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8 October 2008 Chapter 7 Sensory Physiology Friday: Return Take-Home Quiz on van Gammeren et al. paper. 2) Take in-class quiz on Cranial Nerves and Somatic & Autonomic Motor Systems. Aspects of a stimulus that must be encoded using only action potentials What? (modality & labeled line)
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8 October 2008 • Chapter 7 Sensory Physiology • Friday: • Return Take-Home Quiz on van Gammeren et al. paper. • 2) Take in-class quiz on Cranial Nerves and Somatic & Autonomic Motor Systems
Aspects of a stimulus that must be encoded using only action potentials What? (modality & labeled line) Where? (location enhanced by lateral inhibition) How long (duration, onset/offset.. Adaptation)? How strong (intensity)? Board diagram listing stimulus modal and classifications as special senses, somatic senses, and internal (subconscious) senses.
Figure 7.01 1st order sensory neuron 1st order sensory neuron Example: a rod or cone of the retina
Figure 7.16 Adequate Stimulus & Labeled Line Each type of receptor responds best to a specific stimulus called its adequate stimulus.
Figure 7.11 Examples: waistband of underwear, top of socks, earrings, mechanoreceptors in carotid arteries for blood pressure
Figure 7.04 Review definition of receptive field; 1st, 2nd, and 3rd order sensory neurons each have receptive fields. = 1st order sensory neuron
Figure 7.05 Within a cell’s receptive field, stimulus intensity is encoded by frequency of action potentials.
Figure 7.06 The size of receptive fields varies dramatically in different regions of skin (i.e. lips, palm, fingertip, calf). For touch discrimination, small receptive fields allow greater accuracy in “two point discrimination” test (upcoming lab!)
Figure 7.07 This 1st order sensory neuron will have a higher frequency of action potentials if the stimulus is in the center if its receptive field. However, this neuron also uses action potential frequency to encode stimulus intensity. Therefore, this neuron would not be very good at encoding the precise location at which a stimulus was delivered.
Figure 7.08 Receptive fields of different neurons often overlap such that any patch of skin may have several receptors of the same type (modality) and receptors of different types (different modalities I.e. touch, pain temperature, etc.) Overlapping receptive fields of touch receptors (Meissners, Merkels) allow for more precise localization of a stimulus via the mechanism of lateral inhibition (next slide.)
Figure 7.09 Lateral inhibition exaggerates the difference in stimulus intensity detected by adjacent neurons.
Figure 7.10 Lateral inhibition improve stimulus localization.
Figure 7.12 Descending pathways from brain (from periaqueductal gray matter) can suppress sensory input (recall example of suppression of pain.)
Figure 7.13 1st order somato-sensory neurons have cell bodies in DRG or cranial nerve ganglia and synapse onto second order neurons within the CNS.
Figure 7.14 =Post-central gyrus Damage to specific areas (stroke) is correlated with specific sensory deficits.
