Ear

Question 1

Describe the different parts of the ear

Answer 1

The ear is the organ of hearing and balance. It has three parts ( Fig. 8.113 ):

▪ The first part is the external ear consisting of the part attached to the lateral aspect of the head and the canal leading inward.
▪ The second part is the middle ear —a cavity in the petrous part of the temporal bone bounded laterally, and separated from the external canal, by a membrane and connected internally to the pharynx by a narrow tube.
▪ The third part is the internal ear consisting of a series of cavities within the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially

The internal ear converts the mechanical signals received from the middle ear, which start as sound captured by the external ear, into electrical signals to transfer information to the brain. The internal ear also contains receptors that detect motion and position.

Question 2

Summarise the external ear

Answer 2

The external ear consists of two parts. The part projecting from the side of the head is the auricle ( pinna ) and the canal leading inward is the external acoustic meatus .

Question 3

Describe the anatomy of the external ear

Answer 3

The auricle is on the side of the head and assists in capturing sound. It consists of cartilage covered with skin and arranged in a pattern of various elevations and depressions
The large outside rim of the auricle is the helix . It ends inferiorly at the fleshy lobule, the only part of the auricle not supported by cartilage.

The hollow center of the auricle is the concha of the auricle . The external acoustic meatus leaves from the depths of this area.

Just anterior to the opening of the external acoustic meatus, in front of the concha, is an elevation (the tragus ). Opposite the tragus, and above the fleshy lobule , is another elevation (the antitragus ). A smaller curved rim, parallel and anterior to the helix, is the antihelix .

Question 4

Describe the muscles of the external ear

Answer 4

Numerous intrinsic and extrinsic muscles are associated with the auricle:

▪ The intrinsic muscles pass between the cartilaginous parts of the auricle and may change the shape of the auricle.
▪ The extrinsic muscles, the anterior, superior, and posterior auricular muscles, pass from the scalp or skull to the auricle and may also play a role in positioning of the auricle (see Fig. 8.56 ).
Both groups of muscles are innervated by the facial nerve [VI

Question 5

Summarise the innervation of the external ear

Answer 5

▪ The outer more superficial surfaces of the auricle are supplied by the great auricular nerve (anterior and posterior inferior portions) and the lesser occipital nerve (posterosuperior portion) from the cervical plexus and the auriculotemporal branch of the mandibular nerve [V 3 ] (anterosuperior portion).
▪ The deeper parts of the auricle are supplied by the vagus nerve [X] (the auricular branch) and the facial nerve [VII] (which sends a branch to the auricular branch of the vagus nerve [X]).

Question 6

Describe the anatomy of the external acoustic meatus

Answer 6

The external acoustic meatus extends from the deepest part of the concha to the tympanic membrane (eardrum), a distance of approximately 1 inch (2.5 cm) ( Fig. 8.116 ). Its walls consist of cartilage and bone. The lateral one-third is formed from cartilaginous extensions from some of the auricular cartilages and the medial two-thirds is a bony tunnel in the temporal bone.
Throughout its length the external acoustic meatus is covered with skin, some of which contains hair and modified sweat glands producing cerumen (earwax). Its diameter varies, being wider laterally and narrow medially.

Question 7

Describe the course of the external acoustic meatus

Answer 7

The external acoustic meatus does not follow a straight course. From the external opening it passes upward in an anterior direction, then turns slightly posteriorly still passing upward, and finally, turns again in an anterior direction with a slight descent. For examination purposes, observation of the external acoustic meatus and tympanic membrane can be improved by pulling the ear superiorly, posteriorly, and slightly laterally.

Question 8

Describe the innervation of the EAM

Answer 8

Sensory innervation of the external acoustic meatus is from several of the cranial nerves. The major sensory input travels through branches of the auriculotemporal nerve, a branch of the mandibular nerve [V 3 ] (anterior and superior walls), and in the auricular branch of the vagus nerve [X] (posterior and inferior walls). A minor sensory input may also come from a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X].

