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Lecture 3

Lecture 3 Reading.docx

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Department
Biology
Course
BIO271H1
Professor
Melanie Woodin
Semester
Winter

Description
Lecture 3 Reading – p.248-261 Sensory receptor cells take incoming stimuli and transduce them into changes in membrane potential - Specialized receptor proteins absorb energy from the stimulus  undergo conformational change - Activation of a signal transduction pathway that (in)directly opens/closes ion channels in the cell membrane  change in membrane potential  signal sent to integrating centres Sense organ – complex structure consisting of multiple tissues that work together to let an organism detect incoming stimuli Sensory receptor – cell that is specialized to detect incoming sensory stimuli - Can be found w/in complex sensory organs - Receptor proteins – specialized to detect incoming sensory signals; found on the membranes of sensory receptor cells Afferent neurons – send signals in the form of APs from the periphery to integrating centres - Some sensory receptors are afferent neurons (sensory neurons) - Receptor protein in dendrite detects the incoming sensory signal  changes conformation  alters activity of signal transduction pathway  change in membrane potential of receptor o Generator potential – spreads along membrane to spike-initiating (trigger) zone of the neuron, where it generates APs in the axon if generator potential > threshold potential Receptor potential – initial graded potential in the sensory receptor cell when it’s separate from the afferent sensory neuron - Spreads across sensory receptor cell to the site of the synapse with the afferent neuron, where it triggers the release of neurotransmitter Function of a sensory receptor – to detect incoming stimuli and transduce them into changes in membrane potential that convey information to integrating centres Classification of sensory receptors based on location of stimulus - Telereceptors – locations at some distance from the body (vision, hearing) - Exteroceptors – outside of the body (pressure, temperature) - Interoceptors – inside thebody (blood pressure, blood oxygen) Classification of sensory receptors based on type of stimulus they can detect (stimulus modality) - Chemoreceptors – chemical signals - Mechanoreceptors – pressure and movement o Proprioception – sense of body position - Photoreceptors – light - Thermoreceptors – temperature - Electroreceptors – electric fields - Magnetoreceptors – magnetic fields Adequate stimulus – a receptor’s preferred (or most sensitive) stimulus modality Polymodal receptors – able to detect more than one class of stimulus - Nociceptors – detect extremely strong stimuli of various kinds; responsible for the sensation of pain In order for an incoming signal to be interpreted properly, 4 pieces of info must be known about the stimulus Stimulus modality – signals in an afferent neuron have to represent a specific stimulus modality - Sensory units – multiple sensory receptors that form synapses with one afferent neuron - Relative firing of several adjacent sensory cells may carry information regarding stimulus modality Stimulus location – coded by location of the stimulated receptor on the body - Receptive field – corresponds to the region of skin that causes a response in that particular afferent neuron (usually those involved in touch) - Acuity – localization of stimuli o Neurons w/small receptive fields detect stimuli across a smaller area than neurons w/large receptive fields; thus, they have greater acuity - Population coding – a stimulus that causes two adjacent neurons to respond must be located w/in the area of overlap btw receptive fields of those two neurons - Lateral inhibition – lateral interneurons form synapses btw axon terminals (Figure 6.3, page 254) o Strong response of one neuron  release neurotransmitter onto lateral interneurons  inhibitory neurotransmitter released from lateral interneurons  prevents release of neurotransmitter from neurons on either side of the responsive neuron o As a result, secondary neurons don’t fire; increases contrast btw neurons @ centre of stimulus and neurons on the edge; finer discrimination Dynamic range – a relatively limited range of intensities over which most sensory receptor cells are able to encode stimuli - APs code stimulus intensity through changes in frequency o Strong – high-frequency series (trains) of APs o Weak – lower-frequency trains of APs - Threshold of detection – weakest stimulus that produces a response in a
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