W5-L1: Muscle

Question 1

Cardiac vs skeletal vs smooth muscle

Answer 1

Cardiac

• Only in the heart
• Involuntary
• Striated
• Contract or shorten
• Under nonconscious regulation

Skeletal

• Voluntary control
• Striated
• Contract or shorten

Smooth

• Non-striated appearance
• Involuntary
• Under nonconscious regulation

Question 2

What are the 3 layers of Skeletal Muscle Architecture?

Answer 2

Endomysium:
connective tissue that wraps around each muscle fibers

Perimysium:
surrounds a bundle of up to 150 fibers called fascicles

Epimysium:
surrounds entire muscle

fiber size increases but not the number

Question 3

What is chemical composition of muscle?

Answer 3

• 75% water
• 20% protein
• 5% salts and other substances, including highenergy phosphates

Question 4

What are the proteins found in muscle?

10

Answer 4

titin, myosin, actin, and tropomyosin, myoglobin, troponin,
a-actinin, V-actinin, M protein, C protein

Question 5

Skeletal Muscle Ultrastructure

What are myofibrils?

Answer 5

Single multinucleate muscle fiber contains myofibrils that lie parallel to fiber’s long axis

Question 6

What are myofilaments?

Answer 6

Myofibrils contain smaller subunits called myofilaments that lie parallel to long axis of myofibril

Question 7

What are the components of the myofilaments?

Answer 7

actin and myosin

Question 8

What are the components of the muscle from superficial to deep?

Answer 8

Muscle fiber –> Myofibrils -> Myofilaments (actin and myosin)

Question 9

The Sarcomere

What are the bands of The Sarcomere?

Answer 9

I band represents lighter area

A band represents darker area

M band consists of protein structures that support arrangement of myosin filaments

Z line bisects I band and adheres to sarcolemma to provide structural stability

Question 10

What is defined as one sacromere?

Answer 10

• Sarcomere consists of basic repeating unit between two Z lines; comprises the functional unit of a muscle fiber
• Sarcomeres lie in series and their filaments have a parallel configuration within a given fiber
• Sarcomere length determines the muscle’s functional properties

Question 11

Sarcomere structure

Answer 11

only 1 I band

Question 12

Filament structure – Thick filament

What is known as the thick filament?

4

Answer 12

• Composed of protein myosin
• Has 2 large polypeptide heavy chains and 4 small light chains
• They form 2 globular heads and a long tail
• 2 binding sites

Question 13

Filament structure - thin filaments

What makes up the thin filament?

Answer 13

protein constituents:

actin: helical arrangement binding site for myosin

tropomyosin: blocks myosin-binding site on actin (at rest)

troponin

Question 14

What are the regulatory proteins of the body?
(check that)

Answer 14

troponin and tropomyosin

Question 15

What is the sliding filament mechanism?

Answer 15

The theory proposes a muscle shortens or lengthens because thick and thin filaments slide past each other without changing length. The myosin cross bridges cyclically attach, rotate, and detach from the actin filaments with energy from ATP hydrolysis and provide the molecular motor to drive fiber shortening.

key

Question 16

What is a power stroke?

Answer 16

power stroke pulls thin filaments towards center of sarcomere

Question 17

How are Crossbridges formed?

Answer 17

• Globular myosin heads extend perpendicularly to latch onto actin strands to create a structural and functional link between myofilaments
• ATP hydrolysis activates myosin’s two heads, placing them in an optimal orientation to bind actin’s active sites
• pulls thin filaments and Z lines of sarcomere toward middle
• Tropomyosin and troponin regulate make-andbreak contacts between the myofilaments during muscle action

Question 18

All sarcomeres contract simultaneously.
What happens to the zones?

Answer 18

H zone and I band decrease, eventually disappear

The A band stays the same length during muscle contraction because it represents the length of the myosin filaments, which do not change in length but instead slide past the actin filaments.

Question 19

What is sacroplasmic reticulum?

Answer 19

stores and releases calcium

Lateral end of tubule channel within muscle fiber terminates in saclike vesicle that stores Ca2+

Question 20

What is a T-tubule?

Answer 20

T-tubule system runs perpendicular to myofibril; functions as microtransportation network by spreading action potential from outer membrane

Question 21

How does muscle contraction initiate?
What causes the muscle to relax?

Answer 21

• Ca2+ is released and diffuses a short distance to “activate” actin filaments
• Muscle action begins when myosin filament crossbridges attach to active sites on actin
• Electrical excitation ceases, Ca2+ concentration in cytoplasm decreases, and the muscle relaxes

Question 22

What is the Intracellular Tubule Systems?

Answer 22

• Lateral end of tubule channel terminates in saclike vesicle that stores Ca2+
• T-tubule system functions as microtransportation network by spreading action potential from outer membrane
• Ca2+ is released to “activate” actin filaments
• Muscle action begins when myosin filament crossbridges attach to active sites on actin
• Electrical excitation ceases, Ca2+ concentration in cytoplasm decreases, and the muscle relaxes

Question 23

What powers cross bridge formation?

Answer 23

Globular head of myosin crossbridge provides mechanical power stroke for actin and myosin to slide past each other

Cyclic, oscillating to-and-fro motion of crossbridges powered by ATP hydrolysis

Question 24

What is actomyosin?

Answer 24

About 50% of crossbridges make contact with actin to form protein complex actomyosin

Question 25

Sequence of Muscle Action Events

Answer 25

check 131 notes