muscle contraction

Question 1

motor unit

Answer 1

motor neuron + it’s muscle fibers

large fibers - large movement

small - fine movement (eye)

Question 2

NMJ

Answer 2

presyn = axon terminal

postsyn = muscle endplate

Question 3

steps at the NMJ

Answer 3

1. Ap conducted into pre-syn terminal
2. depolarize pre-syn terminal
3. Opening of VG-Ca2+ channels and entry
4. fusion of vesicles w membrane - Ach into cleft
5. Ach binds receptor on post-syn membrane
6. opening of channels on post-syn membrane - Na and K travel down gradient
7. generation of EPP
8. Ach broken down into coline and acetate - choline back to pre-syn

10.

Question 4

EEP characteristics

Answer 4

latency - delay from AP –> muscle

graded - size dep on how many vesicles of Ach released

quantal - goes up step by step (each vesicle) - adds up to full potential

decremental conduction - gets smaller further away from end plate

high safety factory (skel muscle) - as long as EPP what it’s supposed to be you will get AP!

Question 5

decremental conduction

Answer 5

if EEP but NOT AP

at nmj you can still see the EEP but it goes away (still see same strong AP far away)

Question 6

muscle structure

Answer 6

muscle - fascile - muscle cell (fiber) - myofibrils (in muscle cell covered by SR) - myofibrils - sarcomere (with actin and myosin)

Question 7

T tubules

Answer 7

formed from invaginations of plasma membrane

Question 8

triad

Answer 8

sarcoplasmic reticulum cisterna on either side of transverse tubule

Question 9

skeletal muscle excitation

Answer 9

1. AP into T tubules
2. VG L-type Ca channel conformational change
3. Ca release channel open (mechanically cated, Ca gated)
4. mytoplasmic [Ca] increases

Ca DOES NOT MOVE through L-type channels in the T tubules

Question 10

how do skeletal and cardiac muscle excitation differ

Answer 10

1. Ca enters through L type channels
2. no mechanical link between L type and SR ca release (80% from SR, 20% from membrane)
3. can be modulated

Question 11

tropomyosin

Answer 11

binds to actin and troponin

Question 12

TnT

Answer 12

troponin T

binds to tropomyosin

Question 13

TnC

Answer 13

tropinon

binds to Calcium

Question 14

TnI

Answer 14

interferes

troponin

Question 15

how does troponin work

Answer 15

increased Ca –> binds to TnC –> actomyosin complex formed –> tension increases

Question 16

E-C coupling in skeletal muscle

Answer 16

muscle action potential

increase in Ca - myoplasm

Ca-troponin

increase muscle tension

decrease muscle tension

Question 17

SERCA

Answer 17

Ca-ATPase - pumps Ca back into SR

primary active transport

Question 18

calsequestrian

Answer 18

bound to ca in SR

Question 19

relaxation in skeletal musche

Answer 19

1. l type Ca channels close
2. Ca-gated channel inactivated
3. SERCA pump back in
4. Ca binding proteins in cytoplasm

Question 20

differences betwen cardiac and skeletal uscle relaxation

Answer 20

sarcolemma:

Ca-Na pump

Ca pump

SR:

PLN –> increases SERCA

all can be regulated

Question 21

Ca release channels in skeletal muscles

Answer 21

mechanically and ionically

Question 22

crossbridge system

Answer 22

Question 23

isometric tension

Answer 23

length - no change

tension - increasing

head rotates developing isometric contraction

acheives 45% by stretching neck of myosin (not enough tension to shorten sarcomere)

recruits more and more muscle fibers until enough muscle tension

Question 24

isotonic tension

Answer 24

length - shortening

tension - no change

muscles can’t change length and tension at same time

Question 26

muscle resting length-tensison

Answer 26

more stretched - increased resting tension

Question 27

Titan

Answer 27

mechanism of passive and restoring force generation when tighten muscle - titan stretches molecular basis for resting tension

Question 28

fused tetanus

Answer 28

summation of tetanic stimulus until it fuses

Question 29

how to increase active tension

Answer 29

increase stimulus frequency recruit motor units

Question 30

active tension

Answer 30

total tension when contract (measured) - resting tension hihest at resting length

Question 31

sliding filament model

Answer 31

1. F due to interaction of thick and thin filaments 2. muscle filament length is constant 3. filaments can slide past each other 4. isometric F is proportional to thick and tin filament overlap

Question 32

isometric force and length

Answer 32

due to interaction of thick and thin filaments 0 tension when 0 overlap or full over lap most tension when meet - no overlap middle when slight overlap same in cardiac and skeletal muc

Question 33

length-tension plot

Answer 33

shows changesin isometric tension with sarcomere (muscle) length

Question 34

isometric

Answer 34

for more tension - add crossbridges and muscle fibers same length - recruit more don't shorten until have enough tension

Question 35

isotonic

Answer 35

when muscle begins to shorten - no more crossbridges or muscle fibers are added

Question 36

what if lifting more than you can hold up isometrically?

Answer 36

first need titan to lift for a second but then will drop it

Question 37

preload

Answer 37

determines initial muscle length determined by amt of blood in the heart (resting tension)

Question 38

afterload

Answer 38

determines force required to shorten and end muscle length pressure in orta (what pushing against but doesn't know it's there)

Question 39

shortening velocity

Answer 39

depends on myosin isoform (ATPase) and force against which muscle contracts (afterload) at heaviest load - muscle can't contract - V = 0 AND preload (at heavy - few xb available for fast cycling, at light - many xb available for fast cycling) high BP- can't contract as fast bc so much afterload 1. afterload 2. preload 3. myosin isoform(ATPase)

Question 40

velocity and afterload

Answer 40

bigger F pumping against - lower Velocity

Question 41

shortening velocity and myosin ATPase

Answer 41

Myosin ATPase (EC 3.6.4.1) is an enzyme with system name ATP phosphohydrolase (actin-translocating). [1] This enzyme catalyses the following chemical reaction ATP + H2O ADP + phosphate. ATP hydrolysis provides energy for actomyosin contraction.

Question 42

shortening velocity and preload

Answer 42

resting length - number of crossbridges ready to be formed for fast cycling

Question 43

power

Answer 43

afterload x velocity of showertening max power = 1/3 max load rate of doing work dep on: 1. myosin ATPase 2. load (afterload) 3. resting load (preload)