Table of Contents
- 1 How does a motor unit related to muscle contraction?
- 2 What determines the strength of a contraction?
- 3 How motor unit composition and innervation affects the strength of muscle contractions?
- 4 What is a motor unit and how does recruitment work to increase strength?
- 5 What regulates the strength of muscle contraction?
- 6 How do motor units improve recruitment?
- 7 What makes up the motor unit of the skeletal muscle?
- 8 How much tension does the gastrocnemius muscle produce?
When a motor unit is activated, all of its fibers contract. In vertebrates, the force of a muscle contraction is controlled by the number of activated motor units. Muscles which possess more motor units (and thus have greater individual motor neuron innervation) are able to control force output more finely.
What is a motor unit and how motor units are related to strength?
Motor units measure the number of motor neurons that are activated in a muscle for a task. A higher amount of motor neurons are needed for stronger muscle contractions, while fewer are required for less effort.
What determines the strength of a contraction?
A motor unit is a motor neuron and all of the muscle cells (muscle fibers) it stimulates. The strength of a muscle contraction is determined by the size and number of motor units being stimulated.
What is the relationship between the strength of the muscle contraction and the number of motor units which are stimulated?
QR1: Contraction of Motor Units
| Question | Answer |
|---|---|
| 3. When a motor neuron fires, how many muscle fibers are stimulated (give a range)? | 5-1000 |
| 4. What is the relationship between the strength of a muscle contraction and the number of motor units which are stimulated? | more motor units means more strength |
How motor unit composition and innervation affects the strength of muscle contractions?
A motor unit consists of one motor neuron and all of the muscle fibers it stimulates. The activation of one motor neuron will result in a weak but distributed muscle contraction. The activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction.
What is a motor unit and what is its role in muscle contraction?
A motor unit, the functional unit of muscle contraction, is a single motor nerve and the associated muscle fibers that are innervated upon stimulation from the nerve. A collection of motor units is referred to as a motor pool.
What is a motor unit and how does recruitment work to increase strength?
Motor unit recruitment may be defined as “the successive activation of the same and additional motor units with increasing strength of voluntary muscle contraction.” Increasing the firing rate (firing frequency) at which individual motor units fire to optimize the summated tension generated (ie, temporal recruitment)
What is a motor unit and motor unit recruitment describe the effect of the size of the motor unit on its strength of its contraction?
Starting with the smallest motor units, progressively larger units are recruited with increasing strength of muscle contraction. The result is an orderly addition of sequentially larger and stronger motor units resulting in a smooth increase in muscle strength.
What regulates the strength of muscle contraction?
Vertebrate striated muscle contraction is controlled (regulated) by the action of the proteins troponin and tropomyosin on the actin filaments. Nervous stimulation causes a depolarisation of the muscle membrane (sarcolemma) which triggers the release of calcium ions from the sarcoplasmic reticulum.
How does a motor unit help us to control the force generated in a muscle?
A motor neuron controls the amount of force that is exerted by muscle fibers. Motor neurons use a rate code to signal the amount of force to be exerted by a muscle. An increase in the rate of action potentials fired by the motor neuron causes an increase in the amount of force that the motor unit generates.
How do motor units improve recruitment?
Answer
- Increasing the number of active motor units (ie, spatial recruitment)
- Increasing the firing rate (firing frequency) at which individual motor units fire to optimize the summated tension generated (ie, temporal recruitment)
How does the number of motor units affect muscle contraction?
The strength of the resultant whole muscular contraction depends upon the number of motor units recruited. Another way of increasing the strength of a muscle contraction is by decreasing the time between impulses so that the muscle fibres do not have time to relax, resulting in a continuous wave of contractions known as wave summation.
What makes up the motor unit of the skeletal muscle?
The motor unit consists of a motor neuron and the group of skeletal muscle fibers which it innervates. An entire muscle may be composed of thousands of such units representing millions of individual muscle fibers A single skeletal muscle is composed of many thousands to millions of long, narrow contractile cells called muscle fibers (Fig-1).
How does the law of all or none apply to motor units?
The ‘all or none’ law as mentioned above also applies to the contraction of fibres within a motor unit. When a motor unit activates, all of the fibres within the unit contract and at full force, there is no strong or weak contraction. The strength of the resultant whole muscular contraction depends upon the number of motor units recruited.
How much tension does the gastrocnemius muscle produce?
As might be expected from the relatively large motor units found in the gastrocnemius muscle, the average tension per unit is higher (35 g per unit) with its largest units producing up to 120 g.