WEEK 7 (Skeletal muscle mechanics) Flashcards
Describe the role of connective tissue in fibers
- Each muscle is sheathed by connective tissue that penetrates from the surface into the muscle to ENVELOP each individual fiber and divide the muscle into BUNDLES
- connective tissue extends beyond the ends of the muscle to form TOUGH, COLLAGENOUS TENDONS that attach the muscle to bones
Sarcomeres are not attached to bone, what is instead?
Tendons
Tension generated by these contractile elements must be transmitted to the bone via tendon before the bone can be moved
What is another name for tendons?
Series-elastic component
A _______ is typically attached to at least two bones across a joint by means of tendons that extend from each end of the muscle
muscle
Define the ‘Origin’ and ‘Insertion’
Origin is the end of the muscle attached to the more stationary part of the skeleton
Insertion is the end attached to the skeletal part that moves
Since muscle contraction can only pull and not push bone, what happens?
Two different antagonistic muscles or muscle groups are situated to pull on opposite sides of the joint
What are the differences between Isotonic contraction, Isokinetic contraction & Isometric contraction?
Isotonic contraction = the load remains constant as the muscle changes length
Isokinetic contraction = the velocity of shortening remains constant as the muscle changes length
Isometric contraction = the muscle is prevented from shortening so tension develops at constant muscle length
What are the stages of muscle contraction?
1) Muscle excitation turns on the tension-generating contractile process
2) Cross bridges start cycling
3) Filament sliding shortens the sarcomeres which stretches the series-elastic components to exert forces on the bones at the sites of the muscle’s origin and insertion
What happens in Isotonic contraction?
- weight of object does not change as it is lifted
- the angle of the joint changes while the object is being lifted so MUSCLE TENSION must change to counterbalance the load. Thus, muscle tension does not remain constant throughout the period of shortening
- CONCENTRIC: muscle length SHORTENS during contraction
- ECCENTRIC: muscle length INCREASES during contraction
What happens in Isokinetic contraction?
- occur when muscle fibers shorten at a constant velocity or speed
- angular speed is constant during contraction
- more rapid development of muscle strength
What happens in Isometric contraction?
- no change in muscle length
- takes place when the tension developed in the muscle is less than needed to move the load
What is the difference between concentric and eccentric contractions?
CONCENTRIC CONTRACTIONS = muscle shortens
ECCENTRIC CONTRACTIONS = muscle lengthens
What are Sphincters?
- muscles not attached to bone at all and prevent movement
- voluntarily controlled rings of skeletal muscle that when contracted, close an opening which guides movement of material through the opening
Describe the load-velocity relationship for concentric contractions
The speed of shortening is maximal when there is no external load, and falls to zero when the load cannot be overcome by maximal tension. Load and velocity for shortening are INVERSELY related for concentric contractions.
How is the relationship between load and shortening velocity a fundamental property of muscle?
Since the power stroke slows when the myosin head tilts against a greater load
Describe the load-velocity relationship for eccentric contractions
Load and velocity for lengthening are DIRECTLY related for eccentric contractions. An external force (load) greater than a muscle’s maximal contraction force causes the muscle to lengthen, with the velocity of lengthening being directly dependent on the load.
Define Work and Force
Work is force multiplied by distance
Force is the muscle tension required to overcome the load
Most skeletal muscles are attached to bones across joints, forming lever systems. What is a lever?
A lever is a rigid structure capable of moving around a pivot point known as a FULCRUM
What is the Power arm?
The portion of a lever between the fulcrum and the point where a force is applied by the muscle
What is the Load arm?
The portion between the fulcrum and the force exerted by a load
What are the two primary factors that can be adjusted to accomplish gradation of whole muscle tension?
- number of muscle fibers contracting within a muscle
- tension developed by each contracting fiber
A single action potential in a muscle fiber produces a brief, weak contraction called a __________
twitch
Why can larger muscles consisting of more muscle fibers generate more tension than smaller muscles with fewer fibers?
Since the greater the number of fibers contracting, the greater the total muscle tension.
What are the properties of motor neurons & muscle fibers?
- One motor neuron innervates a number of muscle fibers but each muscle fiber is supplied by only one motor neuron
- Muscle fibers that compose a motor unit are dispersed throughout the whole muscle so their simultaneous contraction results in an evenly distributed, although weak, contraction of the whole muscle
What is a motor unit?
One motor neuron plus all the muscle fibers it innervates
What is motor unit recruitment?
For stronger and stronger contractions, more and more motor units are recruited, or stimulated to contract simultaneously
What can influence the extent to which tension can be developed?
- Frequency of stimulation
- Length of the fiber at the onset of contraction
- Extent of fatigue
- Thickness of the fiber
What is Twitch summation?
A process when two twitches from two action potentials add together, or sum, to produce greater tension in the fiber than that produce by a single action potential
What is Tetanus?
Produced when the muscle fiber is stimulated so rapidly that it does not have a chance to relax at all between stimuli. It is a smooth, sustained contraction of maximal strength.
