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Unit 3 Sensory Systems - Part 2.docx

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BIOL 373
Heidi Engelhardt

Unit 3 Sensory Systems – Part 2 Enters spinal cord via dorsal root and synapses in the grey matter (in the dorsal horn of the spinal cord) to the second order neurons -crosses as it dives into the white matter -spino-______ is ascending (ex. Spinothalamic) -sensory nerve may also cross in the medulla (instead of the spinal cord); info from the right side of the body will cross to the left hemisphere (and vice versa) Thalamus is a relay point for all senses except smell! NOTE: The location of the synapse between the primary and secondary neurons varies according to the type of receptor -ex. neurons associated with receptors for nociception, temperature, and course touch synapse onto their secondary neurons shortly after entering the spinal cord, whereas fine touch, vibration, and proprioceptive neurons have long axons that project up the spinal cord and synapse to the secondary neuron in the medulla Ascending: dorsal columns & spinothalamic tract Descending: corticospinal tract The somatosensory cortex is the part of the brain the recognizes where ascending sensory tracts originate (depending on where the neurons terminate in the somatosensory cortex) Neuron with free nerve ending are most common and most mysterious Pacinian corpuscles: respond to vibration and one of the largest receptors in the body (vibrations open mechanically gated ion channels) -composed of nerve endings encapsulated in layers of connective tissue -pacinian corpuscles are rapidly adapting phasic receptors (which allow them to respond to a change in touch but then ignore it (RECALL FROM PREVIOUS LECTURE) -Pacinian corpuscles are and Ruffini corpuscles tend to be deep in the sk
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