Question 9

What is the tympanic membrane

Answer 9

The tympanic membrane separates the external acoustic meatus from the middle ear ( Figs. 8.117 and 8.118 ). It is at an angle, sloping medially from top to bottom and posteriorly to anteriorly. Its lateral surface therefore faces inferiorly and anteriorly. It consists of a connective tissue core lined with skin on the outside and mucous membrane on the inside.

Question 10

Describe the anatomy of the tympanic membrane

Answer 10

Around the periphery of the tympanic membrane a fibrocartilaginous ring attaches it to the tympanic part of the temporal bone. At its center, a concavity is produced by the attachment on its internal surface of the lower end of the handle of the malleus , part of the malleus bone in the middle ear. This point of attachment is the umbo of the tympanic membrane .

Anteroinferior to the umbo of the tympanic membrane a bright reflection of light, referred to as the cone of light, is usually visible when examining the tympanic membrane with an otoscope.

Superior to the umbo in an anterior direction is the attachment of the rest of the handle of the malleus ( Fig. 8.118 ). At the most superior extent of this line of attachment a small bulge in the membrane marks the position of the lateral process of the malleus as it projects against the internal surface of the tympanic membrane. Extending away from this elevation, on the internal surface of the membrane, are the anterior and posterior malleolar folds . Superior to these folds the tympanic membrane is thin and slack (the pars flaccida ), whereas the rest of the membrane is thick and taut (the pars tensa ).

Question 11

Describe innervation of the tympanic membrane

Answer 11

Innervation of the external and internal surfaces of the tympanic membrane is by several cranial nerves:

▪ Sensory innervation of the skin on the outer surface of the tympanic membrane is primarily by the auriculotemporal nerve, a branch of the mandibular nerve [V 3 ] with additional participation of the auricular branch of the vagus nerve [X], a small contribution by a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X], and possibly a contribution from the glossopharyngeal nerve [IX].
▪ Sensory innervation of the mucous membrane on the inner surface of the tympanic membrane is carried entirely by the glossopharyngeal [IX] nerve.

Question 12

Describe ottis media

Answer 12

The eustachian tube links the middle ear and pharynx and balances the pressure between the outer and middle ear. Colds and allergies, particularly in children, can result in swelling of the lining of the eustachian tube, which can then impair normal drainage of fluid from the middle ear. The fluid then builds up behind the tympanic membrane, providing an attractive environment for bacteria and viruses to grow and cause otitis media. Left untreated, otitis media can lead to perforation of the tympanic membrane, hearing loss, meningitis, and brain abscess.

Question 13

Describe examination of the external ear

Answer 13

The external ear is easily examined. The external acoustic meatus and the tympanic membrane require otoscopic examination ( Fig. 8.118B ). An otoscope is a device through which light can be shone and the image magnified to inspect the external acoustic meatus and the tympanic membrane.

The examination begins by grasping the posterosuperior aspect of the ear and gently retracting it to straighten the external auditory meatus. The normal tympanic membrane is relatively translucent and has a gray–reddish tinge. The handle of the malleus is visible near the center of the membrane. In the 5 o’clock position a cone of light is always demonstrated.

Question 14

Describe examination of the middle and inner ear

Answer 14

The middle ear is investigated by CT and MRI to visualize the malleus, incus, and stapes. The relationship of these bones to the middle ear cavity is determined and any masses identified.

The inner ear is also assessed by CT and MRI.

Question 15

Describe tympanic membrane perforation

Answer 15

Although perforation of the tympanic membrane (eardrum) has many causes, trauma and infection are the most common.

Ruptures of the tympanic membrane tend to heal spontaneously, but surgical intervention may be necessary if the rupture is large.

Occasionally, it may be necessary to enter the middle ear through the tympanic membrane. Because the chorda tympani runs in the upper one-third of the tympanic membrane, incisions are always below this level. The richer blood supply to the posterior aspect of the tympanic membrane determines the standard surgical approach in the posteroinferior aspect.

Otitis media (infection of the middle ear) is common and can lead to perforation of the tympanic membrane. The infection can usually be treated with antibiotics. If the infection persists, the chronic inflammatory change may damage the ossicular chain and other structures within the middle ear to produce deafness.

