Muscle

Question 1

Striated muscles

Answer 1

Skeletal, cardiac

Question 2

Multinucleated muscles

Answer 2

Skeletal only

Question 3

Motor unit

Answer 3

Group of muscle fibers that function together and the somatic motor neuron that controls them. All muscle fibers in a motor unit are of the same type and this is determined by the somatic neuron during development. Motor units can contain as little as a few fibers. All fibers in the same motor unit fire together and are of the same fiber type.

Question 4

Antagonistic muscle pairs

Answer 4

Ex: bicep & tricep; skeletal muscles largely exist in antagonistic pairs

Question 5

Muscle origin

Answer 5

Part of the muscle closest to the trunk or more stationary

Question 6

Muscle insertion

Answer 6

Part of the muscle that is more distal or mobile

Question 7

Ligaments

Answer 7

Connect two bones

Question 8

Tendons

Answer 8

Connect muscle to bone

Question 9

Muscle “growth”

Answer 9

Satellite cells are muscle stem cells that contribute extra nuclei to skeletal muscles for muscle “growth”

Question 10

Components of the sarcomere

Answer 10

Sarcomere = basic structural unit of skeletal muscle

Myofibrils are made up of back to back sarcomere.

Sarcomere is composed of thick (myosin) and thin (actin) filaments. Thick filaments are stabilized by titin and nebulous helps align actin filaments.

Each end of the sarcomere is the Z disk. The center of the sarcomere is the M line.

Question 11

Sliding filament theory

Answer 11

Thick and thin filaments slide past each other in muscle contraction shortening the distance between the M line and Z disk. The myosin heads form crossbridges with actin of the thin filament.

Question 12

Function of the t-tubule

Answer 12

Brings action potentials into the interior of the muscle fiber

Question 13

Protein that blocks myosin-actin binding sites

Answer 13

Tropomyosin

Question 14

Protein that sits atop tropomyosin and moves tropomyosin when bound to Ca2+

Answer 14

Troponin

Question 15

Relationship between myosin and actin in the relaxed state

Answer 15

Myosin head is cocked and weakly bound to actin

Question 16

Relationship between myosin and actin in power stroke

Answer 16

Myosin is bound strongly to actin causing actin filament to move in power stroke

Question 17

Events that lead to the firing of an AP at the neuromuscular junction

Answer 17

Somatic neuron releases ACh which binds to ligand-gated Na+ channels in sarcolemma of motor end plate. Na+ flows into the cell, depolarizing it and causing more voltage-gated Na+ channels to open. Further depolarization causes an AP which travels down the t-tubule to the DHP (dihydropyridine L-type calcium channel).

Question 18

How does an AP lead to an increase in [Ca2+] in the cytosol?

Answer 18

DHP is stimulated by the AP to “tug” on RyR (ryanodine receptor-channel) which causes the release of Ca2+ from the sarcoplasmic reticulum. Ca2+ then binds to troponin and muscle contraction begins.

Question 19

What causes a decrease in [Ca2+] in the cytosol which allows the muscle fiber to relax?

Answer 19

Sarcoplasmic Ca2+-ATPase pumps Ca2+ back into the sarcoplasmic reticulum

Question 20

What occurs during the latent period between muscle fiber AP and development of tension during muscle twitch?

Answer 20

Ca2+ releases, binds to troponin, troponin moves tropomyosin

Question 21

Types & causes of muscle fatigue

Answer 21

CNS fatigue - largely psychological
PNS fatigue - failure of excitation-contraction coupling, acidosis, elevated inorganic phosphate slows release of inorganic phosphate from myosin or binds to Ca2+, ion imbalances which change sodium potassium pump activity

Question 22

Ways that muscle cells make ATP

Answer 22

Substrate-level phosphorylation using creative phosphate
Oxidative phosphorylation
Substrate-level phosphorylations of glycolysis

Question 23

Slow twitch vs fast twitch

Answer 23

Slow - oxidative ATP synthesis which is slower but generates more ATP, requires more oxygen so more vascularized & contains more myoglobin, smaller diameter allows more efficient oxygen diffusion

Fast - glycolytic & creative ATP synthesis which is faster but generates less ATP, not dependent on oxygen so not as vascularized/lighter in color b/c less myoglobin/ larger diameter due to glycogen stores; fatigues more quickly

Question 24

Fastest source of energy in the muscle fiber

Answer 24

ATP and CP stores

Question 25

Intermediate source of energy in the muscle fiber

Answer 25

ATP from glycolysis

Question 26

Slowest but most sustainable source of energy in the muscle fiber

Answer 26

ATP from oxidative phosphorylation

Question 27

In which type of muscle fiber would you expect to find more mitochondria?

Answer 27

Slow-twitch

Question 28

Which type of muscle fiber do you expect to undergo glycolytic then oxidative phosphorylation as energy needs continue?

Answer 28

Fast-twitch oxidative-glycolytic (intermediate)

Question 29

Which muscle fibers are most easily fatigued?

Answer 29

Fast-twitch

Question 30

Why does too much actin/myosin overlap result in reduced fiber tension?

Answer 30

TBD

Question 31

Why does too little actin/myosin overlap result in reduced fiber tension?

Answer 31

Too few crossbridge linkages to generate much force

Question 32

Muscle twitches can undergo ______ summation

Answer 32

Temporal (not spatial)

Question 33

What determines how long a muscle is contracted?

