Sensory systems Flashcards
(90 cards)
1
Q
What are the layers of the wall of the eye?
A
3 layers - coats/tunics
- Outer (fibrous) coat = cornea and sclera
- Middle (vascular, uveal) coat = iris, ciliary body, choroid
- Inner (retinal) coat = retinal pigmented epithelium (RPE) and neural retina
2
Q
What are the chambers of the eye?
A
3 chambers
- Anterior - between cornea and iris
- Posterior - between back of iris and lens with attached fibers
- Vitreous cavity - between lens and retina
3
Q
What is the conjuctiva?
A
Thin membrane that covers a portion of the exposed surface of the eye and continues onto the inner surface of the eyelid. Stratified columnar epithelium with mucus cells.
4
Q
Describe the cornea.
A
- Transparent, with a convex shape that aids in focusing light and images on retina
- Avascular, with no blood or lymph in the central portion
- 5 different layers
- Can be transplanted without rejection
5
Q
How does the cornea get nutrients?
A
- Central part gets nutrients by diffusion from the aqueous humor
- Peripheral part supplied by blood from limbus vessels
6
Q
What are the corneal layers?
A
Epithelium, Bowman’s layer, stroma, Decemet’s membrane, corneal endothelium
7
Q
Describe the corneal epithelium
A
Anterior layer, non-keritanized stratified squamous epithelium with small microvilli. Has pain receptors (trigeminal and oculomotor nerves) and can regenerate.
8
Q
Describe the corneal Bowman’s layer/”membrane”
A
Layer of Type 1 collagen, cannot regenerate. Part of stroma.
9
Q
Describe the corneal stroma
A
Lattice of Type 1 and Type 5 collagen fibers with an ECM rich in chondroitin and keratan sulfate.
10
Q
Describe the corneal Decemet’s membrane
A
Thick (5-10 micrometer) basement membrane (contains Type 7 collagen) produced by corneal endothelium.
11
Q
Describe the corneal endothelium
A
Surface faces anterior eye chamber. Impermeable intercellular spaces prevent leakage of fluid into corneal stroma.
12
Q
Describe the structure and function of the sclera.
A
- Dense irregular connective tissue - opaque
- Provides protection, structural support, and is an insertion point for the extraocular muscles
13
Q
What is the limbus?
A
The limbus is the corneoscleral junction. It is adjacent to the trabecular meshwork and canal of Schlemm.
14
Q
What is aqueous humor?
A
It is fluid which resembles plasma, but with less protein.
15
Q
What is the pathway aqueous humor follows?
A
Produced by ciliary body epithelium –> flows into anterior chamber through pupil –> drains through a trabecular meshwork at the limbus –> enters canal of Schlemm –> aqueous veins –> episcleral veins
16
Q
What is glaucoma?
A
-Obstruction of aqueous humor flow leading to increased pressure in the eye
17
Q
Describe the choroid
A
Highly vascular nutrient supplier to all eye layers. Contains melanin. 3 layers - Bruch’s membrane, choriocapillaris, chroidal stroma.
18
Q
Describe the ciliary body. How many (named) parts does the ciliary body have?
A
Wedge-shaped expansion of the choroid peripheral to the lens. Smooth muscle (primarily)
2 parts - uveal and neuroepithelial portions
19
Q
Describe the uveal portion of the ciliary body.
A
Outer layer of choroid (supraciliaris), ciliary muscle attached to suspensory ligament, and layer of fenestrated capillaries
20
Q
Describe the neuroepithelial portion of the ciliary body.
A
2 layers of ciliary epithelium consisting of an outer pigmented layer continuous with retinal pigmented epithelium, and inner nonpigmented layer
21
Q
Describe the anterior portion of the ciliary body epithelium.
A
The anterior portion of the CB epithelium is folded to form ciliary processes. Epithelium in this region produce the aqueous humor.
22
Q
What is the iris?
A
Continuation of the ciliary body. Anterior part of middle coat (uvea). Has smooth muscle which controls size of pupil.
23
Q
What are the smooth muscle layers of the iris?
A
2 smooth muscle layers - circular and radial.
Smaller size pupil - constrictor muscle (circular) - parasympathetic.
Dilated pupil - dilator muscle (radial) - sympathetic.
24
Q
Describe the lens.
A
Avascular, transparent, elastic, and biconvex in shape.
25
What is the lens capsule?
