Ch 12: Muscles Flashcards
Cardiac & skeletal muscles contain?
- Striations
- Muscle fiber
- Nucleus
“How you interact with external environment” is due to?
Skeletal muscle
Smooth muscles is found where?
Where you have an interior & want muscle around it to contract it
- By uterus, bladder
What does smooth muscle lack?
Striations
Types of muscles
- Skeletal
- Cardiac
- Smooth
Skeletal muscle - Antagonistic muscles: Flexion
Triceps - muscle relaxes
Biceps - muscle contracts (flexor)
Skeletal muscle - Antagonistic muscles: Extension
Triceps - muscle contracts (extensor)
Biceps - muscle relaxes
Muscle contraction is energetically ___________?
Expensive
Muscle fiber
Muscle cell
- can be long, but NOT as long as neurons
Modified ER
Sarcoplasmic reticulum
- stores Ca2+
Cytoplasm
Sarcoplasm
Cell membrane
Sarcolemma
Striated (skeletal) muscle occupies how much of the adult human body by mass?
40-50%
At rest, skeletal muscle accounts for ____ of oxygen consumed?
25%, can triple during exercise
Sarco
Muscle
Ultrastructure of Muscle
A. Contractile proteins
B. Regulatory proteins
Contractile proteins
- Myosin
- Actin
Myosin
Part of thick filament
- approx. 250 individual myosin molecules join to form thick filament
- each single myosin molecule has 4 subunits: 2 heavy chains forming a tail, 2 lighter chains forming the head
Actin
Part of the thin filament
- double helix of G-actin (globular) molecules
- each G-actin has binding site for myosin (convenient)
- strand of G-actin called F-actin (fibrous)
Regulatory proteins
Both found on thin filament
1. Tropomyosin
2. Troponin
Tropomyosin
Regulatory protein that covers the binding sites on F-actin (covers 7 actin molecules)
Troponin
Regulatory protein (composed of 3 subunits) bound to tropomyosin & has a binding site for Ca2+
Actin-Myosin Cross Bridge Cycle
- Increased intracellular Ca2+ levels, Ca2+ binds to troponin
- Troponin changes shape & pulls tropomyosin off binding sites
- Actin & myosin attach
- Pi is released
- Power strokes occurs, shortens sarcomere
- ADP is released
- Fresh ATP, if available, binds to myosin head
- Myosin detaches from actin
- ATP hydrolyzed, energy re-cocks myosin head
- If Ca2+ still present, myosin attaches to actin, cycle repeats
- If Ca2+ is removed, tropomyosin covers binding sites preventing actin-myosin cross bridge
Skeletal muscle group composed of?
Fibers aka cells
Why is skeletal muscle multi-nucleated?
Due to fusion of myoblasts during development
- cannot undergo mitosis
Epimysium
Connective tissue
Perimysium
Fascicle - bundle of muscle fibers
Endomysium
muscle fiber (cell)
Myofibril
Contains thin and thick filament
T-tubule
Brings action potentials into interior of muscle fiber
Terminal cisterna
Big place for storage
- lateral sacs
- regions of SR that are T-tubules
Sarcomere
Functional unit of skeletal muscle
- Z line to Z line
- the contractile unit of striated muscles
Each myosin head contains a binding site for?
Actin & ATPase site
- can only bind to ONE, NOT BOTH
A flexible hinge allows the head to undergo _________
The powerstroke
Actin attached to?
Z-line
Actin helix
Backbone of thin filament
Sliding filament theory
Force is generated as fixed-length filaments slide pass one another
