Gradation of sensory signals, muscle spindle, Golgi tendon organ

3 Pages

Health + Exercise Science
Course Code
HES 319
Brian Tracy

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26 February Gradation of sensory signals – cellular communication The input signal (a receptor or synaptic potential) is graded in amplitude, proportional to the amplitude and duration of the stimulus. The trigger zone integrates the input signal – the receptor potential in sensory neurons, or synaptic potential in motor neurons – into a trigger action that produces action potentials that will be propagated along the axon. An action potential is generated only if the input signal is greater than a certain spike threshold. Once the input signal surpasses this threshold, any further increase in amplitude of the input signal increases the frequency with which the action potentials are generated, not their amplitude. The duration of the input signal determines the number of action potentials. Thus, the graded nature of input signals is translated into a frequency code of action potentials at the trigger zone. Action potentials are all-or-none. Every action potential has the same amplitude and duration, and thus the same wave form on an oscilloscope. Since action potentials are conducted without fail along the full length of the axon to the synaptic terminals, the information in the signal is represented only by the frequency and number of spikes, not by the amplitude. When the action potential reaches the synaptic terminal, the cell releases a chemical neurotransmitter that serves as the output signal. The total number of action potentials in a given period of time determines exactly how much neurotransmitter will be released by the cell. The anatomical location of muscle spindles and Golgi tendon organs underlies their roles as length and tension sensors, respectively. Length and tension are extremely important – proprioception Embedded in belly of muscle (muscle spindle) A force sensor would exist between the tendon and muscle (Golgi tendon organ) Have efferent neurons Muscle spindles – important length sensors Muscle spindles sense changes in muscle length Muscle length changes with joint position Muscle spindles, therefore, can provide information about
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