sensory physiology - napa valley...
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Sensory PhysiologyBio 219
Napa Valley CollegeDr. Adam Ross
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Sensory Receptor
• Specialized receptor that detects a specific stimulus
• Transduces stimuli into a change in membrane potential• Signal then sent to brain or spine for response
• Signal causes changes in ionic conductance via opening of ion channels• Can be direct or indirect
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Classes of Sensory Receptors
• Chemoreceptors• Specific chemicals, function in taste in olfaction, detecting pH and 02
• Mechanoreceptors• Touch, pressure, vibration, texture, stretch, movement
• Photoreceptors• Light
• Thermoreceptors• Hot and cold
• Nociceptors• Pain, noxious stimuli (chemical, mechanical, thermal)
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Sensory Transduction
• Sensory receptors receive graded potentials in response to stimuli
• Sensory neurons convert graded potentials into Aps
• Stimulus → Sensory Receptor → Sensory Neuron → CNS
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Receptive Field
• The area supplied or covered by a single sensory neuron• May or may not have sensors everywhere
• Neurons with smaller receptive fields give better sensitivity to stimulus• 2 point discrimination test
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Transmission of Sensory Signals
• Afferent division of peripheral nervous system sends AP from sensory neuron to CNS• Somatic sensory
• Touch, temp, pain, proprioception
• Visceral sensory• Mechanical and chemical stimuli from internal organs
• Special senses• Vision, hearing, equilibrium, olfaction, taste
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Sensory Pathways in CNS
• Ascending tracts in spinal cord• 1st order: from sensory receptor to spinal cord or brainstem
• 2nd order: from spinal cord or brainstem to thalamus
• 3rd order: from thalamus to cerebral cortex
• Also have cranial nerve sensory pathways
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Sensory Areas of the Cerebral Cortex
• Somatosensory Cortex• Parietal lobs (postcentral gyrus)
• Visual Cortex• Occipital lobe
• Auditory Cortex• Temporal lobe
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CNS Integration of Sensory Information
• Properties of stimulus:• Modality
• Location
• Intensity
• Duration
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Modality• Indicated by:
• Specificity of the neurons and receptors being activated
• Specific neural pathway being activated in the CNS (specific areas of the brain)• Labeled line coding
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Localization• Where is the stimulus being presented?
• Specific neural pathways connect receptive fields to specific parts of the brain• Sound localization uses differences in timing between left and right ears
• Lateral inhibition (see image)• Increases contrast between adjacent receptive fields
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Intensity of Stimulus
• Number of receptors activated (spatial)
• Frequency of action potentials (temporal)
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Duration of Stimulus
• Coded by duration of APs
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Receptor Adaptation
• Decrease in response to a persistent stimulus over time• Tonic receptors: non, or slowly adapting (muscle spindle stretch receptors)
• Phasic receptors: rapidly adapting (olfactory receptors)
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TRP Channels
• Transient Receptor Potential Channels• Rapidly adapting receptors
• Quickly inactivate after activation
• Involved in numerous cellular processes
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TRP Channels
• Several classes of TRP Channels• TRPC
• Classical or canonical TRP channels• Membrane stretch
• TRPM• Melastatin
• Sensitive to Menthol and Eucalyptol
• TRPA• Ankyrin repeat
• Sensitive to mechanical stress and extreme cold
• TRPV• Vanilloid
• Sensitive to capsaicin and thermal pain
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Thermosensation