Chapter 46 Sensory

Chapter 46 Sensory - How many senses do we have? Five?...

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How many senses do we have? Five? Sight Hearing Touch Smell Taste
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How many senses do we have? Sight: Details + color + motion for conscious awareness Light intensity for pupillary constriction Light intensity for circadian (day/night) rhythms Motions to direct eye and body position Hearing: Different tone frequencies Touch: Fine detail (shape) Fine detail (texture) Course detail (flutter) Course detail (deep pressure) Hair follicles Pain Hot Cold Taste: Sweet (a few) + sour + salty + bitter (30?) + others Smell: ~350
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There’s more! Proprioception (part of somatosensation) Joint receptors Muscle stretch receptors (muscle spindles) Golgi tendon organs (tendons and ligaments – force) Balance Three semicircular canals: angular rotation Vestibular: gravity, linear acceleration Internal chemosensors Carbon dioxide Oxygen Glucose Many hormones! Internal blood pressure receptors (baroreceptors) Internal pain receptors Meninges Gut Internal temperature receptors
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Metabotropic Transduction The first step is transduction , conversion of some form of energy or signal into an electrical signal , generally by opening or closing of ion channels in the receptor cell and a change in membrane potential. In metabotropic sensory detection, the receptor protein is linked to a G protein that activates a cascade of intracellular events that eventually open or close ion channels.
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Ionotropic transduction In ionotropic sensory detection, the receptor protein itself is part of the ion channel and, by changing its conformation, opens or closes the channel pore.
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Membrane receptor proteins of sensory cells generally cause ion channels to open or close, causing a change in membrane potential. This change is called a receptor potential . The receptor potential may simply modify the rate of release of neurotransmitter. Or, the cell may fire action potentials . An example of the latter is the crayfish stretch receptor. More intense stimuli generate larger receptor potentials, causing greater changes in the rate of release of neurotransmitter or higher firing rates of spikes.
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Labeled lines Since the outcome of a sensory system is a change in firing rate, how does the brain know which sense was activated? Different senses connect to different targets. This explanation is called “labeled lines.”
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Olfaction Like a metabotropic receptor for a neurotransmitter, chemoreceptor cells have receptor proteins that bind to specific molecules. Binding of an odorant molecule to a receptor protein activates a G protein , which triggers a cascade that causes production of a second messenger (cAMP) in the chemoreceptor cell. The second messenger binds (from the inside!) to ion channels for Na+, opening them, and causing depolarization and action potentials . Why action potentials?
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Coding of odor Here are two competing hypotheses: coding of odor might be based on a small number of "primaries,” or coding of odor might be based on a large number of highly specific receptor
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This note was uploaded on 04/19/2011 for the course LS 2 taught by Professor Pires during the Spring '08 term at UCLA.

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Chapter 46 Sensory - How many senses do we have? Five?...

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