Biol 118 1st Edition Lecture 29 Outline of Last Lecture I Synapses II Vertebrate Nervous System Outline of Current Lecture I How Do Sensory Organs Convey Information to the Brain II Mechanoreception Sensing Pressure Changes III Photoreception Sensing Light IV Chemoreception Sensing Chemicals V Other Sensory Systmes Current Lecture How Do Sensory Organs Convey Information to the Brain Each type of sensory information is detected by a sensory neuron or a specialized receptor cell that makes a synapse with a sensory neuron Ability to sense a change in the environment depends on 3 processes o Transduction conversion of an external stimulus to an internal signal in the form of action potentials along sensory neurons All sensory input is transduced to a change in membrane potential Ch 46 o Amplification of the signal o Transmission of the signal to the central nervous system Receptor cells tend to be highly specific e g hearing receptors some are more able to hear high pitches other low pitches Each type of sensory neuron sends its signal to a specific portion of the braindifferent regions of the brain are specialized for interpreting different types of stimuli Mechanoreception Sensing Pressure Changes Mechanoreception sensation of pressure changes Statocyst organ in crabs that helps them sense pressure created by gravity o Lined with pressure receptor cells contains small calcium rich particle that rests on the bottom o When crab flips over particles press against receptor NOT on bottom and muscles activate to reposition These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Direct physical pressure on a plasma membrane or distortion of membrane structures by bending changes the conformation of ion channels in the membrane causes the channels to open or close o Results in hyperpolarization or depolarization changing pattern of action potentials in a sensory neuron Ion channels that respond to pressure are often found in hair cells o Pressure receptor cells named for hairy looking stereocilia outgrowths o Have single kinocilium true cilium that has 9 2 arrangement of microtubules o Found in ears of vertebrates lateral line system of fish and amphibians o Equilibrium potential is 0 mV Bending opens ion channels o Inflow of calcium ions increases neurotransmitter release at synapse o More likely to fire an action potential Hearing sensation produced by the wavelike changes in the air called sound o Consists of waves of pressure in air or water o Frequency number of pressure waves that occur in one second Pitch different sound frequencies 3 components of the ear outer ear middle ear inner ear o Outer ear collects the sounds funnels them through ear canal o Waves strike tympanic membrane ear drum o Ear drum vibrates at same frequency of sounds o Passed to the ossicles which vibrate against one another o Stapes last ossicle vibrates against oval window membrane o Waves are generated in fluid in cochlea o Sensed by hair cells in cochlea Middle ear amplifies the sounds collected by the outer ear Rows of hair cells are embedded in tissue in basilar membrane o Stereocilia touch smaller surface tectorial membrane o Certain portions of basilar membrane vibrate in response to specific frequencies result in bending of stereocilia Elephants have best hearing of any land mammal Echolocation using sound echoes to navigate o High frequency waves bounce off surfaces Lateral line system pressure sensitive sensory organ in fishes larval amphibians Photoreception Sensing Light A species sensory abilities correlate with its environment Compound eye An eye formed of many independent light sensing structures ommatidia anthropods o Ommatidium has a lens that focuses light onto normally 4 receptor cells at a time Vertebrate eye simple eye structure with single lens that focuses incoming light onto a layer of many receptor cells o Sclera outermost layer tough white tissue o Cornea Front of the sclera transparent sheet of connective tissue o o o Iris pigmented round muscle inside cornea controls amount of light that enters the eye Lens curved clear lens Retina thin layer of cells with photoreceptors and several layers of neurons 3layers Photoreceptors sensory cells that respond to light are held in place by pigmented epithelium Photoreceptors synapse with an intermediate layer of connecting neurons called bipolar cells Bipolar cells connect with ganglion cells and form innermost Rods rod shaped cells that are sensitive to dim light but not color o Rhodopsin 2 molecule complex of opsin transmembrane proteins retinal pigment Cones cone shaped cells that aren t as sensitive to faint light but are stimulated by different wavelengths colors Molecular basis of vision is a shape change in retinal that closes ion channels decreases the amount of neurotransmitter being released to the sensory neuron Retina contains 3 types of color sensitive receptors blue green red cones o Different opsin molecules cause each type to respond to different range of wavelengths of light Animals that are active at night have relatively few cones many rods cannot see colors well Chemoreception Sensing Chemicals Chemoreception occurs when chemicals bind to chemoreceptors to initiate action potentials in sensory neurons Gustation sense of taste Olfaction sense of smell Taste buds structures that are clusters of taste chemoreceptor cells Salt and sour sensation result from activity of ion channels o Salt is due to sodium ions dissolved in food that flow through open Na channels depolarize cell membranes o Sourness is due to protons that depolarize the membrane Umami meaty taste of MSG Odorants airborne molecules that convey info about the food or the environment o Activate olfactory neurons by binding to membrane bound receptor proteins in the nose o Axons from the neurons project to olfactory bulb part of the brain where olfactory signals are processed interpreted Each olfactory neurons has only one type of receptor neurons with the same type of receptor are linked to distinct regions in the olfactory bulb of the brain glomeruli Pheromone a chemical secreted into the environment affects the behavior or physiology of animals of the same species o Pheromone receptors are often located in vomeronasal organ sensory organ in nasal region that s distinct from olfactory bulb Other Sensory Systems Thermoreception sensory system where receptors are
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