Transcript Document
UNIT 5: Nervous System Senses Somatic Senses • Somatic senses are associated with receptors in the skin, muscles, joints, and viscera (organs of the body) – Include senses of touch, pressure, temperature, & pain • Warmth Ruffini’s end organ • Touch Meissner’s corpuscle • Deep pressure Pacinian corpuscle Encapsulated receptors Type of stimulus Name of the nerve receptor • Cold Krause’s end bulbs • Pain (free nerve ending)(no special name) Receptors may also exhibit a characteristic known as adaptation • Means that the frequency of the receptor potential decreases over time in response to a continuous stimulus – Axon sends fewer impulses, therefore the intensity of the sensation decreases • Ex. Feeling your clothes on your skin Olfaction (Smell) and Gustation (Taste) • Our senses of smell and taste are closely related – Both play a role in food selection because we smell food at the same time we taste it – Receptors for both smell and taste are chemoreceptors – Sense chemicals that dissolve in fluids Sense of Taste (Gustation) • Taste buds are the sense organs that respond to gustatory stimuli • Chemoreceptors that respond to chemicals broken down from food in the saliva • Taste buds are small elevated projections on the tongue called papillae – About 10,000 on your tongue, 1,000 on the roof of mouth • Each taste bud contains specialized gustatory cells – Tiny cilia-like gustatory hairs extend from each gustatory cell into an opening called a taste pore – Taste occurs when the gustatory hairs are stimulated by chemicals in the saliva Taste buds will respond to chemicals for sweet, sour, salty, and bitter – All taste buds will respond to each chemical to some degree, but respond most effectively to one of the four – The tastes we perceive are from a mixture of the four and our sense of smell – Our taste buds may also sense a 5th taste: metallic, alkaline, umami (MSG) Sense of Smell (Olfaction) • Olfactory receptors are also chemoreceptors • Olfactory cells have cilia extending into nasal mucosa – Lines nasal cavity and septum • Smell occurs when enough odorant molecules stimulate a receptor and trigger an action potential • We have over 400 types of olfactory receptors which sense different odorant molecules • With a few hundred types of olfactory receptors we are also able to sense thousands of smells – Odorant molecules will bind in different patterns to receptors which the brain interprets as different smells More Smell Info • The olfactory receptors are located high in the nasal cavity so a person may have to sniff forcefully to smell light odors • We also will “adapt” to smells – Smells may seem to become less intense Sense of Hearing: The Ear • The ear has two sensory functions – Sense of Hearing and Balance Structure of the Ear • The ear is divided into three parts: the external ear, the middle ear, and the inner ear Auditory (Eustachian) Tube- composed partly of bone and partly of cartilage • Extends from the middle ear cavity into the throat • Helps to equalize pressure between the middle and outer ear and prevents membrane rupture; occurs when you yawn or swallow Inner Ear • Has structures that help to produce both hearing and balance – cochlea (hearing), vestibule (balance), semicircular canals (balance) • Cochlea and Cochlear duct – cochlea means “snail” – Organ of Corti- contains the hearing receptors attached to hair cells Sense of Hearing • Sound occurs from vibrations that travel through the ear and move fluid in the cochlea – Fluid then stimulates hair cells in the Organ of Corti Vision: • The eye is the sense organ for vision and converts light into electrical impulses • Retina- incomplete innermost layer of the eyeball – Has no anterior portion – Optic disk: “blind spot” – Retina also contains photoreceptor neurons: rods and cones – More rods than cones – Cones are densely packed in the fovea centralis – No rods in the fovea The Process of Seeing • For vision to occur, an image is focused on the retina to stimulate rods and cones, and the resulting nerve impulses must be conducted to the visual areas in the cerebral cortex to be interpreted Animation! Click picture for animation The Role of Photopigments • Both rods and cones contain photopigments, which are light-sensitive compounds – In the presence of lights, photopigments undergo structural changes which trigger an impulse (action potential) for the brain to interpret • Rods: much more sensitive to light help you see when there is less light • Cones: detect color