Chapter 11 Muscular Tissue

Front 1

muscle fiber

Back 1

a bundle of myofibrils

a muscle fiber is a multinucleated muscle cell

muscle fiber = muscle cell

Front 2

sarcolemma

Back 2

plasma membrane around a muscle fiber

Front 3

T tubules (location)

Back 3

extend across the sarcolemma

Front 4

sarcoplasmic reticulum (SR)

[Facts]

Back 4

-specialized smooth ER
-network of tubules that surround the myofibrils
-regions of SR called terminal cisternae surround the T tubules

Front 5

triad

Back 5

one T tubule between two cisternae

Front 6

myofibrils

Back 6

bundle of myofilaments

Actin & Myosin

Front 7

myosin

Back 7

thick filaments; golf-club shaped

Front 8

actin

Back 8

thin filaments; look like beads on a string

Front 9

actin and myosin are?

Back 9

proteins

Front 10

two other important proteins in muscle?

Back 10

troponin and tropomyosin

Front 11

troponin and tropomyosin

Back 11

-both are attached to actin
-both have a role in muscle contraction

Front 12

sarcomere

Back 12

-the contractile unit of a muscle
-arranged end-to-end in a myofibril
-sliding filament model
-shows how a muscle contracts

Front 13

synapse

Back 13

place where a nerve and its target meet

Front 14

NMJ

Back 14

a synapse consisting of a motor nerve

meeting a muscle

Front 15

synaptic knob

Back 15

at end of motor nerve; rests on

motor end plate of the sarcolemma

Front 16

synaptic cleft

Back 16

small space between the synaptic-

knob & motor end plate

Front 17

acetylcholine (ACh)

Back 17

a neurotransmitter released from synaptic vesicles of the synaptic knob
attaches to ACh receptors on the

motor end plate

Front 18

acetylcholinesterase

Back 18

enzyme that destroys ACh, thus ending

a muscle contraction

Front 19

Excitation Step 1

Back 19

1) nerve signal arrives at synaptic knob

Front 20

Excitation Step 2

Back 20

2) Voltage-gated Ca+2 channels (in synaptic knob) open; Ca+2 enters knob

Front 21

Excitation Step 3

Back 21

3) acetylcholine is released, travels across synaptic cleft, binds to its receptors on the sarcolemma of the muscle fiber

Front 22

Excitation Step 4

Back 22

4) other ion channels in sarcolemma open, and ions move in and out of the sarcolemma

produces an electrical signal called the end plate potential (EPP)

Front 23

Excitation Step 5

Back 23

5) this EPP starts an action potential that travels through the sarcolemma

Front 24

Excitation-Contraction Coupling Describes...

Back 24

the connection between action potential in the sarcolemma, and activation of myosin

Front 25

Excitation-Contraction Coupling Step 1

Back 25

1) action potential spreads across sarcolemma, then down T tubules, then into sarcoplasm

Front 26

Excitation-Contraction Coupling Step 2

Back 26

2) sarcoplasmic reticulum releases calcium ion

calcium ion enters the cytosol

Front 27

Excitation-Contraction Coupling Step 3

Back 27

3) calcium ion binds to troponin on actin (troponin looks like little spheres)

Front 28

Excitation-Contraction Coupling Step 4

Back 28

4) tropomyosin twists to reveal the myosin binding sites of actin

Front 29

Contraction Step 1

Back 29

1) myosin head “cocks”
-requires ATP, which is attached to myosin
-ATP becomes ADP + P, but stays attached to myosin

Front 30

Contraction Step 2

Back 30

2) cocked myosin binds to actin at myosin binding site

Front 31

Contraction Step 3

Back 31

3) power stroke
-myosin moves, moving actin with it
-as this happens, the ADP and P are released from myosin

Front 32

Contraction Step 4

Back 32

4) recovery stroke
-myosin releases from the binding site
-at same time, myosin gets a new ATP bound to it
-myosin is now ready to “re-cock” and repeat the power stroke to pull again, and contract the muscle fiber more
-at any given time, some myosin are cocking and some are pulling
-this prevents the filaments from sliding back to where they started from

Front 33

Contraction Step 5

Back 33

5) final result:
-thick and thin filaments slide over each other
-the muscle fiber contracts (shortens)
-note that the individuals filaments (actin and myosin) do not shorten, they just slide past each other

Front 34

Relaxation Step 1

Back 34

1) nerve signal traveling to the NMJ stops
-ACh release stops

Front 35

Relaxation Step 1

Back 35

1) nerve signal traveling to the NMJ stops
-ACh release stops

Front 36

Relaxation Step 2

Back 36

2) ACh dissociates from its receptors and ACh-ase breaks down ACh
-ACh components are recycled to make new ACh

Front 37

Relaxation Step 3

Back 37

3) calcium ion is pumped back into the SR cisternae from the cytosol

Front 38

Relaxation Step 4

Back 38

4) calcium ions come off troponin and return to SR

Front 39

Relaxation Step 5

Back 39

5) tropomyosin moves back into place and binding sites are covered
-this prevents myosin from binding to actin

Front 40

Relaxation Step 6

Back 40

6) muscle returns to its resting length
-fibers have elastic recoil (due to elastic fibers)
-contraction of antagonistic muscle may also occur to return it to resting length