11.1 HY The Muscular System

Question 1

What does the musculoskeletal system help with? (x6)

Answer 1

1. Venous and Lymph drainage return
2. Body movement
3. Thermoregulation, shivering
4. Digestive system (smooth muscle)
5. Blood pressure regulation
6. Cardiac blood flow (heart)

Question 2

What are sarcomeres?

Answer 2

It is the arrangement of actin and myosin, and appeared striated or striped under the microscope.

They are also multinucleated

Question 3

What’s the difference between red fibers and white fibers?

Answer 3

Red fibers (AKA Slow twitch)- high myoglobin content, derive energy aerobically. Also have a lot of mitochondria.

White Fibers (AKA Fast Twitch)- contain less myoglobin, these are muscles that contract quickly but loose energy and fatigue rapidly as well.

Question 4

What is myoglobin?

Answer 4

It is an oxygen carrier that uses iron in a heme group to bind oxygen, and gives red color.

Question 5

How is smooth muscle different than skeletal muscle?

Answer 5

1. It is not well organized, so striations cannot be seen.
2. Capable of mores sustained contractions, called tonus
3. Can contract without nervous system input, known as myogenic activity

Same: both have actin and myosin.

Question 6

How is cardiac muscle similar and different from smooth and skeletal muscle?

Answer 6

Nuclei: can have 1-2 nuclei
Contractions: can contract without nervous system input, called myogenic activity (like Smooth muscle)
Appearance: they appear striated, like skeletal muscle

Question 7

How are cardiac muscles connected?

Answer 7

Connected by intercalated discs, which contain many gap junctions, allowing for the flow of ions directly through the cell.

Question 8

What drives the heart to speed up and slow down?

Answer 8

Speed up: norepinephrine from sympathetic system
Slow down: vagus nerve, from parasympathetic system.

Question 8

What drives the heart to speed up and slow down?

Answer 8

Speed up: norepinerphrine from sympathetic system

Slow down: vagus nerve, from parasympathetic system.

Question 9

Draw out the table of skeletal, cardiac muscle, and smooth muscle. Also name:
1. Appearance
2. Innervation and voluntary vs involuntary control
3. Number of nuclei

Answer 9

Question 10

What do the thick and thin filaments of the sarcomere contain?

Answer 10

Thick: myosin
Thin: actin, including troponin and tropomyosin

Question 11

What does titin do?

Answer 11

It acts as a spring and anchors the actin and myosin filaments together.

Question 12

What is the:
Z-line
M-line
I-band
H-zone
A-band

Answer 12

Z-line- defines the boundaries between each sarcomere
M-line- runs down the center of the sarcomere, through the middle of the myosin filaments
I-band- region containing exclusively thin filaments
H-zone- contains only thick filaments
A-band- contains the thick filaments in their entirety, including any overlap with thin filaments.

Question 13

What happens during contraction to the:
Z-line
M-line
I-band
H-zone
A-band

Answer 13

This distance between H-Zone, I band, and Z-lines, and M-lines become smaller

A-band size remain constant.

Question 14

What is the sarcoplasmic reticulum?

Answer 14

It is a modified endoplasmic reticulum that contains a high concentration of calcium ions.

Question 15

What are myofibrils?

Answer 15

They are sarcomeres that are attached end-to-end to form myofibrils.

Question 16

What is the sarcoplasm?

Answer 16

This is a modified cytoplasm of the myocyte.

Question 17

What is the sarcolemma?

Answer 17

It is the cell membrane of the myocyte.
It is capable of propagating an action potential and can distribute the cation potential to all sarcomeres in a muscle using a system of transverse tubules that are oriented perpendicularly to the myofibrils

Question 18

What is a muscle fiber?

Answer 18

These contain many myofibrils arranged in parallel

Question 19

What are transverse tubules?

Answer 19

This is a system in tubules that are oriented perpendicularly that can propagate the action potential.

Question 20

What’s the mnemonic for the parts of the sarcomere?

Answer 20

Z- Z is in the end of the alphabet, and end of sarcomere.
M-Middle of the Myosin filaments
I-I is a thin letter, (thin filaments only)
H- H is a tick letter (thick filaments only)
A-All of the thick filament, whether or not it is overlapping.

Question 21

Where does muscle contraction start?

Answer 21

At the neuromuscular junction, where it communicates with muscles via a motor (efferent) neuron.

The motor end plate is the neuromuscular junction with the muscles cells

Question 22

What is the neurotransmitter that works on skeletal muscles, and what does it do?

Answer 22

Acetylcholine

It binds to receptors on the sarcolemma, causing depolarization.

Question 23

What is the motor unit?

Answer 23

It is the nerve terminal and the group of myocytes it’s affiliated with.

Question 24

What does depolarization cause in the myocyte?

Answer 24

1. Spreads down the sarcolemma to the t-tubules 2. Travels down the T-tubules into the muscle tissues to the sarcoplasmic reticulum. 3. In the sarcoplasmic reticulum, calcium is released. 4. The calcium ions bind to a **regulatory subunit in troponin**, triggering a **change in the confirmation of tropomyosin**, to which troponin is bound 5. This **exposes** the **myosin binding site**. 6. Free globular heads of the myosin move toward and bind with exposed sites on actin. 7. The newly formed **actin-myosin cross bridges** allow myosin to pull on actin, which draws the thin filaments towards the M-line, resulting in shortening of the sarcomere.

Question 25

Walk me through the Actin-Myosin Cross-bridge Cycle.

Answer 25

1. Myosin carrying hydrolyzed ATP (ADP and inorganic phosphate) is able to bind with the myosin-binding site. 2. The **release of the inorganic phosphate and ADP** in rapid succession provides the energy for the power stroke, resulting in the sliding of the actin filament over the myosin filament. 3.** ATP binds to the myosin head**, **releasing it from actin**. 4. ATP is hydrolyzed to ADP and Pi, which re-cocks the myosin head so that is in position to initiate another cross-bridge cycle. 5. This causes sequential shortening of the sarcomere

Question 26

How does relaxation occur?

Answer 26

**Acetylcholine is degraded** by the enzyme **acetylcholinesterase**. This results in the termination of the signal at the neuromuscular junction and ultimately allows the sarcolemma to repolarizes. As the signal decays, **calcium release stops**, and the SR takes up the calcium from the sarcoplasm. Without the calcium, the **myosin-binding sites are covered by tropomyosin** and contraction is prevented.

Question 27

What is a simple twitch? What does it consist of ? What is the latent period?

Answer 27

It is a response of a single muscle fiber to a brief stimulus at or above the threshold. It consists of a **latent period, contraction period, and relaxation period**. The action potential spreads along the muscle and allows for calcium to be released from the sarcoplasmic reticulum

Question 28

What is frequency summation & tetanus?

Answer 28

This happens when the muscle fiber is exposed to frequent and prolonged stimulation, not allowing for sufficient time to relax. If it is unable to relax at all, it is called tetanus.

Question 29

What is **creatine phosphate**?

Answer 29

It is a supplemental energy reserve. It is created by transferring a phosphate group from ATP to creatine during times of rest.

Question 30

What is **myoglobin**?

Answer 30

It can serve as an energy reserve to keep aerobic metabolism going.

Question 31

What is the **oxygen debt**?

Answer 31

It is the difference between the amount of oxygen needed by the muscles and the actual amount present.

Question 32

What are the two forms of supplemental energy reserve? In the muscle

Answer 32

1. myoglobin 2. Creatinine phosphate.