what is motor unit?
-one motor neuron and all muscle fibers it innervates
describe the two sizes of motor unit
-small motor unit: one neuron -> few fibers -> fine control
-large motor unit: one neuron -> many fibers -> simple movement
what is the function of motor units
-sends action potential making all fibers in unit contract simultaneously
what does motor unit recruitment do?
-controls how many motor units are activated to adjust force
examples of each motor unit size
-small motor unit: extraocular muscles (eye)
-large motor unit: leg, back muscles
what are the control of sizes of motor units?
-small motor unit: high precision
-large motor unit: less precision, more force
why multiple motor unit can be recruited together?
to control strength of contraction
what is the role of nervous system in contraction?
-initiates and controls muscle contraction by sending action potentials which triggers calcium release which leads to contraction
where is atp needed during muscle activity?
-cross-bridge cycling
-calcium reuptake into SR
-resting membrane potential
what is the relationship between calcium reuptake into SR and ATP during muscle activity?
-SERCA pump actively transports calcium back into terminal cisternae using ATP
what is the relationship between cross-bridge cycling and ATP during muscle activity?
-ATP binds -> releases myosin from actin
-ATP hydrolyzed -> recocks myosin head
what is the relationship between resting membrane potential and ATP during muscle activity?
-Na+/K+ ATPase pump restores ion gradients after depolarization
what happens if inefficient calcium reuptake?
persistent contraction (calcium remains bound to troponin)
what are the sources of ATP for muscle contraction? describe each
- stored ATP: small amount already in fibers
- creatine phosphate: creatine kinase transfers phosphate from CP -> ADP -> ATP
- glycolysis: glucose -> pyruvate -> lactic acid
- aerobic cellular respiration- glucose + oxyge -> co2 + water + ATP
what source of ATP for muscle contraction requires oxygen?
aerobic cellular respiration
what is the ATP yield for each sources of ATP for muscle contraction?
- stored ATP: minimal
- CP: small
- glycolysis: 2 ATP/glucose
- approx. 30-36 ATP/glucose
what is the duration of energy for each sources of ATP for muscle contraction?
- stored ATP: approx. 5-6s
- CP: approx. 10-15s
- glycolysis: approx. 10s-few minutes
- aerobic: minutes to hours
explain the energy use during activity based on their intensity/duration
-immediate (few seconds): stored ATP + CP
-short-term (seconds-minutes): glycolysis
-long-term (minutes+): aerobic
what are the two main criteria of muscle fiber classification? define each
- speed of contraction- determined by ATPase enzyme speed
- ATP source- glycolysis vs aerobic
describe red fibers (slow-twitch)
-high myoglobin (binds oxygen)- red color
-many mitochondria -aerobic
-slow ATPase- slow contraction speed
-fatigue-resistant; long-term activity
example of red fibers (slow-twitch)
-postural muscles, distance running
desribe white fibers (fast-twitch)
-low myoglobin, few mitochondria
-use anaerobic respiration (quick, inefficient)
-fatigue quickly
example of white fibers (fast-twitch)
sprinting, jumping
describe pink fibers (intermediate/fast oxidative-glycolytic)
-mix of red and white properties
-can use glycolysis or aerobic respiration
-moderation contraction speed and endurance
