Ear

Question 1

What structures make up the external ear?

Answer 1

auricle, external acoustic meatus and

outer tympanic membrane

Question 2

Auricle:

Answer 2

A shell-shape flap of cartilage covered with skin.

Major topographic (surface) parts include the concha, helix, antihelix, tragus, antitragus and 
lobule.

Directs sound waves into the external acoustic meatus.

Ridges of the auricle are spaced to reinforce sounds in the 1-3 kilohertz region of the sound spectrum – the range of human speech.

A: Carotid. N: Cutaneous: Cervical plexus – C2, 3 from great auricular n., C2, lesser occipital, Auriculotemporal branch of CN V3. External tempanic memb innerv by auriculotemporal of V3 and Auricular branch of Vagus n. w/ fibers from CN VII (somatic afferents)

Question 3

External Acoustic Meatus:

Answer 3

2-3 cm canal that leads from the auricle to the
tympanic membrane - directs sound pressure waves to the tympanic membrane.

Wall of the lateral 1/3 of the canal is cartilaginous
and lined with skin that produces the waxy cerumen.

Wall of the medial 2/3 is bony as the canal traverses temporal bone; lined with thin
skin that forms the outer layer of the tympanic membrane.

Question 4

Tympanic Membrane:

Answer 4

Separates the external acoustic meatus from the tympanic cavity.

Oval membrane about 1 cm in diameter;

made of thin skin and its inner surface is lined with
mucous membrane.

Meatal (i.e., lateral) side is concave and bears a central depression, the umbo

On physical exam, the membrane is a semitransparent and pearly gray. A “cone of light” radiates antero-inferiorly from the umbo.

The handle of the malleus is attached to the internal surface of the membrane, passing from the superior border to the umbo.

The flaccid part (pars flaccida) of the membrane lies superior to the handle of the malleus and the tense part (pars tensa) straddles the handle of malleus.

The tympanic membrane vibrates in response to sound waves striking its surface; vibrations are transmitted to the ossicles of the middle ear.

Question 5

Sensory Innervation of External Ear: auricle

Answer 5

The auricle is innervated primarily by
the great auricular nerve (from cervical plexus) and the auriculotemporal branch of V3 with minor contributions from CNs VII and X.

Question 6

Sensory Innervation of External Ear: external tympanic membrane

Answer 6

The external tympanic membrane is innervated by the auriculotemporal and the auricular branch of CN X

Question 7

Sensory Innervation of External Ear: internal tympanic membrane

Answer 7

internal tympanic membrane is supplied by CN IX.

Question 8

What makes up the middle ear?

Answer 8

-air-filled chamber in the petrous temporal
bone, the tympanic cavity. The tympanic cavity is lined with mucous membrane and contains three auditory ossicles, two skeletal muscles, two nerves and a nerve
plexus.

Question 9

What are the contents of the middle ear?

Answer 9

The tympanic cavity is lined with mucous membrane and contains three auditory ossicles, two skeletal muscles, two nerves and a nerve
plexus.

Question 10

Name the nerve that provides sensory innervation for the middle ear.

Answer 10

Innervated by somatic afferents (sensory), CN IX or Glossopharyngeal (posterior Eustachian tube), CN V2 innervates anterior portion of Eustachian tube

Question 11

Name the spaces and tubes that are connected to the middle ear.

Answer 11

Tympanic cavity proper, the space medial to the tympanic membrane

Epitympanic recess, the space superior to the tympanic membrane.

Antero-medially, the pharyngotympanic tube connects the middle ear with the nasopharynx.

Posterosuperiorly, the tympanic cavity connects with the mastoid air cells via the mastoid antrum.

Question 12

Identify the three ossicles of the middle ear. Describe their relative positions, functions and pertinent relationships. What are they covered by?

Answer 12

Auditory Ossicles: The tympanic cavity is spanned by a tiny chain of three ossicles, that form a movable bridge from the tympanic membrane to the oval window.

From lateral to medial the ossicles are malleus, incus and stapes and are united by synovial joints. The ossicles are covered with mucous membrane and don’t have periosteum.

Question 13

Describe the Malleus:

Answer 13

Head lies in epitympanic recess
-articulates with incus
Handle attached tro tympanic membrane
-Muscles attachment: tensor tympani muscle to handle

-head, neck, handle and two processes.
-head lies in the epitympanic recess, the neck lies
against the pars flaccida and the handle and two processes are attached to the tympanic membrane. -moves with the tympanic membrane.
-head of the malleus articulates with the incus and the tendon of tensor tympani (see below) inserts near the neck.

