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Semester II - GHD > Ears > Flashcards

Ears Flashcards

1
Q

What’s the role of the Cochlea?

A

Hearing (auditory)

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2
Q

What’s the role of the Semicircular canals?

A

Balance (vestibular)

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3
Q

What are the anatomical divisions of the ear?

A
  1. External (outer)
  2. Middle
  3. Inner (auditory apparatus aka cochlea)
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4
Q

What are the features of the external ear?

A

Auricle = collects the sound

External auditory meatus + canal = the opening of the auricle where the longitudinal sound waves funnels though to the tympanic membrane

Lateral surface of the tympanic membrane = possesses hearing function

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5
Q

What are the features of the Middle ear?

A

Medial surface of tympanic membrane = facial and corda tympani nerve located nearby

Tympanic cavity = middle ear

Ossicles = smallest bonds which transmit sound waves energy and vibrate - convert sound to mechanical energy

Pharyngotympanic (auditory) tube = hearing function + connects to nasopharynx

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6
Q

What are the features of the Inner ear?

A

Auditory apparatus/cochlea = picks up the mechanical energy and transfers to fluids - stimulate nerves - superior temporal nerve

Vestibular apparatus/semicircular canals = orientated in the 3 dimensions we perceive and aid balance

Internal auditory meatus

Vestibulocochlear nearve (CN VIII)

Oval + round window (hearing + balance function) = windows through which the sound travels middle to inner ear + transfers waves back into the middle ear to dissipate energy in the inner ear

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7
Q

What are the features of the External auditory canal?

A

4cm long

Lateral 1/3: elastic cartilage hair follicles, sweat + sebaceous glands, ceruminous glands = (cerumen/wax)

Medial 2/3: Bone lined with stratified squamous epithelium

S-shaped

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8
Q

What’s the Tympanic membrane and what are its featrues?

A

Ear Drum

Surface forms a dome into the middle ear (umbo)

Lateral = stratified squamous epithelium
Medial = mucous membrane

Chorda tympani run from posterior to anterior across tympanic membrane + passes between malleus and incus

Malleus (handle) attaches to medial surface

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9
Q

Where does the Chordi Tympani run to?

A

Sensory nerve for tongue (taste) and sublingual salivary glands

Ear infection can cause nerve irritation or damage - symptom is metallic taste in mouth

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10
Q

What happens when the tympanic membrane vibrates?

A
  1. Sound waves cause Malleus then incus then staps to vibrate (connected by synovial joints)

Their joint capacity decreases overtime = CONDUCTION DEAFNESS

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11
Q

What’s the Middle ear also called?

A

Tympanic Cavity

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12
Q

What’s the roof of the Tympanic cavity?

A

Petrous temporal bone - space below is the EPITYMPANIC RECESS

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13
Q

What’s the significance of the Epitympanic Recess?

A

Connected to the mastoid air cells via the Aditus ad Antrum

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14
Q

What’s the function of the mastoid air cells?

A

Air cell system, in combination with the continuous blood flow through the adjacent large vessels, makes up a compound functional unit that serves to protect the sensitive vestibular part of the inner ear from inadequate stimulation by external temperature changes

&

Pressure Regulator

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15
Q

What are the features of the Tympanic Cavities Anterior wall?

A
  • Connected to the auditory tube - connects the middle ear with Nasopharynx = equilibrates pressure on either side of the tympanic membrane and allows proper drainage of middle ear
  • Tensor Tympani muscle: Tenses tympanic membrane and helps dampen sound vibrations – Trigeminal Nerve V3 mandibular – inserts on handle of Malleus
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16
Q

What are the features of the Tympanic Cavities Posterior wall?

A
  • Facial canal: contains facial nerve – passes superoinferiorly immediately posterior to middle ear until it terminates at Stylomastoid foramen
  • Mastoid antrum
  • PYRAMID: Hollow projection from posterior wall; contains tendon of Stapedius muscle
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17
Q

What’s the function of Stapedius muscle?

A

Dampens excessive Stapes sound vibrations

Innervation: Facial Nerve (CN VII) Stapedius branch

  • Originates from the Pyramid on the posterior wall of tympanic cavity
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18
Q

What are the features of the Tympanic Cavities Lateral wall?

