
Could cause lose of sensation to 2/3 of the tongue
- Branch of VII
cochlea function &how it detects sound to send to medulla
1) external sound waves travel through external auditory meatus hitting tympanic membrane
2) tympanic vibrates oval window transfering vibrations to ossicles
2) ossicles amplify sound shifting tectorial &basilar membranes against cochlear endolymph hair cells
3) Hair cells displace& bend stimulating organ of corti hair cells to covert sound vibrations into nerve impulses
4) CN VIII sends impulses to brain
inner hair cells:
- 10- 25% of the cells with 90% of the innervation.
- Responsible for sound transmission converting sound mechanical energy to electrochemical signals.
- Not replaced hence can lead to deafness.
- fewer
outer hair cells:
-75-90% of cells with 10% of the innervation.
- Responsible to for somatic electromotility - amplification of the incoming sound waves. The cells can change length leading to amplification feedback.
Hearing - the hair cell receptor
*Hair cells discharge in relation to the excursion of the basilar membrane
*The tips of the cilia are project close to the tectorial membrane and so are flexed by sound vibrations
*Each cilium contains mechanically-gated non-selective cation channels. K+ is the main cation in endolymph
condution causes of deafness
Blockage of sound transmission via:
- Otitis
- Wax
- Tumors
- tympanic rupture
Which area do low frequencies stimulate on cochlea and why?
cochlea apex/top with narrow tip &is more flexible, loose & wider
which area do high frequencies stimulate on cochlea & why?
cochlea base/ opening near oval window thats more stiff & narrow
nerve causes of deafness
- congenital/genetic
ex: (white cats with blue eyes, dalmatians) - age: hair starts to die
- aminoglycoside antibiotics
function of semi- circular canals
head rotates causing endolymph to flow through corresponding canal displacing cupula &bending hair cells in opposite directions innervating CN VIII
what does posterior semicircular canal detect?
head tilting
what does Anterior semicircular canal detect?
head moving forwards & backwards (nodding)
what does the lateral/horizontal semicircular canal detect?
horizontal head movement, control balance
maculae control?
linear movement / acceleration
components of vestibular complex, their orientation &trigger plane of movement
1) Saccular macule: vertical so vertical movements trigger
2) utricular macule: horizontal so horizontal movements trigger
Explain macule role in linear acceleration
Head tilts cause gravity to shift otolithic membrane over sacculus relative to sensory epithelium displacing hair bundles in macula triggering impulses via CN VIII
Unilateral vestibular signs:
What do semicircular canals control?
balance
