5. Skeletal Muscle Flashcards
Structure of skeletal muscle
Striated, voluntary, many nuclei
Major functions of skeletal muscle
Exert force and produce heat
Structure of smooth muscle
No striations, involuntary, single nuclear. Located in the walls of hollow organs.
Functions of smooth muscle
Peristalsis and control of blood flow
Structure of cardiac muscle
Striated, spontaneously active, involuntary, single nucleus
Function of cardiac muscle
Pumping blood
Intercalated discs
A feature of cardiac muscle that holds the cells together and allows them to act as one unit
Origin and insertion of skeletal muscle
Point of attachment to skeleton closest to spine is origin and point of distal attachment is insertion.
Origin and insertion occur through tendons.
Extensor and flexor
Muscles that act in opposition
5 levels of skeletal muscle organization
- skeletal muscle
- fasciculus
- muscle fiber
- myofibril
- myofilaments
Sacromere
Basic contractile unit in skeletal muscle
Fasciculus
Compartments full of muscle fibers
Bands of sacromere
1/2 light, 1/2 dark
Size of skeletal muscle fibers
A few millimeters to several centimeters long, but 50-60um diameter
Function of myofilaments
Intracellular contractile proteins that generate force.
Appearance of myofilaments
Arranged longitudinally to sacromeres. Striated appearance is a result of serial and parallel repitition of myofilaments and the differing abilities of actin and myosin containing areas to transmit light.
A band
Anisotropic band. Dark, myosin. Thick filament. Centre of the sacromere.
I band
Isotropic band. Light, actin. Thin filament. Anchored to Z lines.
Components of thin filaments
Two chains of globular actin molecules (G-actin) twisted into two strands to form filamentous actin (F-actin).
Troponin complex and tropomyosin.
Three globular proteins that make up troponin
- Troponin T (TnT): attaches the troponin complex to tropomyosin.
- Troponin I (TnI): inhibits actin and myosin interaction.
- Troponin C (TnC): binding of 4 molecules of Ca2+ to troponin C removes inhibition and permits actin and myosin interaction.
What allows the actin filament to move
Binding and unbinding of tropi=onin complex
How many actin monomers does tropomyosin span
7
Components of thick myosin filaments
A protein with a high molecular weight (~480kDa)
One pair of heavy chains that form long rodlike segment with globular heads. Two pairs of light chains associated with the heads.
A tail region and a cross-bridge region.
The light chains are important in myosin ATPase activity.
How many neurons supply each muscle fiber
One motor neuron