Histology of the Ear PDF

# Histology of the ear ## Prepared by: - Dr. Ahmed Morsi - Assistant professor of Histology & Cell biology ## Learning objectives: - By the end of this lecture, you will be able to: - Define the anatomical parts of the ear and the structural component of each - Understand the structural...

# Histology of the ear ## Prepared by: - Dr. Ahmed Morsi - Assistant professor of Histology & Cell biology ## Learning objectives: - By the end of this lecture, you will be able to: - Define the anatomical parts of the ear and the structural component of each - Understand the structural components of the inner ear - Describe the structure and function of membranous labyrinth ## EAR - The ear is divided into 3 parts: - **External ear**: receive sound waves - **Middle ear**: transmission of mechanical vibrations to the inner ear. - **Inner ear**: mechanical vibrations are transduced to nerve impulses to auditory nerve to CNS. ## I. External ear: - Ear pinna: elastic cartilage covered by skin - External auditory canal: lined by hairy skin with ceruminous (wax) glands. - Tympanic membrane (ear drum): CT core covered externally by epidermis and internally by simple cubical epithelium. ## II. Middle ear: - Air-filled cavity within temporal bone lined by simple squamous epithelium. It contains: - **Bony ossicles**: malleus, incus, stapes - **Muscles**: tensor tympani and stapedius - **Chorda tympani** ## III. Inner ear: - Located in temporal bone, interconnected spaces (bony labyrinth) enhousing smaller membranous labyrinth. - **Bony labyrinth**: perilymph - **Membranous labyrinth**: endolymph (red) / perilymph (blue) - Spaces within the petrous part of the temporal bone - Cochlea - Vestibule - Semicircular canals (SCC) - Sacs within bony labyrinth - Cochlear duct - Utricle & Saccule - Semicircular ducts ## Inner ear - Components: 1. Irregular central cavity (vestibule) that houses the utricle & saccule. 2. Behind, 3 semicircular canals (SCC) that contain 3 semicircular ducts. 3. On the other side of the vestibule, the bony cochlea contains cochlear duct. Cochlea is 3.5 cm long that makes 2.75 turns around a bony core (modiolus). ## Sensory regions in Membranous Labyrinth - Neuroreceptors with columnar sensory cells (hair cells) that mediate the functions of the inner ear: - Two maculae (**equilibrium**) - Three crista ampullares (**equilibrium**) - Long spiral organ of Corti (**hearing**) ## Structure and function of the inner ear | Bony Labyrinth Component (Containing Perilymph and the Membranous Labyrinth) | Membranous Labyrinth Component (Within Bony Labyrinth and Containing Endolymph) | Structures with Sensory Receptors | Major Function | |---|---|---|---| | Vestibule | Utricle, saccule | Maculae | Detect linear movements and static position of the head | | Semicircular canals | Semicircular ducts | Cristae ampullares | Detect rotational movements of the head | | Cochlea | Cochlear duct | Spiral organ | Detect sounds | ## Cochlear duct - Part of the membranous labyrinth that follows a spiral course within the bony cochlea. - Held in place within bony cochlea, it forms one of 3 parallel compartments: - **Scala media**: formed by cochlear duct itself, filled with endolymph. - **Scala vestibule**: separated form scale media by Reissner's (vestibular) membrane, filled with perilymph. - **Scale tympani**: separated form scale media by fibroelastic basilar membrane, filled by perilymph. - Cochlear duct is bounded above and below by vestibular and basilar membranes respectively and stria vascularis in its lateral wall. - **Strai vascularis** is a crowd of stratified epithelial cells with intraepithelial capillary loop. It secretes endolymph. - **Organ of Corti**: sensory receptor concerned with hearing, formed of hair cells and other supporting cells resting on the basilar membrane. ## Clinical notes: 1. **Otitis media**: viral or bacterial inflammation of the middle ear due to extension of upper respiratory tract infections via Eustachian (auditory) tube. It is more common in children due to short straightened Eustachian tube. 2. **Vertigo**: dizziness, a sense of body rotation and lack of equilibrium due to problems of the vestibular system. Overstimulation of the **cristae ampullaris** (for example: spinning the body) can produce vertigo. Overstimulation of the **maculae** of the utricle caused by repetitive changes in linear acceleration and directional changes can normally lead to motion sickness (seasickness). 3. **Meniere disease**: episodes of vertigo (dizziness)+ **deafness**(hearing loss)+ **tinnitus** (ringing in the ear) due to increase pressure within membranous labyrinth and endolymphatic dilation. ## Deafness (hearing loss) - **Conductive hearing loss** may be due to outer ear (impacted wax) or middle ear problems such as otosclerosis that interfere with vibration of ossicles. Otitis media is another cause that can reduce sound conduction due to fluid accumulation in that cavity. - **Sensorineural deafness** can be congenital or acquired and due to defects in any structure or cell from the cochlea to the auditory centers of the brain. ## Utericle and saccule - Part of the membranous labyrinth (sac like bodies) found within the bony vestibule, lined by simple squamous epithelium, filled by endolymph and contain 2 neuroreceptors perpendicular to each others called **maculae**. ## Semicircular ducts - Three membranous ducts within the bony semicircular canals, filled with endolymph. - Each contains a neuroreceptor called **Crista ampullaris** in its dilated part (ampulla). ## Reference: - Junqueira's Basic Histology: Text and atlas, 13th Edition, 2013. - Anthony L. Mescher The document describes the different components of the ear. This includes the external ear, the middle ear, and the inner ear. Furthermore, it explains the structure and function of the inner ear, including the cochlear duct, the spiral organ, and the neuroreceptors that mediate the functions of hearing and balance.