Lecture 26: Skeletal muscle activation

Question 1

What is a motor unit?

Answer 1

A single motor neuron and the skeletal muscle fibres it inneravates

Question 2

A muscle fibre is innervated by only ONE:

Answer 2

neuron

Question 3

When one motor neuron innervates multiple muscle fibres it indicated precision of:

Answer 3

function

Question 4

What is the function of t-tubules?

Answer 4

• allow AP to move deeper into the cell

- triggers the release of Ca+ from adjacent sacs in the sacroplasmic reticulum

Question 5

What occurs in excitation?

Answer 5

• AP depolarise the presynaptic bouton
• depolarisation triggers the voltage-gated Ca+ channels to open
• influx of Ca+ triggers vesicles to move and fuse with the membrane releasing neuron tranmitters via exocytosis
• Ach is released and binds to nictonic receptors on the adjacent sacrolemma
• AP is induced across the sacrolemma

Question 6

What occurs in contraction

Answer 6

• Ca+ is released from the sacroplasmic reticulum
• Ca+ binds to troponin —-> tropin tropomyosin complex
• causes a shift in the tropomyosin - shift exposes active binding sites on the actin filament
• energised myosin heads bind to exposed active sites —–> crossbridge
• pull actin past itself —-> Z lines mover closer—-> contraction

Question 7

What occurs in relaxation

Answer 7

• Reuptake of Ca+ into internal stores
• ATP is required to pump Ca+ against its concentration gradient —-> no cross bridges
• ATP binds to myosin which detaches breaking cross bridges

Question 8

What processes require ATP

Answer 8

• Contraction & Relaxation