anatomy and physiology unit 2

transverse plane

cut horizontally below nose

medial

closer to middle

lateral

closer to edges

sagittal plane

cut down the nose into right vs. left

posterior

towards the back

anterior

towards the front

coronal plane

cut into front and back

superior

upwards

inferior

downwards

dextral

right

sinistral

left

ipsilateral

on the same side

contralateral

on the opposite side

proximal

near point of reference

distal

further from point of reference

modes of operations of ear

acoustic, mechanical, mech/hydromech/electrochem, electrochemical

impedance matching

process of equating output impedance of one component to the input impedance of another

impedance matching of auditory system

air to TM, TM to ossicular chain, ossicular chain to cochlear fluid

acoustic units

pressure

mechanical units

velocity

hydromechanical units

displacement

electrochemical units

electrical potential

transfer function

process of filtering input to produce different output

parts of outer ear

pinna, external canal, TM

extrinsic muscles

posterior, superior, anterior auricular muscles

intrinsic muscles

muscles of helix and antitragus

makeup of ear canal

first 2/3 cartilaginous, last 1/3 bone

adult canal info

25 mm long, 8mm diameter, pointed superiorly

infant canal info

14 mm long, <5mm diameter, pointed horizontally

cough reflex

triggered by mechanical stimulation of auricular branch of Vagus nerve

TM info

10 mm diameter, .08 mm thick

TM tissue layers

cutaneous, fibrous, internal mucosa

radial fibers

become more concentrated as they converge on manubrium

spiral fibers

thicker towards periphery and thinner at umbo

pars flaccida

loose but thick

pars tensa

tense but thin

TM angles

the acute angle creates 10 dB differences from top to bottom

TM motion

low frequencies = standing waves, high frequencies = traveling waves

at high frequencies, the TM moves

at different times from other parts, which creates the ripple effect

where are all resonances summed up on the TM

the umbo

how to measure resonance of ear canal

probe (in the ear canal), reference microphone (outside ear), sound source (front/side of head)

how is the sound level at reference vs. probe plotted?

as function of frequency

external ear effect/sound field transform

combination of sound interacting with head, torso, pinna, and ear canal (mostly ear canal)

temporal bone

bone that sits on the side of the face, most important for audiology

parts of temporal bone

squamous portion, tympanic portion, styloid process, mastoid process, petrous portion

squamous portion

origin of zygomatic process (part of cheekbone)

where are the sutures of skull strong?

between temporal and parietal bones

styloid process

attaches to stylopharyngeus, styloglossus, stylohyoideus, stylomandibular, and stylohyoid

mastoid process

forms part of tympanic cavity and EAM, houses mastoid air cells

petrous portion

houses auditory and vestibular organs

ossicles

smallest bones in body, transduce sound and overcome impedance mismatch

incudomallear, incudostapedial

joints of ossicles

malleus

hammer, head is half of epitympanic space

incus

anvil, head occupies other half of epitympanic space, size of long process is shorter than manubrium, behind malleus and turns 90º to attach to stapes

stapes

stirrup, no bone marrow makes it very light but cannot regenerate

footplate

part bone and part cartilage base of stapes

crura

arches of stapes that allow force to be distributed to the footplate

muscle

tissue that provides motion

tendon

tissue that connects muscle to bone, transmits the force that muscle exerts

ligament

band of tissue that support/suspend structures

TM, malleal and incudal ligaments, tensor tympani, stapedius, annular ligament

holds ossicular chain in place

bony canals

where muscles of middle ear reside within the ear

tensor tympani

parallel to Eustachian tube, holds malleus in place

stapedius

near stapes, pulls stapes down and slightly out, MUCH smaller than tensor tympani

tegman tympanum

superior wall of tympanic cavity

separates ME from jugular

inferior wall of tympanic cavity

oval/round windows, promontory

medial wall of tympanic cavity

tympanic aditus, stapedius, chorda tympani

posterior wall of tympanic cavity

opening of Eustachian tube, tensor tympani

anterior wall of tympanic cavity

Eustachian tube

evacuates fluid from ME and equalizes pressure

tube, osseous and cartilaginous portion, isthmus, muscles

parts of Eustachian tube

tube

goes from ear to back of throat

isthmus

point between bony and cartilaginous portions, the narrowest point

tensor veli palitini, levator veli palitini

muscles of Eustachian tube

impedance matching

pressure of sound wave must be increased between tympanic membrane and stapes footplate

area ratio

larger area of TM increases pressure applied to area of stapes footplate

24 dB

pressure increase from area ratio

lever ratio

length of malleus is longer than incus, which makes a lever movement to move stapes

2.3 dB

pressure increase from lever ratio

buckling of TM

velocity of TM motion doubles pressure at oval window

6 dB

pressure increase of TM buckling

32 dB

total pressure increase from impedance matching

middle ear transfer function

1000 Hz is resonant frequency, mismatched impedance causes loss of potential, middle ear is bandpass filter

acoustic reflex

caused by sounds that are 80 dB SL, 2000 Hz and 200 msec

acoustic reflex activation

stapedius and tensor tympani contract, stapes and malleus pulls opposite, mechanical energy attenuated

purpose of acoustic reflex

moderate variations in signal level, reduce distortion of ossicular chain, not to protect hearing

slow, low and mid frequencies, reflex only for short time

why acoustic reflex cannot protect hearing

oval window and round window

two windows of cochlea

cochlea info

35 mm long, 2.5 turns

perilymph

similar to cerebrospinal fluid, not very charged fluid

semicircular canals, utricle/saccule, scala media, endolymphatic sac

four parts of membranous labyrinth

where does new fluid always come from

endolymphatic sac

reissner’s membrane

separates scala media from scala vestibuli

basilar membrane

flexible and easily moved with fluid movement

endolymph

also CSF, highly positively charged with different electrical potential

sensory cells

inner hair cells, outer hair cells, stereocilia, reticular lamina, nerve fibers

supporting cells

rods for corti, phalangeal cells, deiters cells, tectorial membrane

non-mitotic

no replication

inner hair cells

closest to modiolus, pear shaped, 1 row to apex

~3500 per cochlea

number of IHCs