Sensors Sensory Physiology Chapter 13 Detect changes in environmental conditions Primary Sensors neurons modified to undergo action potentials in response to specific stimuli (e.g. chemical, mechanical) Secondary Sensors Cells that respond to environmental change by releasing neurotransmitters to neurons Transduction Conversion of environmental change into an electrical signal Receptor responds to stimulus by opening ion channels (primary sensors) releasing neurotransmitter to a neuron (secondary sensors) receptor potential (graded) Lead to action potential formation in sensory neurons Rate of AP generation is proportional to stimulus strength Types of Environmental Stimuli Chemoreception Mechanoreception Electromagnetic Reception Chemoreception Detection of chemical types and concentrations Gustation (Taste) chemicals in contact with the animal Olfaction (Smell) chemicals concentrated at a distance Internal Chemoreceptors (P O2, P CO2, ph) Taste Buds (Contact Chemoreceptors) Detect chemicals from sources in contact with animal Contain microvilli that project to the external surface Chemicals come into contact with these hairs Release neurotransmitter to sensory neurons Action potentials are generated in neuron 1
Olfactory Receptors (Distance Receptors) Detection chemicals from distant sources Modified neurons receptors located in nasal epithelium in the nasal cavity Have hair-like projections that respond to chemicals in air Squamate Tongues Tongue collects chemicals then retracts swab chemicals over vomeronasal organ (Jacobson s organ) chemical perception forked tongue gives directional perception Insect Antennae Mechanoreception Detection of Mechanical Energy and Force Tactile (touch and pressure) Proprioception (movement, body position) Equilibrium (gravity and acceleration) Vibrations (sound) Pheromonal Reception Tactile Receptors Proprioceptors Insect cuticular receptors Bristle/hair receptors Vertebrate cutaneous receptors Expanded dendritic endings Ruffini endings and Merkel's disks Touch Encapsulated endings Meissner's corpuscles, Krause's corpuscles, Pacinian corpusles Pressure Detect changes in length and tension of the muscles 2
Equilibrium: Hair Cells located deep inside the ear vibrations bend hairs (stereocilia) opens/closes physically gated ion channels alters release of neurotransmitter to sensory neurons Equilibrium: Invertebrate Statocysts Central statolith stimulates different hair cells based on orientation to gravity Equilibrium: Vertebrate Vestibular Organs Fluid-filled compartments in the inner ear Semi-circular canals Rotation of the head Otolith organs linear movement of head and orientation relative to gravity Vibration Vertebrate Cochlea Elongate structure containing hair cells Fluid pressure waves induce vibration of the basilar membrane Stimulates hair cells Vibrations: Insect Ears Tympanic Organs Terminal Cerci Johnston s organ Wind receptor May be tuned to specific frequencies Vibrations: Lateral Lines Fish and aquatic amphibians Hair cells distributed along lateral line Detect vibrations in water and flow of water Animation: http://www.blackwellpublishing.co m/matthews/haircell.html 3
Electromagnetic and Thermal Perception Vision Vision Temperature Electric Magnetism Perception of electromagnetic radiation portion of the EM spectrum Advanced Eyes: Refraction of Light Light refracted by transparent/translucent structures bending of light leads to projection of focused image on the retina Vertebrate Photoreceptors rods - light intensity cones - color Each photoreceptor has two segments Inner segment metabolic machinery synaptic endings Outer segment contains layers of internal membranes containing photopigments Transduction of Light Cells change metabolic activity with activation of photopigments Stimulate sensory neurons Compound Eyes (Arthropods) Consist of many ommotadia Each with lens and photoreceptor cells E.g., Green, Blue, Ultraviolet in honeybees Images from many ommotadia processed into a single visual picture 4
Thermal Perception Modified neurons E.g. cutaneous heat and cold receptors Thermosensory pits (snakes) Detect heat from warm prey, thermal conditions in habitat Electroreception Marine elasmobranchs ampullae of Lorenzini detect electrical fields generated by other fish Freshwater teleosts caudal electric organs generates electrical field around animal objects near animal alter electric field detected by cells in lateral line Platypus Mucous/serous gland electroreceptor Neurons surround pores of mucous and serous glands Magnetic Field Perception Long distance orientation Follow the earth s magnetic field Mechanism (?) Magnetite (Fe 3 O 4 ) present in various receptor cell types Photoreceptors birds, salamanders Electroreceptors elasmobranchs Olfactor receptors - trout 5