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 Type of stimulus receptor Name of the nerve receptor Cold Krause s end bulbs Warmth Ruffini s end organ Touch Meissner s corpuscle Deep pressure Pacinian corpuscle Pain (free nerve ending)(no special name) Receptors may also exhibit a characteristic known as adaptation Means that the 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 Sense of Taste (Gustation) & Smell (Olfaction) 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 TASTE: 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 located on small elevated projections on the tongue called About Each taste bud contains specialized gustatory cells extend from each gustatory cell into an opening called a
Taste occurs when the in the saliva Taste buds will respond to 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 Our taste buds may also sense a 6 th taste: metallic, alkaline, umami (MSG) SMELL: Olfactory receptors are also Olfactory cells have cilia extending into nasal mucosa -Lines nasal cavity and septum Smell occurs when enough and 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 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 and Structure of the Ear The ear is divided into three parts: the external ear, the middle ear, and the inner ear External Ear Consists of three parts 1. (pinna)- flap on the side of the head 2. - ear canal, which leads from the auricle into the ear canal Modified sweat glands secrete cerumen (ear wax) 3. (eardrum)- stretches across the inner end of the auditory canal, separating it from the middle ear Middle Ear (Tympanic Cavity) Auditory Ossicles- Malleus, incus, stapes 3 very small bones named for their shape ( ); amplify sound waves Several openings into the inner ear responsible for passing sound vibrations Ex: Oval Window, opening into the auditory (Eustachian) tube Auditory (Eustachian) Tube- composed partly of bone and partly of cartilage Extends from the middle ear cavity into the throat Helps to between the middle and outer ear and prevents membrane rupture; occurs when you yawn or swallow Inner Ear Complex system of communicating chambers & tubes Has structures that help to produce both hearing and balance (hearing), (balance), (balance)
Sense of Hearing Sound occurs from cochlea means snail Fluid then stimulates hair cells in the Organ of Corti Organ of Corti- contains the Pathway of Sound Waves Sound waves enter outer ear & vibrate this causes the to move the the incus moves the this bone sitting in the oval window to move the fluid moves the basilar membrane which of the Organ of Corti Sense of Balance or Equilibrium This sense is really two senses using two different sense organs within the ear Vestibule (static) FYI Sense the position of the head; maintains stability & posture when the head and body are still Semicircular Canals (dynamic) FYI When the head or body suddenly move or rotate; Detect motion & aid in maintaining balance
VISION The eye is the sense organ for vision and converts light into electrical impulses Structure of the Eye Approximately 5/6 of the eye lies within the bony protection of the orbit, leaving only the small anterior surface exposed 3 layers of tissues make up the eyeball:,, and the Outermost layer: Sclera becomes the cornea in front Middle layer: Choroid becomes the iris in front Retina- incomplete innermost layer of the eyeball Has no anterior portion Optic disk: Retina also contains : 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, and the resulting nerve impulses must be conducted to the visual areas in the cerebral cortex to be interpreted Light bends in eye fluid Lens actively bends light to focus an image on the retina The Role of Photopigments Both rods and cones contain, 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: help you see when there is less light Cones: Vitamin A is necessary to make photopigments in rod cells