Question 16

Summarise the middle ear

Answer 16

The middle ear is an air-filled, mucous membrane–lined space in the temporal bone between the tympanic membrane laterally and the lateral wall of the internal ear medially. It is described as consisting of two parts ( Fig. 8.119 ):

▪ the tympanic cavity immediately adjacent to the tympanic membrane, and
▪ the epitympanic recess superiorly.

Question 17

Summarise the anatomy of the middle ear

Answer 17

The middle ear communicates with the mastoid area posteriorly and the nasopharynx (via the pharyngotympanic tube) anteriorly. Its basic function is to transmit vibrations of the tympanic membrane across the cavity of the middle ear to the internal ear. It accomplishes this through three interconnected but movable bones that bridge the space between the tympanic membrane and the internal ear. These bones are the malleus (connected to the tympanic membrane), the incus (connected to the malleus by a synovial joint), and the stapes (connected to the incus by a synovial joint, and attached to the lateral wall of the internal ear at the oval window).

Question 18

Describe the roof and floor of the middle ear

Answer 18

Tegmental wall
The tegmental wall (roof) of the middle ear consists of a thin layer of bone, which separates the middle ear from the middle cranial fossa. This layer of bone is the tegmen tympani on the anterior surface of the petrous part of the temporal bone.

Jugular wall
The jugular wall (floor) of the middle ear consists of a thin layer of bone that separates it from the internal jugular vein. Occasionally, the floor is thickened by the presence of mastoid air cells.

Near the medial border of the floor is a small aperture, through which the tympanic branch from the glossopharyngeal nerve [IX] enters the middle ear.

Question 19

Describe the lateral wall of the middle ear

Answer 19

Membranous wall
The membranous (lateral) wall of the middle ear consists almost entirely of the tympanic membrane, but because the tympanic membrane does not extend superiorly into the epitympanic recess, the upper part of the membranous wall of the middle ear is the bony lateral wall of the epitympanic recess.

Question 20

Describe the posterior wall of the middle ear

Answer 20

The mastoid (posterior) wall of the middle ear is only partially complete. The lower part of this wall consists of a bony partition between the tympanic cavity and mastoid air cells. Superiorly, the epitympanic recess is continuous with the aditus to the mastoid antrum
Associated with the mastoid wall are:

▪ the pyramidal eminence, a small elevation through which the tendon of the stapedius muscle enters the middle ear; and
▪ the opening through which the chorda tympani nerve, a branch of the facial nerve [VII], enters the middle ear.

Question 21

Describe the anterior wall of the middle ear

Answer 21

The anterior wall of the middle ear is only partially complete. The lower part consists of a thin layer of bone that separates the tympanic cavity from the internal carotid artery. Superiorly, the wall is deficient because of the presence of:

▪ a large opening for the entrance of the pharyngotympanic tube into the middle ear, and
▪ a smaller opening for the canal containing the tensor tympani muscle.
The foramen for the exit of the chorda tympani nerve from the middle ear is also associated with this wall

Question 22

Describe the anatomy of the medial wall of the middle ear

Answer 22

The labyrinthine (medial) wall of the middle ear is also the lateral wall of the internal ear. A prominent structure on this wall is a rounded bulge (the promontory ) produced by the basal coil of the cochlea , which is an internal ear structure involved with hearing ( Fig. 8.120 ).

Associated with the mucous membrane covering the promontory is a plexus of nerves (the tympanic plexus ), which consists primarily of contributions from the tympanic branch of the glossopharyngeal nerve [IX] and branches from the internal carotid plexus. It supplies the mucous membrane of the middle ear, the mastoid area, and the pharyngotympanic tube.

Additionally, a branch of the tympanic plexus (the lesser petrosal nerve) leaves the promontory and the middle ear, travels across the anterior surface of the petrous part of the temporal bone, and leaves the middle cranial fossa through the foramen ovale to enter the otic ganglion. Other structures associated with the labyrinthine wall are two openings, the oval and round windows, and two prominent elevation

Question 23

Describe the key features of the medial wall of the middle ear

Answer 23

▪ The oval window is posterosuperior to the promontory, is the point of attachment for the base of the stapes ( footplate ), and ends the chain of bones that transfer vibrations initiated by the tympanic membrane to the cochlea of the internal ear.
▪ The round window is posteroinferior to the promontory.
▪ Posterior and superior to the oval window on the medial wall is the prominence of the facial canal , which is a ridge of bone produced by the facial nerve [VII] in its canal as it passes through the temporal bone.
▪ Just above and posterior to the prominence of the facial canal is a broader ridge of bone ( prominence of the lateral semicircular canal ) produced by the lateral semicircular canal, which is a structure involved in detecting motion.

