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Chapter 29 The Senses PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko SENSORY RECEPTION © 2012 Pearson Education, Inc. Fig. 27.2 Sensory Receptors Sensory receptors = specialized cells or neurons that detect – conditions of the external and internal world Sensory receptors convert stimulus to action potential – This is called sensory transduction Message of stimulus carried to CNS – Interpretation of stimulus depends on area of CNS stimulated © 2012 Pearson Education, Inc. • Sensory transduction begins with a receptor protein that opens or closes ion channels in response to stimulus • Changes in ion flow change membrane potential of sensory cell • Receptor potential = membrane potential of sensory cell Sensory Receptor May be Found on Plasma Membrane of a Separate Sensory Cell or on a Sensory Neuron © 2012 Pearson Education, Inc. Figure 29.3A Heat Light touch Pain Cold Hair Epidermis Dermis Nerve to brain Connective tissue Hair movement Strong pressure Sensory receptor on Separate Sensory Cell – Vision – Taste – Hearing – balance Sensory receptor on specialized sensory nerve ending – Pain – Heat – Touch – smell Changes in receptor potential lead to formation of action potentials in sensory neurons If receptor found on sensory neuron stimulus triggers action potentials in receptor cell itself © 2012 Pearson Education, Inc. Changes in receptor potential lead to formation of action potentials in sensory neurons If receptor found on separate cell - stimulus triggers release of neurotransmitters from sensory cell “Hairs” of a receptor cell Neurotransmitter at a synapse Sensory neuron Action potentials Action potentials © 2012 Pearson Education, Inc. Figure 29.2A Sugar molecule Taste pore 1 Taste bud Sensory receptor cells Sensory neuron Sweet receptor 2 Sugar molecule (stimulus) Membrane of a sensory receptor cell Signal transduction pathway 3 Ion channels 4 Sensory receptor cell Ion Receptor potential 5 Neurotransmitter Sensory neuron mV Action potential to the brain 6 No sugar Sugar present Rates of action potentials Figure 29.2A_1 Sugar molecule Taste pore Taste bud 1 Sensory receptor cells 1. sugar molecules enter the taste bud Sensory neuron Sweet receptor 2. sugar molecules bind to sweet receptors 2 Sugar molecule (stimulus) Membrane of a sensory receptor cell Signal transduction 3 pathway Ion channels Sensory receptor cell 4 Ion 3. the binding triggers some ion channels (usually Na channels) in the membrane to close and others to open 4. Change in ion flow changes membrane potential (receptor potential) of sensory cell 5. Change receptor potential triggers release of neurotransmitter Ion channels Sensory receptor cell 4 Ion Receptor potential 5 6. AP triggered in sensory neuron Neurotransmitter Sensory neuron mV Action potential to the brain 6 No sugar Sugar present Rates of action potentials LE 49-14 Taste pore Sugar molecule Sensory receptor cells Taste bud Tongue Sensory neuron G protein Adenylyl cyclase Sugar Sugar receptor ATP cAMP Protein kinase A SENSORY RECEPTOR K+ CELL Synaptic vesicle Ca2+ Neurotransmitter Sensory neuron Note: Release of neurotransmitter from taste bud due to opening of Ca2+ channels!! How is stimulus interpreted? Different stimuli trigger different receptors and sensory cells; which trigger different sensory neurons and travel to different parts of brain “Sugar” interneuron “Salt” interneuron Sugar receptor cell Salt receptor cell Brain Taste bud Sensory neurons No sugar Increasing sweetness Taste bud No salt Increasing saltiness How is INTENSITY of stimulus detected? The stronger the stimulus, – the more neurotransmitter released by the receptor cell and – the more frequently the sensory neuron transmits action potentials to the brain. Repeated stimuli may lead to sensory adaptation, the tendency of some sensory receptors to become less sensitive when they are stimulated repeatedly. © 2012 Pearson Education, Inc. The stronger the stimulus, – the more neurotransmitter released by the receptor cell and – the more frequently the sensory neuron transmits action potentials to the brain. “Hairs” of a receptor cell Neurotransmitter at a synapse Sensory neuron Fluid movement Fluid movement More neurotransmitter molecules Fewer neurotransmitter molecules Action potentials Action potentials 1 Receptor cell at rest 2 Fluid moving in one direction 3 Fluid moving in the other direction Repeated stimuli may lead to sensory adaptation, the tendency of some sensory receptors to become less sensitive when they are stimulated repeatedly. LE 49-2a Weak muscle stretch Muscle Stretch receptor Membrane potential (mV) Dendrites Strong muscle stretch –50 Receptor potential –50 –70 –70 Action potentials 0 0 –70 –70 Axon 0 1 2 3 4 5 6 