Tympanic Membrane Eardrum consists of three layers

A. Keratinized stratified squamous epithelium covers the external surface.

B. Connective tissue that is vascularized and innervated constitutes the middle layer.

C. Simple squamous epithelium covers the internal surface.

II. MEMBRANOUS LABYRINTH is contained within the osseous labyrinth. The membranous labyrinth is filled with endolymph. The osseous labyrinth is filled with perilymph.

A. Kinetic labyrinth (semicircular ducts; Figure 27-1A)

1. Type I and type II hair cells within cristae ampullaris have stereocilia and a single cilium (kinocilium) on their apical border. These cells are in contact with bipolar neurons of the vestibular ganglion of cranial nerve (CN) VIII.

2. The kinetic labyrinth also contains supporting cells.

3. Hair cells and supporting cells are covered by a gelatinous mass called a cupula.

4. The semicircular ducts respond to angular acceleration and deceleration of the head.

B. Static labyrinth (utricle and saccule; Figure 27-1B)

1. Type I and type II hair cells within maculae have stereocilia and a single cilium (kinocilium) on their apical border. These cclls are in contact with bipolar neurons of the vestibular ganglion of CN VIII.

2. The static labyrinth also contains supporting cells.

3. Hair cells and supporting cells are covered by a gelatinous mass called the otolithic membrane, which contains calcium carbonate crystals (otoliths).

4. The utricle and saccule respond to the position of the head with respect to linear acceleration and pull of gravity.

C. Cochlear duct (Figure 27-1C; Figure 27-2)

1. This triangular duct comprises a vestibular membrane (roof), basilar membrane (floor), and stria vascularis (lateral wall). The stria vascularis participates in the formation of endolymph.

2. The cochlear duct contains the organ of Corti.

a. The organ of Corti contains inner and outer hair cells that have stereocilia (but no kinocilium) on their apical border and are in contact with bipolar neurons of the cochlear ganglion of CN VIII.

A. Vestibular nuclei

B. Flocculonodular node of cerebellum

Type I hair cell

Vestibular ganglion

Flocullo Oculor Node

Cupula

Type II hair cell Supporting cells

Otoliths

Type II hair cell

Otolithic membrane Type I hair cell

Supporting cells

A. Vestibular nuclei

B. Flocculonodular node of cerebellum

Type I hair cell

Cupula

Type II hair cell Supporting cells

Vestibular ganglion

Resting

Resting

Acceleration

Acceleration

Tectorial membrane Inner and outer hair cells Stria vascularis

Basilar membrane

Figure 27-1. (A) Kinetic labyrinth (semicircular ducts). Note the deflection of the cupula during acceleration, which stimulates the hair cells. (B) Static labyrinth (utricle and saccule). (C) Cochlear duct. The organ of Corn is the receptor for sound. The scala vestibuli and scala tympani are part of the osseous labyrinth and are filled with perilymph.

Vestibular membrane

Cochlear nuclei

Spiral ganglion

Inner Ear Stria Vascularis

Tectorial membrane Inner and outer hair cells Stria vascularis

Basilar membrane

Figure 27-1. (A) Kinetic labyrinth (semicircular ducts). Note the deflection of the cupula during acceleration, which stimulates the hair cells. (B) Static labyrinth (utricle and saccule). (C) Cochlear duct. The organ of Corn is the receptor for sound. The scala vestibuli and scala tympani are part of the osseous labyrinth and are filled with perilymph.

Vestibular membrane

Cochlear nuclei

Spiral ganglion

Figure 27-2. Light micrograph of the cochlear duct containing the organ of Corri. Note the vestibular membrane (vm), tectorial membrane (tm), basilar membrane (km), bipolar neurons of the spiral ganglion (sg), stria vascularis (sv), outer hair cells (oh), scala vestibuli containing perilymph (vestibuli), scala media containing en-dolymph (media), and scala rympani containing perilymph (tympani).

Figure 27-2. Light micrograph of the cochlear duct containing the organ of Corri. Note the vestibular membrane (vm), tectorial membrane (tm), basilar membrane (km), bipolar neurons of the spiral ganglion (sg), stria vascularis (sv), outer hair cells (oh), scala vestibuli containing perilymph (vestibuli), scala media containing en-dolymph (media), and scala rympani containing perilymph (tympani).

b. It also contains different types of supporting cells.

C. Hair cells and supporting cells are covered by a gelatinous mass called the tectorial membrane.

d. The organ of Corti responds to sounds, which induce vibrations of the basilar membrane.

III. CLINICAL CONSIDERATION. The organ of Corti may be damaged by exposure to rubella virus during week 7 and week 8 of embryologie development.

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