Muscle physiology week 2 Flashcards
Excitation-Contraction Coupling
the series of events linking muscle excitation to muscle contraction .
the link between excitation and contraction.
Calcium
Calcium release
Relaxation
occurs when Calcium is returned to the lateral sacs when local electrical activity stops
Sarcoplasmic/endoplasmic reticulum Calcium–ATPase (SERCA) pump
The sarcoendoplasmic reticulum (SR) calcium transport ATPase (SERCA) is a pump that transports calcium ions from the cytoplasm into the SR.
No Calcium
– Actin and Myosin can’t bind
https://www.youtube.com/watch?v=BVcgO4p88AA
A single action potential in a skeletal muscle fiber lasts only
1 to 2 msec.
latent period.
The time delay between stimulation and onset of
contraction
Whole muscles are groups of muscle fibers bundled together and attached to bones.
Can range from only a few hundred fibers to several hundred thousand fibers.
attach muscle to bones
attach muscle to bones
How is muscle tension is transmitted
Muscle tension is transmitted to bone as the contractile component (sarcomere) tightens the series-elastic component.
A muscle is typically attached to
at least two bones across a joint by means of tendons that extend from each end of the muscle.
T/F
all muscle contractions shorten muscles and move bones
False
Not all muscle contractions shorten muscles and move bones
Three primary types of contraction:
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.
T/F
The same internal events occur in isotonic, isokinetic, and isometric contractions
True
T/F
Muscle contractions often are not of one pure primary type
True
https://www.youtube.com/watch?v=T00U5lMWAWQ
Muscle tension, length, and velocity of shortening may
vary throughout a range of motion
There are also two other descriptors of muscle contraction:
Concentric contraction
Eccentric contraction
Velocity of shortening is related to
The load
It is an important determinant of the velocity with which a muscle changes length.
Load – Velocity relationship
Contractions of a whole muscle can be of varying strength
A single action potential in a muscle fiber produces a brief, weak contraction called a twitch.
You can vary the force you exert by the same muscle.
Two primary factors can be adjusted
(1) Number of muscle fibers contracting within a muscle
(2) Tension developed by each contracting fiber
What leads to greater muscle tension
The greater the number of fibers contracting, the greater the total muscle tension
Each whole muscle is innervated by a number of :
different motor neurons - Motor Unit –>Motor Unit Recruitment
Contraction strength depends on
motor unit size
In muscles that produce precise, delicate movements
a single motor unit may contain a few muscle fibers
In muscles designed for powerful, coarsely controlled movement,
a single motor unit may contain many muscle fibers
Muscle fatigue
the inability to maintain muscle tension at a given level
The body _______ to prevent or delay fatigue
alternates motor unit activity
The body alternates motor unit activity to prevent or delay fatigue
How is this possible?
Muscles consist of a mixture of fiber types that differ metabolically, some being more resistant to fatigue than others.
Various factors influence the extent to which tension can be developed, including the following:
- Frequency of stimulation
- Length of the fiber at the onset of contraction
- Extent of fatigue
- Thickness of the fiber
Twitch Summation and Tetanus
Muscle Length – Tension Relationship
Muscle Metabolism
-Four steps in the excitation, contraction, and relaxation processes require ATP:
- Myosin ATPase Splits ATP to provide energy for the power stroke of the cross bridge.
- Binding of a fresh molecule of ATP to myosin lets the cross bridge detach from the actin filament at the end of a power stroke.
- Active transport of Ca2+ back into the lateral sacs of the SR during relaxation
- The ATP-dependent Na+–K1+ pump actively returns the ions that moved during the generation of an action potential in the muscle cell.
There are two types of fatigue:
Muscle fatigue
Central fatigue
There are three major types of muscle fibers:
- Slow-oxidative (type I) fibers
- Fast-oxidative (type IIa) fibers
- Fast-glycolytic (type IIx) fibers
https://www.youtube.com/watch?v=8x8H-GFtwyU&t=6s
Two types of changes can be induced in muscle fibers:
Changes in their oxidative capacity
Changes in their diameter (hypertrophy)
- Influence of Testosterone
- Interconversion Between Fast Muscle Types
Use memo 1, 2, 3 in summaries!!
