Motor unit summation or spatial summation is the recruitment of additional motor units within a muscle to develop more force. Motor unit summation occurs until sufficient force is developed within the muscle to move a load. A maximum contraction is generated when all the motor units are activated within a muscle.
How are motor units involved in the process of spatial summation?
Motor units within a muscle are activated at slightly different times and not all together. By spreading out the contraction and relaxation, the muscle is able to sustain a continuous contraction over a period of time; not just a split second. This staggering of contractions within a muscle is called Spatial Summation.
What is the difference between multiple motor unit summation and wave summation?
Treppe is when the muscle comes to rest before contracting again, but each contraction is stronger than the last. Wave summation is rapid stimulation that does not have a full rest in between.
What are motor units?
A motor unit is defined as a single efferent neuron and all of the muscle fibers it controls. Each muscle contains multiple motor units.
What is multiple motor unit summation?
The combined effect of a number of motor units acting within a muscle at any given time.
Where does the motor unit fit into the nervous and muscular system?
A motor unit is made up of a motor neuron and all of the skeletal muscle fibers innervated by the neuron’s axon terminals. Groups of motor units often work together as a motor pool to coordinate the contractions of a single muscle. The concept was proposed by Charles Scott Sherrington.
What is temporal summation in muscle contraction?
wave summation = temporal summation – The physiological phenomenon in which the tension developed in a muscle fiber during a muscle twitch will be greater in a second twitch compared to a first twitch because the second stimulus was applied before the muscle had relaxed completely after the first twitch, despite the …
Why does summation occur in muscle?
At the molecular level, summation occurs because the second stimulus triggers the release of more Ca++ ions, which become available to activate additional sarcomeres while the muscle is still contracting from the first stimulus. Summation results in greater contraction of the motor unit.
What are the 3 phases of muscle contraction?
The contraction generated by a single action potential is called a muscle twitch. A single muscle twitch has three components. The latent period, or lag phase, the contraction phase, and the relaxation phase.
Why is there a latent period for muscle contraction?
The first phase is the latent period, during which the action potential is being propagated along the sarcolemma and Ca++ ions are released from the sarcoplasmic reticulum. This is the phase during which excitation and contraction are being coupled but contraction has yet to occur.
What is the smallest motor unit in the human body?
Because an action potential generated by a motor neuron normally brings to threshold all of the muscle fibers it contacts, a single α motor neuron and its associated muscle fibers together constitute the smallest unit of force that can be activated to produce movement.
What is the difference between a large and small motor unit?
A small motor unit is an arrangement where a single motor neuron supplies a small number of muscle fibers in a muscle. … A large motor unit is an arrangement where a single motor neuron supplies a large number of muscle fibers in a muscle.
How many motor units are in a muscle?
Each individual muscle fiber in a muscle is innervated by one, and only one, motor neuron (make sure you understand the difference between a muscle and a muscle fiber).
What is asynchronous recruitment of motor units?
Asynchronous recruitment. -When the nervous system modulates the firing rates of the motor so that different motor units take turns maintaining muscle tension. -The alteration of active motor units allows some of the motor units to rest between contractions and prevents fatigue.
How are motor units recruited?
As a general rule, motor units are recruited in order of their size. When the muscle is activated initially, the first motor units to fire are small in size and weak in the degree of tension they can generate.
What produces muscle tetanus?
A tetanic contraction (also called tetanized state, tetanus, or physiologic tetanus, the latter to differentiate from the disease called tetanus) is a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate.