Ear and Eye Anatomy and Physiology Lecture Notes PDF

THE EAR and EYE Dr. LSK 10/16/2024 LSK lecture series 1  Content objectives To understand general arrangement of parts of the ear. To understand the functions of the ear. To understand the clinical application of the ear. 10/16/2024 LSK l...

THE EAR and EYE Dr. LSK 10/16/2024 LSK lecture series 1  Content objectives To understand general arrangement of parts of the ear. To understand the functions of the ear. To understand the clinical application of the ear. 10/16/2024 LSK lecture series 2  short note 30 days - inner ear End of 6wks - middle ear End of 8wk - outer ear 10/16/2024 LSK lecture series 3  The ear (Gross) For purposes of description, the ear is divided into: External ear Middle ear (tympanic cavity) which is separated from the external ear canal by a tympanic membrane, but opening into the pharynx through the Eustachian tube Internal ear which receives sound vibrations transmitted to it through the middle ear and has to do also with the balance of the head and body. 10/16/2024 LSK lecture series 4  Middle Ear and Inner Ear 10/16/2024 LSK lecture series 5  Parts of the ear 10/16/2024 LSK lecture series 6  Transmission of sound 10/16/2024 LSK lecture series 7  EXTERNAL EAR The two parts of the external ear are the auricle and the external acoustic meatus. The auricle - This is the projecting part of the ear whose skin is firmly attached to the perichondrium that covers the auricular cartilage The lobule consists of skin and intervening connective tissue. It is the only part of the auricle that is not 10/16/2024 supported by cartilage. LSK lecture series 8  The Pinna 10/16/2024 LSK lecture series 9  External acoustic meatus contd. It leads to the tympanic membrane or eardrum. It is not straight nor is it of uniform diameter throughout as it is traced inward. In the newborn, the bony canal has almost no length, for it is formed primarily by the small piece of bone known as the tympanic ring, to which the eardrum is attached. 10/16/2024 LSK lecture series 10  External auditory meatus 10/16/2024 LSK lecture series 11  Tympanic membrane It is at the medial end of the acoustic meatus and separates this from the middle ear or tympanic cavity. It is oblique, sloping medially from top to bottom and medially from posterior to anterior so that the anterior wall and floor of the external meatus are longer than its roof and posterior wall. 10/16/2024 LSK lecture series 12  Tympanic membrane contd. The tympanic membrane centre gives attachment to the handle of the malleus. The malleus, in turn, articulates with a second bone, and this articulates with a third. Through the movement of this chain of bones, are transmitted across the middle ear cavity to the internal ear. 10/16/2024 LSK lecture series 13  MIDDLE EAR The middle ear or tympanic cavity lies in the temporal bone. It has a greater height than the meatus and the tympanic membrane. Its floor is a little below the level of the inferior border of the membrane, and it extends well above the upper border. This upper extension of the tympanic cavity is the epitympanic recess, often referred to by clinicians as the “attic.” 10/16/2024 LSK lecture series 14  Middle ear 10/16/2024 LSK lecture series 15  Tympanic cavity contd The medial or labyrinthine wall of the tympanic cavity is of special interest. The prominent bulge of this medial wall is the promontory, formed by the large basal coil of the cochlea. 10/16/2024 LSK lecture series 16  Demonstrating.......Tensor Tympani and Stapedius Vibrations of malleus and stapes damped down by muscles tensor tympani (V3) and stapedius (VII) respectively 10/16/2024 LSK lecture series 17 Tympanic cavity contd Above the oval window, directed posteriorly and somewhat downward, is the prominence of the facial canal produced by the facial nerve after it has left the geniculate ganglion. 10/16/2024 LSK lecture series 18  Communication of middle ear Anteriorly: The auditory tube opens through the anterior wall of the tympanic cavity. (Eustachian tube/ Pharyngotympanic tube) with nasopharyngeal. Posteriorly: Mastoid/tympanic antrum (mastoid air cell of the temporal bone ( PCF). Superiorly: though separated by thin bone called tegmen tympanic ( middle cranial fossa). 