- When a skeletal muscle was passively stretched, it contracted reflexly. However, when the muscle was over stretched in dos way it showed sudden cessation of contraction followed by relaxation, The following statements provided the possible explanation of these observations:
A. The passive stretching of muscle caused stretching of muscle spindle
B. The’ over stretching of muscle stimulated Golgi tendon organ
C. Group lb sensory nerve fibers were stimulated by stretching of muscle spindle
D. Group lb sensory nerve fibers stimulated α-motor neurons that supplied the muscle from which these fibers arose.
E. Group la sensory nerve fibers were connected to Golgi tendon organ.
F. The stimulation of group la sensory fibers led to the production of lPSP on the α – motor neurons that supplied the muscle from which these fibers arose.
Which of the above statement(s) is/are correct?
(1) A and B (2) C and D
(3) E and F (4) C and FReflex Contraction on Passive Stretch
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A. Passive stretching of muscle causes stretching of the muscle spindle.
Muscle spindles are sensory receptors within the muscle that detect changes in muscle length. Stretching the muscle increases firing of group Ia sensory afferent fibers of the muscle spindle. -
D. Group Ia sensory fibers excites α-motor neurons that innervate the stretched muscle, causing contraction.
This is the classic stretch reflex or myotatic reflex, where excitation of α-motor neurons causes the muscle to contract, resisting the stretch.
Relaxation on Overstretching: The Protective Autogenic Inhibition
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B. Overstretching stimulates the Golgi tendon organ (GTO).
The Golgi tendon organ is a sensory receptor located in the muscle tendon that senses tension, especially during forceful or excessive stretching. -
C. Group Ib sensory fibers are stimulated by Golgi tendon organ activation.
These fibers respond to tension and relay signals indicating muscle overload. -
Ib afferents inhibit α-motor neuron activity, thus causing relaxation of the muscle to prevent injury, a phenomenon called autogenic inhibition.
Analyzing the Statements
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E. Group Ia sensory fibers are connected to Golgi tendon organ: Incorrect. Group Ia fibers arise from the muscle spindle, not the Golgi tendon organ.
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F. Stimulation of Group Ia sensory fibers leads to IPSP on α-motor neurons: Incorrect. Group Ia stimulation causes excitatory postsynaptic potentials (EPSP), leading to contraction, not inhibitory postsynaptic potentials (IPSP).
Correct Statements
The correct statements relating to the reflex contraction and relaxation during stretch and overstretch are:
(1) A and B
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1 Comment
Kirti Agarwal
September 16, 2025Statement a and b