muscle histology

Question 1

nerve stimulation of a skeletal muscle fiber

Answer 1

occurs via somatomotor neurons in spinal and cranial nerves

1. nerve impulse causes Ach release from end plate synaptic vesicles into synaptic cleft of sarcolemma
2. opening of ACh gated Na+ channels causes local depolarization of sarcolemma
3. depolarization spreads to T tubules
4. at the triad, depolarization enters the cell through T tubules at the junction of A and I bands
5. depolarization activates voltage sensitive Ca channels on the T tubule membrane
6. Ca released from sarcoplasmic reticulum into sarcoplasm
7. initiation of muscle contraction

Question 2

thin filaments

Answer 2

• actin, troponin, and tropomyosin

- present in Z, I, A bands

Question 3

defining characteristic of muscle tissue

Answer 3

ability to contract!

• shortening/lengthening of skeletal muscle
• contraction of smooth muscle

Question 4

smooth muscle

Answer 4

• involuntary movement
• no striations
• actin and myosin connected by dense bodies (a-actinin + IFs (desmin and vimentin))

Question 5

sarcomeric unit

Answer 5

• gives skeletal muscle striated appearance
• Z lines = boundaries
• I band = actin myofilaments
• A band = myosin overlapping with actin
• H band = isolated mysoin
• M band = cross linked myosin (middle)

Question 6

skeletal muscle histology

Answer 6

• longitudinal eosinophilic fiber filled with myofibrils
• multiple nuclei per cell; all pushed to the edges
• striations perpendicular to length of myocyte
• in cross-section: striations not visble but individual myofibrils are

Question 7

smooth muscle histology

Answer 7

• eosinophilic cytoplasm

- cigar shaped nuclei

Question 8

cardiac muscle contraction

Answer 8

• similar to skeletal muscle (also dependent on Ca ions)

Question 9

cardiac muscle histology

Answer 9

• also striated
• shorter, branching myofibrils
• central nuclei
• cells attach at ends via intercalated disks (junctions that propagate depolarization)

Question 10

initiation of smooth muscle contraction

Answer 10

1. autonomic nerve impulses from nerves terminating in adjacent connective tissue open voltage-gated Ca channels (After 10-20 µM diffusion of NTs)
2. smooth muscle stretching opens mechanosensitive Ca channels
3. surface receptors of hormones trigger 2nd messengers that act on gated ER channels to release Ca

Question 11

subdivisions of muscle (small -> large)

Answer 11

• myofilament = complex of actin and myosin
• myofibril = bundle of myofilaments = back to back sarcomeres
• muscle fiber = cell = bundle of myofibrils surrounded by endomysium
• muscle fascile = made of fibers surrounded by perimysium
• skeletal muscle = made of fasciles and covered by epimysium

Question 12

skeletal muscle

Answer 12

• voluntary movement
• striated
• covered by thin layer of fascia
• parallel arrays of muscle fibers
• external basal lamina

Question 13

smooth muscle contraction

Answer 13

1. initiation of contraction by nerve impulse, stretch, or hormones
2. intracellular Ca increase
3. calcium binds calmodulin, which activates myosin light chain kinase
4. phosphorylation of myosin
5. myosin-P binds actin (no troponin involved)
6. with ATP, myosin head will bend and induce contraction

Question 14

structural elements of a muscle fiber

Answer 14

• sarcolemma = plasma membrane
• myofibrils surrounded by layer of sarcoplasm containing mitochondria and sarcoplasmic reticulum
• T tubules = entrances through sarcolemma
• Triad = t tubule adjacent to two terminal cisternae of the sarcoplasmic reticulum

Question 15

thick filaments

Answer 15

• myosin

- present in A, H, M bands

Question 16

contraction of skeletal muscle

Answer 16

0. relaxed state: troponin/tropomyosin bind myosin
1. muscle stimulation = Ca release
2. Ca binds to troponin on thin filaments, freeing myosin
3. myosin binds actin
4. power stroke: myosin pulls actin, pulling thin filaments towards M-line
5. ATP binding allows for myosin release of actin