The Ear and Facial Nerve Flashcards Preview

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Flashcards in The Ear and Facial Nerve Deck (97):
1

Located within the pertrous portion of the temporal bone

The auditory and vestibular apparatus and the majority of the course of the facial nerve (CN VII)

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The ear is divided into what three portions?

External, middle, and inner

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Serves as the collector and conductor of sound waves

External ear

4

The external ear is composed of the

Pinna and External ear canal

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The external ear canal is derived from the

-Lined by ectoderm epithelium

First pharyngeal cleft

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The outer portion of the external ear is cartilaginous and the inner portion is

Bony

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Modified sweat glands in the skin of the external ear

Ceruminous glands

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Secrete cerumen (ear wax) which functions to keep the canal moist and to protect it from bacteria and infection

Ceruminous glands

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Derived from 6 swellings (hillocks) on the first and second pharyngeal arches that border the pharyngeal cleft

Auricle

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The canal leads to the

Tympanic membrane

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The tympanic membrane is derived from fusion of the

Ectoderm of first pharyngeal cleft and endoderm of first pharyngeal pouch

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Separates the external ear from the middle ear

Tympanic membrane

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The external ear receives MOST of its innervation from

CN V3

-also receives innervation from branches of CN VII, IX, and X

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Air filled cavity containing structures that allow it to serve as a conductor and amplifier of sound vibrations

Middle Ear (Tympanic cavity)

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What are the three ossicles within the middle ear?

Malleus, inus, and stapes

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Attached to the inner surface of the tympanic membrane

Malleus

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There are synovial joint connecting

Malleus to incus and incus to stapes

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The footplate of the stapes lies within the

Oval window of the inner ear

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The impingment of sound waveson the tympanic membrane causes the membrane to

Vibrte

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This in turn causes the ossicles to vibrate, which transmits the vibration to the

Inner ear

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The combination of the ratio of size of tympanic membrane to the size of the stapes footplate, and the shape and orientation of the ossicles result in amplification of approximately

30 dB

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this compensates for the loss of energy at the

Air/water interface of the inner ear

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The sensory receptors of the organ of Corti in the cochlea are in an

Aqueous environment

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What are the two muscles in the inner ear?

-reduce the amplitude of vibration that reaches the inner ear

Tensor tympani and stapedius

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The tensor tympani and stapedius reduce the amplitude of vibration that reaches the inner ear, which protects the

Cochlear hair cells

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A lesion of the facial nerve (VII) may cause

Hyperacusis

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And increased perception of loudness because of the loss of action of the stapedius

Hyperacusis

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The middle ear is connected to the nasopharynx by the

Auditory (Eustachian) tube

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Allows for equalization of air pressure between the middle ear and the environment

-provides the pathway for spread ofinfection from the pharynx to the middle ear

Auditory (Eustachian) tube

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The middle ear cavity is also continuous with the

Mastoid air cells

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A middle ear infection can spread to the

Pharnx or mastoid air cells

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The middle ear, auditory tube, and mastoid air cells are all derived from the

First pharyngeal pouch (lined by endodermal epithelium)

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The malleus, incus (neural crest) and tensor tympani (mesoderm) are derived from the

First pharyngeal arch

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The stapes (neural crest) and stapedius (mesoderm) are derived from the

Second pharyngeal arch

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The tensor tympani is innervated by

CN V3 (nerve of the first arch)

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The stapedius is innervated by

CN VII (nerve of the second arch)

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The mucosa of the middle ear cavity is innervated by

-also innervates mucosa of pharynx

CN IX (tympanic branch)

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Contains the organ for audition, the cochlea, and the organs for vestibular sensation

Inner ear

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What are the organs for vestibular sensation?

3 semicircle canls, utricle, and saccule

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Detect rotational movements of the head

-in the three planes of space and each is perpendicular to the other two

The 3 semicircle canals

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Detect translational movements of the head

Utricle and saccule

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Detects linear motion in a horizontal plane

Utricle

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Detects linear motion in a verticle plane

Saccule

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Within the cochlea is the cochlear duct, which contains the

Organ of Corti

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On the organ of corti is where we find the

Cochlear hair cells

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With agin, there is often a loss of hair cells beginning at the high frequency end of the cochlea, resulting in

Hearing loss (presbycusis)

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The cochlear duct is filled with

Endolymph

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The cochlear duct is surrounded by

Perilymph

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In contact with the footplate of the stapes at the oval window

Perilymph

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Vibration at the footplate of the stapes causes a vibratory wave through the perilymph, which in turn causes vibration of the

Organ of Corti

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This vibration is transduced by the hair cells to a neural impulse which is carried by the

Cochlear division of CN VIII

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Innervates the hair cells

Cochlear division of CN VIII

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Within the semicircular canals, the utricle and saccule are the maculae, which contains the

Vestibular hair cells

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The maculae also contians

Endolymph

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Movement of the head causes displacement of these hair cells, and this displacement is transduced into nerve impulses which are carried in the

Vestibular division of CN VIII (innervates the hair cells)

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The inner ear is derived from a thickening of the skin ectoderm called the

Otic placode

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Hearing losses may be categorized as

Conductive hearing loss or sensorineural hearing loss

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If there is a defect in the external or middle ear that prevents or diminishes the conduction of vibration to the inner ear, it is a

Conductive hearing loss

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A ruptured tympanic membrane, otosclerosis, dislocation of ossicular joints, or excessive cerumen in external ear canal are all examples of

Conductive hearing loss

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If there is a defect in the inner ear or neural pathway or neural pathway from the inner ear to the auditory cortex of the brain, we have a

Sensorineural hearing loss

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Damage to cochlear hear cells from overstimulation, aging or infection, or a lesion of CN VIII or the auditory pathways of the brain are examples of

Sensorineural hearing loss

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What is one way we test for sensorineural and conductive hearing loss?

