2) Exercising Muscle: Structure and Function

Question 1

Types of Muscle

Label the image
Skeletal Muscle is Striated/Unstriated and Voluntary/involuntary

Cardiac muscle is Striated/Unstriated and Voluntary/involuntary

Smooth muscle is Striated/Unstriated and Voluntary/involuntary

Answer 1

Skeletal Muscle is Striated and Voluntary

Cardiac muscle is Striated and involuntary

Smooth muscle is Unstriated and involuntary

Question 2

Four properties of Muscle
1. ?: capacity of muscle to respond to a stimulus
2. ?: Ability of muscle to shorten and generate pulling force
3. ?: Muscle can be stretched back to its original length
4. ?: Ability of muscle to recoil to original resting length after stretched

Answer 2

Four properties of Muscle
1. Excitability: capacity of muscle to respond to a stimulus
2. Contractility: Ability of muscle to shorten and generate pulling force
3. Extensibility: Muscle can be stretched back to its original length
4. Elasticity: Ability of muscle to recoil to original resting length after stretched

Question 3

Four properties of Muscle
1. Excitability: ?
2. Contractility: ?
3. Extensibility: ?
4. Elasticity: ?

Answer 3

Four properties of Muscle
1. Excitability: capacity of muscle to respond to a stimulus
2. Contractility: Ability of muscle to shorten and generate pulling force
3. Extensibility: Muscle can be stretched back to its original length
4. Elasticity: Ability of muscle to recoil to original resting length after stretched

Question 4

Skeletal muscle

3 Functions of Skeletal Muscle

Answer 4

1. Production of force for movement and breathing
2. Production of force for postural support
3. Heat production during cold

Question 5

Label the Skeletal Muscle
Red =
Orange =
Yellow =
Green =
Blue =
Gold =
Purple =
Pink =

Answer 5

Red = Muscle
Orange =Perimysium
Yellow = Epimysium
Green = Fascicles
Blue = Muscle Fibers

Gold = Fascicle
Purple = Muscle Fibers
Pink = Perimysium

Fascicles = Bundle of muscle fibers within a muscle // supplied by nerves and blood vessels and enclosed in a fibrous perimysium separating it from neighboring fascicles

Question 6

What is a Fascicle?

Fascicle = ? within a muscle
- supplied by ? and ?
- enclosed in a ? separating it from neighboring fascicles

Answer 6

Fascicle = Bundle of muscle fibers within a muscle - supplied by nerves and blood vessels
- enclosed in a fibrous perimysium separating it from neighboring fascicles

Question 7

What separates neighbouring fascicles?

Answer 7

Fibrous Perimysium

Question 8

Label the Muscle Fiber
Red =
Orange =
Yellow =
Green =

Answer 8

Label the Muscle Fiber
Red = Sarcolemma
Orange = Z-disc
Yellow = Myofibrils
Green = Myofilaments

Question 9

What is A muscle Fiber?
- ?
- appearance?
- Enclosed in a specialized Plasma membrane (?)
- Contains densely packed bundles (?) of ?
- Multiple ? immediately beneath the sarcolemma
- Extensive network of specialized smooth endoplasmic reticulum (?)
- Enclosed in a thin fibrous sleeve called ?

Answer 9

Muscle Fiber:
- Single muscle cell
- Slender, elongated, threadlike
- Enclosed in a specialized Plasma membrane (SARCOLEMMA)
- Contains densely packed bundles (Myofibrils) of contractile protein filaments
- Multiple nuclei immediately beneath the sarcolemma
- Extensive network of specialized smooth endoplasmic reticulum (Sarcoplasmic Reticulum)
- Enclosed in a thin fibrous sleeve called endomysium

Question 10

Label the Myofibril

Red
Orange
Yellow
Green

Answer 10

Red = Z-disc
Orange = T tubule
Yellow = Sarcoplasmic Reticulum
Green = Myofilaments (thick and thin)

Question 11

Myofibril:
- Bundle of ? within a ?
- Fills most of the ?
- Surrounded by ? and ?
- Has a banded (striated) appearance due to orderly overlap of ?

Answer 11

Myofibril:
- Bundle of protein myofilaments within a muscle fiber
- Fills most of the cytoplasm
- Surrounded by sarcoplasmic Reticulum and mitochondria
- Has a banded (striated) appearance due to orderly overlap of protein myofilaments

Question 12

Label the Sarcomere
Red
Orange
Yellow

Answer 12

Red = Z-disc
Orange = Thick Filament (myosin)
Yellow = Thin Filament (Actin)

Question 13

What is A Sarcomere?

Segment of myofibril from one ? to the next in the fiber’s striation pattern
Hundreds of sarcomeres end to end compose a ?

