Muscle physiology week 1

Question 1

Structure of Skeletal Muscle (Micro anatomy)

Answer 1

Sarcomere
Actin
Myosin
Troponin
Tropomyosin
Titin

Question 2

Muscle Tissue Types

makeup 30 - 40 % of body weight

Answer 2

Smooth Muscle
Cardiac Muscle
Skeletal muscle

Question 3

Skeletal muscle

Answer 3

• striated muscle
• Single muscle cell = muscle fiber
• multiple nuclei per fiber
• voluntary muscle
• attach to bones via tendons and enable movement
• Can produce powerful fast movements or small precise movements
• Can stretch and retract

Question 4

Question 5

Fixator muscles

Answer 5

• skeletal muscle
• stabilizes joints
  [ rotator cuff muscles ]

Question 6

Involuntary muscle

Answer 6

• smooth muscle
• Found in walls of hollow organs
  [ stomach, esophagus, bronchi, and blood vessels ]
• contract and relax automatically

Question 7

Cardiac muscle

Answer 7

• only found in walls of the heart
• similar to skeletal muscle - has a striped appearance
• similar top smooth muscle - involuntary
• Highly specialized
  > resistant to fatigue
  > due to presence of large number of mitochondria,
  myoglobin and good blood supply

Question 8

Skeletal muscle:

Question 9

Myofibril

Answer 9

= specialized contractile elements
- Contain highly organized microfilaments
> Thick and thin filaments

Question 10

Question 11

The functional unit

Answer 11

sarcomere

Question 12

A myofibril displays alternating bands

Answer 12

dark bands (the A bands) and light bands (the I bands)

Question 13

A band

Answer 13

stacked set of thick filaments along with the portions of the thin filaments

Question 14

H zone

Answer 14

Middle of A band

Question 15

M line

Answer 15

supporting proteins

Question 16

I band

Answer 16

Thin filaments that don’t project into the A band

Question 17

sarcomere

Answer 17

the distance between the Z-lines

Question 18

Z line

Answer 18

any of the dark thin bands across a striated muscle fiber that mark the junction of actin filaments in adjacent sarcomeres.

Question 19

Question 20

Growth

Answer 20

increase in length by adding new sarcomeres

Question 21

Titin

Answer 21

[ Highly elastic protein ]

• Scaffolding
• Elastic spring
• Signal transduction

Question 22

Question 23

Myosin

Answer 23

• can bend at hinge points in two locations
• Heads form the cross bridges
• Actin binding site
• Myosin ATPase site

Question 24

Thin filaments contain 3 proteins

Answer 24

Actin
Tropomyosin
Troponin

Question 25

Actin

Answer 25

• Contains binding sites for attachment with myosin cross bridge

Question 26

Tropomyosin

Answer 26

covers the actin sites that bind with the cross bridges

Question 27

Troponin

Answer 27

stabilizes tropomyosin in its blocking position over actin’s cross-bridge binding sites

Question 28

Question 29

in a relaxed muscle fiber

Answer 29

1. No excitation
2. No cross-bridge binding because cross-bridge binding site on actin is physically covered by troponin-tropomyosin complex
3. muscle fiber is relaxed

Question 30

in an excited muscle fiber

Answer 30

1. muscle fiber is excited and Ca2+ is released
2. released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site
3. cross-bridge binding occurs
4. binding of actin and myosin cross-bridge triggers power stroke that pulls thin filament inward during contraction

Question 30

in an excited muscle fiber

Answer 30

1. muscle fiber is excited and Ca2+ is released
2. released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site
3. cross-bridge binding occurs
4. binding of actin and myosin cross-bridge triggers power stroke that pulls thin filament inward during contraction

Question 31

Question 32

Sliding Filament Theory

Answer 32

Thin filaments on each side of a sarcomere slide inward over the thick stationary filaments toward the A band’s center during contraction.
Thin filaments pull the Z lines closer together,
so in effect, the sarcomere shortens.
All sarcomeres throughout the length of the Muscle fiber shorten simultaneously – the entire muscle fiber shortens

Question 33

Power Stroke

Answer 33

1. Myosin cross bridges “walk” along an actin filament to pull it inward relative to the thick stationary filament.
2. When actin and myosin bind, myosin’s head tilts inward
3. Bending at this neck hinge point creates a “stroking” motion
4. Thin filament is pulled toward the center of the sarcomere
5. stroke of a cross bridge

Question 34

Question 35

In contracting muscle all cross-bridge strokes directed towards:

Answer 35

The center of thick filament

Question 36

How does cross-bridge interaction between actin and myosin bring about muscle contraction?

Answer 36

Once the myosin-binding sites are exposed, and if sufficient ATP is present, myosin binds to actin to begin cross-bridge cycling. Then the sarcomere shortens and the muscle contracts. In the absence of calcium, this binding does not occur, so the presence of free calcium is an important regulator of muscle contraction.

Question 37

How does a muscle action potential trigger this contractile process?

Answer 37

A Muscle Contraction Is Triggered When an Action Potential Travels Along the Nerves to the Muscles. Muscle contraction begins when the nervous system generates a signal. The signal, an impulse called an action potential, travels through a type of nerve cell called a motor neuron.
The neuromuscular junction is the name of the place where the motor neuron reaches a muscle cell. Skeletal muscle tissue is composed of cells called muscle fibers. When the nervous system signal reaches the neuromuscular junction a chemical message is released by the motor neuron. The chemical message, a neurotransmitter called acetylcholine, binds to receptors on the outside of the muscle fiber. That starts a chemical reaction within the muscle.

Question 38

What is the source of the Calcium that permits cross-bridge binding?

Answer 38

The sarcoplasmic reticulum stores calcium ions, which it releases when a muscle cell is stimulated; the calcium ions then enable the cross-bridge muscle contraction cycle.