Unformatted text preview: s from the
musculoskeletal system (i.e.,
muscles, tendons, joint capsules
and ligaments) there are many kind also in joints stretch==velocity • Proprioceptors are low threshold
mechanoreceptors that inform
CNS about movement and
position by detecting the stretch of
the tissue in which they lie. 7 7/4/12 UNDERSTAND!!!!! Muscle Spindle
• Cigar-shaped (fusiform) structures that run in parallel to regular
(extrafusal) muscle fibers muscle spindles--fusiform(cigar shaped)
run parralel to muscle ﬁbers.
they are INTRAFUSAL FIBERS!!!!!!! these sense forces
extrafusla ﬁbers produce force
---they are both in the freaking muscles!!!!!
-high position ﬁne motor skills like vision and touch are ﬁlled with many
intrafusla ﬁbers like spindles!!!!!!!!!!!
quads dont have them so densly packed because its gross Muscle Spindle
• Density of muscle spindles vary from muscle to muscle.
• Muscles used for precision movements (extraocular eye
muscles, intrinsic muscles of the hand and small muscles in
the neck joints) have a higher density of spindles. KNOW THIS WILL BE TESTED!!!!!!!!!!!!!!!!!! Muscle Spindle know what innervates what!!
extrafusal muscle innervated
by the alpha (α) motor neuron Intrafusal muscle
innervated by the
gamma (γ) motor
neuron 8 7/4/12 know the second bullet point!!!!!!!! Muscle Spindle
low threshold mecanoreceptors
• Intrafusal muscle fibers only show
striations at their ends and therefore can
only contract in these areas
• There are two types of sensory fibers that
monitor the intrafusal muscle. Both are
slow adapting, low threshold
" secondary afferent mechano recptors have to be stimulated by---mechanical stimulus primary afferent " mean the action potential is easier to obtain. it doesnt have to
depolarize as much---so the stimulus can be much less. a photorecptor for example needs--- duh light photons son Sensitivity of the muscle spindle
• Muscle spindle afferents respond to stretching of the intrafusa...
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- Fall '08