Ear Ossicles

OSSICLES:
  • The ossicles conduct sound energy from the tympanic membrane to the oval window. There are three middle ear ossicles.
  • Malleus (Hammer): It consists of a head, neck, handle (manubrium), a lateral and an anterior process. It is the largest ossicle and measures 8 mm in length.
  • Head and Neck: They lie in the attic.
  • Developed from First arch
  • Manubrium(handle): It is embedded in the fibrous layer of the tympanic membrane.
  • Anterior process: bony spicule connected to petrotympanic fissure by ligamentous fibres
  • Lateral process: It appears as a knob-like projection on the outer surface of the tympanic membrane and provides attachments to the anterior and posterior malleal folds. 
 2. Incus (Anvil):
  • Developed from First arch
  • It consists of following parts:
  • Body and Short process: They lie in the attic. Short pr. Is connected to fossa incudis by lig. fibres in epitympanic recess
  • Long process: It hangs vertically and medial & parallel to malleus handle and forms incudostapedial joint with the head of stapes by its lenticular process.
3. Stapes (Stirrup):
  • This smallest bone of body measures about 3.5 mm.
  • stapes is a derivative of 2nd branchial arch
  • It consists of head, neck, anterior and posterior crura and footplate.
  • The footplate is positioned in the oval window by annular ligament
  • Foot plate of stapes is developed from Reicherts cartilage
LIGAMENTS OF OSSICLES:
Malleus
  • Anterior ligament of Malleus: neck of malleus to ant wall of tympanic cavity
  • Developed from First arch
  • Contains muscle fibers called as Laxator tympani/ Musculus externus mallei
  • Lateral ligament of Malleus: triangular band, from post border of tympanic inscisure to head of malleus
  • Superior ligament of Malleus head of malleus to roof of epitympanic recess
2. Incus
  • Posterior ligament of Incus: from end of short process to fossa incudis
  • Developed from First arch
  • Superior ligament of Incus: body to roof of epitympanic recess
3. Stapes
  • Vestibular surf & rim of stapedial base covered with hyaline cartilage, which is attached to margin of fen. vestibuli by annular ligament
MUSCLES OF TYMPANIC CAVITY:

MUSCLE ORIGIN INSERTION NERVE SUPPLY BLOOD SUPPLY ACTION
Tensor Tympani Bony Tunnel,E.tube,& adjoining part of greater wing of sphenoid Just below the neck of malleus Branch of the nerve to medial pterygoid Sup. tympanic br of middle meningeal artery Tenses the tympanic membrane by drawing the handle of malleus medially
Contract together with stapes to stiffen the ossicular chain and protect the inner ear from noise damage
Movement of stapes causes vibration in Scala vestibuli
Stapedius Conical cavity and canal within pyramid (on post. tymp wall) It inserts to the neck stapes CN VII (nerve to stapedius of facial nerve) Posterior auricular, anterior tympanic & middle meningeal arteries Damp down excessive sound vibrations.
Opposes action of tensor tympani which pushes the stapes more tightly into fenestra vestibuli
  • Acoustic Reflex
  • When noises are loud, there occurs reflex contraction of stapedius and tensor tympani which helps to dampen the movement of ossicular chain before vibrations reach the internal ear. Afferent pathway: auditory component of 8th Cr Nr
  • Efferent Pathway: Facial Nerve – Stapedius & Mandibular Nerve – Tensor tympani
Exam Question
  • Stapes is a derivative of 2nd branchial arch
  • Stapes foot plate covers Oval window
  • Handle of the malleus is attached to the center of the tympanic membrane
  • Tensor Tympani contract together with stapes to stiffen the ossicular chain and protect the inner ear from noise damage
  • The nerve supply to tensor tympani is by Branch of the nerve to medial pterygoid branch of V3
  • Malleus and Incus are derived from First arch
  • Foot plate of stapes is developed from Reicherts cartilage
  • Superior maleolar ligament connects Head of malleus to roof of epitympanum
  • Cone of light is due to Handle of malleus
  • Stapedial reflex is a protective reflex against loud
  • Body of incus ,Head of malleus,Chorda tympani are components of epitympanum
  • Movement of stapes causes vibration in Scala vestibuli
  • Bones of middle ear are responsible for Reduction of impedance to sound transmission
  • Tendon of stapedius muscle passes through the pyramid in middle ear
  • Fossa incudis is related to Short process of incus
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