Apologia Advanced Biology Module 5

Front 1

Contractility

Back 1

Muscle can contract (shorten) forcefully.

Front 2

Excitability

Back 2

This means it can be stimulated by nerves and hormones. This allows the nervous system and the endocrine system to control the muscle system.

Front 3

Extensibility

Back 3

Under normal conditions, it can be stretched out.

Front 4

Elasticity

Back 4

This means that when the muscles are extended beyond their normal length, they can recoil back to their normal length.

Front 5

three kinds of muscle tissue?

Back 5

skeletal muscle, smooth muscle, and cardiac muscle

Front 6

6 Skeletal Muscle Characteristics

Back 6

1. striated (striped)
2. multiple nuclei
3. arranged as many, long, cylindrical cells bundled together
4. several bundles enclosed in tough connective tissue sheath to form a muscle
5. they are responsible for voluntary movement
6. generally connected to bones via tendons.

Front 7

Belly of the muscle

Back 7

is composed of the actual muscle cells.

Front 8

Fascicles

Back 8

whole muscle is divided into bundles of cells

Front 9

Muscle fiber (cell)

Back 9

Very long compared with most other cells, up to several cm long, 10-100 micrometers in diameter

Front 10

Endomysium

Back 10

a thin collagen layer that wraps each cell.

Front 11

Perimysium

Back 11

the collagen layer that wraps each fascicle.

Front 12

Epimysium

Back 12

another collagen layer that wraps the perimysium fascicles and differentiates one muscle from the other.

Front 13

Fascia

Back 13

a sheet of tissue that lies underneath the skin.

Front 14

Sarcolemma

Back 14

which is the plasma membrane of the muscle fiber. The prefix “sarco” means literally “flesh” or “meat.”

Front 15

Sarcoplasmic reticulum

Back 15

the endoplasmic reticulum of a muscle fiber. the sarcoplasmic reticulum surrounds regions which are packed with myofibrils.

Front 16

T-tubules

Back 16

form pits in the sarcolemma. allows a muscle signal to get down to the sarcoplasmic reticulum and make it possible for the message to get to where it needs to be in order to stimulate muscle movement.

Front 17

Myofibrils

Back 17

thread-like structures which are only a few micrometers in diameter. They extend from one end of the cell to the other. They are structured in repeating units that causes striations.

Front 18

Myofilaments

Back 18

two filaments of the myofibril which are further separated into two types:actin myofilaments and myosin myofilaments .

Front 19

How do you know if a sample is complete muscle?

Back 19

If an epimysium is present, it is a complete muscle.

Front 20

Sarcoplasm

Back 20

is the cytoplasm of a muscle fiber

Front 21

In the contraction of a sarcomere, the following things happen:

Back 21

1. Ca2+ binds to troponin, exposing the active sites on the actin, allowing the myosin heads to grab onto the actin.
2. The power stroke.
3. ATP binds to the myosin heads, making them release the active sites on the actin.
4. The return stroke.

Front 22

actin

Back 22

thin filament proteins

Front 23

myosin

Back 23

thick filament proteins

Front 24

2 other proteins associated with thin filaments

Back 24

tropomyosin and troponin

Front 25

Z-line

Back 25

= disc-like structures to which actin filaments attach on both sides; composed of alpha-actinin and a dense amorphous matrix

Front 26

A-band

Back 26

"anisotropic" band: thick dark stripes are indicative of where the myosin is.

Front 27

I-band

Back 27

"isotropic" band: lighter areas where the actin is.

Front 28

H-zone

Back 28

pale central region in A-band; due to absence of thin filaments; is the area between the ends of the actin myofilaments which point to one another from opposite ends of the sarcomere.

Front 29

M-line

Back 29

thick filaments interconnected by cross-linking fine radial filaments, acts to maintain regular spacing and arrangement of thick filaments

Front 30

cross bridge

Back 30

the combination of a myosin head with the active site of an actin myofilament.

Front 31

ADP

Back 31

Adenosine Diphosphate

Front 32

P molecules

Back 32

Phosphate molecules

Front 33

Motor neurons

Back 33

cells specifically designed to carry signals from the brain and spinal cord to the skeletal muscles at a high velocity.

