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Histology_L2, Ear

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 L2, Ear

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Auricle (ear pinna)

It consists of a funnel-like plate of yellow elastic cartilage in-between 2 layers of thin skin containing hairs and sebaceous and sweat glands. The auricle collects and focuses sound waves toward the external auditory meatus.

External auditory meatus

It is surrounded by yellow elastic cartilage (outer 1/3) and by bone (inner 2/3) and is lined with skin. The outer 1/3 has hairs and sebaceous and modified apocrine sweat glands called ceruminous gland, that produce a waxy secretion called cerumen. The hairs and the wax provide a sticky barrier لزج that prevents the entrance of foreign bodies.

Middle ear

Mucous membrane:
It is lined with simple columnar or cuboidal
epithelium. Near the auditory tube the columnar cells are ciliated with gobletcells. 
Auditory ossicles:
They are 3 tiny compact bones (malleus, incus and stapes) which transmit the vibrations of the tympanic membrane to the perilymph of the internal ear.
Muscles of the ossicles:
Two striated small muscles are attached to the malleus (tensor
tympani) and to the stapes (stapedius)

Internal ear (labyrinth)

The internal ear or labyrinth is located in the temporal bone and consists of bony labyrinth and membranous labyrinths.
The bony labyrinth protects and supports the delicate membranous labyrinth which is a closed system of membranous ducts and sacs within the bony labyrinth.The space between 2 labyrinths is filled with perilymph. The membranous labyrinth is filled with endolymph.The inner ear has 2 sensory organs which differ functionally and morphologically. These are called vestibular apparatus (for equilibrium) and auditory apparatus (for hearing).

Vestibular apparatus:

It is formed of a bony labyrinth (vestibule and semicircular canals) and amembranous labyrinth(utricle and saccule and semicircular ducts).

Bony labyrinth:
_Vestibule:
It is the central part of the bony labyrinth and lie posterior to the cochlea and anterior to the semicircular canals. The lateral wall of the vestibule has both oval and round windows.
_Semicircular canals:
It is formed of 3 thin semicircular canals oriented in 3 distinct planes at right angles to each other. They open into the posterior part of the vestibule.

Membranous labyrinth:
_Utricle and saccule:
The utricle is the largest membranous component of the vestibular system. It is connected with the semicircular duct and cochlear duct by a small duct; ductus reunions.The saccule is smaller and spherical part and communicates with utricle through utriclo-saccular duct.
Utricle and saccule are lined with simple squamous epithelium except in certain areas covered with special neuroepithelial cells (receptors) for vestibular impulses.
These sensory areas are called maculae.
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