Skeletal Muscle Tissue chapter 9

Question 1

Muscle Tissue

Answer 1

is one of the four primary tissue types

• converts the chemical energy of ATP into mechanical energy
• muscle contraction

Question 2

Important functions of skeletal muscle include

Answer 2

-movement

• contractions pull on tendons to move the bones of the skeleton

-maintain posture

• constant tension maintains body position

-guard openings to the digestive and urinary systems

• support soft tissues
• protect and support visceral organs
• thermoregulation
• heat generation from muscle contraction

Question 3

Skeletal muscles are comprised of layers muscle fibers an connective tissue:

Answer 3

epimysium is an exterior collagen layer covering muscle

• blends between muscles and other tissue

perimysium is a dividing layer of connective tissue surrounding bundles of cells called a fascicle

• allows for blood vessels and nerves to penetrate muscle tissue

endomysium is a thin areolar tissue layer around each muscle fiber

• contains capillaries, terminal axons, and myosatellite cells

Question 4

Endomysium, perimysium, and epimysium form connective tissue attachments to bone

Answer 4

form tendons/aponeuroses that merges into periosteum as perforating fibers

• tendons attach at points; aponeuroses attach broad areas

Question 5

Stress will break a bone before

Answer 5

pulling the tendon/aponeurosis loose

Question 6

connective tissue

Answer 6

Question 7

Skeletal muscle

Answer 7

are long, striated muscles attached to bones containing multiple nuclei that develop via fusion of myoblasts

Question 8

Muscle Fibers

Answer 8

sarcolemma
cell membrane of muscle fiber that holds sarcoplasm
stores glycogen and myoglobin

myofibrils
subdivision of muscle fibers responsible for contraction
exhibits alternating light and dark striations due to overlapping arrangement of myofilaments (actin and myosin)

sarcoplasmic reticulum
surrounds myofibril and forms terminal cisternae (to store and concentrate Ca2+)

transverse tubules (T tubules)
transmits action potential allowing whole fiber to contract simultaneously
triad is 1 T tubule and 2 terminal cisternae

sarcomere

Question 9

Skeletal Muscle Fibers

Answer 9

Question 10

Sarcomeres

Answer 10

are the basic functional, contractile units of muscle

• comprised of myofilaments (-fibrils) that form striations with muscle fibers

Question 11

3 types of myofilaments

Answer 11

myosin (thick)
arranged in a bundle with heads directed outward in a spiral
interact with actin to form cross-bridges that pivot to produce motion

actin (thin)
intertwined strands of (G) actin with an active site

Ca2+ binds to actin receptors causing a shape change in troponin-tropomyosin complex that exposes active sites
active sites bind to myosin

Question 12

Muscle contraction is caused by the interactions of

Answer 12

myosin and actin filaments

Question 13

Sarcomeres and Striations

Answer 13

Actin and myosin are abundant and highly organized in sarcomere of muscle tissue

Question 14

Lines and Bands of actin and myosin

Answer 14

M line and Z line
M line is center of A band (midline of sarcomere)
Z disc is center of I band (ends of sarcomere)

A band
dark region consisting of thick filaments

I band
light region consisting of thin filaments

H band (zone)
area around M line that has only thick filaments

Question 15

Sliding filament theory

Answer 15

thin filaments of sarcomere slide towards M line in between thick filaments

• width of A band stays same; H and I bands get smaller

Question 16

In muscle contractions, sarcomeres are pulled towards center; that is,

Answer 16

Z lines shorten the I band to produce tension

Question 17

Neuromuscular junction

Answer 17

is the location of neural stimulation; functional connection between nerve fiber and muscle cell

