Muscles 3 Flashcards
Tension produced in individual muscle fibers can vary due to?
- length-tension relationship
- frequency of stimulation
Tension produced by entire muscle can vary even more widely due to?
- number of muscle cells receiving nerve stimulation, commanding them to contract
- muscle cells are grouped in motor units
all the muscle fibers innervated by?
one motor neuron
Amount of tension produced in a muscle determined by?
number of motor units activated
What kind of motor unit summation for sustained contractions?
asynchronous motor unit summation
Small motor unit
precise control
-one motor neuron innervates a small number of muscle fibers
large motor unit
gross movement control
-one motor neuron innervates a large number of muscle fibers
muscle tone is caused by?
- resting tension in skeletal muscle
- Some motor units are always active; tense and firm the muscle
- active motor units are constantly changing, muscle tone is not produced by a specific subset of motor units
Muscle tone functions
- stabilizes bones and joints
- greater resting muscle tone causes higher resting rate of metabolism
Isotonic contraction
tension rises, length of muscle changes
Concentric contraction
muscle tension exceeds resistance and muscle shortens
Eccentric contraction
peak tension developed is less than the resistance, muscle elongates
physiology of isometric contractions
- tension produced never exceeds resistance
- individual muscle fibers shorten until internal connective tissues and tendons are taut
- cannot shorten further bc tension doesn’t exceed resistance
lengthening a muscle
- no active mechanism for muscle fiber elongation
- muscle cell doesn’t cause itself to length after contraction process ends
how does a muscle return to resting length?
- recoil in elastic components in connective tissue
- contraction of opposing muscle groups
- gravity
How long to high energy molecules in the muscle last and what are they?
~15 sec once contraction begins, of ATP and creatine phosphate (CP)
Creatine Phosphate reserves
- muscle cell makes more ATP than needed; extra ATP transfers high energy phosphate to creatine for storage
- CP reserves releases stored energy to convert ADP to ATP when ATP is needed
Cellular respiraton
uses O2 and releases CO2
- occurs in mitochondria
- citric acid cycle
- electron transport chain
citric acid cycle
CO2 is produced
Electron transport chain
- ATP synthesis
- O2 is used
Resting muscle fibers rely o what to generate ATP?
Aerobic metabolism of fatty acids
how is aerobic metabolism of FA used to generate ATP?
- FA absorbed from circulation
- broken down to 2 C units of acetyl CoA which enter into the CAC
- Excess ATP used to store glucose into glycogen, create creatine phosphate
explain pyruvate metabolism
Anaerobic
-insufficient oxygen converts pyruvate to lactic acid
What does conversion of pyruvate to lactic acid do to cofactors
Recycles cofactors needed by glycolysis enzymes
what happens in resting muscle metabolism?
fatty acids to mitochondria to produce atp
what happens in moderately active muscle metabolism
still functions aerobically, glucose and fatty acids are catabolized, ATP produces is used to power contraction
What happens in peak activity muscle metabolism?
ATP is produced through glycolysis with lactic acid as a by-product. Mitochondrial activity provides 1/3 of the ATP consumed.
Advantage of anaerobic metabolism
produces ATP rapidly at an O2 deficit
Disadvantage of anaerobic metabolism
inefficient use of glucose
-lactic acid lowers intracellular pH
When does the recovery period starts?
immediately after activity ends
What is oxygen debt?
- excess post-exercise oxygen consumption
- more intense exercise=larger O2 debt
- amt of O2 req. during resting period needed to get rid of lactic acid and restore creatine phosphate reserves
What happens during the recovery period?
- oxygen debt
- rebuild ATP and creatine phosphate levels
- recycle lactic acid to make pyruvate
- rebuild glycogen reserves
Fatigued muscle
a muscle that can no longer perform at required level of activity
causes of fatigue
- exhaustion of energy resources
- build up of lactic acid and lowering of pH
- psychological fatigue
