Lect 9 - Skeletal Muscle; Contraction, Tension, Fibre Types

Flashcards covering actin-myosin interaction, cross-bridge cycling, recruitment, frequency of stimulation, length-tension relationship, and fibre types.

Actin

Thin filament with a rope-like structure that runs along the myofilament.

Myosin

Thick filament that acts as a motor molecule to create contraction by hooking onto actin and pulling.

What happens when calcium is present?

Actin and myosin bind together, allowing contraction to occur.

Attached State

Myofilament has just finished a power stroke; actin/myosin cross-bridges are still present.

Released State

A molecule of ATP binds to myosin, causing the myosin head to release actin; actin/myosin cross-bridges are not present.

Cocked State

The myosin head burns ATP to make energy, storing the energy by changing shape to prepare to pull on actin again; actin/myosin cross-bridges are not present.

Cross-Bridge State

The energised myosin head can now bind to actin, forming a cross-bridge and initiating a contraction.

Power-Stroke State

The myosin uses its stored energy to pull, causing the actin filament to slide, shortening the sarcomere, and resulting in contraction.

Recruitment

The process of activating more muscle fibers to generate greater force by activating more neurons

What happens when action potentials fire in rapid sequence?

Many action potentials fired in rapid sequence that results in a sustained release of Ca2+ from the SR, a sustained period of actin-myosin interaction, and a sustained period of contraction (summation)

Tetanus

Maximal signaling and contraction capability of the muscle where force plateaus.

Length-Tension Relationship

Each muscle has an optimal length where it will be strongest, becoming weaker when either longer or shorter.

Fast Fibres:

fibre diameter:

capillary supply:

mitochondria:

colour:

fatigue resistance:

time to peak tension:

fibre diameter: large

capillary supply: few

mitochondria: few

colour: white

fatigue resistance: low

time to peak tension: fast

Slow Fibres:

fibre diameter:

capillary supply:

mitochondria:

colour:

fatigue resistance:

time to peak tension:

fibre diameter: small

capillary supply: many

mitochondria: many

colour: red

fatigue resistance: high

time to peak tension: slow

What are the steps of cross-bridge cycling in order starting from the attached state?

1. Attached state

2. Released state

3. Cocked state

4. Cross-bridge state

5. Power-stroke state

6. Attached state