Lecture 14: Muscle physiology 3

Question 1

What does summation mean in the context of muscle contraction. Compare to tetanus

Answer 1

This is when more force is developed from an isolated muscle when you decrease the interval between the stimuli

Tetanus is where the summation of force goes to max level where there is no relaxation between APs. This is normal.

Question 2

Why does muscle reduce in tension despite continous stimulation

Answer 2

There is fatigue

Question 3

Compare isometric and isotonic contraction

Answer 3

Isometric is where there is no external shortening and the force of load = tension generated
Whereas Isotonic is where there a mismatch between tension generated and force of load leading to movement and external shortening

Question 4

What are the two types of isometric contraction

Answer 4

Concentric and eccentric

Question 5

Compare concentric and eccentric contraction

Answer 5

Concentric is where muscle length decreases against an opposing load because muscle force is greater

Whereas eccentric contraction is where the muscle length increases as it resists a load but in a controlled way as the force developed by muscles isn’t enough

Question 6

What is the force length relationship

Answer 6

Each sarcomere has an optimal resting length ( z to z disc) which gives the best overlap for force generation
Too short- no more left.
Too long- no overlap for cross bridges to form/ fewer cross bridges to cycle

Question 7

How does DOMS happen- delayed onset muscle soreness

Answer 7

Not all sarcomeres lengthen evening during eccentric contractions. When the muscle is lengthening and contracting, some weaker sarcomeres will be stretched beyond their optimal length and developed less force and then will pop.
This plus inflammation will cause some DOMS

Question 8

Why can eccentric contractions be damaging

Answer 8

DOMS: Delayed Onset Muscle Soreness and muscle injury

Question 9

What is the force velocity relationship of muscle

Answer 9

There is maximum velocity of contraction when there is no load. As the load increases the velocity of shortening decreases. If one is constant so should the other

Question 10

At what length is contraction of muscle the most efficient

Answer 10

1/3 the max rate of shortening

Question 11

If load is equal to max force generated by muscle what is the contraction. What if its is more than force generated?

Answer 11

= isometric contraction

more than = eccentric contraction

Question 12

What are the 3 sources of ATP in the muscle cell and for what time frame are they used in

Answer 12

1. Creatine phosphate-> Creatine used to give a Pi to ADP: immediate energy 10s
2. Oxidative phosphorylation (aerobic respiration) : long term: 3 min +
3. Glycolysis which forms lactate. Short term: 1 min

Question 13

What are type 1 fibre: colour, purpose, eg.

Answer 13

Red bc of myoglobin with lots of mitochondria for aerobic Resistant to muscle fatigue. Eg. postural

Question 14

Define muscle fatigue

Answer 14

Failure to maintain the required or expected power output leading to reduced muscle performance

Question 15

What are type 2a

colour, purpose,

Answer 15

Red bc of myoglobin

• can use both aerobic and anaerobic
• more fatigue than type 1

Question 16

What are type 2b

colour, purpose,

Answer 16

White in colour and slow production of ATP by anaerobic metabolism but can do short bursts of power
- easily fatigued

Question 17

What muscle fibre type can be changed to another

Answer 17

type 2b to type 2a

Question 18

What metabolites building up lead to peripheral muscle fatigue

Answer 18

Decreased membrane excitability because of increased extracellular K+ in t tubules

• build up of Pi due to lots of ATP turnover
• NH4 inhibit myosin
• Free radicals causing protein damage
• lactic acid

Question 19

What is Duchenne muscular dystrophy

Answer 19

X linked genetic disease causing dystrophin loss leads to[ progressive skeletal muscle degeneration respiratory muscle failure

Question 20

What is sarcopenia

Answer 20

Irreversable loss of muscle mass related to age. New muscle formation not impaired but denervation of fast fatiguing muscle fibres and motor units, and motor unit remodelling. Exercise and diet can slow progression

Question 21

What is peripheral fatigue and are the proposed causes

Answer 21

The smaller Ca2+ transient, reduced Ca2+ sensitivity of myofilaments and slower cross bridge cycling which leads to less force generated

Caused by accumulation of metabolites and depletion of muscle energy supplies (eg glycogen)