Lect 8 - Skeletal Muscle Structure & Function

Flashcards covering the structure and function of skeletal muscles.

Features of smooth muscle?

Muscles lining hollow organs, nor under voluntary control

Features of cardiac muscle?

Muscles located in the heart —> generate force to pump blood around the body, not under voluntary control

Features of skeletal muscle?

Muscle applies force to bones to control posture and body movements, voluntary control, support and protect soft internal organs, allows the passage of substances in or out of the body, converts energy to heat —> used to maintain core temperature

What are muscle fibres comprised of?

Bundles of myofibrils

What makes up myofibrils?

Repeating units (sarcomeres)

What are the contractile proteins that make up sarcomeres?

Actin (thin filament) and Myosin (thick filament)

What gives muscle its striated appearance?

Organisation of myofilaments

What is the function of transverse tubules (T-tubules)?

Tub-like extensions of the sarcolemma that conduct electrical signals (action potentials) deep into the core of the fibre

What is the job of the sarcoplasmic reticulum (SR)?

To take up and store calcium (Ca2+) while the muscle is relaxed, and then release calcium into the cytoplasm when the muscle contracts

What is the function of the voltage-gated sensor (DHPR) in excitation-contraction coupling?

Receives signals from the T-tubules and interacts with the ryanodine receptors

What is the function of the ryanodine receptor (RyR)?

A passive calcium channel on the SR that can open to allow Ca2+ out into the cell

What is the function of the SR calcium-ATPase (SERCA)?

An active calcium pump that uses ATP to move Ca2+ back into SR against its concentration gradient

What is the 9 step process of Excitation–contraction coupling in order?

1. Signal transmitted down T-tubules. 2. Excitation signal moves inside the cell. 3. Voltage sensor (DHPR) is activated. 4. Active DHPR interacts with ryanodine receptors (RyR). 5. RyR opens, calcium pours out of SR. 6. Calcium activates myofilaments 7. SERCA Senses rise in intracellular calcium 8. SERCA pumps calcium back into the SR, against the concentration gradient 9. This removes the calcium from the cell, stopping the signalling event and allowing the muscle to relax

What are individual muscle cells?

Muscle fibres

Muscle fibres bundle to become…?

Fascicles

Fascicles bundle to become…?

Muscles

Whole muscle structure?

Fibres, fascicles, and muscles contain blood vessels and nerves which are sheathed in connective tissue —> gathers together to make tendons

What is the sarcolemma?

The cell membrane of the muscle fibre

What is the structure of the sarcoplasmic reticulum (SR)?

An extensive membrane network associated with the T-tubules at regular intervals