Muscle tone and motor unit
Describe (not just define!) the functional unit called a motor unit. Explain the relationship between motor unit size in finely vs. coarsely controlled muscles. Explain how motor units act to establish muscle tone. What are the functions of muscle tone?
Motor Unit- One motor neuron and all the muscles it innervates. Each muscle will respond to one motor nerve which contains axons that can have up to 100’s of neurons that branch into terminals that form NMJ with ONE fiber. When a motor neuron sends an action potential, it will cause all of the connected muscle fibers to contract.
The number of muscle fibers per motor unit varies from thousands to only a few, and the size varies based on the type of control that muscle has. Muscles that exert fine control, such as the muscles controlling eye movement or fingers have small motor units because they have precise movements that require very rapid and brief twitches. On the other hand, bigger muscles such as the gastrocnemius in the calf contract slower and for a longer period because they bear more weight and are not as precise, have large motor units.
Muscle fibers are not clustered together in one spot, but are spread throughout the entire muscle. This is why when stimulated, the whole muscle contracts. Spinal reflects at rest cause one motor unit to activate, and then another does, which causes a slight tension in the whole muscle. This is so the muscle is ready to act and stays healthy. The more fit someone is, the more low levels of contracting they have, hence the more muscle tone they have. Muscle tone helps stabilize joints and maintain posture because the temperature of the muscle fibers is higher. It also keeps the myofilaments at an optimal length. Even in a relaxed state, the motor unit contractions provide a constant low-level tension and resistance, which aids in muscle tone. Without this constant stimulation, there would be much less tone because the muscle would be flaccid. The spinal cord
Motor Unit- One motor neuron and all the muscles it innervates. Each muscle will respond to one motor nerve which contains axons that can have up to 100’s of neurons that branch into terminals that form NMJ with ONE fiber. When a motor neuron sends an action potential, it will cause all of the connected muscle fibers to contract.
The number of muscle fibers per motor unit varies from thousands to only a few, and the size varies based on the type of control that muscle has. Muscles that exert fine control, such as the muscles controlling eye movement or fingers have small motor units because they have precise movements that require very rapid and brief twitches. On the other hand, bigger muscles such as the gastrocnemius in the calf contract slower and for a longer period because they bear more weight and are not as precise, have large motor units.
Muscle fibers are not clustered together in one spot, but are spread throughout the entire muscle. This is why when stimulated, the whole muscle contracts. Spinal reflects at rest cause one motor unit to activate, and then another does, which causes a slight tension in the whole muscle. This is so the muscle is ready to act and stays healthy. The more fit someone is, the more low levels of contracting they have, hence the more muscle tone they have. Muscle tone helps stabilize joints and maintain posture because the temperature of the muscle fibers is higher. It also keeps the myofilaments at an optimal length. Even in a relaxed state, the motor unit contractions provide a constant low-level tension and resistance, which aids in muscle tone. Without this constant stimulation, there would be much less tone because the muscle would be flaccid. The spinal cord