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• Topic: EARS

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• The ear is an organ of balance and hearing.

• It has three parts: Outer Ear, Middle Ear, Inner Ear.

• The Outer Ear consists of the Pinna, Vertical canal, Auricular cartilage (vertical), Horizontal Auricular Tympani, Middle Auditory canal cartilage, and membrai ear tube (horizontal).

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• The External Ear has two main components: Pinna (Auricle) and External Auditory Meatus (Ear Canal).

• The Pinna is a fleshy appendage attached to the side of the skull by muscles and ligaments.

• The Pinna catches and directs soundwaves to the middle ear.

• The External Auditory Meatus is the passageway from the pinna to the eardrum.

• In dogs, there is a vertical canal and horizontal canal in the ear canal.

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• The Pinna has several anatomical features:

  • Scapha: large flap concave internal side of the auricle

  • Helix: entire free margin of the auricle

  • Cutaneous marginal pouch: Fold of skin at the proximal lateral portion of the helix

  • Anthelix: Transverse fold of cartilage on the concave surface of the pinna

  • Tragus: thick, blunt, irregularly quadrangular plate of cartilage from the rostral border of entrance to the external auditory meatus

  • Antitragus: thin elongated projection of cartilage

  • Intertragic incisure notch: separates the tragus and antitragus

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• List of dog breeds: Irish Setter, Golden Retriever, Cocker Spaniel, Collie, Basset Hound, Cairn Terrier, Pharaoh Hound, Boxer (cropped), Greyhound.

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• The ear has three auricular branches: Intermediate auricular branch, Medial auricular branch, Lateral auricular branch.

• Mention of Auricular Hematoma.

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• The Middle Ear is the part inside the tympanic cavity containing the auditory ossicles and opening to the auditory tube.

• The Tympanic membrane (Eardrum) is a thin semitransparent partition between the external auditory meatus and the middle ear.

• The incoming sound waves vibrate the eardrum and deliver this information to the bony ossicles.

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• Mention of various bones of the skull: Frontal, Nasal, Incisive, Parietal, Maxilla, Zygomatic, Temporal, Mandible.

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• The Middle Ear has two main components: Tympanic membrane (Eardrum) and Auditory ossicles.

• The Auditory ossicles are three bones extending across the middle ear from the eardrum into the oval window of the cochlea.

• The three bones are: Malleus (hammer), Incus (anvil), Stapes (smallest bone of the body).

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• List of individual bones of the skull.

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• The Middle Ear has several openings: Tympanic membrane (Eardrum), Vestibular window (Oval Window), Cochlear window (Round Window).

• The Vestibular window is filled by the base of the stapes which pushes inward.

• The Cochlear window is located below the oval window and covered by a secondary tympanic membrane that bulges outward with fluid movement.

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• The Middle Ear has a passageway called the Eustachian tube (auditory tube) between the middle ear and nasopharynx.

• The Eustachian tube equalizes the pressure in both sides of the eardrum, protecting it from rupture.

• Swallowing opens the auditory tube allowing air into the middle ear.

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• Mention of Perilymph, Bony labyrinth, Membranous labyrinth, Semicircular duct filled with endolymph, Utricle, Cochlea, Macula, Vestibule, Semicircular canals, Ampulla, Crista, Round window, Oval window.

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• Mention of Bony labyrinth, Membranous labyrinth, Vestibular nerve, Anterior semicircular canal, Cochlear nerve, Lateral semicircular canal, Posterior semicircular canal.

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• The Inner Ear has several components: Pinna, Urticle, Cochlea, Horizontal Inner ear Canal, Vertical canal, Auricular cartilage (vertical), Vestibule, Saccule, Horizontal Auricular Tympanic, Middle Auditory canal cartilage, membrane ear tube (horizontal).

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• The Inner Ear has three main components: Cochlea, Scala vestibuli, Scala tympani.

• The Cochlea is a snail shell-like structure associated with hearing.

• The Scala vestibuli is superior and communicates with the vestibule, middle ear at the oval window, and the scala tympani at the apex of the cochlea.

• The Scala tympani is more inferior and is a continuation of the scala vestibule from the apex of the cochlea to the round window.

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• The Inner Ear has another component called the Vestibule, which is the central expanded portion of the inner ear.

• The Vestibule contains two sacs: Saccule and Utricle.

• Both the Saccule and Utricle contain areas of sensory hair cells known as macula surrounded by jelly-like material containing Calcium carbonate particles or otoliths.

• The Maculae are static equilibrium receptors located perpendicular to each other in the utricle and saccule.

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• Mention of membranes in the vestibule, otoliths, otolithic membrane, hair tuft, hair cell, supporting cell, nerve fibers of vestibular division of cranial nerve VIII.

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• Mention of upright head and tilted head positions.

• The Utricle detects horizontal (left & right) acceleration, while the Saccule detects vertical (up & down) acceleration.

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• Mention of Perilymph, Bony labyrinth, Membranous labyrinth, Semicircular duct filled with endolymph, Utricle, Cochlea, Macula, Vestibule, Semicircular canals, Ampulla, Crista, Round window, Oval window.

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• The Inner Ear has three semicircular canals: an anterior, a posterior, and a lateral canal.

• These canals are filled with fluid called endolymph.

• Each canal has an ampulla that is connected to the utricle.

• The Semicircular ducts are the membranous labyrinth of the semicircular canals communicating with the utricle.

• The Crista is a receptor organ found in the ampulla of each semicircular duct, composed of hair (receptor) cells and supporting cells. It senses motion of the head (dynamic).

• The Cupula is a gelatinous mass covering the crista.

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• Mention of Semicircular Canals, Anatomy, Ampulla, Semicircular Endolymph, Cupula, canal, Kinocilium, Stereocilia, Hair cell, Cristae, Support cells, Vestibular nerve, Afferents of the vestibular nerve, Cupula, Cilia, Hair cells, Afferents of vestibular n., Vestibular n., CN VIII, CNS.

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• As the head accelerates through rotation, the endolymph within one or more of the semicircular canals begins to move.

• The movement of the endolymph pushes against the cupula, causing the hair bundles to bend.

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• Mention of Bony labyrinth, Membranous labyrinth, Perilymph, Endolymph, Cochlea, Vestibule, Semi-circular canals.

Page 26: Organ of Corti (Spiral organ)

• The organ of hearing is composed of a series of hair cells on the inner surface of the membranous labyrinth.

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• The hair cells in the organ of Corti are responsible for converting sound vibrations into electrical signals.

  • These electrical signals are then transmitted to the brain via the auditory nerve.

• The organ of Corti is located within the cochlea, which is a spiral-shaped structure in the inner ear.

  • The cochlea is filled with fluid and is responsible for detecting sound vibrations.

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• The organ of Corti is made up of several layers of specialized cells.

  • The inner hair cells are responsible for transmitting sound signals to the brain.

  • The outer hair cells amplify sound vibrations and enhance the sensitivity of the inner hair cells.

• The hair cells in the organ of Corti are arranged in rows along the length of the cochlea.

  • Each row of hair cells is tuned to a specific frequency of sound.

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• The organ of Corti is surrounded by supporting cells that provide structural support and nourishment to the hair cells.

• The movement of the fluid in the cochlea causes the hair cells to bend, which triggers the release of neurotransmitters.

  • These neurotransmitters then stimulate the auditory nerve fibers, which carry the electrical signals to the brain.

• Damage to the hair cells in the organ of Corti can result in hearing loss or impairment.