ANAT2411-2023 Sensory Organs Lecture Slides PDF

ANAT2241 Histology: Basic & Systematic Sensory Organs Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Michigan Resources Recommended reading: Textbook chapter (Wheat...

ANAT2241 Histology: Basic & Systematic Sensory Organs Dr. Reza Shirazi Department of Anatomy, School of Medical Sciences Faculty of Medicine & Health, UNSW Sydney [email protected] Image by Dr John Abramyan, University of Michigan Resources Recommended reading: Textbook chapter (Wheather's online): Special Sense Organs Textbook chapter (Junqueira’s Basic Histology: Text and Atlas, 16e online): The Eye & Ear: Special Sense Organs Chapman Histology https://www.youtube.com/channel/UCvSvCkHjCbHn8aGd6OPno_A/featured Learning Objectives 1. To understand the different types of sensory organs 2. To understand the histological features of the taste buds 3. To understand the features of the olfactory mucosa 4. To understand the different types of the mechanoreceptors in skin 5. To understand the function and components of eyeball 6. To understand the histological features of the layers of eyeball 7. To understand the architecture of sclera, cornea, choroid, and retina 8. To understand the accessory Structures of the Eye 9. To understand the three parts of the ear 10. To understand the histological features of inner ear and organ of Corti Sensory Organs Sensory organs/receptors: Conveying information about the external world to the central nervous system; including: 1- Taste buds 2- Olfactory epithelium 3- Mechanoreceptors that mediate the sense of touch in the skin (Merkel's disks, Meissner's corpuscles, Ruffini endings, and Pacinian corpuscle) 4- Eye 5- Ear Taste Buds Ovoid structures within the stratified epithelium on: • • • • Vallate papilla (250 taste buds are present on the lateral surface of each vallate papilla) Fungiform papilla Foliate papilla Widely scattered elsewhere on the dorsal and lateral surfaces of the tongue Sample the general chemical composition of ingested material Taste Buds (X45; Filiform papillae) (X45; Fungiform papillae) • Arrows: dermal papillae (X45; Foliate papillae) • Arrows: deep cleft (X25; Circumvallate papillae) Taste Buds 50-100 cells in each taste bud Cell types in the taste buds: 1- Gustatory (taste) cells: • Basal end: synapse with afferent sensory axons • Apical end: has microvilli projecting toward an opening in the structure called the taste pore 2- Supportive cells 3- Basal stem cells (X1,100; Tate bud Olfactory Mucosa Composed of two layers: • Epithelium: pseudostratified Columnar Epithelium • Lamina propria: containing large serous glands called olfactory glands (of Bowman) (X200; H&E; Olfactory mucosa) • LP: lamina propria • B: olfactory basal cells • ON: bipolar olfactory neurons • S: supporting cells • C: non-motile cilia (olfactory hairs) • M: a layer of mucus Olfactory Mucosa: (1) Olfactory Epithelium A pseudostratified columnar epithelium composed of 3 cell types: 1- Olfactory neurons: • Bipolar neurons with: § An irregular row of nuclei near the middle of this thick epithelium § Apical (luminal) pole: dendrite end with nonmotile cilia (olfactory hairs) § Basal end: axon end 2- Supporting cells: • Columnar cells extending microvilli into the fluid layer 3- Basal cells: • Small, spherical, or cone-shaped cells near the basal lamina • Stem cells for the other two types, replacing the olfactory neurons every 2-3 months and support cells less frequently (X200; H&E; Olfactory mucosa) • LP: lamina propria • B: olfactory basal cells • ON: bipolar olfactory neurons • S: supporting cells • C: non-motile cilia (olfactory hairs) • M: a layer of mucus Olfactory Mucosa: (2) Lamina Propria A loose connective tissue which is directly contiguous with the periosteum of the underlying bone containing: • Blood & lymphatic vessels • Olfactory nerves • Olfactory glands (of Bowman) § Serous glands § Produce a constant flow of fluid surrounding the olfactory cilia o Facilitating the access of new odoriferous substances (X240; Olfactory mucosa) Mechanoreceptors Receptors Phasic