• The ?, ? unit of the muscle fiber

Answer 13

Segment of myofibril from one Z disc to the next in the fiber’s striation pattern
Hundreds of sarcomeres end to end compose a myofibril

• The functional, contractile unit of the muscle fiber

Question 14

Chemical Composition of Muscle

What is myoglobin?

Answer 14

Red protein containing heme which carries and stores oxygen in myscle cells
Skeletal muscle releases myoglobin when damaged
Myoglobin in urine indicates muscle damage

Question 15

Presence of what protein in urine is indicative of muscle damage?

Answer 15

Myoglobin
- Protein containing heme
- Released by skeletal mm in response to damage

Question 16

6 proteins in muscle

Answer 16

1. Myosin
2. Actin
3. Tropomyosin
4. troponin
5. Titin
6. myoglobin

Question 17

Why is skeletal muscle multinucleated?

Answer 17

• The formation and growth of multinucleated myofibers or myotubes occur through a process known as myogenesis.
• During myogenesis, mononucleated myoblasts withdraw from the cell cycle, initiate muscle specific gene expression, and subsequently fuse with one another to form nascent, multinucleated myofibers
• They are multi-nucleated because they are formed from the fusion of embryonic myoblasts.
  Each nucleus regulates the metabolic requirements of the sarcoplasm around it.

Satellite cells are myogenic stem cells responsible for muscle regeneration throughout the lifespan. Given their capacity to expand, differentiate, and provide a new source of nuclei to growing myofibres, their role in muscle adaptation to exercise was inferred.

Question 18

What are three types of Connective tissue found in skeletal muscle
(from outermost to innermost)

Answer 18

1. Epimysium
2. Perimysium
3. Endomysium

Epimysium:
- surrounds entire muscle
- Separates muscle from surrounding tissues/organs
- Connected to deep fascia

Perimysium:
- Collagen and elastic fibers surrounding a group of muscle fibers (ie fascicle)

Endomysium:
- sheath of Connective tissue covers each individual muscle fiber

Question 19

Connective tissue

Epimysium:
- surrounds ?
- Separates muscle from ?
- Connected to ?

Perimysium:
- ? and ? surrounding a group of muscle fibers (ie ?)

Endomysium:
- sheath of Connective tissue covers ?

Answer 19

Epimysium:
- surrounds entire muscle
- Separates muscle from surrounding tissues/organs
- Connected to deep fascia

Perimysium:
- Collagen and elastic fibers surrounding a group of muscle fibers (ie fascicle)

Endomysium:
- sheath of Connective tissue covers each individual muscle fiber

Question 20

Label and describe:

Muscle fiber: ?

Myofibril: ?

Tendon: ?

Fascicles: ?

Answer 20

Muscle fiber = a muscle cell

Myofibril: any of the longitudinal parallel contractile elements of a muscle cell
- Myofilaments: actin and myosin

Tendon: Attaches Muscle to Bone

Fascicles: Small bundles of muscle fibers wrapped in a connective tissue sheath

Question 21

Structure of a single muscle fiber

What is the Sarcolemma
Sarcolemma:
- ?

Function?
- Series of ? when fiber is contracted or in resting state; ? disappear on stretching
– Muscle fiber can stretch without disrupting ?
- Junctional folds at ? aid in transmission of ?
- Transport ? from capillary blood into muscle fiber

Answer 21

Sarcolemma:
- Plasma membrane

Function?
- Series of shallow folds when fiber is contracted or in resting state; folds disappear on stretching
– Muscle fiber can stretch without disrupting sarcolemma
- Junctional folds at motor end plate aid in transmission of action potential
- Transport metabolites from capillary blood into muscle fiber

The triad is a skeletal muscle substructure responsible for the regulation of excitation-contraction coupling. It is formed by the close apposition of the T-tubule and the terminal sarcoplasmic reticulum.

Question 22

Sarcoplasm:
- ?-like substance that fills spaces within and between ?; the ? of muscle fiber
- Contains stored ?, ?, ? and ?

Answer 22

Sarcoplasm:
- Gelatin-like substance that fills spaces within and between myofibrils; the cytoplasm of muscle fiber
- Contains stored glycogen, fat, enzymes and oxygen-binding myoglobin

Question 23

Transverse-tubules
- Transverse tubules (t- tubules): ? system that synchronizes the release of ? ion ? from the ? of the sarcoplasmic reticulum

• Extensions of ?
• Carry “?”, ? and ? deep into cell
  – Rapid transmission of ? to individual ?

