Muscle Tissue Flashcards
1
Q
Muscle fibers of skeletal muscle characteristics and function?
A
- Function: force generation
- multinucleated
- nuclei at periphery
- rich capillary network to meet metabolic demands
- collagenous CT
2
Q
Purpose of connective tissue in skeletal muscle?
A
- transfers force to bone
- contains high amounts collagenous
- fibers aligned parallel to greatest force
3
Q
Where does skeletal muscle develop from?
A
Somites (dermomyotomes)
4
Q
Process of skeletal muscle development?
A
- Dermomyotome splits off into dorsal and ventral muscle masses
- Myoblasts (single cells) migrate from somite
- Myoblasts fuse together and make multinucleated cells called Myotubes
- process called syncytium
5
Q
Sarcoplasm?
A
muscle cell cytoplasm
6
Q
Sarcolemma?
A
muscle cell membrane
7
Q
Outer layer of muscle cell membrane?
A
- interacts with ECM and coatings
- transmits force
8
Q
Inner layer of muscle cell membrane?
A
- true cell membrane
- lipid layer
9
Q
Muscle cell contents?
A
- primarily myofibrils packed into tubes
- gives striated appearance
10
Q
Cardiac Muscle characteristics?
A
- Net like organization
- striated
- complex junctions
- intercalated discs (transmits force)
- found only in heart - Fatigue Resistance
- one or two nuclei
- larger more numerous T tubules
- extensive Mitochondria (continuously functioning)
11
Q
Skeletal muscle organization of Myofibril?
A
- A band: made of Myosin thick filaments
- I band: made of Actin, Troponin, Tropomyosin thin filaments, attached to Z line
- Z band: filament anchoring site
- H band: middle of A band
- M line: myosin anchoring site
12
Q
Length of Sarcomere?
A
extends from one Z line to the next Z line
13
Q
Sarcomere thick filaments?
A
Myosin (A band)
- Myosin contains enzyme ATPase which hydrolyzes ATP to ADP + P (cofactor: Actin)
- reaction binds Myosin heads to Actin
- two heavy chain- tail region
- four light chain- globular heads
- hinge region- aids in movement of head
14
Q
Sarcomere thin filament?
A
Actin (I band):
- F and G actin
- Troponin (T, C, I)- bound to Tropomyosin, prevents Actin and Myosin binding
- Tropomyosin- binds to F actin
- Globular actin (G) binds Myosin
- moves in response to calcium
15
Q
What does Myosin anchor to?
A
M line
16
Q
What does Actin anchor to?
A
Z line
17
Q
Steps of Muscle contraction in the myofiber?
A
- Influx of calcium
- Calcium binds Troponin
- Troponin moves to expose Actin binding site
- Myosin heads bind to Actin binding site
- Hinge region of Myosin deforms (as a result of ATP hydrolysis)
- Power stroke- Myosin moves against Actin
-result of hundreds of actin/myosin cross bridges happening
18
Q
How long does a muscle contraction last?
A
continues until calcium is depleted
19
Q
What happens to the size of I and H bands during muscle contraction?
A
- I band: decreases in size
- A band: decreases in size
- Z lines come closer together
20
Q
Reason for Rigor Mortis?
A
- calcium leaks from SR
- binds to Troponin, exposing Actin
- Myosin bind Actin, tightening the muscle
- lack of ATP causes inability of Myosin to release Actin
21
Q
Where does Calcium in muscle cell come from?
A
Sarcoplasmic Reticulum (ER)
22
Q
Muscle cell Triad?
A
-formed by SR and T tubule
23
Q
What are Transverse (T) tubules?
A
- invaginations of Sarcolemma
- transmit depolarization
- surround A and I bands
24
Q
Depolarization of cell membrane?
A
- T tubules are connected to SR via gates
- Depolarization of T tubule physically stimulates SR
- causes mechanical deformation and triggers release of calcium from SR
- SR releases calcium into cytoplasm
25
Motor unit?
single motor neuron and the muscle fascicles it innervates
26
Myoneural junction?
- motor nerves branch out within perimysial layer
- motor unit
- end foot: nerve terminal
- motor end plate: end of motor neuron where it attaches to muscle cell
27
What determines the precision of movement in motor units?
- related to number of muscle fibers innervated by motor neuron
- single motor units for fine motor control in fingers
- motor unit where nerve innervates many muscle fibers for more gross movements (quads)
28
Steps of skeletal muscle contraction at motor end plate to inside cell?
1. Action potential at nerve terminal
2. Acetylcholine released at synaptic cleft
3. ACh binds to receptors on Sarcolemma
4. Sodium influx into myofiber
5. Membrane depolarized
6. T tubules depolarized
7. SR mechanically deformed
8. Calcium released from SR
9. Contraction stimulated
10. Excess ACh hydrolyzed by Acetylcholinesterase
11. Muscle returns to resting state
29
Epimysium?
- external sheath of dense irregular connective tissue around entire muscle
- transmits the force
30
Permysium?
layer covering each bundle of muscle fibers (fascicles)
31
Endomysium?
layer covering each individual muscle fiber
32
Dystroglycan Complex parts?
1. Dystrophin binds actin at end
2. Dystroglycans (alpha-DG and beta GD) binds with Actin
3. Sarcoglycans (alpha, beta, gamma, delta) attach with beta DG
- associated proteins (NOS)
33
Function of Dystroglycan Complex?
- connect Actin in cytoplasm to ECM
| - transmit generated force from inside Sarcolemma to CT outside
34
Dystroglycan pathologies?
1. Duchenne Muscular Dystrophy
- mutation in Dystrophin
2. Limb Girdle Muscular Dystrophy (LGMD)
- mutations in Dystroglycans, Sarcoglycans, or other associated proteins
35
Intercalated Discs 3 components?
1. Fascia Adherens (hemi-Z bands)
- connects sarcomeres to membranes
2. Macula Adherens
- connects cells to cells
3. Gap junctions
- communications
- signal in one cell triggers contraction in next cell
36
2 Types of Smooth Muscle?
1. Single Unit
- single neuron innervates many muscular cells
- walls of hollow viscera (esophagus)
- Function: propel luminal contents, regulate flow of contents (peristalsis)
3. Multiunit
- single neuron innervates one muscular cell
- found in trachea, iris of eye, hair of skin
- Function: piloerection, shape changes
37
Smooth Muscle contraction steps?
1. Intracellular calcium increases from calcium channels and release from SR
2. Calcium binds to Calmodulin (CaM)
3. Calmodulin activates Myosin light chain Kinase (MLCK)- Myosin heads
4. Phosphorylated Myosin light chain combines with Actin
5. Contraction occurs
6. ATP is broken down
38
Dense bodies function?
1. Two types:
- membrane
- cytoplasmic
2. attachment for thin and intermediate filaments
3. made of alpha actinin (Z disk protein)
4. Allow for transmission of force from cell to cell in smooth muscle,
- found within lattice network of smooth muscle
5. external lattice interacts with membrane of other cells in response to what goes into internal lattice, allows smooth muscle to work in coordinated fashion
39
Convergent muscles?
- muscles where origin is wider than the point of insertion
| - pec major
40
Parallel muscles?
- more force over long distance
| - sartorius
41
Bipennate muscles?
- fascicles on both sides of central tendon
- Interossei
- rectus femoris
42
Multipennate muscles?
- more force over shorter distance
| - deltoid
43
Vectors of muscle?
-muscle contraction is the sum of vectors generated by muscle
44
Effective distance vs force generated?
1. small distance contraction = high force generated
- Gastrocnemius
2. large distance contraction= low force generated
- Lat Dorsi
