Ch 9 - Muscles & Muscle Tissue

Question 1

Functions of Muscle Tissue

Answer 1

1) Movement
2) Body posture & body position
3) Joint stability
4) Maintaining body temperature

Question 2

Muscle Characteristics

Answer 2

1) Excitability - Generate action potentials in response to stimulus
2) Contractility - Muscle cells shorten when they contract
3) Exensibility - Muscles cells can lengthen/stretch
4) Elasticity - Healthy muscle cells return to their original shape

Question 3

Types of Muscle Tissue

Answer 3

1) Skeletal muscle tissue
2) Smooth muscle tissue
3) Cardiac muscle tissue

Question 4

Muscle tissue identification

Voluntary muscle tissue, striated

Answer 4

Skeletal muscle tissue
Creates most force, but needs most rest, adaptable

Question 5

Muscle tissue identification

Involuntary muscle tissue, not striated

Answer 5

Smooth muscle tissue
moves fluid through body
uninucleate

Question 6

Muscle tissue identification

Involuntary muscle tissue, striated

Answer 6

Cardiac muscle tissue
moves blood through the body (rate set by pacemaker cells)
uninucleate

Question 7

Innervation & Vascularization of Skeletal Muscle

Answer 7

Innervation: each muscle fiber synapses with 1 motor nerve, can be served by multiple motor neurons
Vascularizaton: each muscle recieves 1 artery, 1+ vein (bring in nutrients, remove waste)

Question 8

Connective Tissue Sheaths of Muscle Tissue

Answer 8

1) Endomysium: innermost layer (ind. muscle fibers; called myocytes)
2) Perimysium: middle layer (grouped muscle fibers - form fascicles)
3) Epimysium: outermost layer (entire muscle)

Question 9

Individual muscle fiber/cell is called

Answer 9

myocyte

Question 10

Groups of muscle fibers joined by perimysium

Answer 10

fascicles

Question 11

Skeletal Muscle Attachment Types

Answer 11

Direct: epimysium of muscle fuses directly to bone/cartilage
Indirect: involves tendons

Question 12

Skeletal Muscle Attachment Points

Answer 12

1) Origin: where the muscle attaches to a less movable bone (always proximal)
2) Insertion: where the muscle attaches to a movable bone (always distal)

Question 13

Plasma membrane of muscle fiber

Answer 13

Sarcolemma

Question 14

Cytoplasm of muscle fiber

Answer 14

Sarcoplasm

Contains high numbers of
A) Glycosomes (glycogen organelle)
B) Myoglobin (oxygen organelle)

Question 15

Protein filaments in muscle tissue (& types)

Answer 15

Myofilaments
1) Myosin - thick filament
2) Actin - thin filament

Question 16

Thick filament of muscle tissue

Answer 16

Myosin
has 2 heavy chains, with myosin head found at end of each chain

Myosin head used to link two types of myofilaments during contraction

Question 17

Binding sites of myosin

Answer 17

2 total;
1 for ATP
1 for actin

Myosin head used to link two types of myofilaments during contraction

Question 18

Thin filament of muscle tissue

Answer 18

Actin
Chains of G actin proteins with myosin binding sites

Myosin head binds to myosin binding site of actin during muscle contraction

Question 19

Actin regulatory proteins

Answer 19

1) Tropomyosin: arranged along length; blocks myosin binding sites when muscle is relaxed
2) Troponin: globular protein; binds tropomyosin to position it on the actin filament

Question 20

Rod-like organelles inside muscle cells that create striations

Answer 20

Myofibrils
Made up of bands of actin & myosin

Question 21

Myofibril bands

Answer 21

1) A band: region of myofibril where actin and myosin filaments overlap
2) I band: region of myofibril with only actin filaments (z disc at center holds actin filaments in place)

Question 22

Region of myofibril where actin and myosin filaments overlap

Answer 22

A band

Question 23

Region of myofibril with only actin filaments

Answer 23

I band

Question 24

Center of I band, which holds the actin filaments in place

Answer 24

Z disc

Question 25

Region of a myofibril found between neighboring Z discs

Answer 25

**Sarcomere** - the smallest contractile unit of skeletal muscle tissue

Question 26

Extensions of the sarcolemma that wrap around *deeper* myofibrils

Answer 26

**T-Tubules** - increase surface area of sarcolemma ## Footnote importance: changes in membrane potentia can reach myofibrils that are **not** in direct contact with sarcolemma

Question 27

Organelle that wraps around myofibrils

Answer 27

**Sarcoplasmic reticulum** - stores and releases Ca2+ for muscle contraction & relaxation ## Footnote : : Form **terminal cisterns** around T-tubules; action potentials travel down T-tubules to stimulate release of Ca2+

Question 28

Site of synapse between a somatic motor neuron and a muscle fiber

Answer 28

**Neuromuscular Junction** ACh released

Question 29

Steps for muscle fiber stimulation to occur

Answer 29

1) **Neuromuscular junction ACh release** 2) **Generation of EPP & action potential across sacrolemma**- ACh opens ion channels to generate an End Plate Potential (graded potential) - depolarizing 3) **Excitation-Contraction Coupling** - occurs when action potential spreads from sarcolemma to T-tubules 4) **Cross Bridge Formation & Muscle Contraction** - attachment of myosin to actin

Question 30

Process of Cross Bridge Formation

Answer 30

a) Ca2+ binds troponin - troponin changes shape b) Change in troponin shape - tropomysin rolls to the side c) When tropomyosin is moved - myosin binding site on actin is exposed d) Myosin head splits APT into ADP + P (allows myosin head to bind to actin) e) ADP + P is released from myosin head, causing the myosin head to change shape & bend (pulls actin fillament toward center of sarcomere - called power stroke) f) Myosin head binds to another ATP - myosin head detaches from actin binding site ## Footnote Need to write out!!