Thick basement membrane-like material enclosing the lens
26
When does the lens change shape?
When tension on suspensory ligament fibers (zonular fibers) changes
27
Describe the vitreous humor.
Gel-like, transparent, water and hyaluronic acid, fills vitreous chamber/cavity, keeps lens and retina in place
28
What is a cataract?
Opacity of the lens associated with aging
29
What is the retinal pigmented epithelium (RPE) - retinal layer #1?
- Absorbs scattered light rays
- Phagocytosis of worn out discs shed from rods
- Stores and releases vitamin A to photoreceptors
- RPE closely adhered to choroid. There can be a space between the RPE and the rest of the retina (embryonic development). Trauma can dislodge retina at this site.
30
What is retinal layer #2?
Layer of rods and cones (photoreceptors)
31
Describe rods.
Tall cylindrical cells. Function in low light and peripheral vision. Outer segments - modified cilia. Have discs derived from plasma membrane containing rhodopsin pigment (transducer of light energy)
32
Describe cones.
Shorter cone-shaped cells. Color vision and bright light. Outer segments - modified cilia. Have discs and pigments sensitive to red, green, and blue light. Located more centrally.
33
What kind of cells can be found in the fovea?
Only cones.
34
Describe the renewal process of photoreceptors.
Outer discs of old rods are shed into the space between outer segments and the RPE, which phagocytoses them. New discs made from below and move upward, replacing the old. Cones' discs shed and replaced more slowly.
35
What are the macula lutea and the optic disc?
Posterior retina landmarks, can be viewed through the pupil by a scope.
36
Describe the optic disc.
The optic disc is made of papilla where optic nerve fibers exit the retina, but no photoreceptors.
37
Describe the fovea. Why are they important?
A pit in the center of the macula. Fovea are important for visual acuity. 100% cones, very closely packed. these cones are highly represented in the optic nerve and visual cortex. This is "macular" vision.
38
Describe the macula.
Macula has no retinal vessels, but choroid vessels are abundant on the outside.
39
What is a detached retina?
Neural retina separates from RPE and from choroidal capillaries which feed photoreceptors, especially in the fovea.
40
What is age-related macular degeneration?
A leading cause of blindness. Macular area and fovea lose function due to pigment epithelium behind the retina degenerating and forming drusen (white spots) and allowing fluid leakage behind fovea. Foveal cones die = central visual loss = cannot read or see fine detail.
41
What is glaucoma?
- Common problem related with aging - pressure within eye elevated.
- Pressure rises because anterior eye chamber cannot exchange fluid properly by normal aqueous outflow. Increased pressure in vitreous compromises blood vessels of optic nerve and also axons of the ganglion cells.
42
What is retinitis pigmentosa?
- Hereditary disease with no cure. Many different forms.
- Rods of peripheral retina degenerate in early stages of disease. Night blindness is the first sign of disease. Patients develop tunnel vision - only the fovea is spared.
- Black pigment in peripheral retina and thinned blood vessels at optic nerve head.
43
What is diabetic retinopathy?
- Eye blood vessels become distorted and multiply.
| - Treated with laser treatment to stop blood vessel proliferation and fluid leakage.
44
What is hereditary retinal dystrophy?
Inability of RPE to phagocytize worn out discs from rods.
45
Describe the lacrimal gland.
Compound tubuloalveolar gland which secretes tears. Tears drain by ducts into conjunctival region. Tears contain lysozyme.
46
What is the auricle?
Outer ear - Irregularly shaped core of elastic cartilage covered by thin skin with hair and sebaceous glands.
47
Describe the external auditory meatus.
- Outer half supported by elastic cartilage.
- Inner half is a tunnel through the temporal bone
- Thin skin with large sebaceous and coiled tubuloalveolar ceruminous glands lines the entire meatus and outer surface of ear drum
48
What is ear wax?
Mixture of ceruminous and sebaceous secretions and desquamated meatal cells
49
What structures comprise the outer ear?
The auricle, external auditory meatus and canal, and tympanic membrane (eardrum)
50
What structures are found in the middle ear (tympanic cavity)?
Auditory (eustachian) tube, oval and round windows, auditory ossicles (malleus, incus, and stapes), and the tensor tympani and stapedius muscles (insert into the malleus and stapes)
51
Describe the tympanic cavity.
- Houses ossicles and connected to pharynx by eustachian tube.
