Muscle Function Flashcards
What does the process of skeletal muscle contraction involve?
- neural stimulation of the sarcolemma: causes excitation-contraction coupling
- muscle fibre contraction:interaction of thick and thin filaments
- tension (force) production
What do synaptic vesicles contain?
Acetylcholine
The sliding filament theory
Vertical lines at side are z line
Thick horizontal lines are myosin filament
Thin horizontal lines are actin filament
Describe the six stages of the contractile cycle (skeletal muscle)
- Contraction cycle begins
- Active site exposure
- cross-bridge formation
- myosin head pivoting
- cross-bridge detachment
- myosin reactivation
Where does the energy for contraction come from?
- ATP is essential for contraction
- The enzyme myofibrillar ATPase (mATPase) located in myosin head
- ATP is also required to pump calcium back into the SR during relaxation
What are the two individual fibre types?
Slow fibres and fast fibres
What are the slow fibres?
- type 1 fibres:
- slow-twitch fibres
- slow-oxidative fibres
- large amounts of mitochondria
- myoglobin
What are the fast fibres?
- type 11b fibres:
- fast twitch fibres
- fast-glycolytic fibres
- larger in diameter
- type 11a fibres:
- intermediate fibres
- fast-oxidative fibres
- hybrid of type 1 and 11b
Power athletes such as sprinters have what kind of fibres?
Possess high percentage of fast fibres
What type of fibres do endurance athletes such as distance runners have?
Have high percentage of slow fibres
What type of fibres do others have such as cyclists and non athletes?
Have about 50% slow and 50% fast fibres
Discuss slow oxidative type 1 muscle fibres
Contraction- slow twitch Fibre size-small Colour-red Myoglobin concentration-high Mitochondrial content-high
Discuss fast oxidative type 11a muscle fibres
Contraction- fast twitch Fibre size-intermediate Colour-red Myoglobin concentration-high Mitochondrial content-high
Discuss fast glycolytic (type 11b) muscle fibres
Contraction- fast twitch Fibre size-large Colour-White Myoglobin concentration-low Mitochondrial content-low
What is used to see fibre types more clearly?
Histochemical staining
What is muscle tone?
The resting tension in a muscle
In tension production and contraction types, the contractions are classified based on the resulting patterns of tension production, what are they?
- isotonic contraction
- isometric contraction
With isotonic contraction what happens when the skeletal muscle changes length?
This results in motion
With isotonic contraction what happens if the muscle tension is more than the load (resistance)?
Muscle shortens (concentric contraction)
With isotonic contraction what happens if the muscle tension is less than the load (resistance)?
Muscle lengthens( eccentric contraction)
Discuss isometric contraction
Skeletal muscle develops tension, but is prevented from changing length
Iso= same, metric=measure
Load and speed of contraction are inversely related, what does this mean?
The heavier the load (resistance) on a muscle
- the longer it takes for shortening to begin
- the less muscle will shorten
With regards to speed of muscle contraction/relaxation, discuss muscle twitch
- contraction as the result of a single stimulus
- latent period: lasting only 2ms
- contraction: tension is developed-15ms
- relaxation:25ms
Describe the development of tension in a twitch
As time(ms) and tension increase from resting phase, stimulus occurs at 0 which results in a resting potential half way between 0 and 5. Between 5 and 15 ms there is the contraction phase until maximum tension development is reached and then between 15 and 40ms it falls during the relaxation phase
The tension over time for a twitch is different in what?
Different skeletal muscles
What is a motor unit?
A motor neuron and all of the muscle cells it stimulates
What is the optimal resting length?
The normal range of sarcomere lengths in the body is 75 to 130 percent of the optimal length
With force regulation in muscle, what is the relationship between types and numbers of motor units recruited?
More motor units=greater force
Fast motor units= greater force
Initial muscle length is?
Optimum overlap produces greatest amount of tension
Nature of the motor unit neural stimulation
Frequency of stimulation…
Simple twitch, summation and tetanus
What is a single muscle twitch composed of?
Latent contraction, and relaxation periods
What does the increase of frequency of stimulation do?
Increasing the frequency provides temporal summation and increased muscle tension
With regards to the number of motor units recruited, what does the stimulation of more motor neurone produce?
Increased muscle tension
What is the starting length of a muscle?
Optimum stretch permits maximum binding of cross bridges for maximum muscle tension
Receptors in muscle: discuss muscle spindle
- detect dynamic and static changes in muscle length
- stretch reflex
- stretch on muscle causes reflex contraction
Receptors in muscle: discuss Golgi tendon organ (GTO)
- monitor tension developed in muscle
- prevents damage during excessive force generation
- stimulation results in reflex relaxation of muscles
Muscle fatigue: when a muscle can no longer perform at the required level of activity:
- depletion of metabolic reserves
- a decline in pH within the muscle fibre- lactic acid
- a sense of weariness due to low blood pH
- damage to sarcolemma or sarcoplasmic reticulum
- pathological conditions-premature fatigue-heart problems, blood loss etc.
Anaerobic pathway produces what?
Lactic acid
What is muscle atrophy and what does it do?
- results due to lack of activity or loss of neuronal innervation
- reduction in muscle fibre size, tone and power
- examples are sedentary lifestyle, bed rest and spinal cord injury
What is hypertrophy and what does it result in?
- results due to repeated, exhaustive stimulation
- muscle fibre increases in diameter
- number of muscle fibre remains the same
- there is an increase in mitochondria, glycolytic enzymes, larger glycogen reserves
