Where are more than half the sensory receptors of human body contained?
the eye
What protects the eye?
accessory structures
- eyelids
- extraoccular muscles
- lacrimal apparatus
What are the layers of the eyeball? What type of tissues are they?
- fibrous layer (tunica)
- vascular layer (middle layer)
- nervous layer
- these are connective tissues
What is 5/6ths of the posterior part of the fibrous layer? What does it do?
- the posterior 5/6ths of it is made up of whitish dense connective tissue called the sclera
- it protects the inner parts of the eyeball and serves as the attachment site for extraocular muscles and maintains the shape of the eyeball
Where does the optic nerve and blood vessels penetrate the fibrous layer?
the posterior aspect of the sclera
What is the anterior 1/6th of the fibrous layer?
What does it do?
- called the cornea
- transparent and lacks blood vessels
- covered by conjunctiva
- anteriorly convex so it helps focusing the light onto the retina
What are the parts of the vascular layer of the eyeball?
- choroid
- ciliary body
- iris
What forms the 5/6ths of the vascular layer?
What does it do?
- choroid
- lines the inner surface of the sclera
- highly vascularized and nourishes the retina
- the choroid carries melanin pigments that absorb the light rays and prevents the reflection of light within the eyeball
What is the anterior continuation of the choroid layer of the vascular layer? What does it do? What is it composed of?
- the ciliary body
- secretes aqueous humour
- modifies the convexity of the lens
- the core is formed by the circular smooth muscle fibres, the ciliary muscle
- suspensory ligaments stretch between the inner surface of the ciliary body and the circumference of the lens
What is the suspensory ligament? Where is it?
- it is a delicate fibre
- located between the inner surface of the ciliary body and the circumference of the lens of the eye
What causes the lens to adapt to near vision? What about far vision?
- contractions of the ciliary muscles alters the convexity of the lens to allow for near vision
- relaxation of the muscle causes far vision
What forms the anterior 1/6th of the vascular layer of the eye? How is it made? What does it do?
- the iris
- forms a vertical disk in front of the lens and behind the cornea
- the core of iris is made by smooth muscle fibers that are arranged in circular or radial manner
- the iris carries melanin pigments that determines the colour of the eye based upon the amount of pigment there is
How is the pupil altered? What does this do?
- via contraction of the muscle fibers of the iris
- the parasympathetic activation contracts the circular muscle fibers that entails constriction of the pupil
- the sympathetic activation contracts the radial muscle fibers that leads to dilation of the pupil
- determines the amount of light entering the eyeball
What the parts to the nervous layer of the eye?
- retina
- anterior 1/4th
What makes up the posterior 3/4ths of the nervous layer? What is it composed of?
- the retina
- carries photoreceptors
Where is the optic nerve in the eye? What is its’ effect on vision?
- it is the optic disc of the retina
- causes a blindspot in vision
What does the macula lutea do in the eye? What is it composed of? Where is it located?
- very sensitive to light
- it is composed of color detecting photoreceptors
- situated lateral to the optic disc
Where is the highest concentration of photoreceptors?
the fovea which is the center of the macula lutea
What does the anterior 1/4th of the the nervous layer do? What is it made of?
- has no photoreceptors
- carries pigments
- lines the ciliary body and the posterior surface of the iris
What is the lens made of?
- transparent, biconvex, elastic body
- lacks blood vessles
Where is the lens located?
posterior to the iris
How is the lens held in place?
by suspensory ligaments that act as the tendons of the ciliary muscles
What are the 3 chambers of the eye?
- anterior
- posterior
- vitreous
Where is the anterior chamber located?
between the cornea and the iris
