7 - Muscle tendon unit and force production

Question 1

How is voluntary movement created and controlled?

Answer 1

brain > spinal cord > motor neuron > muscle > movement > sensory receptor > spinal cord > brain

Question 2

What are the properties of skeletal muscles and describe them

Answer 2

Passive:
extensibility - can change length
elasticity - will return to the original length

Active:
contractility - can produce force

Question 3

What percentage increase/decrease can a muscle have?

Answer 3

40/50%

Question 4

What are the two types of muscle architecture?

Answer 4

fusi form, pennate

Question 5

Describe fusi form

Answer 5

long fibres arranged along the line of action of the muscle

e.g. bicep brachii

Question 6

Describe pennate

Answer 6

short fibres arranged at an angle to the line of action of the muscle
e.g. gastrocnemius

Question 7

Describe the architecture of fusi form

Answer 7

large length change, high velocity

Question 8

Describe the architecture of pennate

Answer 8

larger physiological cross section area (PCSA), larger force, longer tendon

Question 9

How can we measure the force production in humans?

Answer 9

• isokinetic dynamometers
• measure the force produced by groups of muscles that move a joint in a given plane
• isometric contractions
• concentric and eccentric contraction at constant velocity

Question 10

What is the amount of force developed directly proportional to?

Answer 10

the number of cross-bridges formed

Question 11

What does the number of cross bridges depend upon?

Answer 11

length of the muscle
contraction velocity
level of activation
time since onset of activation

Question 12

What is the hierarchical structure of skeletal muscle?

Answer 12

muscle > fibre bundle > fascicle > fibre > myofibrils > filament > sarcomere

Question 13

What is the membrane of the skeletal muscle called?

Answer 13

Epimysium

Question 14

What is the hierarchical structure of a muscle?

Answer 14

bundle (membrane called perimysium) > sarcolemma (endomysium split the sarcolemmas) > myofibrils

Question 15

What makes up the fascia?

Answer 15

epimysium, perimysium, endomysium

Question 16

What is a myofibril?

Answer 16

• made up of many sarcomeres
• contractile machinery of muscle
• two filaments: thick (myosin), thin (actin)

Question 17

What does actin and myosin do?

Answer 17

• work together to form cross bridges

- the myosin has myosin heads which connect to the action to produce movement

Question 18

Describe the structure of the sarcomere

Answer 18

Z line - at the ends of the thin/thick filament

M line - between the two thick filaments

Question 19

What are the mechanics of contraction?

Answer 19

• action potential travels along the sarcomere
• action potential enters at transverse tubules and triggers the release of calcium into the cell
• calcium binds with troponin which causes tropomyosin to ‘unblock’ the actin filaments
• myosin heads bind with the action to form cross bridges and complete power strokes
• ATP fuels the pumping back of calcium to the SR which resets the system

Question 20

Describe the sliding filaments mechanism

Answer 20

• lever movement of myosin heads drives displacement of the action relative to myosin
• this deforms internal elastic structures developing force
• thick and thin filaments ‘slide’ relative to each other