mechanoreceptors responding rapidly to stimuli on the skin Encapsulated receptors Four mechanoreceptors are recognized in human skin, although only the first two are seen in routine preparations: 1- Meissner’s corpuscles 2- Lamellated (pacinian) corpuscles 3- Krause end bulbs • Have extremely thin, collagenous capsules penetrated by a sensory fiber • Found primarily in the skin of the penis and clitoris where they sense low-frequency vibrations 4- Ruffini corpuscles • Have collagenous, fusiform capsules • Stimulated by stretch (tension) or twisting (torque) in the skin • Detecting tissue distortion Meissner’s Corpuscles Elliptical structures Structure: • Consisting of sensory axons winding among flattened Schwann cells Location: • Elliptical structures arranged perpendicular to the epidermis in the dermal papillae • Numerous in the fingertips, palms, and soles but decline slowly in number during aging after puberty Function: • Stimulated by light-touch or low-frequency stimuli against skin temporarily deform their shape (X150; H&E; Meissner’s corpuscles) • DP: dermal papilla Inset: A higher magnification of a Meissner’s corpuscle. (X320) Lamellated (Pacinian) Corpuscles Large oval structures Structure: • An outer capsule: 15-50 thin, concentric lamellae of flattened Schwann cells and collagen • A highly branched, unmyelinated axon surrounded by the capsule Function: • Sensing coarse touch, pressure (sustained touch), and high-frequency vibrations Location: • Deep in the reticular dermis and hypodermis • In the connective tissue of organs located deep in the body, including the wall of the rectum and urinary bladder (X85; Pacinian corpuscles) • N: nerves • Arrow: The neural portion Eye: The Photoreceptor System o Highly developed photosensitive organs o Protected by orbit and adipose cushions Each eye is composed of three concentric tunics or layers, some structures, and chambers: Tunics/Layers: 1- Fibrous layer: tough external layer • Sclera • Cornea 2- Vascular layer/Uvea: middle layer • Choroid • Ciliary body • Iris 3- Retina: inner sensory layer Communicates with the cerebrum through the posterior optic nerve Structures: 1- Lens: transparent biconvex structure 2- Aqueous humor 3- Vitreous humor/body Chambers: 1- Anterior chamber 2- Posterior chamber 3- Vitreous chamber Fibrous Layer: Sclera and Cornea Fibrous Layer: (1) Sclera • White posterior five-sixths of fibrous layer • Protects the more delicate internal structures and provides sites for muscle insertion • Consists mainly of dense connective tissue • Posteriorly the sclera joins with the epineurium covering the optic nerve Fibrous Layer: (2) Cornea • Anterior one-sixth of the fibrous layer • Transparent and completely avascular Composed of five distinct layers: 1- Corneal epithelium: • External layer • Non-keratinized stratified squamous epithelium • Five or six cell layers thick 2- Anterior limiting membrane (Bowman membrane): • Basement membrane beneath the corneal epithelium 3- Stroma: • A thick layer • Consists of approximately 60 layers of parallel collagen bundles aligned at approximately right angles to each other and extending almost the full diameter of the cornea • Between the collagen, lamellae are cytoplasmic extensions of flattened fibroblast-like cells called keratocytes 4- Posterior limiting membrane (Descemet membrane): • Basement membrane of the endothelium 5- Endothelium: • Inner simple squamous epithelium (X85; Cornea) • E: corneal epithelium • S: stroma • EN: endothelium (X85; Anterior surface of the cornea) • E: corneal epithelium • B: Bowman’s membrane • S: stroma (X85; Posterior surface of the cornea) • EN: endothelium • D: Descemet membrane • S: stroma Fibrous Layer: Limbus (Corneoscleral junction) Containing scleral venous sinus (canal of Schlemm) • Receiving aqueous humor from the anterior chamber • From this sinus, aqueous humor drains into small blood vessels (veins) of the sclera Vascular Layer: Choroid, Ciliary Body and Iris Vascular Layer; Uvea: (1) Choroid • Posterior two-thirds of the eye • Consists of loose, well-vascularized connective