Skeletal Muscle Flashcards
Key Molecules for xb formation/cycling
- Ca
- ATP
Calcium Function
enables myosin heads to attach to actin by revealing myson binding sites
ATP Function
binds to myosin which:
1) provides energy for powerstroke
2) allows myosin to detach from actin
ATP is then hyrolyzed and turns into ADP+P
Troponin Function
pulls tropomyosin away from myosin binding sites
and is activated by calcium
Contraction Cycle
1) Myosin hydrolyzes ATP, energy rotates the myosin head and weakly binds to Actin
2) Calcium activates troponin to move tropomyosin, which triggers the power stroke
3) Myosin releases ADP at the end of the power stroke
4) Tight binding in rigor state
5) ATP binds to myosin, myosin releases actin
Sarcomere Length Changes
I band and H zone change lengths
Sarcomere shortens
Excitation-Contraction Coupling
1) motor neuron releases ACh at NMJ
2) Na entry causes end plate potentials which is a graded potential, the summation leads to a AP
3) AP in t-tubule alters DHP receptor
4) DHP receptor opens RyR calcium release channels in SR
5) Calcium binds to troponin allowing actin-myosin binding
Skeletal Muscle Relaxation
1) Calcium pumped back into the SR
2) Decreased Ca causes less troponin binding
3) tropomyosin covers myosin binding site
SR-Ca ATPase (SERCA) function
pumps calcium from sacromere back into the Sarcoplasmic Reticulum
Summation
- increased force and contraction
- close stimuli do not allow muscle to relax
Unfused Tetanus
stimuli are far enough apart to allow muscles to relax slightly between stimuli
Complete Tetanus
muscle reaches steady tension, fatigue causes tension loss despite continuous stimuli
Refined Movements
require fewer fibres per motor unit
number and order of motor units is related to the power needed to generate movement
Sarcomere length/tension relationship
max force occurs at medium resting length, this has the most amount of xb’s
