EXAM 4: Muscle Histology Flashcards
What is the sacrolemma
Muscle cell membrane
Sacroplasm
Cytoplasm of a muscle cell
What is inside the sacroplasm
Myofibrils, myoglobin, glycogen
What is a myofibril
Long bundles of proteins
Function of myoglobin
Stores oxygen for use
What are transverse tubules (T-tubules)
Tube-like structures in the sarcolemma that penetrate the interior of the cell
They are filled with extracellular fluid
what are terminal cisternae
sacs of the SR, closely associate with T-tubules
What are the three types of proteins in the myofibrils
Thick filaments, thin filaments and elastic filaments
What are filaments responsible for
Muscle contraction
What are thick filaments made up of
A polymer of Myosin proteins
(Hundreds of myosin proteins)
What are thin filaments made up of
A polymer of Actin
troponin and tropomyosin accessory proteins
What are elastic filaments made up of
Titin
What are sacromeres
Functional units of filaments
What is a single myosin shaped like
A golf club (the head is mobile and can extend and flex)
Function of myosin
Myosin can bind and hydrolyze ATP
- The release of energy allows the head to change shape (flex) and ultimately generate force
What does each actin monomer have
An active site that can bind to the head of a myosin protein
Function of tropomyosin
Blocks the active site of myosin in relaxed muscles
Function of troponin
Binds to and regulates tropomyosin
What happens to troponin and tropomyosin in the presence of calcium
Troponin moves tropomyosin off active sites of actin
What are striations
The pattern created by thick and thin filaments overlapping each other
L band
Light region, only thin filaments
A band
Dark region, thick filaments
Z disks
Boundary between sacromeres
M line
Midline of sarcomere
H zone
Contains thick filaments, no thin filaments
Sliding filaments model
Interactions between thin and thick filaments (with ATP hydrolysis) causes sarcomeres to slide closer to each other
- Thin filaments are pulled along thick filaments toward the M-line of the sacromere
- contraction of many sarcomeres, in my myofibrils, in many cells causes the muscle to contract as a whole
- (note that not all muscle cells may be excited at the same time)