Answer 23

Transverse-tubules
- Transverse tubules (t- tubules): duct system that synchronizes the release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum

• Extensions of sarcolemma/surface membrane
• Carry “ions”, nutrients and action potentials deep into cell
  – Rapid transmission of nerve impulses to individual myofibrils

Question 24

Sarcoplasmic reticulum:
Network of ?
Storage site for ?
Speeds up ? in skeletal muscle because Ca2+ has shorter distances to diffuse i.e. 0.25 μm opposed to 50 μm (200 x)

Answer 24

Sarcoplasmic reticulum:
Network of tubules
Storage site for calcium
Speeds up contraction in skeletal muscle because Ca2+ has shorter distances to diffuse i.e. 0.25 μm opposed to 50 μm (200 x)

Question 25

# Structure of a single muscle fiber Terminal cisternae: - Enlarged area of **?** surrounding **?** Compartment from which **?** is released following an **?** ## Footnote Triad: Composed of: **?** – **?** – **?** Couples **?** to **?**

Answer 25

Terminal cisternae: - Enlarged area of **sarcoplasmic reticulum** surrounding **transverse tubules** Compartment from which **Ca2+** is released following an **action potential** ## Footnote Triad: Terminal cisternae – t-tubule – terminal cisternae Couples excitation to contraction

Question 26

# Structure of single muscle fiber Triad: Composed of: **?** – **?** – **?** Couples **?** to **?**

Answer 26

Triad: **Terminal cisternae** – **t-tubule** – **terminal cisternae** Couples **excitation** to **contraction**

Question 27

What are Satellite cells?

Answer 27

Skeletal muscle satellite cells are considered to play a crucial role in **muscle fiber maintenance, repair and remodeling**. Mononucleated cells “wedged” between the basement membrane and plasma membrane of the muscle fiber. Act as *stem cells* and are responsible for the further **growth and development of skeletal muscles.**

Question 28

Satellite cells Function: **? and ? of ?** When muscle hypertrophy occurs cell volume **?** A single nuclei can only maintain/produce proteins for a finite **?** Satellite cells merge with the muscle fiber and become **?** for that fiber Increases the number of **?** for the fiber allowing for greater **?** Important for **?** to strength training

Answer 28

Satellite cells Function: **Growth and repair of muscle cell** When muscle hypertrophy occurs cell volume **increases** A single nuclei can only maintain/produce proteins for a finite **volume** Satellite cells merge with the muscle fiber and become **new nuclei** for that fiber Increases the number of **nuclei** for the fiber allowing for greater **protein synthesis** Important for **adaptations** to strength training

Question 29

Sarcomere - **Striped** appearance - Basic **contractile unit** of muscle - **Z-line (disk)** to **Z-line** - Because sarcomeres are joined end to end throughout an entire **muscle fiber**, their simultaneous contraction **shortens the entire muscle**

Answer 29

Sarcomere - **Striped** appearance - Basic **contractile unit** of muscle - **Z-line (disk)** to **Z-line** - Because sarcomeres are joined end to end throughout an entire **muscle fiber**, their simultaneous contraction **shortens the entire muscle**

Question 30

Label 1. Z-line 2. Titin 3. Thick filament 4. M line 5. Thin filament 6. I band 7. A band 8. H zone 9. Sarcomere

Answer 30

Red = I band Orange = A band Yellow = H- Zone Green = Z-disk Grey = Titin Cyan = Thin filament (actin) Navy = M-line Purple = Thick filament (Myosin)

Question 31

# Microscopic structure of muscle What part of the sarcomere is being described: Dark with slightly lighter region in the center; contains thick and thin filaments

Answer 31

**A Band** Dark with slightly lighter region in the center; contains thick and thin filaments

Question 32

# Microscopic structure of muscle What part of the sarcomere is being described: Light region in the middle of the A band; **contains only thick filaments**

Answer 32

**H Zone** Light region in the middle of the A band - contains only THICK filaments (ie myosin only)

Question 33

# Microscopic structure of muscle What part of the sarcomere is being described: Transverse line in the middle of H zone; composed of proteins that serve as the *attachment site* of the thick filaments and *stabilizes* structure of sarcomere; **myosin anchor site**

Answer 33

**M Line** Transverse line in the middle of H zone; composed of proteins that serve as the attachment site of the thick filaments and stabilizes structure of sarcomere; myosin anchor site

Question 34

# Microscopic structure of muscle What part of the sarcomere is being described: Light regions; regions of sarcomere where there are **thin filaments** (no thick filaments) Actin; troponin, tropomyosin Only

Answer 34

**I Bands** Light regions; regions of sarcomere where there are thin filaments (no thick filaments)

Question 35

# Microscopic structure of muscle What part of the sarcomere is being described: - Narrow dark line in the middle of the I band; - site of attachment for titin, thin filaments

Answer 35

**Z line** - Narrow dark line in the middle of the I band; - site of attachment for titin, thin filaments

Question 36

# Microscopic structure of muscle What part of the sarcomere is being described: - Narrow dark line in the middle of the I band; - site of attachment for titin, thin filaments

Answer 36

**Z line** - Narrow dark line in the middle of the I band; - site of attachment for titin, thin filaments

Question 37

The distance from Z line to Z line is a **?**

Answer 37

The distance from Z line to Z line is a **Sarcomere (2-3um)**

Question 38

How do sarcomeres in a muscle fiber differ?

