Anatomy of the Eye and Ear Lecture PDF

THE EYE and EAR Term 3, 2023-24 Anatomy & Physiology of Nervous System (APNS-211) Basic Sciences Department, COSHP, KSAU-HS, KSA  The Eye and Ear By the end of the lecture, students should be able to: Explain briefly the accessory stru...

THE EYE and EAR Term 3, 2023-24 Anatomy & Physiology of Nervous System (APNS-211) Basic Sciences Department, COSHP, KSAU-HS, KSA  The Eye and Ear By the end of the lecture, students should be able to: Explain briefly the accessory structures of the eye. Enumerate the extraocular muscles along with their nerve supply and actions. List the three coats/tunics of the eyeball and enumerate the parts of outer, middle and inner coats. Describe briefly the anatomy of the cornea, Lens, iris, pupil, retina, fundus, the optic disc, the macula, aqueous humor, and vitreous humor Describe briefly the anatomy of the external ear, middle ear (tympanic cavity) and inner ear.  The eye and accessory structures LO-1 1. Eyebrows: short, coarse hair that lie over the supraorbital margins of the skull. 2. Eyelids (palpebrae): separated by the eyelid slit (palpebral fissure). 3. Conjunctiva: lines the eyelids and the eyes; secretes mucus to lubricate the eyes.  Lacrimal apparatus LO-1 Consists of: o Lacrimal glands: which secrete tears. o Lacrimal canaliculi: that drain lacrimal secretions (tears) into the lacrimal sac. o Lacrimal sac: drains excessive tears to the nasolacrimal duct o Nasolacrimal duct: ultimately drains into nasal cavity Lacrimal secretions contain mucus, antibodies and lysozymes (destroy bacteria). Cleans and protects the eye. Accessory Structures of the Eye LO-1 Lacrimal punctum Lacrimal sac Lacrimal gland Excretory ducts of lacrimal gland Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril Flow of Tears: Lacrimal gland Excretory ducts to eye(blink) across eye Lacrimal puncta Lacrimal canaliculi Lacrimal sac (in lacrimal fossa) Naso-lacrimal duct Nasal cavity Extraocular Muscles of the Eye LO-2  Extraocular Muscles of the Eye LO-2 Muscles Actions Nerve supply Lateral rectus Moves eye laterally (abducts) CN VI (abducens) Medial rectus Moves eye medially (adducts) CN III ( oculomotor) Superior rectus Elevates eye and turns it medially CN III ( oculomotor) Inferior rectus Depresses eye and turns it medially CN III ( oculomotor) Inferior oblique Elevates eye and turns it laterally CN III ( oculomotor) Superior oblique Depresses eye and turns it laterally CN IV (trochlear)  Eyeball LO-3 Its an organ of vision. It contains special sensory receptors of vision, i.e. rods and cones It is present in the orbit of skull.  Layers of the Eyeball LO-3 The eyeball is a hollow sphere filled with fluids (humor). It is composed of 3 layers: Fibrous layer (outermost): Cornea Sclera Vascular layer (middle): Iris Ciliary body Choroid Sensory layer (innermost): Retina  Layer 1: Fibrous Layer (Outermost) LO-4 The fibrous layer is made up of posterior 5/6 opaque part, the sclera and an anterior 1\6 transparent part, the cornea.  Sclera: white opaque connective tissue (white of the eye).  Cornea: forms the central anterior portion through which light enters the eye. It is transparent and bends light rays to focus them on the retina (refraction). Sclera Cornea Sclera  Layer 2: Vascular Layer (Middle) LO-4 Middle, pigmented layer; consists of 3 regions: 1. Choroid: It forms posterior 5/6 of the vascular coat and is highly vascular 2. Ciliary body & Ciliary muscle: It forms an anterior thickened ring of tissue that encircles the lens & controls its shape 3. Iris: It is a visible colored part of the eye. It forms most anterior part of the vascular layer with central aperture, the pupil. Ciliarybody Choroid Iris  Lens LO-4 Biconvex crystal-like transparent structure Held in place by a suspensory ligament attached to the ciliary body Cornea Iris Canal of Schlemm Lens Sclera Choroid Ciliary muscle Retina Suspensory ligament  Layer 3: Sensory Layer (Innermost) LO-4 The retina is most inner and sensory layer. It contains receptor cells (photoreceptors), the Rods and Cones. Signals pass from photoreceptors and leave the retina toward the brain through the optic nerve.  Layer 3: Sensory Layer (Innermost) LO-4 Fundus of retina: The interior Fundus lining of the eyeball, includes Optic disk the retina (the light-sensitive Macula screen), optic disc (the head of the nerve to the eye), and the macula (the small spot in the Fovea retina where vision is keenest). The macula is part of the retina at the back of the eye and is responsible for the central, high-resolution, color vision that is possible in good light. The center of the macula is known as fovea centralis.  Segments of Eyeball LO-4 The “eyeball” is divided into 2 segments by the lens Both segments are filled with the fluid called (humor) 1. Anterior segment divided into anterior and posterior chambers which contain Aqueous humor. 2. Posterior segment which contain Vitreous body (humor)  The Ear LO-5 Houses two senses: The ear is divided into three parts: o Hearing  BY Cochlea  Outer (external) ear o Equilibrium, (balance)  BY Vestibule & Semicircular canals  Middle ear  Inner ear The Ear LO-5  The External Ear LO-5 Involved in hearing only Structures of the external ear oPinna (auricle). oExternal auditory canal. Narrow chamber in the temporal bone  Lined with skin Contains Ceruminous (wax) glands Ends at the tympanic membrane (ear drum)  The Middle Ear or Tympanic Cavity LO-5 It is an air-filled cavity within the temporal bone between tympanic membrane and inner ear. Only involved in the sense of hearing-transfer sound from external to inner ear.  The Middle Ear or Tympanic Cavity LO-5 There are 3 pairs of bones ( Ear Ossicles) present within the middle ear cavity: 1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup): foot process of the stapes fixed on the Oval window  The Middle Ear or Tympanic Cavity LO-5 The auditory tube connecting the middle ear with the throat (nasopharynx) o Allows for equalizing pressure during yawning or swallowing. o This tube is otherwise collapsed.  The Inner Ear LO-5 Includes sense organs for hearing and balance It consists of the bony labyrinth and membranous labyrinth filled with perilymph and endolymph, respectively. Parts of bony labryinth Vestibule Semicircular canals Cochlea  The Inner Ear LO-5 Parts of membranous Sensory receptors in membranous Functions labryinth labryinth Utricle and saccule maculae Balance Semicircular ducts Crista ampullaris Balance Cochlear ducts Organ of corti Hearing LO-5  Temporal Perilymph in scala vestibuli bone Spiral Vestibular organ of membrane Corti Afferent fibers of the cochlear nerve Temporal bone Scala media (contains Perilymph in endolymph) scala tympani (a)