38 Questions
What is the definition of a motor unit?
A motor neuron and all the muscle cells that it innervates
What happens when a muscle group contracts?
Thousands of individual muscle cells, called fibers, contract
What is the term for the process of activating more motor units to lead to the contraction of more muscle fibers?
Recruitment
Why does resistance training increase the strength of a muscle?
It increases the diameter of individual muscle fibers by packing in more actin and myosin filaments
What is a common effect of aging on muscle?
A decrease in muscle fibers
What is the basis of electromyography?
The detection of changes in voltage produced by action potentials occurring in underlying skeletal muscle contraction
What is the term for the recording obtained through electromyography?
Electromyogram
What is the effect of recruiting more motor units on muscle contraction?
It leads to the contraction of more muscle fibers
What determines the number of motor units activated?
The amount of work required
What is the direct proportionality of the strength of the electrical signal?
Number of motor units firing
What is the term for the decline in ability of the muscle to maintain force despite stimulation?
Fatigue
What is the result of aerobic activities and endurance training on muscle composition?
Increase in mitochondria and myoglobin molecules
What is the term for the recording obtained through the detection of changes in skin voltage produced by action potentials?
Electromyogram (EMG)
What determines the strength of contraction in a muscle?
Number of motor units activated
What is the term for the small amounts of muscle contractions to maintain postural tone?
Muscle tonus
What is the relationship between the amplitude of the EMG and the force of contraction?
The amplitude of the EMG is directly proportional to the force of contraction
What is the term for the activation of additional motor units if a greater contraction strength is needed?
Recruitment
What type of muscle fibers are most resistant to fatigue?
Slow-oxidative fibers
What is the term for a somatic motor neuron plus all of the muscle fibers it controls?
Motor unit
The number of motor units activated is inversely proportional to the amount of work required.
False
Skeletal muscle contracts when the heart activates motor units.
False
The maximum clench force is the same among all individuals.
False
Electromyography measures the changes in voltage produced by action potentials in smooth muscle.
False
As we age, muscle fibers tend to increase in number.
False
The arrangement of cells within a muscle is such that it is not possible to recruit more muscle fibers by activating more motor units.
False
The electrical signals from individual muscle fibers are large enough to be measured by electrodes placed on the surface of the skin.
False
Most skeletal muscle is composed of only a few motor units.
False
Resistance training always results in a decrease in muscle strength.
False
The strength of the electrical signal is directly proportional to the number of muscle fibers firing.
False
Muscle fatigue is a permanent condition.
False
Aerobic activities and endurance training can decrease the number of mitochondria in muscle fibers.
False
The amplitude of the EMG is inversely proportional to the force of contraction.
False
Muscle tonus is the same as muscle fatigue.
False
The proportion of slow-oxidative fibers in a muscle determines its endurance.
True
Electromyography is the term for the process of activating more motor units to lead to the contraction of more muscle fibers.
False
Recruitment is the process of deactivating motor units to reduce muscle contraction strength.
False
The strength of contraction depends on the type of muscle fibers contributing to the force of contraction.
False
Angiogenesis in active muscles can decrease blood flow to the muscle.
False
Study Notes
Skeletal Muscle Contraction
- Skeletal muscle contraction occurs when the brain or spinal cord activates motor units, consisting of a motor neuron and the muscle cells it innervates.
- A muscle group contraction involves thousands of individual muscle cells, called fibers, contracting.
- Most skeletal muscle is composed of hundreds of motor units.
Motor Unit Recruitment
- The number of motor units activated is proportional to the amount of work required.
- Activating more motor units leads to the contraction of more muscle fibers, known as recruitment.
- Recruitment allows for increased muscle force by activating more motor units.
Muscle Fiber Characteristics
- Individual muscle fibers can increase in diameter through resistance training, allowing for more powerful contractions.
- Muscle fibers are lost with age, resulting in a decline in strength.
Electromyography (EMG)
- EMG measures the electrical signals generated by muscle contractions, with the strength of the signal directly proportional to the number of motor units firing.
- EMG recordings are measured in millivolts (mV).
Muscle Fatigue
- Muscle fatigue occurs when muscle cells are no longer able to sustain the force of contraction.
- The rate of muscle fatigue depends on the proportion of slow-oxidative, fast-oxidative, and fast-glycolytic fibers within a given muscle.
Muscle Adaptation
- Aerobic activities and endurance training can change the composition of muscle fibers, increasing blood flow and ATP production.
- This adaptation leads to increased muscle endurance and strength.
Key Terminology
- Electromyogram (EMG): recording of muscle contraction electrical signals.
- Motor unit: a somatic motor neuron and the muscle fibers it controls.
- Graded contraction: variable strength in muscle contraction.
- Recruitment: activation of additional motor units for increased contraction strength.
- Fatigue: decline in muscle force despite stimulation.
- Muscle tonus: small amounts of muscle contractions to maintain postural tone.
Skeletal Muscle Contraction
- Skeletal muscle contraction occurs when the brain or spinal cord activates motor units, consisting of a motor neuron and the muscle cells it innervates.
- A muscle group contraction involves thousands of individual muscle cells, called fibers, contracting.
- Most skeletal muscle is composed of hundreds of motor units.
Motor Unit Recruitment
- The number of motor units activated is proportional to the amount of work required.
- Activating more motor units leads to the contraction of more muscle fibers, known as recruitment.
- Recruitment allows for increased muscle force by activating more motor units.
Muscle Fiber Characteristics
- Individual muscle fibers can increase in diameter through resistance training, allowing for more powerful contractions.
- Muscle fibers are lost with age, resulting in a decline in strength.
Electromyography (EMG)
- EMG measures the electrical signals generated by muscle contractions, with the strength of the signal directly proportional to the number of motor units firing.
- EMG recordings are measured in millivolts (mV).
Muscle Fatigue
- Muscle fatigue occurs when muscle cells are no longer able to sustain the force of contraction.
- The rate of muscle fatigue depends on the proportion of slow-oxidative, fast-oxidative, and fast-glycolytic fibers within a given muscle.
Muscle Adaptation
- Aerobic activities and endurance training can change the composition of muscle fibers, increasing blood flow and ATP production.
- This adaptation leads to increased muscle endurance and strength.
Key Terminology
- Electromyogram (EMG): recording of muscle contraction electrical signals.
- Motor unit: a somatic motor neuron and the muscle fibers it controls.
- Graded contraction: variable strength in muscle contraction.
- Recruitment: activation of additional motor units for increased contraction strength.
- Fatigue: decline in muscle force despite stimulation.
- Muscle tonus: small amounts of muscle contractions to maintain postural tone.
Learn about the contraction of skeletal muscles, motor units, and how the brain and spinal cord activate them. Discover how muscle fibers work together to achieve movement.
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