Chapter 45

Question 1

Movement

Answer 1

way for animals to respond to stimuli from
their environment

Question 2

Locomotion

Answer 2

movements generated by muscle contraction
are key innovations in animal evolution

Question 3

Muscle & skeletal systems

Answer 3

work together to produce movement

Question 4

What is the skeletal system stimulated to contract by

Answer 4

Nervous system

Question 5

Muscle structure

Answer 5

Consists of a bundle of long fibers, each a
single cell, running the length of the muscle

Each muscle fiber is itself a bundle of
smaller myofibril

Question 6

Sarcomere

Answer 6

functional unit of muscle contraction

Bordered by z lines and made up of thin and thick filaments

Are the alternating light-dark units that produce the banded appearance of myofibrils, which are the strands that make up each muscle fiber.

Question 7

Thin filaments

Answer 7

Consists of 2 chains of the protein actin

One end of each thin filament is bound to Z disk,

which forms end of sarcomere & anchors the filament– Other end is free to interact with thick filamen

Question 8

Thick filament

Answer 8

Thick filaments composed of several strands of myosin

Myosin has two subunits: head & tail

Question 9

What happens when actin and myosin interact

Answer 9

Shortening of sarcomere and muscle contraction

Question 10

Process of Actin-Myosin interaction

Answer 10

1. When Ca2^+ ions are released, they bind to the protein complexes and allow binding of the myosin head to actin
2. The thin filament pulled toward the center of the sarcomere.
3. When the myosin head binds ATP, it detaches from actin
4. Then, the myosin head hydrolyzes ATP to ADP and Pi,
   which extends the myosin head and puts it in position to bind actin once again
5. The result of repeated cycles is the shortening of the sarcomere, and ultimately, contraction of the muscle.

Question 11

Troponin and Tropomyosin

Answer 11

Proteins in thin filaments that form a complex to block myosin binding sites so that the actin and myosin cannot slide past each other (muscle at rest.

When muscle contraction occurs, calcium ions are released to bind to troponin, causing a change in the troponin tropomyosin complex so that actin can interact with myosin (filaments can now slide against each other

Question 12

How do neurons cause muscle contraction

Answer 12

Action potential moves down the T tubules, it triggers Ca2+ channels in the sarcoplasmic reticulum to open

2. Ca2+ ions rush into the cytosol. and diffuse into the myofibrils, where they enable muscle contraction to begin, completing action potential
3. The Ca2+ channels in the sarcoplasmic reticulum close, and Ca2+ ions are again pumped back into the sarcoplasmic reticulum.
4. The cytosolic level of Ca2+ drops, Ca2+ ions diffuse out of the myofibrils, stopping muscle contraction.

Question 13

Synaptic terminal

Answer 13

• most distal portion of neuron’s axon and is critical for neural communication

-calcium floods neuron and allows synaptic vesicles to fuse with the membrane and release stored neurotransmitters to target cells

Question 14

Mitochondrian

Answer 14

Important sites for energy production needed to sustain normal muscle contraction.

Question 15

How nervous system causes muscle contraction

Answer 15

1. Action potential arrives at neuromuscular junction

2.. When it action potential reaches end of axon terminal, it causes release of neurotransmitter ACh from synaptic vesicles

3. The ACh molecules diffuse across the synaptic cleft and bind to the muscle fiber receptors, thereby initiating a muscle contraction.
4. It is initiated with the with the depolarization of the sarcolemma caused by the sodium ions’ entrance through the sodium channels associated with the ACh receptors.
5. The T tubules are periodic invaginations in sarcolemma where the propagation of an action potential occurs
6. T tubules carry action potential into interior of the cell and trigger opening of calcium channels in the membrane of adjacent SR causing Ca++ to diffuse out of the SR and into the sarcoplasm, where Ca++ initiates contraction of the muscle fiber by its sarcomeres

Question 16

T tubules

Answer 16

Drive propagation of an action potential

Carry action potential via voltage-gated Na+ and K+ channels

Question 17

Sarcoplasmic reticulum (SR)

Answer 17

membrane -bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca 2+).

Question 18

Three types of muscle

Answer 18

Smooth muscle
Cardiac muscle
Skeletal muscle

Question 19

Cardiac muscle

Answer 19

Location: Only in heart

Function: Pump blood

Characteristics
- Striated
- branched cells
- ends connected via intercalated discs
- Contains sarcomeres
- Activity is involuntary

Question 20

Smooth muscle

Answer 20

Location: Intestines, arteries

Function: Essential to function of lungs, blood vessels, digestive system, urinary bladder and reproductive system

Characteristics
- organized in thin sheets
- unbranched, unstriated and lack myofibrils
- action is involuntary and does not require a signal from motor neuron

Question 21

Skeletal muscle

Answer 21

Location: Attached to skeleton

Function: Move skeleton

Cell characteristics
- Multinucleate
- Striated
- Unbranched
- Contains sarcomeres
- Activity is voluntary
- attach to antagonistic pairs to bones

Question 22

Intercalated
discs

Answer 22

critical to flow of electrical signals from cell to cell to coordinate heartbeat (involuntary

Question 23

First step in the process of an action potential triggering muscle contraction

Answer 23

ACh released into the synaptic cleft is bound by receptors on the muscle cell. This stimulates opening of ligand-gated ion channels, which causes initial depolarization of the muscle cell.

Question 24

In muscle cells, myosin molecules continue moving along actin molecules as long as

Answer 24

ATP is present and the intracellular Ca2+
concentration is high.

Question 25

During contraction, what change in appearance is observed in the sarcomere?

Answer 25

The light band narrows.

Question 26

Why is the dark band in a sarcomere dark and the light band light?

Answer 26

The dark band includes thin filaments as well as thick filaments; the light band consists of thin filaments only.

Question 27

One way your body increases blood pressure is to contract muscles in large veins. What muscle tissue type will be responsible for this function?

Answer 27

Smooth muscle as it is responsible for blood pressure

Question 28

What causes myosin head to release form the action

Answer 28

Binding of ATP to myosin

Question 29

What causes the actin and myosin filaments to slide past one another during muscle contraction?

Answer 29

Release of inorganic phosphate from myosin as it causes the myosin head to pivot inward, pulling the thin filaments inward toward the center of the sarcomere.

Question 30

Sliding filament theory

Answer 30

1. ATP binds to myosin head and releases actin 2. ATP hydrolyze into inorganic phosphate and ADP and causes the head to pivot to new actin subunit 3. When inorganic phosphate is released the head pivots to its original position and moves thin filament towards sarcomere 4. ADP is released and cycle is ready to repeat

Question 31

What is the molecular basis of muscle contraction

Answer 31

The interaction of myosin and thin filaments (actin)

Question 32

What does the motor neuron release into synapse to open channel in plasma membrane of muscle fiber to allow sodium ions into cell to trigger action potential

Answer 32

The neurotransmitter AT

Question 33

What happens in the power stroke of the sliding-filament model

Answer 33

occurs when the myosin head pivots, causing the actin filament to slide past the myosin filaments Characterized by when the phosphate ion is released and causes myosin head to move back to its original position

Question 34

What is the effect of the action potential on the T-tubules

Answer 34

causes T tubules to depolarize, which stimulates the sarcoplasmic reticulum to release calcium ions into the muscle cell.