14 October 2009 Chapter 7 Sensory Physiology Aspects

14 October 2009 Chapter 7 Sensory Physiology

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)

Figure 7. 01 1 st order sensory neuron Example: a rod or cone of the retina

Figure 7. 16 Adequate Stimulus & Labeled Line Stimulus Modality Each type of receptor responds best to a specific stimulus called its adequate stimulus.

Figure 7. 02

Figure 7. 03

Figure 7. 11 Examples: waistband of underwear, top of socks, earrings, mechanoreceptors in carotid arteries for blood pressure You. Tube

Figure 7. 04 Review definition of receptive field; 1 st, 2 nd, and 3 rd order sensory neurons each have receptive fields. = 1 st order sensory neuron

Figure 7. 05 Stimulus Intensity Within a cell’s receptive field, stimulus intensity is encoded by frequency of action potentials.

Figure 7. 06 Stimulus Localization 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 Stimulus Localization This 1 st 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 Stimulus Localization & Intensity 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. Stimulus Localization & Intensity

Figure 7. 10 Stimulus Localization & Intensity Lateral inhibition improves stimulus localization.