18 October 2010 This Week: Today’s Lecture: Sensory Part 2, then Muscle Lab: Vision Part 2 Cutaneous receptor experiments for Abstracts Review of statistical analysis Abstracts due Friday, 29 October Wednesday: 1QQ and the Cranial Nerve Quiz Friday, 22 October: Fall Break

1QQ 19 for 8:30 am What discovery was made by Canadian neurologist Wilder Penfield? Free nerve endings can transduce Tissue damage Movement of a hair Noxious stimuli Vibration Deep pressure

1QQ 19 for 9:30 am What is special about the post-central gyrus? Meissner’s corpuscle are best suited to transduce Tissue damage Movement of a hair Noxious stimuli Rough surfaces Deep pressure

More somatosensory receptors: Proprioceptors Golgi tendon organs for tension Muscle stretch receptors (muscle spindles) Position in skin or muscle, free or encapsulated, types of receptor proteins in the cell membranes…… all these confer modality specificity Adequate stimulus: the stimulus type to which a receptor responds best (lowest threshold.) Regardless of modality, what are some general principles of sensory receptors?

Receptive field = the area of the body that, when stimulated, leads to activity in a neuron. = 1st order sensory neuron Could be encapsulated

Right side Right side Right side Right side Proprioception Receptive field = the area of the body that, when stimulated, leads to activity in a neuron. 1st, 2nd, and 3rd order sensory neurons each have receptive fields. 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

Receptor potentials e.g. somatosensory e.g. gustatory Graded potentials are the result of transduction within a receptor. Transduction produces a receptor potential Amplitude is usually in proportion to the stimulus intensity Other receptors are short, specialty cells with no axon (visual, gustatory, auditory, and vestibular systems). The graded receptor potentials will directly change amount of NT secretion. Receptors with axons (somatosensory and olfactory systems) have a trigger zone and receptor potentials generate action potentials

Receptors and transduction Could be encapsulated 07.05.jpg Activation of mechanically gated channels

Sensations to touch Mechanoreceptors contain receptor proteins that respond to stretching, distortion, or pressure on the peripheral plasma membrane

Fig. 07.05 07.05.jpg Activation of mechanically gated channels and convergence of graded receptor potentials from different parts of the dendritic arbor of the receptor. Thus a receptor cell with a more extensive arbor will likely be more ____________. Why?

What’s left? Location encoded by _______. Duration encoded by _______. Summary to now: Modality encoded by _______. Intensity encoded by _______. What’s left? Location encoded by _______. Duration encoded by _______.

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!)

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 & Intensity Mild inhibition Presynpatic Inhibition Massive inhibition Lateral inhibition exaggerates the difference in stimulus intensity detected by adjacent neurons, aids with LOCALIZATION.

Stimulus Localization & Intensity Lateral inhibition improves stimulus localization.

Adaptation = decrease in frequency of APs with sustained stimulus

Figure 7.11 Examples: waistband of underwear, top of socks, earrings, mechanoreceptors in carotid arteries for blood pressure YouTube