Page 330 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

A. Muscle spindles and Golgi tendon organs
α motoneurons
Ia and II afferents
γ motoneurons

1b fiber Annulospiral
endings
Nuclear bag fibers
Golgi Nuclear chain fibers Stretch Reflex
tendon Muscle spindle
organ Extrafusal
Skeletal muscle muscle fibers
Proprioception,
B. Muscle spindle function
1 Initial length of muscle
Sensor Muscle spindle
Ia

Extrafusal α
muscle fibers γ

2 Spindle activated by “involuntary” muscle stretching Plate 12.4
Ia
Reflex contraction of skeletal muscle
α to bring muscle back to initial length

Supraspinal
3 Supraspinal activation centers
“Voluntary” change in muscle length
with pre-setting (via fibers)
a. A set-point for length (α/γ co-activation)
b. An increased receptor sensitivity α
(fusimotor set) γ
C. Monosynaptic stretch reflex D. Polysynaptic circuits
5 Posterior
2 root
1
To flexor
α
α fibers To 4 Ia, Ib
Ia fiber extensor 3 II

Ib fiber From
Ia/II fibers extensor

Interneuron
Extensor Inhibitory 317
Flexor Stimulatory
Despopoulos, Color Atlas of Physiology © 2003 Thieme
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