A
  • Separates middle and external ear - mainly by the Tympanic membrane with Malleus attached to the membrane at the Umbo
  • Chorda Tympani Nerve: Runs along the tympani membrane and Malleus until it exits through Petrotympanic fissure
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19
Q

What is the Chorda Tympani?

A

No function in the ear; merely transverses through

  • Arises from the mastoid segment of the facial nerve, carrying afferent special sensation from the anterior two-thirds of the tongue via the lingual nerve, as well as efferent parasympathetic secretomotor innervation to the submandibular and sublingual glands.
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20
Q

What are the features of the Tympanic Cavities Medial wall?

A

Separates middle ear from inner ear

  • Protuberance created by Cochlea, bulges for semi-circular and facial canals + round and oval windows
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21
Q

What are the features of the Tympanic Cavity floor?

A
  • Thin bone plate separating cavity from JUGULAR FORAMEN (interal jugular vein) and CAROTID CANAL (Internal carotid artery + sympathetic nerve plexus)
  • Tympanic Canaliculus: Allows tympanic branch of glossopharyngeal nerve to enter the middle ear

Opening of Auditory tube

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22
Q

What’s the significance of the Tympanic branch of Glossopharyngeal nerve?

A

The tympanic nerve arises as the nerve traverses the jugular foramen. It penetrates the temporal bone and enters the cavity of the middle ear. Here, it forms the tympanic plexus – a network of nerves that provide sensory innervation to the middle ear, internal surface of the tympanic membrane and Eustachian tube.

23
Q

What’s the significance Acute Otitis Media?

A

Inflammation of the middle ear cavity

  • Interference of Chorda Tympani Nerve = controls taste in the rear two-thirds of the tongue - distorted taste or parageusia
24
Q

What’s the significance of the Mastoid Antrum?

A

Mastoid part of temporal bone leading from posterior wall of middle ear – communicating posteriorly with the mastoid cells and anteriorly with the epitympanic recess of the middle ear via the aditus to mastoid antrum

Possible pathway for infection spread: - from nose/mouth via pharyngotympanic tube to middle ear -> aditus -> antrum -> mastoid air cells, cerebellum, temporal lobe -> meningitis/brain abscess.

25
Q

What’s the pathway of Chorda Tympani nerve?

A

Temporal:

  • From facial nerve and passes to posterior wall of tympanic cavity
  • Crosses medial surface of tympanic membrane handle of malleus
  • Leave tympanic cavity via Petrotympanic fissure in skull

Extratemporal:

  • Joins lingual nerve in infratemporal fossa
  • Parasympathetic secretomotor fibres to sublingual and submandibular salivary glands
  • Sensory taste fibres to anterior 2/3 of tongue
26
Q

What are the Ossicles?

A

Pass vibrations from the tympanic membrane to the oval window of inner ear

  • Plane synovial joints but these degrade over time = Conduction deafness
    1. Malleus (Hammer): Attaches into the handle of medial surface of tympanic membrane
    2. Incus (Anvil): Articulates with the head of the Malleus and the head f the Stapes
    3. Stapes (Stirrup): Articulates with process of the Incus and the Oval window (Stapedius m. attaches to the neck of the Stapes)
27
Q

What’s found in the middle ear?

A

Semi-circular canals (balance)

Cochlea (hearing)

Oval + round window

28
Q

What the Labryinths within the Inner ear?

A
  • Membranous labyrinth within a bony labyrinth
29
Q

What’s the Bony labyrinth?

A
  • System of canals filled with perilymph (like extra-cellular fluid)

+ Anterior = Cochlea
+ Centre = Vestibule
+ Posterior = Semi-circular canals

30
Q

What’s the Membranous labyrinth?

