LO Muscle Physiology

Question 1

What are the different types of muscles

Answer 1

Striated Muscles -cardiac and skeletal (movement/posture/respiration) and smooth muscles (viscera, blood vessels) .

Question 2

How are skeletal muscles organized?

Answer 2

muscle, fascicle, muscle fibres, myofibrils.
epimysium over whole muscle
perimysium surrounds fascicles
endomysium surrounds muscle fibers
Tendinous junction w finger like extentions conect tendon to myofiber.

Question 3

How are myofibers and myofibirls organized within the muscle fiber?

Answer 3

myofibres long, cylindrical and have nuclei
multinucleated

myofibrils are separated by mitochondria and SR, composed of myofilaments.

Question 4

What is the SR, t-tubule and triad juntion?

Answer 4

SR: smooth ER forms network of tubules, surrounds individual myofibrils, forms terminal cisternae on either side of T-tubules, stores CA+ at rest, releases ca when activated

T-tubues: have AP travel down them in skeletal and cardiac muscle. deep invaginations of sarcolemma,

Triad junction: 1 ttubule and 2 terminal cisternae. tubule has dihydropyridine receptors (voltage gated) and terminal cisternae of SR have ryanodine receptors (allow ca release). these touch and release calcium.
= has calsequestrin that concentrates calcium
= has atpase that pumps calcium back into SR.

Question 5

What are contractile units of a muscle?

Answer 5

sarcomeres. two z disks. every sarcomere has 2 myofilaments, thin and thick.

Question 6

What are contractile units composed of?

Answer 6

Thick myofilament (tail and head-where atpase and binds to actin). make myosin myofilament
Thin actin: made of globular actin, polymerize to form a strand, protein and troponin complex.
tropT: toypomyosin
trop C: calcium
TropI binds atin
At low Ca+, myosin head is blocked by tropomyosin
Ca+ unmasks tropomyosin and myosin head can bind.

Question 7

Sequence of events leading to a muscle contraction

Answer 7

myosin head binds actin (adp and p) then it strokes, releasing ADP and P, then it gains ATP cross-bridge detaches, then it hydrolyzes and the head cocks

Question 8

What is the sliding filament model of contraction?

Answer 8

actin and myosin filaments overlap, slide along them and shorten the sarcomere. actin is not actually getting shorter. myosin myofilaments dont move.

Question 9

What is the basal lamina?

Answer 9

sits under endomysium, has glycoproteins and collagen.
it goes plasma membrane, basal lamina, then endomysium.
Basal lamina binds the myofibre via the dytroglcan-containing complex. Bridges it to the cell.

Question 10

What is a motor unit?

Answer 10

a motor neuron and the muscles it innervates

Question 11

What is a motor end plate?

Answer 11

domain of sarcolemma that initates AP that goes along the myofiber causing contraction. Highly exitable.

Question 12

What is a nmj?

Answer 12

junctional folds only seen in NMJ, active zones filled with a transmitter.
basal lamina is present

Question 13

what is exitation/contraction coupling? for skeletal

Answer 13

release ach into cleft, post synaptic membrane has ach nicotinic receptors at the crests of the folds. Sodium gated end plate AP, travels down sarcolema then down ttubules.

depolarization, AP, calcium increases from 100nm-1um, production of force, ca returns to normal, cell relaxes. 10-90ms

Question 14

what is summation and tetanus?

Answer 14

twitches summate from multiple reccurent APs

tetanus is like getting cramps cause it gets tired, fatigue

Question 15

what are some clinical applications?

Answer 15

botox: inhibits ach at the axon terminal.

DMD(1/3500) and BMD(1/18000): mutations on the dystrophin gene of th e x chromosome. wasting of muscles and mental retardation.
curved spine, waddling walk, tip toes
enlarged calfs (psuedohypertrophy)
loss of ability to write over time, breathing difficulties, heart failure or pneumonia is how you die.
inherited from a carrier mother: recessive gene.
the gene causes a problem with dystrophin complex which makes it a target for degradation.
- c terminal binds beta diystroglycan
- end terminal binds to actin cytoskeleton
over time injuries with contraction

DMD: total dysfunction
BMD: partial dysfunction

Question 16

Dystorphin mouse?

Answer 16

silly mouse walks differently

Question 17

therapeutitic strategies for DMD

Answer 17

cell therapy: myoblast or stem cell transplant
pharmacological approach: reduce inflammation
gene therapy: deliver DNA encoding dystrophin and skip exons

Question 18

Characteristics of cardiac muscle?

Answer 18

• myocardium
• involuntary
• rhythmic
• short and branched cardiomyocytes
• connected via dics
• ONE NUCELUs per fiber (unlike skeletal which have multiple)
• joined by intercalated disks

Question 19

junctions at intercalated disk?

Answer 19

Transverse (perpenticular)
- zonula adherens (anchor actin of terminal sarcomeres to plasma membrane
- desmosomes: bind fibres together to prevent separation during contraction
Lateral (parallel)
- gap junctions

Question 20

Cardiac Action Potential? Main differences?

Answer 20

can’t store calcium so it comes from extracellular fluid in ttubules, and it is a diad not a triad.
Ap takesa bout 150 ms. action potential then calcium then force.

ap travels down t tubueles, ca entry from lumen through dihydropyridine receptors for CICR into SR which leads to more calcium release which unmasks myosin binding sites forms cross bridge, power stroke and contraction. requires atp.

Question 21

CICR?

Answer 21

lumen full of calcium, dihydropyridine calcium voltage gated. AP lets calcium out. this triggers ryanodine receptors to release calcium.

• has SERCA atpase ca pump
• has na/ca2+ exchanger on ttubule.
• has calsequestrin in SR>

Question 22

Types and characteristics of smooth muscles

Answer 22

• gastro, repiratory, blood vessels, involutary, nonstriated, one central nucleus, NO TTUBULES, communicate via gap junction. corkscrew contracted in a mesh

tunica media: thicker in arteries, make up of smooth muscle cells and elastic tissue, control vessel diameter.

intestine: longitudinal: outermost, run parallel, move food down
circular: innermost, constrict so that food doesn’t go up
(like a worm, peristalsis)
oblique layer IN STOMACH: another one that works with circular and longitudinal to move food down the line

Question 23

contractile apparatus in smooth muscle

Answer 23

myosin and actin filaments attached to dense bodies in sarcoplasm or plasma membrane plaques
stretch across the cell

thin filaments
some attached to dense bodies in cytoplasm
some atttach to dense plaques of the plasma membrane

Question 24

electromechanical coupling

Answer 24

requires depolarization for CICr

- has serca and ca2+ pump for extracellular thing.

Question 25

pharmomechanical coupling

Answer 25

nt and hormones release ip3, which binds to ip3 receptors which releases calcium activate MLCK.
- takes 40 seconds (elecrical or hormonal)

Question 26

how are smooth muscles innervated? what is a multi-unit and single unit?

Answer 26

varicosites (synaptic vesicles with NT and hormones) diffuse until they find receptors.

multiunit: groups of cells each group is independant from another (large blood vessels, airways, lens, iris, hair follicles)
single unit: connected through gap junctions (allow electrical and little proteins through), when one contracts they all contract. (viscera and vessels)

Question 27

exitation contraction coupling for smooth muscle

Answer 27

calcium bind calmodium induces activation of MLCK is phosphorylated on myosin myofilaments, cross bridge, contraction!

Question 28

what are caveolae and what is the peripheral sarcoplasmic reticulum?

Answer 28

invaginations instead of ttubules

its the one in smooth muscles.