VPHY 3100: Week of 9/14
VPHY 3100: Week of 9/14 VPHY 3100
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This 6 page Class Notes was uploaded by Lorin Crear on Friday September 18, 2015. The Class Notes belongs to VPHY 3100 at University of Georgia taught by Dr. Li, Dr. Wells, Dr. Brown in Summer 2015. Since its upload, it has received 74 views. For similar materials see Elements of Physiology in Animal Science and Zoology at University of Georgia.
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Date Created: 09/18/15
Chapter 10 Sensory Physiology 0 Six sensory systems 0 Somatosensory Visual Auditory Vestibular Olfactory o Gustatory 0 Steps to any sense 1 Physical stimulus 2 Sensory transduction transformation of input into nerve impulses 3 Formulation of perception higher order cortical integration of many different sensory details 0 Sensory cells and receptors 0 Sensory cells I Some are neurons I Most are specialized epithelial cells that synapse With neurons I Epithelial cells do not experience action potentials 0 Experience small depolarizations that communicate With and may trigger action potentials in neurons 0 Sensory receptors I On surface of sensory cells I Four functional classes 0 Mechanoreceptors 0 Sense pressure and pullingpushing on cell membranes 0 Chemoreceptors 0 Sense chemicals in smells in food 0 Thermoreceptors 0 Sense hot and cold 0 Photoreceptors 0 Sense light waves 0 Information conveyed by sensory system 0 Modality of stimulus I What kind of sensory information is it o Intensity of stimulus I Encoded by frequency of action potentials I Greater intensity greater voltage of generator potentials local depolarizations of membrane greater frequency of action potentials 0 Time course of stimulus I Phasic receptors 0 Causes burst of action potentials When stimulus applied 0 Frequency of action potentials decreases as receptor adapts to stimulus 0 Smaller burst of action potentials When stimulus Withdrawn I Tonic receptors 0 O O O 0 Causes regular pattern of action potentials as long as stimulus endures I Most sensory neurons display phasic behavior 0 Location of stimulus I Each sensory neuron receives information from specific receptive field I Receptive field 0 Center surround area immediately around center 0 Circular geometry 0 Outside of surround displays tonic behavior When stimulus applied 0 Convergence of information from different receptive fields as it goes through medial lemniscal or lateral spinothalamic tract to brain 0 Somatosensory Perception o Modalities detected I Touch I Proprioception 0 Stimuli Within skeletal muscle joints tendons I Temperature I Pain I Itch 0 Receptor types I Cutaneous skin receptors 0 Touchpressure receptors 0 Free nerve endings light touch 0 Merkel s discs sustained touch and pressure 0 Ruffini endings sustained pressure 0 Meissner s corpuscles change in texture slow vibrations o Pacinian corpuscles deep pressure fast vibrations o Hotcold receptors 0 Free nerve endings 0 Nociceptors pain 0 Free nerve endings Corpuscles are sensory neurons With specialized dendrites Corpuscles exhibit phasic behavior Merkel s discs and Ruffini endings are more tonic I Proprioceptors 0 Muscle spindles 0 Golgi tendon organs 0 Joint receptors 0 Visual perception 0 Anatomy I Cornea clear part of sclera that allows light in at the front of the eye refracts light waves I Iris colored portion of eye that adjusts pupil to let in moreless light I Pupil black portion of eye I Lens behind pupil further refracts light to project onto retina I Retina thin tissue that covers back of eye contains photoreceptor cells GPCR to interpret incoming light waves interneurons and ganglia cells I Fovea very small central pit of retina high concentration of cone receptors clearest picture if light hits here 0 Light waves normally make their way through many layers of vascular and nervous tissue on way to retina fewer layers at fovea I Optic nerve bundle of axons at back of eyeball optic disc blind spot of vision is where it meets the retina I Vitreous humor clear gel that fills eyeball o Inversion amp reversal of the visual field I Light waves are projected on the retina upside down and inverted left to right I Each eyeball s visual field split into left and right halves 0 Left side of visual field projected onto right side of retina 0 Crossover of ganglion axons before reaching occipital lobe o All axons with right half of visual fields go to right side of brain 0 All axons with left half of visual fields go to left side of brain 0 Exactly half with crossover o Crossover occurs at optic chiasma before reaching thalamus o Autonomic control of pupil diameter I Iris has both radially and circularly arranged muscle fibers I In dim light radial muscles are stimulated via dladrenergic receptors I In bright light circular muscles stimulated via muscarinic receptors 0 Transduction I Photoreceptor cells PRCs 0 Located in retina o Rods o Dimlight vision 0 Greater sensitivity to light 0 Rhodopsins are lightreceptors GPCRs 0 Cones 0 Color vision 0 Greater visual activity 0 Photopsins are lightreceptors GPCRs I Vertical pathway within retina o PRCs 9 bipolar cells 9 ganglion cells optic nerve 0 Light and impulses