Temporal Bone and Facial Nerve

Question 1

what are the components of the external ear?

Answer 1

auricle, external acoustic meatus, tympanic membrane

Question 2

what two ways does the tympanic membrane slope?

Answer 2

medially from superior to inferior
medially from posterior to anterior

Question 3

what is the middle ear and where is it located?

Answer 3

air filled chamber lined with a mucous memrane in the petrous part of the temporal bone between the tympanic membrane and lateral wall of internal ear

Question 4

what is the main job of the middle ear?

Answer 4

transmit movements of the tympanic membrane to the oval window via the ossicular chain

Question 5

what are the ear ossicles of the middle ear?

Answer 5

incus, stapes and malleus

Question 6

explain the steps of sound transmission

Answer 6

1. sound waves enter the external acoustic meatus and strike the tympanic membrane
2. the tympanic membrane vibrates setting off the ossicular chain
3. the stapes presses on the oval (vestibular) window generating pressure in the perilymph (fluid) of the cochlea
4. the receptor (hair) cells are stimulated and send impulses back to the brain via vestibulocochlear near cN VIII where they are interpreted as sound

Question 7

what muscles insert on two of the ossicles of the middle ear?

Answer 7

tensor tympani innervated by V3 (trigeminal)

stapedius innervated by VII (facial nerve)

Question 8

what do the tensor tympani and stapedius muscles control?

Answer 8

they control or dampen the movement of the ossicular chain and is particularly important with loud sounds to prevent damage to the very sensitive cochlea

Question 9

what is hyperacusis?

Answer 9

when there is paralysis of one or both of the muscles of the middle ear in which the perception of sounds in the ear are louder than normal

Question 10

what is conduction deafness and how is it caused?

Answer 10

a process that interferes with the normal movements of the ossicular chain which causes diminished ability of the ossicles to conduct sounds from the tympanic membrane to the internal ear

can occasionally be caused by obstruction of the external acoustic meatus

Question 11

what is sensorineural deafness?

Answer 11

any lesion in the receptor organ (hair cells) the vestibulocochlear nerve or its terminus in the brain (low pons)

Question 12

why are children more susceptible to middle ear infections?

Answer 12

their auditory tube tends to be shorter and more horizontally placed which permits infectious organisms an easier access point

Question 13

what is the nerve that supplies sensory innervation to the mucosa lining of the middle ear?

Answer 13

tympanic branch of the glossopharyngeal nerve (CN IX)

this is the nerve that is responsible for pain with ear infections

Question 14

middle ear infections can easily spread where? and produce what?

Answer 14

they can spread into the mastoid air cells to cause mastoiditis

they can produce middle cranial fossa or temporal lobe abscess

Question 15

where is the internal ear located and what does it contain ?

Answer 15

series of cavities in the petrous portion of the temporal bone between the medial wall of the ear and internal acoustic meatus

contains cochlea and semicircular canals fir hearing and equilibrium

Question 16

where do people with vertigo mostly have issues?

Answer 16

semicircular canals

Question 17

what are the paths of skeletomotor fibers of CN VII?

Answer 17

enters at the internal auditory meatus

a branch comes off and innervates the stapedius

exits at the stylomastoid foramen to innervate the muscles of facial expression (stylohyoid and posterior belly of digastric)

Question 18

what are the paths of secretomotor fibers of CN VII?

Answer 18

enters at internal auditory meatus

travels to the middle ear cavity and then becomes chorda tympani that synapses at submandibular ganglion and then travels to sublingual and submandibular gland

branch comes off and is named greater petrosal nerve that innervates the pterygoid canal, pterygopalatine ganglion and then the lacrimal gland

Question 19

what are the paths for the fibers of sensory taste for CN VII?

Answer 19

taste from anterior 2/3 of the tongue

courses up the chorda tympani

nerve cell bodies are found in the geniculate ganglion

exits at the internal auditory meatus

Question 20

what is the path of cutaneous sensation for CN VII?

Answer 20

sensation from skin over the mastoid process

nerve cell bodies found in geniculate ganglion

exits at internal auditory meatus

Question 21

a lesion in the facial canal at the stylomastoid foramen would cause what?

Answer 21

facial palsy

Question 22

a lesion in the facial canal above the stylomastoid foramen would cause what?

Answer 22

facial palsy, no taste in anterior 2/3 of tongue, no cutaneous sensation and deficits in the salivary glands in floor of mouth (dry mouth)

Question 23

a lesion below the geniculate in the facial canal would cause what?

Answer 23

facial palsy, no taste in anterior 2/3 of tongue, no cutaneous sensation and deficits in the salivary glands in floor of mouth (dry mouth) AND hyperacusis

Question 24

a lesion above the geniculate in the facial canal would cause what?

Answer 24

facial palsy, no taste in anterior 2/3 of tongue, no cutaneous sensation and deficits in the salivary glands in floor of mouth (dry mouth), hyperacusis AND dry eye and nasal cavity

Question 25

a lesion at the internal auditory meatus would cause what?

Answer 25

facial palsy, no taste in anterior 2/3 of tongue, no cutaneous sensation and deficits in the salivary glands in floor of mouth (dry mouth), hyperacusis, dry eye and nasal cavity AND loss of balance and hearing

Question 26

what two nerves enter at the interal auditory meatus ?

Answer 26

CN VII and CN VIII