tissue and contains numerous melanocytes • Form a characteristic black layer in the choroid and prevent light from entering the eye except through the pupil Two layers make up the choroid: 1- Choroidocapillary lamina (CCL): • Has a rich microvasculature • Important for nutrition of the outer retinal layers 2- Bruch membrane: • A thin extracellular sheet • Composed of collagen and elastic fibers surrounding the adjacent microvasculature and basal lamina of the retina’s pigmented layer (X200; H&E; Sclera, choroid, and retina) • S: sclera • C: choroid • SCL: suprachoroidal lamina • CCL: choroidocapillary lamina • B: Bruch layer • P: pigmented layer • VB: vitreous body Vascular Layer; Uvea: (2) Ciliary Body • Anterior expansion of the uvea • Encircles the lens • Lies posterior to the limbus Vascular Layer; Uvea: (2) Ciliary Body Important structures associated with the ciliary body: 1- Ciliary muscle: • Consists of smooth muscle fibers • Affects the shape of the lens and is important in visual accommodation 2- Ciliary processes 3- Aqueous humor • Secreted by ciliary epithelium from the stromal microvasculature into the posterior chamber 4- Ciliary zonule: • A system of many radially oriented fibers produced by the nonpigmented epithelial cells on the ciliary processes • The fibers extend from grooves between the ciliary processes and attach to the surface of the lens, holding that structure in place Vascular Layer; Uvea: (2) Ciliary Body Vascular Layer; Uvea: (2) Ciliary Body Vascular Layer; Uvea: (2) Ciliary Body Ciliary processes Ciliary processes: • A radially arranged series of ridges extending from the inner highly vascular region of the ciliary body • Covered by a double layer of low columnar epithelial cells (ciliary epithelium): 1- The epithelial cells directly covering the stroma: § Contain much melanin § Correspond to the anterior projection of the pigmented retina epithelium 2- The surface layer of cells: § Lacks melanin § Contiguous with the sensory layer of the retina (X200; PT staining; Epithelium of ciliary processes) • PE: pigmented epithelial cells • NE: non-pigmented epithelial cells • V: blood vessels Vascular Layer; Uvea: (3) Iris Most anterior extension of the middle uveal layer Covers part of the lens, leaving a round central pupil Vascular Layer; Uvea: (3) Iris (X140; H&E; Iris) • P: pupil • AC: anterior chamber • S: stroma • DPM: dilator pupillae muscle • SPM: sphincter pupillae muscle • PE: pigmented epithelium • PC: posterior chamber Structure: 1- Anterior surface: • Exposed to aqueous humor in the anterior chamber • Consists of a dense layer of fibroblasts and melanocytes with interdigitating processes and is unusual for its lack of an epithelial covering 2- Stroma: • Loose connective tissue with melanocytes and sparse microvasculature 3- Posterior surface: • Has a two-layered epithelium continuous with that covering the ciliary processes, but very heavily filled with melanin • Myoepithelial cells form a partially pigmented epithelial layer and extend contractile processes radially as the very thin dilator pupillae muscle • Smooth muscle fibers form a circular bundle near the pupil as the sphincter pupillae muscle (X900;SEM; Stromal fibroblasts at the anterior surface of the iris) (X100; PT; Iris) • Arrows: blood vessels in deep stroma Vascular Layer; Uvea: (3) Iris Color of one’s eyes: • Provided by the melanocytes of the iris stroma • In individuals with very few lightly pigmented cells in the stroma, light with a blue color is reflected back from the black pigmented epithelium on the posterior iris surface • As the number of melanocytes and density of melanin increase in the stroma, the iris color changes through various shades of green, gray, and brown • Individuals with albinism have almost no pigment and the pink color of their irises is due to the reflection of incident light from the blood vessels of the stroma (X570; iris and lens) Retina Composed of two layers: 1- Outer layer: pigmented layer 2- Inner layer: neural layer Retina Pigmented Epithelium Consists of cuboidal or low columnar