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Special Senses Chapter 8 1 • • • • • • • • • • • Outline Types of Sensory Receptors Functions of Sensory Receptors Sensations and Perceptions Cutaneous Receptors Sense of Position in Space- Posture Sense of Taste Sense of Smell Sense of Hearing Sense of Balance (Equilibrium) Sense of Vision Homeostasis 2 Types of Sensory Receptors • Sensory receptors are specialized to detect certain types of stimuli. Can be modified dendrites of sensory neurons or specialized cells that release neurotransmitters that stimulate nearby sensory neuron. – Exteroceptors detect stimuli outside the body. Taste, smell, vision. Indirectly linked to homeostasis. – Interoceptors detect stimuli inside the body. Blood pressure, blood volume, pH. Directly linked to homeostasis. 3 Subtypes of Sensory Receptors • Chemoreceptors. – Respond to chemical substances in the immediate vicinity. • • • Pain Receptors (Nociceptors). Respond to chemicals released by damaged tissue from intense pressure, temperature, light. Photoreceptors. – Respond to light energy. Mechanoreceptors. – Stimulated by mechanical forces. Thermoreceptors. – Stimulated by changes in temperature. 4 • • • • Functions of Sensory Receptors To provide information for the proper maintenance of the body. Significant contributors to homeostasis. Interoceptors are directly involved by monitoring vital functions such as blood pressure and pH. Exteroceptors are indirectly involved by monitoring our external environment, but are just as important; we see the oncoming car and get out of the way; we put a coat on so as not to freeze to death. 5 • • Sensations and Perceptions Sensation occurs when nerve impulses arrive at the cerebral cortex of the brain. Perception occurs when the cerebral cortex interprets the meaning of sensations. – – – Sensory receptors initiate nerve impulses; perception depends on the part of the brain receiving the nerve impulses. Strength of stimulus related to frequency of firing of nerve impulses. Have integration at level of sensory receptor, spinal cord, and brain. 6 Cutaneous Receptors • The dermis contains cutaneous receptors, which include: – Mechanoreceptors. Sensitive to touch. – Nociceptors. Sensitive to pain. – Thermoreceptors. Sensitive to temperature. 7 Cutaneous Receptors 8 Sense of Position in Space- Posture • Proprioceptors are mechanoreceptors that help determine limb position in space by detecting the degree of muscle relaxation, stretch of tendons, and movement of ligaments. – Muscle spindles detect the stretching of muscles; act to increase the degree of muscle contraction. – Tendon receptors detect the tension in the tendons of muscles; act to decrease it. 9 Muscle Spindle 10 Skeletal muscle Sensory neurons of muscle spindle Tendon connecting bone to muscle Muscle spindle Tendon receptor Sensory neuron of tendon stretch receptor Tendon Bone a) Muscle spindle. A muscle spindle responds to muscle length. Passive stretch of a muscle stretches the muscle spindle, stimulating mechanoreceptors in the nerve endings of the sensory neurons. Conversely, muscle contraction shortens the muscle spindle, reducing muscle spindle mechanoreceptor stimulation. © 2012 Pearson Education, Inc. b) Tendon receptor. A tendon receptor responds to tension in tendons. When a muscle contracts and also when it is stretched passively, tension on the tendon increases, activating tendon receptors. Figure 12.3 • Sense of Taste Chemoreceptors for taste are found in taste buds located primarily embedded in tongue epithelium. Five primary tastes. Sweet. Sour. Salty. Bitter. Umami Weighted average integrated response. 12 Figure 8.19 Location and structure of taste buds. Sense of Taste Epiglottis Epithelium of tongue Palatine tonsil Lingual tonsil Surface of the tongue Vallate papilla Taste bud Connective tissue Gustatory (taste) cell Basal cell Sensory nerve fiber Fungiform papillae (a) Taste buds (b) © 2015 Pearson Education, Inc. Gustatory hairs (microvilli) emerging from a taste pore (c) • Sense of Smell Dependent on chemoreceptors on olfactory cells located within olfactory epithelium high in the roof of the nasal cavity. – – – Each olfactory cell (sensory neuron) has only one type of chemoreceptor; there are ~1500 types; odor made up of multiple molecules; multiple different cells stimulated- integration. Olfactory bulbs have direct connections with the limbic system and its centers for emotions and memory. Sense of taste and smell work together to create a combined effect. 