Anatomy of the Ear Flashcards
1
Q
What are the structures that make up the external ear?
A
- outer ear (pinna, tragus)
- external auditory meatus (contains ceruminous glands which secrete ear wax for protection)
- supplied by auricular branch of vagus and auriculotemporal branch of trigeminal
- tympanic membrane (concave, can view handle of malleus, chorda tympani, and Politzer’s triangle)
2
Q
What are the structures that make up the middle ear?
A
- ossicles (transmits vibration from tympanic membrane to inner ear): malleus, incus and stapes
- muscles: tensor tympani and stapedius (protective - acoustic reflex in response to loud noise)
- auditory/eustachian tube (connects middle ear to nasopharynx): actively opened by simultaneous contraction of tensor veli palatini and sapingopharyngeus
- route for infection
3
Q
What makes up the borders of the middle ear cavity?
A
- roof: thin petrous bone separating the middle ear from the middle cranial fossa
- floor (jugular wall): thin layer of bone separating middle ear from IJV
- aditus ad antrum (exit): air spaces in mastoid process of temporal bone
4
Q
What structures make up the inner ear?
A
bony labyrinth (filled with perilymph) with a membranous labyrinth within (filled with endolymph):
- cochlea (cochlear ducts)
- vestibule (utricle and saccule)
- 3 semicircular canals (semicircular ducts)
5
Q
Describe the anatomy of the cochlea
A
- attached to cochlear duct by osseus spiral lamina
- scala vestibuli superior to cochlear duct separated by vestibular membrane
- scala tympani inferior to cochlear duct separated by basilar membrane (contains organs of corti)
6
Q
Describe frequency detection
A
- sound waves deform the basilar membrane of the cochlea in areas specific to the frequency of the vibration and absorbs the kinetic energy
- high frequencies resonate at the base and low frequencies resonate at the apex
- upward deflection of basilar membrane moves inner and outer hair lateral to the tectorial membrane
7
Q
Describe the structures at the organ of Corti
A
- inner hair cells are sensory organs for audition, providing input to auditory nerve fibres to project to brain
- outer hair cells receive descending input from the brain to assist in modulation of inner hair cells
- displacement of hair cells open/closes K+ channels
8
Q
How does the cochlea tune out background noise?
A
- olivocochlear neuronal control
- fibres release ACh onto inner ahir cells causing depolarisation
9
Q
Describe the auditory pathway
A
- 1st order neuron is cochlear nerve formed from central extensions of bipolar neuron at spiral ganglion, synapses on anterior and posterior cochlear nuclei
- 2nd order neurons split, most decussate and travel to synapse on contralateral superior olivary nucleus, some go ipsilaterally
- 3rd order neurons ascend lateral lemniscus and synapse on inferior colliculus
- 4th order neurons project and synapse on MGN in thalamus
- 5th order neurons project to auditory cortex (collaterals to reticular formation and vermis of cerebellum for arousal response)
10
Q
Define sound shadow and sound lag
A
- sound shadow: when sound from one side hits the head, generating a ‘shadow’ on the other side where the volume is less
- sound lag: sound from a particular direction arrives at one ear before the other so there is a delay in ipsilateral projection to the auditory cortex to contralateral
- lag > shadow (due to pinna)
11
Q
Define some causes of conduction and sensory-neural deafness
A
conduction deafness:
- blockage of outer ear
- middle/outer ear infection
- ossification of bones in middle ear
sensory-neural deafness:
- breakdown of cochlea and associated mechanisms
- damage of auditory nerve/cortex
12
Q
What are the 6 primary tastes?
A
- sweet: sugar, glycols, ketones
- sour: H+ ions
- salty: NaCl
- bitter: quinine, alkaloids in toxic plants
- umami: glutamate - truffles, meat, aged cheese, tomatoes
- oleogustus: fatty acids
13
Q
Name the locations on the tongue and the taste buds present there
A
- anterior: fungiform papilla
- along sulcus terminalis: vallate papilla
- lateral: foliate papilla
14
Q
Describe the taste pathway
A
- fibres that carry taste synapse on nucleus solitarius dorsally in gustatory region
- 2nd order neurons ascend ipsilaterally and synapse on thalamus with fibres crossing midline and joining medial lemniscus
- 3rd order neurons project to cortex
(has limbic component via thalamus which can activate brainstem nuclei for salivation/vomiting)
15
Q
Describe the olfactory epithelium and pathway
A
- contain basal cells which can regenerate
- olfactory cilia immersed in mucus to react to smell which activates bipolar receptor cells
- central processes form olfactory nerve that passes through cribriform plate and synapses on olfactory bulb to olfactory tract
- medial olfactory stria goes to limbic system
- lateral olfactory stria goes to olfactory cortex in medial temporal lobe