- Lined by a simple squamous epithelium
- Epithelium changes to pseudostratified ciliated columnar epithelium near the opening to the auditory tube
52
What are the oval and round windows?
Small, membrane-covered regions devoid of bone. They separate the middle ear from the bony labyrinth of the inner ear. The oval window is next to the stapes.
53
What are the ossicles?
Malleus, incus, and stapes. These bones transmit tympanic membrane movements to the oval window. The malleus is attached to the tympanic membrane, and the stapes inserts into the oval window.
54
What do the tensor tympani and stapedius do?
Contraction of the tensor tympani (inserts into malleus) and stapedius (inserts into stapes) in response to loud sounds dampens the vibrations of the auditory ossicles
55
What is the inner ear?
A fluid filled membranous labyrinth is housed within a bony labyrinth.
56
Describe endolymph vs perilymph.
- Fluid within the membranous labyrinth (ML) is endolymph, high in potassium.
- Fluid within the bony labyrinth is perilymph (outside ML), high in sodium. Perilymph is similar to extracellular fluid but with low protein content.
57
What structures lie within/comprise the inner ear?
Bony labyrinth (semicircular canals, cochlea, scala vestibuli, and scala tympani), Membranous labyrinth (vestibular organ = saccule, utricle, cristae ampullae of the semicircular ducts; auditory organ = organ of Corti, cochlear duct)
58
Describe the vestibular organ (includes semicircular canals and ducts, saccule, utricle, and vestibule)
Semicircular canal is the bony structure.
Contain semicircular ducts - part of the membranous labyrinth.
Vestibule (bony structure, continuous with s. canal) contains perilymph
Saccule and utricle are housed within the vestible, membranous, and contain endolymph
59
What is the cochlea? Describe it.
- The cochlea winds 2.5X around a bony core called the modiolus, that has blood vessels and the spiral ganglion.
- The osseous spiral lamina is a lateral extension of the modiolus which extends about halfway to the outer wall of the tube
- The spiral ligament is a thickened periosteum at the outer wall of the tube
- The basilar membrane and bony spiral lamina, together, form the floor of the cochlear duct, upon which the Organ of Corti sits
- Cochlea is subdivided into 3 spaces: perilymph filled scala vestibuli and scala tympani and the endolymph filled scala media (=cochlear duct)
60
Describe endolymph
- Low Na+ content and high K+ content
- Fills the membranous labyrinth
- Similar to intracellular fluid
61
Describe the saccule and utricle
- Located within the vestibule
- Sac-like bodies of connective tissue lined by simple squamous epithelium
- Each gives off a duct and the two ducts join and form the endolymphatic sac
- Contain specialized regions, maculae, that have 2 types of neuroepithelial hair cells
62
What are vestibular hair cells?
- Found in the maculae of the utricle and saccule
- Neuroepithelial cells that have 50-100 rigid stereocilia (sensory microvilli) arranged in rows, and a single cilium (kinocilium). Cilia extend from the apical surface of the hair cells to an overlying gelatinous layer (otolithic membrane)
63
Describe Type 1 (vestibular) hair cells
Bulbar shape with round nuclei. Surrounded by a cup-shaped afferent nerve ending.
64
Describe Type 2 (vestibular) hair cells
Columnar with a round, basal nucleus. Contact small afferent nerve terminals with synaptic vesicles.
65
Describe vestibular support cells.
Columnar with round, basal nuclei. Prominent terminal web.
66
Describe the otolithic membrane.
Thick, gelatinous (glycoprotein) layer. Contains small, calcified particles (otoliths, otoconia). Functions in detection of linear acceleration (uses the mass of the otoliths)
67
Where do the semicircular ducts arise from?
The utricle
68
What are the ampullae?
Dilated area of the semicircular ducts near their junction with the utricle
69
What are cristae ampullae?
Specialized sensory areas in ampullae. Similar to maculae (in utricle and saccule), but with a thicker, cone-shaped glycoprotein layer with no otoliths (cupula).
70
What is the function of the cristae ampullae?
Detects angular acceleration of the head along any of the three axes.
71
What is the endolymphatic duct?
Leads to the endolymphatic sac
72
What is the endolymphatic sac? Describe it.
It is lined by columnar cells with irregularly shaped nuclei, and columnar cells with long microvilli. May find phagocytic cells (macrophages, neutrophils) in the lumen that function in endolymph reabsorbtion.
73
What is the cochlear duct?
