Lecture Notes: Muscular System

Question 1

skeletal muscle structure

Answer 1

muscle fibers, then myofibrils, and then myofilaments

Question 2

muscle fiber (myocytes)

Answer 2

• sacrcolemma (cell memebrane)
• many nuclei adjacent to sarcolemma
• filled with myofibrils
• organelles between myofibrils
• sarcoplasm

Question 3

sarcolemma

Answer 3

transverse tubules, lumen filled with extracellular fluid, transmit AP into muscle fiber

Question 4

sarcoplasmic reticulm

Answer 4

stores calcium ions

Question 5

Myofibrils (thin myofilaments)

Answer 5

-actin, troponin, tropomyosin

Question 6

Actin

Answer 6

• 2 strands of fibrous actin

- each strand is a polymer of globular actin

Question 7

troponin

Answer 7

• regulatory protein

- 3 subunits: ome binds to actin, one binds to calcium ion, one binds to tropomyosin

Question 8

tropomyosin

Answer 8

• regulatory protein

- elongated and covers the active sites where myosin can bind

Question 9

Myosin ( thick filament)

Answer 9

• golf like protein: 2 molecules wound together in rod portion that end in 2 lateral heads:
• heads: have ATPase activity; can form cross bridges with actin; can bend and straighten
• each myofilaments with many myosin molecules

Question 10

sarcomere

Answer 10

• organizational units of myofilaments

- z lines, i band, a band, h zone, m line, titin

Question 11

Z lines

Answer 11

boarders
place of attachment
t tubules located here

Question 12

i band ( isotropic)

Answer 12

from z line to end of myosin ( a band)

only thin

Question 13

a band

Answer 13

complete length of myosin

thin and thick

Question 14

h zone

Answer 14

center of a band

only thick

Question 15

m line

Answer 15

middle of h zones

hold myosin

Question 16

titin

Answer 16

largest known protein
between Z and M lines—hold myosin in center of sarcomere
passive elasticity of muscle

Question 17

sliding filament model

Answer 17

• actin myofilaments slide past myosin myofilaments]
• z lines pulled together sarcomere shortens:
  a) length of actin and myosin filaments do not change
  b) length of A band does not change
  c) length of i band shortens
  d) h zone narrows and disappears

Question 18

Steps to Muscle Contraction/Relaxation

Answer 18

1. Ap in motor neuron reaches neuromuscular synapse and releases acetyl choline
2. increase permeability of sarcolemma to sodium, sodium moves into sarcoplasm, depolarization
3. transverse bundles carry depolarization into muscle fibers
4. SR releases calcium into sarcoplasm
   4a. ap changes conformation of dihydropyradine (DHP), ryanodine (in contact with DHF) opens and allows flow of calcium
5. calcium binds to troponin, tropomyosin changes confomation and exposes mysoin binding sites on actin
6. myosin head ( w/ ADP and inorganic phosphate) binds to active site of myosin and the inorganic phosphate is released
7. Power Stroke
8. ATP binds to myosin head, and then actin is released
9. recovery stroke
10. energy needed for relaxation

Question 19

Power Stoke

Answer 19

adp is released, myosin head bends, muscle contracts

Question 20

Recovery Stroke

Answer 20

Atp is hydrolyzed, ADP + Pi, myosin head back to resting conformation

Question 21

energy needed for relaxation

Answer 21

• active transport of calcium out of sarcoplasm and into sarcoplasmic reticulum, tropomyosin-troponin complex block myosin binding sites on actin
• duration of muscle contraction is in part controlled by how long calcium is maintained in the cytoplasm

Question 22

rigor mortis

Answer 22

ATP production stops
ATP levels decrease
no transport of calcium into sarcoplasmic reticulum (no return)
calcium leaks into the sarcoplasm, cross bridges form, contraction
not enough ATP to release myosin heads from actin