External EarThis is a featured page

Ear


I. External Ear

  • Consists of the auricle and the external acoustic meatus and receives sound waves.
A. Auricle
  • Consists of cartilage connected to the skull by ligaments and muscles and is covered by skin.
  • Funnels sound waves into the external auditory meatus.
  • Receives sensory nerves from the auricular branch of the vagus and facial nerves and the greater
  • auricular nerve, auriculotemporal branch of the trigeminal nerve, and lesser occipital nerves.
  • Receives blood from the superficial temporal and posterior auricular arteries.
  • Has the following features:
    • Helix : the slightly curved rim of the auricle.
    • Antihelix : a broader curved eminence internal to the helix, which divides the auricle into an outer scaphoid fossa and the deeper concha.
    • Concha : the deep cavity in front of the antihelix.
    • Tragus : a small projection from the anterior portion of the external ear anterior to the concha
    • Lobule : a structure made up of areolar tissue and fat but no cartilage.
B. External acoustic (auditory) meatus
  • Is about 2.5 cm long, extending from the concha to the tympanic membrane.
  • Its external one third is formed by cartilage, and the internal two thirds is formed by bone. The cartilaginous portion is wider than the bony portion and has numerous ceruminous glands that produce earwax.
  • Is innervated by the auriculotemporal branch of the trigeminal nerve and the auricular branch of the vagus nerve, which is joined by a branch of the facial nerve and the glossopharyngeal nerve.
  • Receives blood from the superficial temporal, posterior auricular, and maxillary arteries (a deep auricular branch).
C. Tympanic membrane (eardrum)
  • Lies obliquely across the end of the meatus sloping medially from posterosuperiorly to anteroinferiorly; thus, the anterior-inferior wall is longer than the posterior-superior wall.
  • Consists of three layers : an outer (cutaneous), an intermediate (fibrous), and an inner (mucous) layer.
  • Has a thickened fibrocartilaginous ring at the greater part of its circumference, which is fixed in the tympanic sulcus at the inner end of the meatus.
  • Has a small triangular portion between the anterior and posterior malleolar folds called the pars flaccida (deficient ring and lack of fibrous layer). The remainder of the membrane is called the pars tensa.
  • Contains the cone of light , which is a triangular reflection of light seen in the anterior-inferior quadrant.
  • Contains the most depressed center point of the concavity, called the umbo (Latin for the boss on the centre of a shield)
  • Conducts sound waves to the middle ear.
  • Its external (lateral) concave surface is covered by skin and is innervated by the auriculotemporal branch of the trigeminal nerve and the auricular branch of the vagus nerve. The auricular branch is joined by branches of the glossopharyngeal and facial nerves. This surface is supplied by the
  • deep auricular artery of the maxillary artery.
  • Its internal (medial) surface is covered by mucous membrane, is innervated by the tympanic branch of the glossopharyngeal nerve, and serves as an attachment for the handle of the malleus. This surface receives blood from the auricular branch of the occipital artery and the anterior tympanic artery.


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