Lecture 4 Contraction of Skeletal Muscle Flashcards
Hierarchical Organization of Skeletal Muscle
- Epimysium
- Muscle
- Perimysium
- Fascicle
- Endomysium
- Sarcolemma (aka plasmalemma)
- Myofiber (aka muscle cell)
- Myofibril
- Myofilament
Fascicle
Latin for bundle of sticks
Subunit
Covered in perimysium
Myofiber
Muscle fiber
Myfibril
Are the actin/myosin fibrils
They are intracellular
Endo-mysium
Delicate, covers myofiber
Perimysium
Provides support
Sarcolemma
Cell membrane
Where action potential will occur
T-Tubules - invaginations of sarcolemma
Functional unit of muscle
Sarcomere
T-tubules
Invaginations of sarcolemma
Lie close to cisternae of sarcoplasmic reticulum
Form triads with cisternae (swelling)
Two per sarcomere
Sarcoplasmic reticulum
ER of myofiber
Has cisternae
ER in muscle
Sarcoplasmic reticulum
Sarcomere Banding
Banding pattern is determined by actin/myosin placement
Z lines
(aka Z discs)
Anchor actin filaments
Located at each end of a sarcomere
I bands
*in the sarcomere with A bands
Composed entirely of actin
Width changes during contraction
A bands
*in the sarcomere with I bands
Composed of actin and myosin
Width does not change during contraction
H bands
Composed entirely of myosin
Width changes during contraction
This type of band does NOT change during contraction
A bands
Muscle band composed entirely of actin
I bands
Muscle band composed entirely of myosin
H bands
This muscle band demarcates the subcomponents
Z line
Muscle band composed of both actin and mysoin
A bands
Origin of muscle is the
Fixed end
Direction it contracts
Muscle band that represents the length of the myosin filaments
A bands (doesn't change)
2 bands that get smaller during contraction
H and I
Line where myosin contracts in sarcomere
M line
Aligned sarcomeres
Produce banding pattern characteristic of striated muscle
Sliding Filament AKA
Walk Along
Sliding Filament Model Events
- Arrival of action potential at terminal end of nerve fiber
- Opening of voltage-gated calcium channels
- Release of neurotransmitter (Ach) from synaptic vesicles into synaptic cleft
- Opening of ligand-gated sodium channels of sarcolemma
- Generation of action potential on sarcolemma
- Voltage-gated channels on t-tubules (DHP channels) interact with ryanodine receptors on SR membrane
- Opening of ryanodine-sensitive calcium ion release channels
- Increase in calcium ion conc in cytosol
- Activation of sliding filament mechanism
Terminal end
Distal end
Ca+ conc on which side of cell
Outside
Muscle neurotransmitter
Ach
Sliding Filament Mechanism
- Released calcium ions bind to troponin
- Tropomyosin uncovers myosin binding sites on actin
- ATPase heads of myosin molecules split ATP and bind to actin
- Stored E in myosin head causes deformation such that thick and thin filaments slide past one another
- A second ATP binds to myosin and causes it to release actin
- Process is repeated over and over until sliding is complete
- Contraction stops when ATP-dependent calcium pump sequesters calcium ions back into SR
Tropomyosin prevents
Binding
Stored E in myosin head causes
Deformation such that thick and thin filaments slide past one another
Muscle contraction stops when
ATP-dependent calcium pump sequesters calcium ions back into SR
Where ATP is required for muscle contraction
- Most used for sliding filament mechanism
- Pumping calcium ions from sarcoplasm back into sarcoplasmic reticulum
- Pumping sodium and potassium ions through the sarcolemma to reestablish resting potential
Concentration of ATP in muscle fiber
About 4mmol
Enough to maintain contraction for 1-2 seconds
3 Types of Energy for Rephosphorylation
- Phosphocreatine
- Glycolysis
- Oxidative Metabolism
Phosphocreatine and E for Rephosphorylation
Releases E rapidly
Reconstitutes ATP
ATP + phosphocreatine provides enough energy for 5-8 seconds of contraction
Glycolysis
Anaerobic respiration
Can generate ATP in lack of ATP
End up with pyruvate, generate net of 2 ATP
Glycolysis and E for Rephosphorylation
Lactic acid build up
Can sustain contraction for 1 minute
Oxidative metabolism and E for Rephosphorylation
Provides more than 95% of all E needed for long term contraction
2 types of muscle contractions
- Isometric
2. Isotonic
Isometric Muscle Contraction
Same length, contraction is not moving. Doing work, but stays the same.
Isotonic Muscle Contraction
Same tone or contraction strength
Ex. Muscle changes length, NOT always shorter, can be longer.
2 Types : 1. Eccentric 2. Concentric
Eccentric Muscle Contraction
Type of Isotonic
Gets longer
Concentric Muscle Contraction
Type of Isotonic
Gets shorter
2 Muscle Fiber Types
- Fast (white) - contracts quickly, fatigue fast
2. Slow (red) - slow, but last long time
White Muscle Fiber
Fast
Contracts quickly, fatigues fast
Ex. Chicken breast
Red Muscle Fiber
Slow
Contracts slowly, Lasts long time
Ex. Chicken legs, thighs - flight muscles - have most amount of mitochondria, need lots of O2 from ATP
What gives red muscle fiber color?
Myoglobin like hemoglobin when bound to O2 is red.
