Skeletal muscle 1 Flashcards
Describe each muscle fiber
-giant, multinucleated cell formed by fusion of many myoblast cells during development
1 cell= 1 fiber
-peripherally located nuclei
At the end of cells, thin filaments are attached to the PM by _______ and then to the tendons via ________.
- Adherens junctions
- Basal lamina
Within a muscle, a number of myofibers are clustered together in ________ which in turn can be clustered together to form a single muscle
-fascicles
Endomysium
- CT around a single muscle fiber
- electrically insulate them from neighbors
- contains basement membrane
Perimysium
-CT around muscle fascicle
Epimysium
- CT around entire muscle
- aka fascia
Muscle fiber is composed of ______ which are composed of ________.
Myofibrils
Sarcomeres
Tension development is proportional to?
number of myosin heads overlapped by thin filaments
Myosin polymerizes to form ______ filaments
bipolar
What part of myosin is responsible for generating the powerstroke?
-Regulatory domain
Monomeric vs filament actin
Monomeric: G-actin, ATP is hydrolyzed very slowly; this hydrolysis is not what powers contraction
Filament: F-actin; polarized filament; rapidly hydrolyzes ATP, but with slower release of Pi
Ends of F-Actin and which connects to Z-disk
-Pointed end is minus end
Barbed end is plus end; anchored in Z disk
Myosin always moves toward _______ end of actin filaments
Barbed
Rigor complex
-Myosin catalytic/motor domains bind very tightly to actin in absence of ATP
Actin-Myosin interaction is _______ by ATP
-weakened
Myosin ATPase rate is ______ by actin
accelerated
Strong and Weak binding states
Strong: myosin bound with ADP dissociated very slowly and therefore, binds tightly to actin
Weak: myosin with ATP or ADP.Pi dissociates rapidly from actin, so it binds much less strongly
What is the force producing state?
When Pi dissociated from AM:ADP:Pi
Tropomodulin and CapZ
T: capping protein that regulates actin length at pointed end
CapZ: capping protein that regulates actin length at barbed end
Z-disks are aligned and connected to the PM by _________.
Intermediate filaments; ultimately connected to dystrophin complex
Dystrophin
links actin filaments to protein complexes anchored in surface membrane
How can one increase the force of contraction within a twitch?
-increase the force of contraction by increasing the frequency of stimuli, which increases the ca2+ as well
