Chapter 7 Sensory Physiology 16 October 2009 Chapter 7 Sensory Physiology Quiz on Cranial Nerves: Wednesday Lab next week: Sensory Physiology and the Auditory System

Receptors: Encapsulated

Receptors for gustation 5 different receptor types (but not all in the same cell) Receptors for gustation

Stimulus Localization & Intensity 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.)

Stimulus Localization Figure 7.09 Stimulus Localization & Intensity 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. Demonstration: circles in carpet of McMillan Theater = receptive fields

Somatosensory: sensation of touch, vibration, pain, and temperature Misleading diagram: implies different receptor types connected to one sensory axon. Superficial Deep Sustained stimulus Fluctuating stimulus

Stimulus Localization & Modality & Intensity Figure 7.15 Stimulus Localization & Modality & Intensity Three neurons to the cortex! Labeled Line

Wilder Penfield, neurosurgeon and epilepsy

Figure 7.14 =Post-central gyrus Thalamus Damage to specific areas (stroke) is correlated with specific sensory deficits.

Right side Right side Right side Right side Proprioception Figure 7.19 Right side Right side Anterolateral (spinothalamic) tract 1st order synapses onto 2nd order in spinal cord, 2nd order axon decussates in spinal cord, travels to thalamus in contralateral anterolateral tract, synpases onto 3rd order neuron in thalamus, which sends its axon to SSC. Dorsal column-medial lemniscal tract 1st order axons ascend in ipsilateral dorsal columns to synapses onto 2nd order in dorsal column nuclei of brainstem, 2nd order axon decussates in brainstem, travel to thalamus to synpases onto 3rd order neuron, which sends it axons to SSC. Right side Right side Proprioception

Somatotopy in the SSC (post-central gyrus.) Figure 7.20 Somatotopy in the SSC (post-central gyrus.) Homunculus: representation of body in the SSC; somatic sensations from adjacent parts of the body are processed by adjacent regions of SSC, with those body regions more densely innervated by sensory receptors occupying more cortical tissue.

Dermatomes

Figure 7.18 Referred Pain

Watch this 2-3 minute YouTube video. You’ll find it very interesting! http://michaelscomments.wordpress.com/2008/09/19/very-interesting-test-of-perception/