Chapter 15 - The Special Senses Flashcards
Vision: Accessory Structures of the Eye - Eyebrows
a. Location – found over lying the supra orbital margins
b. Function – shade the eyes from sunlight and helps prevent sweat from getting into the eyes
Vision: Accessory Structures of the Eye - Eyelids
Palpebrae, mobile thin skin covered folds
a. Location – anterior skull
b. Function – protect the eye
Vision: Accessory Structures of the Eye - Eyelids: Structures
i. Palpebral fissure – eye lid slit; separates’ the eyelids
ii. Lateral and medial commissures – angles of the eyes (tear ducts)
iii. Lacrimal caruncle – found in the medial commissure; a little bit of flesh – contains sebaceous and sweat glands and produces the secretions during sleep
iv. Orbicularis oculi – found within the eye lid; the eye muscle that close the eye when it contracts
v. Levator palpebrae superioris – muscle; runs within the eyelid and it raises the eye lid to open
vi. Tarsal plate – connective tissue sheets that support the eye lids that anchor the orbicularis oculi muscle and the LPS muscle
vii. Tarsal gland – found embedding in the tarsal plates and their ducts open at the eye lid edge just posterior to the eye lashes; its producing secretion lubricates the eye lids that prevents the eye lids from sticking to each other
viii. Eyelashes – project from the free margin of each eye lid; they are innervated with nerve endings, anything that touches the eyelashes it triggers the blinking reflex
Vision: Accessory Structures of the Eye - Conjunctiva
a. Location – found surround the cornea, covering/lining the eyelids
b. Function – produces lubricating mucus that prevents the eye from drying out
c. Structures
i. Palpebral conjunctiva – conjunctiva that lines the eye lids (top and bottom)
ii. Bulbar conjunctiva – found over the anterior surface of the eye (main body not touching eyelids)
iii. Conjunctival sac – slit like space that occurs between the two conjunctivas, where a contact lies
Vision: Accessory Structures of the Eye - Lacrimal Apparatus
Glands and ducts that drain the secretions to the nasal cavity
a. Location – found surrounding the eye AND in the nasal cavity
b. Function – secrete secretions and drain tears
c. Structures
i. Lacrimal gland – found on the lateral side of the eye, above the orbit; it releases tears
ii. Excretory ducts – excrete tears or lacrimal secretions form the gland (gland to eye)
iii. Lacrimal puncta – two small red dots/openings that are visible on the medial margin of each eye lid
iv. Lacrimal canaliculi – pair that carries tears from the eyeball to the lacrimal sac
v. Lacrimal sac – carries tears from the canaliculi to the nasolacrimal duct
vi. Nasolacrimal duct – carries tears from the lacrimal sac to the nasal cavity
Vision: Accessory Structures of the Eye - Extrinsic Eye Muscles
a. Annular ring – common tendinous ring; found at the back of the oribit and its origin for the rectus muscles
b. Muscles – most preciously and rapidly controlled skeletal muscles of entire body
i. Superior rectus – elevates the eye and turns it medially CNIII
ii. Inferior rectus – depresses the eye and turns it medially CNIII
iii. Medial rectus – move eye medially CNIII
iv. Lateral rectus – move the eye laterally CNVI
v. Superior oblique – depresses the eye and turn it laterally CNIV
A. Trochlea – behaves as a pulley, it’s a fibro cartlenagenous that’s suspended from the frontal bone
vi. Inferior oblique - elevates eye and turns it laterally CNIII
c. Cranial nerves
Eye
- Protection
a. Orbit – cavity, space where the eye is housed
b. Fat – fat occupies all the space that isn’t occupied by the eye - Poles
a. Anterior pole – most anterior part of eye
b. Posterior pole – most posterior part of eye
Eye: Layers - Fibrous Layer
Fibrous layer – outer most coat of the eye, it consists of dense a vascular connective tissue
i. Sclera – from the posterior portion and the bulk of the fibrous layer, it’s very tough and tendon like that protects and shapes the eye ball; it provides a anchoring site from the extrinsic eye muscles
ii. Cornea – a vascular, this is found on the anterior 1/6 of the fibrous layer, this is transparent, it bulges anteriorly from its junction with the sclera; forms a window that lets light enter the eye
Eye: Layers - Vascular Layer
AKA uvea; forms the middle coat of the eye ball
i. Choroid – blood vessel rich; dark brown membrane, it forms the posterior 5/6 of the vascular layer
ii. Ciliary body – choroid anteriorly; it’s a thickened ring of tissue that encircles the lens
A. Ciliary processes – interlacing smooth muscle bundles that control the lens shape; folds that are found near the posterior surface of the lens, that contain capillaries that secrete fluid that fill the anterior segment of the eyeball
B. Ciliary zonule – aka suspensor ligament, that extend from the ciliary process to the lens; encircle and help hold the lens in place
iii. Iris – visible colored part of the eye, most anterior position of the vascular layer, found in between the cornea and the lens, its continuous with the ciliary body posteriorly it has 2 pupillae
A. Pupil – round central opening that allows light to enter the eye