The chorda tympani nerve passes medial to the neck.

Question 14

Describe the Incus:

Answer 14

• body and two limbs.
• The body lies in the epitympanic recess where it articulates with the malleus.
• The lenticular process of the long limb articulates with the stapes

Question 15

Describe the Stapes:

Answer 15

Head articulates with lenticular process of the incus

Base in oval window, attached via annular ligament

Stapedius muscle attaches to head

(Latin for stirrup) has a head, two limbs and a base. -head articulates with the lenticular process of the incus and the base (footplate) inserts into the oval window of the labyrinthine wall, where it is held in place by the annular ligament.
-smaller than the tympanic membrane such that there is a 50-fold increase in the vibratory force on the oval window. This difference in force matches the difference in impedance of air-versus-fluid, and allows for the efficient passage of pressure waves from the air of the outer ear into the fluid medium of the inner ear.

Question 16

Identify the two skeletal muscles of the middle ear and the ossicles to which they attach. Identify which cranial nerve innervates which muscle.

Answer 16

Tensor Tympani: -> malleus

The tensor tympani arises from the pharyngotympanic tube, petrous temporal bone and greater wing of sphenoid. It inserts on the
handle of the malleus.

Reflex contraction of tensor tympani pulls the handle of malleus medially, tensing the tympanic membrane and reducing the amplitude of its movements.

This prevents damage to the middle ear in response to loud noises.

Innervated by the nerve to the tensor tympani, a branch of CN V3. (Note: “TTT” Trigeminal Tensor Tympani)

Stapedius: ->stapes
-encased in a bony cone, the pyramid.
Its tendon inserts near the head of stapes. Reflex contraction pulls the base of stapes tighter into the oval window and prevents excessive movement of the stapes.

Innervated by nerve to the stapedius, a branch of CN VII, (Note: “SS” Seven Stapedius)

Question 17

Describe the walls of the middle ear and the special features associated with each wall:
Tegmental Wall

Answer 17

Tegmental Wall (Tegmental Roof): The roof is formed of tegmen tympani, part of petrous temporal bone that separates the tympanic cavity from the dura mater of the floor of the middle cranial fossa.

Question 18

Jugular Wall is the ——–wall of the tympanic cavity.

Answer 18

Jugular Wall (Floor): The floor, also formed by petrous temporal bone, separates the tympanic cavity from the internal jugular vein.

Question 19

Membranous Wall is the ——–wall of the tympanic cavity.

Answer 19

Membranous Wall (Lateral Wall): The lateral wall is formed of tympanic membrane and the lateral bony wall of the epitympanic recess.

Question 20

Labyrinthine Wall is the ——–wall of the tympanic cavity.

Answer 20

Labyrinthine Wall (Medial Wall):  This wall separates the tympanic cavity from the internal ear. This wall features the promontory, a protuberance 
that overlies the basal turn of the cochlea. Supero-posterior to the promontory is the oval window, closed by the base of the stapes. The facial canal transmitting CN VII creates a ridge. A second ridge is formed by the lateral semicircular canal. Finally, the round window is inferior to the promontory and is closed by a secondary tympanic membrane.

Question 21

Carotid Wall is the ——–wall of the tympanic cavity.

Answer 21

Carotid Wall (Anterior Wall): This wall separates the tympanic cavity from the carotid canal (containing the internal carotid artery). It has openings for the tensor tympani tendon and the pharyngotympanic tube.

Question 22

Mastoid Wall is the ——–wall of the tympanic cavity.

Answer 22

Mastoid Wall (Posterior Wall): The superior part of this wall contains the aditus to the mastoid antrum, a small opening that leads to the mastoid 
antrum and the mastoid air cells. The facial canal, a bony tube traversed by CN VII (facial nerve), can also be seen on the posterior wall of the tympanic cavity. The facial canal is medial to the aditus.

Question 23

Identify the types of fibers found in each of the following middle ear nerves and what functions these different fibers subserve:
chorda tympani

Answer 23

branch of CN VII, parasympathetic to glands and special sensory (taste) to tongue, passes through malleus and incus via petrotympanic fissure anterior to external acoustic meatus to join lingual n.

