Lecture 11 - Special Senses #2 Flashcards
What does the ear do
- > detects sound and movements of your head
- > signals it sends are transmitted to the brain via the vestibulocochlear nerve (CN III)
Names of the three divisions of the ear
- External
- Middle
- Inner
Which structures make up the external ear and what do they do
- Auricle (pinna)
- > your actual ear, made up of skin and elastic cartilage
- > protects entry into ear and directs sound waves into it - External acoustic meatus
- > bone tube extending through the temporal bone (ear canal) - Tympanic membrane (eardrum)
- > explain on other cue card
Explain how the tympanic membrane works
- > it’s a thin, funnel-like structure (directs sound)
- > vibrates when sound waves hit it and transmit that sound wave energy into the middle and inner ear
How does your body protect your tympanic membrane
secretes cerumen (earwax) form ceruminous glands which work with fine hairs within the external acoustic meatus to trap/ slow down foreign objects
Which structures make up the middle ear
Auditory tube (eustachian tube)
- > passage extending from middle ear to nasopharynx
- > allows pressure to equalize within inner ear (valsalva maneuver, popping ears forceful equalization)
Auditory Ossicles
- > malleus, incus, stapes
What are the auditory ossicles and what do they look like
*three smallest bones in the body housed within the tympanic cavity*
- Malleus
- > attaches to tympanic membrane, resembles hammer - Incus
- > middle ossicle resembling an anvil - Stapes
- > resembles a stirrup, marks lateral wall of inner ear
How do the auditory ossicles work?
- > they amplify and transmit sound waves into inner ear by vibrating when sound waves hit the tympanic membrane
- > the vibrations form the four structures causes stapes footplate to move in and out of the oval window, initiating pressure waves in the inner ear fluid
Round window vs oval window
pressure waves created by the stapes enter trough the oval window and exits on the other side of the cochlear duct and out through the round window and into the auditory tube
Order of pressure build up in middle ear
eardrum - > malleus - > incus - > stapes
What are the auditory muscles and what do they do
Stapedius
- > anchors stapes from moving out of alignment when loud noises occur (deafness)
Tensor tympani
- > anchors malleus …..
What structures make up the inner ear and what are they main funtions
Vestibule
- > deals with balance
Cochlea
- > deals with hearing
What makes up the cochlea
- > outer layer is made of spongy bone
- > houses the cochlear duct (scala media)
- > houses the spiral organ (organ of corti) within cochlear duct
Explain the differences between the scala vestibuli, media and tympani
- > scala media is located in between the scala vestibuli (superior) and scala tympani (inferior)
- > the scala media contain endolymph (like intercellular fluid) and the scala vestibuli and tympani contain perilymph (like CSF)
What is a helicotrema
the part of the cochlear labyrinth where the scala tympani and the scala vestibuli meet, at apex of cochlea
Properties of the spiral organ
- > found within scala media
- > thick sensory epithelium consisting of hair cells (stereocilia) and supporting (basal) cells
- > the organ of corti rests on the basilar membrane
- > top layer called tectorial membrane is where the hairs stick to
function of spiral organ
- > responsible for hearing
- > release neurotransmitter molecules to sensory neurons
How do we distinguish different sounds
Depends of the frequency and volume of the noise
Frequency
- > higher pitched sounds displace the basilar membrane closer to the base and lower freq. displaces it further down the structure
Volume
- > depends of the number of hair cells (inner and outer cells) that can detect a noise
Pathway of sound through the ear
What are the different types of movement and which receptors in the inner ear controls them
Linear movement
receptors - > maculae (sacs in vestibule, utricle and saccule)
Rotational Movement
receptors - > crista ampullaris of the semicircular ducts
*both receptors housed in vestibule*
Macula
- > located along internal wall of both sacs (utricle and saccule)
- > composed of layer of hair cells and supporting cells
- > like a snowglobe
Otollithic membrane
made out of gelatinous layer and small hard bone-like structures called otoliths
- > on top of macula
sternocilia vs kinocillium
Stereocillia
- > hairs
Kinocillium
- > king/ biggest stereocilia
both in hair cells
What happens when you tilt you head down vs tilt your head up
Head UP
- > otholithic membrane moves back, bending sterocilia towards kincillium, and exciting nerve signals
Head DOWN
- > otolithic membrane moves down, bending stereocilia away from kinocillium (down) and inhibiting/sloing down signals being sent by hair cells
What is happening to the macula when in normal upright head position
- > otolithic membrane is relatively even and it is contiuously sending signals to the brain (upright…….upright……upright)
Waat are the structures involved with rotational head movement
- Semicircular canal
- > 3 semicircular ducts connecting to utricle - Ampula
- > expanded region within the base of each SD - Crista Ampularis
- > elevated region on ampulla
- > covered by epithelium of hair cells and supporting cells (houses bipolar neurons) - Cupula
- > overlying gelatenous dome which extends across semicircular duct to roof of ampula
- > kinocilia and stereocilia are embedded here
What happens when you rotate your head
While you rotate, fluid in semicircular duct moves and this motion presses on capula, bending stereocilia
Explain bed spins
When you drink too much alcohol, it changes the density of the fluid within ampulae, this causes the capula to move/misfire easier
Explain tinnitus
(ringing ears)
after loud concerts, the constant loud vibrations of sounds damaging/ shearing off hair cells
Hair cells can regenerate in 24 hours
Explain motion sickness
There is a sensory conflict between eyes and vestibulary system. Your eyes sees that you yourself aren’t moving but the vestibulary system registers all the bumps/turns and says you are. Your brain doesn’t know whats happening and urges you to throw up because we have evolved to do so
