Muscle Flashcards
What are the types of muscle?
- Striated
- Smooth muscle
- Contractile filaments
Skeletal muscle is ____
Voluntary
Cardiac muscle is ____
Involuntary
Smooth muscle is ____
Involuntary
Under contractile filaments
Actin and Myosin
CONNECTIVE TISSUE INVESTMENTS:
Epimysium
Perimysium
Endomysium
CONNECTIVE TISSUE INVESTMENTS:
surrounds entire muscle
Epimysium
CONNECTIVE TISSUE INVESTMENTS:
surrounds muscle bundles or fascicles (small bundles)
Perimysium
CONNECTIVE TISSUE INVESTMENTS:
surrounds individual muscle cells
Endomysium
CONNECTIVE TISSUE INVESTMENTS:
Reticular fibers and external lamina
Endomysium
Long, cylindrical, multinucleated
SKELETAL MUSCLE CELLS
Sarcoplasm, sarcolemma with T (transverse) tubules
SKELETAL MUSCLE CELLS
MYOFIBRILS structure has:
- Thick filaments (myosin)
- Thin filaments (actin)
- Dark A bands, light I bands (bisected by Z disks)
- DESMIN (with plectin) glues Z disks together
CROSS-STRIATIONS
TABLE 8.2
A-bands
I-bands
H-bands
M lines
Z disks (lines)
CROSS-STRIATIONS:
Anisotropic; stain dark; thin and thick filaments
A-bands
CROSS-STRIATIONS:
Isotropic; light stain; thin filaments
I-bands
CROSS-STRIATIONS:
Light regions transecting A bands; thick filaments
H-bands
CROSS-STRIATIONS:
Narrow dark regions at center of H bands; cross-bridges
M lines
CROSS-STRIATIONS:
Dense regions bisecting I-band
Z disks (lines)
Z to Z
SARCOMERE
Functional unit of contraction
SARCOMERE
Dilated terminal cisternae that encircle myofibrils at the junction of each A and I band
Sarcoplasmic reticulum
Regulates muscle contraction by calcium sequestration (relax) and release (contract)
Sarcoplasmic reticulum
Central T tubule flanked by 2 terminal cisternae of SR
Triads
Help provide uniform contraction
Triads
Under sarcomere
Sarcoplasmic reticulum
Triads
MOLECULAR ORGANIZATION:
THIN FILAMENTS
F-actin
Tropomyosin
Troponin
double helix arrangement
F-actin
has an active site for interacting with myosin
F-actin
In the grooves of the F-actin helix
Tropomyosin
Troponin:
bind to tropomyosin
TnT
Troponin:
4 binding sites for calcium
Tnc
Troponin:
binds to actin, inhibiting myosin-actin interaction
TnI
MOLECULAR ORGANIZATION:
THICK FILAMENTS
Myosin II
2 identical heavy chains and 2 pairs of light chains
Myosin II
Double-headed golf club
Myosin II
Globular heads (S1 fragments) have ATPase activity but require interaction with actin to release ADP and Pi.
Myosin II
During contraction, thick and thin filaments do not shorten but increase their overlap
Huxley’s Sliding-Filament Model
Thin filaments slide past thick filaments and penetrate more deeply into the A band, which remains constant in length
Huxley’s Sliding-Filament Model
I and H bands shorten as Z disks are drawn closer together
Huxley’s Sliding-Filament Model
INITIATION AND REGULATION OF CONTRACTION
Depolarization + calcium release 🡪 actin-myosin binding 🡪 muscle contraction
INITIATION AND REGULATION OF CONTRACTION:
______ depolarized at MNJ
Sarcolemma
INITIATION AND REGULATION OF CONTRACTION:
______ convey depolarization to myofibrils (voltage-sensitive dihydropyridine (DHP) receptors)
T tubules
INITIATION AND REGULATION OF CONTRACTION:
______ released to cytosol at A-I junction via ________ of SR terminal cisternae opened by activated DHP receptors
Ca 2+, Ca2+ release channels (junctional feet, ryanodine receptors)
INITIATION AND REGULATION OF CONTRACTION:
Sufficient Ca2+ 🡪 continued contraction cycle
Ca2+
Resting state 🡪 myosin-binding sites on actin are partially covered by tropomyosin. TnI is also bound to actin.
Activation of actin by Ca2+
Ca2+ + TnC 🡪 break TnI-actin bond; tropomyosin shifts position and uncovers myosin-binding sites (active state)
Activation of actin by Ca2+
Calcium concentration in the cytosol is reduced enough that TnC loses its bound Ca2+
Relaxation
Relaxation:
SR calcium pump binds Ca2+ to the SR inner membrane with ______
calsequestrin
Motor unit is consists of:
neuron
muscle cell it innervates
