Muscle Contraction

Question 0

What two types of protein filament do Myofibrils consist of?

Answer 0

Actin - thinner and consists of two strands twisted around one another
Myosin - thicker consists of long rid shaped fibrils with bulbous heads that project to the side

Question 1

What are muscles made up of?

Answer 1

Myofibrils

Question 2

Describe the process of muscle contraction?

Answer 2

• action potential opens calcium ion channels on endoplasmic reticulum and calcium ions flood into muscle down diffusion gradient
• calcium ions cause tropomyosin molecules blocking actin filaments binding sites to pull away
• ADP attached to myosin head binds to actin filament forms cross bridge
• now attached to actin filament myosin heads change angle pulling actin filament along as releasing the ADP
• ATP molecule attaches to myosin head causing it to detach from actin filament
• calcium ions activate ATPase to hydrolyse ATP to ADP providing energy for myosin head to change to original shape
• myosin head with ADP then reattached further along actin and cycle repeated

Question 3

What type of contractions do slow twitch muscles carry out?

Answer 3

Slowly and provide less powerful contractions over a long period

Question 4

What type of contractions do fast twitch muscles carry out?

Answer 4

Rapid and produce powerful contractions but only for short period

Question 5

What happens when nervous stimulation ceases?

Answer 5

• Calcium ions are actively transported back into endoplasmic reticulum using energy from hydrolysis of ATP
• reabsorption of calcium ions allows tropomyosin to block actin filaments
• myosin heads unable to bind so contraction ceases

Question 6

What are 4 adaptations of slow twitch muscles?

Answer 6

• Large store of myoglobin
• Supply of glycogen to provide energy
• Rich supply of blood vessels to deliver O2 and glucose
• Numerous mitochondria to produce ATP

Question 7

What are 3 adaptations of fast twitch muscles?

Answer 7

• Thicker more numerous myosin filaments
• high concentration of enzymes involved in anaerobic respiration
• store of phosphocreatine which can rapidly generate ATP providing energy for muscle contractions

Question 8

Why is the theory that muscle contraction is due to filaments themselves shortening my true?

Answer 8

The A-band remains the same width as the width of this band is determined by the length of myosin and the myosin filaments have not become shorter

Question 9

What’s a neuromuscular junction?

Answer 9

The point where a motor neurone meets a skeletal muscle fibre