Lecture Notes: Muscular System Flashcards
skeletal muscle structure
muscle fibers, then myofibrils, and then myofilaments
muscle fiber (myocytes)
- sacrcolemma (cell memebrane)
- many nuclei adjacent to sarcolemma
- filled with myofibrils
- organelles between myofibrils
- sarcoplasm
sarcolemma
transverse tubules, lumen filled with extracellular fluid, transmit AP into muscle fiber
sarcoplasmic reticulm
stores calcium ions
Myofibrils (thin myofilaments)
-actin, troponin, tropomyosin
Actin
- 2 strands of fibrous actin
- each strand is a polymer of globular actin
troponin
- regulatory protein
- 3 subunits: ome binds to actin, one binds to calcium ion, one binds to tropomyosin
tropomyosin
- regulatory protein
- elongated and covers the active sites where myosin can bind
Myosin ( thick filament)
- 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
sarcomere
- organizational units of myofilaments
- z lines, i band, a band, h zone, m line, titin
Z lines
boarders
place of attachment
t tubules located here
i band ( isotropic)
from z line to end of myosin ( a band)
only thin
a band
complete length of myosin
thin and thick
h zone
center of a band
only thick
m line
middle of h zones
hold myosin
titin
largest known protein
between Z and M lines—hold myosin in center of sarcomere
passive elasticity of muscle
sliding filament model
- 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
Steps to Muscle Contraction/Relaxation
- Ap in motor neuron reaches neuromuscular synapse and releases acetyl choline
- increase permeability of sarcolemma to sodium, sodium moves into sarcoplasm, depolarization
- transverse bundles carry depolarization into muscle fibers
- SR releases calcium into sarcoplasm
4a. ap changes conformation of dihydropyradine (DHP), ryanodine (in contact with DHF) opens and allows flow of calcium - calcium binds to troponin, tropomyosin changes confomation and exposes mysoin binding sites on actin
- myosin head ( w/ ADP and inorganic phosphate) binds to active site of myosin and the inorganic phosphate is released
- Power Stroke
- ATP binds to myosin head, and then actin is released
- recovery stroke
- energy needed for relaxation
Power Stoke
adp is released, myosin head bends, muscle contracts
Recovery Stroke
Atp is hydrolyzed, ADP + Pi, myosin head back to resting conformation
energy needed for relaxation
- 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
rigor mortis
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
