Accessory Structures of the Eye

eyebrows

protect and shade eye from sun and sweat

Eyelids

folds of skin that cover and protect the eyes, controlling the amount of light entering.

Palpebral fissure

slit that separates eyelids

Lacrimal caruncle

located at medial commissure contains oil and sweat glands that help lubricate the eye.

tarsal plates

dense connective tissue structures that help structure and anhor the orbicular oculi and levator palpebrae muscles

ciliary glands

modified sweat glands

conjunctiva

transparent mucous membrane that produces a lubricating secretion

palpebral conjuctiva

lines underside of eyelids (waterline)

bulbar conjuctiva

membrane that covers whites of eyes but NOT the cornea

conjuctival sac

area where the perimeter of a contact lens rest

The action and controlling cranial nerve of the lateral rectus

moves the eyeball laterally and is controlled by the abducens

The action and controlling cranial nerve of the medial rectus

moves the eyeball medially and is controlled by the oculomotor nerve.

The action and controlling cranial nerve of the superior rectus

elevates the eyeball, turns it medially and is controlled by the oculomotor nerve

The action and controlling cranial nerve of the inferior rectus

depresses the eye, turns it medially and is controlled by the oculomotor nerve

The action and controlling cranial nerve of the inferior oblique

elevates the eyeball, turns it laterally and is controlled by the oculomotor nerve.

The action and controlling cranial nerve of the superior oblique

depresses the eyeball, turns it laterally and is controlled by the trochlear nerve.

what is the outermost layer of the eye?

the fibrous layer

what is the intermediate layer of the eye?

the vascular layer

what is the inner layer of the eye?

the retinal layer

what is the name of the fluid the retinal layer is filled with

humor

what does the lens in the eye separate

the internal cavity into anterior and posterior segments

the two regions of the fibrous layer

the sclera and the cornea

the sclera

opaque posterior region that shapes the eye and anchors extrinsic eye muscles

the cornea

transparent anterior region that focuses light entering the eye and protects the eye via a thin layer of epithelium

the regions of the vascular layer

the choroid, ciliary body, and iris

the choroid

the middle layer of the eye containing blood vessels that nourish the eye and absorb excess light via brown pigment

ciliary body

a structure that controls the shape of the lens and produces aqueous humor.

the iris

the colored part of the eye found between the cornea and lens that controls the size of the pupil and regulates the amount of light entering the eye.

the pupil

the opening in the center of the iris that regulates the amount of light entering the eye by being constricted

what does distant dim lit vision cause the pupil to do?

The pupil dilates to allow more light to enter

what does close, brightly lit vision cause the pupil to do?

The pupil constricts to reduce the amount of light entering.

What comprises the retinal layer?

the pigmented (outer) and neural (inner) layer

where do photoreceptors live?

in the retinal layer of the eye

phototransduction

a process in which pigment captures photon of light energy and is then converted into a graded receptor potential

Describe the process of rhodopsin generation, breakdown and regeneration

opsin and 11-cis retinal become rhodopsin. light absorption causes 11-cis retinal to change to all-trans retinal, leading to rhodopsin breakdown. The all-trans retinal is converted back to 11-cis retinal, allowing regeneration of rhodopsin.

What is glutamate?

a neurotransmitter released by photoreceptors in the dark, inhibiting bipolar cells by hyperpolarizing them to prevent a strong graded potential from activating a ganglion cell.

What is the role of the retina in the visual stimulant pathway?

convert light into neural signals through phototransduction, enabling the processing of visual information before it is transmitted to the brain via the optic nerve.

What is the role of the optic nerve in the visual stimulant pathway?

process the electrical signals via bipolar or ganglion cells which form at the optic nerve to carry the signal to the brain

what is the role of the optic chiasm in the visual stimulant pathway?

the nerve fibers cross here and signals from the left visual field go to the right visual field and vice versa

what is the role of the lateral geniculate nucleus relay station in the visual stimulant pathway?

After the signal crossing, the signals continue down the optic tracts to this part of the thalamus which organizes and refines the visual input.

what is the role of the primary visual cortex in the visual stimulant pathway?

optic radiations from the lateral geniculate nucleus carries signals to this structure in the occipital lobe that processes edges, shapes and motion

what is the role of the higher-level processing center in the visual stimulant pathway?

this is split into two parts, the dorsal stream and the ventral stream

what is the role of the dorsal stream in the visual stimulant pathway?

processes space (where)

what is the role of the ventral stream in the visual stimulant pathway?

processes objects, colours and faces (what)

macula lutea

contains mostly cones that are responsible for high visual acuity

optic disc

blind spot containing no rods or cones, this is where the optic nerve exits the eye

fovea centralis

a small pit in the retina that contains the highest concentration of cones, providing the sharpest vision.

why does the lens change shape?

so light can be focused onto the fovea centralis found in the macula lutea to get the highest vision possible

Describe the pathway of tears

Tears are produced in the lacrimal glands, then flow across the surface of the eye, draining into the lacrimal puncta, followed by the lacrimal canaliculi, and finally into the nasolacrimal duct, which empties into the nasal cavity.

What effect does light have on photoreceptor cells?

hyperpolarizes the cells that stop the production of glutamate and depolarizes the bipolar cells to activate the ganglion cells that generate action potentials and allow for vision via the optic nerve