Muscle Flashcards
What is the organization of skeletal muscles?
Fasciculus, fibers, myofibrils, myofilaments (actin and myosin)
What do the CT coverings of skeletal muscle do?
Supply blood vessels, nerves, muscle spindles, and provide a means by which contractile forces are transmitted to other tissues
What are the CT coverings of skeletal muscle called?
Endomysium, perimysium and epimysium
What is the structure of the skeletal muscle?
10-110 micrometers in diameter
Up to 50 cm in length
Periphery nuclei
Many myofilaments that create light and dark bands
Striations
What is the functional unit of a skeletal muscle?
Sarcomere
Structure of the sarcomere
0.5- 1.00 micrometers in diameter
2.00 micrometers long
With I band, A band, H band, M line and Z line
Z line to Z line
I band
Only thin (actin) filaments
White thick line next to A bands
A band
Thick (myosin) and thin (actin) filaments
Thick dark line
H band
Pale area in the center of the A band
M line
Runs down the center of the H band
Results from attachment of adjacent myosin filaments
Z line
Dark band in the center of the I band
Skeletal muscle triad
T tubule in the center and SER cisterna on each side
In mammals, each sarcomere exhibits 2 triads one at each A-I band interface
What is the role of SER in the T tubule?
Stores calcium that is released during contraction
What are the 2 types of skeletal muscle fibers?
Red (type 1) and white (type 2) and intermediate (shares both)
Red (type 1) skeletal muscle fiber?
Large amount of myoglobin, numerous mitochondria, energy from oxidative pathway, contract and fatigue slowly
Slow-twitch fibers
White (type II) skeletal muscle fibers
Larger, fewer mitochondria, more extensive SER, energy from anaerobic glycolysis, contract and fatigue more rapidly,
Fast-twitch fibers
Regeneration of the skeletal muscle
Limited
Satellite (stem) cells present
Most injured muscle cells are replaced by CT
Motor Unit
A nerve fiber and the muscle cell it innervates
Motor End Plate
Point of attachment of a nerve with a skeletal muscle fiber
What are the motor end plate modifications at the distal end of axon?
loss of myelin sheath, presence of mitochondria and acetylcholine vesicles, dilation of axon
What are the motor end plate modifications at the muscle fiber?
Folding of cell membranes enclosing sub-neural clefts
Aggregation of mitochondria
Loss of striations
Events of Impulse Conduction
- Depolarization of axolemma
- Release of Ach
- Binding of Ach with Ach receptors present on sarcolemma
- Depolarization of sarcolemma
- Extension of depolarization wave to the T tubule and SER cisternae
- Release of calcium
- Contraction of myofilaments
- Inactivation of Ach by cholinesterase enzyme present in sub–neural clefts
- Active transport of calcium back to the SER
- Relaxation of myofilaments
What are the results of contraction?
I band and sarcomere reduces in length
H band disappears
Huxley’s Sliding Filament Theory
Thick and thin filaments maintain the same length but slide past each other during muscle contraction
Organophosphorus Toxicity
Cholinesterase enzyme is phosphorylated
Results in initial stimulation followed by depression
Botulism
Caused by toxins secreted by Clostridium botulinum
Blocks the release of Ach
Results in Flaccid tetraparesis
Myasthenia Gravis
Caused by deficiency of Ach and/ or antibodies against Ach receptors
Results in weakness in muscles
Structure of the cardiac muscle
10-15 micrometers in diameter
100 micrometers long
1 or 2 nuclei per cell, centrally located
Fibers branch
Striated
No regeneration
What does the point of anastomosis show? (Cardiac)
Intercalated discs
At EM levels consist of gap junctions, desmosomes and fascia
What happens are events of contraction in a cardiac muscle?
Similar to skeletal muscle except T tubules are located at the Z line and take the form of dyads rather than triads
Purkinje Fibers
Impulse conducting modified cardiac fibers
Where are purkinje fibers located?
Interventricular septum and beneath the endocardium
Purkinje fibers structure compared to cardiac muscle cells
Occur in groups
50 micrometers
Contain fewer peripherally located myofibrils
Less developed striations
More glycogen
Smooth muscle structure
Spindle-shaped
Single centrally located nucleus
5-20 micrometers in diameter
20 micrometers to 1 mm or more in length contains actin myosin filaments
Actively divides and regenerates
What surrounds the smooth muscle?
Surrounded by external lamina except at sites of gap junctions
What is present in the striated muscle?
Striations and troponin protein
Myofilaments in the smooth muscle
Attached to dense bodies which are analogous to Z lines of striated muscle
How do smooth muscles communicate?
Via gap junctions
How does contraction in the smooth muscle differ from the skeletal muscle?
Occurs more slowly and lasts longer
Steps of muscle contraction in smooth muscles
- Increase in cytosolic calcium,
- binding of calcium with calmodulin protein,
- activation of myosin kinase
- Phosphorylation of myosin
- interaction of phosphorylated myosin and actin
- contraction
What leads to relaxation in the smooth muscle?
Desphosphorylization of myosin preventing myosin-actin interaction
Urinary smooth muscle contraction
Triggered by stretching of the muscle,
Spreads from cell to cell gap junctions
Generates low level of rhythmic contraction
Increased or decreased autonomic nervous system rather than actually initiating the contraction
Ex; viscera of GI tract
Multi-unit smooth muscle
Triggered by nerve impulses
Precise contractions due to autonomic innervation of each muscle cell
Lack gap junctions
ex: constrictor and dilator muscles of the iris