cells Attached to Bruch membrane and the choroidocapillary lamina of the choroid Forms the other part of the dual epithelium covering the ciliary body and posterior iris Functions: 1- Absorbs scattered light that passes through the neural layer 2- Form an important part of the protective blood-retina barrier isolating retina photoreceptors from the highly vascular choroid 3- Play key roles in the visual cycle of retinal regeneration 4- Phagocytosis of shed components from the adjacent photoreceptors 5- Remove free radicals 6- Support the neural retina (X500; H&E; Pigmented epithelium of retina) • C: choroid • PE: pigmented epithelium • OS: outer segment • IS: inner segment • OLL: outer limiting layer • ONL: outer nuclear layer • OPL: outer plexiform layer Neural Retina/Neural Layer • Thick and stratified with various neurons and photoreceptors • An outpost of the CNS with glia and several interconnected neuronal subtypes in well-organized strata • Although its neural structure and visual function extend anterior only as far as the ora serrata • Continues as part of the dual cuboidal epithelium that covers the surface of the ciliary body and posterior iris Neural Retina/Neural Layer Nine distinct layers comprise the neural retina: 1- Rod and cone layer (RCL): • Which contains the outer segments of rod and cone cells where the photoreceptors are located 2- Outer limiting layer (OLL): • Formed by junctional complexes holding the rod and cone cells to the intervening Müller cells 3- Outer nuclear layer (ONL): • Contains cell bodies and nuclei of photoreceptors (the rod and cone cells) 4- Outer plexiform layer (OPL): • Containing axons of the photoreceptors and dendrites of association neurons in the INL as well as synapses of the bipolar neurons and rod and cone cells (X150; H&E; Layers of the retina) • VB: vitreous body • C: choroid Neural Retina/Neural Layer 5- Inner nuclear layer (INL): • Contains the nuclei of various neurons, notably the bipolar cells, amacrine cells, and horizontal cells which begin to integrate signals from the rod and cone cells 6- Inner plexiform layer (IPL): • Containing fibers and synapses of the ganglion cells and the bipolar neurons of INL 7- Ganglionic layer (GL): • Has neurons (ganglion cells) with much longer axons; thicker near the retina’s center than its periphery 8- Nerve fiber layer (NFL): • Containing the ganglionic cell axons; converge at the optic disc to form the optic nerve 9- Inner limiting membrane (ILM): • A basement membrane covered by expanded processes of Müller cells; not distinguishable in routine preparations (X150; H&E; Layers of the retina) • VB: vitreous body • C: choroid Neural Retina/Neural Layer Rod Cells o Extremely sensitive to light o Allow some vision even with light low levels, such as at dusk or night time Composed of two segments: 1- Outer segment: • A modified primary cilium, photosensitive, and shaped like a short rod 2- Inner segment • Contains glycogen, mitochondria, and polyribosomes for the cell’s biosynthetic activity Cone Cells o Less numerous o Less light-sensitive than rods o Produce color vision in adequately bright light Composed of two segments: 1- Outer segment: • More conical form 2- Inner segment Specialized Areas of the Retina 1- Optic disc/blind spot: • At the posterior of the retina where the axons in the retina’s NFL converge at the optic nerve head and leave the eye as the optic nerve 2- Fovea centralis: • Near the optic disc and directly opposite the pupil • Where visual acuity or sharpness is maximal • Shallow depression within the retina where cells bodies of the ganglionic and INLs are dispersed peripherally, leaving primarily cone cells 3- Macula lutea: • Where axons of the cone cells contain various carotenoids (antioxidant properties), giving this area its yellowish color; helping to protect the cone cells of the fovea (X40; H&E; Optic disc) • OD: optic disc • ON: optic nerve • R: retina • S: sclera • BV: blood vessels • CA: central artery (X100; H&E; Fovea) • F: fovea • S: sclera • C: choroid Lens • A transparent, avascular, highly