When a greater number of motor units are present in a muscle and are able to be simultaneously stimulated causing an increase in muscle force (Sherwood, and Kell 271-272).
True
In skeletal muscle contraction, summation means increasing the number of stimuli that is delivered to a given motor unit per time. This increases the Calcium concentration, which causes more tension and shortening of the muscles.
Wave summation releases more calcium and increases the force of contraction by increasing the firing rate of motor neurons (The second contraction takes place before the first is completely at rest) so each stimulation adds up. This is all within ONE MUSCLE FIBER. Recruitment is the calling up multiple MOTOR UNITS, in order to increase the force of contraction. t has a size principle (those with small diameters, the more delicate ones are called first, then the larger and so on.) There is no added calcium ions as in wave summation. They usually occur together. wave summation can cause tetanus, while recruitment cannot.
Muscle recruitment
Asynchronous recruitment of motor units is used to prevent fatigue. While some motor units are active others are inactive. This pattern of firing of motor neurons prevents fatigue while maintaining contraction by allowing a brief rest for the inactive units.
The body regulates the strength of muscle contractions primarily through two mechanisms: motor unit recruitment and frequency of stimulation. Motor unit recruitment involves activating additional motor units to increase the force of contraction, allowing more muscle fibers to participate in the action. Additionally, the frequency of stimulation refers to the rate at which nerve impulses are sent to the muscle fibers; higher frequencies can lead to greater tension through a process called summation, where successive contractions build on each other.
recruitment
Muscle recruitment refers to the process by which the nervous system activates motor units within a muscle to generate force. When a muscle is needed for movement, the brain sends signals through motor neurons to activate these motor units, which consist of a motor neuron and the muscle fibers it controls. The degree of recruitment can vary depending on the intensity of the activity; for example, more motor units are recruited for heavy lifting compared to light tasks. This process allows the body to efficiently manage energy and strength during various physical activities.
Recruitment affects the number of motor units activated in a muscle, while frequency of stimulation affects the force generated by those motor units. Increasing recruitment leads to more muscle fibers being recruited, increasing force production, while increasing frequency of stimulation produces stronger muscle contractions by increasing the rate at which motor units are activated.
There is no 'multi motor unit' to be different from a single motor unit!A single motor unit is all the muscle fibers controlled by a single motor neuron.Multiple motor unit summation is when a smooth and steady increase in muscle tension is produced by increasing the number of active single motor units.Notice that what's being described is not something having to do with a some non-existent thing called a 'multi motor unit', but rather is a summation of many active singlemotor units.
The all-or-none law of motor unit recruitment states that when a motor neuron fires, all the muscle fibers it innervates contract fully or not at all. This means that a motor unit will either activate completely or remain inactive, depending on the strength of the stimulus reaching the threshold. Consequently, the force of muscle contraction can be increased by recruiting additional motor units rather than varying the strength of contraction within a single unit. This mechanism ensures efficient and coordinated muscle movements.
The amount of motor units that is needed to lift 160 pounds will be greater that the number required when lifting 80 pounds. This is due to the nervous system reading the situation and determining the number of units required. The smaller the muscle, the more delicate the control can be.