Week 4 Review Flashcards
distinguish between exercise and physical activity
- PA = any movement of the body that requires energy expenditure
- Exercise = planned, structures, repetitive, purposeful PA
How does bed rest affect muscle mass? Does this change reflect an adaptation to the stress of activity?
- every time we sleep at night, our bodies begin to detrain (atrophy)
- reflects an adaptation (or de-adaptation) to the decreased level of stress being placed on the muscle
List 6 functions of muscle and associate a type of muscle with that function
- produces body movement (skeletal muscle)
- helps maintain posture (skeletal muscle)
- powers respiration (skeletal muscle)
- produces body heat (skeletal muscle; shivering)
- communicates w other organs/organ systems (smooth muscle)
- regulates diameter of hollow organs and blood vessels (smooth muscle)
What are the 4 general properties of muscle?
- contractility
- excitability
- extensibility
- elasticity
What is contractility and how does it relate to PT?
- ability of a muscle to shorten or attempt to shorten; expending energy and generating force in the process
- strength exercises
what is excitability and how does it relate to PT?
- capacity of a muscle to respond to a stimulus
- skeletal muscle is excitable
- e-stim
what is extensibility and how does it relate to PT?
- ability to go from shortened muscle length to longer muscle length
- ROM
- rubber bands can only stretch to certain limits
- muscles work the same way.. they can shorten/lengthen within a certain range
- reduced ROM can reduce function
what is elasticity and how does it relate to PT?
- ability of a muscle to recoil to its original resting length after being stretched
- stretching
Identify essential differences between skeletal muscle and cardiac muscle
- cardiac muscle = involuntary
- skeletal muscle = voluntary
how is the skeletal muscle in the brachialis different from the cardiac muscle in the heart?
- when your heart beats, every cardiac muscle cell (myocyte) contracts
- when you flex your elbow, not every skeletal muscle cell in the brachialis contracts
- you don’t have control over your heartbeat, but you do have control over your brachialis
Identify essential differences between smooth muscle and striated muscle
- smooth muscle: in organs, involuntary, single nucleus, low power output, fatigue resistant, low energy consumption; no sarcomeres
- striated muscle: in skeletal muscle or cardiac muscle, involuntary or voluntary, contains sarcomeres
muscle contraction
- when a muscle shortens or attempts to shorten
- actin and myosin moving past each other
tension
stretch on muscle when contracting or relaxed
resistance
force opposing the force of the muscle
force
measurable activation needed to overcome opposing resistance
isotonic contraction
- muscle contraction in which the muscle changes length under a constant load
- broad category including concentric and eccentric
concentric contraction
- muscle shortens while contracting
- force generated > opposing force/resistance
Provide an example in daily life where one might make use of concentric contractions
biceps curl
eccentric contraction
- muscle lengthens while contracting
- force generated < opposing force/resistance
Provide an example in daily life where one might make use of eccentric contractions
- plyometrics
- walking down stairs = quads contract to keep your rear end from striking your heels
isometric contraction
- muscle length does not change while actively contracting
- force generated = the resistance
Provide an example in daily life where one might make use of isometric contractions
weightlifter attempting to deadlift too much weight - his biceps are contracting but cannot overcome the opposing force
isokinetic contraction
muscle shortens at constant speed
Provide an example in daily life where one might make use of isokinetic contractions
isokinetic machine → creates different levels of resistance; movements are at a constant speed, no matter how much force is applied
What is the function of satellite cells?
- sits on the outside of a muscle cell and is called into play when a muscle is injured (regrows/replaces the damaged muscle cell)
- lie adjacent to sarcolemma
- Clinician: you will try to activate them as a clinician to try to repair the muscle
define a sarcomere
- basic contractile unit of muscle fiber; the z-lines define the lateral borders of the sarcomere
- sarcomere will span from one z-line to the next
Describe the connective tissue anatomy of a striated muscle (biceps) and explain how it is involved in joint movement
- sarcolemma = plasma membranes of muscle cells
- muscle cells are multinucleated; have many of the same organelles found in other cells
- Endomysium surrounds fibers
- Perimysium surrounds muscle fascicles
- Epimysium surrounds fascicle bundles
What is so unique about the 3 layers of connective tissue in striated muscle?
- this connective tissue matrix allows contraction to be transmitted to the whole muscle
- how we get joint movement
How does building scaffolding relate to the anatomy of striated muscle?
- Epimysium pulls on perimysium, which pulls on endomysium as muscle contracts
- if you pull on one layer, you’re going to pull on the other layers too
What happens when the connective tissue layers are compromised?