elastic, biconvex structure • Suspended immediately behind the iris, which focuses light on the retina • The lens is held in place by fibers of the ciliary zonule, which extend from the lens capsule to the ciliary body • Together with the ciliary muscles, ciliary zonule allows the process of visual accommodation, which permits focusing on near and far objects by changing the curvature of the lens Lens Three principal components of the lens: 1- Lens capsule: • A thick structure composed of proteoglycans and type IV collagen 2- Lens epithelium: • Subcapsular epithelium consists of a single layer of cuboidal cells present only on the anterior surface of the lens; with two ends: § Basal surfaces: attach to the surrounding lens capsule § Apical surfaces: bind to the internal lens fibers 3- Lens fibers: • Highly elongated, terminally differentiated cells that appear as thin, flattened structures (X200; H&E; Lens) • LC: lens capsule • LE: lens epithelium • DFL: differentiating lens fibers • MFL: mature lens fibers Vitreous Body o Occupies the large vitreous chamber behind the lens o Consists of transparent, gel-like connective tissue that is 99% water (vitreous humor), with collagen fibrils and hyaluronate Accessory Structures of the Eye (1) Conjunctiva (2) Eyelids (3) Lacrimal Glands Conjunctiva o A thin, transparent mucosa o Covers the exposed, anterior portion of the sclera and continues as the lining on the inner surface of the eyelids Consists of: 1- Stratified columnar epithelium, with numerous small goblet cells 2- Lamina propria of loose vascular connective tissue Eyelids Pliable, protective structures consisting of: 1- Skin 2- Muscle 3- Tarsus: a dense fibroelastic plate 4- Sebaceous glands: with many acini secreting into a long central duct that opens among the eyelashes 5- Conjunctiva (X12.5; H&E; Eyelid) • S: skin • M: striated muscle • T: tarsus • TG: tarsal glands • D: central duct (X200; H&E; Inner aspect of the eyelid) • C: conjunctiva • LP: lamina propria • T: tarsus • TG: tarsal glands Lacrimal Glands o Located in the upper temporal portion of the the orbit o Produce fluid continuously for the tear film that moistens and lubricates the cornea and conjunctiva and supplies O2 to the corneal epithelial cells o Drain through individual excretory ducts into the recess between the eyelids and the eye Histological feature: • Composed of acini with large serous cells (X400; H&E; Lacrimal gland) • A: acini • M: myoepithelial cells • V: blood vessels • D: intra- and interlobular ducts Ears: The Vestibuloauditory System Mediate the senses of equilibrium and hearing Each ear consists of three major parts: 1- External ear: receives sound waves • Auricle / pinna • External acoustic meatus • Tympanic membrane / eardrum 2- Middle ear: transmits sound waves from air to fluids of the internal ear via a set of small bones 3- Internal ear: contains two organs: a. Cochlea: in which these fluid movements are transduced to nerve impulses passing via the acoustic nerve to the CNS b. Vestibular organ: allows the body to maintain equilibrium External Ear: (1) Auricle or Pinna • An irregular, funnel-shaped plate of elastic cartilage, covered by tightly adherent skin External Ear: (2) External Acoustic Meatus • An air-filled tubular space that follows a slightly S-shaped course for about 25 mm from the auricle to the tympanic membrane (eardrum) • Lined with stratified squamous epithelium • In the skin near its opening : o Hair follicles o Sebaceous glands o Ceruminous glands: modified apocrine sweat glands (X400; H&E; External acoustic meatus) • F: hair follicles • SG: sebaceous glands • CG: ceruminous glands • C: cerumen External Ear: (3) Tympanic Membrane or Eardrum Consists of: 1- Epidermis: external cover 2- Fibroelastic connective tissue 3- Epithelium: internal lining; simple cuboidal epithelium of the mucosa lining the middle ear cavity (X9; Human tympanic membrane) Inset: Higher magnification of the tympanic membrane (X190) • SSE: stratified squamous epithelium • CT: connective tissue • SCE: simple cuboidal epithelium Middle Ear / Tympanic Cavity Internal lining: mucosa 1- Simple cuboidal epithelium 2- lamina propria Anterior wall: o Communicates with the pharynx via the auditory tube (also called the eustachian or pharyngotympanic tube); lining: • Simple cuboidal epithelium: at the beginning of the auditory tube • Ciliated pseudostratified columnar epithelium Middle Ear / Tympanic Cavity Auditory ossicles: • Transmit the mechanical vibrations of the tympanic membrane to the internal ear • Completely covered with simple squamous epithelium 1- Malleus 2- Incus 3- Stapes Skeletal muscles: • Restricting ossicle movements and protecting the oval window and inner ear from potential damage caused by extremely loud sound 1- Tensor tympani 2- Stapedius (X30; Articulated human auditory ossicles) Internal Ear or Labyrinth Located completely within the temporal bone Composed of : 1- Bony labyrinth 2- Membranous labyrinth Bony Labyrinth Containing: 1- Membranous labyrinth 2- Perilymph Major divisions of the bony labyrinth: 1- Vestibule: • An irregular central cavity housing the saccule and the utricle 2- Semicircular canals: • Three osseous enclose the semicircular ducts 3- Cochlea: • Contains the cochlear duct • About 35-mm long and makes 2¾ turns around a bony core called the modiolus Membranous Labyrinth Containing endolymph Major divisions of the membranous labyrinth: 1- Two connected sacs: utricle and saccule 2- Three semicircular ducts: continuous with the utricle 3- Cochlear duct: provides for hearing and is continuous with the saccule Membranous Labyrinth Mediating the functions of the inner ear, each structure in membranous labyrinth contains in its epithelial lining large areas with columnar mechanoreceptor cells, (called hair cells) in specialized sensory regions: 1- Two maculae of the utricle and saccule: • Utricular macula • Saccular macula 2- Three cristae ampullares in the enlarged ampullary regions of each semicircular duct 3- The long spiral organ of Corti in the cochlear duct Utricle and Saccule Composed of: A very thin connective tissue sheath lined with simple squamous epithelium Containing small specialized regions in epithelium called maculae: • Columnar neuroepithelial cells innervated by branches of the vestibular nerve; with two cell types: 1- Hair cells: covered by otolithic membrane 2- Supporting cells Semicircular Ducts Lie in three different spatial planes, at approximately right angles to one another Containing small specialized regions in epithelium called crista ampullaris; with two cell types: 1- Hair cells: covered by cupula 2- Supporting cells Inner Ear (Labyrinth) Cochlear Duct o o Held in place within the bony cochlea One of three parallel compartments, or scalae which coil 2¾ turns within the cochlea 1- Cochlear duct (scala media): • Middle compartment, filled with endolymph • Continuous with the saccule and ends at the apex of the cochlea • Contains organ of Corti that allows auditory function 2- Scala vestibuli: • Contains perilymph • Separated from the scala media by the very thin vestibular membrane (Reissner membrane) lined on each side by simple squamous epithelium 3- Scala tympani: • Contains perilymph • Separated from the scala media by the fibroelastic basilar membrane Organ of Corti / Spiral Organ Consists of hair cells and supporting cells supported by the basilar membrane Two major types of hair cells are present (covered by tectorial membrane): 1- Outer hair cells: • Occur in three to five rows • Each columnar outer hair cell bears a V-shaped bundle of stereocilia 2- Inner hair cells: • Form a single row of cells • Each with a single more linear array of shorter stereocilia Organ of Corti / Spiral Organ Consists of hair cells and supporting cells supported by the basilar membrane Two major types of hair cells are present (covered by tectorial membrane): 1- Outer hair cells: • Occur in three to five rows • Each columnar outer hair cell bears a V-shaped bundle of stereocilia 2- Inner hair cells: • Form a single row of cells • Each with a single more linear array of shorter stereocilia Organ of Corti / Spiral Organ