14 Sense of Smell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. olfactory bulb neuron olfactory tract frontal lobe of cerebral hemisphere olfactory bulb olfactory epithelium nasal cavity odor molecules bone of skull sensory nerve fibers olfactory epithelium a. supporting olfactory cell cell b. olfactory cilia of olfactory cell odor molecules 15 • Sense of Hearing Anatomy of the Ear. – Outer ear: pinna; auditory canal. – Middle ear: tympanic membrane; malleus, incus, and stapes (ossicles); round window; oval window. – Inner ear: semicircular canals, vestibule, and cochlea. 16 Figure 8.12 Anatomy of the ear. External (outer) ear Middle ear Internal (inner) ear Vestibulocochlear nerve Auricle (pinna) Semicircular canals Oval window Cochlea Vestibule Round window Pharyngotympanic (auditory) tube © 2015 Pearson Education, Inc. Tympanic membrane (eardrum) Hammer Anvil Stirrup (malleus) (incus) (stapes) External acoustic meatus Auditory ossicles (auditory canal) Frequency (cycles/sec) Soft, low tone Loud, low tone Soft, high tone Amplitude Loud, high tone 0 1 2 3 4 5 Time (msec) © 2012 Pearson Education, Inc. Figure 12.8 Loudness determined by number of hair cells stimulated. High-frequency sounds Oval window Sound wave Round window Auditory tube Low-frequency sounds Pitch determined by region of basilar membrane stimulated. a) The cochlea as it might appear if it were uncoiled. Higher-frequency sounds are converted to impulses near the oval window, whereas lower-frequency sounds are converted near the tapered tip. Vestibular canal Organ of Corti Cochlear duct Hairs of hair cells Tectorial membrane Hair cells To auditory nerve Hair cells Tympanic canal Basilar membrane b) A cross section through the cochlea. Pressure waves passing from the vestibular canal to the tympanic canal through the cochlear duct cause the basilar membrane to vibrate. c) A section through part of the cochlea, showing hair cells with their hairs embedded in the tectorial membrane. Vibration of the basilar membrane bends the hairs, ultimately generating impulses in sensory neurons. © 2012 Pearson Education, Inc. d) SEM ( 4,200) of healthy hair cells. Figure 12.10 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 20 “Hairs” of hair cell Neurotransmitter More neurotransmitter Less neurotransmitter Sensory neuron Action potentials a) Hair cell at rest. b) Hairs moving in one direction. © 2012 Pearson Education, Inc. c) Hairs moving in other direction. Figure 12.11 Sense of Balance (Equilibrium) • • Rotational Equilibrium – Cupula movement within the semicircular canals detects rotation and/or angular movement of the head. Gravitational Equilibrium. – Movement of the otolithic membrane within the utricle and the saccule detects position of the head in the vertical and horizontal planes compared to gravity and detects acceleration. 22 The inner ear: Balance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. semicircular canals receptor in ampulla endolymph Vestibular nerve ampullae cochlea utricle saccule endolymph cupula otoliths stereocilia otolithic membrane Hair cell hair cell Supporting cell supporting cell vestibular nerve Vestibular nerve flow of endolymph Flow of otolithic membrane The mechanoreceptors of the inner ear and the sense of balance. a. Rotational equilibrium: receptors in ampullae of semicircular canal kinocilium stereocilia b. Gravitational equilibrium: receptors in utricle and saccule of vestibule 24 Sense of Vision • • The eyeball has three layers. – Sclera. – Choroid. – Retina. The retina contains two types of photoreceptors. – Rod cells. – Cone cells. 25 Anatomy of the Human Eye 26 Anatomy of the Human Eye (Cont.) • The Lacrimal Apparatus & Conjunctiva – – – – – Lacrimal glands- lateral end of each eye; release tears continuously, flush across eyes; contains lysozymeantibacterial protein Lacrimal canaliculi- channels that help drain tears Lacrimal sac- drains tears into nasolacrimal duct Nasolacrimal duct- tube that conducts tears to nasal cavity Conjunctiva- thin membranes line eyelids & covers surface of eyes; produces mucus, helps lubricate eye movements & keeps surface moist 27 Figure 8.2 Accessory structures of the eye. Lacrimal gland Lacrimal gland Excretory duct of lacrimal gland Conjunctiva Anterior aspect Eyelid Eyelashes (a) © 2015 Pearson Education, Inc. Excretory ducts of lacrimal gland Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Tarsal glands Nostril Eyelid (b) Lacrimal sac Focusing • Observing object, light rays pass through the cornea, the aqueous humor, the pupil, the lens, the vitreous humor, and are focused on the retina. – – Focusing involves the cornea, the lens and the humors. Focusing for close objects (accommodation) involves the ciliary muscles and the changing shape of the lens. 29 Focusing 30 Figure 8.9 Relative convexity of the lens during focusing for distant and close vision. Retina Light from distant source Focal point (a) Light from near source Focal point Retina (b) © 2015 Pearson Education, Inc. Photoreceptors • Vision begins once light has been focused on the photoreceptors in the retina. – Rod cells; black and white vision; very sensitive to light; provide night and peripheral vision. – Cone cells allow detection of fine detail and color. Color vision depends on three different kinds of cones which are sensitive to different wavelengths (kinds of light); blue, green, and red light. 