PRACTICE QUIZ UNIT 16

Question 1

The sarcoplasmic reticulum in skeletal muscle fibres is used for what

Answer 1

Storing Ca2+

Question 2

Regulatory protein only found in thin filaments of skeletal muscle fibres

Answer 2

Tropomyosin and troponin

Question 3

Connective tissue layer surrounding fascicle

Answer 3

Perimysium

Question 4

Inflated ends of sarcoplasmic reticulum

Answer 4

Terminal cisternae

Question 5

In NT junctions, synaptic vesicles containing acetylcholine are suspended in

Answer 5

Synaptic end bulb

Question 6

Sequence of structures that action potential must move through to excite skeletal muscle contraction

Answer 6

Axon of neuron, sarcolemma, T tubules

Question 7

What structure release calcium to trigger skeletal muscle contraction

Answer 7

Terminal cisternae of SR

Question 8

When are calcium ions released from SR into cytosol

Answer 8

At the beginning of a contraction

Question 9

What energizes the myosin head

Answer 9

ATP hydrolysis reaction

Question 10

What two chemicals decide how long the skeletal muscle contractions will occur

Answer 10

As long as the calcium ions and ATP are available in cytosol of muscle fibre

Question 11

Order of NT junction

Answer 11

1. Nervous action potential arrives at synaptic end bulb
2. ACH released from synaptic vesicles
3. ACH binds to ACH receptor
4. Muscle action potential is produced

Question 12

Difference between tropomyosin and troponin

Answer 12

Tropomyosin blocks the myosin binding sites when muscle not contracting, and troponin acts as sites for calcium ions to bind and exposes the myosin binding sites on actin

Question 13

Rotation of myosin heads towards M line

Answer 13

Power stroke

Question 14

Structure of neuromuscular junction

Answer 14

• THE SYNAPTIC END BULB OF THE AXON TERMINAL OF THE MOTOR NEURON MEETS THE SARCOLEMMA OF A MUSCLE FIBER AT THE NEUROMUSCULAR JUNCTION.
• THE SMALL SPACE BETWEEN THE SYNAPTIC END BULB AND THE SARCOLEMMA IS FILLED WITH EXTRACELLULAR FLUID AND TERMED THE SYNAPTIC CLEFT.
• THE PRESYNAPTIC MEMBRANE OF THE SYNAPTIC END BULB SITS ON ONE SIDE OF THE SYNAPTIC CLEFT.
• THE POSTSYNAPTIC MEMBRANE OF THE SARCLEMMA SITS ON THE OTHER SIDE OF THE SYNAPTIC CLEFT.
• THE POSTSYNAPTIC MEMBRANE AREA IS CALLED THE MOTOR END PLATE AND CONTAINS FOLDINGS OF THE SARCOLEMMA CALLED JUNCTIONAL FOLDS.
• EMBEDDED IN THE SARCOLEMMA AT THE MOTOR END PLATE ARE ACETYLCHOLINE RECEPTOR PROTEINS.

Question 15

Calcium functions in muscle contraction

Answer 15

• Calcium ions trigger exocytosis of ACH into synaptic cleft
• Calcium ions bind to troponin and expose myosin binding site on actin

Question 16

Steps involved in contraction cycle

Answer 16

1. ADP AND INORGANIC PHOSPHATE (PRODUCTS OF ATP HYDROLYSIS) ATTACH TO THE MYOSIN HEAD, ENERGIZING IT.
2. ENERGIZED MYOSIN HEAD AND ACTIN SPONTANEOUSLY FORM A CROSSBRIDGE.
3. PHOSPHATE LEAVES THE MYOSIN HEAD, STRENGTHENING THE CROSSBRIDGE.
4. ADP LEAVES THE MYOSIN HEAD, COUSING THE POWER STROKE.
5. POWER STROKE PUSHES THE THIN FILAMENT TOWARDS THE M-LINE, SHORTENING THE
   SARCOMERE.
6. ATP UNDEGOES HYDROLYSIS AND BREAKS THE CROSSBRIDGE.
7. GO TO STEP 1