Answer 38

They dont All sarcomeres in a muscle fiber are identical

Question 39

What is Nebulin? Function?

Answer 39

Anchoring protein for actin; regulatory role in actin and myosin interactions - helps anchor actin filament to Z disks

Question 40

Thin filaments contain **?** to bind myosin heads

Answer 40

Thin filaments contain **active sites** to bind myosin heads

Question 41

Actin: **?** proteins (**?**) in 2 helical strands (**?**)

Answer 41

Actin: **Globular** proteins (**G-actin**) in 2 helical strands (**F-actin**)

Question 42

What is tropomyosin?

Answer 42

Tropomyosin: Tubular protein of two identical alpha helices, shadows the actin double helix

Question 43

Describe troponin What are the three types?

Answer 43

Troponin is a heterotrimer 1. **TnT** = binds to tropomyosin 2. **TnC** = binds Ca2+ (4 calcium binding sites in skeletal muscle) 3. **TnI** = Binds to the actin monomer (inhibitory)

Question 44

Describe the three subunits of troponin: The troponin complex is a **?** composed of: 1. troponin C (TnC): the **?** subunit // binds to **?**, 2. troponin I (TnI), the **?** subunit // binds to **?** 3. troponin T (TnT), the **?** subunit // binds to **?**

Answer 44

The troponin complex is a heterotrimer composed of: 1. troponin C (TnC): the **Ca2+-binding** subunit, 2. troponin I (TnI): the **inhibitory subunit** // binds to the **actin monomer** 3. troponin T (TnT): the **Tropomyosin (Tm)-binding** subunit.

Question 45

Thick filaments are **?** of proteins (**?**) Each myosin molecule is a **?** consisting of: 1. Two intertwined **?** 2. Two **?** light chains 3. Two **?** light chains

Answer 45

Thick filaments are **polymers** of proteins (**myosin II**) Each myosin molecule is a **double trimer** consisting of: 1. Two intertwined **heavy chains** 2. Two **regulatory** light chains 3. Two **Alkali (essential)** light chains ## Footnote The 2 heavy chains have 3 regions: rod (tail), hinge and head region Rods (tails) are α helices Hinge regions flare into two globular heads Heads: (i) are cross bridges (ii) contain binding sites for actin (iii) contain sites for binding and hydrolyzing ATP

Question 46

Thick filaments are polymers of proteins (myosin II) Each myosin molecule is a double trimer consisting of: 1. Two intertwined heavy chains 2. Two regulatory light chains 3. Two Alkali (essential) light chains - The 2 heavy chains have 3 regions: **1**, **2** and **3** region - **?** are α helices - **?** regions flare into two globular heads - **?:** (i) are cross bridges (ii) contain binding sites for actin (iii) contain sites for binding and hydrolyzing ATP

Answer 46

Thick filaments are polymers of proteins (myosin II) Each myosin molecule is a double trimer consisting of: 1. Two intertwined heavy chains 2. Two regulatory light chains 3. Two Alkali (essential) light chains - The 2 heavy chains have 3 regions: **rod (tail)**, **hinge** and **head** region - **Rods (tails)** are α helices - **Hinge** regions flare into two globular heads - **Heads:** (i) are cross bridges (ii) contain binding sites for actin (iii) contain sites for binding and hydrolyzing ATP

Question 47

Thick filaments are polymers of proteins (myosin II) Each myosin molecule is a double trimer consisting of: 1. Two intertwined heavy chains 2. Two regulatory light chains 3. Two Alkali (essential) light chains - The 2 heavy chains have 3 regions: rod (tail), hinge and head region - Rods (tails) are **?** - Hinge regions flare into **?** - Heads: (i) are **?** (ii) contain binding sites for **?** (iii) contain sites for binding and hydrolyzing **?**

Answer 47

Thick filaments are polymers of proteins (myosin II) Each myosin molecule is a double trimer consisting of: 1. Two intertwined heavy chains 2. Two regulatory light chains 3. Two Alkali (essential) light chains - The 2 heavy chains have 3 regions: rod (tail), hinge and head region - Rods (tails) are **α helices** - Hinge regions flare into **two globular heads** - Heads: (i) are **cross bridges** (ii) contain binding sites for **actin** (iii) contain sites for binding and hydrolyzing **ATP**

Question 48

# Accessory proteins What is Titin? Role? Prevents? Provides?

Answer 48

Titin: - large elastic protein - anchors thick myosin filament to the Z disk - Prevents overstretching - Provides elastic recoil

Question 49

What is alpha-actinin?

Answer 49

Attachment of actin filament to Z-disk