External and Accessory Structures The accessory structures of the eye include the extrinsic eye muscles, eyelids, conjunctiva, and lacrimal apparatus. It also can appear yellow in the elderly due to the accumulation of a pigment associated with age-related wear and tear in the tissue. When light strikes a rod or cone cell, it passes the signal to a bipolar cell, which passes it on to the ganglion cells, which perform the first level of information processing. Tunica vasculosa refers to the middle vascular layer. The eyes are located within the orbits, where they are protected by seven bones Connective tissues provide support and protective cushioning for the eyes. The lens, iris and cornea are nourished by clear fluid, aqueous humor, formed by the ciliary body and fill the space between lens and cornea. Option D: Each taste cell contains hairlike processes, called taste hairs.
This is also called the uvea. A tough white sheet called sclera covers the outside of the eye. The mechanism of vision may be summarized as follows figure 9. Most vertebrate animals have eyes that are essentially the same as the human eye. The Levator palpebræ raises the upper eyelid, and is the direct antagonist of the Orbicularis oculi.
The transparent inner neural layer of the retina contains millions of receptor cells, the rods and cones, which are called photoreceptors because they respond to light. Then the film must be developed or the digital images downloaded. Layers Forming the Wall of the Eyeball Now that we have covered the general anatomy of the eyeball, we are ready to get specific. This fluid provides a sort of circulatory system for the front of the eye. When the ciliary muscle is relaxed, the ligaments bands of tissue attached to the lens pull the lens flat and therefore less curved and weakly refractive. The breakdown of these pigments results in the formation of nerve impulses. The middle lamella, largely made up of non-striped muscular fibers, is inserted into the upper margin of the superior tarsus, while the deepest lamella blends with an expansion from the sheath of the Rectus superior and with it is attached to the superior fornix of the conjunctiva.
Depth perception is a result of stereoscopic vision. The sensory structures that detect taste stimuli are the: A. A camera needs an operator, a housing box to hold onto and to contain the working parts and film, an aperture to let the light in preferably one that allows for different light conditions , a lens for focusing the image, and film for capturing the image. It helps maintain the shape of the eye and provides attachment sites for the extrinsic eye muscles. Lacrimal gland The are the sites of tear production.
Passing lateralward, backward, and upward, at first between the Rectus inferior and the floor of the orbit, and then between the bulb of the eye and the Rectus lateralis, it is inserted into the lateral part of the sclera between the Rectus superior and Rectus lateralis, near to, but somewhat behind the insertion of the Obliquus superior. Each type of photopigment absorbs a different wavelength of light. Extrinsic eye muscles control the movement of the eyeballs. Both rods and cones contain light-sensitive pigments that break down into simpler substances when light is absorbed. Options A and C: The sensory retina contains photoreceptor cells called rods and cones, which respond to light. The middle layer vascular tunic mostly provides for internal maintenance functions, as well as for aperture and fine focusing control.
Phototransduction Vision occurs through the process of. The line of reflection of the conjunctiva from the upper eyelid on to the bulb of the eye is named the superior fornix, and that from the lower lid the inferior fornix. It lacks blood vessels and nerves that would block light rays from entering the eye. The tendon is reflected backward, lateralward, and downward beneath the Rectus superior to the lateral part of the bulb of the eye, and is inserted into the sclera, behind the equator of the eyeball, the insertion of the muscle lying between the Rectus superior and Rectus lateralis. Middle Ear The middle ear, or tympanic cavity, is a small, air-filled, mucosa-lined cavity within the temporal bone. Visual Fields and Visual Pathways to the Brain Axons carrying impulses from the retina are bundled together at the posterior aspect of the eyeball and issue from the back of the eye as the optic nerve. Conjunctiva is a transparent mucous membrane.
Most posterior is the choroid, a -rich nutritive tunic that contains a dark pigment; the pigment prevents light from scattering inside the eye. The eyelids have glands that produce lubricating secretions. Physiology of the Special Senses The processes that makes our special senses work include the following: Pathway of Light through the Eye and Light Refraction When light passes from one substance to another substance that has a different density, its speed changes and its rays are bent, or refracted. Sometimes the corresponding Recti of the two eyes act in unison, and at other times the opposite Recti act together. Because cones require bright light to function, only rods allow us to see in dim light.
They are imbedded in grooves in the inner surfaces of the tarsi, and correspond in length with the breadth of these plates; they are, consequently, longer in the upper than in the lower eyelid. Tears perform an important function in keeping the anterior surface of the eye moist and in washing away foreign particles. These fissures enable the hyaloids artery to reach the inner chamber of the eye, supplying it with blood. Be sure to grab a pen and paper to write down your answers. One type responds best to red light, another type responds best to green light, and the third type responds to blue light.
These receptors relay information concerning deep pressure, vibration, and position. The ocular muscles are the: Levator palpebræ superioris Rectus medialis. Some nocturnal animals have a reflective Structure of the human eye. The iris is made of two sets of smooth muscle that contract to produce pupil dilation or constriction; this brainstem reflex controls the intensity of the light reaching the innermost sensory layer, the retina. The relaxation of the ciliary muscles increases tension on the fibrous strands of the ciliary zonule and causes the lens to take on a more flattened shape. Middle Layer The middle layer includes the choroid, ciliary body, and iris.
Although the light-sensitive pigments are different in cones, they function in a similar way to rhodopsin. The ability of the eye to focus specifically for close objects those less than 20 feet away is called accommodation. The dorsal tongue surface is covered with small peg-like projections, or papillae. This leads to the formation of the double-layered optic cup. Some have simple eyespots that do not form images, detecting only the presence of light. The size of the pupil is adjusted by variable contractions of the iris muscles to control the amount of light entering.