Special Senses (Eye) Flashcards
What is the eye?
organ of vision very important to human survival
What is contained within the eye?
more than ½ of sensory receptors of human body
What is 40% of the cerebral cortex for?
devoted to processing of visual information
What is the eyeball supported and protected by?
accessory structures including eyelids, extraocular muscles, and lacrimal apparatus
Eyeball
What is the shape?
symmetric, spherical structure
Eyeball
What is the eyeball surrounded by?
layer of loose connective tissue that allows its relatively free movement within orbital cavity
Eyeball
What are the 3 layers or tunics of the eyeball?
fibrous layer (tunic)
vascular layer
nervous layer
Eyeball - Fibrous Layer (Tunic)
What is the fibrous layer (tunic)?
outermost layer
Eyeball - Fibrous Layer (Tunic)
What is the sclera?
posterior ⅚ of fibrous layer made up of white-ish dense connective tissue
Eyeball - Fibrous Layer (Tunic)
What does the sclera do?
- protects inner parts of eyeball
- serves as attachment site for extraocular muscles
- maintains shape of eyeball
Eyeball - Fibrous Layer (Tunic)
What penetrates the posterior aspect of the sclera?
- optic nerve
- blood vessels
Eyeball - Fibrous Layer (Tunic)
What is the cornea?
anterior ⅙ of layer that is transparent, lacks blood vessels, and is covered by conjunctiva
Eyeball - Fibrous Layer (Tunic)
What does the cornea do?
contribute in focusing light onto retina
Eyeball - Vascular Layer
What is the vascular layer?
middle layer that consists of 3 parts
- choroid
- ciliary body
- iris
Eyeball - Vascular Layer
What is the choroid?
forms posterior ⅚ of layer and lines inner surface of sclera
Eyeball - Vascular Layer
What does the choroid do?
- highly vascularized and nourishes retina
- carries melanin pigments that absorbs light rays and prevents reflection of light within eyeball
Eyeball - Vascular Layer
What is the ciliary body?
anterior continuation of choroid
Eyeball - Vascular Layer
What does the ciliary body do?
secretes aqueous humour and modifies convexity of lens
Eyeball - Vascular Layer
What is the core of the ciliary body formed by?
ciliary muscle (circular smooth muscles fibers)
Eyeball - Vascular Layer
What are suspensory ligaments?
delicate fibres stretched between inner surface of ciliary body, and circumference of lens
Eyeball - Vascular Layer
What does contraction of ciliary muscle do?
alters convexity of lens to adapt for near vision
Eyeball - Vascular Layer
What does relaxation of ciliary muscle do?
alters convexity of lens to adapt for far vision
Eyeball - Vascular Layer
What is the iris?
anterior ⅙ of vascular layer
Eyeball - Vascular Layer
What does the iris form?
vertical disc in front of lens, and behind cornea
Eyeball - Vascular Layer
What is the core of the iris formed by?
smooth muscle fibers arranged in circular or radial manner
Eyeball - Vascular Layer
What is the pupil?
central opening of iris whose diameter is altered by contraction of smooth muscles fibers, which determines amount of light entering eyeball
Eyeball - Vascular Layer
What does parasympathetic activation of the iris do?
contracts circular muscle fibers that entails constriction of pupil
Eyeball - Vascular Layer
What does sympathetic activation of the iris do?
contracts radial muscle fibers that leads to dilation on pupil
Eyeball - Vascular Layer
What does the iris carry?
melanin pigments, and the amount determines eye colour
Eyeball - Nervous Layer
How many parts of the nervous layer are there?
