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lecture_notes_12_(ta) - NPB 101 Notes Wednesday SUMMARY OF...

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NPB 101 Notes: Wednesday, January 22, 2003 SUMMARY OF THE SENSORY SYSTEM 6 MAJOR SENSES 1. VISION 2. AUDITION 3. SOMATOSENSORY 4. OLFACTION 5. GUSTATORY 6. VESTIBULAR (SENSE OF BALANCE) GENERAL ORGANIZATION RECEPTOR, RELAY NUCLEUS, THALAMUS, PRIMARY CORTEX, SECONDARY CORTEX RECEPTOR PHYSIOLOGY SIGNAL FLOW RECEPTOR POTENTIAL -GRADED POTENTIALS IN PHOTORECEPTORS AND HAIR CELLS MODALITY SPECIFICITY -E.G., PHOTONS ACTIVATE PHOTORECEPTORS AND NOT HAIR CELLS. RECEPTIVE FIELD - WHICH STIMULI WILL ACTIVATE THE NEURON. FOR EXAMPLE, PHOTORECEPTORS ONLY RESPOND TO VISUAL STIMULATION FROM CERTAIN REGIONS OF SPACE. SENSORY MAPS -E.G., SENSORY HOMUNCULUS. OVERLYING ORGANIZATION OF SENSORY SYSTEMS THAT MAINTAINS THE MAPS OF THE SENSORY RECEPTORS. SENSORY ACUITY IS ALSO REFLECTED IN THESE MAPS. THERE IS MORE AREA OF THE SOMATOSENSORY CORTEX DEDICATED TO THE HIGH ACUITY HANDS THEN THERE IS TO THE LOW ACUITY BACK. Lecture 11: Sensory Systems III – Central Processing Reading: same as Lecture 9 Central Processing Somatosensory System Afferent signals from the skin, muscles and tendons are relayed to the CNS by receptor cells located in the dorsal root ganglia (Figure 5-30) . The central projections of these cells enter the doral horn of the spinal cord and then project to the somatosensory thalamus on the other (contralateral) side of the brain (Figure 5-33) . The recipient thalamic neurons then project to the primary somatosensory cortex, which in turn projects to the secondary somatosensory cortex. The perception of tactile stimuli takes place in these cortical and thalamic structures. The spatial relationships among the receptors on the skin surface are preserved at each step of the pathway. In this manner a topographic map of the body surface is maintained for each somtatosensory modality (Figure 5-12) . The crossover of the pathways insures that the left half of the body surface is represented on the right half of the brain and vice versa. Visual Afferent signals from the photoreceptors are relayed to the output neurons of the retina, the ganglion cells, which send their axons out of the eye to form the optic nerve (Figure 6-22) . Half of the fibers in each optic nerve cross at a junction called the optic chiasm , and then project to the visual thalamus. This crossover insures that the left half of the visual field will be represented in the right thalamus and vice versa (Figure 6-31) . The thalamic neurons project to the primary visual cortex, where information from the two eyes is first integrated
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(Figure 6-32) . The primary visual cortex sends its projections to multiple secondary visual cortical areas. Processing in these areas is responsible for our perception of the visual world. The spatial relationships among the photoreceptors in the retina are preserved at each step of the pathway. In this manner a retinotopic map of the contralateral visual field
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