7 – Ear and Guttural Pouches Flashcards
Ear is a:
-vestibulocochlear organ
*both hearing and BALANCE
Middle and inner ear within:
-temporal bone
2 parts of external ear:
-auricles (pinna)
-cutaneous MARGINAL pouch (Henry’s pocket)
Auricles:
-visible part of ear
-in domestic animals, each can INDEPENDENTLY turn toward sound by auricular muscles
Auricular muscles:
-directly or indirectly (through SCUTIFORM cartilage) pull ear
-innervated by facial nerve (VII)
Cutaneous marginal pouch:
-in cat and some dog
-should be checked for parasites
Auricular cartilage:
-supports and shapes auricle
-PERFORATED to allow vessels across
-funnel-shaped (rolled up to channel sound)
Parts of auricular cartilage:
-tragus and antitragus cartilages
-intertragic and pretragic notches (incisures)
External acoustic meatus (EAM):
-ear canal
-passageway connecting pinna to ear drum
*7cm long in dog
EAM begins where:
-rolled up part of auricular cartilage narrows
EAM ends at:
-tympanic membrane (ear drum)
Dog and cat canal angles:
-like a hockey stick
>sharply turns ROSTRO-MEDIALLY
Otoscope in dog and cats:
-hard to do
-must straighten canal by pulling ear first caudally then ventrally
EAM lined by:
-skin with holocrine (sebaceous) and apocrine (ceruminous-earwax) glands
EAM parts:
-cartilaginous
-osseous
Cartilaginous part of EAM:
-rolled up part of auricular cartilage
-ANNULAR cartilage
Osseous part of EAM:
-PETROUS temporal bone
Middle ear: tympanic membrane
-separates external ear from CAVITY of middle ear
-stretched across lumen of body ear canal
Tympanic membrane SA:
*10x15mm
-SLANTED
>dorsal part more lateral than ventral part
*SA is larger than diameter of ear canal
Layers of tympanic membrane:
-outer surface continuous with EPIDERMIS of canal
-middle fibrous layer
-medial surface continuous with mucosa of tympanic cavity
Handle of malleolus is EMBEDDED:
-in medial surface of eardrum
-shines through
What pulls eardrum medially?
-tension by ossicles
Chorda tympani nerve:
-crosses MEDIAL side of eardrum
Tympanic cavity:
-small air-filled space in temporal bone
-lined by MUCOSA
-divided into dorsal, medial and ventral parts
Dorsal tympanic cavity:
-3 auditory ossicles (malleus, incus, stapes)
-2 muscles (stapedius, tensor tympani)
Middle tympanic cavity:
-eardrum laterally
-opens rostrally to NASOPHARYNX by auditory tube
Ventral tympanic cavity:
-enlarged bulbous part of TEMPORAL bone: tympanic bulla
Tympanic bulla:
-varies in different species
-some: divided into bony cells
-may help with very low or very high frequencies
What is exposed in the tympanic cavity?
-part of facial nerve (VII) and its branch, chorda tympani
*VII can be affected by severe otitis media
Chorda tympani:
-branch off facial nerve
*taste from ROSTRAL 2/3rd of tongue
Auditory tube:
-Eustachian tube
-passageway connecting tympanic cavity to nasopharynx
-narrow lumen
-inverted TROUGH-shaped cartilage support
-small muscle bundles DILATE opening
Pharyngeal openings of auditory tubes:
-have lymphoid tissue (tubal tonsils)
Cartilage of auditory tube:
-extends to stiffen pharyngeal opening
>in dog: opening are 0.5cm and on top of small pimple-like elevations
Horse auditory tube:
*opens are 3cm
Auditory tube function:
-allow equalization of pressures on 2 sides of ear drums
-momentarily open during swallowing or yawning
Guttural pouch:
-unique to horse
-pair of diverticular of auditory tubes
-thin-wall sacs, (each 300-500mL air)
-L and R do NOT communicate
*floor molded over STYLOHYOID to incompletely divide into medial and lateral compartments
Guttural pouch formed by:
-EXPANSION of tube’s mucosa thru a ventral slit between sides of cartilages
Dorsally guttural pouch:
-between base of skull and ATLAS
Ventrally guttural pouch:
-pharynx and retropharyngeal lymph nodes
Laterally guttural pouch:
-PTERYGOID muscles
-parotid and mandibular salivary glands
Medially guttural pouch:
-lower parts of R and L meet: forming a thin median septum
-upper parts separated by muscles
>rectus capitis ventails and longus capitis
Medial compartment of guttural pouch:
-internal carotid
-cranial nerves: glossopharyngeal (IX), vagus (X), accessory (XI) and hypoglossal (XII)
-sympathetic trunk and cranial cervical ganglion
Lateral compartment of guttural pouch:
-external carotid artery and branches (maxillary and superficial temporal arteries)
-brief contact with facial nerve (VII)
Function of guttural pouch:
-extensive contact between INTERNAL carotid artery and very thin pouch wall COOLS major blood supply to brain
*causes a 2degree C drop in blood during intense exercise
Guttural pouch endoscopic view through:
-ventral meatus into FLAP and into GP to examine, drain or levage
GP clinical implication in foal:
-if flap has excess mucosal folds, it may act as a 1 way valve
>only let air in, so GP becomes visibly extended
>*GP TYMPANY
Grazing and GP:
-allows normal GP draining
If GP is blocked:
-fluid accumulates and infection can follow or spread from middle ear or lymph nodes
Erosive GP infection (mycosis) can cause:
-ruptured carotid artery (EPISTAXIS, usually fatal)
-damaged pharyngeal branches of IX or X (dysphagia)
-damaged laryngeal branches of X (‘roaring)
-damaged sympathetic trunk (Horner’s syndrome)
Horner’s syndrome:
-nasal congestion
-drooping of upper eyelid
-protrusion of 3rd eyelid
-pupil constriction
-sweating
-hot skin over affected side
Access GP by endoscopy or by open SURGERY thru Viborg’s triangle:
-caudal border of mandible
-tendon of sternocephalicus
-linguofacial vein
