CAS NE 203 Lecture Notes - Lecture 3: Intrafusal Muscle Fiber, Extrafusal Muscle Fiber, Afferent Nerve Fiber
4 Apr 2016
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Ch9: the somatic sensory system - touch and proprioception. Afferent fibers convey somatic sensory information to the cns. Somatic sensation originates from afferent nerve fibers whose cell bodies are in spinal ganglia: pseudounipolar = attached to the cell body in drgs by a single process. Aps generated in afferent fibers propagate along the fiber and past the location of the cell body in the ganglia, until they reach the fibers" synaptic terminals. Rate of ap firing proportional to magnitude of depolarization. Mechanoreceptors = help tune the afferent fiber to particular features of tactile stim. Free nerve endings = afferent fibers that lack specialized receptor cells: important in pain. Afferents with encapsulated endings: lower thresholds more sensitive to stim than free nerve. Drgs arise from an iterated series of embryonic tissue masses called somites. Territory innervated by each spinal nerve is called a dermatome. Dermatomes overlap substantially, more extensive for sensations of touch/pressure/vibration. Axon diameter differentiates classes of somatic afferents.