A
  • Continuous system of ducts and sacs lining the bony labyrinth
  • Suspended in Perilymph but contains Endolymph (like intra-cellular fluid)

+ Cochlear duct: Starts at cochlea apex and ends where it joins saccule via ductus reuniens + triangular shape

+ Saccule: Small structure within Vestibule of bony labyrinth and connected utricle + contain sensory receptors (Maculae)

+ Utricle: Located in Vestibule, contain sensory receptors (Maculae)

+ Semi-circular ducts: Located within semi-circular canals and open into the Utricle via 5 openings + Sensory receptors called Cristae are located in Ampullae (bulges) of Semi-circular ducts

31
Q

What is Maculae?

A

Sensory receptor which respond to pull of gravity and report on changes of head position

32
Q

What is an Ampulla?

A

Houses a equilibrium sensing area called the ampullary crest – responds to rotational movements of head

  • Sensors record movements of the endolymph in the plane of the duct
33
Q

What are Hair cells and Ampullary Cupula?

A

Located in Ampullae

  • Cupula is gelatinous
  • Cupula has hair cells embedded within it
  1. Head rotation causes lagged endolymph movement = cupula is deflected opposite the direction of head movement
  2. As endolymph pushes the cupula, the sterocilia are bent as well simulating the hair cells
  3. Hair cells stimulation transmits the corresponding signals to the brain via the Vestibulocohlear Nerve (CN VIII)
34
Q

What’s the Cochlea?

A

Snail-shaped spiral bony chamber

  • Spiral turns around the bony Modiolus
35
Q

What’s the process of hearing?

A
  1. Sound waves arrive at the tympanic membrane
  2. Movement of the tympanic membrane causes displacement of auditory ossicles
  3. Movement of Stapes at the oval window establishes pressure waves in the perilymph of the scala vestibuli
  4. Pressure waves distort the basilar mebrane on their way to the round window of the Scala Tympani
    - High frequency sounds (very short wavelength) vibrate the basilar membrane near the oval window
    - Lower frequency sounds (longer wavelength) the farther from the oval window is the maximum distortion = information about frequency is translated into information about position along the basilar membrane
  5. Vibration of the basilar membrane causes hair cells to vibrate against the tectorial membrane
    - Vibrations in affected regions of the basilar membrane move hair cells against the tectorial reocilia –> opens ion channels in the plasma membranes of the hair cells = inrush of ions depolarises the hair cells –> release of neurotransmitter = sensory neurons stimulation
  6. Information about he region and the intensity of stimulation is relayed to the CNS over the Cochlear branch of CNVIII
    - Cell bodies of the bipolar sensory neurons that monitor cochlear hair cells are located at the center of the bony cochlea in the SPIRAL GANGLION
    + Then, information is carried by cochlear branch of CN VIII to cochlear nuclei of Medulla oblongata for distribution in brain.
36
Q

What are the Auditory Pathways?

A
  1. Stimulation of hair cells activates sensory neurons whose cell bodies are in the adjacent spiral ganglion. The afferent fibres of these neurons form the COCHLEAR BRANCH of VESTIBULOCOCHLEAR NERVE (CN VIII) - These axons enter medulla oblongata, then synapse COCHLEAR NUCLEUS
  2. Information then ascends to SUPERIOR OLIVARY NUCLEUS of the Pons and both INFERIOR COLLICULI of the mid-brain
  3. Mid-brain processing centre coordinates a no. of responses to acoustic stimuli including auditory reflexes involving skeletal muscles of the head, face and trunk
  4. These reflexes automatically change position of your head in response to a sudden load noise - before reaching cerebral cortex and your awareness, ascending auditory sensations synapse in the medial geniculate nucleus of the thalamus
  5. Projections then deliver the information to the auditory cortex of the temporal lobe
  6. Information travels to the cortex over labeled lines: High frequency sounds activate one portion of the cortex
    Low frequency sounds another = auditory cortex maps the cochlea
37
Q

What’s the range (Hz) that humans can detect?

A

20 - 20,000 Hz

38
Q

What are the safe amplitudes (dB) for humans?

