Muscle Cells

Question 1

sarcoplasm

Answer 1

cytoplasm

Question 2

sarcolemma

Answer 2

plasma membrane

Question 3

sarcoplasmic reticulum

Answer 3

smooth endoplasmic reticulum (stores Ca)

Question 4

transverse tubules (T-tubes)

Answer 4

deep invaginations in sarcolemma; extend into sarcoplasm

Question 5

terminal cisternae

Answer 5

Ca filled sacs at the end of sarcoplasmic reticulum

Question 6

Excitation-Contraction Coupling

Answer 6

1. somatic neuron releases ACh into NMJ
2. net entry of Na through receptor channel initiates muscle AP
3. action potential in T-tube alters conformation of DHP receptors
4. DHP receptor opens RyRs (Ca release channels in SR) and Ca enters cytoplasm
5. Ca binds to troponin; allowing actin-myosin binding
6. myosin heads initiate power stroke
7. actin filaments slide towards center of sarcomere

Question 7

myofibrils

Answer 7

cylindrical protein based fibrous structures that extend the entire length of the cell
located in muscle fiber cytoplasm
have the ability to shorten, causing contraction of muscle

Question 8

sarcomere

Answer 8

functional contractile unit of skeletal muscle fiber
myofibrils contain multiple and repeating sarcomeres

Question 9

myofibrils are composed of…

Answer 9

short bundles of myofilaments

Question 10

myofilaments

Answer 10

do not run the entire length of cell but are composed into repetitive groups (sarcomeres)

Question 11

what are myofilaments comprised of?

Answer 11

thin filaments= actin
thick filaments= myosin

Question 12

Thin filaments

Answer 12

5-6 nm in diameter
double helix of two strands of bead shaped actin twisted around each other

Question 13

What is a polymer of actin made up of?

Answer 13

globular G-actin= a single actin molecule
filamentous F-actin= G-actin monomers create a strand

Question 14

What are the regulatory proteins present in thin filaments?

Answer 14

tropomyosin- blocks active site on f-actin until Ca signal is present
troponin C- recognizes and binds to Ca, causing tropomyosin to move

Question 15

Thick filaments

Answer 15

bundles of myosin molecules
- thick globular heads
- long filamentous tails
myosin heads form cross-bridges with actin filaments during contraction

Question 16

Sliding filament theory

Answer 16

thin filaments slide together across thick filaments towards the m-line
as each sarcomere contracts, the whole fiber contracts

Question 17

Sliding filament theory steps

Answer 17

1. Ca levels increase in cytosol
2. Ca binds to troponin
3. troponin-Ca complex pulls tropomyosin away from actin-myosin binding site
4. myosin binds strongly to actin and creates power stroke
5. actin filament moves (crossbridge cycle)
   ATP requires to spring load myosin and remove it from actin

Question 18

Rigor Mortis

Answer 18

stiffening of muscles in a recently deceased person

Question 19

What causes Rigor Mortis

Answer 19

crossbridges cannot break because the body is not producing ATP