KINE 3020 Lecture Notes - Lecture 4: Motor Neuron, Alpha Motor Neuron, Mechanoreceptor

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Proprioception
Where are we?
Sensing all our parts
Sensory Feedback from Muscle
Proprioception
o sense of Position of the Limbs …
… in Space; … relative to Body
Kinesthesia
o sense of Movement
to detect the Position & Motion of our Body Parts
Muscle Spindles
o 4 ~ 7 Intrafusal Muscle Fibers
o Muscle Stretch or Muscle Length
Type II sensory neuron: Static length
Type Ia sensory neuron: Static & Dynamic length
γ motor neuron
Golgi Tendon Organs
o GTO
o Muscle Tension or Muscle Force (instead of Length)
Type Ib sensory neuron: Force of Contraction
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Sensing the position
Proprioception & kinesthesia are all about the 'Feedback.'
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Muscle spindle ---> length & stretch
GTO ---> force & tension
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Muscle Spindles
Muscle Stretch / Length
Circumference of the Intrafusal Muscle Fiber is related to the Length of the Muscle
o Intrafusal Fibers are swollen in the Middle
Fatter & shorter = Contraction
Thinner & longer = no contraction
Intrafusal Muscle Fibers are wrapped around in Capsule
o Each Intrafusal Muscle Fiber has Sensory neurons wrapped around it
Tells the thickness of the Intrafusal Muscle Fiber
γ Motor Neurons
o γ Motor Neurons innervate the Ends of the Intrafusal Muscle Fibers
Intrafusal Fibers
γ Motor Neuron Fibers
Type II & Type Ia Sensory neurons
i.e. circumference
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Types of Muscle Spindles
Muscle Spindle
o A bundle of Intrafusal Muscle Fibers wrapped with
Gamma Motor Neurons
Sensory Neurons
a Capsule
o Different Shape, different functions
Within the Muscle Spindles
o Nuclear Bag
Round shape
Fatter (middle), skinner (ends)
as stretch … more change in Circumference
Much more sensitive to changes in Muscle Length
Dynamic & Static (?) Length (Type Ia)
o How Fast it is getting longer
o How fast it is contracting
o Nuclear Chain
Thin … as stretches … becomes thinner evenly all along the chain
good for detecting the Length of the Muscle
Static Length (Type II)
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