10. Organs of Special Senses – iv

Sensation of hearing

SENSATION OF HEARING

  • Hearing, or auditory perception, is the ability to perceive sounds by detecting vibrations, changes in the pressure of the surrounding medium through time, through an organ such as the ear. 
  • The academic field concerned with hearing is auditory science.
  • In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. 
  • The outer ear consists of the pinna and the ear canal. Since the outer ear is the only visible portion of the ear in most animals, the word “ear” often refers to the external part alone.
  • The middle ear includes the tympanic cavity and the three ossicles. 
  • The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. 
  • The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localisation.

Outer Ear

  • The outer ear is the external portion of the ear and includes the fleshy visible pinna (also called the auricle), the ear canal, and the outer layer of the eardrum (also called the tympanic membrane).
  • The pinna consists of the curving outer rim called the helix, the inner curved rim called the antihelix, and opens into the ear canal.
  • The hollow region in front of the ear canal is called the concha.
  • The first part of the canal is surrounded by cartilage, while the second part near the eardrum is surrounded by bone. 
  • This bony part is known as the auditory bulla and is formed by the tympanic part of the temporal bone.
  • Two sets of muscles are associated with the outer ear: the intrinsic and extrinsic muscles.
  • The ear muscles are supplied by the facial nerve, which also supplies sensation to the skin of the ear itself, as well as to the external ear cavity. 
  • The great auricular nerve, auricular nerve, auriculotemporal nerve, and lesser and greater occipital nerves of the cervical plexus all supply sensation to parts of the outer ear and the surrounding skin.
  • The pinna consists of a single piece of elastic cartilage with a complicated relief on its inner surface and a fairly smooth configuration on its posterior surface
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