Question 24

Identify the types of fibers found in each of the following middle ear nerves and what functions these different fibers subserve: 
tympanic nerve (of Jacobson)

Answer 24

– enters via tympanic calaiculus, branch of CN IX, joins tempanic plexus, has sensory and pre-ganglionic parasympathetic fibers. Sensory to middle ear and inner leaflet of tempanic membrane, PNS departs as lesser petrosal nerve to otic ganglion  parotid gland

Question 25

Identify the types of fibers found in each of the following middle ear nerves and what functions these different fibers subserve:
tympanic plexus

Answer 25

– overlies promontory of medial wall, comprised of tempanic n of Jacobson + sympathetic fibers, provides sensation to middle ear and Eustachian tube. Fibers pass thru tempanic plexus and converge into lesser petrosal nerve of middle cranial fossa

Question 26

Describe the structure and function of the pharyngotympanic tube, as well as its sensory innervation.

Answer 26

Posterior 1/3 is bony, anterior 2/3 is cartilaginous, covered w/ mucous membrane. Functions to equalize pressure between tympanic membrane and atmosphere.

Innervated by Glossopharyngeal n. (CN IX) via tempanic plexus posteriorly and Trigeminal Maxillary branch (CN V2) anteriorly

Question 27

Describe the significance of the aditus, mastoid antrum and mastoid air cells.

Answer 27

Aditus is a small opening in the posterior wall of the tempanic cavity that connects it to the mastoid antrum and mastoid air cells. This is significant clinically in that infections can spread through this

Question 28

Describe the otic capsule.

Answer 28

Otic capsule: densest part of the petrous portion of temporal bone that houses the inner ear apparatus

Question 29

Describe the bony labyrinth.

Answer 29

Inner ear: Bony labyrinth: within the petrous temporal bone and then an even harder bone filled w/ perilymph. Curly area is cochlea, then there are the anterior, lateral and posterior semicircular canals. Ampullae goes to the canals from the vestibule which is attached to the cochlea. Vestibule contains oval and round windows adjacent to tympanic cavity.

Question 30

Describe the cochlea:

Answer 30

Inner ear: Cochlea – encloses spiral canal that turns 2.5 times around modeolus - spongy bone that contains branches of cochlear n.

Question 31

Describe the Vestibule:

Answer 31

Inner Ear Vestibule – continuous anteriorly w/ cochlea and posteriorly w/ semicircular canals. Contain utricle and saccule (parts of membranous labyrinth) and are separated from the vestibule by perilymph.

Question 32

Nerves of the Middle Ear:

Answer 32

• chorda tympani
• tympanic nerve (of Jacobson) is a twig from CN IX.
• tympanic plexus

Question 33

Describe the chorda tympani in relationship to the middle ear:

Answer 33

is a branch of CN VII that traverses a small posterior opening and crosses the tympanic cavity between malleus and incus. It does not innervate any structures in the middle ear (its destination and function will be covered later).

Question 34

Describe the tympanic nerve (of Jacobson) in relationship to the middle ear:

Answer 34

-enters the tympanic cavity through a tiny hole in the floor of the tympanic cavity (the tympanic canaliculus) and helps form the tympanic
plexus.

Question 35

Describe the tympanic plexus in relationship to the middle ear:

Answer 35

-overlies the promontory and is formed by contributions from the tympanic nerve, as well as sympathetic fibers entering with blood vessels.

It provides sensation to the middle ear and most of the pharyngotympanic tube. Other fibers in the tympanic plexus pass through the middle ear without innervating anything, and form the lesser petrosal nerve of the middle cranial fossa.

Question 36

Internal Ear: Description, Location, Contents

Answer 36

• complex vestibulocochear organ concerned with the perception of sound and perception of balance.
• housed in the densest part of the petrous temporal bone, the otic capsule.
• consists of a complex series of channels within the bone, which contain a membranous sac.
• bony walls of these channels is called the bony labyrinth;
• the membranous sac within the channels is called the membranous labyrinth.

Question 37

What does the bony labyrinth consist of?

Answer 37

chochlea and vestibule

Question 38

Cochlea

Answer 38

encloses the spiral canal that turns 2½ times
around a bony hub, the modeolus. The apex of the modeolus points anterior, lateral and inferior. The modeolus, made of spongy bone, contains branches of the cochlear nerve. The spiral canal contains a portion of the membranous labyrinth called the membranous cochlear duct; the surrounding portions of the cochlea comprise the scala vestibuli and the scala tympani, both of which are filled with perilymph. The basal turn of the cochlea produces the promontory of the labyrinthine wall of the tympanic cavity. Close by is the round window closed by the secondary tympanic membrane.

