Muscle Flashcards
What are the components of a muscle from smallest to largest?
myofilaments -> myofibrils -> muscle fiber (cell) -> fascicle -> whole muscle
What is the function of tropomyosin?
To block the binding sites on actin when the muscle is resting
Which protein makes up thick filaments?
myosin
What are 3 parts of myosin?
Actin binding side, hinge region, ATPase binding site
What is elastic filament made of?
titin (connectin)
What is the purpose of elastic filament?
it holds the thick filament in position and helps to prevent sarcomeres from pulling apart when they shorten during contraction
Where do sarcomeres begin and end?
from Z disc to Z disc
What covers the active site of each globular actin protein?
tropomyosin
How do calcium ions activate myosin?
Calcium ions activate myosin by binding to troponin.
What are the 4 steps of muscle contraction, in order?
- cross bridge formation
- the power stroke
- cross bridge detachment
- resetting the system
What are 4 functional properties of muscle tissue?
- Excitability
- Contractility
- Extensibility
- Elasticity
What is the cause of atrophy?
prolonged inactivity due to bed rest, casting or local nerve damage
What is the cause of muscle cramps?
- circulatory impairment
- heat disorders which lead to electrolyte disorders
- diuretic intake
- unknown causes
What is the cause of muscular dystrophy?
- X linked recessive disorder in 1/2 of all cases
- defective gene for dystrophin causing dystrophin to be absent or abnormal
What is the cause of myasthenia gravis?
- defective transmission at the neuromuscular junction due to a reduction in the number of Ach receptors
What are the characteristics of myasthenia gravis?
fatigue, chronic respiratory infections, and muscle weakness
What are the characteristics of muscle cramps?
sustained involuntary contractions of a skeletal muscle
What are the characteristics of muscular dystrophy?
- a reduction in the number of muscle fibers and necrosis and replacement with endomysial CT and fat
- delayed sitting/walking/standing
- progressive weakness in the shoulder and pelvic girdles
What are the characteristics of disuse atrophy?
shortening of muscle fibers and decrease in muscle mass/size
What factors influence muscle contractile force?
- The rate (frequency) of stimulation,
- The number of motor units recruited
- The starting length of the sarcomere (degree of stretch)
What factors influence muscle contractile velocity?
- the load
- muscle fiber type
- the number of motor units contracting
The most common lever systems in the body are those that have the applied force between the fulcrum and the resistance. These are called __________ levers.
Third-class
Most skeletal muscles of the body act as _______-class lever systems.
third-class
Where is the fulcrum located in first-class levers?
mid-way inbetween the force and the load
In the body, _______ are the levers, _______ are the fulcrums, and _________________ exert the effort at their insertions.
bones, joints, skeletal muscles
muscles that help maintain upright posture are ___________.
fixators
The muscles of which functional group has the major responsibility for producing a specific movement?
prime mover (or agonist)
There is a mechanical advantage when a the force is _______ from the fulcrum than the load is.
What is the type of lever called?
farther
a power level
There is a mechanical DISadvantage when a the force is _______ to the fulcrum than the load is.
What is the type of lever called?
closer
a speed lever
In a ________-class lever, the effort is applied at one end of the lever and the load is at the other, with the fulcrum somewhere between.
What tool is an example of this lever?
What is one example in the body?
first
scissors
head & neck (weight of the head is the load, neck is the fulcrum)
In a ________-class lever, the effort is applied at one end of the lever and the fulcrum is located at the other, with the load between them
What tool is an example of this lever?
What is one example in the body?
second
wheelbarrow
standing on your toes
_____-class levers are uncommon in the body.
second
All ______-class levers in the body work at a mechanical advantage because the muscle insertion is always farther from the fulcrum than is the load
second
In this type of lever, the effort is applied between the load and the fulcrum. It is at a mechanical disadvantage and is ideal for fast, large movements.
third-class lever
Most skeletal muscles of the body act as ______-class levers.
third
If the muscle generates tension but does not shorted or lengthen and the resistance (load) is greater than the tension, what type of contraction is it?
isometric
If the muscle changes length and moves a load, and the tension generated by the muscle exceeds resistance, what type of contraction is it?
isotonic
multiple motor unit summation uses __________
recruitment
What are the four functions of muscles?
- move internal and external body parts
- maintain posture
- stabilize joints
- generate heat
The average number of muscle fibers per motor unit is ___
150
What do we call it when a second stimulus is applied to a muscle before it finishes relaxing?
wave summation
What do we call prolonged, smooth contraction that results from very rapid stimulation?
complete tetanus
What are three things that would increase the strength (tension) of a contraction?
- Increase the rate (frequency) of stimulation
- Increase the strength of the stimulus
- starting length of the sarcomere
The force of muscle contraction is affected by:
- the number and size of contracting muscle cells (the more and the larger the cells, the greater the force)
- the frequency of stimulation
- the degree of muscle stretch.
Factors determining the velocity and duration of muscle contraction are:
- muscle fiber types
- the load (the greater the load, the slower the contraction)
- how many motor units are recruited.
What are the three main functions of ATP during contraction?
- fuels the power stroke: moves the cross bridges from low energy to high energy positions
- detach cross bridges after the power stroke: new ATP binds to cross bridges, allowing them to break free from the actin filaments
- sarcomere relaxation: used to pump calcium back into the sarcoplasmic reticulum
What are the three types of muscle fibers?
- fast glycolytic (fatigable)
- slow oxidative (fatigue-resistant)
- fast oxidative (fatigue-resistant)
Which metabolism pathway takes place in the mitochondria?
aerobic
What is the energy source of direct phosphorylation metabolism?
Creatine phosphate
What are the end products of the anaerobic metabolic pathway?
2 ATP (per glucose) + lactic acic
Which metabolic pathways use glucose?
anaerobic & aerobic
What are the end products of the aerobic pathway?
32 ATP (per glucose), water, carbon dioxide
Which metabolic pathway can produce up to 3 minutes of contraction?
anaerobic
How is smooth muscle contraction different from skeletal muscle contraction?
- calveloi: action potentials cause calveoli (bubbles in the membrane) to open/allow calcium into smooth muscle cells
- calmodulin: calcium binds to calmodulin after entering smooth muscle cells
-myosin light chain kinase: calcium-calmodulin activates this enzyme in smooth muscle which helps create cross bridges
How does smooth muscle cell structure differs from skeletal muscle cell structure?
In smooth muscle:
- Thick and thin filaments are arranged diagonally
- an intermediate filament-dense body network exists to reduce tension (dense bodies correspond to Z discs)
- Thick filaments are fewer, but have myosin heads along their entire length
- NO TROPONIN
True or False: both skeletal and smooth muscle has SR (Sarcoplasmic Reticulum)
True
What specific action initiates an action potential in a sarcolemma?
Ach (acetylcholine) diffuses across the synaptic cleft and binds to Ach receptors on the motor end plate of the muscle cell
What explains the decreased contractile force generated by a stretched muscle?
Stretching of myofibrils within the muscle fibers decreases the overlap between thin and thick myofilaments.
Which occurs during the recovery period following strenuous exercise?
Glycogen is formed from glucose (replenishing glycogen reserves that were used as fuel during prolonged muscle activity)