32 Cone Sensitivity to Light 33 Photoreceptors in the Eye 34 • Integration of Visual Signals in the Retina The retina has three layers. – – – • • • Layer closest to choroid contains rod cells and cone cells. Middle layer contains bipolar cells. Innermost layer contains ganglion cells. Rod and cone cells in back of retina thus light must penetrate to the back before they are stimulated. Many rod cells connected to one ganglion cell. One cone cell connected to one ganglion cell (within fovea centralis). 35 Integration of Visual Signals in the Retina 36 Integration of Visual Signals in the Brain • The visual pathway begins in the retina and passes through the thalamus before reaching the cerebral cortex. – – – The visual fields from both eyes overlap allow you to see depth & around edges (three-dimensional vision). The pathway and visual cortex take the visual field apart, possibly to extract more information like color, form, motion. The cortex rebuilds it so we correctly perceive the field and with possibly a better understanding of it. 37 Figure 8.11 Visual fields of the eyes and visual pathway to the brain. Fixation point Right eye Left eye Optic nerve Optic tract Optic chiasma Optic radiation Thalamus © 2015 Pearson Education, Inc. Occipital lobe (visual cortex) Integration of Visual Signals in the Brain 39 Abnormalities of the Eye • • • Color blindness. – Particular type of cone is lacking. Distance Vision – Nearsighted. Elongated eyeball. – Farsighted. Shortened eyeball. Astigmatism. – Uneven cornea. 40 Focal plane a) The normal eye. Correction Concave lens b) Nearsightedness (myopia). Nearsighted persons can see near objects clearly, but distant objects are out of focus because the focal point is in front of the retina. Convex lens c) Farsightedness (hyperopia). Farsighted persons can see distant objects clearly, but near objects are out of focus. d) Astigmatism. Astigmatism is due to an abnormal curvature of either the cornea or the lens. © 2012 Pearson Education, Inc. Figure 12.17 • • • • Homeostasis To provide information for the proper maintenance of the body. Significant contributors to homeostasis. Interoceptors are directly involved by monitoring vital functions such as blood pressure and pH. Exteroceptors are indirectly involved by monitoring our external environment, but are just as important; we see the oncoming car and get out of the way; we put a coat on so as not to freeze to death. 42 Need to Know 1. Types of Sensory Receptors Exteroceptors Interoceptors A. B. 2. Subtypes of Sensory Receptors Chemo A. B. C. D. 3. Pain Photo Mechano Thermo Function in Homeostasis of Sensory Receptor A. B. C. Proper functioning of body Interoceptors monitor vital functions Exteroceptors monitor external environment 43 Need to Know (Cont.) Difference Between Sensation and Perception 4. A. B. C. D. Sensation: nerve impulses to the brain Perception: the meaning of sensations Part of perception is strength: comes from frequency Part of perception is integration: occurs at receptors, spinal cord, brain Sense of Vision 5. A. B. C. D. Basic anatomy including lacrimal apparatus & conjunctiva Focusing: how it works Photoreceptors: rod and cone cells; what they are sensitive to Integration of visual signals: many rod cells, one ganglion cell; one cone cell, one ganglion cell 44 Need to Know (Cont.) 6. 7. Sense of Hearing A. Basic anatomy B. How sound is transferred to cochlea: malleus, incus, stapes C. How Organ of Corti works: hair cells and basilar membrane Sense of Smell A. Basic anatomy B. Each olfactory cell has only one chemoreceptor type C. Odor involves multiple cell stimulation; integration 45 Need to Know (Cont.) Sense of Taste 8. A. Taste cells respond to sweet, sour, salty, bitter, umami Integration of incoming signals with sense of smell B. C. 9. Sense of Position in Space A. B. 10. Basic anatomy Basic anatomy Proprioceptors: sensitive to stretch; tell brain where our limbs are Sense of Balance (Equilibrium) A. B. Rotational Equilibrium: cupula in semicircular channels Gravitational Equilibrium: otolithic membrane in utricle and saccule of vestibule 46