Lab 10 11 Senses PDF

## Special Senses - Vision, hearing, taste, smell, and cutaneous sensation ### The Senses - **Skin** - **Nose** - **Ear** - **Tongue** - **Eye** ### Senses - **General senses of touch (tactile)** - Temperature- thermoreceptors (heat) - Pressure- mechanoreceptors (movement) - Pain- m...

## Special Senses - Vision, hearing, taste, smell, and cutaneous sensation ### The Senses - **Skin** - **Nose** - **Ear** - **Tongue** - **Eye** ### Senses - **General senses of touch (tactile)** - Temperature- thermoreceptors (heat) - Pressure- mechanoreceptors (movement) - Pain- mechanoreceptors - **Special senses** - Smell- chemoreceptors (chemicals) - Taste- chemoreceptors - Sight- photoreceptors (light) - Hearing- mechanoreceptors - Equilibrium- (balance) mechanoreceptors ### Eye: Outgrowth of the brain - **Cornea:** transparent front layer of the eye. Gets O2 via diffusion. Only human tissue that can be transplanted without the fear of rejection. - **Pupil:** Black hole of the eye (due to absorption of light by tissue) located in the center of the iris. Gets wider in the dark, and narrower in the light to control for the amount of light coming onto the retina. - **Iris:** Mostly smooth muscle. Controls the diameter of the pupil. Responsible for eye color. - **Lens:** Biconvex structure of the eye that allows for focus of light onto the retina via a process called refraction - light changes direction as it passes through the eye. - **Ciliary muscles:** Contract and relax to change the shape of the lens. - **Suspensory ligaments:** Holds the lens in position, attached to the ciliary muscles. - **Anterior chamber:** Between the lens and cornea. Contains Aqueous humor - watery fluid provides nutrition to the lens and cornea, maintains intraocular pressure, reabsorbs into the venous blood via the canal of Schlemm. - **Posterior chamber:** Behind the lens. Contains the Vitreous humor - gel-like fluid that keeps the eye from collapsing, lasts a lifetime, and is not replaced! - **Sclera:** White (outer of the three) portion of the eye. - **Choroid:** The dark middle layer of the eye responsible for absorption of the excess light that prevents light from scattering. Many animals' choroid have the tapetum retroreflector, which reflects visible light back through the retina, increasing the light available to the photoreceptors - therefore, their eyes glow at night. - **Retina:** Highly vascular, contains the photoreceptors. Signals leaving the retina travel via optic nerve to the brain. - **Macula lutea:** Located on the retina, responsible for high color vision in good light - due to high conc. of cones. - **Fovea centralis:** Located in the center of the macula lutea, contains packed and high conc. of cones - the sharpest area of vision in light. - **Optic disc:** Surrounds the optic nerve. Also known as the blind spot as a consequence of no photoreceptors in this area. ### Visual acuity (V.A) - Measurement of the spatial resolving capacity of the eye and is applied to central vision. - When you stand 20 feet from the chart and can read the letters on a line designed to be read at 20 feet, you are said to have 20/20 vision. If you are only capable of reading the line labeled 200 feet, you are said to have 20/200 vision (legally blind). ### Astigmatism - The lens has an uneven curvature on one of its surfaces. - Causes the image one sees to be blurred in one axis and sharp in other axes ### Photoreceptors - **Cones:** Detect color. 3 types of cones, other colors are due to stimulation intensity of 2 or more cones. The degree of stimulation from each cone type determines the color that is perceived by the brain. White light is a mixture of all cones being stimulated equally. - Green Cones - Red Cones - Blue Cones - **Rods:** responsible for vision at low light and are responsible for peripheral vision. - Main reason why colors are much less apparent in dim light. ### Color Blindness - Color blindness is a sex-linked hereditary condition which affects 8% of males and only 0.5% of females. The most common type is red-green color blindness, in which either the red or green cones are lacking. - If red cones are lacking, a condition called protanopia exists. Individuals that have this condition see blue green and purplish-tinted reds as gray. - A lack of green cones is designated as deuteranopia. ### Depth Perception - The ability to distinguish relative position or distance is dependent on a difference in position that the image presents upon the two retinas. Therefore, binocular