Muscle Physiology

Question 1

Muscles contain bundles of fibers called _______

Answer 1

Myofibrils

Question 2

Review the sarcomere on 6-2. Know I band, A band, Z line, M line

Answer 2

Always comes back to haunt us

Question 3

What is an H zone?

Answer 3

A central region of A band where thin filaments do not overlap with thick filaments

Question 4

Do thick or thin filaments change length in muscle contraciton?

Answer 4

No

Question 5

What theory explains muscle contraction?

Answer 5

The Sliding Filament Hypothesis

Question 6

What are thick filaments made of?

Answer 6

Myosin

Question 7

What proteins are thin filaments made of?

Answer 7

Actin, Tropomyosin, and Troponin

Question 8

Structure of actin in a thin filament?

Answer 8

Polymerized globular protein entwined in a helix

Question 9

Function of troponin/tropomyosin?

Answer 9

regulate the interaction of myosin with the actin molecule

Question 10

What does the hydrolysis of ATP bound to myosin do?

Answer 10

Causes the myosin head to pivot

Question 11

Describe the cross-bridge cycle

Answer 11

1. Baseline – Myosin with ATP is next to Actin
2. Hydrolysis of ATP causes pivot of the myosin head
3. Pivoted head binds Actin
4. ADP+Pi is released, causing myosin head to un-pivot, pulling actin
5. ATP binds, causing the myosin head to release the Actin

Question 12

In resting muscle, what covers the myosin binding site?

Answer 12

Tropomyosin

Question 13

Purpose of troponin?

Answer 13

Locks tropomyosin in position

Question 14

What causes the troponin-tropomyosin complex to release actin for binding?

Answer 14

Ca ions

Question 15

Where do the Ca ions that free up the actin come from?

Answer 15

Sarcoplasmic Reticulum

Question 16

What triggers Sarcoplasmic Reticulum release of Ca?

Answer 16

AP traveling the transverse tubule system.

Linkage of calcium-induced calcium-release channels lead to channel changes.

Question 17

What is the Transverse Tubule system?

Answer 17

Periodic infoldings of the plasma membrane

Question 18

Describe the two receptors involved in Calcium release.

Answer 18

Voltage activated Ca channel in T Tubule activated calcium induced calcium release channel.

Question 19

Main difference between skeletal and heart muscle?

Answer 19

Individual cardiac muscle cells are linked via gap junctions.

Question 20

How does smooth muscle signalling get going

Answer 20

Phosphatidyl inositol cleaved to IP3
IP3 binds to calcium release channel to sarcoplasmic reticulum
Calcium release

Question 21

What major player is no longer involved in smooth muscle

Answer 21

Troponin

Question 22

How is smooth muscle myosin regulated?

Answer 22

Phosphorylation-dephosphorylation of myosin

Myosin Light Chain Kinase and Myosin Light Chain Phosphotase

Question 23

What regulates MLCK?

Answer 23

Calmodulin

Question 24

What determines the force of a muscle fiber?

Answer 24

Amount of overlap of thick and thin filaments

Question 25

During a maintained contraction, how much of the muscle's ATP is used to fuel the cross bridge? Pumping into the Sarc?

Answer 25

50-80% | 20-30%

Question 26

Two methods muscles use to generate ATP

Answer 26

Ox Phos and Anerobic glycolysis

Question 27

Pros and Cons of Ox Phos?

Answer 27

Efficient, can operate continually | Slow process, cannot meet maximal ATP consumption rated

Question 28

Pros and Cons on Anerobic glycolysis?

Answer 28

Fast | Limited by glycogen stores, inefficient

Question 29

How many muscle fibers can a neuron innervate?

Answer 29

Many

Question 30

How many neurons can innervate a muscle fiber?

Answer 30

One

Question 31

What is the innervation ratio?

Answer 31

The number of fibers innervated by a single motoneuron.

Question 32

Which is longer, muscle AP or twitch?

Answer 32

The twitch (10 to 100 ms)

Question 33

What happens when repeated stimulations are happening faster than twitches are ending?

Answer 33

Tension developed by twitches summates

Question 34

What happens if you make the muscles stimulate at their highest frequencies?

Answer 34

Twitches fuse -- Tetanus

Question 35

Three categories of motor units.

Answer 35

Slow, Fast Fatigue Resistant (FR), and Fast Fatiguable (FF)

Question 36

Describe S units.

Answer 36

Contract slow, small peak force | Highly resistant to fatigue

Question 37

Describe FF units

Answer 37

Contract fast, forcefully | Easy to fatigue

Question 38

Describe FR units.

Answer 38

Similar to FF, but with smaller peak forces and higher fatigue resistance

Question 39

Nerve properties may influence what properties of muscles.

Answer 39

Metabolic and contractile characteristics

Question 40

How is force of contraction increased?

Answer 40

1. Recruiting more motor units | 2. Increasing firing rate of individual units

Question 41

Order in which recruitment occurs.

Answer 41

S --> FR --> FF | FR and FF only for strenuous activities

Question 42

Name for the rule about the order in which recruitment occurs.

Answer 42

The Size Principle

Question 43

What does the size principle allow?

Answer 43

Higher motor centers determine the overall level of drive and not the exact combination of motor units to be recruited

Question 44

What is malignant hypothermia? What do you do?

Answer 44

A mutation of ryanodine receptors. Provide muscle relaxants

Question 45

What is myotonic dystrophy?

Answer 45

A disease with muscle weakness, cataracts, baldness, heart disease, and muscle failure.