move in opposite directions 0 Anatomy of Retina I Layers I Ganglion cells make up innermost layer closest to inside of eyeball I PRCs sit at the back of the retina 0 Take in light rays and change membrane voltage Outer segments composed of layers of membrane that contain all equipment needed by light receptors to transduce light 0 Rods layers composed of vesicle membranes 0 Cones layers composed of plasma membrane Exist at rest in depolarized state 40 mV due to dark current I Pigment epithelium in outer layer of retina keeps receptor cells healthy Reactivates retinal molecules photopigment that have become inactive after being hit by light to be used again When hit by light cisretinal which senses light will become transretinal which does not Transretinal dissociates from photoreceptors and makes it way to pigment epithelium I Horizontal interneurons mediate lateral ow of information 0 Dark Current I In dark 1 2 3 U P I In light 1 2 3 99 ng 10 ll 12 13 High concentration of cGMP secondary messenger in rods cGMP binds to ion channels Channels allow sodium and calcium to enter down electrochemical gradients Causes depolarization Glutamate released by rods in synapse with bipolar cells Glutamate interacts with metabotropic receptor on bipolar cell membrane IPSP Bipolar cell does not stimulate ganglion cell Called a signinverting synapse because more activity in synapse less activity in postsynaptic cell Photon activates rhodopsin Rhodopsin activates Gt transducin or subunit of GTP activates enzyme cGMPdependent phosphodiesterase PDE PDE decreases cGMP levels cGMP dissociates from ion channel channel closes dark current is turned off Hyperpolarization occurs in rod Rod releases less glutamate Bipolar cell is not inhibited Bipolar cell releases glutamate into synapse with ganglion cell Glutamate interacts with inotropic receptor on ganglion cell membrane EPSP Ganglion cell fires off action potentials o Rods and Cones I Rods I Cones Absorb blue green light waves 0 Small cones absorb blue light waves 0 Medium cones absorb green light waves 0 Large cones absorb red light waves I Only cones at fovea concentration of rods increases and concentrations of cones decreases with increasing distance from fovea 0 Convergence and receptor fields I Ganglion cells typically harvest information from hundreds of PRCs 0 Creates larger receptor field for ganglion cells 0 Less convergence in cones than rods 0 No convergence at fovea I Receptive field made of central center and peripheral surround parts with circular geometry 0 Ganglion cells are most stimulated by contrast between center and surround o Oncenter ganglion cells I Most stimulated by central illumination and darkness in surround o Offcenter ganglion cells I Most stimulated by surround illumination and darkness in center Chapter 9 The Autonomic Nervous System 0 CNS and PNS o CNS brain and spinal cord PNS nerves and ganglia outside CNS 12 pairs of cranial nerves exit brain 31 pairs of spinal nerves exit spinal cord Most nerves are mixed composed of sensory and motor fibers 0 The Autonomic Nervous System ANS 0 Regulation of cardiac muscle smooth muscle and glands cells that secrete 0 Control of involuntary visceral organs and blood vessels 0 Autonomic vs Somatic Motor Systems I Somatic affects skeletal muscle autonomic affects those listed above I Autonomic nervous system is involuntary somatic nervous system is voluntary I Presence of ganglia 0 Neurons in somatic motor system run from spinal cord to effectors in skeletal muscle 0 Neurons in autonomic motor system synapse at ganglia on way from CNS to effectors I Somatic only sends excitatory impulses autonomic can send excitatory or inhibitory I Denervation 0 Disconnection on nerve fiber 0 Causes accid paralysis of muscle in somatic nervous system 0 O O O I Muscles of ANS Will maintain tone and function and become hypersensitive o Divisions of ANS I Both consist of preganglionic neurons cell bodies in CNS and postganglionic neurons cell bodies in PNS I Sympathetic fight or ight Preganglionic fibers originate in thoracic and lumbar regions Chain of ganglia on either side of spinal cord 0 0 Most preganglionic fibers go here after passing through paravertebral ganglia Some preganglionic fibers synapse With postganglionic fibers here Others pass through chain and synapse Within collateral prevertebral ganglia Others do not synapse at all and innervate the adrenal medulla causing secretion of epinephrine and norepinephrine Entire system usually activated as single unit I Parasympathetic rest and digest Preganglionic fibers originate in cranial from brain stem and sacral regions No chain of ganglia Preganglionic fibers synapse With postganglionic fibers in terminal ganglia close to or Within target organs Most fibers not bundled in spinal nerves Four cranial nerve pairs including vagus carry preganglionic fibers Vagus Nerves O O 0 Primary route of parasympathetic innervation Preganglionic fibers originate in medulla Target organs heart lungs esophagus stomach pancreas liver intestines Otto LoeWi s experiment I Discovered signaling across synapse was chemical I Vagus nerve uses acetylcholine
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