vision is required for depth perception. ### Myopia - **Nearsightedness:** difficulty of seeing objects at a distance. - The eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. - **Concave lenses** are used to correct the problem. ### Hyperopia - **Farsightedness:** is when light entering the eye focuses behind the retina. - **Hyperopic eyes** are shorter than normal. - **Hyperopia** is treated using a **convex lens**. ### Ear - **Houses 2 senses:** - **Hearing:** Interpreted in the temporal lobe - **Equilibrium/Balance:** Interpreted in the Cerebellum - **Divided into 3 areas:** - **Outer/External ear:** For hearing only, ends at the tympanic membrane (eardrum) - **Structures:** Pinna (Auricle) - Collects sound, External auditory canal - Channels sounds inward. - **Middle ear:** For hearing only, Conducts the sound into the inner ear - **Structures:** 3 bones - Stapes, Malleus, Incus. - Vibration of the tympanic membrane moves the malleus. These bones transfer sound to the inner ear. - **Inner ear/ Bonny Labyrinth/ Osseus Labyrinth** - Contains sensory organs for hearing and balance, filled with perilymph. - **Structures:** - Equilibrium: Vestibule, Semicircular canals - Hearing: Cochlea ### Nerve and conduction deafness - Although deafness may have many different origins, there are essentially two principal categories. - If the cochlea or cochlear nerve is damaged, the condition is referred to as **nerve deafness**. - Damage to the eardrum or ossicles, on the other hand, will result in **conduction deafness**. ### Three simple hearing tests: - **Rinne Test** - **Weber Test** - **Audiometry** ### Gustation (Taste) - Taste and smell complement each other and respond to many of the same stimuli. - The tongue is covered by projections called papillae, which contain taste buds. Each taste bud contains many gustatory cells, and each cell has many microvilli cells dissolved in saliva. ### Taste Sensation Receptors and their stimuli: - **Sweet receptors:** Mostly mono and disaccharides (relatively insensitive) - **Salty receptors:** Sodium and some other metals - **Sour receptors:** Acid - **Bitter receptors:** Alkaloids/base (most sensitive) - **Umami receptors:** Glutamate, MSG, aspartate, meats ### Olfaction (Smell) - Receptors are bipolar neurons which extend through the Cribiform plate of the ethmoid bone and synapse in the olfactory bulb. - Can be categorized into seven areas: camphorous, musky, floral, peppermint, ethereal, pungent, & putrid. - Fastest sense to be fatigued - we lose about 50% of sensation within the first second. ### Cutaneous Sensation - Contains a variety of receptors, specific to touch, pressure, temperature, and pain. - Know these receptors: free nerve endings, Meissner's corpuscles, and Pacinian corpuscles. - Deeper pressure is sensed by Pacinian corpuscles. ### Structure Function Table (eye) | Structure | Function | |-----------------|------------------------------------------------------------------------------------------------------| | Anterior chamber | | | Posterior chamber| | | Choroid | | | Fovea centralis | | | Macula lutea | | | Iris | Made up of muscles which contract and relax to control the size of the pupil and therefore the amount of light that enters the eye.| | Pupil | A hole located in the centre of the iris which allows light to strike the retina. | | Lens | The lens is a clear disc, which is controlled by the ciliary muscles and suspensory ligaments. The lens focuses the light rays in order to produce a clear image on the retina. | | Cornea | This is a transparent area of the sclera at the front of the eyeball. This lets light into the eye and has an important role of focusing the light rays onto the retina. | | Suspensory ligament | The suspensory ligaments sit either side of the lens and are important for holding the lens in position.| | Ciliary muscle | The muscles are attached to the suspensory ligaments and by contracting/relaxing control the position of the lens so that it can focus the light.| | Retina | This is the area at the back of the eye, which contains clusters of light-sensitive cells. | | Sclera | This is the white, outer layer of the eye. The sclera is quite tough and also strong so that little damage can come to the eyeball. | | Optic nerve | When light-sensitive cells in the retina are stimulated, the impulses are sent along sensory neurones in the optic nerve to the brain to be interpreted. | | Blind Spot | The point where the optic nerve leaves the eye has no retina, therefore no light-sensitive cells.|