Muscles and Blood Glucose

Question 1

When the action potential arrives at the neuromuscular junction, it results in the secretion of acetylcholine into the synaptic cleft. Explain how (3)

Answer 1

• the presynaptic neurone depolarises
• Ca2+ channels open
• Ca2+ diffuses in
• vesicles fuse with acetylcholine in to presynaptic membrane

Question 2

Explain what causes the decrease in length for the I band and H zone? (2)

Answer 2

• The actin filaments slide in between the myosin filaments
• The Z-lines are pulled closer together
• The thin (actin) filaments enter the H zone

Question 3

Explain the importance of ATPase during muscle contraction (2)

Answer 3

• ATPase speeds up the hydrolysis of ATP to ADP

- The energy released is used for the myosin head to return to its normal position

Question 4

Describe how the banding pattern will be different when the muscle fibril is contracted (2)

Answer 4

• The H zone narrows

- The I (light band) narrows

Question 5

Describe what causes the different bands seen in the muscle fibril (2)

Answer 5

• The A band is darker because both Actin and Myosin overlap
• The I bands are lighter because it only contains Actin and proteins don’t overlap
• The H-zones only contains Myosin

Question 6

Describe the part played by Myosin in Myofibril contraction (2)

Answer 6

• The myosin heads bind with actin filaments to form an actin-myosin cross-bridge
• The myosin detaches when ATP is attached to the myosin so it can bind further along the actin

Question 7

Describe the part played by Tropomyosin in myofibril contraction (2)

Answer 7

• Prevents the myosin head from attaching to its binding site on the actin filament
• Moves away from the binding site when Ca2+ binds to it

Question 8

Explain how glucagon would affect a person’s blood glucose concentration (2)

Answer 8

• Glycogen is converted into glucose

- Glucose is converted from a non-carbohydrate (Gluconeogenesis)

Question 9

What is negative feedback (1)

Answer 9

A change to the normal level initiates a response which reduces the effect and goes back to the normal level.

Question 10

Explain the importance of the distribution of mitochondria inside the slow muscle fibres (3)

Answer 10

• The mitochondria are near the outside
• So there’s a short distance for diffusion of oxygen
• The oxygen is used by the mitochondria (in the electron-transport chain)

Question 11

You could use an optical microscope and a slide of stained muscle tissue to find the diameter of one of the muscle fibres. Explain how (2)

Answer 11

• Measure with graticule

- Calibrate against something of a known size

Question 12

Give two ways in which people with type 1 diabetes control their blood glucose concentration (2)

Answer 12

• Treat with insulin injections

- Control sugar intake

Question 13

Both slow and fast muscle fibres contain ATPase. Explain why (2)

Answer 13

• Muscle contraction requires ATP

- Myosin requires ATP

Question 14

Describe the role of calcium ions and ATP in muscle contraction (5)

Answer 14

• Ca2+ moves the tropomyosin away from the binding site of the myosin
• Allows the myosin heads to attach to actin filaments
• The binding of ATP causes the myosin head to detach from the actin
• The hydrolysis of ATP releases energy to change the myosin heads configuration