B. Sphincter pupillae – circular muscles, close vision/bright light it contracts and the pupil constricts
C. Dilator pupillae – radial muscles, distant vision/dim light it contract and the pupils dilate (allowing more light to enter the eye)
Eye: Layers - Inner Layer
Inner most layer of the eye ball, very delicate. Two layer retina
A. Pigmented layer – outer layer, single thick lining it’s found next to the choroid, it extends anteriorly to over the ciliary body and the posterior face of the iris, and it absorbs light and prevents it from scattering
B. Neural layer – transparent inner layer it extends anteriorly to the posterior margin of the ciliary body
1. Ora serrata – saw toothed margin where the neural layer blends into the ciliary body
2. Photoreceptors – they are found next to the pigmented layer that helps spread signals in response to the light
a. Rods – more numerous, dim light, and peripheral receptors (b&w)
b. Cones – operate in bright light and they provide color vision
3. Bipolar cells – receive signals from the photoreceptors and send signals to the inner most ganglion cells
4. Ganglion cells – where the action potential is generated; they come together and make a right angle turn at the inner face of the retina, then leave the posterior aspect of the eye as the thick optic nerve
5. Horizontal cells and amacrine cells – other types of neurons that play a role visual processing
6. Optic nerve – made of ganglion cells it leaves the eye from the posterior aspect
7. Optic disc – blind spot; this region lacks photoreceptors, where the optic nerve exits the eye
8. Macula lutea – oval region that’s found lateral to the blind spot of each eye, and its located at the eyes posterior pole
9. Fovea centralis – small pit in the center of each macula lutea
10. Central artery and central vein – serves the inner 2/3 of the neural retina and they enter and exit through the optic nerve
Eye: Segments and Humors
Divided into segments from ciliary zonule and lens
a. Posterior segment – It’s larger and its filled with a clear gel (vitreous humor)
i. Vitreous humor – is formed in the embryo and lasts the entire lifetime; 1. Helps transmit light, 2. 3. Contributes to intraocular pressure helping to counter act the pulling force of the SO
b. Anterior segment – subdivided by the iris
i. Posterior chamber – area found in between the iris and the lens
ii. Anterior chamber – found between the cornea and iris
iii. Aqueous humor – fill the entire anterior segment, it’s a clear fluid that similar to blood plasma
iv. Scleral venous sinus – canal scalmm, unusual channel that encircles the eye at the sclea cornea junction
Eye: Lens
Lens – feels and looks like a marble (only oval), biconvex, transparent flexible structure that can change shape that allows focusing of light onto the retina; its enclosed in a thin elastic capsule that’s held in place by the it’s a vascular, it contains two regions
a. lens epithelium – confined to the anterior lens surface, that consists of cuboidal cells that differentiate into lens fibers
b. lens fibers – form the bulk of the lens, contain no nuclei and very few originals, they contain proteins crystallins
Olfactory
- Olfactory cilia – increase the receptive surface area; they lie flat on the nasal epithelium and are covered by a coat of thin mucus
a. Mucus – solvent that captures and dissolves air borne irritates
b. Olfactory glands – help produce mucus and they’re found in the underlying connective tissue - Filaments of olfactory nerve – CNI; slender unmylinated axons of the olfactory receptor cells that gather into small fascicles; project superiorly through the openings in the cribiform plate of the ethmoid bone
a. Olfactory bulb – the distal ends of the olfactory tract
b. Olfactory tract – composed of mytrol cell axons, it helps relay impulses to two destinations
Gustation (taste buds)
A. Locations
1. Fungiform papillae – mushroom shaped, scattered over the entire tongue surface
2. Foliate papillae – found on the side walls and they contain taste buds
3. Vallate papillae – largest and least numerous (7-12) form an inverted V at the back of the tongue
B. Structure
1. Gustatory cells – aka taste cells, type of epithelia cell that makes up the taste buds
a. Taste pore – neck like opening of each taste bud
b. Gustatory hairs – long microvilli that project off the tips of all gustatory cells; sensitive membrane
c. Taste fibers – cranial nerve fibers; they supply taste buds
2. Basal cells – dynamic stem cells that divide into new gustatory cells
Hearing: External Ear
- Auricle – aka pinna; shell shaped projections that found surround the external acoustic meatus (elastic cartledge)
a. Helix – thick rim of the auricle
b. Lobule – aka ear lobe; fleshy, dangling that lacks connective tissue
c. Tragous – triangle projections
d. Antitragous – connected to the lobe and helix
e. Anti helix – inner rim
f. Triangular fossa – inner part of the auricle
g. Conchea – inner part of the helix, external part of the external acoustic meatus - External acoustic meatus – auditory cannal; short curved tube that extends from the auricle to the ear drum
a. Ceruminous glands – modified aplecrin sweat gland that secrete serumen (ear wax) – it’s a sticky trap for foreign bodies and helps repel insects
