M7, L2 Skeletal muscle part II Flashcards
What is the optimal resting length of skeletal muscle-where the maximal active force is developed
2.0-2.2 um.
At lengths < 2.0 what is happening in the sarcomere and what is the relative active passive force
the ends of filaments collide and start to interfere with each other therefore active force development is reduced
At lengths > 2.2 what is happening in the sarcomere and what is the relative active passive force
The elastic connective tissue around muscle cells is stretched so passive force increases. The active force declines as the extent of overlap between filaments reduces which reduces the number of possible cross bridge interactions along the sarcomere
Which type of contraction does length tension relationship work for
isometric- the muscle doesn’t shorten so the overlap of the filaments is determinant of number of cross bridges formed
What is passive force
The resistance to stretching out the muscle even more due to connective tissue titin.
What is total tension
active + passive force
What is a motor unit
1 motor neuron and all the muscle fibres it innervates
What is excitation contraction coupling
The overall process that connects an AP to a muscle contraction
How does AP stimulated by ACh at Neuromuscular junction result in release of calcium from SR
The action potential is conducted down the t-tubule, coming in close contact with the SR. The voltage sensor in T-tubule + Ca channel in SR = voltage gated Ca2+ channels in the SR that open when the membrane becomes more positive and releases Ca2+ into the cytosol.
Ca2+ conc in myoplasm goes from 10-7 to 10-5, what does this cause
When Ca2+ conc reach critical threshold, the myosin binding sites on actin filament are exposed, allowing cross bridge cycle to occur.
How does the muscle relax
Contraction ends when Ca2+ levels fall. This happens as Ca2+ is pumped back to the SR by Ca-ATPase. and Ca2+ channels in SR close. As a result amount of calcium bound to troponin decrease and this leads to an inhibition of interaction of actin and myosin. Muscle twitch complete
How many ca2+ bind to troponin to cause conformational change
2
What are the 3 ways muscle can get ATP
creatine phosphate stored in cells, aerobic respiration and anaerobic glycolysis
How do you get ATP from Creatine phosphate and how long can u get energy for
Pi from creatine phosphate can be given to ADP to change it to ATP, and creatine P becomes creatine (anaerobic). Energy lasts for less than 15s
what enzyme catalyses the reaction makes ATP and AMP from 2 molecules of ADP
adenylate kinase
How do you get ATP from anaerobic glycolysis and how long can u get energy for
1 glucose molecule (from muscle glycogen or blood) produces 2 pyruvic acid and 2 ATP (3 if glycogen used) . this is dominant system for 10-30s/30-40s of maximal effort. Pyruvic acid is converted to lactic acid which is the rate limiting step as build up of lactate and H+ limits max duration to 120s
How do you get ATP from aerobic metabolism and how long can u get energy for
Uses many sources : fatty acids, pyruvic acid, amino acids and requires oxygen to produce heat, CO2, H2O and 36 ATP. It is efficient but slow, lasting for minutes to hours.
Which type of metabolism is better for what activity
Anaerobic for sprinting and weightlifting: power > 300 W. Aerobic for postural muscles and endurance exercise: Max 300 W.
What limits aerobic exercise capacity
The work rate increases as O2 consumption increases but it will plateau at Vo2 max where she can’t use any more O2 : passing the capability of the system. Contracted muscles get less blood flow therefore less O2
What stops anaerobic respiration
running out of glycogen stores, accumulation of metabolic products inhibit cell reactions. acidification inhibits phosphofructokinase reaction - important for glycolysis
What are the 3 types of muscle fibres
Type 1 (slow oxidative) Type 2B (fast glycolytic) and Type 2A (fast oxidative)
What are Type 1 muscle fibres used for and why
Type one are used for posturing and low energy exercise: because they have slow max ATP rate, small diameter, high access to mitochondria and oxygen carriers, moderate SR pumping capacity and glycolytic capacity
What are type 2 fibres (esp type 2B in humans) used for and why
short duration, high power exercise: because they have fast max ATP rate, high SR pumping capacity with large diameter and high glycolytic capacity bc main ATP pathway is anaerobic glycolysis.
How does Type 2A muscle differ from Type 2B
It has the same fast max ATPase rate, high SR pumping capacity, high glycolytic capacity but has a medium diameter and very high o2 supply because it does Aerobic mainly
How many different types of fibres can a nerve innervate
only one type.
How do you regulate the tension produced by skeletal muscle fibres so it can be graded
the rate of the stimulation of individual motor units-> the number of action potentials in one motor unit that can merge to make bigger force as well as the number of motor units recruited.
What is fused (complete tetanus) vs unfused tetanus
Low stimulation frequency but APs still applied before muscle relaxes completely so temporal summation-= unfused tetanus but high stimulation frequency there is no relaxation= fused tetanus
why can temporal summation happen in muscle cell
The muscle twitch caused by (calcium transient) is longer than the duration of AP so AP can be initiated before Ca2+ returns to resting levels.
In what order are motor units recruited
small oxidative fibres with low wattage are recruited first then fewer larger glycolytic motor units as they only go for short time.
Greater voltage applied on the nerve-> greater number of neurons stimulated so
greater response
