Lecture 7: Skeletal Muscle Excitation-Contraction Coupling

What is the structure of the muscle?

fascicle -> muscle fiber cell -> myofibril

True or false: sarcomere is well preserved among species

true

1 multiple choice option

What does the striated appearance of skeletal muscles reflect?

banding of actin and myosin filaments

What are A bands?

dark bands where mysoin and actin overlap

What are I bands?

light bands where only actin reside

What is the Z line?

anchors thin filaments between sarcomeres

What is the M line?

middle of sarcomere where mysoin attaches (contains creatine kinase)

What is the H band?

middle of sarcomere that decreases when contracts (between actin on each side of sarcomere)

How many thick filaments are connecting to one thin filament?

3

How many thin filaments connect to a thick filament?

6

What is the intermyofibrillar space?

between myofibrils and contains SR, mitochondria, glycogen, lipids

What makes up intermediate anchoring filaments?

vimentin, desmin, vinculin

What do vimentin, desmin, and vinculin do?

create scaffolding to stabilize and organize myofibrils especially around the Z lines

What is titin?

elastic protein, that anchors M bands and prevents overstretching; also keeps thick filament where it is supposed to be

What are the structural features of myosin?

2 polypeptides in alpha helix arrangement with globular head region (ATP binding site)

What degree do myosin heads in relation to actin chain?

60 degrees (and then move to 90 degrees to contract)

How are actin filaments structured?

G actin, 2 F-actin that form an alpha helix

What is tropomyosin?

long fibrous protein that spans actin myosin binding sites

What happens to tropomyosin when the muscle relaxes?

it is elevated out of the actin helical groove

What binds to move troponin, free up tropomyosin?

Ca

What is the sarcolemma?

outer membrane of a muscle cell

How are each muscles cells connected?

the sarcolemma is attached to the endomysium (tissue that surrounds each muscle fiber) through CT and through the t-tubule system to allow an AP to travel throughout

What is dystrophin?

Links thin filaments to proteins of sarcolemma

Why is dystrophin important?

it provides structure and stability by linking the actin filaments to the sarcolemma (cell membrane) and then to the EC matrix; it basically links the internal structures to the external structures to allow for a concise, coordinated contraction between muscle cells