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Sensory Perception Chapter 34 Part 1 Impacts, Issues A Whale of a Dilemma Whales communicate and sense the world around them using sound – a problem when ships and defense-systems testing flood the seas with noise 34.1 Overview of Sensory Pathways Sensory receptors determine what stimuli an animal can detect and respond to Different kinds of sensory receptors produce action potentials in response to different types of stimuli Sensory Receptor Diversity Mechanoreceptors: mechanical energy • Body position or acceleration • Touch or stretching • Pressure waves (hearing) Pain receptors (nociceptors): tissue damage • Some reflexes Osmoreceptors: change in solute concentration Sensory Receptor Diversity Thermoreceptors: specific temperature or temperature change Chemoreceptors: specific solutes dissolved in fluid (also function in smell) Photoreceptors: light energy • Including UV receptors in insects Sensory Receptors Mechanoreceptors in bat hearing, thermoreceptors in snakes Photoreceptors and UV Light From Sensing to Sensation In animals with a brain, input from sensory neurons can give rise to sensation The brain determines stimulus location and strength by which axons respond, how many respond, and frequency of action potentials In sensory adaptation, sensory neurons cease firing under continued stimulation Sensory Information in Action 34.1 Key Concepts How Sensory Pathways Work Sensory receptors detect specific stimuli Different animals have receptors for different stimuli Information from sensory receptors becomes encoded in the number and frequency of action potentials sent to the brain along particular nerve pathways 34.2 Somatic and Visceral Sensations Somatic sensations are signals from receptors in the skin, joints, and skeletal muscles • They travel along sensory neuron axons, to the spinal cord, to the somatosensory cortex Visceral sensations are signals from sensory neurons in walls of internal organs • Relayed to the spinal cord and the brain The Somatosensory Cortex Somatosensory cortex • Part of the cerebral cortex • Like the motor cortex, neurons are mapped to a plan of the body Example: Skin receptors • Free nerve endings around roots of hairs, Meissner’s corpuscles (touch), Pacinian capsules (pressure), Ruffini endings, bulb of Krause Body Regions in the Somatosensory Cortex Sensory Receptors in Human Skin hair shaft inside follicle epidermis dermis free nerve endings Pacinian corpuscle Ruffini endings bulb of Meissner’s Krause corpuscle Fig. 34-6, p. 581 Animation: Sensory receptors in the human skin Pain Pain • Perception of a somatic or visceral tissue injury • Injured cells release chemicals that stimulate pain receptors, affected by neuromodulators Referred pain • Because pain signals usually originate with somatic sources, the brain sometimes misinterprets visceral pain as coming from the skin or joints Referred Pain lungs, diaphragm heart stomach liver, gallbladder pancreas small intestine ovaries colon appendix urinary bladder kidney ureter Fig. 34-7, p. 581 Animation: Referred pain 34.2 Key Concepts Somatic and Visceral Senses Somatic sensations such as touch are easily localized and stem from receptors in the skin, muscles, or near joints Visceral sensations, such as a feeling of fullness in your stomach, are less easily pinpointed; they arise from receptors in the walls of internal organs 34.3 Sampling the Chemical World Both smell and taste begin when chemoreceptors are stimulated by the binding of specific dissolved molecules Sense of Smell Olfaction (sense of smell) • Olfactory receptors detect water-soluble or volatile chemicals, send signals to olfactory bulbs • Olfactory nerves send signals to cerebral cortex Pheromone • A type of signaling molecule secreted by an individual that affects others of the same species • Detected by a vomeronasal organ Sense of Smell olfactory tract from receptors to the brain olfactory bulb bony plate ciliated endings of olfactory receptor that project into mucus inside nose Fig. 34-8, p. 582 Sense of Taste Taste receptors detect chemicals dissolved in fluid, and have different structures and locations in different animals Humans have taste buds (in epithelial papillae on the tongue) that detect five main sensations: sweet, sour, salty, bitter, and umami Sense of Taste 34.3 Key Concepts Chemical Senses The senses of smell and taste require chemoreceptors, which bind molecules of specific substances dissolved in the fluid bathing them 34.4 Sense of Balance Organs inside your inner ear are essential to maintaining posture and a sense of balance Somatic sensory receptors also contribute to balance Organs of Equilibrium Organs of equilibrium • Parts of sensory systems that monitor the body’s positions and motions Vestibular apparatus • Contains organs of equilibrium in vertebrates • Semicircular canals, sacs, saccule and utricle Hair cells • Mechanoreceptors with modified cilia Organs of Equilibrium in the Inner Ear semicircular canals vestibular nerve A Vestibular apparatus inside a human inner ear. The organs of equilibrium in its fluidfilled sacs and canals contribute to a sense of balance. saccule utricle gelatinous membrane in a semicircular canal hair cells with their cilia embedded in membrane sensory neurons B Components of one of the organs inside a semicircular canal. Shifts in the position of the head bend hair cells and alter their frequency of action potentials. Fig. 34-10, p. 583 Animation: Dynamic equilibrium 34.5 Sense of Hearing Hearing • Perception of sound (mechanical energy) Sound waves • Human ears collect, amplify, and sort out sound waves (pressure waves traveling through air) • Wave amplitude determines loudness • Wave frequency determines pitch Wave Properties Amplitude one cycle Frequency per unit time Soft Loud Same frequency, different amplitude Low note High note Same amplitude, different frequency Fig. 34-11, p. 584 Animation: Properties of sound The Vertebrate Ear Outer ear gathers sound Middle ear amplifies and transmits air waves • Vibrations are transmitted from eardrum (tympanic membrane), to hammer, anvil and stirrup bones, to oval window Inner ear (vestibular apparatus and cochlea) • Cochlea contains organs of Corti with hairs cells that generate action potentials How Humans Hear Fig. 34-12a, p. 584 INNER EAR vestibular apparatus, cochlea OUTER EAR pinna, auditory canal MIDDLE EAR eardrum, ear bones A The outer ear’s flap and canal collect sound waves. Fig. 34-12a, p. 584 Fig. 34-12b, p. 584 oval window (behind stirrup) MIDDLE EAR BONES: stirrup anvil auditory nerve hammer auditory canal EARDRUM round window COCHLEA B The eardrum and middle ear bones amplify sound. Fig. 34-12b, p. 584 Fig. 34-12 (c-e), p. 585 Fig. 34-12c, p. 585 the cochlea, “uncoiled” for clarity waves of air pressure oval window vestibular duct waves of fluid pressure eardrum cochlear duct tympanic duct round window C Pressure waves are transferred to fluid inside the ducts of the cochlea (shown here uncoiled). Fig. 34-12c, p. 585 Fig. 34-12d, p. 585 vestibular duct cochlear duct organ of Corti sensory neurons (to the auditory nerve) tympanic duct D Pressure waves are detected by the organ of Corti in the cochlear duct. Fig. 34-12d, p. 585 Fig. 34-12e, p. 585 hair cells of organ of Corti tectorial membrane basilar membrane E Movement of the basilar membrane (the floor of the cochlear duct) bends hair cells against the organ of Corti’s tectorial membrane. This bending causes hair cells to fire. The action potentials travel along the auditory nerve to the brain. Fig. 34-12e, p. 585 Animation: Ear structure and function Animation: Action potentials Animation: Olfactory pathway Animation: Somatosensory cortex Animation: Taste receptors