limbs and back week 3 Flashcards
Describe the ATP pool in skeletal muscle
it is small and capable of supplying only for a very few contractions if not replenisehd
Why are ATP supplies only moderately depleted even as the muscle fatigues?
It is continually replenished
What is the function of creatine phosphate?
It is used to convert ADP to ATP and thus replenish the ATP store during muscle contraction.
Represents the immediate high-energy source for replacing the ATP supply in skeletal muscle, especially during intense exercise
What enzyme catalyses the reaction between ADP and creatine phosphate?
creatine phosphokinase
Where is CPK found?
Mostly in the sarcoplasm but some at the myosin heads too
How big is the creatine phosphate store?
Only 5 times to size of the ATP store and can’t last over 1 minute
How is creatine phosphate replenished?
During recovery from fatigue by using the ATP synthesised by oxidative phosphorylation
Where do muscles get carbohydrates from?
Muscle cells contain glycogen stores which can be metabolised during muscle contraction to provide glucose for oxidative phosphorylation and glycolysis
Muscle cells can also take up glucose from the blood
ATP yields are dependent on an adequate oxygen supply
When are fatty acids important sources of energy for muscle?
During prolonged exercise
Where do muscles get fatty acids from?
Muscle cells contain fatty acids
they can uptake fatty acids from the blood
muscle cells can store triglycerides, which can be hydrolysed to produce fatty acids
How are fatty acids metabolised in muscle?
they are converted into acyl-carnitine in the cytosol then transported into the mitochondria
Then they are converted into acyl-CoA
Within the mitochondria acyl-CoA is then subjected to Beta oxidation and yields acetyl-CoA
This enters the citric acid cycle and ultimately produces ATP.
What is fatigue?
The inability to maintain power output of muscle, reversible by rest
What occurs as a result of fatigue?
reduced force, shortening and relaxation rate
Describe central fatigue
within the nervous system
loss of excitability of the motor cortex, possible reflex inputs from “metabo-receptors” in muscle
can include failure of transition in peripheral nerve and neuromuscular junctions (usually pathological)
Describe peripheral fatigue
within the muscle fibres
failure of excitation - contraction coupling, T-tubule action potential, SR activation, Ca2+ release
How can you determine the type of fatigue?
external stimulation - if direct muscle stimulation delivers smaller forces then fatigue is peripheral. If stimulation delivers “normal” forces, then fatigue is central
Describe excitation failure
most likely in short intensity exercise
High AP firing rates leads to accumulation of K+ ions in tubules
This would make the T-tubule unexcitable and impairs excitation contraction coupling
recovery from this type of fatigue would be rapid
When is central fatigue likely?
Probably likely in occupational work and recreational sport. sensation of fatigue may involve discomfort and lack of motivation.
probably not a factor in elite sport
When does peripheral fatigue occur?
fatigue is not due to decreased ATP
In fatigue concentrations of H+, Pi and ADP all increase
these changes impair calcium fluxes and impair force delivery at cross bridges
Why does the build up of ADP, Pi and H+ inhibit the function of ATP?
An increase in the right and side of the equation will shift the equilibrium to the left and hence slow the break down of ATP
What else do ADP, Pi and H+ all inhibit?
Ca2+ release and reuptake into the sarcoplasmic reticulum. This affects the force and speed of shortening and relaxation.
H+ also competes with Ca2+ for troponin binding
What is the main energy source for long duration exercise?
Carbohydrate and lipid metabolism
What is the main energy source for moderate duration exercise?
aerobic, fuel mix uses more carbohydrates
What is the main energy source for short duration exercise?
aerobic and anaerobic metabolism, carbohydrate dependent, inefficient glycolytic metabolism
Describe the processes of training
requires multiple repetitions of the exercise concerned
for strength - small numbers of high power contractions
for endurance - large numbers of low force contractions
in strength training type 2 fibres enlarge
in true endurance training (e.g. marathon) no demand for increased strength, type 1 fibres may enlarge but type 2 decrease. Usually there is a loss of fat.
Describe the neural phase of strength training
first 4-6 weeks
CNS response, increased recruitment of largest motor units and higher maximum firing rates
Describe the hypertrophy phase of strength training
large motor units grow
significant hormonal changes - after strenuous strength training, GH, local growth hormones and testosterone are all elevated for hours
connective tissues also strengthen
hypertrophy is slow
starts with the development of new filaments attached laterally to existing myofibrils
Later there is fibril splitting - the most enlarged fibrils split longitudinally - thus become more numerous
How can skeletal muscle fibres be classified?
As fast twitch (2a/2b) or slow twitch (1)
How can the different types of muscle fibres be distinguished from one another?
the activities of oxidative and glycolytic pathways.
Describe fast twitch fibres
the activity of the glycolytic enzymes is high and the activity of the oxidative enzymes is low. -
very few mitochondria
more extensive sarcoplasmic reticulum than slow twitch
fatigue quickly
Describe slow twitch fibres
meet metabolic demands by oxidative phosphorylation
fatigue more slowly
What is special about 2a fibres?
They contain both high glycolytic and oxidative capacity - rare in humans
What is spacial summation?
Since fast-twitch muscle fibres are more difficult to excite slow twitch muscle fibre motor units are recruited first.
As more force is required, fast fibres are recruited
What are the advantages of spacial summation?
The first muscle fibres recruited have high resistance to fatigue
the small size of the slow-twitch muscle units allows fine motor control
What are the three bones of the elbow joint?
The humerus, ulna and radius
What are the two articulations of the elbow joint?
Humeri-ulnar = between the trochlea of the humerus and the trochlear notch of the ulna
Humero-radial = between the capitulum and upper surface of the radial head
What limits movement at the elbow joint?
fossas
Describe movement at the elbow joint
Flexion and extension - hinge joint, very stable, not likely to dislocate
How can hyperextension occur?
If the olecranon fossa forms a foreman instead, the olecranon of the ulna can pass right through
Describe the proximal radioulnar joint
also contained within the elbow joint capsule
the articulation between the head of the radius and the radial notch of the ulna
annular ligament wraps around the head of the radius and maintains stability of the radius
allows rotation during pronation and supination of the forearm.
Primary supination muscle is the biceps
What are the 3 flexors of the elbow joint?
Brachialis (primary flexor)
Brachioradialis (accesorry) only when forearm is mid-pronated
Biceps bracchi - only if palm is upwards
What is the extensor muscle of the elbow joint?
triceps brachii (long head, lateral head, medial head)