Front 34

Neuron

Back 34

The functional unit of the nervous system, a nerve cell

Front 35

Neuromuscular junction

Back 35

When the axon of a motor neuron reaches the perimysium surrounding several muscle fibers, it branches several times, each branch connecting with one muscle fiber.

Front 36

Explain the 1st step of a sarcomere contraction

Back 36

Before contraction, the active sites on the actin on the myofilament are not exposed. The myosin myofilament heads are ready, but there isn't anything to do yet.

Front 37

Explain the 2nd step of a sarcomere contraction

Back 37

start contraction - Ca2+ ions bind to the tropinin, causing the proteins in the actin myofilament to re-arrange. This exposes active sites where the heads can bind. Phosphate ejects when the head binds.

Front 38

Explain the 3rd step of a sarcomere contraction

Back 38

Power Stroke - the heads bend pulling the actin myofilament. ADP ejects.

Front 39

Explain the 4th step of a sarcomere contraction

Back 39

ATP molecules bind to the heads, releasing the active sites, the actin myofilament moves.

Front 40

Explain the 5th step of a sarcomere contraction

Back 40

Return Stroke - ATP molecules break down into ADP and P still bound to the myosin head. Energy releases, heads spring back - repeats.

Front 41

Synaptic cleft

Back 41

a gap between the end of the axon and the muscle fiber.

Front 42

Synapse

Back 42

The interface between a nerve cell and another cell

Front 43

Presynaptic terminal

Back 43

the very end of the nerve

Front 44

Postsynaptic membrane

Back 44

the membrane of the muscle fiber in the synaptic cleft region.

Front 45

Synaptic vesicles

Back 45

mitochondria which produce energy and stimulate muscle with acetylcholine Ach – a neurotransmitter.

Front 46

what are the 7 steps of muscle contraction?

Back 46

1. An action potential travels down the axon of a motor neuron.
2. ACh is released from the presynaptic terminal.
3. ACh travels across the synaptic cleft.
4. ACh interacts with the muscle fiber membrane to create a muscle action potential.
5. The action potential travels down a T-tubule.
6. Calcium ions are released from the sarcoplasmic reticulum.
7. Calcium ions bind to the troponin in an actin myofilament.

Front 47

what are the 6 steps of muscle relaxation?

Back 47

1. an enzyme called acetylcholinesterase inactivates ACh.
2. the muscle action potential is gone, the diffusion of calcium ions out of the sarcoplasmic reticulum stops.
3. Sarcoplasmic reticulum goes back to actively transport calcium ions back inside itself.
4. The active transport of calcium ions into the sarcoplasmic reticulum removes those ions from the troponin that is on the actin myofilaments.
5. troponin and tropomyosin rearrange again to hide the active actin sites.
6. the myosin heads have nothing to grab onto, and no cross bridges can form.

Front 48

ATP molecules are bound to the myosin heads in a sarcomere and are breaking down. Is this the return stroke or the power stroke?

Back 48

return stroke

Front 49

Suppose you were looking at the Ca2+ concentration in the sarcoplasmic reticulum of a muscle fiber. If the Ca2+ concentration in the sarcoplasmic reticulum suddenly increased dramatically, is the muscle starting its contraction or has it finished contracting?

Back 49

finished contracting

Front 50

When the sarcoplasmic reticulum releases Ca2+ ions in response to the action potential, do the ions move through the membrane of the sarcoplasmic reticulum via osmosis or diffusion? Is this active or passive transport?

Back 50

this is diffusion, and it is passive transport

Front 51

Suppose someone is working out and is pushing himself well beyond the limit. In fact, he gets so fatigued that he runs out of energy, and his muscle fibers can no longer produce ATP. What will happen in his sarcomeres?

Back 51

the muscle would temporarily cramp or stiffen, much like rigor mortis.

Front 52

When a muscle fiber contracts, what happens to the distance between the Z disks?

Back 52

The distance between the Z disks decreases, because the contraction pulls the Z disks
together.

Front 53

When a muscle fiber contracts, what happens to the length of the A band?

Back 53

The length of the A band remains the same. Remember, the length of the myosin
myofilament does not change. Thus, the A band, which is defined by the length of the myosin
myofilament, stays the same.

Front 54

When a muscle fiber contracts, what happens to the length of the I band?

