The Human Eye
Lecture test #1 - 2/4/14
Terms in this set (38)
..., Anterior transparent region of the modified sclera that admits light into the eye. Most of it has very compact layers of collagen fibrils and thin flat fibroblasts; covered by a thin stratified squamous epithelium anteriorly and a simple squamous epithelium posteriorly. Clear, allows for vision; anterior; modified into transparent, avascular;
A ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.
Equilibrium and balance, hearing, vision, smell and taste
A hard working structure that changes shape & size to focus. It is clear and avascular. A cataract is a clouding of the lens inside the eye which leads to a decrease in vision. It is the most common cause of blindness and is conventionally treated with surgery. Visual loss occurs because of opacification of the lens prevents light from passing through and being focused on the retina at the back of the eye.
posterior cavity of the eye
contains Vitreous Humor (transparent gel 99% water) - very gentle with dissections because high probability of cutting too deep and water spilling everywhere, fills most of the eyeball helps keep the retina in place, not produced until you are 4-5 years old, only half full by the time you are 70 years old, it is not replaced, can lead to floaters (see floaters with age - caused by detatchment of vitreous humor because of the water), CHANGES FROM A GEL TO A LIQUID WITH AGE
anterior cavity of the eye
space between the cornea and the lens; filled with aqueous liquid, contains aqueous humor that helps maintain shape of eyeball and supplies oxygen and nutrients to the lens and cornea
The inner layer of the eye which translate light, shadow, movement, and contrast into recognizable images. The photoreceptors known as rods and cones, capture light, which is instantly changed to electrical impulses. These signals then travel from nerve cell to nerve cell, along the optic nerve, and ultimately to the brain, which converts them to understandable forms.
Known as the white or white of the eye, is the opaque, fibrous, protective, outer layer of the eye containing collagen and elastic fibre.
Tissue on the inner side of the eyelid (pink eye is an infection of it)
A protective membrane which secrets mucus like substance., One of the accessory structures of the eye. A transparent mucous membrane. Lines the eyelids as the Palpebral conjuctiva and reflects into the bulbar conjuctiva which covers "white" of the eye. Very thin and blood vessels underneath are easily visible. Slitlike space between eyeball and eyelid is known as conjunctival sac. Main function is to provide a mucus to lubricate the eyes and prevent drying out of the eyes.
Clear membrane covering the exposed scelera is used for protection. Infection causes pink eye.
A raised area around the foevaThis area contains approximately 6 million is where the visual image arrives after it passes through the cornea and lens. Contains no rods. The very highest concentration of cones occures at the center of the macula, an area called the "fovea centralis" or just the "foeva".
the central area of the macula which has the highest concentration of cones. It is the site of sharpest vision. Although the foeva makes up only 5% of the macula, it takes 50% of occipital lobe of the brain to process this small area.
4 non-photo-receptors cells of the eye
Amacrine, bipolar, ganglion and horizontal.
A neuron that transmits signals laterally in the retina. Amacrine cells synapse with bipolar cells and ganglion cells.
Abnormal blind spots that are fixed in position
Rods and cones are imbedded in pigmented epithelium which has a reflective surface
Controlled by the autonomic nervous system. In bright light pupils constrict to reduce the intensity of the light (controlled by the sympathetic nervous system). In the dark the allows for more light to enter by causing the pupils to dilate (this reactions is controlled by the parasympathetic nervous system).
retina bi-polar cells
These cells receive information from the photoreceptors (either multiple rods or a single cone) and delivers information to the ganglion cell dendrites. They also synapse with amicron cells.
All axons of these neurons extend back to the optic disk; part of the sclera, which contains perforations through which the fibers emerge from the eyeball as the optic nerve.
rods and cones
Light enters the eye throught the transparent cornea, it then passes through the lens and it is focused on the retina. In the retina there are cells which are sensitive to light called RODS and CONES. Rod cells are responsible for nigh vision and respond to light of low intensity. They are located primarily around the periphery of the retina. Cone cells are responsible for color vision and only respond to light of high intensity. We have most of our cones in the FOVEA where the light from the center field is focused. When light stimulates rods and cones, they send impulses to the brain along the optic nerve. The brain interprets these impulses to make a picture.
rod and cone cells
The photoreceptor consists of 1) an outer segment, filled with stacks of membranes (like a stack of poker chips) containing the visual pigment molecules such as rhodopsins, 2) an inner segment containing mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs, 3) a cell body containing the nucleus of the photoreceptor cell and 4) a synaptic terminal where neurotransmission to second order neurons occurs.
types of cones
Different cones respond to different colors of red, green and blue. This response is due to the amount of rhodospin in each cone. Some people have different amounts of cones leading to color blindness.
Respond to shades of grey and are stimulated in dim light.
The Visual Pathways
The crossover of some nerve fibers occurs at the optic chiasm. As a result, each hemisphere receives visual information from the medial half of the field of vision of the eye on that side, and from the lateral half of the field of vision of the eye on the opposite side. Visual association areas integrate this information to develope a composite picture of the entire field of vision.
The optic disc is also called the blind spot. It is called this because there are no photoreceptors in this part of the retina. This is where all of the axons of the ganglion cells exit the retina to form the optic nerve.
occurs if aqueous humor cannot drain nto the scleral venous sinus, intraocular pressure rises because of the continued production of aqueous humor.
is a fluid that circulates within the anterior cavity, passing from the posterior chamber to the anterior chamber through the pupil. It also freely diffuses through the vitreous body and across the surface of the retina. Is formed through active secretion by epithelial cells of the cilary body's cilary processes. Because it circulates if forms an important route for nutrient and waste transport in addition to forming a fluid cushion.
6 muscles of the eye
superior rectus, inferior rectus, lateral rectus and medial rectus, each which move the eye up, down, and side to side. The superior oblique and the inferior oblique.
(oblique=neither perpendicular nor parallel)the superior oblique attaches to the eyeball on an angle and has a tendon that passes through a trochlea (pulley or wheel) that allows the eyeball to roll downward
attaches at an angle and allows the eye to roll up and outward.
cranial nerve II - optic nerve
innervates the retina of the eye.
cranial nerve III - oculomoter
inferior, medial, superior rectus, inferior oblique and levator palpebrae superioris muscles, intertrinsic eye muscles.
cranial nerve IV - trochlear
Superior oblique muscle.
lateral rectus muscle.
the inner layer commonly called the retina. It is the start of the visual pathway. Interestingly it is the only place in the body where blood vessels can be directly observed for vascular pathologies (hypertension, diabetes) .
aka blind spot is the area where the optic nerve (II) and retinal blood vessels enter the eye.,
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