Ch.9 part II Flashcards
Excitation-contraction coupling
- mechanism by which an action potential causes contraction of a muscle fiber
- involves sarcolemma, T tubules, sarcoplasmic reticulum, Ca 2+ and troponin
T tubules
-action potential enters into cell here, which triggers Ca 2+ gated channels to open
Sarcoplasmic reticulum
-enlarges due to the lumen of the t tubule being filled with extracellular fluid to form terminal cisternae
Terminal cisternae
-enlarged portion of sarcoplasmic reticulum
Triad
-t tubule and two adjacent terminal cisternae
Cross bridge cycling
- the process by which each myosin molecule undergoes the cycle of cross bridge formation, movement, release, and return to original position
- requires ATP
Power stroke
- myosin heads move actin with every ATP that is added
- several power strokes happen with every action potential
Recovery stroke
-happens when myosin head returns to resting place and awaits for next ATP to start another power stroke
Muscle twitch phase
- a single, brief contraction and relaxation cycle in a muscle fiber
- consists of a lag phase, contraction phase, and relaxation phase
- does not last long enough or generate enough tension to perform any work
Lag phase
-time between action potential coming from nerve and the Ca 2+ actually bindin with troponin
Contraction phase
-maximum contraction happens when actin molecules meet within a sacromere
Relaxation phase
-Ca 2+ pops off of troponin, tropomyosin covers active sites which makes myosin release from actin, titin pushes actin apart to equilibrium, complete contraction back to resting place
Motor unit
- one nerve coming in will have a set of muscle fibers
- not all fibers are signalled at once (axons only innervate a few fibers)
- the finer the movement, the fewer fibers that are innervated
Motot unit response
-treppe, multiple motor unit summation, multiple wave summation, tetanus
Summation
-involves increasing the force of contraction of the muscle fibers within the muscle
Recruitment
-involves increasing the number of muscle fibers contracting
Treppe
- when a rested muscle is stimulated repeatedly with maximal stimuli at a low frequency (which allows complete relaxation between stimuli)
- second contraction produces a slightly greater tension and the third contraction produces even greater tension until equilibrium is reached
- stimulus is maximal but delivered at low frequency
Multiple motor unit summation
-the relationship between increased stimulus strength and an increased number of contracting motor units
Multiple wave summation
- in incomplete tetnus, muscle fibers produce action potentials so rapidly that no relaxation occurs
- as the frequency of contraction increases, these are produced due to increased tension
Tetanus
- sacromeres don’t have time to reset
- Ca 2+ never leaves and the power stroke never stops
- muscle is locked into maximum contraction
- stimulus is at threshold but delivered at high frequency
Muscle contractions
-can be isometric or isotonic
Isometric
- length of the muscle does not change, but tension increases during contraction
- “posture”
Isotonic
- amount of tension during contraction is constant but the length of the muscle changes
- include concentric and eccentric
Concentric contraction
- the tension in the muscle is great enough to overcome the opposing resistance
- increasing tension, muscle shortening
- “starbucks curl”
Eccentric contraction
- tension is maintained but the opposing resistance is great enough to cause the muscle to increase in length
- slowly letting muscles stretch out under control
Energy sources for muscle contraction
-creating phosphate, anaerobic respiration, aerobic respiration
Creatine phosphate
- stockpiled in muscle fibers; requires use of creatine kinase
- instant source of unlimited ATP for a very short period of time (8-10 secs)
- only releases 1 ATP
Anaerobic respiration
- generates ATP rapidly after creatine phosphate is used up
- releases 2 ATP
Aerobic respiration
- happens all of the time; very efficient
- releases 36 ATP
- includes the use of glycogen and pyruvate
- -glucose goes through glycolosis forming 2 pyruvate (2 ATP) which then goes through krebs cycle (34 ATP)
Oxygen debt
- caused by creatine/anaerobic mess
- the process of reseting molecules burned through
- insufficient oxygen consumption relative to increased activity
Oxygen recovery
-repays oxygen debt which is time consuming
Muscle fiber types
-type I, type IIa, type IIb
Type I (slow twitch)
- adaptive for long haul
- very efficient
- postural muscles
Type IIa (fast twitch oxidative)
- combo of slow twitch and fast twitch glycolytic)
- efficient and instantaneous
- lower limbs
Type IIb (fast twitch glycolytic)
- adapted for instantaneous response
- polar opposite of slow twitch
- upper limbs
Myoglobin
- has high affinity for oxygen
- inside of mitochondria and suck oxygen away from hemoglobin (slow twitch)
Smooth muscle
- neurally or hormonally controlled
- contain dense bodies, dense areas, intermediate filaments, caveolae, myosin kinase, calmodulin, myosin phophatase
Dense bodies
-inside sarcoplasm
Dense areas
-on the surface, attached to the sarcolemma
Intermediate filaments
- mesh around sarcolemma
- attached to dense bodies which form the intracellular cytoskeleton
Caveolae
- shallow, invaginated areas along the surface of the sarcolemma
- comparable to t tubules
Calmodulin
-protein in which Ca 2+ bind with in smooth muscle
Myosin kinase
-enzyme that transfers phosphate group from ATP to myosin molecules in smooth muscle
Myosin phosphatase
- removes the phosphate group from the myosin molecules allowing the relaxation of smooth muscle
- timing of this enzyme is important because it can cause relaxation or contraction for long periods of time
Latch state
-period of sustained tensions due to the timing of myosin phosphatase