Question 31

How does the cross-bridge formation end

Answer 31

- Motor impulses no longer sent to muscle fiber - Ca2+ is returned to sarcoplasmic reticulum - When Ca2+ levels in sarcoplasm drop, it can no longer bind to troponin - Troponin returns to original shape; tropomyosin covers actin binding sites again

Question 32

How does the sliding filament model of contraction work?

Answer 32

Myosin heads "slide" thin filaments toward the center of the sarcomere, shortening the sarcomere without changing length of filaments

Question 33

# Definition Motor unit

Answer 33

A single motor neuron and all the muscle fibers it innervates

Question 34

Rules of a motor unit

Answer 34

1) when the motor unit fires, all fibers it innervates will contract (can be spread out in muscle) 2) number of muscle fibers a motor neuron innervates influences movement

Question 35

Muscle contraction that is modified by the nervous system to produce varying amounts of force

Answer 35

**Graded Muscle Contractions:** 1) **Temporal summation** - increasing frequency of stimulation 2) **Motor unit summation** - increasing the number of motor units used

Question 36

Types of temporal summation:

Answer 36

1) **Unfused (incomplete) tetanus** - muscle fiber has very little time to relax before next stimulus 2) **Fused (complete) tetanus** - no relaxation occurs in the muscle fiber (contractions from individual stimuli fuse into one contraction)

Question 37

Increasing muscle force by increasing the number of motor units used during contraction

Answer 37

**Motor unit summation** Motor units recruited asynchronously, with a **size principal** - motor units w/ smallest muscle fibers recruited first, increases incrementally

Question 38

Muscle tone

Answer 38

Relaxed muscles are always slightly contracted - called muscle tone ## Footnote Does not produce movememt, keeps tissue healthy and responsive, stabilizes joints, maintains posture

Question 39

Types of Muscle Contraction

Answer 39

1) **Isotonic Contraction:** muscle tension develops to overcome the load & muscle shortening occurs 2) **Isometric Contraction:** tension develops in a muscle, but the length of the muscle does not change

Question 40

Types of Isotonic Contraction

Answer 40

1) **Concentric contraction:** muscle *shortens* and does work 2) **Eccentric contraction:** muscle *lengthens* while under tension

Question 41

How does Isometric Contraction work?

Answer 41

Cross bridge formation still occurs, but the sarcomeres do not shorten

Question 42

How is ATP used/generated in Muscle Contraction

Answer 42

Attaches to Myosin to allow binding, will only produce the amount of ATP as needed

Question 43

Pathways for ATP Regeneration

Answer 43

1) **Direct phosphorylation** 2) **Anaerobic pathways** 3) **Aerobic pathways**

Question 44

Direct Phosphorylation Reaction

Answer 44

Creates ATP using **creatine phosphate (CP)** via criatine kinase - 1 ATP per CP molecule Whole process supplies ~15s worth of ATP ## Footnote Does not require oxygen

Question 45

**Anaerobic Pathway**: Glycolysis

Answer 45

Glucose broken down to form **2 ATP** & **pyruvic acid** and converted to lactic acid Creatine phosphate and glycolysis provide ~1 minute of ATP

Question 46

Benefits and Drawbacks of **Anaerobic Pathway**

Answer 46

**Benefits:** does not require oxygen, produces ATP quickly **Drawbacks:** low ATP yeild (2 ATP per glucose) lactic acid build-up MIGHT cause muscle fatige or soreness

Question 47

**Aerobic Pathway:** Cellular Respiration

Answer 47

Produces 30-32 ATP per glucose, ~95% of ATP used by muscle during rest and light-to-moderate long-term exercise

Question 48

Benefits and Drawbacks of **Cellular Respiration**

Answer 48

**Benefits:** produces 30-32 ATP **Drawbacks:** slow, requires mitochondria, constant O2 and glucose

Question 49

When muscle is physiologically incapable of contracting

Answer 49

**Muscle Fatigue** - rate & duration depends on activity High intensity = quicker rate, lower duration, vice versa

Question 50

Factors that affect speed of contraction

Answer 50

1) How fast ATP is split - how fast cross bridges can form & break 2) Electrical activity of motor neurons - fast neurons = fast connections 3) Pathway of ATP production

Question 51

Types of Muscle Fibers (velocity and duration)

Answer 51

1) **Fast glycolytic fibers** - contract quickly, use anaerobic pathways (high glycogen, low myoglobin/mitochondria/blood) 2) **Fast oxidative fibers** - contract quickly, use aerobic pathways (some glycogen, lots of myoglobin/mitochondria/blood) 3) **Slow oxidative fibers** - contract slowly, use aerobic pathways (low glycogen, high myoglobin, lots of mitochondria/blood)

Question 52

Gross anatomy of smooth muscle tissue

Answer 52

2 layers of smooth muscle that never contract simultaneously: 1) **Longitudinal layer** along the length of the organ (widening) 2) **Circular layer** muscle fiber runs the circumference of the organ (narrowing)