Biol 118 1st Edition Lecture 29 Outline of Last Lecture I. SynapsesII. Vertebrate Nervous SystemOutline of Current Lecture I. How Do Sensory Organs Convey Information to the Brain?II. Mechanoreception: Sensing Pressure ChangesIII. Photoreception: Sensing LightIV. Chemoreception: Sensing ChemicalsV. Other Sensory SystmesCurrent LectureHow 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 signalo 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 brain- different regions of the brain are specialized for interpreting different types of stimuliMechanoreception: 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 thebottomo When crab flips over, particles press against receptor NOT on bottom and muscles activate to repositionThese 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 cellso Pressure-receptor cells named for hairy looking stereocilia outgrowthso Have single kinocilium: true cilium that has 9 +2 arrangement of microtubuleso Found in ears of vertebrates & lateral line system of fish and amphibianso Equilibrium potential is 0 mV - Bending opens ion channelso Inflow of calcium ions increases neurotransmitter release at synapseo More likely to fire an action potential- Hearing: sensation produced by the wavelike changes in the air called soundo 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 canalo Waves strike tympanic membrane (ear drum) o Ear drum vibrates at same frequency of soundso Passed to the ossicles which vibrate against one another o Stapes (last ossicle) vibrates against oval window membraneo Waves are generated in fluid in cochleao 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 membraneo Stereocilia touch smaller surface tectorial membraneo Certain portions of basilar membrane vibrate in response to specific frequencies & resultin bending of stereocilia- Elephants have best hearing of any land mammal- Echolocation: using sound echoes to navigateo High-frequency waves bounce off surfaces - Lateral line system: pressure-sensitive sensory organ in fishes & larval amphibiansPhotoreception: Sensing Light- A species’ sensory abilities correlate with its environment- Compound eye: An eye formed of many independent light sensing structures (ommatidia)- anthropodso 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 tissueo Cornea: Front of the sclera; transparent sheet of connective tissueo Iris: pigmented, round muscle inside cornea; controls amount of light that enters the eyeo Lens: curved clear lens o 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 calledbipolar cells Bipolar cells connect with ganglion cells and form innermost - Rods: rod-shaped cells that are sensitive to dim light but not coloro 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 coneso 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 wellChemoreception: 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 channelso Salt is due to sodium ions dissolved in food that flow through open Na+ channels & depolarize cell membraneso 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 environmento Activate olfactory neurons by binding to membrane-bound receptor proteins in the noseo 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 specieso Pheromone receptors are often located in vomeronasal
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