Lecture 25: Ear & Auditory Canal Flashcards
What makes up the outer ear and what are its features?
Auricle - collects sound and is supported by cartilage
Where is the tragus?
Anterior to the ear canal/external auditory meatus
What supports the external acoustic meatus?
Laterally supported by cartilage and medially supported by bone (temporal)
What lines the external acoustic meatus?
Cerumen glands and hairy skin
What do the cerumen glands present?
Produce wax to prevent maceration of skin and water
What is the nerve supply to the outer ear?
Posterior and inferior surface is innervated by vagus and anterior superior surface of external auditory meatus is innervated by the auriculotemporal nerve (branch of mandibular/V3 branch of trigeminal nerve
Where is pain in the outer ear referred?
Lower teeth - mandible
What forms the indentation of the tympanic membrane?
Small bone in the middle ear (malleolus)
What is the shape of the tympanic membrane?
Concave laterally - dependent on the pressure that exits medial to it in the middle ear
What is the cone of light?
Position of light when you shine light into the anterioinferior quadrant - if light is in a different position there has been a pressure change
What is the middle ear?
Space between tympanic membrane and petrous part of temporal bone
What is the middle ear split into?
Tympanic cavity proper and epitympanic recess
What does the epitympanic recess communicate with?
Mastoid air cells - openings from middle ear to spaces in mastoid bone
How do the middle ear and nasopharynx communicate?
Auditory tube
What is the position of the auditory tube?
Projects anterior and inferior towards the nasopharynx
What is the auditory canal made up of?
Cartilaginous where it opens into the nasopharynx and embedded in bone near the tympanic cavity
What happens due to the auditory canal opening downwards?
Migratory pathway for bacteria
What does infection in the ear cause?
Disrupted movement of the ossicles, reduced sound transport, impaired hearing
What are the ossicles and where do they attach?
Little bones in the middle ear. Malleus is shaped like a hammer, incus is shaped like an anvil and stapes is shaped like a stirrup (lateral to medial). Attach laterally to tympanic membrane.
How does the auditory tube change from infancy to adulthood?
Tube starts out short and horizontal (lots of ear infections) and becomes more vertical and longer
What innervates tensor tympani and what does it attach to?
Trigeminal nerve, anterior wall to malleus
What innervates stepedius and what does it innervate?
Facial nerve - stapes and posterior wall
What is the function of the small muscles in the middle ear?
When muscles contract they dampen the amplitude of vibration of the bones - reflex response to loud sounds. If energy is too large - amplitude will be too loud and damage sensory auditory structures. Reflex contraction of muscles to stop vibration of ossicles when we hear a really loud sound. Same frequency of sound but reduced amplitude.
What happens to hearing in facial nerve palsy?
Stapedius muscle function disrupted - less reflex to reduce loud noise - increased sensitivity to hearing
What is the round window?
Opening related to big swelling on medial wall – promontory – basal turn of cochlear
What is chorda tympani?
Small nerve in the ear, a branch of the facial nerve (intermediate division), takes tortuous path and ends up on anterior 2/3 of the tongue (info on taste), branch of facial nerve in petrous portion of temporal bone, runs through middle ear to get there, continues with linguinal branch of trigeminal nerve to reach tongue
What is the relationship of the internal carotid artery and the ear?
Runs close by - when there is fluid near the tympanic membrane mechanical energy is formed and you can hear the artery pumping
What is the inner ear?
System of spaces and membranes imbedded in petrous part of temporal bone
What is the bony labyrinth and what fluid is it filled with?
System of spaces in temporal bone - perilymph
What is the membranous labyrinth and what fluid is it filled with?
Single closed sac within boy labyrinth - endolymph
What does the vestibule connect?
Cochlea to semicircular canals
What are the semicircular ducts?
Ducts that sit within canals
What is at the base of each duct?
Ampulla - sensory fibres for dynamic equilibrium
What are the swellings in the vestibule?
Utricle and saccule - sensory receptors for static equilibrium
What nerves come together to form the vestibulocochlear neve?
Vestibular and cochlear nerves
How is sound transmitted?
Sound transmitted onto vibrations of tympanic membrane; vibrate with frequency with amplitude relative to sound, transmitted through ossicles to inner ear via oval window. Once in perilymph transferred into membranous labyrinth into the endolymph and vibrates sensory receptors that sit on a membrane that forms part of the organ of corti (complex that contains sensory receptors for hearing)
Where do high and low frequency receptors sit?
High - base of cochlea
Low - apex of cochlea
What happens in static equilibrium?
Put head in any one position, otolithic membrane flops down due to gravity and stays in one spot - deflect hair cells in direction affected by gravity
