Term
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Definition
Hearing and Balance (Vestibulocochlear Organ)
Hearing (Transformation of mechanical sound waves into nerve impulses)
Balance (Changes in fluid levels within inner ear) |
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Term
| Parts of the External Ear |
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Definition
Auricle or Pinna - “Ear”
External Acoustic Meatus - Canal connecting base of auricle to tympanic membrane (eardrum) |
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Term
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Definition
Funnel Shaped: Wide distally, Narrows to connection with external acoustic meatus
Mobile: Can be orientated towards sound
Superficial muscles |
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Term
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Definition
Determined by auricular cartilage
Variable stiffness
May maintain position of ear at all times |
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Term
| Cartilages of External Ears |
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Definition
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Term
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Definition
Tympanic cavity (contains but often referred to as tympanic bulla)
Tympanic Membrane
Auditory Ossicles
Auditory tube (Eustacian Tube) |
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Definition
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Term
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Definition
Divides External Acoustic Meatus from Middle Ear
Tilted
Surface area greater than cross section of meatus
Epidermal (outer) and mucosal (inner) covering
Fibrous attachment to tympanic ring of temporal bone
Medial surface attached to ossicles |
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Term
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Definition
Malleus (“Hammer”)
Incus (“Anvil”)
Stapes (“Stirrup”)
Handle/Manubrium of malleus attached to eardrum
Base of stapes inserts into vestibular window |
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Term
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Definition
Connects tympanic cavity to nasopharynx
Openings in lateral wall of nasopharynx
Runs in cartilage trough
Out-pouching in horses = Guttural Pouch
Usually collapsed
When open allows equalisation of pressure on either side of tympanic membrane
Allows drainage of material from tympanic cavity |
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Term
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Definition
Hearing - transformation of mechanical stimuli (sound) into nerve impulses
Organs of balance |
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Definition
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Term
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Definition
Maculae (otolith organs)
Crystals (statoconia, otoliths) adhere to sensory hairs
Determine position of head relative to gravity |
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Term
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Definition
Orientated at right angles
Anterior, Posterior and Lateral
Ampullae at one insertion into utriculus
Fluid moves with head movement |
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Term
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Definition
Central Chamber: Vestibule (Contains ultriculus and sacculus)
Semicircular Canals: Contain semicircular ducts
Cochlea: Contains cochlear duct, Spiral – resembles snail shell, Central osseous pyramid (modiolus) with canal running around and projecting spiral lamina |
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Term
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Definition
| Membrane from spiral lamina divides into three channels: Scala Vestibuli, Cochlear Duct, Scala Tympani |
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Term
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Definition
Vibrations at vestibular window (from stapes) and cochlear window
Transmitted through perilymphatic space
Causes vibration of basement membrane and movement of sensory cilia
Registered by neuroreceptors
Transmitted to vestibulocochlear nerve (VIII). |
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Term
| Nerve Supply to Inner Ear |
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Definition
Vestibulocochlear nerve CN VIII)
Divides into vestibular and cochlear parts at internal acoustic meatus
Vestibular – balance
Cochlear – hearing
Facial nerve (CN VII)
Stapedius m
Mandibular nerve (CN V)
Tensor tympani m |
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Term
| Relationship of nerves in the face |
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Definition
Facial nerve passes through inner and middle ears
Sympathetic supply to eye passes between tympanic bulla and petrous temporal bone
Both can be damaged by ear disease |
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Term
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Definition
External Ear:
Arterial: external carotid via caudal auricular
Venous: maxillary vein
Middle and Inner ear
Arterial: Occipital Artery, branching from external carotid |
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Term
| Diagnostic Tools for the Ear |
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Definition
Otoscope: Direct examination of external ear
Radiography: Widely available
Tympanic bulla superimposed on other skull structures
Advanced Imaging (CT/MRI): Clear imaging of inner and middle ear, Expensive |
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Term
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Definition
Inflammation or Infection of ear
Otitis Externa: External Ear
Otitis Media: Middle Ear
Otitis Interna: Inner Ear |
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Term
| Embryological Development of the Ear |
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Definition
External Ear: Ectoderm of 1st Branchial Groove
Middle Ear: Endoderm of 1st pharyngeal pouch
Inner Ear: Ectoderm lateral to hindbrain |
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Term
| Hearing Range of Animals (pitch) |
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Definition
Humans: 20 – 20,000 Hz
Dogs: 67 – 45,000
Cats: 45 – 64,000
Horse: 55 – 33,500
Elephant: 16 – 12,000
Chicken: 125 – 2000
Bat: 2000 – 110,000 |
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Term
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Definition
| Cochlea converts sound (pressure waves) into action potentials |
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