2
Eyeball - Nervous Layer
What is the retina?
posterior ¾ of nervous layer that carries photoreceptors that are sensitive to light
Eyeball - Nervous Layer
Describe the anterior ¼ of the nervous layer.
doesn’t have any photoreceptor, but carries pigments and lines ciliary body and posterior surface of iris
Eyeball - Nervous Layer
Where does the optic nerve leave the retina?
optic disc (blind spot), which lacks photoreceptors
Eyeball - Nervous Layer
What is the macula lutea?
situated lateral to optic disc, and is very sensitive to light due to abundance of colour detecting photoreceptors
Eyeball - Nervous Layer
What is the fovea centralis?
center of macula lutea that contains highest concentration of these colour detecting photoreceptors
Lens
What is the lens?
transparent, biconvex, elastic body that lacks blood vessels
Lens
Where is the lens?
posterior to iris
Lens
What holds the lens in place?
suspensory ligaments that act as tendons of ciliary muscles
Interior of Eyeball
What are the 3 chambers?
anterior chamber
posterior chamber
vitreous chamber
Interior of Eyeball
Where is the anterior chamber?
lies between cornea and iris
Interior of Eyeball
What is the anterior chamber filled with?
aqueous humour (a clear fluid)
Interior of Eyeball
What does aqueous humour do?
- cushions lens and cornea
- provides transport system for nutrients and waste materials
Interior of Eyeball
Where is the posterior chamber?
lies behind iris and in front of lens, and is continuous with anterior chamber through pupil
Interior of Eyeball
What is the posterior chamber filled with?
aqueous humour, that is secreted by ciliary body
Interior of Eyeball
Where does aqueous humour flow in the posterior chamber?
fills posterior chamber, flows through pupil, fills anterior chamber, and eventually drains into canal of Schlemm (scleral venous sinus) at junction of sclera and cornea
Interior of Eyeball
Where is the vitreous chamber?
lies between lens and retina
Interior of Eyeball
What is the vitreous chamber filled with?
vitreous body (vitreous humour) - clear jelly-like substance
Interior of Eyeball
What does vitreous body (vitreous humour) do?
- helps maintain shape of eyeball
- cushions lens
- holds retina against choroid
Interior of Eyeball
When does vitreous body (vitreous humour) form?
during embryonic life
Interior of Eyeball
Compare vitreous body (vitreous humour) vs. aqueous humour.
vitreous body (vitreous humour) does not undergo constant turnover, unlike aqueous humour
What are the 3 accessory structures of the eye?
- eyelids (palpebrae)
- lacrimal apparatus
- extraocular muscles
Eyelids (Palpebrae)
What are eyelids?
thin skin folds in front of eyeball that protect eye against excessive light and foreign objects
Eyelids (Palpebrae)
What is the core of the eyelids formed by?
tarsal plate (fibroelastic plate) and skeletal muscles
Eyelids (Palpebrae)
What is the inner surface lined by?
conjunctiva - mucous membrane that reflects on eyeball to cover cornea
Eyelids (Palpebrae)
What is found at the free margin of eyelids? (3)
eyelashes
sweat glands
sebaceous glands
Lacrimal Apparatus
What is the lacrimal apparatus composed of? (4)
group of structures that produce and drain tears
- lacrimal gland
- lacrimal canaliculi
- lacrimal sac
- nasolacrimal duct
Lacrimal Apparatus
Where is the lacrimal gland?
occupies superolateral part of orbital cavity
Lacrimal Apparatus
What does the lacrimal gland do?
release tears on surface of eye – tears are swept across ocular surface by blinking movements of eyelids and are collected at medial corner of eye
Lacrimal Apparatus
What are the lacrimal canaliculi?
pair of small tubes on medial corner of eye that drain tears into lacrimal sac
Lacrimal Apparatus
What is the lacrimal punctum?
opening of lacrimal canaliculi
Lacrimal Apparatus
What is the lacrimal sac?
membranous sac that fills lacrimal groove of lacrimal bone, and receives tears from lacrimal canaliculi
Lacrimal Apparatus
What is the nasolacrimal duct?
distal continuation of lacrimal sac which empties into lateral wall of nasal cavity at inferior nasal meatus
Extraocular Muscles
What are extraocular muscles?
extrinsic muscles of eye that arise from different parts of orbit, and insert to sclera
skeletal muscles that move eyeball in different directions
Extraocular Muscles
What are the intrinsic muscles of the eye?
smooth muscles of iris and ciliary body