Question 18

3 parts of neromusclar junctions

Answer 18

synaptic knob
swollen end of nerve fiber (contains acetylcholine - ACh)

motor end plate and junctional folds (sarcolemma)
increases surface area for ACh receptors
contains acetylcholinesterase (AChE) that breaks down ACh and causes relaxation

synaptic cleft
gap between nerve and muscle cell

Question 19

Skeletal muscle must be stimulated by a nerve or

Answer 19

it will not contract

Question 20

Neuromuscular Junction: Neural Stimulation steps

Answer 20

1. Neural action potential reaches synaptic knob
2. Synaptic terminal releases acetylcholine (Ach) into the cleft
3. Acetylcholine (Ach) :binds to receptors on junctional folds of sarcolemma to propagate action potential
4. Ach is removed by acetylcholinesterase (AChE)Action potential causes Na+ (in extracellular fluid) to travel to T tubule

-Ca2+ from terminal cisternae is released causing actin-myosin interaction

Question 21

Muscle function is a repeating cycle of

Answer 21

contraction and relaxation

Question 22

Activation encompasses

Answer 22

excitation
neural stimulation leads to action potentials in muscle fiber

excitation-contraction coupling
action potentials on the sarcolemma activate myofilaments

contraction
shortening of muscle fiber

relaxation
return to resting length

Question 23

Muscle contraction is ____; muscle relaxation is____

Answer 23

active; passive

Question 24

Excitation

Answer 24

is the process leading to an action potential in the muscle fiber

Question 25

Steps in excitation:

Answer 25

**-nerve stimulus** arrives at synaptic knob causes Ca2+ to allow release of Ach -Ach diffuses across cleft and binds to receptors on sarcolemma receptors change shape and allow Na+ and K+ to cross plasma membrane -Na+/K+ movements alter resting membrane potential (-90mV) and create an action potential muscle fiber is now excited

Question 26

Excitation-Contraction Coupling

Answer 26

refers to the activation of the myofilaments

Question 27

Steps of excitation-contraction coupling:

Answer 27

**-action potential spreads to T tubules** * terminal cisternae of SR release stored Ca2+ into sarcoplasm - Ca2+ binds to troponin-tropomyosin molecules of actin causing a shape change **-active sites on** actin are exposed * actin-myosin cross bridges can now form

Question 28

Contraction

Answer 28

refers to the development of tension in the muscle fiber

Question 29

Steps in contraction:

Answer 29

- myosin head, using ATP, activates and “cocks” into extended position * myosin binds to actin and a cross bridge is formed - myosin head flexes, pulling actin filament towards H zone * referred to as power stroke - myosin binds to new ATP and process repeats

Question 30

Myosin heads contract sequentially so as to not allow actin to

Answer 30

slide back to the resting position

Question 31

Relaxation

Answer 31

is the process of a muscle “passively” returning to resting length

Question 32

Steps in relaxation:

Answer 32

**-nerve stimulation stops** ACh is no longer released and is broken down by AChE **-Ca2+** is actively transported back into cisternae Ca2+ also dissociates from troponin-tropomyosin causing a shape change -active sites on actin are blocked myosin can no longer bind to actin

Question 33

Rigor mortis

Answer 33

is a stiffening of the body beginning 3 to 6 hours after death - deteriorating sarcoplasmic reticulum releases Ca2+ * activates actin-myosin cross bridges so muscle contracts but cannot relax - relaxation requires ATP and ATP production is no longer produced after death

Question 34

Fibers remain contracted until

Answer 34

myofilaments decay

Question 35

Rigor mortis is a temporary condition lasting about

Answer 35

24-48 hrs

Question 36

Tension

Answer 36

generated during contraction depends on length of muscle before it was stimulated - i.e. thick filaments are overly contracted and too close to Z discs; can’t slide far * weak contraction results - i.e. little overlap of thin and thick is too stretched; does not allow for many cross bridges to form * weak contraction results

Question 37

Muscle tone

Answer 37

Muscle tone (firmness of muscle at rest due to partial contraction) is maintained by the CNS ensuring optimal resting length - produces greatest force when muscle contracts * increasing muscle tone increases metabolic energy used, even at rest

Question 38

Weak stimuli do not cause

Answer 38

muscle contraction muscle tissue has a threshold level which the strength or frequency of stimuli will cause a contraction

