Lecture 8: Activation and mechanical properties of skeletal muscle

Question 1

What is isotonic contraction?

Answer 1

Movement against a load

Question 2

What is isometeric contraction?

Answer 2

Muscle contracting against an immovable force

Question 3

Why is isometeric contraction still considered a contraction?

Answer 3

Ca2+ is still being released and interacting with troponin

Question 4

What is the force that acts against the muscle’s movement called?

Answer 4

Afterload (or load)

Question 5

What determines the active force of a muscle?

Answer 5

The amount of overlap between thin and thick filaments (length of sarcomere)

Question 6

What produces passive force?

Answer 6

Elastic proteins such as titin

Question 7

Why does passive tension increase with sarcomere length?

Answer 7

The elastic proteins stretch like springs

Question 8

Other than creating contractile force when muscle is extended, what else does titin do?

Answer 8

Ensures that thick filaments stay parallel to thin filaments

Question 9

What is total tension the sum of?

Answer 9

Passive and active tension

Question 10

What three factors affect tension?

Answer 10

Fibre length
Fibre diameter
Energetics of muscle contraction

Question 11

How can slow and fast fibres be differentiated histologically?

Answer 11

Length, diameter, colour

Question 12

What is a type I fibre?

Answer 12

Slow-oxidative fiber

Question 13

Type I fibres vs. type IIX fiber: Speed

Answer 13

Type I: Slow

Type IIX: Fast

Question 14

Type I fibres vs. type IIX fiber: resistance to fatigue

Answer 14

I: High
IIX: Low

Question 15

Type I fibres vs. type IIX fiber: Oxidative phosphorylation capacity

Answer 15

I: High
IIX: Low

Question 16

Type I fibres vs. type IIX fiber: Enzymes for anaerobic glycoloysis

Answer 16

I: Low
IIX: High

Question 17

Type I fibres vs. type IIX fiber: Mitochondria

Answer 17

I: Many
IIX: Few

Question 18

Type I fibres vs. type IIX fiber: Capillaries

Answer 18

I: Many
IIX: Few

Question 19

Type I fibres vs. type IIX fiber: Myoglobin content

Answer 19

I: high
IIX: low

Question 20

Type I fibres vs. type IIX fiber: Color of fibre

Answer 20

I: Red
IIX: white

Question 21

Type I fibres vs. type IIX fiber: Glycogen content

Answer 21

I: Low
IIX: high

Question 22

Give 2 examples of type I fibers

Answer 22

Postural muslces

Soleus (used in walking, long distance running)

Question 23

Give examples of type II fibers

Answer 23

Sprinting
Weight lifting (e.g. gastrocnemius)

Question 24

What is a motor unit?

Answer 24

All fibres innervated by a single neuron

Question 25

What determines motor unit size?

Answer 25

Muscle type, level of fetail and range of force requires for overall muscle

Question 26

What are the two types of force summation?

Answer 26

Spatial summation

Frequency summation

Question 27

What is spatial vs frequency summation?

Answer 27

Increasing number of motor units vs. increasing frequency of contractions

Question 28

What are three types of temporal summation?

Answer 28

Single twitch, twitch summation and tetanus

Question 29

Joints have to have what two types of muscle to be useful?

Answer 29

Agonist (muscle contracting)

Antagonist (Muscle relaxing)