Chapter 15 Sensory System

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sclera

3 tunic layers of the eye. The outer layer of is the sclera, the middle layer is the choroid, and the inner layer is the retina. Each layer consists of additional structures and provides specific functions related to sight.

Oblique

Oblique means slanted and therefore an oblique muscle appears slanted.

eyes

The eyes are located in the bony orbits at the front of the skull. The structures of the eyes are arranged in three layers also called tunics. The eyes receive light rays, band, or refract, those rays and transmit the nerve impulses generated by the light rays to the occipital lobe of the brain. After the impulses reach the occipital lobe, they are interpreted as images and we are able to "see". Our vision is dependent on our health of our eyes, our sight-related nerves, and our brain.

3 Tunic Layers

The outer layer of is the sclera, the middle layer is the choroid, and the inner layer is the retina. Each layer consists of additional structures and provides specific functions related to sight.

conjunctiva

The outer layer of the eye consists of the sclera, cornea, and conjunctiva. The conjunctiva is a mucous membrane that lines the outer surface of the eye and the inside if the eyelid.

Retina

The posterior cavity makes up the remaining two-thirds of the eyeball. The retina lines the posterior cavity.

Tunics

The structures of the eyes are arranged in three layers, also called tunics.

Vitreous humor

Vitreous humor, also called vitreous gel, is a soft, clear, jellylike substance that contains millions of fine fibers. These fibers are attached to the retina and also help the eyeball retain its shape. Vitreous humor is necessary for gift. If the eyeball is injured and vitreous humor escapes, blindness can result. Both aqueous and vitreous humor help bend light rays as they pass through the eye and focus on the retina.

conjunctiv/o : word root

conjunctiva

corne/o : word root

cornea

kerat/o : word root

cornea

ocul/o : word root

eye

ophthalm/o : word root

eye

opt/o : word root

eye; vision

blephar/o : word root

eyelid

palpebr/o : word root

eyelid

vitre/o : word root

glassy; jellylike

ir/o; irid/o : word root

iris

phac/o; phak/o : word root

lens

photo/o : word root

light

pupill/o : word root

pupil

retin/o : word root

retina

scler/o : word root

sclera; hard

glauc/o : word root

silver; gray

dacryocyst/o : word root

tear sac

dacry/o : word root

tears

lacrim/o : word root

tears

uve/o : word root

uvea

aque/o : word root

watery

Accessory Structures:

Accessory structures of the eye include the orbit, eyebrows, eyelashes, oil glands, and lacrimal glands, fluid, sacs, and ducts. The purpose of the accessory structures is to protect the eye from disease and injury.

Three pairs of major eye muscles

In addition to the accessory structure, there are three pairs of major eye muscles. The six muscles: 1. superior oblique, superior rectus, lateral rectus, inferior rectus, inferior oblique, allow the eyes to execute a wide range of very precise movements. Rectus means straight and therefore a rectus muscle appears straight. Oblique means slanted and therefore an oblique muscle appears slanted.

Intraocular pressure

Intraocular pressure is a measurement of the fluid pressure inside the eyeball.

Uvea

The choroid, iris, and ciliary body are collectively known as the uvea.

How we see

The ciliary body and suspensatory ligaments adjust the shape of the lens to help focus light rays on the retina. When an object is near, the lens is shortened and becomes thicker; when an object is near, the lens is shortened and becomes thicker; when an object is distant, the lens is lengthened and becomes thinner.

Lacrimal Ducts : Accessory Structures

The lacrimal ducts drain lacrimal fluid away from from the eye and into the nose via the nasolacrimal duct.

Cones

The retina is the sensory nerve tissue that coats the inside of the eye. It contains nerve cells called rods and cones, which convert light rays into nerve impulses. Cones are responsible for the vision in bright light, central vision, and color vision.

Rods

The retina is the sensory nerve tissue that coats the inside of the eye. It contains nerve cells called rods and cones, which convert light rays into nerve impulses. Rods are responsible for vision in dim light and also peripheral vision.

Upper and Lower Eyelids: Accessory Structures

The upper and lower eyelids and eyelashes, along with the eyebrows, prevent foreign matter from reaching the eyes.

Lacrimal Sac : Accessory Structures

The upper expanded portion of the nasolacrimal duct is called the lacrimal sac.

Meibomian Glands: Accessory Structures

The meibomian glands, located between the conjunctiva and the tissue of the upper and lower eyelids, are small oil glands that lubricate the eyes. These glands are not visible unless they become obstructed.

choroid

3 tunic layers of the eye. The outer layer of is the sclera, the middle layer is the choroid, and the inner layer is the retina. Each layer consists of additional structures and provides specific functions related to sight.

retina

3 tunic layers of the eye. The outer layer of is the sclera, the middle layer is the choroid, and the inner layer is the retina. Each layer consists of additional structures and provides specific functions related to sight.

Rectus

Rectus means straight and therefore a rectus muscle appears straight.

