Presentation on theme: "The Senses Nestor T. Hilvano, M.D., M.P.H."— Presentation transcript:
1 The Senses Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain, Textbook, 2012.)
2 Learning Objectives State the functions of sensory pathways. Define sensory receptors and describe the 5 general categories of sensory receptors.Describe the human eye and its function.Compare the rods and cones of retina.Explain myopia, hyperopia, presbyopia and astigmatism.List the structure of ear in the order in which they participate in hearing.Explain how body position and movement are sense in the ear.Discuss how odor and taste receptors function.
3 Sensations All stimuli represent forms of energy Sensation involves converting energy into a change in the membrane potential of sensory receptorsThe brain interprets sensations, giving the perception of stimuliGeneral senses (Somatic)- skin, muscles, joint, and viscera (internal organs)Special senses- sight (vision), smell (olfaction), taste (gustation), hearing (audition), and vestibular (balance/equilibrium)
4 Fig. 50-2Functions of Sensory Pathways: sensory reception, transduction, transmission, and integration (brain perception)Weak receptor potentialAction potentialsMembrane potential (mV)–50Membrane potential (mV)–70Slight bend: weak stimulus–70Brain perceives slight bend.DendritesStretch receptorTime (sec)124Axon3BrainMuscleBrain perceives large bend.Action potentialsLarge bend: strong stimulusStrong receptor potentialMembrane potential (mV)Figure 50.2 A simple sensory pathway: Response of a crayfish stretch receptor to bendingMembrane potential (mV)–50–701Reception–70Time (sec)2Transduction3Transmission4Perception
5 Sensory Receptors: Transduce Stimuli into Action Potential Classification of Receptors:Pain (nociceptors) receptors – inflame/damage tissuesThermoreceptors – change in temp., hot or coldMechanoreceptors – change in pressure or fluid movement; touch, pressure, stretching of muscles, motion, soundChemoreceptors – change in odor and tasteElectromagnetic receptors – electricity, magnetism, and light (photoreceptors)Receptors for General senses:Pain - free nerve endingsTemperature –Ruffini (hot); Kraus End Bulb (cold)Crude (light) touch -Meissner’s corpuscleProprioception (deep touch and pressure) -pacinian corpuscleReceptors for Special senses:Vision – rods and conesAudition – organ of cortiVestibular – maculae, cristaeOlfaction- olfactory cellGustation- taste bud
6 Figure 30.13 Some Mechanoreceptors in Human Skin Human skin contains many different types of neurons and sensory cells that provide detailed information about mechanical stimuli.
7 Eyeball - Vision Fibrous (outermost) layer = sclera and cornea Vascular (middle) layer = choroid, ciliary body, and iris*pupil – central opening* Light passes through a transparentlens that focuses images on the retinaNervous (innermost) layer = retina,photoreceptor layer (rods and cones)Rods - sensitive to low level of light; night visionCones - detect colors of light; day vision_____ - center of sharpest vision (cones only)_____ - Blind spot (w/ nerve & b.v.)a. optic disc b. fovea centralisAqueous humor filled the chamber in front of the lensVitreous humor filled the chamber behind the lens
8 Figure 30.14 Major Features of the Human Eye A pupil adjusts the amount of light entering through the lens. The lens focuses images on the retina, where photoreceptor cells generate nerve impulses in sensory neurons that are closely associated with them.
9 Figure 30.17 Sensory Neurons in the Retina Send Visual Information to the Brain Layers of sensory neurons stacked above the rods and cones process visual information to some degree before sending it to the brain via the optic nerve.
11 Visual Problems Passage of light: Light cornea aqueous humor pupil lensvitreous humor retinaNearsightedness (myopia)- Can’t see far distance; eyeball is longer; focus distant objects in front of retina; corrective lenses that are thinner in the middleFarsightedness (hyperopia)- Can’t see near distance; eyeball is short; focal point is behind the retina; corrective lenses that are thicker in the middle*presbyopia – hyperopia in old age, inelasticity of lensAstigmatism – blurred vision caused by misshapen lens or cornea; corrective asymetrical lens
12 Clinical Correlation ___ = clouding of lens aging, diabetes, smoking, and UV light___ = death of retinal cells due to elevated pressure within the eye___ = pink eye, results from damage or irritation of conjunctival surface.a. glaucoma b. conjunctivitis c. cataract
13 Ear: Hearing Mechanoreceptor (change in pressure due to sound waves) Outer ear = pinna and auditory canal* tympanic membraneMiddle ear = contain ossicles(malleus, incus, stapes)* oval windowInner ear = cochlea (contains organ of corti)Auditory nerveSound volume (loudness) rangingfrom 0 to 120 db. (long exposure to90 db can cause hearing loss)Pitch (frequency) from 20 – 20,00 Hz.Sound at pinna auditory canal tympanic membrane middle ear oval window cochlea (organ of corti) send impulses to the brain (auditory cortex)
14 Semicircular canals (function in balance) Skull bones Oval window Figure 29.4BSemicircular canals(function in balance)Skull bonesOvalwindow(behindthestirrup)Auditorynerve,to the brainHammerAnvilStirrupEardrumFigure 29.4B The middle ear and the inner earCochleaEustachiantube(connects tothe pharynx)14
15 Ear: Vestibular Sense: (Body Position and Balance) Inner ear – houses organs of balancea) Semicircular canals = crista ampullaris, receptor for changes in head’s rate of rotationb) Utricle and saccule – maculae, receptor for head position relative to the force of gravity and linear motion
16 Semicircular canals Flow of fluid Vestibular nerve Cupula Hairs FigSemicircular canalsFlow of fluidVestibular nerveCupulaHairsHair cellsVestibuleFigure Organs of equilibrium in the inner earAxonsUtricleBody movementSaccule
17 Taste Receptors Chemoreceptors in taste buds 4 types a) sweet b) sour c) saltyd) bitterA fifth taste perception called umami (elicited by glutamate)Taste perception varies with individuals and may be related to genetic traits
18 Figure Taste in HumansTaste buds consist of groups of chemoreceptor cells and supporting cells. The receptor cells respond to chemicals that lodge in the tongue during eating.
19 Smell ReceptorsChemoreceptors in nose (olfactory mucosa) – olfactory (bipolar) cellsIntegration of signals in the brain results in an odor perceptionSmell is tied with limbic system, evoking emotions and memories.
21 HomeworkDefine terms: rods, cones, presbyopia, myopia, hyperopia, astigmatism, cornea, lens, tympanic membrane, semicircular canals, utricle and saccule, cataract, glaucoma, conjunctivitis, optic disc, fovea centralis, macula, cristae ampullaris.Give the sensory receptors of the following:__ pain a. bipolar (olfactory) cells__ pressure and deep touch b. organ of corti__ taste c. free nerve endings__ olfaction d. pacinian corpuscle__ hearing e. taste budClassify the receptors of the items listed below:__ change in pressure or fluid movement a. chemoreceptor__ change in light perception b. thermoreceptor__ change in smell of CO2 c. photoreceptor__ change in climate’s temperature d. mechanoreceptor