Special Senses

Cones

-Brighter light stimulates cones, which produce color vision

Lens

By changing its shape, the lens changes the focal distance of the eye. In other words, it focuses the light rays that pass through it (and onto the retina) in order to create clear images of objects that are positioned at various distances. It also works together with the cornea to refract, or bend, light.

Olfactory Nerve

It is the nerve which transmits special sensory information, allowing us to have a sense of smell.

Pupil constriction and dilation

Pupil dilates as radial muscles of iris contract (sympathetic_ Pupil constricts as circular muscles of iris contract (parasympathetic)

Ciliary Body

the ciliary body is a circular structure just behind the iris composed of the ciliary muscle and ciliary processes which attach to the lens. The ciliary processes secrete the aqueous fluid, and the ciliary muscle modifies focus by changing the shape of the lens adapting it for near and far vision

Rods

-Allows us to see in dim light, such as moonlight -Because rods do not provide color vision, in dim light we can see only black, white, and all shades of gray in between.

Accommodation

-When the eye is focusing on a close object, the lens becomes more curved, causing greater refraction of light rays. -The increase in curvature of the lens for near vision is called accomodation

How does accommodation occur?

-When you view a close object, the ciliary muscle contracts, which pulls the ciliary process and choroid forward toward the lens -This action releases tension on the lens and zonular fibers. -The lens becomes more spherical, which increases its focusing power and causes greater convergence of the light rays. -Parasympathetic fibers of the oculomotor nerve innervate the ciliary muscle of the ciliary body- mediating the process of accommodation

Photopigment

-a colored protein that undergoes structural changes when it absorbs light, in the outer segment of a photoreceptor.

Optic Disc- Also called the Blind Spot

-contains no rods or cones -cannot see images that strike the blind spot Thus, any light focused on the optic disc cannot be converted into sensory impulses nor sent to the brain for interpretation.

Iris

-function is to regulate the amount of light entering the eyeball through the pupil -The muscular iris moves to shrink the pupil if there is too much light and widen it if there is not enough

Fovea

-located in the center of macula -contains only cones -the area of highest visual acuity (sharpness of vision) due to high amount of cones When you bring your gaze to an object to examine it intently in bright light, the eyes orient so that the object's image falls on the fovea.

Sclera

-makes up the "white" of the eye -Functions - covers the entire eyeball except the cornea -gives shape to the eyeball - makes eyeball more rigid - protects the inner parts of the eye - serves as an attachment site for the extrinsic eye muscles

Convergence of the eyes

-refers to this medial movement of the two eyeballs so that both are directed toward the object being viewed. -The coordinated action of the extrinsic eye muscles brings about convergence

Choroid

-the posterior portion of the vascular tunic, lines most of the internal surface of the sclera -function is to provide nutrients to the posterior surface of the retina - also, produces melanocytes that make melanin. Melanin in choroid prevents reflection and scattering of light within the eyeball; resulting in clear and sharp images cast on the retina by cornea and lens

Rhodopsin

-the single type of photopigment in rods

Cornea

-transparent coat that covers the colored iris and the pupil -helps focus light onto the retina -allows light to enter the eye for vision

Vitreous Humor

Along with maintaining the shape of the eye, the vitreous helps absorb shocks to the eye and keeps the retina properly connected to the back wall of the eye. Light passes through the vitreous on its way to the retina.

Aqueous Humor

Aqueous is a thin, watery fluid located in the anterior and posterior chambers of the eye. The anterior chamber lies between the iris (colored part of the eye) and the inner surface of the cornea (the front of the eye). The posterior chamber is located behind the iris and in front of the lens. In addition to supporting the shape of this area, aqueous supplies nutrients and nourishment to parts of the eye that lack blood supply. It also removes waste.

The Intrinsic Eye Muscles and their innervation

The intrinsic muscles of the eye are the dilator (radial), the sphincter pupillae (circular) constrictor muscle and the ciliary muscle. Ciliary muscle and sphincter innervated by the parasympathetic component of cranial nerve II Dilator muscle innervated by the ascending cervical sympathetic system with its long course from spinal segments T1 through T3

Optic Nerve

The optic nerve is located in the back of the eye. ... The job of the optic nerve is to transfer visual information from the retina to the vision centers of the brain via electrical impulses. The optic nerve is made of ganglionic cells or nerve cells. It consists of over one million nerve fibers.

Pupil

The pupil is essentially a hole in the center of your iris that controls how much light enters the eye. It's size is controlled by the relaxing and contracting of the iris. When there is high light intensity, the pupil shrinks while it grows in low light intensity. This is to ensure there is enough light for vision without damaging the sensitive retina

Retina

The retina is a thin layer of tissue that lines the back of the eye on the inside. It is located near the optic nerve. The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition

Olfactory Tract

a long narrow triangular band of white tissue originating in the olfactory bulb and extending back to the point at which its fibres enter the base of the cerebrum

Olfactory Epithelium

a specialized epithelial tissue inside the nasal cavity that is involved in smell. In humans, it measures about 1 square centimeter (on each side) and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils. The olfactory epithelium is the part of the olfactory system directly responsible for detecting odor

Olfactory Bulb

structure located in the forebrain of vertebrates that receives neural input about odours detected by cells in the nasal cavity. The axons of olfactory receptor (smell receptor) cells extend directly into the highly organized olfactory bulb, where information about odours is processed.

olfactory cells

very slender nerve cells, with large nuclei and surmounted by 6-8 long, sensitive cilia in the olfactory epithelium at the roof of the nose; they are the receptors for smell.