- Extensibility becomes compromised
- Connective tissue repairs very slowly. If it is not repaired correctly, it can impact movement and limit functionality.
- Depending on how injured an athlete gets, they may not heal all the way to return to the athletic level they had before injury.
What is a muscle fascicle?
- Bundle of fibers wrapped in perimysium
- Like a bundle of firewood
Describe anatomic changes in a skeletal muscle that might develop into a contracture
Rigid muscles fixed and at a particular length, there is a lack of extensibility
Which sarcomeric band keeps the same length or width during an isotonic muscle contraction?
- A band
- thick filaments (myosin)
- dark part of striations
The length of which sarcomeric zone shortens during an isotonic muscle contraction?
- I band move closer together -H zone shortens in width
* thin filaments moves and crawls on the A Band*
Describe the myotendinous junction (MTJ)
- bridging structure between muscle and tendon
- when a skeletal muscle cell shortens/attempts to shorten, it pulls on the MTJ which in turn is pulling on the tendon
True or false: the myotendinous junction is a weak point
- true
- if the tendon cannot match the strength of the muscle cell, there’s a tendency for the muscle cells to be pulled away from the tendon, causing injury
- MTJ can adapt to greater force, particularly with resistance training
What is a costamere?
- component of striated muscle cells that connects sarcomere to cell membrane
- forces are transmitted laterally through the costamere within the cytoskeleton of the fiber into the ECM and neighboring skeletal muscle
force production by muscle is not just transmitted ____ but also ____ thanks to the costamere
longitudinally; laterally
What happens to the sarcomere during an eccentric contraction?
lengthens
What happens to the A band during an eccentric contraction?
stays the same length
What happens to the I band during an eccentric contraction?
widens
What happens to the H zone during an eccentric contraction?
widens
Is there force production with an eccentric contraction?
- Force production declines; is predicated in part by the amount of overlap between the thick and thin filaments
- If there is little overlap, fewer cross bridges link the thick and thin filaments
What happens when a muscle is supracontracted?
- there is too much overlap b/w thick and thin filaments
- m-line disappears due to the overlapping of the thin filaments
- force production will also decline at this point (Atrial de-fibrillation device)
What happens to the amount of overlap between the thick and thin filaments during an eccentric contraction?
- amount of overlap decreases
- z lines move further apart
- thin filaments move away
- fewer opportunities for cross bridges to form b/w thin and thick filaments
What happens to the amount of overlap between the thick and thin filaments during an isometric contraction?
nothing, stays the same
What happens to the amount of overlap between the thick and thin filaments during hyperextension?
even less overlap than normal
What happens to the amount of overlap between the thick and thin filaments during a supra-maximal skeletal muscle contraction?
- z lines move closer together
- thin and thick filaments overlap
- thin filament move towards center and M line ultimately disappears
- thin filaments overlap to where no more optimal contraction can occur
- outermost thin filament cannot form cross bridge, so force production goes down
What is the role of troponin in muscle contraction?
Covers up binding site for myosin head when muscle is relaxed
What role(s) does Ca+ play in striated muscle contraction?
- Binds to troponin and reveals the myosin binding sites
- once muscle relaxes, Ca unbinds from Troponin, which blocks the active sites again (ex: Rigor Mortis)
In skeletal muscle, the source of the Ca+ that drives contraction is found in what organelle?
sarcoplasmic reticulum
What roles does ATP play in muscle contraction?
- ) Ca 2+ binds to the troponin C, active site revealed, cross bridge forms b/w myosin and actin
- ) The myosin head serves as a myosin ATPase enzyme, splitting ATP into ADP & Pi
- ) Pi & ADP released and the cross bridge is flexed
- ) Release of Pi introduces a powerstroke that pulls the thin filament (z-disks move toward the center)
- ) After the powerstroke the myosin head straightens out and binds a new ATP molecule which is then split into ADP & Pi
- ) Ca2+ is actively removed from cytoplasm
- ) The action is repeated tens of thousands of times
Why is the use of a tug-of-war match a poor analogy for sarcomeric shortening?
- There is only muscle action in one direction; no counter force being produced by actin; myosin binds and pulls the actin inward on the sarcomere
- Sk. Musc. move the z-discs together
- Muscle contraction brings the z-discs closer together
- When ATP binds there is flexion in cross-bridge; if there is one cross-bridge on one side, it pulls the z-line in one direction (towards the midline) and the other side pulls it in the opposite direction, pulling the Z-line together