Aqueous humor

The anterior cavity makes up the front one-third of the eyeball. The anterior cavity consists of the anterior chamber, the area in the front of the iris; and the posterior chamber, the area behind the iris and in front of the ligaments that hold the lens in place. These chambers are filled with a watery fluid called aqueous humor. Aqueous humor helps the eyeball maintain its shape, maintains the proper pressure within the eye; and nourishes structures in the eyeball. Intraocular pressure is a measurement of the fluid pressure inside the eyeball.

The Anterior Cavity

The anterior cavity makes up the front one-third of the eyeball. The anterior cavity consists of the anterior chamber, the area in the front of the iris; and the posterior chamber, the area behind the iris and in front of the ligaments that hold the lens in place. These chambers are filled with a watery fluid called aqueous humor. Aqueous humor helps the eyeball maintain its shape, maintains the proper pressure within the eye; and nourishes structures in the eyeball. Intraocular pressure is a measurement of the fluid pressure inside the eyeball.

refract

The eyes receive light rays, band, or refract, those rays and transmit the nerve impulses generated by the light rays to the occipital lobe of the brain.

Retina: Inner layer

The inner layer of the eye includes the retina, nerve cells, and optic disk. The retina is the sensory nerve tissue that coats the inside of the eye. It contains nerve cells called rods and cones, which convert light rays into nerve impulses. Rods are responsible for vision in dim light and also peripheral vision. Cones are responsible for the vision in bright light, central vision, and color vision. The optic disk, located at the back of the eye, is the area where the nerve endings of the retina come together to form the optic nerve. The optic nerve transmits impulses to the occipital lobe of the brain.

2 Interior eye cavities

The interior of the eye has two cavities: the anterior cavity and the posterior cavity. The anterior cavity makes up the front one-third of the eyeball. The anterior cavity consists of the anterior chamber, the area in the front of the iris; and the posterior chamber, the area behind the iris and in front of the ligaments that holds the lens in place. These chambers are filled with a watery fluid called aqueous humor. Aqueous humor helps the eyeball maintain its shape; maintains the proper pressure within the eye; and nourishes structures in the eyeball. Intraocular pressure is a measurement of the fluid pressure inside the eyeball. The posterior cavity makes up the remaining two-thirds of the eyeball. The retina lines the posterior cavity. Vitreous humor, also called vitreous gel, is a soft, clear, jellylike substance that contains millions of fine fibers. These fibers are attached to the retina and also help the eyeball retain its shape. Vitreous humor is necessary for gift. If the eyeball is injured and vitreous humor escapes, blindness can result. Both aqueous and vitreous humor help bend light rays as they pass through the eye and focus on the retina.

Iris

The iris which gives our eyes their unique color, is a muscular ring that surrounds the pupil. The iris adjusts the opening of the pupil to control the amount of light that enters the eye.

Lacrimal Glands : Accessory Structures

The lacrimal Glands located above the outer corner of each eye, produce lacrimal fluid that moisten the anterior surface of the eyeball.

nasolacrimal duct : Accessory Structures

The lacrimal ducts drain lacrimal fluid away from from the eye and into the nose via the nasolacrimal duct.

Lens

The lens also called the crystalline lens, is connected to the choroid by the ciliary body and the suspensatory ligaments.

Choroid: middle layer

The middle layer of the eye included the choroid, iris, pupil, lens, and ciliary body. The choroid is a layer of tissue beneath the sclera that contains blood vessels that supply oxygen and nutrients to the eye. The iris which gives our eyes their unique color, is a muscular ring that surrounds the pupil. The iris adjusts the opening of the pupil to control the amount of light that enters the eye. The lens also called the crystalline lens, is connected to the choroid by the ciliary body and the suspensatory ligaments. The choroid, iris, and ciliary body are collectively known as the uvea.

Optic Disk

The optic disk, located at the back of the eye, is the area where the nerve endings of the retina come together to form the optic nerve.

Optic Nerve

The optic disk, located at the back of the eye, is the area where the nerve endings of the retina come together to form the optic nerve. The optic nerve transmits impulses to the occipital lobe of the brain.

Orbit: Accessory Structures

The orbit, also called the eye socket, is the bony cavity of the skull that houses and protects the eyeball.

Cornea

The outer layer of the eye consists of the sclera, cornea, and conjunctiva. The cornea is the transparent anterior portion of the sclera that covers the iris.

sclera: outer layer

The outer layer of the eye consists of the sclera, cornea, and conjunctiva. The sclera is a tough or fibrous tissue that maintains the shape of the eyeball and serves as its protective covering. The sclera is commonly called the "white of the eyes".

posterior cavity

The posterior cavity makes up the remaining two-thirds of the eyeball. The retina lines the posterior cavity. Vitreous humor, also called vitreous gel, is a soft, clear, jellylike substance that contains millions of fine fibers. These fibers are attached to the retina and also help the eyeball retain its shape. Vitreous humor is necessary for gift. If the eyeball is injured and vitreous humor escapes, blindness can result. Both aqueous and vitreous humor help bend light rays as they pass through the eye and focus on the retina.


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