Question 39

Describe the structure and functions of the various portions of the membranous labyrinth - ducts

Answer 39

Ducts for membrane (canal for bone), same as above, but filled w/ endolymph and hair cells/supporting stxrs membranous labyrinth contained within bony labyrinth but not adhered to bony wall.

Question 40

Describe the structure and functions of the various portions of the membranous labyrinth - cochlear duct

Answer 40

Cochlear duct:
Between lateral surface of spiral canal and modeolus. Cochlear duct separates scala vestibule and scala tempani which are continuous w/hemicotrema at apex. Houses organ of Corti = collection of hair cells and support stxrs that respond to distortion from sound waves. Sound wave transmitted from stapes  cochlea via perilymph of scala vestibuli  Reisner’s membrane of cochlear duct  endoperilymph of cochlear duct  tectorial membrane  hair cells

Question 41

Describe the structure and functions of the various portions of the membranous labyrinth - vestibule

Answer 41

Vestibule:
Semicircular canals are at right angles to each other, so we have one in each plane. Cilia from ampulla moved when we move.
Utricle - continuous w/ semicircular ducts, macula is horizontally oriented
saccule - connected to cochlear duct, macula is vertically oriented
hair cells in ampulla stimulated by movement of endolymph - displaced by gravity, detect static head position and changes in head position - centrifugal and vertical acceleration (utricle) and linear acceleration (saccule). Innervated by vestibular portion of CN VIII

Question 42

Describe the functions of the cochlear and the vestibular portions of CN VIII

Answer 42

Cochlear: spiral ganglion of Vestibulocochlear . The actual ganglion spiral around cochlea, n. comes to sensory apparatus. Runs in between Scala vestibule and scala tympani, cochlear duct is superior. Sound waves move stapes in oval membrane  P waves in perilymph of scala vestibuli  displace cochlear duct  tectorial membrane in cochlear duct, and this membrane moves the cilia of the organ of corti  secrete NTs onto sensory nerve endings on the spiral ganglion  fire  AP  cochlear division of CN VIII  CNS
Bipolar bodies in ganglion

Vestibular: head movement bends cilia, they secrete NT onto sensory receptors of neurons in vestibular ganglion  fire  AP to vestibular div of CN VIII

Internal acoustic meatus – vestibulocochlear and facial n. move through, once in fossa vestibulocochlear splits into vestibular and cochlear, then past it facial joins geniculate ganglion

Question 43

Describe the semicircular canal

Answer 43

-three bony channels (anterior, posterior, lateral) that lie postero-superior to the vestibule and
open into it (the anterior and posterior canals share one common limb). - occupy three planes in space at right angles to each another.

Each canal is about 2/3 of a circle and at one end has an enlarged ampulla.

The semicircular ducts, parts of the membranous labyrinth concerned with balance, are suspended in the semicircular canals and separated from them by perilymph.

Question 44

Describe the membraneous labyrinth and what does it contain?

Answer 44

maze of contiguous sacs and channels that generally mimic the shape of the bony labyrinth.

• contains endolymph that differs in composition to
  perilymph; fine fibers and a ligament secure it to the bony labyrinth.

-subdivided into vestibular and cochlear labyrinths.

Question 45

What is endolymph?

Answer 45

inside membraneous labyrinth
unique extracellular fluid – it is high in potassium and low in sodium.
-subserves the physiology of the “hair cells” of the various parts of the membranous labyrinth.

Question 46

What are the two sacs in the vestibular labyrinth?

Answer 46

small utricle and saccule are connecting sacs
inside the vestibule.

utricle connects to the semicircular ducts

saccule connects to the cochlear duct.

Question 47

What is maculae and where are they found?

Answer 47

The utricle and saccule contain maculae that are oriented in two planes: the macula of the utricle is
horizontal and that of the saccule is vertical.

• contain hair cells that are stimulated by movement of the endolymph that accompanies changes in the position of the head.
• hair cells are innervated by fibers of the vestibular division of the vestibulocochlear nerve (CN VIII) from ganglion cells in the vestibular ganglion (within internal acoustic meatus).

Question 48

What is a semicicular duct? Where is it found? What is found near the opening into utricle? What does it contain?

Answer 48

The semicircular ducts (anterior, posterior, lateral) are inside the semicircular canals.

