Ear Histology Overview

Study Notes

The ear is divided into three parts: external, middle, and inner.
The external ear receives sound waves.
The middle ear transmits mechanical vibrations to the inner ear.
The inner ear transforms mechanical vibrations into nerve impulses to the auditory nerve, which then transmits the impulses to the central nervous system (CNS).

Define the anatomical parts of the ear and the structural components of each part.
Understand the structural components of the inner ear.
Describe the structure and function of the membranous labyrinth.

Ear pinna: elastic cartilage covered by skin.
External auditory canal: lined by hairy skin with ceruminous (wax) glands.
Tympanic membrane (eardrum): a connective tissue core covered externally by epidermis and internally by simple cuboidal epithelium.

This is an air-filled cavity within the temporal bone, lined by simple squamous epithelium.
It contains three bony ossicles: malleus, incus, and stapes.
Muscles: tensor tympani and stapedius.
Chorda tympani.

Located in the temporal bone, it has interconnected spaces called the bony labyrinth, which surround a smaller membranous labyrinth.
Bony labyrinth: filled with perilymph
Membranous labyrinth: filled with endolymph; contains:
- Cochlea
- Vestibule
- Semicircular canals (SCC)s

Bony Labyrinth Component (containing perilymph and membranous labyrinth)
Membranous Labyrinth Component (within the bony labyrinth & containing endolymph)
Structures with Sensory Receptors
- Vestibule: utricle, saccule, maculae: Detect linear movements and static position of the head.
- Semi-circular canals: semi-circular ducts, cristae ampullares: Detect rotational movements of the head.
- Cochlea: cochlear duct, spiral organ: Detect sounds.

Part of the membranous labyrinth, spirals within the bony cochlea.
Consists of three parallel compartments:
- Scala media: Filled with endolymph
- Scala vestibuli: Separated from the scala media by Reissner's membrane, filled with perilymph.
- Scala tympani: Separated from the scala media by the basilar membrane, filled with perilymph; cochlear duct is bounded by vestibular and basilar membranes and stria vascularis laterally.

Stria vascularis: Epithelial cells with an intraepithelial capillary loop; secretes endolymph.
Organ of Corti: Sensory receptor for hearing; consists of hair cells and supporting cells resting on the basilar membrane.

Otitis media: Viral or bacterial inflammation of the middle ear caused by the extension of upper respiratory tract infections via the Eustachian tube (more common in children due to the shorter and straighter tube).
Vertigo: Dizziness caused by problems in the vestibular system; overstimulation of cristae ampullaris (e.g., spinning); overstimulation of the maculae of the utricle (repetitive linear acceleration changes).
Meniere's disease: Episodes of vertigo, deafness, tinnitus due to increased pressure within the membranous labyrinth and endolymphatic dilation.

Conductive: Outer ear (wax) or middle ear problems (otosclerosis, interfering with the vibrations of the ossicles); otitis media can also contribute to this type due to fluid buildup.
Sensorineural: Defects in structures or cells in the cochlea and auditory centers in the brain.

Part of the membranous labyrinth, sac-like structures in the bony vestibule; lined by simple squamous epithelium and filled with endolymph.
Contain two neuroreceptors, perpendicular to each other, called maculae.

Three membranous ducts in the bony semicircular canals, filled with endolymph.
Each contains a neuroreceptor called crista ampullaris in its dilated part (ampulla).