M7, L2 Skeletal muscle part II

Question 1

What is the optimal resting length of skeletal muscle-where the maximal active force is developed

Answer 1

2.0-2.2 um.

Question 2

At lengths < 2.0 what is happening in the sarcomere and what is the relative active passive force

Answer 2

the ends of filaments collide and start to interfere with each other therefore active force development is reduced

Question 3

At lengths > 2.2 what is happening in the sarcomere and what is the relative active passive force

Answer 3

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

Question 4

Which type of contraction does length tension relationship work for

Answer 4

isometric- the muscle doesn’t shorten so the overlap of the filaments is determinant of number of cross bridges formed

Question 5

What is passive force

Answer 5

The resistance to stretching out the muscle even more due to connective tissue titin.

Question 6

What is total tension

Answer 6

active + passive force

Question 7

What is a motor unit

Answer 7

1 motor neuron and all the muscle fibres it innervates

Question 8

What is excitation contraction coupling

Answer 8

The overall process that connects an AP to a muscle contraction

Question 9

How does AP stimulated by ACh at Neuromuscular junction result in release of calcium from SR

Answer 9

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.

Question 10

Ca2+ conc in myoplasm goes from 10-7 to 10-5, what does this cause

Answer 10

When Ca2+ conc reach critical threshold, the myosin binding sites on actin filament are exposed, allowing cross bridge cycle to occur.

Question 11

How does the muscle relax

Answer 11

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

Question 12

How many ca2+ bind to troponin to cause conformational change

Answer 12

2

Question 13

What are the 3 ways muscle can get ATP

Answer 13

creatine phosphate stored in cells, aerobic respiration and anaerobic glycolysis

Question 14

How do you get ATP from Creatine phosphate and how long can u get energy for

Answer 14

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

Question 15

what enzyme catalyses the reaction makes ATP and AMP from 2 molecules of ADP

Answer 15

adenylate kinase

Question 16

How do you get ATP from anaerobic glycolysis and how long can u get energy for

Answer 16

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

Question 17

How do you get ATP from aerobic metabolism and how long can u get energy for

Answer 17

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.

Question 18

Which type of metabolism is better for what activity

Answer 18

Anaerobic for sprinting and weightlifting: power > 300 W. Aerobic for postural muscles and endurance exercise: Max 300 W.

Question 19

What limits aerobic exercise capacity

Answer 19

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

Question 20

What stops anaerobic respiration

Answer 20

running out of glycogen stores, accumulation of metabolic products inhibit cell reactions. acidification inhibits phosphofructokinase reaction - important for glycolysis

Question 21

What are the 3 types of muscle fibres

Answer 21

Type 1 (slow oxidative) Type 2B (fast glycolytic) and Type 2A (fast oxidative)

Question 22

What are Type 1 muscle fibres used for and why

Answer 22

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

Question 23

What are type 2 fibres (esp type 2B in humans) used for and why

Answer 23

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.

Question 24

How does Type 2A muscle differ from Type 2B

Answer 24

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

Question 25

How many different types of fibres can a nerve innervate

Answer 25

only one type.

Question 26

How do you regulate the tension produced by skeletal muscle fibres so it can be graded

Answer 26

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.

Question 27

What is fused (complete tetanus) vs unfused tetanus

Answer 27

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

Question 28

why can temporal summation happen in muscle cell

Answer 28

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.

Question 29

In what order are motor units recruited

Answer 29

small oxidative fibres with low wattage are recruited first then fewer larger glycolytic motor units as they only go for short time.

Question 30

Greater voltage applied on the nerve-> greater number of neurons stimulated so

Answer 30

greater response