Lecture 10 Flashcards
What is a Muscle
A bundle of muscle fibers, anchored to a bone by tendons
What is a Muscle Fiber
A multinucleated muscle cell
What is a Myofibril
Longitudinal component inside a striated muscle cell, composed of a series of sacromeres
What is a Sarcomere
The contractile unit of striated muscle, composed of myofilaments
What are the Two Types of Myofilaments bound by Z disks in each Sarcomere?
- Actin thin filaments
- Myosin thick filaments
What is a Thin Filament (in a sarcomere)
A two-strand actin helix + the filamentous protein tropomyosin + the troponin complex
What is a Thick Filament ( in a sarcomere)
Hundreds of identical myosin proteins
The head Regions of Myosin (what it contains and what it forms)
- Contains actin- and ATP-binding sites
- Form cross-bridges with the thin filament during contraction
The Sliding-Filament Theory:
Sarcomeres shorten during muscle contraction because the thin filaments actively slide along the thick filaments
What do Cross-bridges Do?
Convert chemical energy into mechanical energy
Without ATP myosin where does it Bind?
Binds irreversibly to actin (rigor mortis)
Binding to Cross-bridges (ATP):
Hydrolysis of ATP causes myosin head to extend and attach to actin
Power Stroke of Cross-Bridges:
Release of phosphate promotes myosin head rotation
Release of Cross-Bridges
Binding of ATP causes myosin to detach from actin
Regulation of Muscle Contraction (When Ca 2+ is Low):
Tropomyosin blocks the myosin binding sites on actin
Regulation of Muscle Contraction (When Ca 2+ is High):
Ca 2+ binding to troponin removes an attachment inhibition between myosin cross-bridges and thin filaments
How are APs Conducted to Skeletal Muscles:
Through large myelinated motor neurons
What Does the Neuromuscular Junction Include:
Pre- and post-synaptic specialization
Excitation-Contraction Coupling - Why do Muscle Fibers Contract:
When a postsynaptic end plate potential at the neuromuscular junction causes a propagated AP in the fiber sarcolemma
An AP in the Muscle Fiber Changes What (in regards to Ca 2+):
The free [Ca 2+] in the cytosol
What do Transverse (T) Tubules Do:
Conduct APs into the cell interior, causing Ca 2+ release from the sarcoplasmic reticulum that surround the myofibrils
Control of Free [Ca 2+] in the Cytosol (DHPR and RyR):
Voltage-sensitive DHPR and RyR work together, linking depolarization of the T tubule to the opening of Ca 2+ channels in the SR membrane
Control of Free [Ca 2+] in the Cytosol (Ca 2+ Pumps):
In the SR membrane re-sequester Ca 2+ from the cytosol
Control of Free [Ca 2+] in the Cytosol (Calsequestrin):
Inside the SR binds Ca 2+ reducing the free [Ca 2+] inside the SR
Excitation Contraction Coupling (Skeletal):
DHPR and RyR physically interact –> depolarization-induced Ca 2+ release
Excitation Contraction Coupling (Cardiac):
Entrance of extracellular Ca 2+ through DHPR triggers opening of RyR –> Ca 2+ induced Ca 2+ release
