Lecture 5 Skeletal Muscle 3 Flashcards
What are the different muscle fibre types?
.There are two types of skeletal muscle fibers, fast-twitch and slow-twitch
Describe and explain the force-length relationship for skeletal muscle.
.The force -length relationship indicates that muscles generate the greatest force when at their resting (ideal) length, and the least amount of force when shortened or stretched relative to the resting length.
Describe and explain the force-velocity relationship for skeletal muscle
.The force-velocity relationship in muscle relates the speed at which a muscle changes length with the force of this contraction and the resultant power output (force x velocity = power).
What are the two types of forces occurring at the same time during muscle contraction?
Insertional or muscle force
External load/force
If muscle force is smaller than load force, will the muscle lengthen or shorten?
It will increase in length
If the muscle force is equal to the load force what will happen to the muscle?
The muscle will not move and remain at constant length
What contraction occurs when a muscle increases in length
Eccentric contraction
What contraction occurs when a muscle stays the same length when activated
Isometric contraction
If the muscle force is greater to the load force what will happen to the muscle?
The muscle will shorten in length
What contraction occurs when a muscle shortens in length when activated
Concentric contraction
What happens if external load is more than myosin force?
Sarcomere lengthens away from the centre.
What happens if external load is less than myosin force?
Sarcomere shortens towards the centre
What happens if external load is equal to the myosin force?
Sarcomere remains at a constant length
Does the cross-bridge cycle still occur during an isometric contraction?
Yes, all 4 phases of the cycle proceed normally.
What are two other types of contractions that start with Iso
Isotonic and Isokinetic
How does summed myosin force vary with changes in thick and thin filament overlap?
Once all the myosin heads attach to their counter-part actin there is no more myosin heads to attach to actin and therefore a plateau occurs. Shortening any further will result in the currently attached myosin heads to be detached due to the other end of actin now pushing their way through to the other side which decreases the force admitted. It further decreases once the myosin filament is squished against the Z-discs.
What happens to force when it is rapidly increasing velocity during concentric contractions?
Force declines rapidly
Why would force decline rapidly with increased velocity during concentric contractions?
Some proportions of the myosin heads cannot detach in time and thus create a drag fore that opposes the muscle force.
Also, some myosin heads cannot attach in time, and thus do not contribute to the development of force.
The ability to produce force at high velocities is heavily influenced by what?
The enzymatic rate of myosin ATPase
The ability of a sarcomere to develop force is greater than expected during which contraction?
Eccentric contractions.
There are three types of Myosin isoforms that all start with MHC, what’s the full name of all three?
MHC-I (Slow)
MHC-IIA (Fast)
MHC-IIX (Fast)
What are different about the three myosin isoforms
The speed in which they attach to actin.
The number of Mitochondria in type MHC-IIX is
low
The number of Mitochondria in type MHC-I is
High
The resistance to fatigue in type MHC-IIX is
Low
What is the predominate energy system in type MHC-IIX?
Anaerobic
ATPase activity is at what rate in Type MHC-IIX?
Highest
Vmax (speed of shortening is at what rate in MHC-IIX?
Highest
How Efficient is MHC-IIX
Low
The number of Mitochondria in type MHC-IIA is
High/Moderate
The resistance to fatigue in type MHC-IIA is
High/Moderate
What is the predominate energy system in type MHC-IIA?
Combination of Anaerobic and Aerobic
ATPase activity is at what rate in Type MHC-IIA?
High
Vmax (speed of shortening is at what rate in MHC-IIA?
High
How Efficient is MHC-IIA
Moderate
The resistance to fatigue in type MHC-I is
High
What is the predominate energy system in type MHC-I?
Aerobic
ATPase activity is at what rate in Type MHC-I?
Low
Vmax (speed of shortening is at what rate in MHC-I?
Low
How Efficient is MHC-I
High