Question 24

Describe the key features of the mastoid area of the middle ear

Answer 24

Posterior to the epitympanic recess of the middle ear is the aditus to the mastoid antrum, which is the opening to the mastoid antrum ( Fig. 8.121 ).

The mastoid antrum is a cavity continuous with collections of air-filled spaces (the mastoid cells ), throughout the mastoid part of the temporal bone, including the mastoid process. The mastoid antrum is separated from the middle cranial fossa above by only the thin tegmen tympani.

The mucous membrane lining the mastoid air cells is continuous with the mucous membrane throughout the middle ear. Therefore infections in the middle ear can easily spread into the mastoid area.

Question 25

Describe the anatomy of the pharyngotympanic tube

Answer 25

The pharyngotympanic tube connects the middle ear with the nasopharynx ( Fig. 8.122 ) and equalizes pressure on both sides of the tympanic membrane. Its opening in the middle ear is on the anterior wall, and from here it extends forward, medially, and downward to enter the nasopharynx just posterior to the inferior meatus of the nasal cavity. It consists of:

▪ a bony part (the one-third nearest the middle ear); and
▪ a cartilaginous part (the remaining two-thirds).

The opening of the bony part is clearly visible on the inferior surface of the skull at the junction of the squamous and petrous parts of the temporal bone immediately posterior to the foramen ovale and foramen spinosum.

Question 26

Describe the innervation of the pharyngotympanic tube

Answer 26

Innervation of the mucous membrane lining the pharyngotympanic tube is primarily from the tympanic plexus because it is continuous with the mucous membrane lining the tympanic cavity, the internal surface of the tympanic membrane, and the mastoid antrum and mastoid cells. This plexus receives its major contribution from the tympanic nerve, a branch of the glossopharyngeal nerve [IX].

Question 27

Summarise the auditory ossicles

Answer 27

The bones of the middle ear consist of the malleus, incus, and stapes. They form an osseous chain across the middle ear from the tympanic membrane to the oval window of the internal ear
Muscles associated with the auditory ossicles modulate movement during the transmission of vibrations.

Question 28

Describe the malleus

Answer 28

The malleus is the largest of the auditory ossicles and is attached to the tympanic membrane. Identifiable parts include the head of the malleus , neck of the malleus , anterior and lateral processes , and handle of the malleus ( Fig. 8.123 ). The head of the malleus is the rounded upper part of the malleus in the epitympanic recess. Its posterior surface articulates with the incus.

Inferior to the head of the malleus is the constricted neck of the malleus, and below this are the anterior and lateral processes:

▪ The anterior process is attached to the anterior wall of the middle ear by a ligament.
▪ The lateral process is attached to the anterior and posterior malleolar folds of the tympanic membrane.
The downward extension of the malleus, below the anterior and lateral processes, is the handle of the malleus, which is attached to the tympanic membrane.

Question 29

Describe the incus

Answer 29

The second bone in the series of auditory ossicles is the incus. It consists of the body of the incus and long and short limbs ( Fig. 8.123 ):

▪ The enlarged body of the incus articulates with the head of the malleus and is in the epitympanic recess.
▪ The long limb extends downward from the body, paralleling the handle of the malleus, and ends by bending medially to articulate with the stapes.
▪ The short limb extends posteriorly and is attached by a ligament to the upper posterior wall of the middle ear.

Question 30

Describe the stapes

Answer 30

The stapes is the most medial bone in the osseous chain and is attached to the oval window. It consists of the head of the stapes , anterior and posterior limbs , and the base of the stapes ( Fig. 8.123 ):

▪ The head of the stapes is directed laterally and articulates with the long process of the incus.
▪ The two limbs separate from each other and attach to the oval base.
▪ The base of the stapes fits into the oval window on the labyrinthine wall of the middle ear.

