VETA 106: Microscopic Anatomy 2 - Lecture Notes PDF

VETA 106: Microscopic Anatomy 2 Lecture topic 12: Special sense organs by: M. J. Ang, DVM, Ph.D. Version 1 (20221116) Eyes Overview sclera= dense connective tissue. cornea= transparent; ○ layers include: the anterior epithelium anterior limiting membrane substantia...

VETA 106: Microscopic Anatomy 2 Lecture topic 12: Special sense organs by: M. J. Ang, DVM, Ph.D. Version 1 (20221116) Eyes Overview sclera= dense connective tissue. cornea= transparent; ○ layers include: the anterior epithelium anterior limiting membrane substantia propria posterior limiting membrane posterior epithelium Eyes Overview vascular tunic= include: choroid, ciliary body and iris lens= capsule surrounds the epithelium and fibers retina= has ten histologic layers ○ including: the pigmented epithelium, three neurons, intervening synaptic regions,processes of supporting cells, and axons of the optic nerve anterior compartment= contains aqueous humor posterior compartment= contains the vitreous body Eyes the eye gathers and focuses light transmits resulting nervous impulses to the brain for interpretation as images Eyes Fibrous Tunic ○ includes the sclera and cornea sclera ○ dense white connective tissue ○ forms the outer covering of the posterior eye ○ bone or cartilage may be present in avians Eyes Fibrous Tunic cornea ○ highly transparent outer layer of the anterior eye ○ anterior epithelium is nonkeratinized stratified squamous epithelium which is rich with nerve endings ○ anterior limiting membrane (Bowman’s membrane)= composed of a basement membrane and collagen network; present in primates ○ substantia propria= collagen fibers, which are highly ordered for transparency ○ posterior limiting membrane (Descemet’s membrane) = separates the substantia propria from the simple squamous or cuboidal posterior epithelium (corneal endothelium) Eyes Vascular Tunic ○ lies deep to the sclera ○ comprised of: choroid ciliary body iris Eyes Vascular Tunic choroid ○ outer layer= suprachoroid (connective tissue) ○ inner layer= vascular layer. ○ tapetum lucidum= light reflective layer present in most domestic species except for the pig between the vascular layer and the choriocapillary layer ○ The basal complex (Bruch’s membrane) separates the capillaries in the choriocapillary layer from the retina. Eyes Vascular Tunic ciliary body ciliary processes= covered with two layers of cuboidal epithelium deep layer of epithelial cells= pigmented. ciliary processes produce aqueous humor zonular fibers extend from the processes and attach to the lens. smooth ciliary muscle at the base of the processes contracts to change the shape of the lens Eyes Vascular Tunic iris controls the amount of light entering the eye through the pupil anterior surface (aka stratum avasculorum)= connective tissue rather than epithelium stroma=pigment in the stroma beneath determines the color of the eye contains pupillary dilator and sphincter muscles posterior surface epithelium= heavily pigmented. Eyes Lens outer surface= capsule which is the basement membrane of the lens epithelium ○ epithelium= simple cuboidal and is confined to the anterior surface of the lens underneath the capsule. ○ epithelial cells elongate to form spindle-shaped lens fibers at the equator ○ fibers lose their nuclei and sink toward the center of the lens throughout life Eyes Retina comprised of three neurons with intervening synaptic regions outer layer= pigmented epithelium of cuboidal cells which protect the photoreceptors above Eyes Retina Rods and cones= contain rhodopsin and iodopsin, the visual pigment of the eye ○ these cells shed disks which are phagocytized by the pigmented epithelium ○ Nuclei of rods and cones, bipolar cells, and ganglion cells form the nucleated layers of the retina ○ Processes of radial gliocytes (Müeller cells) form the supporting outer and inner limiting membranes. Eyes Retina outer plexiform layer is the synaptic region between the photoreceptor and bipolar cells inner plexiform layer represents the synapses between the bipolar and ganglion cells optic nerve fiber layer= ganglion cell axons which converge at the optic disk to form the optic nerve which exits to the brain Eyes Compartments of the Eye anterior compartment ○ anterior chamber= extends from the cornea to the iris ○ posterior chamber= extends from the iris to the lens. ○ aqueous humor fluid produced by the ciliary processes flows through the iris and drains at the iridial angle between the cornea and iris posterior compartment ○ located between the lens and the retina ○ contains the vitreous body= gelatinous structure of hyaluron, collagen and water. Eyes Eyelids, Nictitating Membrane and Lacrimal Gland eyelid ○ fold of skin with large sebaceous tarsal glands along the margin ○ hair is present on the outer surface of the eyelid nictitating membrane ○ conjunctival fold ○ contains hyaline or elastic cartilage and lymphatic nodules lacrimal gland ○ mucous in the pig ○ seromucous in the dog ○ serous in other domestic species Ears