Question 39

After threshold is reached, a latent period of no contraction follows:

Answer 39

- time required for excitation, excitation-contraction coupling, and internal tension to build * i.e., the contraction cycle has not begun

Question 40

Contraction (external tension)

Answer 40

followed by relaxation occurs -Ca2+ is released (cross-bridges form) and tension peaks but Ca2+ is quickly reabsorbed (cross-bridges detach) * contraction phase is shorter than relaxation phase

Question 41

Twitch

Answer 41

is a single stimulus (latency)–contraction-relaxation sequence:

Question 42

twitch is a single stimulus (latency)–contraction-relaxation sequence:

Answer 42

- treppe (staircase phenomenon) - faster stimuli produce stronger twitches * rare for skeletal muscles - wave summation - higher frequency stimuli arrives before muscle relaxes and recovers gradually producing more tension * incomplete tetanus (sustained, fluttering peak tension) is a form of wave summation - complete tetanus is when twitches fuse into a prolonged, continuous contraction * maximum frequency stimulation gives muscles no time to relax - rarely occurs in the body

Question 43

Motor unit

Answer 43

is a motor neuron and all the muscle fibers it innervates; dispersed within muscle causing weak contractions over wide area

Question 44

2 motor units

Answer 44

- small motor units * fine control units and may contain as few as 20 muscle fibers per nerve fiber - eye and hand muscles - large motor units * strength control units and may contain 200 or more muscle fibers per nerve fiber - gastrocnemius muscle (1000 fibers per nerve fiber)

Question 45

Muscles contain multiple motor units to sustain long term contraction; motor units alternate

Answer 45

to prevent fatigue (asynchronus motor unit summation)

Answer 46

Motor Units

Question 47

Isotonic and Isometric Contractions

Answer 47

Muscle contraction does not always change the muscle length but tension will always develop

Question 48

Types of tension development:

Answer 48

**isotonic muscle contraction** develops tension while changing muscle length * tension while shortening is concentric (isotonic) contraction * muscle tension \> resistance* * tension while lengthening is eccentric (isotonic) contraction * muscle tension \< resistance* **isometric muscle contraction** develops tension without changing length * important in postural muscle function and antagonistic muscle joint stabilization

Question 49

Answer 49

Isometric and Isotonic Contractions

Question 50

ATP, CP and Pyruvic Acid ATP

Answer 50

Sustained muscle contraction uses a lot of ATP (adenosine triphosphate) -muscles store enough energy via CP (creatine phosphate) to start contraction * must manufacture more ATP as needed - mitochondria are responsible for the production of ATP

Question 51

Glucose is metabolized into

Answer 51

ATP

Question 52

Different mechanisms synthesize ATP depending on

Answer 52

exercise duration

Question 53

Cells produce ATP in 2 ways:

Answer 53

glycolysis aerobic metabolism

Question 54

glycolysis

Answer 54

* breaks down glucose from glycogen stored in skeletal muscles when stored ATP is exhausted - produces 2 ATP and 2 pyruvate molecules per glucose molecule; a lactic acid byproduct is also produced \>\>\>\>lactic acid is the “feel the burn” of exercise

Question 55

aerobic metabolism

Answer 55

* mitochondria utilize pyruvate, O2, ADP to enzymatically synthesize ATP - produces net 34 ATP per glucose molecule (17 per 1 pyruvate molecule created by glycolysis) \>\>\>primary source of ATP for resting muscles

Question 56

Active muscles utilize glycolysis (approximately 10 mins) until oxygen consumption allows

Answer 56

aerobic respiration to resume

Question 57

Citric acid cycle

Answer 57

to remove and deliver H+ from organic molecules to the ETS (via coenzymes NAD/FAD) - 2-carbon molecule (acetate) is attached to coenzyme A, forming acetyl-CoA * acetyl group is removed and attached to a 4-carbon molecule forming citric acid - 1 ATP is produced for each processed acetyl group

