NSCI 175- Somatic Sensory I, II LOs

Define dermatome

Area of skin innervated by the right and left dorsal roots of a single spinal segment

Describe the somatosensory pathways to the brain + Predict how a lesion in the pathway would impact sensation

Dorsal Column Medial Leminiscal touch and vibration Decussates at medulla (medulla to thalamus) Touch information from right side of body perceived by left S1 cortex. Trigeminal

Identify and describe different types of sensory receptors int he skin

Free Nerve endings: pain Hair follicle receptor: Meissner's corpuscles: light touch, rough texture Merkel's disks: light touch, gentle pressure Pacinian corpuscle: vibration, pressure Ruffini corpuscle: STRETCH

Describe how a sensory event is encoded in APs in sensory fibers

Generator potentials like EPSPs, when they sum together and reach threshold, an AP is fired. Size of generator potential: proportional to the intensity of the stimulus Unmyelinated axon terminals with membranes with mechanosensitive ion channels: convert mechanical force into change of ionic current Force can be applied: a. By membrane itself when it is stretched or bent b. Through connections between channels, extracellular proteins or intracellular cytoskeletal components c. Mechanical stimuli may trigger release of second messenger that secondarily regulate ion channels

Compare and contrast rapidly-adapting and slowly-adapting receptor firing patterns + Relate the structure of the Pacinian corpuscle to adaptation in the receptor

Meissner and Pacinian: respond quickly at first, stop firing even w continued stimulation (RAPID ADAPTATION) Merkel, Ruffini: consistent AP firing (SLOW ADAPTATION) + Layered Pacinian corpuscle (20-70 layers) capsule: vibration / high frequency sensitive, not sensitive to steady pressure. Layers with fluid in between are able to slip past each other.

Distinguish somatic sensory receptors based on their receptive field size

Meissner's, Merkel: small receptive field Pacinian, Ruffini: large receptive field

Plan an experiment to map the receptive field of a somatic sensory receptor

Record from single sensory axon (need a recording electrode), stimulus probe moved to map the receptive field Meissner's, Merkel: small receptive field Pacinian, Ruffinin: large receptive field

Discuss why our ability to discriminate a somatic sensory stimulus across different regions of the body varies

Two-point discrimination Ex: Fingertips have highest resolution. Why? Higher density of mechnanoreceptors Enriched in receptors types with small receptor fields More brain tissue dedicated to sensory information of each mm of fingertip than anywhere else +special neural mechanisms