Ch. 20

Question 1

Define striated muscle

Answer 1

Muscle that consists of cells in which the thick myosin and thin actin filaments are arranged in sarcomeres (in vertebrates, skeletal and cardiac muscle)

Question 2

Name and define the three muscle types

Answer 2

Skeletal - produces locomotory movements or other external movements of the body, attached to the endoskeleton within vertebrates

Smooth - consists of small, spindle-shaped uninucleate cells without any striations (myosin and actin present, but not organized into sarcomeres), found in hollow organs such as the intestine

Cardiac - forms the wall of the heart, consists of striated cells connected by intercalated discs

Question 3

Define myofibril

Answer 3

Longitudinal component of a striated muscle cell that consists of a series of sarcomeres and extends the length of the cell

Question 4

Define sacromere

Answer 4

The contractile unit of striated muscle that consists of contractile, regulatory, and cytoskeletal proteins running in series separated by Z discs

Question 5

Define thin filament

Answer 5

Polymers of G-actin monomers in muscle cells

Question 6

Define thick filament

Answer 6

Polymers of myosin molecules in muscle cells

Question 7

Define cross bridges

Answer 7

The head of a myosin molecule interacting with actin molecules to produce muscle contraction

Question 8

Define excitation-contraction coupling

Answer 8

The linkage of electrical excitation of the cell membrane with contractile activity facilitated by available Ca2+ in the cytoplasm

Question 9

Define isometric contraction

Answer 9

A contraction in which a muscle does not shorten significantly as it exerts force (tension) against a load it cannot move

Question 10

Define isotonic contraction

Answer 10

A contraction in which muscle force remains constant as the muscle changes length, rarely occurring in nature

Question 11

Define intercalated disc

Answer 11

An intercellular contact between adjacent cardiac muscle fibers of vertebrates that contains desmosomes and gap junctions

Question 12

Define motor unit

Answer 12

A motor neuron and all the muscle fibers it innervates

Question 13

Name the order of muscle structure from largest to smallest.

Answer 13

1. Muscle
2. Muscle fiber
3. Myofibril
4. Sarcomere
5. Myofilaments (actin and myosin)

Question 14

What are Z lines?

Answer 14

Indicators of the start and finish of a single sarcomere

Question 15

What are I bands?

Answer 15

Contain only thin filaments

Question 16

What are A bands?

Answer 16

Contain thin and thick filaments

Question 17

What is the H zone?

Answer 17

Contains only thick filaments

Question 18

What is the M line?

Answer 18

Splits the H zone in half

Question 19

What are the three key proteins within thin filaments?

Answer 19

Actin (g-actin), troponin, and tropomyosin

Question 20

How many binding sites does the myosin cross-bridge contain?

Answer 20

Two; one for ATP and one for actin

Question 21

Which bands shorten during a contraction?

Answer 21

I and H bands

Question 22

Define rigor

Answer 22

A state of constant contraction that occurs when there is no ATP available to release myosin from actin

Question 23

Describe the step at which the cross-bridge cycle is typically found.

Answer 23

ATP has been hydrolyzed, so myosin is loosely bound to actin and waiting for Ca2+ to continue the cycle

Question 24

What would happen to a muscle without ATP?

Answer 24

Stuck in rigor without ATP releasing cross bridge

Question 25

What would happen to a muscle without ATPase?

Answer 25

Stuck in relaxed state without ATP hydrolysis

Question 26

What would happen to a muscle without calcium ions?

Answer 26

Stuck in relaxed state without Ca2+ to initiate power stroke

Question 27

What does tropomyosin do?

Answer 27

Blocks myosin-binding sites in g-actin until moved by troponin-Ca2+

Question 28

What does troponin do?

Answer 28

When bound to Ca2+, it shifts tropomyosin to expose myosin-binding sites to initiate the power stroke

Question 29

________ is released by motor neurons in an action potential.

Answer 29

Acetylcholine

Question 30

How does initial sarcolemma depolarization occur?

Answer 30

Acetylcholine binds to its receptors, which opens Na+/K+ channels to depolarize the membrane

Question 31

How is DHPR activated?

Answer 31

DHPR is voltage-sensitive, so depolarization of the sarcolemma continues into the t-tubules to change its conformation

Question 32

How are RyR calcium channels opened in the SR?

Answer 32

Activated DHPR goes through a conformation change, which allows RyRs to open and release calcium ions into the cytoplasm

Question 33

Muscle contraction _________________ (uses/produces) a lot of energy.

Answer 33

uses

Question 34

What metabolic pathways are used to supply ATP for muscle contraction? (3)

Answer 34

1. Creatine phosphate to creatine 2. Glycolysis 3. Oxidative phosphorylation

Question 35

Define tonic muscles

Answer 35

Postural muscles that can stay "on" for long periods of time, also found in fish, no action potentials

Question 36

Define a twitch

Answer 36

The mechanical response of a muscle to a single action potential

Question 37

Name the three types of twitch muscles

Answer 37

1. Slow oxidative 2. Fast oxidative glycolytic 3. Fast glycolytic

Question 38

Define muscle antagonism

Answer 38

One muscle shortens and an opposed muscle lengthens

Question 39

Define load

Answer 39

The object muscle exerts force onto

Question 40

Define tension

Answer 40

The force exerted on a load by muscle

Question 41

Describe isometric contraction

Answer 41

Elastic components remain the same, and sarcomeres contract

Question 42

Describe isotonic concentric contraction

Answer 42

Elastic components stretch inward, shortening sarcomeres

Question 43

Describe isotonic eccentric contraction

Answer 43

Elastic components stretch outward to prevent damage from heavier loads

Question 44

Describe load scaling

Answer 44

The same amount of force is not going to be used for the same two objects (i.e., 200-pound weight vs phone)

Question 45

Cardiac muscle cells are separated by what?

Answer 45

intercalated disc