Muscles Flashcards
What is a muscle fiber?
A single muscle cell enclosed in a cell membrane - the sarcolemma
What are the two types of skeletal muscle?
- Muscle tissue - contractile
2. Connective tissue - noncontractile
What type of the muscle fiber is the contractile structure?
Myofibrils
What are the two types of filaments and what proteins are associated with them?
- Thin - actin
2. Thick - myosin
Which protein contains tropomyosin and troponin?
Actin
Which protein has the heads?
Myosin
What happens during contraction in regards to the filaments?
The thick filament grabs onto the thin filaments
What band is associated with actin?
I band
What band is associated with thick filaments?
A band
What forms the borders of the sarcomere?
Z discs
Describe cross-bridge interaction.
- Nerve impulses arrive at the motor end plate
- Evokes an electrical impulse - action potential
- Release of calcium ions
- Calcium ions attach to troponin and cause troponin to repositions the tropomyosin molecules
- Tropomyosin molecules are repositions and actin receptor sites become exposed for the heads of myosin to bind
What are the three types of muscle contraction?
- Isometric - no movement
- Concentric - shortening (sarcomere gets smaller)
- Eccentric - lengthening (sarcomere gets larger)
What force is winning in an eccentric contraction?
External force
What force is winning in a concentric contraction?
Muscle force
What is DOMS?
Delayed onset muscle soreness - mechanical strain in the muscle fiber and associated connective tissue (injury due to eccentric exercise)
What is reverse action?
The proximal segment moves and the distal segment is stationary (ex: chin up)
What are the two parts of a motor unit?
- Alpha motor neuron
2. Muscle fiber it innervates
Describe the characteristics of a large motor unit.
- Large axon
- Many fibers (primarily Type II)
- Recruited in forceful contractions
Describe the characteristics of a small motor unit.
- Small axon
- Fewer fibers (primarily Type I)
- Recruited first in most activities
What is the size principle of motor unit recruitment?
The small motor units are recruited first and as the force increase the larger motor units are recruited
What are some factors affecting active muscle tension?
- Number of muscle fibers - more muscle fibers –> greater muscle tension produced
- Diameter of axon - greater diameter –> more fibers can be recruited
- Number of motor units firing
- Frequency of motor units firing - quicker signals –> greater muscle tension produced
- Type of muscle fiber
What are the three types of muscle fibers?
- Type I - slow oxidative
- Type II - fast oxidative glycolytic
- Type IIX - fast glycolytic
Describe the characteristics of Type I fibers.
Small diameter, red color, dense blood flow, high myoglobin content, slow speed of contraction, and slow fatigue rate
Describe the characteristics of Type II fibers.
Medium diameter, red color, dense blood flow, medium myoglobin content, fast contraction, and medium fatigue rate
Describe the characteristics of Type IIX fibers.
Large diameter, white color, sparse blood flow, low myoglobin content, fast contraction, and fast fatigue rate
What are Type I fibers good for?
Stability and posture (ex: soleus)
What are Type II fibers good for?
Mobility or nonpostural activities
What are the three factors of muscle architecture?
Size, arrangement, and length
What is the relationship of the physiological cross-sectional area?
The amount of force is proportional to the number of sarcomeres aligned side by side
What is the pennation angle?
Angle that the muscles fiber goes into the fascia
What is the effect of the pennation angle during contraction?
The pennation angle increases during contraction
What are the four types of arrangements of fascicles?
- Fusiform
- Unipennate
- Bipennate
- Multipennate
What are fusiform muscles?
Fascicles are arranged in parallel to the muscle - not built for heavy contractions but rather a lot of movement (ex: SCM)
What are unipennate muscles?
Fibers go diagonal into the fascia - allow for a fair amount of movement but work together to produce more strength (ex: flexor pollucis longus)
What are bipennate muscles?
Fibers coming in from both sides of the fascia - more strength produced and a fair amount of movement (ex: biceps femoris)
What are three types of connective tissue?
Fascia, aponeuroses, and sheaths
What is the parallel elastic component of a muscle?
Connective tissue - passive elastic component
What is the series elastic component of a muscle?
Tendon
What are the two types of muscle tension?
Passive - tension developed in passive elastic component
Active - tension developed by contractile components
What does the sarcomere isometric length-tension relationship explain?
A muscle will have optimal force when the sarcomere is neutral (mid-position) - not too stretched or too contracted
What is active insufficiency?
A muscle that crosses one joint will have a decrease in torque when all joints are placed at end ROM (when the muscle is in the shortened position) - muscle will be the weakest
What is passive insufficiency?
When a multi-joint muscle is passively elongated to the point where it does not allow for full ROM - ROM is decreased
When is more force produced with concentric contractions?
When the movement is slow - allows more time to recruit more muscle fibers and more time for cross bridging to occur
When is more force produced with eccentric contractions?
When the movement is quicker
What are two types of strength testing?
Isokinetic - speed is constant - greater torque at slower speeds
Isotonic - force is constant
What is an agonist muscle?
Prime mover - muscle responsible for causing the movement
What is a synergist muscle?
Secondary mover - muscle that assists the prime mover - produces force to prevent unwanted movement
What is an antagonist muscle?
Performs the opposite movement of the agonist
What happens when the agonist and antagonist work together?
More stability
What is the GTO?
Golgi tendon organ - sensory receptor responsible for adjusting muscle tension
What are two types of sensory receptors?
- GTO
2. Muscle spindle
What is the function of the muscle spindle?
Relates to when the muscle gets stretched - stops sending messages
What is the function of the tendon reflex?
When you hit the tendon, the tendon stretches out causes the muscle to contract
What are two types of immobilization?
- Prolonged shortening - decrease in # of sarcomeres
2. Prolonged lengthening - increase in # of sarcomeres
What are some changes in muscle function?
Increased activity level –> hypertrophy
Decreased activity level –> atrophy
Age –> sarcopenia (loss of muscle mass)
What is the importance of the stretch-shortening cycle?
If you stretch a muscle or tendon before a concentric contraction you will have greater torque to produce more force
What is the relationship with eccentric contractions and the stretch-shortening cycle?
Peak concentric power doubles when you produce an eccentric phase first
What is muscle power and its relationship?
Work/time (more work in a shorter amount of time = more power)
What is muscle work?
Force x distance
What are the three ways in which muscle power can be increased?
- Increase work done per unit of time
- Decrease time to perform unit of work
- Both simultaneously
What are multipennate muscles?
Crosses only one joint - do not allow for a lot of movement (ex: soleus)
