SOMATIC SENSATION AC Brown page 1 A7b SENSATION A. General Sequence 1. When stimulated, an afferent nerve ending (sensory receptor) generates one or more action potentials(1st order or primary afferent neuron) 2. These action potentials are conducted into the Central Nervous System(spinal cord and brain), where they excite adjacent nerve cells (2nd order, 3rd order, etc. neurons) 3. By this mechanism, excitation eventually reaches specialized regions of the cerebral cortexwhere conscious sensation occurs; sensory pathways have a minimum of one-three synapses (two-four neurons), depending on modality 4. If this sequence is interrupted, conscious sensation is lost (anesthesia) DIMENSIONS OF SENSATION A. Modality 1. Define: quality of sensation 2. Basis: receptor stimulated and its adequate stimulus a. many types of stimuli can excite a given sensory receptor if sufficiently strong, but in normal circumstances, only a single type of stimulus causes excitation. This type is termed the receptor's adequate stimulus. b. the sensation evoked by stimulation of a receptor or its pathway is sensed as being caused by the receptor's adequate stimulus, no matter what the actual stimulus ("Doctrine of Specific Nerve Energies")
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