Muscle Physio I Flashcards
What are the Types of Muscles?
- Skeletal Muscles
- Cardiac Muscles
- Smooth Muscles
Describe the Skeletal Muscle.
Striated, voluntary, multinucleate cells that are attached to the bones of the skeleton.
They help in movement of body in relation to the external environment.
Describe the Cardiac Muscle.
Striated, involuntary cells connected by intercalated discs located in the wall of the heart.
They help in pumping out of the blood from the heart.
What type of contraction is experienced by the Cardiac Muscle?
Coordinated Contraction
Describe the Smooth Muscle.
Unstriated, involuntary cells that are locates in the walls of hollow organs and tubes.
They help in the movement of the contents of these hollow tubes.
What are the functions of the Skeletal Muscle?
- Movement
- Posture and Body Position
- Joints
- Heat
- Protection of Internal Organs
How is the organisation of Skeletal Muscle fibers?
Parallel arrangement; Bundled by connective tissue (fascia)
What are Muscle Fibers composed of?
Myofibrils (Regular arrangement of Thick and Thin Filaments)
What is the A band?
Overlap of thick and thin filaments
What is the I band?
Remaining portion of thin filaments that dont overlap
Where do Cross-Bridges project from?
Each thick filament in six directions toward the surrounding thin filaments
Where is the Sarcomere located?
Between Z lines
Describe the Structure of the Thick Filament.
Composition: Myosin protein (2 intertwined golf club units)
Heads of Myosin form a bridge
Has an Actin-binding Site and ATP-ase site
Describe the Structure of the Thin Filament.
Main Structural Component: Actin
Interacts with myosin cross-bridges
Tropomyosin (block Actin-binding site on Myosin) and Troponin (changes structure of Tropomyosin) lie across surface of Actin
What regulates Actin-Myosin binding?
Ca2+ (binds with troponin)
What does the Stroking Motion do?
Pull Thin Filament towards centre of sarcomere
What are the stages of the Power Stroke?
- Binding: Myosin to Actin
- Power Stroke: Cross-bridge bends
- Detachment: Cross-bridge detaches
What shortens the muscle?
Repeated Cross-Bridge Binding and Power Stroke
What is the Sliding Filament mechanism?
Thin filaments from opposite sides of each sarcomere sliding closer together between thick filaments
What changes does the Sarcomere undergo during Contraction?
H zone and I band becomes shorter; Sarcomere shortens; A band remains the same
What controls muscle contraction?
Ca2+
What controls Ca2+ levels?
Motor Neurons (Acetylcholine)
What can 1 motor neuron control?
A small group of muscle fibers
How does the AP spread?
Down T tubule (close to SR and attached to cell membrane)
Where is Ca2+ stored?
Sarcoplasmic Reticulum (SR)
What does the T tubules contain?
Dihydropyridine receptors (voltage-gated Ca2+ channels)
What does SR contain?
Ryanodine receptor (Ca2+ releasing channels)
How is Ca2+ released?
From SR via RR
What are the steps in Excitation-contraction coupling?
- AP propagated along sarcolemma down T tubule
2. Ca2+ released
Why does the Contraction outlast the AP?
Ca2+ reuptake requires time
Describe the process of the ATP-powered cross-bridge cycling.
- Energized: splitting of ATP for energy
2a. Resting: No Ca2+ released
2b. Binding: Ca2+ released - Bending: Power stroke (P and ADP released)
4a. Detachment: Linkage broken, ATP hydrolysed
4b. Rigor complex: No fresh ATP avail
What are the 4 steps in Excitation, Contraction and Relaxation?
- Splitting of ATP by Myosin ATPase provides energy for power stroke
- Binding of ATP to Myosing breaks cross-bridges
- Active Transport of Ca2+ back into SR during Relaxation
- Activity of Na+-K+ pump during AP production
What are the different pathways of ATP production by muscle fibers?
- Creatine Phosphate
- Glycolysis
- Oxidative Phosphorylation
Describe the Creatine Phosphate pathway.
Fast; Only 1 enzyme required (Creatine Kinase); Phosphate and ADP produced; Supports short burst of hi intensity contraction
Describe the Glycolytic pathway.
X O2; 2 ATP and 2 Pyruvic Acid produced; Supports anaerobic hi intensity exercise
Describe the Oxidative Phosphorylative pathway.
O2 and Mitochondria needed; 36/32 ATP produced; Supports aerobic or endurance exercise
How is the Energy Usage during Short-duration Exercise?
6s: Stored ATP used first
10s: Creatine Phosphate pathway
30-40s: Glycogen is broken down and oxidised
How is the Energy Usage during Long-duration Exercise?
Hours: Breakdown of several nutrient energy fuels by aerobic pathway (Uses O2 released from myoglobin or hemoglobin); O2 deficit
What are the 2 types of Fatigue?
- Muscle Fatigue: Exercising muscle no longer respond to stimulation with same degree of contractile of activity
- Central Fatigue: CNS no longer activates motor neurons
What are the possible factors contributing to Muscle Fatigue?
- Leakage of Ca2+
- Local increase of Phosphate
- Depletion of Glycogen
What is necessary to recover from exercise?
Increased O2 consumption
What are the Types of Skeletal Muscle Fibers?
- Type I: Slow-Oxidative
- Type IIa: Fast-Oxidative
- Type IIx: Fast-Glycolytic
What is the difference between Fast and Slow fibers?
Fast > Slow
- Higher myosin ATP-ase activity
- Faster speed of contraction
What is the difference between Oxidative and Glycolytic fibers?
In ATP-synthesising Ability (Higher OP capacity and Myoglobin Content, More Mitochondria and Capillaries, Red Colour)
How is the Genetic Endowment of Muscle fiber types determined?
Type of activity for which muscle is specialised
How do the Fibers differ w.r.t Resistance to Fatigue?
Type I: Hi
Type IIa: Intermediate
Type IIx: Lo
How do the Fibers differ w.r.t Enzymes for Anaerobic Glycolysis?
Type I: Lo
Type IIa: Intermediate
Type IIx: Hi
How do the Fibers differ w.r.t Glycogen Content?
Type I: Lo
Type IIa: Intermediate
Type IIx: Hi