Near its opening into the utricle (one shared limb as above), each duct has a swelling – the ampulla –containing an ampullary crest with hair cells; stimulated by movements of the endolymph that accompanies rotation of the head in the plane of a given duct.

Hair cells are innervated by fibers of the vestibular division of the vestibulocochlear nerve (CN VIII) from ganglion cells in the vestibular ganglion (also known as Scarpa’s ganglion).

Question 49

What is the cochlear labyrinth? What does it contain? How is it innervated?

Answer 49

The cochlear duct constitutes the cochlear labyrinth.
The cochlear duct is suspended within the spiral canal between the lateral surface of the cochlea and the modeolus.

Duct contains endolymph, houses the spiral organ of corti that is a collection of hair cells and support cells that responds to deformation of the cochlear duct induced by vibrations related to sound waves.

Hair cells are innervated by fibers from the cochlear division of the vestibulocochlear nerve (CN VIII) from ganglion cells forming the cochlear ganglion (also known as the Spiral Ganglion)

Question 50

What are the channels that are divided by the cochlear duct?

Answer 50

divides the spiral canal in two perilymph-filled channels.

• scala vestibuli
• scala tympani

channels are continuous at the helicotrema at the apex of the modiolus (they meet here, low frequency best heard here)

Question 51

Which hair cells detect static head movement?

Answer 51

Hair cells located in the maculae of the
saccule and utricle elaborate cilia that are embedded in the otolithic membranes that
overlies these maculae.

Little crystal precipitates – the otoliths – are embedded in the otolithic membrane, making it non-bouyant and weighing down the otolithic membrane.

With each position of the head, the otolithic membranes are bent by the force of gravity
slightly differently, and this results in the stimulation of different sets of hair cells -> secrete neurotransmitter onto the sensory
nerve endings of neuronal subpopulations in the vestibular ganglion -> Action potentials are then carried by the vestibular division of the eighth cranial nerve into the CNS where they activate specific nuclei involved in the perception of
static head position.

Question 52

How We Perceive Dynamic Rotational Movements of the Head:

Answer 52

Hair cells located in the ampullae of the semi-circular canals elaborate cilia that are embedded in the gelatinous cupula forming a membrane across each ampulla.

Rotational movements of the head move the bony and membranous labyrinths, but don’t move the fluid (at least initially) lying within the membranous labyrinth. = fluid pressing up against
the one or another side of the ampullae, bending them and thereby bending the cilia within them = activation of the hair cells, which in turn, secrete neurotransmitter onto the sensory nerve endings of other neurons in the vestibular ganglion, exciting them to fire. Action potentials are then carried by the vestibular division of the eighth cranial nerve into the CNS where they activate specific nuclei involved in the perception of dynamic rotational movements of the head.

Question 53

How We Hear:

Answer 53

Sound waves in the air strike the tympanic membrane of the outer ear, -> ossicles -> base of the stapes in the oval window of the
middle ear. Movements of the oval window create pressure waves in the perilymph of the scala vestibuli of the inner ear that travel through the perilymph and displace the cochlear duct. Hair cells within the Organ of Corti of the cochlear duct are activated by shearing forces caused by displacement of the cochlear duct, and secrete
neurotransmitter onto the sensory nerve endings of neurons in the spiral ganglion, exciting them to fire. Action potentials -> cochlear division of the eighth cranial nerve into the CNS where they activate specific nuclei involved in the perception of sound.

(Note: after displacing the cochlea, the pressure waves travel through the scala tympani to the round window, where the energy of the pressure waves is dissipates into the air of the middle ear.)

Question 54

What do ossicles do?

Answer 54

match the difference in impedance between gaseous and fluid media.

Question 55

Where does the choda tympani exit the skull?

Answer 55

petrotympani fissure

Question 56

Middle ear is continuous wiht which spaces?

Answer 56

aditus as antrum (mastoid air cells) and pharynx (pharyngotympanic tube)

Question 57

What is the function of the internal ear?

Answer 57

audition and vestibular senses

Question 58

What innervates the internal ear

Answer 58

vestibularchoclear n.

Question 59

Where does the internal ear lie?

Answer 59

petrous temporal bone

Question 60

Define semicircular canals:

Answer 60

perceive dynampic rotational movements of the head, independent of gravity

Question 61

Define utricle and saccule:

Answer 61

percieve static head positions and linear acceleration, depends on gravity