Special senses - ears Flashcards
What are the middle and inner ear housed in?
Temporal bone
What is the outer ear flap bit called?
Auricle/pinna
Ear canal name?
External auditory meatus
What nerve moves the auricle?
Facial nerve
What is the main notch in the ear called and what is it between?
Intertragic notch - between the tragus and antitragus
What is the margin of the auricle called?
Helix
What is it called when there is an ear infection and wat is used to treat it?
Erythema - red
Lateral wall resection
What is the external acoustic meatus lined with?
Skin containing sebaceous and ceruminous glands
What is the external acoustic meatus between?
Base of auricle and ear drum/tympanic membrane
What is the air filled space in the middle ear called?
Tympanic cavity
What is the middle ear in?
Petrous part of the temporal bone - more dense bone
What is the bulge behind the ear called?
Tympanic bulla - involved in improving sound
What is the tympanic membrane made up of?
Double layer of epithelium with connective tissue between
Medial epithelium - cuboidal
What is the tympanic membrnae innervated by?
The auriculotemporal branch of mandibular branch of trigeminal nerve
auricular branch of vagus nerve
How does the middle ear communicate with the nasopharynx? Why?
Via auditory tube
Equalises pressure
What are the windows between the middle and inner ear called?
Fenestra
What are the names of the two fenestra? Which are dorsal and ventral?
Vestibular/oval window - more dorsal
Cochlear/round window - more ventral
What are the names of the ossicles?
Malleus
Incus
Stapes
What attaches to the oval window?
Stapes
WHat is the function of ossicles?
Mediate the transmission of sound into the inner ear
What is the relationship of the middle ear with the facial nerve?
Enters the internal acoustic meatus with the vestibulocochlear nerve
Crosses the temporal bone
Exits at the stylomastoid foramen
What branch of the facial nerve is associated with the middle ear?
Chorda tympani branch
What does the chorda tympani branch do?
Lies on the upper part of the tympanic membrane
Supplies taste to the rostral 2/3 of the tongue
What are the two parts of the inner ear?
Membranous labyrinth
Bony labyrinth
What is in the membranous labyrinth?
Endolymph
What make up the bony labyrinth?
Semicircular canals
Cochlear
Vestibule - containing utricle and saccule
What does the cochlea do?
Converts sound to an electrical signal
What are the 3 sections of the cochlea?
Scala vestibuli
Scala tympani
Scala media
What do the scala tympani and scala vestibuli contain?
Perilymph
What does the scala media contain?
Endolymph
What does the scala vestibuli do?
Take the sound waves from the stapes/oval window to the helicotrema (apex)
What does the scala tympani do?
Take sound waves from the helicotrema to the round window
What separates scala media from scala vestibuli?
Vestibular membrane
What separates scala media from scala tympani?
Basilar membrane
What other membrane does the scala media contain?
Tectorial membrane
What is the main thing that is in the scala media?
Organ of Corti
What specialised receptors detect rotational movement?
Ampullary crests
What specialised receptors detect position of head and linear movements?
Maculae - otolith organs
What are the semicircular canals filled with?
Endolymph
What contains the hair cells in the semicircular canals?
Ampulla
What do the stereocilia of the hair cells in the semicircular canals project into?
Cupola
What does the utricle detect?
Horizontal movements
What does the saccule detect?
Vertical movements
What do the stereocilia project into in the maculae?
Otolith membrane
What is in the otolish membrane and why?
Calcium carbonate crystals to increase the mass so it lags behind in acceleration
What are the two parts of the maculae
Utricle and saccule
What are the outer and middle ear refered to as compared to the inner ear?
Outer and middle - conductive
Inner - sensory
What is impedance matching?
Fluid has greater inertia so takes more energy to move it
Therefore eardrum has a bigger SA than the oval window and ossicles have a lever action
What is the makeup of perilymph?
Low potassion conc
Potential of 0mV
What is the makeup of endolymph?
High potassium conc
High potential of 18mV
Where is the organ of corti located?
On the basilar membrane in the scala media
What do the stereocilia of the hair cells in the cochlea project into?
The tectorial membrane
What are the two type sof hair cells in the cochlea?
Inner hair cells and outer hair cells
What shape are inner hair cells?
Flask shaped
What type of innervation are inner hair cells?
Afferent
What shape are outer hair cells?
Columnar
What type of innervation are outer hair cells?
Efferent
How many rows of hairs are on outer and inner hair cells?
1 on inner
3 on outer
What are inner hair cells responsible for?
Sound encoding - turning sounds into electrical signals
What are outer hair cells responsible for?
Sound amplification and tuning
What does movement of the stereocilia cause?
Tension on the tip links which opens transducer channels causing depolarisation
What is the phase locking mechanism?
Where the electrical activity is linked to the peak of the wave of the initial stimulus
doesnt happen at higher freqs than 4kHz
What allows hearing of higher frequencies?
Tonotopy
What is tonotopy?
The spacial arrangement of frequency information provided by the basilar membrane
What are the structural differences in the basilar membrane?
Narrow and stiff at base - high freqs
Wide and floppy at apex - low freqs
How are these different regions of the basilar membrane detected in the brain?
Isofrequency bands in the auditory cortex
How is loudness encoded?
Different afferent nerves
High spontaneous rate fibers - low sounds
medium “
Low “ - only activated at highest frequency, dont get saturated
What does depolarisation of the outer hair cells cause?
Activation of prestin which causes cells to shorted and amplify the movement of het basilar membrane
What is the primary central pathway?
Spiral ganglion - ventral cochlear nucleus - superior olive - inferior colliculus - medial geniculate nucleus -auditory cortex
How is sound localised?
Low freqs - time difference to each ear
High freqs - interaural intensity difference
What reflex detects deafness?
Preyer’s reflex - startle
How are vestibular cells activated?
Directionally sensitive
Towards tallest kinocilia - depolarisation, excitation
Towards shortest - hyperpolarisation, less excitation
What is the place in the utricle and saccule where the stereocilia are oriented in opposite directions?
Striola
What does orthogonal mean?
Oriented at 90 degrees to each other