7 Time (sec) Crayfish stretch receptors have dendrites embedded in abdominal muscles. When the abdomen bends, muscles and dendrites stretch, producing a receptor potential in the stretch receptor. The receptor potential triggers action potentials 0 1 2 3 4 5 6 7 Time (sec) in the axon of the stretch receptor. A stronger stretch produces a larger receptor potential and higher frequency of action potentials. HEARING AND BALANCE Both hearing and balance use hair cells as sensory cells Hair cells = type of mechanoreceptor © 2012 Pearson Education, Inc. LE 49-8 Middle ear Inner ear Outer ear Semicircular canals Stapes Middle ear Incus Skull bones Auditory nerve, to brain Malleus Pinna Tympanic Auditory membrane canal Eustachian tube You do not need to all the parts of the ear Tympanic membrane Oval window Cochlea Round window Eustachian tube Tectorial membrane Hair cells Bone Cochlea duct Vestibular canal Basilar membrane Axons of To auditory sensory neurons nerve Auditory nerve Tympanic canal Organ of Corti Outer ear Middle ear Eardrum Bones Inner ear Organ of Corti (inside the cochlea) Pressure waves transmitted to the fluid of the cochlea – bend hair cells in the organ of Corti against the basilar membrane and – trigger nerve signals to the brain. Louder sounds generate more action potentials. Various pitches stimulate different regions of the organ of Corti. LE 49-9 Cochlea Stapes Vestibular canal Oval window Perilymph Apex Base Round window Tympanic canal Axons of sensory neurons Basilar membrane LE 49-10 Cochlea (uncoiled) Basilar membrane Apex (wide and flexible) 500 Hz (low pitch) 1 kHz 2 kHz 4 kHz 8 kHz 16 kHz (high pitch) Base (narrow and stiff) Frequency producing maximum vibration Fig. 27.13a Fig. 27.13b 29.5 The inner ear houses our organs of balance The three semicircular canals detect changes in the head’s rotation or angular movement. © 2012 Pearson Education, Inc. Figure 29.5 Semicircular canals Nerve Cochlea Utricle Saccule Flow of fluid Flow of fluid Cupula Hairs Hair cell Nerve fibers Cupula Direction of body movement Fig. 27.14a Fig. 27.14b VISION All animal light detectors are based on cells called photoreceptors that contain pigment molecules that absorb light. © 2012 Pearson Education, Inc. Figure 29.7A Figure 29.7B 29.10 The human retina contains two types of photoreceptors: rods and cones The human retina contains two types of photoreceptors. 1. Rods – contain the visual pigment rhodopsin, which can absorb dim light, and – can detect shades of gray in dim light. 2. Cones – contain the visual pigment photopsin, which absorbs bright colored light, and – allow us to see color in bright light. © 2012 Pearson Education, Inc. 29.10 The human retina contains two types of photoreceptors: rods and cones When rhodopsin and photopsin absorb light, – they change chemically, and – the change alters the permeability of the cell’s membrane to ions – The resulting receptor potential triggers a change in the release of neurotransmitter © 2012 Pearson Education, Inc. Figure 29.7C Sclera Choroid Ciliary body Retina Ligament Cornea Fovea (center of visual field) Iris Pupil Optic nerve Aqueous humor Lens Vitreous humor Artery and vein Blind spot Figure 29.10B Retina Optic nerve Retina Neurons Photoreceptors Rod Cone Optic nerve fibers To the brain Figure 29.10B_1 Retina Neurons Photoreceptors Rod Cone Optic nerve fibers To the brain Figure 29.10A Rod Synaptic terminals Cell body Membranous disks containing visual pigments Cone Fig. 27.10 LE 49-20 Rod Outer segment Disks Inside of disk Cell body cis isomer Light Enzymes Synaptic terminal Cytosol Retinal Rhodopsin Opsin trans isomer Page 543 TASTE AND SMELL © 2012 Pearson Education, Inc. Figure 29.12 29.11 Taste and odor receptors detect chemicals present in solution or air Taste and smell depend on chemoreceptors that detect specific chemicals in the environment. Chemoreceptors – in taste buds detect molecules in solution and – lining the nasal cavity detect airborne molecules. Taste and smell interact. Much of what we taste is really smell. © 2012 Pearson Education, Inc. 29.11 Taste and odor receptors detect chemicals present in solution or air Taste receptors – are located in taste buds on the tongue and – produce five taste sensations: 1. sweet, 2. salty, 3. sour, 4. bitter, and 5. umami (the savory flavor of meats and cheeses). © 2012 Pearson Education, Inc. Figure 29.11 Brain Olfactory bulb Bone Nasal cavity Epithelial cell Sensory neuron (chemoreceptor) Odorous substance Cilia Mucus Figure 29.UN04 Sensory receptors are grouped into several types (a) (b) involved in touch, hearing, balance many are (d) pain and thermoreceptors involved in many types found in taste and smell human skin electromagnetic receptors sensitive to (c) most common are (e)