Transcript The Senses
Objectives Classify sense organs as special or general and explain the basic differences between the two groups. Describe how a stimulus is converted into a sensation. Discuss the general sense organs and their functions. Classification of Sense Organs 1. General sense organs A. Individual cells or receptor units B. Widely distributed throughout the body 2. Special sense organs A. Large and complex B. Localized grouping of specialized receptors 3. Classification by presence or absence of covering capsule A. Encapsulated B. Unencapsulated (“free” or “naked”) 4. Classification by type of stimuli required to activate receptors A. Photoreceptors (light) B. Chemoreceptors (chemicals) C. Pain receptors (injury) D. Thermoreceptors (temperature change) E. Mechanoreceptors (movement or deforming of capsule) F. Proprioreceptors (portion of body parts or changes in muscle length or tension) Converting a Stimulus Into a Sensation All sense organs have common functional characteristics 1. All are able to detect a particular stimuli 2. A stimulus is converted into a nerve impulse 3. A nerve impulse is perceived as a sensation in the CNS General Sense Organs 1. Distribution is widespread 2. Single-cell receptors are common 3. Examples: A. Free nerve endings – pain and crude touch; skin and epithelial layers B. Meissner’s corpuscles – fine touch and vibration; skin, numerous in fingertips and lips C. Ruffini’s corpuscles – touch and pressure; skin and subcutaneous tissue of fingers D. Pacinian corpuscles – pressure and vibration; around joints, in mammary glands and external genitalia of both sexes E. Krause’s end bulbs – touch; skin, mucosa of lips and eyelids, external genitals F. Golgi tendon receptors – proprioreception (sense of muscle tension); near junction of muscles and tendons G. Muscle spindles - proprioreception (sense of muscle length); skeletal muscles General Sense Receptors Objectives 1. List the major senses. 2. List the special sense organs and its receptor. 3. Describe the structure of the eye and the functions of its components. 4. Describe the structure of the ear and the functions of its components. Major Senses Sight Hearing Taste Smell Touch Special Sense Organs Eye Rods and Cones Photoreceptor Vision The Eye Three primary layers of the eyeball 1. Sclera – tough, outermost, white layer that surrounds and protects the eye Its front surface (cornea) is transparent to let light enter the eye. 2. Choroid – middle layer; contains iris (colored portion of the eye) The hole in the center of the iris is the pupil. Light enters the pupil and the size of the pupil is regulated by the iris. The lens lies directly behind the pupil and is held in place by ciliary muscles. It focuses images. 3. Retina – innermost layer that contains rods (dim light, night vision) and cones (color, day vision) Cones – less numerous than rods; densely concentrated in fovea (small depression in macula lutea, found near center of retina) Aqueous humor and vitreous humor are fluids that fill the hollow inside the eyeball, thus giving it shape. Ear 1. Organ of Corti Mechanoreceptor; hearing 2. Cristae ampullares Mechanoreceptor; balance Nose Olfactory cells Chemoreceptor Smell Taste buds Gustatory cells Chemoreceptor Taste