Question 58

ETS function

Answer 58

to transfer (e-) from H+ (oxidation) creating a concentration gradient which results in the production of ATP * cytochromes pass (e-) to generate energy that pumps H+ out of mitochondrial interior * * diffusion of H+ powers attachment of high-energy phosphate to ADP (phosphorylation) using ATP synthase -(e-) transferred to oxygen, eventually forming water

Question 59

Answer 59

ATP Production

Question 60

Fatigue

Answer 60

causes muscles to become progressively weaker; causes include: - ATP synthesis declines as glycogen is consumed - lactic acid inhibits enzyme function * lowers pH causing decreased Ca2+ troponin binding After exercise, the body needs more O2 than

Question 61

After exercise, the body needs more O2 than usual to normalize metabolic activities resulting in

Answer 61

oxygen debt

Question 62

oxygen debt

Answer 62

* replenishes O2 reserves * replenishes ATP and CP resting levels * reoxides lactic acid into pyruvic acid - pyruvic acid is converted back to glucose to be stored * serves metabolic rate - active muscles produce heat and raise body temperature and consume extra oxygen

Question 63

Muscle Fiber types

Answer 63

Slow-twitch Fibers Fast Twitch Fibers

Question 64

Slow-twitch fibers

Answer 64

have more mitochondria, myoglobin and capillaries (aerobic respiration) - small diameter; slow contractions and are resistant to fatigue * soleus and postural muscles of the back

Question 65

Fast-twitch fibers

Answer 65

Fast-twitch fibers have enzymes for glycogen-lactic acid systems (anaerobic fermentation) - large diameter; quicker/more forceful contractions; not resistant to fatigue * extraocular eye muscles, gastrocnemius and biceps brachii

Question 66

Intermediate fibers

Answer 66

are similar to fast-twitch fibers but more have capillaries; more fatigue resistant

Question 67

All muscles contain all fiber types;

Answer 67

proportions are genetically determined

Question 68

Answer 68

Slow vs. Fast Fibers

Question 69

Muscle Performance

Answer 69

is a measure of strength and conditioning strength depends on: * muscle size and fascicle arrangement -length of muscle at start of contraction \>\>length-tension relationship * # of motor units utilized

Question 70

conditioning depends on:

Answer 70

* resistance training (weight lifting) stimulates cell enlargement due to synthesis of more myofilaments * endurance training (aerobic exercise) produces an increase in mitochondria, glycogen and density of capillaries

Question 71

Muscle performance ultimately depends on the types of

Answer 71

muscle fibers and to lesser extent physical conditioning

Question 72

Hypertrophy:

Answer 72

muscle growth from heavy training * increases diameter of muscle fibers and number of myofibrils * increases mitochondria and glycogen reserves

Question 73

Atrophy:

Answer 73

-muscle shrinkage from lack of exercise * reduction in diameter of muscle and number of myofibrils * nominal decrease in mitochondria

Question 74

Muscles become flaccid when inactive for days or weeks;

Answer 74

what you don’t use, you lose

Question 75

Cardiac Muscle Cells

Answer 75

are involuntary, thick with a single large nucleus and notched ends -have less developed SR with no cisternae but have wide T tubules **-use aerobic respiration** resistant to fatigue but very vulnerable to interruptions in oxygen supply **-intercalated discs** link heart cells mechanically (desomosomes), chemically and electrically (gap junctions) heart functions as a single fused mass of cells -demonstrate **automaticity**

Question 76

Answer 76

Structure of Cardiac Cells

Question 77

Smooth Muscle

Answer 77

are involuntary, spindle-shaped cells with a single central nucleus - no **striations, sarcomeres or Z discs** - SR is scanty and there are no T tubules * Ca2+ for contraction comes from extracellular fluid - *disorderly* arrangement of actin and myosin filaments * **dense bodies** transmit contraction from cell to cell - nerve supply is autonomic (if present) * releases either ACh or norepinephrine

Question 78

Myofilaments are scattered so resting length is not related to tension development; functions

Answer 78

over a wide range of lengths (plasticity)

Question 79

Answer 79

Smooth Muscle