skeletal muscle tissue contraction chapter 10 anatomy and physiology mr. knowles liberty senior high...
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Skeletal Muscle Tissue Contraction
Chapter 10
Anatomy and Physiology
Mr. Knowles
Liberty Senior High School
A Brief Review of Skeletal Muscle Tissue
Connective Tissue• Epimysium separates
the…
• Perimysium divides the muscle into…
• Endomysium surrounds the…
Structures Entire muscle from other
tissue.
Bundles of muscle fibers- fascicles.
Individual skeletal muscle fibers.
How does a skeletal muscle cell differ from most other eukaryotic
cells?
A ComparisonMost Cells
• Small; < 100 μm long• One Nucleus• Normal metabolism-needs
normal enzymes; one copy of genes.
• 100’s of mitochondria• Endoplasmic Reticulum• No myofibrils
Skeletal Muscle • Large; 12 inches long• Multiple Nuclei• High metabolism-needs
more enzymes; more genes.
• 1,000’s of mitochond.• Sarcoplasmic Reticulum• Myofibrils
Nucleus
Sarcolemma
Sarcoplasm
Special Terms for Muscle Fibers• Sarcoplasm- cytoplasm of a muscle fiber.• Sarcolemma- unique cell membrane of a
muscle fiber.• The sarcolemma forms tubes that travel into
sarcoplasm at right angles- Transverse Tubules (T tubules).
• Action Potentials (unequal charges) travel down these T tubules.
Inside a Muscle Fiber…• Each T tubule encircles cylindrical structures-
myofibrils.• Myofibrils- 1-2 μm in diameter and as long as
entire cell. 100’s – 1,000’s of myofibrils/cell.• Myofibrils – are bundles of myofilaments – 2
kinds of protein filaments called actin (thin filaments) and myosin (thick filaments).
Inside the muscle fiber…• Myofibrils can shorten and contract the
muscle fiber.• Myofibrils are attached to the sarcolemma on
its inner surface.• Collagen fibers are attached to the
sarcolemma on its outer surface. These fibers extend into the tendon.
• Myofibrils pull on sarcolemma pulls on tendon muscle contraction.
Muscle Fiber
Tendon
Intracellular Extracellular
Collagen
Myofibrils
Sarcolemma
Terminal Cisternae
T Tubule
Triad
Sarcoplasmic Reticulum• Pumps Ca+2 out of the sarcoplasm and stores
it.• The resting cell has very little Ca+2 in the
sarcoplasm. 1000X more Ca+2 in the SR than in the sarcoplasm.
• The SR is made up of terminal cisternae that lie on above the junction of thin and thick filaments in the sarcomeres.
The Organization of the Myofibril
• Myofilaments are organized into repeating functional units- Sarcomere- smallest functional unit of the fiber.
• Sarcomere = myosin + actin + other stabilizing proteins.
Fig. 10-3. P. 282
Inside the Sarcomere…• Have two regions or Bands:
1. A BandsA Bands- are dArk bands and have three parts. a. M line- a protein that connects
neighboring thick filaments, keeps their position.b. H zone- a region with only thick filaments.c. Zone of Overlap- thin and thick filaments
overlap.
Inside the Sarcomere…• Have two Bands:
2. I BandsI Bands- are lIght bands; only find thin filaments.a. Z lines- mark the boundaries between the adjacent sarcomeres on the myofibril; have connectin – a connecting protein that interconnects thin filaments.b. Titin- a protein that aligns thick and thin filaments; resist extreme stretching.
A Band
Z Line
I Band
Sarcomere
Z lines
M line
Myofibril
Thin Filaments (Actin)Contains three proteins:
• F actin- a twisted strand of 300-400 globular (G) actin molecules.– Each G actin has an active site- a region
where thick filaments can bind.• Tropomyosin are strands of protein that wrap
around F actin. They cover the active site. This prevents actin-myosin interaction.
Thin Filaments (Actin)• Troponin- three globular subunits (parts).
– One subunit binds to tropomyosin and locks the two together.
– Another subunit binds to a G actin molecule, holding troponin and tropomyosin to the actin.
– The third subunit binds to a Ca+2 ion. Resting cells have low Ca+2 and so this subunit is empty in the resting cell.
Thick Filaments (Myosin)• Made of 500 myosin molecules.• Each myosin – two subunits twisted
around each other.• Myosin has a long, attached tail
bound to other myosin molecules in the thick filament.
Thick Filaments (Myosin)• The free head projects outward, toward the
nearest thin filament. Head can bind to the active site on the G actin.
• Between the head and the tail there is a flexible hinge that lets the head swing back and forth.
• All myosin molecules are arranged with their tails pointing toward the M line.
Supporting the Myofibrils• Desmin- is a complex network of
protein that twists around each Z line and connects adjacent myofibrils.
• Vertical bands of desmin can be seen with a light microscope and give the fiber a banded appearance-striated muscle.
The Sliding Filament
TheoryAn explanation of how
skeletal muscle cells contract.