The Musculo-Skeletal System
Animal SkeletonsFunctions: •Support •Protection •Movement (T11.2.U1)
all movement results from: muscle working against a skeleton
3 Types of skeletons •hydrostatic (e.g. worm, cnidarians) •exoskeleton (e.g. arthropods) •endoskeleton
Thigh bone connected to the...• The mammalian skeleton is built from more than 200 bones
• Some fused together and others connected at joints by ligaments that allow freedom of movement
• are bones alive?• osteoblasts, osteocytes
Types of synovial joints in the appendicular skeletonT11.2.U2
Vertebrate Skeletal Muscle
Contraction
Muscles move the skeleton• What is always the action of muscle cells? • Skeletal muscles are attached to the skeleton in antagonistic
pairs (T11.2.U3) • Flexors vs Extensors • If one contracts, the other relaxes
Vertebrate Skeletal Muscle
Vertebrate Skeletal Muscle
• Muscle fibers contain many myofibrils (T11.2.U5) • each myofibril = many sarcomeres
• contractile subunit (T11.2.U6)
Vertebrate Skeletal Muscle
Sliding filament theory
• Mechanism of contraction? • thick and thin filaments... • slide past one another.
• Mechanism of sliding filaments? • Interaction between...
• actin and myosin: • The “head” of a myosin molecule binds to an actin
filament • Forming a cross-bridge and pulling the thin filament
toward the center of the sarcomere
T11.2.U7-9
Sliding filament theory
•ATP binds to myosin head •Head releases from actin site
Sliding filament theory
•Energized by phosphoryllation of ATP, •Myosin head now able to bind to actin site
Sliding filament theory
Sliding filament theory
•Binding to actin site releases ADP + Phosphate •Myosin head bends into low E config
Sliding filament theory
ActinTropomyosin Ca2+-binding sites
Troponin complex
(a) Myosin-binding sites blocked
• If ATP available, why doesn’t muscle just keep contracting? • Regulation
• Contraction stimulated by: • a motor neuron
• At rest, myosin-binding sites blocked by: • tropomyosin (regulatory protein)
The Role of Calcium and Regulatory Proteins
The Role of Calcium and Regulatory Proteins
Ca2+
Myosin-binding site
(b) Myosin-binding sites exposed
• What do calcium ions (Ca2+) do? • Bind to the troponin complex, • which uncovers myosin-binding sites
• Where does Ca2+ come from? How do Ca2+ ions get released? • Action potential (AP) in a motor neuron that synapses w/
the muscle fiber… • releases acetylcholine (n.t.)… • depolarizes the muscle and causing it to produce an AP • causes the sarcoplasmic reticulum (SR) to release Ca2+
• “SR?” • = modified ER
The Role of Calcium and Regulatory Proteins
Types of Muscle FibersFast TwitchSlow Twitch
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