Muscular System G.R.

Answers

Chapter 12

1. Arrange these skeletal system components in order, from outermost to innermost: sarcolemma, connective tissue sheath, myofilaments, myofibrils

Connective Tissue– Sarcolemma

Myofibrils–Myofilaments

2. Why are the ends of the A band the darkest region off the sarcomere when viewed under a light microscope?

That is the region where there is overlap between the thick and thin filaments.

3. What are the characteristics of the three types of muscles in the human body? Where is each type found?

Skeletal: Striated, multi-nucleated, voluntary movements– Attached to skeleton

Cardiac: Striated, branched, intercalated disks, uni-nucleated, involuntary– Walls of heart

Smooth: non-striated, stacked, uni-nucleated, involuntary– Walls of internal organs

4. What are the microscopic levels of structure in a skeletal muscle?

Thick Filaments: myosin chains Thin Filaments: actin Sarcomere: contractile unit (Z-disk - Z-disk)

– I-Band: thin filaments only– H-zone: thick filaments only– A-band: entire length of thick filaments– Z-Disk: attachment site for thin

filaments– M-Line: attachment site for thick

filaments

5. How does contraction of a skeletal muscle come about?

Initiated by Motor Neuron synapsing at neuromuscular junction.– ACh is released and binds to receptor of

sarcolemma– Action potential travels down sarcolemma and

T-tubules– DHP receptors (voltage-sensitive) trigger

Calcium release from S.R.– Ca2+ binds to troponin, opening up binding site

for myosin head, leading to Power Stroke:ATP hydrolyzed, Myosin head attaches to

actin, ADP and Pi released power stroke occurs pulling the actin filaments.

6. What is the role of ATP in muscle contraction?

ATP is the energy source for the power stroke.

When ATP is hydrolyzed it produces potential energy that powers the movement of the myosin head.

ATP binding to myosin causes the myosin head to return to resting position

7. Compare and contrast the different ways our muscle cells produce ATP.

1. Creatine Phosphate– Anaerobic– Creatine phosphate broken down to produce

ATP– Short-term high intensity exercise (5 secs)

2. Fermentation– Glucose broken down to Lactate

anaerobically– 2 ATP produced per glucose– Glycogen is broken down to produce the

glucose– Fast-acting

3. Cellular Respiration– Aerobic– Oxygen delivered to Mitochondria via

myoglobin– Glucose comes from either stored

glycogen, glucose from blood, and/or fatty acids from fat digestion.

– 32 ATP produced per glucose!!– Slower acting

8. How are slow-twitch and fast-twitch designed to perform their respective roles?

Fast Twitch: – Motor units with many fibers– Anaerobic = explosions of energy, but

fatigue easily– Strength– Pump Ca2+ into S.R. more quickly =

faster twitches

Slow-Twitch– Large amounts of myoglobin (an

oxygen-transport protein to the mitochondria)

– Large amounts of mitochondria– Aerobic respiration– High resistance to fatigue– Used for posture and endurance sports

9. Describe the sliding filament model of muscle contraction within a sarcomere. Begin with nerve impulses and end with the relaxation of the muscle.

Refer back to earlier question of Calcium exiting S.R. and binding to troponin, which moves tropomyosin and allows myosin to bind to actin.

ATP is hydrolyzed, myosin head binds to actin

Power Stroke: Myosin head pulls actin towards the M-Line; ADP and Pi are released

ATP binding causes myosin head to return to resting rate.