Specialized area of the saccle that has the spiral organ of Corti. The scala vestibuli lies above, and the scala tympani lies below. These 2 scalae (contain perilymph) communicate with each other by a small hole near the cochlear apex called the helicotrema.
74
What is the vestibular (Reissner) membrane of the cochlea?
Composed of 2 layers of flattened squamous epithelium separated by basement membrane. Functions to maintain ionic gradients between perilymph in the scala vestibuli and endolymph in the cochlear duct
75
What is the stria vascularis?
Vascularized pseudostratified epithelium wich lines the lateral aspect (outer wall) of the cochlear duct. May secrete endolymph.
76
What is the spiral prominence?
Epithelium-covered protuberance on lateral aspect of cochlear duct - extends the length of the cochlear duct. Epithelium is continuous with the stria vascularis and is reflected onto the basilar membrane. #18 on http://hereditaryhearingloss.org/main.aspx?c=.HHH&n=87162
77
What is the basilar membrane? (Describe)
Thick layer of amorphous material with keratin-like fibers
78
What is the tectorial membrane?
Makes contact with the processes of hair cells. Secreted by interdental cells of the spiral sulcus. #3 on http://hereditaryhearingloss.org/main.aspx?c=.HHH&n=87143
79
What is the spiral organ of Corti?
Contains hair cells and several supporting cells. Lies on the basilar membrane. Contains inner tunnel of Corti and outer tunnel (where is the outer tunnel?). These two tunnels communicate with each other via intercellular spaces.
80
Describe hair cells (in the cochlea)?
Neuroepithelial cells with round, basally located nuclei. Have many long, stiff stereocilia and no kinocilium (in contrast to hair cells in the vestibular organ). Inner and outer hair cells in the cochlear duct.
81
Describe inner hair cells.
Organized in a single row along the length of the cochlear duct. Receive afferent synaptic terminals on the basal surface. Also function in sound reception.
82
Describe outer hair cells.
Organized in 3-5 rows with a cup-shaped afferent nerve ending. Function in sound reception and respond to different sound frequencies. Stereocilia are embedded in the gelatinous tectorial membrane.
83
What are inner and outer pillar cell? Why do they exist?
Closely associated with each other and rest on the basilar membrane. Enclose and support the inner tunnel of Corti.
84
What are inner and outer phalangeal cells? Why do they exist?
Closely associated with inner and outer hair cells, respectively. Support the nerve fibers that form synapses with hair cells.
85
What are cells of Hensen and border cells?
These mark the inner and outer borders of the spiral organ of Corti (Hensen the border guard?)
86
Describe the mechanism of hearing/the function of the auditory organ.
- Sound strikes the timpanic membrane.
- Vibration via ossicle bones and movement of stapes at oval window disturbs perilymph and deflects the basilar membrane in the organ of Corti.
- The pillar cells attached to the basilar membrane move laterally in response to this deflection, which causes a lateral shearing of the stereocilia on sensory hair cells against the tectorial membrane.
- Movement of the stereocilia is transduced into electrical impulses, which travel via the cochlear nerve to the brain.
- For more details, see "Ear functions - auditory - more detail" (not in flashcards)
87
Describe the function of the vestibular organ.
- Change in head position causes a flow of the endolymph in the semicircular ducts (circular) or in the saccules and utricles (linear).
- Endolymph movement in the semicircular ducts displaces the cupula overlying the cristae ampullae and bending of the stereocilia on sensory hair cells.
- Endolymph movement in saccules and utricles displaces otoliths. Displacement transmitted to the maculae via the overlying gelatinous layer, causing bending of stereocilia on sensory hair cells.
- Movement of stereocilia is transduced into electrical impulses, which are transmitted to the brain via vestibular nerve fibers.
88
What is nerve deafness? What are some causes?
Lesion in nerves transmitting impulses from organ of Corti. Some causes include: disease, drugs, or prolonged loud noise.
89
What is conductive hearing loss? What are some causes?
Hearing loss that occurs prior to the oval window - a defect in sound wave conduction. Some causes are inflammation (otitis media) or otosclerosis in the middle ear (fusion of the ossicles).
90
How can conductive hearing loss be tested for?
Use "bone conduction." When a tuning fork is touched to the head, vibrations conduct directly to the cochlea through the bone. A person with only conductive hearing loss can detect tuning fork sounds as well as someone with normal hearing.