Answer 33

[Ca2+] is continually high in the cytosol

Question 34

Tetanus & difference between infused and complete tetanus

Answer 34

Tetanus - Continuous maximum muscle tension Unfused - brief moments of slight relaxation occur during this period Complete - no relaxation - complete maximum tension until muscle fatigue causes the muscle to lose tension despite continuing stimuli

Question 35

How to lift heavy :)

Answer 35

Recruit more motor units

Question 36

Isotonic vs isometric contractions

Answer 36

Isotonic - muscle contracts, shortens, and creates enough force to move a load Isometric - muscle contractions, does NOT shorten, force does NOT move the load Elastic tendons compensate for muscle shortening in isometric contractions

Question 37

Types of smooth muscle + examples

Answer 37

Phasic that is usually relaxed; ex: esophagus Phasic that cycles between contraction and relaxation; ex: intestine Tonic that is usually contracted; ex: sphincter Tonic that contracts variably; ex: vascular smooth muscle

Question 38

Contracted smooth muscle appears _____

Answer 38

Bulky instead of shortened

Question 39

Why are single unit smooth muscle cells connected by gap junctions?

Answer 39

Allows the signal from the autonomic neuron varicosity to travel between cells so they all contract as a unit. Ex: small intestine

Question 40

Why are multi-unit smooth muscle cells electrically independent?

Answer 40

Each cell can be stimulated independently which allows for more precise movements. Ex: eye

Question 41

Which muscle cells have the longest contraction-relaxation cycle?

Answer 41

Smooth (then cardiac, and skeletal is fastest)

Question 42

Slow wave potential vs pacemaker potential

Answer 42

Periodic subthreshold depolarization which may eventually reach threshold causing an AP Periodic suprathreshold depolarization which causes an AP to fire every time. Present in cardiac and smooth muscle cells.

Question 43

Steps involved in smooth muscle contraction

Answer 43

1. Signal arrives for Ca2+ to enter the cell (vague, but roll with it) 2. Entry of Ca2+ initiates release from the SR (aka calcium spark) 3. Ca2+ binds to calmodulin 4. Calmodulin activates MLCK (kinase) 5. MLCK phosphorylates the myosin head and increases myosin ATPase activity 6. Crossbridge cycling is enabled

Question 44

How does smooth fiber myosin differ from skeletal fiber myosin?

Answer 44

Smooth fiber myosin does not have an ATP binding site

Question 45

Why does smooth muscle have lower ATP requirements than skeletal muscle?

Answer 45

TBD

Question 46

Troponin exists in which muscle fiber types?

Answer 46

Skeletal and cardiac, not smooth

Question 47

Steps involved in smooth muscle relaxation

Answer 47

1. Ca2+ is removed from the cytosol by: a) primary active transport into SR, b) primary active transport into ECF, c) secondary active transport using Na+ gradient into ECF 2. Ca2+ is released from calmodulin (law of mass action) 3. MLCK activity decreases 4. MLCP removes phosphates from myosin heads and decreases myosin ATPase activity 5. Cross-bridge cycling decreases

Question 48

Why do cardiac muscle cells have larger t-tubules?

Answer 48

Spread the depolarization faster

Question 49

Why do cardiac muscle cells have intercalated disks?

Answer 49

Contain demsmosomes and gap junctions which help in cell-to-cell communication and thus coordinated muscle contraction and provide mechanical strength to the small cardiac fibers

Question 50

Why do cardiac muscle cells have smaller SR?

Answer 50

Some Ca2+ comes from outside of the cell

Question 51

Pacemaker cells

Answer 51

A patch of cells independent of the CNS which fire action potentials at a given rate and depolarize the cardiac fiber

Question 52

Process of excitation-contraction coupling in cardiac muscle

Answer 52

1. Depolarization/Na+ entry —> fires AP 2. Depolarization opens DHP Ca2+ channels in T-tubules 3. Small amount of Ca2+ Enters cell binding to RyR in SR membrane causing it to open 4. Ca2+ flows into cytosol 5. Ca2+ binds troponin, enables crossbridge cycling/sliding filaments 6. Ca2+ pumped back into SR/ECF via primary/secondary active transport 7. Membrane is repolarized when K+ exits cell and ends AP

Question 53

Biggest difference between cardiac and skeletal excitation-contraction coupling

Answer 53

DHP physically tugs on RyR in skeletal muscle while in cardiac muscle, DHP allows a trigger amount of Ca2+ into the cell to bind to RyR

Question 54

Why does cardiac muscle have a long refractory period and action potential?

Answer 54

Influx of Ca2+ contributes to the formation of the AP TBD

Question 55

What activates the myosin head for cross-bridge cycling?

Answer 55

ATP!

Question 56

What breaks the bond between myosin head and actin filament to end cross bridge cycling?

Answer 56

ATP!

Question 57

What is on the myosin head when in the cocked position?

Answer 57

ADP and inorganic phosphate

Question 58

What is released from the myosin head to bind it more strongly to actin?

Answer 58

inorganic phosphate

Question 59

What is released from the myosin head to make the head pivot, performing the full cross bridge?

Answer 59

ADP

Question 60

What is the cause of rigor mortis?

Answer 60

Tension requires ATP...but so does relaxation! Lack of ATP means that myosin heads remain bound to actin, so your muscles tense up completely. That's why a corpse is called a 'stiff'.

Question 61

Tight binding in rigor state for myosin head

Answer 61

Myosin is tightly bound to actin, but has already pivoted and not yet cocked. NO ATP, NO Pi, NO ADP. NOTHING!