Muscle Organization And Contraction

Question 1

What are skeletal mucscles composed of

Answer 1

They’re usually anchored to the bones
Made of :

Muscle fibres

Myofibrils

Sarcomeres

Question 2

What are muscle fibres

Answer 2

A skeletal muscle cell made of hundreds to myofibrils

Question 3

What are myofibrils

Answer 3

Made of actin and myosin and composed of repeating contractile units called sarcomeres

Question 4

What are sarcomeres

Answer 4

contractile unit the has a characteristic banding pattern

Make up myofibrils

Question 5

What are the thick and thin filaments of sarcomeres

Answer 5

Thick: purple myosin

Thin: orange actin

Question 6

How far does one sarcomere extend

Answer 6

From one z line to the other z line

All other components are inside this boundary

Question 7

What is the z line of sarcomeres

Answer 7

Contains the proteins that are important for the sarcomeres structure and stability

Question 8

What is the m line of the sarcomere

Answer 8

Dark line down the centre of the sarcomere

Contains anchoring protiens

Question 9

What are the i bands of the sarcomere

Answer 9

They light stain

Contain only the thin actin filaments with the + end pointing towards the z lines

Between the a band and the z line

Question 10

What is the h zone

Answer 10

Contains only thick filaments

Surrounds the m line

Inside the A band

Question 11

What is the A band

Answer 11

Dark staining

Overlap of thick and thin filaments also includes the H zone

Question 12

In a sarcomere each myosin thick filament is surrounded by

Answer 12

6 thin actin filaments

Question 13

When a muscle is contracted which zones in the sarcomere decrease in length

Which don’t change

Answer 13

I band and h zone (this means the thin filaments slide toward the centre of the sarcomere)

The a band

Question 14

Myosin 2 is non processive, what does this mean

Answer 14

It’s only in contact with actin for a fraction of the time

Meaning different myosin heads are acting at different times (not synchronized)

This causes the smooth sliding of the actin filaments to the centre of the sarcomere for contraction

Question 15

How far does a single myosin power stroke move an actin filament

Answer 15

10nm (large distance)

Question 16

What does the neck of the myosin filament act as

Answer 16

Acts as a lever to move the actin filament to the center and enhance the power stroke to move it a great distance

Question 17

What is step 1 of the actin myosin contraction cycle

Answer 17

Myosin is attached to the actin

ATP binds to the myosin head and the myosin dissociates from the actin

Question 18

What is step 2 of the actin myosin contraction cycle

Answer 18

The atp is hydrolyzed by the myosin head and ADP and Pi are still bound to the myosin

Question 19

What is step 3 of the actin myosin contraction cycle

Answer 19

The hydrolysis of the atp energized the myosin so that it can bind to actin again

Question 20

What is step 4 of the actin myosin contraction cycle

Answer 20

The Pi that was bound to the myosin leaves

This trigger a power stroke which helps the actin move towards the centre of the sarcomere

Question 21

What is step 5 of the actin myosin contraction cycle

Answer 21

The adp still on the myosin head is released and once atp is introduced the cycle continues again

Question 22

What do motor neurons do

Answer 22

There are muscle fibres within a motor unit

these motor units get stimulated by a single motor neuron

The motor neuron stimulates many muscle fibres/cells at the same time

Question 23

What is a neuromuscular junction

Answer 23

The point where the motor neuron and muscle fibre contact each other

The site of transmission of the nerve impulse that stimulates the muscle cell

Question 24

What gets transferred from a. Motor neuron to a muscle cell to get it stimulated?

Answer 24

Neurotransmitters (such as acetylcholine)

These stimulate an action potential to occur to excite the muscle cell

Question 25

Once a nerve impulse has arrived at a muscles cell, what happens

Answer 25

Excitation contraction coupling

The nerve impulse travels through to the transverse tubules (t-tubules) that are basically membrane folds that bring the impulse to the inside of the muscle cell

It’s brought to the sarcoplasmic reticulum

Question 26

What is the sarcoplasmic reticulum

Answer 26

The special smooth ER in muscle cells that stores Ca2+ in its lumen

The ca is pump into the lumen from the cytosol

Question 27

After the action potential reaches the sarcoplasmic reticulum what happens

Answer 27

The presence of the action potential opens the Ca2+ channels

The ca from the sarcoplasm in the SR move into the cytoplasm out side the SR

The myofibrils are now bathing in calcium

Question 28

The thin filaments contains actin and what else

Answer 28

Tropomyosin (rod)

Troponin (globular)

Question 29

What does the presence of calcium do for muscle contraction

Answer 29

It controls the interaction between the myosin heads and the actin

Question 30

In the absense of calcium what happens

Answer 30

Troponin controls the position of tropomyosin which blocks the myosin head binding sites on actin

Stops the head from binding the actin by controlling tropomyosin

This cause a resting relaxed stat of the miscle

Question 31

In the presence of calcium what happens

Answer 31

Them the myofibrils are bathing in the newly released calcium

So the ca binds to Troponin which then moves tropomyosin so it’s not blocking the myosin head binding site anymore

The head can now bind to the actin and undergo the power stroke atp cycle to contract the muscle