Weber test

-tuning fork placed against the bone of the skull at the mid line. If sound is heard equally on both sides than things are normal

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If there is a sensorineural hearing loss on one side, then with the Weber test, the patient will perceive the sound as coming from the

Contralateral side (the normal side)

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The Weber test allows the clinician to bypass the conductive portion of the ear (external and middle ear) by having the vibration reach the inner ear bone by

Conduction

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With a Weber test. if there is a CONDUCTIVE hearing loss, what will we see?

Patient will perceive sound as coming from the side with the hearing loss

66

Ambiguous with regard to which type of hearing loss exists on which side

Weber test

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A vibrating tuning fork is initially placed on the patient’s mastoid process. The vibration is conducted to the patient’s inner ear by bone conduction

RInne test

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In the Rinne test, as the amplitude of the vibration decreases, the sound perceived by the patient decreases in volume. The patient is asked to tell the examiner when the sound can no longer be heard. At that point, the examiner moves the vibrating tuning fork to the outside of the

External ear canal

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If the patient reports that they can hear the sound again then they are normal, but if they can not hear the sound outside of the external ear, then they have a

Conductive hearing loss

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The Rinne test will detect

CONDUCTIVE hearing loss

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The facial nerve enters the temporal bone through the

Internal auditory meatus

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The facial nerve then passes across the top of the inner ear to reach the

Geniculate ganglion

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In the geniculate ganglion are found the cell bodies of the

General sensory and special sensory neurons of the facial nerve

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Because the geniculate ganglion is a sensory ganglion, it contains only sensory cell bodies and there are

No synapses in this ganglion

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Pass through the geniculate ganglion

Motor fibers (somatic and preganglionic parasympathetic) of facial nerve

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At the geniculate ganglion, the facial canal, which contains the facial nerve turns posteriorly (the genu) and then continues along the

Wall of the middle ear

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At the genu, the facial nerve gives rise to the

Greater petrosal nerve

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The greater petrosal nerve contains preganglionic parasympathetic fibers destined for the

Pterygopalatine ganglion

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Also contains special sensory taste fibers destined for the palate

Greater petrosal nerve

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As the facial nerve continues through the facial canal, it gives rise to the branches to the

Stapediues (somatic motor) and also the chorda tympani

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Contains special sensory taste fibers coming from the anterior 2/3 of the tongue

Chorda tympani

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The chorda tympani also contains preganglionic parasympathetic fibers destined for the

Submandibular ganglion (via the lingual nerve)

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The chorda tympani leaves the facial canal and passes through the middle ear cavity, passing BETWEEN the

Malleus and incus (to reach the petrotympanic fissure)

84

Does NOT innervate anything in the middle ear

Chorda tympani

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After exiting through the petrotympanic fissure, the chorda tympani enters the infratemporal fossa and joins the

Lingual nerve (branch of CN V3)

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Serves as the pathway to carry the sensory taste fibers to the anterior 2/3 of the tongue and to carry preganglionic parasympathetic fibers to the floos of the mouth where the submandibular ganglion is located

Lingual nerve

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The preganglionic parasympathetic fibers from the lingual nerve are headed to the

Submandibular ganglion

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The facial nerve leaves the temporal bone by exiting through the

Stylomastoid foramen (in the mandibular fossa)

89

After leaving through the stylomastoid foramen, the facial nerve gives off the

Posterior auricular branch

90

Provides sensory innervation behind the ear and somatic motor innervation to some skeletal muscle of the posterior portion of the scalp

Posterior auricular branch of facial nerve

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The facial nerve then passes through the parotid bed to reach and innervate the

Muscles of facial expression, the posterior belly of the digastric and the stylohyoid muscles

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Weakness or paralysis of facial muscles, loss of taste or sensation of the anterior 2/3 of the tongue, and decreased salivation are all symptoms of a

Facial nerve lesion

93

A major sign of a facial nerve lesion proximal to the geniculate ganglion is

Reduced lacrimation

94

A major sign of a facial nerve lesion between the geniculate ganglion and stapedius is

Hyperacusis

95

We would not expect lacrimation or hyperacusis, but we would expect all other symptoms with a lesion of the facial nerve between

Stapedius and chorda tympani

96

A lesion of the facial nerve between the chorda tympani and stylomastoid foramen would present with

Los of facial muscle function and sensory abnormality behind the ear

97

A lesion of the facial nerve within the parotid gland would only present with

Loss of facial muscle function

Decks in Structure and Function Test 1 Class (61):