Question 31

Describe the tensor tympani

Answer 31

The tensor tympani muscle lies in a bony canal above the pharyngotympanic tube. It originates from the cartilaginous part of the pharyngotympanic tube, the greater wing of the sphenoid, and its own bony canal, and passes through its canal in a posterior direction, ending in a rounded tendon that inserts into the upper part of the handle of the malleus.

Innervation of the tensor tympani is by a branch from the mandibular nerve [V 3 ].

Contraction of the tensor tympani pulls the handle of the malleus medially. This tenses the tympanic membrane, reducing the force of vibrations in response to loud noises.

Question 32

Describe the stapedius

Answer 32

The stapedius muscle is a very small muscle that originates from inside the pyramidal eminence, which is a small projection on the mastoid wall of the middle ear ( Fig. 8.124 ). Its tendon emerges from the apex of the pyramidal eminence and passes forward to attach to the posterior surface of the neck of the stapes.

The stapedius is innervated by a branch from the facial nerve [VII].

Contraction of the stapedius muscle, usually in response to loud noises, pulls the stapes posteriorly and prevents excessive oscillation

Question 33

Summarise the anatomy of the internal ear

Answer 33

The internal ear consists of a series of bony cavities (the bony labyrinth ) and membranous ducts and sacs (the membranous labyrinth ) within these cavities. All these structures are in the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially

Question 34

Summarise the different parts of the internal ear

Answer 34

The bony labyrinth consists of the vestibule , three semicircular canals , and the cochlea ( Fig. 8.128 ). These bony cavities are lined with periosteum and contain a clear fluid (the perilymph ).

Suspended within the perilymph but not filling all spaces of the bony labyrinth is the membranous labyrinth, which consists of the semicircular ducts , the cochlear duct , and two sacs (the utricle and the saccule ). These membranous spaces are filled with endolymph

Question 35

Summarise the function of the structures in the internal ear

Answer 35

The structures in the internal ear convey information to the brain about balance and hearing:

▪ The cochlear duct is the organ of hearing.
▪ The semicircular ducts, utricle, and saccule are the organs of balance.
The nerve responsible for these functions is the vestibulocochlear nerve [VIII], which divides into vestibular (balance) and cochlear (hearing) parts after entering the internal acoustic meatus

Question 36

Describe the anatomy of the bony labyrinth

Answer 36

The vestibule, which contains the oval window in its lateral wall, is the central part of the bony labyrinth ( Fig. 8.129 ). It communicates anteriorly with the cochlea and posterosuperiorly with the semicircular canals.
A narrow canal (the vestibular aqueduct ) leaves the vestibule, and passes through the temporal bone to open on the posterior surface of the petrous part of the temporal bone.

Question 37

Where is the cochlea found

Answer 37

Projecting in an anterior direction from the vestibule is the cochlea, which is a bony structure that twists on itself two and one-half to two and three-quarter times around a central column of bone (the modiolus ). This arrangement produces a cone-shaped structure with a base of the cochlea that faces posteromedially and an apex that faces anterolaterally ( Fig. 8.130 ). This positions the wide base of the modiolus near the internal acoustic meatus, where it is entered by branches of the cochlear part of the vestibulocochlear nerve [VIII].

Question 38

Describe the anatomy of the cochlea

Answer 38

Extending laterally throughout the length of the modiolus is a thin lamina of bone (the lamina of the modiolus , or spiral lamina ). Circling around the modiolus, and held in a central position by its attachment to the lamina of the modiolus, is the cochlear duct, which is a component of the membranous labyrinth.

Attached peripherally to the outer wall of the cochlea, the cochlear duct creates two canals (the scala vestibuli and the scala tympani ), which extend throughout the cochlea and are continuous with each other at the apex through a narrow slit (the helicotrema ):

▪ The scala vestibuli is continuous with the vestibule.
▪ The scala tympani is separated from the middle ear by the secondary tympanic membrane covering the round window

Question 39

What is the cochlea canaliculus

Answer 39

Finally, near the round window is a small channel (the cochlear canaliculus ), which passes through the temporal bone and opens on its inferior surface into the posterior cranial fossa. This provides a connection between the perilymph-containing cochlea and the subarachnoid space

Question 40

Summarise the membranous labyrinth

Answer 40

The membranous labyrinth is a continuous system of ducts and sacs within the bony labyrinth. It is filled with endolymph and separated from the periosteum that covers the walls of the bony labyrinth by perilymph.