10/16/2024 LSK lecture series 19  Auditory Ossicles ( BONES) The three bones of the middle ear cavity are the malleus (hammer), incus (anvil), and stapes (stirrup). They form a mobile chain of small bones across the tympanic cavity from the tympanic membrane to the oval window leading to internal ear. 10/16/2024 LSK lecture series 20  Auditor y Ossicles 10/16/2024 LSK lecture series 21  INTERNAL EAR The internal ear consists of a series of cavities in the petrous part of the temporal bone osseous labyrinth within which lies a correspondingly complex fluid filled sac and ducts the membranous labyrinth. 10/16/2024 LSK lecture series 22  Inner Ear 10/16/2024 LSK lecture series 23 Internal ear contd. The space between the membranous and bony labyrinths is filled with perilymph or perilymphatic fluid. Similarly, the membranous labyrinth is filled with endolymph or endolymphatic fluid. 10/16/2024 LSK lecture series 24 Internal ear contd. The parts of the osseous labyrinth are in order from front to back: cochlear canal or the cochlea, vestibule semicircular canals. 10/16/2024 LSK lecture series 25  Internal ear contd. The parts of the membranous labyrinth are: cochlear duct (concerned with hearing) utricle and saccule (within the vestibule and concerned with static balance), semicircular ducts (within semicircular canals and concerned with kinetic balance. 10/16/2024 LSK lecture series 26  Cochlear 10/16/2024 LSK lecture series 27 Spiral organ (of Corti) The histology of the complicated spiral organ (of Corti) has among its tall epithelial cells some neuroepithelial hair cells, from the outer surface of which project tiny hair-like processes. 10/16/2024 LSK lecture series 28 Spiral organ (of Corti) Nerve fibers end around these epithelial cells, and some of their hair-like processes are attached, in the living condition, to a fibrogelatinous mass, the tectorial membrane, that lies against the otherwise free surface of the spiral organ. 10/16/2024 LSK lecture series 29  Cochlear 10/16/2024 LSK lecture series 30  Scala vestibuli and tympani 10/16/2024 LSK lecture series 31  Vestibulocochlear nerve 10/16/2024 LSK lecture series 32  Summary of meddle ear Lateral wall ( tympanic wall) ; tympanic membrane Medial wall ( labynrinthin wall ) oval n round window, fenestra cochlea, F. vestibule & promontary Roof ( tegmen tympani: Tegmen tympani, MCF 10/16/2024 LSK lecture series 33  Summary of meddle ear ( cont’d communication Anteriorly : phargngotympanic tube= pharygnx Posteriorly : Mastiod air cell, tympanic antrum/ PCF thru sigmoid sinus non-direct communication ROOF: tegmen tympanic: middle CF, and Temporal lone 10/16/2024 LSK lecture series 34  contents of middle ear Auditory ossicles : Malleus, Incus & Stapes Stapedius & tensor tympani, a branch of cranial nerve Tympanic plexus of nerves formed by fascial nerve and glossopharyngeal nerve 10/16/2024 LSK lecture series 35 Summary of inner ear Made up of 4 basic structures: Vestibule, 3 semi circular canal , cochlear & internal acoustic meatus Cochlear ( scali vestibuli , cochlear duct & scali tympani) ( perilymph & Endolymph), oval window& round window Vestibule ( saccular & utricle) Semi circular canal ( ant, post & lat), ampullary crest : kinetic balance 10/16/2024 LSK lecture series 36  Applied anatomy Most congenital disorders of the ears are caused by genetic factors or intrauterine infections such as rubella virus Auditory Impairment(conductive & sensorineural deafness Congenital deafness (Causes of hearing loss in newborns include infections, such as rubella or herpes simplex virus) External otitis Acute purulent otitis media ( intact TM but infection in the middle ear and may result in fluid building up in the middle ear- Otitis media effusion) Perforation of the tympanic membrane Otosclerosis (formation of new bone around the base of the stapes resulting in progressive hearing loss). 10/16/2024 LSK lecture series 37  Of the three types of hearing loss, sensorineural hearing loss is the most common. Sensorineural hearing loss is a result of damaged inner ear nerves and hair cells. Because of this, the pathway from your inner ear to your brain is impacted. This is caused by a variety of factors, such as the normal aging process, noise exposure, medications, heredity, and certain health conditions like stroke, meningitis, or diabetes.  