Lecture 7

Question 1

What is a Sarcomere?

Answer 1

Basic unit of striated muscle

Question 2

Hundreds of thousands of sarcomeres are arranged in a

Answer 2

Repeated pattern over and over again

Question 3

Z-disks function to

Answer 3

Provide plate for actin filaments to attach to

Question 4

The Sliding filament model is the

Answer 4

Sequence of events in actin-myosin based muscle contraction

Question 5

Myosin molecule extends by

Answer 5

Straightening its neck

Question 6

A cross bridge is formed when

Answer 6

Myosin head forms a bond with actin filaments

Question 7

What happens when Myosin pulls on the Actin filaments?

Answer 7

The two Z-disks are pulled together, shortening the sarcomere

Question 8

A power stroke is when

Answer 8

The myosin head pulls on the filament

Question 9

The arrangement of actin and myosin before contraction determines the

Answer 9

Contraction force

Question 10

What happens if the arrangement of actin and myosin is disrupted?

Answer 10

The force generated by each sarcomere in the muscle will decrease

Question 11

How is the force if Z-disks are originally too close?

Answer 11

Force will decrease because actin filaments will collide and there is no room for shortening

Question 12

How is the force if Z-disks are originally too far?

Answer 12

Force will decrease because myosin will not overlap with thin filaments and fewer cross-bridges will form

Question 13

The relationship between the length of the sarcomere before contraction and resulting force generated is

Answer 13

Bell shaped

Question 14

If the sarcomere is lengthened or shortened from this optimal length, the force of contraction will

Answer 14

Decrease

Question 15

What is a Myofibril?

Answer 15

Single continuous stretch of interconnected sarcomeres

Question 16

Myofibril are covered in a plasma membrane called a

Answer 16

Sarcolemma

Question 17

What are considered as muscle cells?

Answer 17

Myofibril

Question 18

What is the first step of muscle contraction?

Answer 18

AP travels down the motor neuron and reaches the axon terminal, triggering the release of Acetylcholine that has a receptor on the sarcolemma

Question 19

The binding of Acetylcholine to its receptor on the sarcolemma results in

Answer 19

A graded potential to form in the myofibril

Question 20

What happens if enough sodium enters the muscle cell?

Answer 20

The membrane potential will cross the threshold potential of -50 mV

Question 21

AP is formed in the muscle cell and consists of

Answer 21

Depolarization, repolarization and hyperpolarization

Question 22

Newly created AP spreads along the

Answer 22

Sarcolemma, down the T-tubules

Question 23

What happens when AP goes down the T-tubules?

Answer 23

This causes the release of Ca2+ from the Sarcoplasmic Reticulum through voltage-gated calcium channels on the SR

Question 24

What stimulates the sarcomeres to contract with the help of Troponin and Tropomyosin?

Answer 24

Released Ca2+

Question 25

What are Troponin’s three subunits?

Answer 25

• TnC: Ca2+ sensor that can bind to Ca2+
• TnI: blocks myosin binding site on actin
• TnT: Binds to tropomyosin, which keeps troponin associated with actin

Question 26

In a relaxed muscle, IC Ca2+ is

Answer 26

Low, with Ca2+ binding sites on TnC open

Question 27

Low Ca2+ results in

Answer 27

TnI blocking myosin binding sites on actin

Question 28

When Ca2+ leaves SR and enters muscle, it binds to

Answer 28

TnC

Question 29

What happens when Ca2+ binds to TnC?

Answer 29

This binding induces a conformational change where TnI moves away from the myosin binding site on actin by sliding down tropomyosin, exposing the myosin binding site on the actin

Question 30

Muscle contraction is stopped via the enzyme

Answer 30

Acetylcholinesterase

Question 31

Acetylcholinesterase functions to

Answer 31

Break the acetylcholine bound to the acetylcholine receptor

Question 32

With acetylcholine broken down, ligand-gated Na+ channels close, stopping

Answer 32

Graded potentials from forming, further stopping AP from being created

Question 33

Without AP, Ca2+ moves back into

Answer 33

The SR

Question 34

Without AP, Ca2+ levels inside the muscle

Answer 34

Lower, causing Ca2+ binding sites on TnC to be available

Question 35

Myosin binding sites on actin are blocked by TnI when

Answer 35

Ca2+ levels are low