A

1 - 80 dB

39
Q

Overview of hearing

A

In cross section, the cochlea can be seen to be separated into 3 main canals: the tympanic canal, the vestibular canal and the middle canal. The sound vibrations in the cochlear fluid are transmitted to a long thin membrane that separates the tympanic and vestibular canals, the basilar membrane. It broadens as it runs the length of the coiled cochlea. High pitch sounds maximally vibrate the thin basal (proximal) end, while low pitch sounds maximally vibrate the broader apical (distal) end. Movement of the basilar membrane causes displacement of the organ of corti, which is comprised of the sensory hair cells and their supporting cells, as well as auditory nerve endings that innervate the hair cells. The cilia of the hair cells are in contact with the overlying tectorial membrane. Each hair cell has 3 rows of cilia of progressively increasing length. Movement of the hair cells due to the vibration of the basilar membrane causes the hair cell cilia to move relative to the tectorial membrane. Displacement of the hair cells leads to increased or decreased firing of the auditory nerve endings, depending on the direction of movement of the cilia.

Reissner’s membrane separates the vestibular and middle canals

  • Fluid waves cause the basilar and tectorial membrane to flex  moves the hairs  creates action potential
40
Q

Overview of sound transmission

A
  1. Sound waves in the air strike the tympanic membrane
  2. Sound wave energy is transferred to bones (ossicles) of the middle ear, which vibrate
  3. The vibrations are transmitted via the oval window to the fluid within the vestibular duct and create a fluid wave within the cochlea
  4. The fluid waves push on the flexible membrane of the cochlear duct
  5. Sound waves are transmitted to the tympanic duct and dissipated back into air by the movement of the round window.
  6. Deformation of the cochlear duct causes the tectorial membrane to move and activate stereocilia of the hair cells.
41
Q

What’s Conductive deafness?

A

Defects in the conduction of sound to the inner ear - blockage of sounds reaching the transduction mechanism in the inner ear

42
Q

Name 5 causes of Conductive deafness?

A
  1. Wax buildup in the External acoustic meatus
  2. Blockage of eustachian tube
  3. Inflammation (otitis)
  4. Damage to eardrum - inability for Malleus to function correctly
  5. Osteoclerosis (bone growth)

Typically these are all

43
Q

What’s Sensorineural deafness?

A

Involves the transduction mechanism or conduction down the auditory nerve

44
Q

Name 6 causes of Sensorineural deafness?

A
  1. Hair cell damage in organ of Corti - can be due to endolymph fluid build up
  2. Meniere’s disease (increased endolymph - fluid surrounding hair cells)
  3. Trauma
  4. Ageing
  5. Infection
  6. Drugs
45
Q

What’s the problem with Sensorineural deafness?

A

If the hair cells are damaged then they cannot be regenerated

46
Q

What’s Nerve deafness?

A

Damage to the auditory nerve

47
Q

What is the cause of Nerve deafness?

A
  1. Trauma
  2. Age
  3. Infection
  4. Atherosclerosis (thickening of arterial walls can reduce blood flow to the nerve)
48
Q

What’s Tinnitus?

A

Ringing in the ears

  • Continuous or discontinuous
  • Degeneration of corti organ (mainly elderly)
  • Result of external or middle ear problems
  • Acoustic neuroma*
49
Q

What’s Hereditary deafness?

A

Wide-ranging impairment which can display:

  1. Profound congenital deafness
  2. Slowly-progressing, adult onset
50
Q

What’s Equilibrium?

A

State of balance that allows us to position our body in 3D space under normal gravitational conditions

  • It has 2 components:
    1. Dynamic = sensing the rotational movement of the head
    2. Static component that senses head displacement via linear acceleration and the associated gravitational changes
51
Q

How are rotational movements detected?

A

Hair cells found within the ampulla linked to the semicircular canals

52
Q

How are gravitational changes detected?

A

By otolith organs found within the maculae at the base of the semicircular canals

53
Q

How is Equilibrium balance maintained?

A

Hair cells in the fluid filled vestibular apparatus

+

Hair cells in the semicircular canals of the inner ear

54
Q

How do Cochlea hair cells detect rotation?

A
  1. Discharge rate in a hair cell afferent changes when the hairs are bent in opposite directions
  2. Rotation of the head displaces endolymph to bend hairs in either direction depending on the direction of rotation
  3. Head rotation increases the firing frequency in canals on one side and reduces in the other

This increase tells your brain which side you have rotated your head

Semester II - GHD (20 decks)

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