Special Senses: Ear Lecture

Parts of the External Ear

auricle, external acoustic meatus, tympanic membrane

Tissue of the mucosa of the external acoustic meatus

lined with stratified squamous epithelium

Mucosa of the external acoustic meatus

lamina propria of loose connective tissue

Submucosa of external ear

Consists of:

Hair follicles, sebaceous glands and ceruminous glands (modified apocrine sweat glands)

Submuscosa of external ear location

Located near the opening of the meatus

Ceruminous Glands

Modified apocrine glands producing earwax.

Elastic cartilage of external ear

supports outer third of the walls if the external acostic meatus

What is the inner part of the external ear enclosed by?

Osseous tissue (temporal bone)

Tympanic membrane or eardrum externally

Fibroelastic tissue covered with epidermis.

Tympanic membrane internally

lined by simple cuboidal epithelium

Middle Ear

Continuous with the nasopharynx and the mastoid cells of temporal bone

Tissue within the middle ear

Lined by simple cuboidal epithelium

What does the middle ear become in the auditory tube?

respiratory epithelium

Lamina propria of loose CT in middle ear is continuous with?

periosteum (CT covering bone)

Ossicles are covered with what tissue

periosteum and simple squamous epithelium

Tensor Tympani Muscle

Skeletal muscle attached to the malleus.

Stapedius Muscle

Skeletal muscle attached to the stapes.

Internal Ear

Contains bony and membranous labyrinths.

Bony Labyrinth

Rigid structure contains perilymph fluid.

Membranous Labyrinth

Flexible structure filled with endolymph fluid.

What type of tissue is the membranous labyrinth covered with?

lined with epithelium

Divisions of membranous labyrinth

1. Utricle + saccule (interconnected)

2. Three semicircular ducts (continuous with utricle)

3. Cochlear duct (continuous with saccule)

Utricle and Saccule

Interconnected

Semicircular Ducts

continuous with utricle

Cochlear Duct

continuous with saccule

Hair Cells

Mechanoreceptors within the sensory regions.

Hair cells are found:

maculae, cristae ampullares, organ of Corti

Maculae are found

one in utricle and one in saccule

Cristae Ampullares are found

ampullae of semicircular canals

Spiral Organ or Organ of Corti are found

cochlear duct

Regions of bony labyrinth

1. vestibule

2. semicircular canals

3. cochlea

Modiolous of bony labyrinth

-Surrounded by the cochlea

-Blood vessels

-Surrounds the cell bodies and processes of acoustic branch of VIII cranial nerve

What type of tissue is utricle and saccule?

Very thin CT sheaths lined with simple squamous epithelium

How is the utricle and saccule attached to the periosteum?

bound to the periosteum of bony labyrinth by a vascularized layer of collagen fibers

Maculae

Areas of columnar neuroepithelial cells (inneverated by branches of VIII nerve)

Macula of saccule position

Macula of saccule lies perpendicular to the macula of the utricle

What surrounds columnar hair cells?

surrounded by supporting cells and synaptic connections

Function of maculae

Static position and linear acceleration of the head

Hair cells structure

One apical, long, rigid kinocilium

Bundle of 30-50 rigid, unbranched stereocilia

How is the stereocilium connected?

connected to an actin-rich region in the apical cytoplasm: the cuticular plate

How is the stereocilia arranged?

In rows of decreasing length: the longest adjacent to

the kinocilium.

Types of hair cells

Two types with basal synapses with afferent nerve endings

Type I Hair cells

rounded basal ends completely surrounded by an afferent terminal calyx

Type II hair cells

These types of hair cells are more numerous, and are columnar, with bouton endings from afferent nerves.

Similarities between type I and type II hair cells

Both are associated to efferent nerve fibers from the brain (modulation)

Supporting cells of hair cells

provide metabolic and physical support for the mechanoreceptors

Otolithic membrane

Gelatinous material with otoliths (otoconia) located in the outer region of the macula

Otolithic membrane contains

proteins and CaCO3

What is embedded in the otolithic membrane?

Tips of kinocilium and stereocilia

Semicircular ducts

Extend from and return to the wall of the utricle

How many planes does the semicircular ducts have?

three

Each duct consists of what?

ampulla with hair cells and supporting cells on a crest of the wall: the crista ampullaris

Differences between cristae and maculae

1.The proteoglycan layer is called the cupula,

2. Is attached to the apical part of the hair cells

3. Lacks otoliths

4. Is thicker

Location of cupula

extends across the ampulla and reaches the non-sensory wall

Mechanoreceptors of semicircular ducts

detect rotational movements of the head as the endolymph moves within the ducts

Cochlear duct

A spiral tube with the hair cells and other structures

How many ducts or scalae does the cochlear duct form?

three parallel ducts or scalae that coil 2 ¾ turns within the cochlea

What are the three scalae in cochlear duct?

scala media, scala vestibuli, scala tympani

Scala media

middle chamber filled with endolymph, continuous with the saccule and ending at the apex of cochlea

Scala vestibuli

upper chamber contains perilymph, separated by the scala media by the vestibular (Reissner) membrane

Reissner membrane

lined by simple squamous epithelium on each side

What membrane separates scala vestibuli and scala media?

vestibular (Reissner) membrane

Scala tympani

contains perilymph, separated from the

scala media by the fibroelastic basilar membrane

What membrane separates scala tympani and scala media

basilar membrane

Where does the scala vestibuli begin?

oval window

Where does the scala tympani end?

round window

Where do the scala vestibuli and scala tympani communicate?

at the apex via the helicotrema

Helicotrema

where the perilymph of scala vestibuli and perilymph of scala tympani will meet

Stria Vascularis

Produces K+-rich endolymph in scala media.

Tissue of stria vascularis

stratified epithelium

Where is the stria vascularis?

lateral wall of scala media

function of stria vascularis

surrounds capillaries and produce K+ rich endolymph

What is unusual about the stria vascularis?

unusual intraepithelial plexus

Organ of corti

Detects sound vibrations of different frequencies

What is organ of Corti consist of?

Inner and outer hair cells in a V-shaped arrangement

Major characteristics of organ of Corti

No kinocilum, only stereocilia

Supportive cells present of the basilar membrane

inner and outer phalangeal cells; pillar cells

Inner and outer phalangeal cells

Apical processes surround and support basolateral parts of inner and outer hear cells and synaptic nerve endings

Pillar cells

stiffened by bundles of keratin and outline the inner tunnel

Inner tunnel

Triangular space between outer and inner complexes of hair cells and phalangeal cells

Tectorial membrane

•Gel-like

•Bundles of collagen (type II. V, IX, and XI)

•Contains the tips of tallest stereocilia of hair cells

What type of collagen is in tectorial membrane?

type II, V, IX, and XI

Spiral ganglion

•Afferent bipolar neurons

•Found in the modiolus

Outer hair cells structure

columnar cells

Outer hair cells number

12,000

Outer hair cells arrangment

Organized in three rows up to five rows near the apex

Outer hair cells consists

Each bears a V-shaped bundle of stereocilia

Inner hair cells structure

shorter than the outer hair cells

Inner hair cells arrangement

Form a single row of approximately 3,500 cells

How is the sterocilia in inner hair cells?

Stereocilia are shorter in a more linear arrangement