Overview pinna= skin with a cartilaginous core. ceruminous glands= modified sweat glands. tympanic membrane is two layers of epithelium separated by connective tissue respiratory epithelium lines the auditory tube vestibular apparatus includes the semicircular canals, ampula, utricle and saccule crista ampullaris and maculae send neural impulses to the brain via the vestibular nerve. Ears Overview auditory apparatus includes the scala vestibuli, scala tympani and cochlear duct sensory cells in the spiral organ transmit neural impulses to the auditory nerve for hearing endolymph fills the cochlear duct while perilymph fills the scala vestibuli and scala tympani. Ears The ear captures vibrations and transmits resulting neural impulses to the brain for interpretation as sounds. Ears External Ear Pinna, or ear flap= skin with hair on the surface and underlying connective tissue Hyaline or elastic cartilage= forms the central core, and attached skeletal muscle can be contracted to move the pinna. external auditory meatus, or ear canal= lined with skin containing fine hair, sebaceous glands and ceruminous glands. Ears External Ear Ceruminous glands= modified apocrine sweat glands. Cerumen= a waxy substance from the glands, includes sebum, sloughed cells and other ceruminous gland secretions. auditory meatus= ends at the tympanic membrane Ears Middle Ear tympanic membrane, or eardrum= separates the auditory meatus from the middle ear cavity ○ composed of two layers of simple squamous epithelium with fine connective tissue between the epithelia tympanic cavity= lined by simple squamous or cuboidal epithelium which covers the auditory ossicles and their muscles Ears Middle Ear auditory ossicles= small bones which conduct vibrations across the middle ear cavity to the inner ear ○ Lined by ciliated pseudostratified epithelium auditory tube (eustachian tube)= connects the middle ear cavity with the pharynx Ears Inner Ear has both osseous and membranous labyrinths ○ osseous labyrinth= space within the temporal bone ○ contains the membranous labyrinth vestibular apparatus auditory apparatus vestibular apparatus ○ functions in balance and proprioception. ○ 3 semicircular canals in the osseous labyrinth are oriented at right angles to each other Ears Inner Ear ○ vestibule another small space in the osseous labyrinth, lies between the semicircular canals and the cochlea ○ semicircular ducts= membranous, epithelial-lined tubules within the semicircular canals Each duct dilates to form an ampula at one end Within each ampula, sensory hair cells covered by a gelatinous cupula form the crista ampullaris which senses acceleration and deceleration Ears Inner Ear ○ sensory cells= characterized by multiple stereocilia and a single, long kinocilium ○ utricle and saccule= two membranous depressions within the vestibule Receptor organs within these structures are the macula utriculi and macula sacculi respectively ○ Hair cells of the maculae and an overlying gelatinous mass with calcium carbonate crystals form the statoconial membrane Ears Inner Ear ○ When the head moves, the hair cells are triggered, sending impulses along the vestibular branch of the vestibulocochlear nerve to the brain where spatial positioning is interpreted. auditory apparatus ○ cochlea= a spiral shaped bony tube, and the membranous cochlear duct within ○ the cochlear duct partitions the cochlear cavity into the upper scala vestibuli and the lower scala tympani. Ears Inner Ear Beginning at the vestibular window (oval window), the scala vestibuli spirals to the top of the cochlea where it bends and returns as the scala tympani which ends at the cochlear window (round window). vestibular membrane= separates the cochlear duct from the scala vestibuli, basilar membrane= partitions the duct from the scala tympani. Ears Inner Ear Endolymph= clear fluid formed by the stria vascularis,fills the cochlear duct. Perilymph= derived from cerebrospinal fluid, is found in the spaces of the bony labyrinth including the scala vestibuli and scala tympani. spiral organ (organ of Corti)= Within the cochlear duct; sensory and supporting cells with the tectorial membrane ○ axons innervating the sensory cells in the spiral organ converge and pass to the spiral ganglion in the center of the cochlear spiral The cochlear branch of the vestibulocochlear nerve exits the ganglion and continues to the brain. Ears Auditory Mechanisms Vibrations deflect the tympanic membrane and are transferred to the auditory ossicles of the middle ear The ossicles then transmit the vibrations through the vestibular window into the perilymph of the cochlea High frequency vibrations remain at the base of the cochlea while low frequency vibrations travel to the top of the spiral The vibrations are transferred from the perilymph to the endolymph of the cochlear duct The basilar membrane vibrates and sensory cells deform beneath the tectorial membrane Deformation of the sensory cells creates neural impulses which travel along the cochlear nerve to the brain for interpretation as sounds