the stimulus for muscle contraction normally originates in the brain.
the stimulus for muscle contraction normally originates in the brain.
where does the stimulus for muscle contraction normally originate in the body?
the brain
a gamma motor neuron (γ motor neuron), also called gamma motoneuron, is a type of lower motor neuron that takes part in the process of muscle contraction, and represents about 30% of (aγ) fibers going to the muscle. like alpha motor neurons, their cell bodies are located in the anterior grey column of the spinal cord. they receive input from the reticular formation of the pons in the brainstem. their axons are smaller than those of the alpha motor neurons, with a diameter of only 5 μm. unlike the alpha motor neurons, gamma motor neurons do not directly adjust the lengthening or shortening of muscles. however, their role is important in keeping muscle spindles taut, thereby allowing the continued firing of alpha neurons, leading to muscle contraction. these neurons also play a role in adjusting the sensitivity of muscle spindles.
gamma motor neuron
the muscle contraction of a ballistic muscle movement can exhibit a muscle coactivation of concurrent agonist and antagonist muscles or the characteristic triphasic agonist/antagonist/agonist muscle activation. electromyography (emg) recordings of demonstrate the triphasic muscle activation begins with a brief agonist motor unit activation signal with firing rates of 60 to 120 hz that may last for 100ms and occurs 50 to 100ms before movement begins. the firing rates of ballistic movements are much higher than that of slow ramp movements (5–15 hz). the brief agonist muscle contraction is thus followed by antagonist muscle unit activation. the degree of antagonist muscle unit activation is dependent on the task at hand unlike the first agonist muscle activation which is independent to environmental stimuli. the function of the antagonist muscle contraction is believed to control the amplitude and timing of ballistic movements. antagonist muscle contraction may serve to prevent injury to joints by preventing the limb from overextending itself and also function to control the distance and time the limb is being moved. experiments involving ballistic movement of small amplitudes show a marked increase in antagonist muscle activation and experiments where distance moved is not controlled antagonist muscle activation was decreased or absent. the second agonist muscle activation is suggested to terminate the negative acceleration of the antagonist muscle contraction and thus the ballistic movement.
ballistic movement