Back 54

The length of the I band decreases. The actin myofilaments are pulled towards the center of
the sarcomere. This increases the amount of overlap between the actin and myosin
myofilaments. The I band is defined as the region with actin myofilament only. Since more
actin overlaps with myosin, the length of the actin myofilament only region goes down.

Front 55

When a muscle fiber contracts, what happens to the length of the H zone?

Back 55

The length of the H zone decreases. The actin myofilaments from each side of the sarcomere
are pulled closer. This reduces the length of the region in which there is only myosin, which is
the definition of the H zone.

Front 56

When a muscle fiber contracts, what happens to the length of the myosin myofilament?

Back 56

The length of the myosin myofilament remains the same. The myofilaments never change in length. The amount that they overlap changes.

Front 57

When a muscle fiber contracts, what happens to the length of the actin myofilament?

Back 57

The length of the actin myofilament remains the same. The myofilaments never change in length. The amount that they overlap changes.

Front 58

The concentration of calcium ions in the sarcoplasmic reticulum is decreasing. Is the muscle fiber starting to contract or has it finished contracting?

Back 58

If the calcium ion concentration is decreasing, that means calcium ions are heading into the
sarcomere. This means the muscle is starting to contract, because calcium ions bind to the
troponin on the actin myofilaments to begin contraction.

Front 59

The myosin heads of a sarcomere have just received a boost of energy. Is the power stroke or the return stroke about to happen?

Back 59

If the myosin heads have just received a boost of energy, ATP must have bound to them and
then broken down into ADP and P. This means the return stroke is about to start. Remember,
the myosin heads get “primed” with energy during the return stroke. They then use that energy on the power stroke.

Front 60

A myosin head has ADP attached to it but not an individual phosphate. Which is going to happen next: the return stroke or the power stroke?

Back 60

If ADP but no P is attached, that means the myosin head has bound to the active site (that’s what bumps the P off). Thus, the power stroke is about to happen. That will kick off the ADP.

Front 61

If you could look at several muscle fibers while they are in action, how could you determine which cells are a part of the same motor unit?

Back 61

All of the cells in the same motor unit will contract identically at the same time. If you could see several muscle cells always contracting in unison, that is a motor unit.

Front 62

What is the function of acetylcholinesterase?

Back 62

Acetylcholinesterase inactivates ACh after it has interacted with the postsynaptic membrane.

Front 63

If it were not for acetylcholinesterase, what
would happen to a muscle?

Back 63

the muscle cell could never relax once it started contracting!

Front 64

There are two major roles that ATP plays in muscle contraction and relaxation. The first involves the sarcoplasmic reticulum, while the second involves the myosin head. What are those
two roles?

Back 64

ATP provides the sarcoplasmic reticulum with energy for the active transport of calcium
ions into itself. This is critical for muscle relaxation. ATP attaches to the myosin heads, making
them release the active sites and giving them energy for the return stroke. Without this step, the
myosin heads would never let go of the active sites, and the muscle could neither relax nor
contract.

Front 65

A muscle is stiff. It can neither contract nor relax. What is wrong in the sarcomere? What causes this?

Back 65

The myosin heads must be gripping the active sites and not letting go. This must be due to a lack of ATP in the sarcomere.

Front 66

When a muscle fiber relaxes, does it automatically stretch back to its resting size?

Back 66

No. When a muscle cell relaxes, the myosin heads let go of the active sites. This makes it very easy for the muscle to stretch out, but that does not automatically happen. Something else (gravity or another muscle’s contraction) must cause the relaxed muscle to extend.

Front 67

Label the following structures of a whole muscle:

Back 67

a. epimysium b. perimysium c. endomysium d. muscle cell (fiber) e. fascicle

Front 68

Label the parts of the sarcomere below:

Back 68

a. actin myofilament b. myosin myofilament c. Z disk d. H zone e. A band f. I band

Front 69

In terms of their nuclei, skeletal muscle fibers are different than most cells in two ways.
What are those ways?

Back 69

Skeletal muscle cells have many nuclei rather than just one. Also, the nuclei are at the edge of the cell rather than near the center.

Front 70

Label the parts of the neuromuscular junction:

Back 70

a. presynaptic terminal b. mitochondria c. synaptic vesicle d. synaptic cleft
e. postsynaptic membrane