Physiology Chapter 12: Muscle Physiology

Front 1

Classification of Muscle (3)

Back 1

Skeletal muscle
Smooth muscle
Cardiac muscle

Front 2

Structure of Skeletal Muscle (2)

Back 2

-Muscle = group of fascicles
-Muscle fibers extend length of muscle from tendon to tendon

Front 3

Components of a Muscle Fiber (4)

Back 3

-Muscle fibers surrounded by connective tissue
-Sarcolemma
+Plasma membrane
-Multinucleated
-Sarcoplasm
+Cytoplasm

Front 4

Components of a Muscle Fiber (4)

Back 4

-Contains many myofibrils
-Sarcoplasmic reticulum
+Smooth ER
-Contains many mitochondria—high energy
-Transverse tubules
+T tubules

Front 5

Myofibrils (2)

Back 5

-Myofibrils give skeletal and cardiac muscle striated appearance
-Composed of thick and thin filaments
+Actin
+Myosin

Front 6

Structure at the Molecular Level (2)

Back 6

-Striations due to thick and thin filaments which run parallel to long axis
-Filaments form sarcomeres

Front 7

Structure of a Sarcomere (6)

Back 7

-A band
+Dark band
+Thick filaments
-H zone
+Thick filaments
+No overlap
-M line
+Link thick filaments
-I band
+Light band
+Thin filament
+No overlapping
-Z line
+Link thin filaments
-Sarcomere
+Functional unit
+Z line to Z line

Front 8

Thick Myofilament (3)

Back 8

-Myosin tail is toward M line
-Myosin head is toward I band
-Myosin head binding sites
+Actin binding site
+Binding site for ATP and ATPase

Front 9

Actin

Back 9

Each actin has a binding site for myosin

Front 10

Tropomyosin (2)

Back 10

-Regulatory protein
-Overlaps binding sites on actin for myosin

Front 11

Troponin (2)

Back 11

-Complex of three proteins
+Attaches to actin
+Attaches to tropomyosin
+Binds calcium
-Calcium binding to troponin regulates contraction

Front 12

Titin (3)

Back 12

-Supports protein in muscle
-Anchors thick filaments between M-line and Z-line
-Provides structural support and elasticity

Front 13

Sliding-Filament Mechanism (4)

Back 13

-Muscle contraction
+Shortening of muscle
-Thick and thin filaments overlap
-Neither thick nor thin filaments shorten
-Filaments slide past each other

Front 14

Sliding-Filament Mechanism (2)

Back 14

-Within a sarcomere during contraction
+A band stays same length
+I band shortens
+H zone shortens
+Sarcomere shortens
-Sliding is due to cyclical formation and breaking of cross bridges = crossbridge cycle

Front 15

Crossbridge Cycle (2)

Back 15

-Myosin head undergoes changes swiveling back-and-forth
-Relies on ATP hydrolysis

Front 16

Crossbridge Cycle (3)

Back 16

-Analogous to rowing boat through water
-Oar paddle = cross bridge
-Link of thick filament to thin filament (oar contact with water)

Front 17

Crossbridge Cycle (3)

Back 17

-Power stroke—myosin head moves propelling thin filament toward center of muscle (movement of oar propelling boat)
-Thick and thin filaments detach (oar breaks contact with water)
-Myosin head returns to initial position (oar moved to new position, cycle starts again)

Front 18

Asynchronous Cycling (2)

Back 18

-Muscle cell continuously generates force during contraction
-Crossbridge cycles of different myosin molecules out of phase
+Never break complete contact between thick and thin filaments during contraction phase

Front 19

Role of Calcium in Contraction (no)

Back 19

-No Calcium—troponin holds tropomyosin over myosin binding sites on actin
+No crossbridges form between actin and myosin
+Muscle relaxed

Front 20

Role of Calcium in Contraction (yes)

Back 20

-Calcium Present—binds to troponin, causing movement of troponin, causing movement of tropomyosin, exposing binding sites for myosin on actin
+Crossbridges form between actin and myosin
+Cycle occurs, muscle contracts

Front 21

Steps of Excitation-Contraction Coupling (6)

Back 21

1. Action potential in sarcolemma
2. Action potential down T tubules
3. Receptors of T tubules open Ca2+ channels in Sarcoplasmic Reticulum
4. Calcium increases in cytosol
5. Calcium binds to troponin shifting tropomyosin
6. Crossbridge cycling occurs

Front 22

Termination of Contraction (2)

Back 22

-Calcium must leave troponin, allowing tropomyosin to cover myosin binding sites on actin
-To remove calcium from cytosol
+Ca2+ ATPase in sarcoplasmic reticulum
+Transports calcium from cytosol into sarcoplasmic reticulum

Front 23

Sarcomeres (3)

Back 23

-Are units of skeletal muscle between 2 Z discs/lines
-M lines are structural proteins that anchor myosin during contraction
-Titin is elastic protein attaching myosin to Z disc that contributes to recoil of muscle

Front 24

Muscle Action
Begins with Nerve action (6)

Back 24

-Depolarization - Na+ enters
-At axon end - near synapse - Ca+2 enters
-Ca+2 causes release of Ach into synapse

-Stimulates Na+ entry into motor end plate
-Action potential along sarcolemma and T tubules
(muscle cell membrane)
-Action potential triggers sarcoplasmic reticulum to release Ca+2

Front 25

Muscle contraction (8)

Back 25

-Ca+2 released into sarcomere (A and M)
-Ca+2 binds to Troponin/Tropomyosin - complex shifts
-Actin binding sites exposed
-ATP straightens cross-bridge allowing it to bind
-Myosin cross bridges bind to actin
-Cross-bridges pivot (phosphate from ATP needed)
-Actin slides - Contraction
-New ATP needed for release of cross-bridge

Front 26

Rigor Mortis (2)

Back 26

-A new ATP is required to allow Myosin to detach from actin
-When a muscle dies calcium leaks from the Sacoplasmic reticulum
+Cross-bridges attach
+ATP is no longer generated so they do not detach

Front 27

Slow- & Fast-Twitch Fibers (2)

Back 27

-Skeletal muscle fibers can be divided on basis of contraction speed & resistance to fatigue:
Slow-twitch, slow fatigue (Type I fibers)
Fast-twitch, fast fatigue (Type IIA & IIX fibers)
-Twitch speed due to different myosin ATPases that are slow or fast