Consisting of two sacs (the utricle and the saccule) and four ducts (the three semicircular ducts and the cochlear duct), the membranous labyrinth has unique functions related to balance and hearing:

▪ The utricle, saccule, and three semicircular ducts are part of the vestibular apparatus (i.e., organs of balance).
▪ The cochlear duct is the organ of hearing.
The general organization of the parts of the membranous labyrinth ( Fig. 8.131 ) places:

▪ the cochlear duct within the cochlea of the bony labyrinth, anteriorly,
▪ the three semicircular ducts within the three semicircular canals of the bony labyrinth, posteriorly, and
▪ the saccule and utricle within the vestibule of the bony labyrinth, in the middle.

Question 41

Summarise where the facial nerve emerges and its functions

Answer 41

Lateral surface of brainstem between pons and medulla
Motor (large)
Muscles of facial expression, stapedius, digastric (posterior belly), stylohyoid.
Sensory (smaller – intermediate nerve)
Taste (ant 2/3 tongue), parasympathetic (lacrimal glands, mucous glands of nasal cavity, hard and soft palates, sublingual and submandibular glands).
General sensation from external acoustic meatus and deeper parts of auricle.

Question 42

Describe the passage of the facial nerve through the IAM

Answer 42

The facial nerve [VII] is closely associated with the vestibulocochlear nerve [VIII] as it enters the internal acoustic meatus of the temporal bone. Traveling through the temporal bone, its path and several of its branches are directly related to the internal and middle ears.

The facial nerve [VII] enters the internal acoustic meatus in the petrous part of the temporal bone ( Fig. 8.133A ). The vestibulocochlear nerve and the labyrinthine artery accompany it.

Question 43

What happens to the facial nerve at the distal end of the IAM

Answer 43

At the distal end of the internal acoustic meatus, the facial nerve [VII] enters the facial canal and continues laterally between the internal and middle ears. At this point the facial nerve [VII] enlarges and bends posteriorly and laterally. The enlargement is the sensory geniculate ganglion . As the facial canal continues, the facial nerve [VII] turns sharply downward, and running in an almost vertical direction, it exits the skull through the stylomastoid foramen

Question 44

Describe the greater petrosal branch of the facial nerve

Answer 44

At the geniculate ganglion, the facial nerve [VII] gives off the greater petrosal nerve ( Fig. 8.133A ). This is the first branch of the facial nerve [VII]. The greater petrosal nerve leaves the geniculate ganglion, travels anteromedially through the temporal bone, and emerges through the hiatus for the greater petrosal nerve on the anterior surface of the petrous part of the temporal bone (see Fig. 8.126 ). The greater petrosal nerve carries preganglionic parasympathetic fibers to the pterygopalatine ganglion.

Continuing beyond the bend, the position of the facial nerve [VII] is indicated on the medial wall of the middle ear by a bulge

Question 45

Describe the other branches of the facial nerve

Answer 45

Near the beginning of its vertical descent, the facial nerve [VII] gives off a small branch, the nerve to the stapedius ( Fig. 8.133 ), which innervates the stapedius muscle, and just before it exits the skull the facial nerve [VII] gives off the chorda tympani nerve.

The chorda tympani does not immediately exit the temporal bone, but ascends to enter the middle ear through its posterior wall, passing near the upper aspect of the tympanic membrane between the malleus and incus ( Fig. 8.133B ). It then exits the middle ear through a canal leading to the petrotympanic fissure and exits the skull through this fissure to join the lingual nerve in the infratemporal fossa.

Question 46

What is the role of the greater petrosal nerve

Answer 46

Lacrimal glands, mucous glands of nasal cavity, hard and soft palates

Question 47

What is the role of the chordates tympani

Answer 47

Taste from anterior 2/3 tongue, submandibular and sublingual glands