Extrafusal fibers are innervated by which neurons?

Extrafusal fibers are innervated by which neurons?

• A. Alpha motor neurons
• B. Gamma motor neurons
• C. Interneurons
• D. Sensory Neurons

Answer: (A)

Extrafusal muscle fibers are the main force-generating fibers of skeletal muscle, and they are activated by alpha motor neurons. When an alpha motor neuron fires, it releases acetylcholine at the neuromuscular junction, depolarizing the extrafusal fibers and causing them to contract. This is the basis of a motor unit: one alpha motor neuron and all the extrafusal fibers it innervates. Gamma motor neurons, in contrast, specifically innervate intrafusal fibers within the muscle spindle and adjust the sensitivity of the spindle to stretch. Interneurons mediate connections within the spinal cord and help modulate motor output, while sensory neurons carry afferent information from the muscle to the CNS.

Extrafusal muscle fibers are the main force-generating fibers of skeletal muscle, and they are activated by alpha motor neurons. When an alpha motor neuron fires, it releases acetylcholine at the neuromuscular junction, depolarizing the extrafusal fibers and causing them to contract. This is the basis of a motor unit: one alpha motor neuron and all the extrafusal fibers it innervates.

Gamma motor neurons, in contrast, specifically innervate intrafusal fibers within the muscle spindle and adjust the sensitivity of the spindle to stretch. Interneurons mediate connections within the spinal cord and help modulate motor output, while sensory neurons carry afferent information from the muscle to the CNS.