sensorineural hearing loss can be managed by using hearing aids. Applied anatomy ( cont’d) aggressive infection in the middle ear can spread to the middle cranial fossa thru tegmen tympani, goes as far as temporal lobe of the cerebal cortex, causing temporal cerebral abscesses. 10/16/2024 LSK lecture series 40 Practice questions 1. The middle ear is separated from the inner ear by (a) the cochlear window. (b) the tympanic membrane. (c) the vestibular window. (d) both a and c. 2. A chronic infection in the middle ear can result in facial palsy. TRUE OR FALSE 10/16/2024 LSK lecture series 41 Eye diagram Fibrous layer The fibrous layer consists of Cornea and Sclera, and both continue with each other. Function: provide shape to the eye and support the deeper structures Cornea : is transparent and centrally placed at the front of the eye, it helps to refract the light entering the eye. Sclera: it is visible as the white part of the eye, outer walls, hard, like a light-tight box.  fibrous layer ( 85%) it gives attachment to extraocular muscles. Vascular layer The vascular: lie underneath the fibrous layer and consists of: Choroid: connective tissue and blood vessel, it provides nourishment to outer layers of the retina. Ciliary body: Ciliary muscle and ciliary processes. It controls the shape of the lens, contribute to the formation of aqueous humor Iris: like diaphragms or stop in a camera. The diameter of the pupil is altered by smooth muscles within the Iris Pupil: camera aperture. An aperture at the center of the Iris Inner layer: RETINA Retina: at the back of eyeball, like the film. It has : 1. Pigmental outer layer: absorbing light and continue around the whole inner surface of the eye 2. Neural layer: it located posteriorly and laterally in the eye. Consists photoreceptors Retina Structure Light sensitive layer is made of photo- receptors: rods (120 millions) and cones (7 millions) which absorb the light. Plexiform Layer: nerve cells that process the signals generated by rods and cones and relay them to the optical nerve. Choroid: carries mayor blood vessels to nourish the retina and absorb the light so that it will not be reflected back (dark pupil!) Sensitivity Cones: slow, fine grain, like color film. Need high level of light (photopic condition, day) High density, high resolution. Rods: fast, coarse grain, black & white film Low level of light (scotopic condition, at night). Adaptation: Changing of retina sensitivity. Other related structures of the eye Eyelid: skin and muscle, protect eye from mechanical injury and cover the pupil and lens. Conjutiva: mucous membrane that lines the eyelid and surface ( clear and colorless). Vitreous body: Transparent get at the posterior segment of the eyeball. Support the lens, contribute to eye magnifying power and holds retina in place. Aqueous humor and Vitreous humor The Aqueous Humor is the clear liquid between the cornea and the lens. It has the benefit of being fairly homogenous and, as a result, the optical properties are easily measured. The space that it inhabits is called the anterior chamber. The Vitreous Humor is the clear liquid between the lens and the retina. The space that it fills is called the vitreous body.  CLINICAL ANATOMY Oculomotor nerve palsy Conjunctivitis ( Viral, Bacterial, allergic) Glaucoma (drainage of aqueous humor through the scleral venous sinus decreases and damage to optic nerve ) Central retinal artery occlusion Paralysis of the extraocular muscles (diplopia- double vision) Horner syndrome ( spinal cord injury, stroke, nerve injury). Presbyopia and cataracts ( old age and cloudy lens) Clinical Anatomy(CONTD) Liquefaction of this vitreous gel takes place during ageing and in 25-30% of the cases the separation of vitreous takes place from retina, which ultimately results into posterior vitreous detachment. This process plays a central role in various blinding conditions, which includes proliferative diabetic retinopathy and macular hole formation.