skeleton muscle lecture copy -...
TRANSCRIPT
The Musculo-Skeletal System
Animal SkeletonsFunctions: •Support •Protection •Movement
all movement results from: muscle working against a skeleton
3 Types of skeletons •hydrostatic •exoskeleton •endoskeleton
Hydrostatic Skeletons• A hydrostatic skeleton • fluid held under pressure in a closed body
compartment • typical of • cnidarians • flatworms • nematodes • annelids
Earthworm peristaltic movement
ExoskeletonHard encasement deposited on outside of animal Typical of
mollusca arthropoda
EndoskeletonHard supporting elements deposited on inside of animal
Typical of sponges echinoderms chordates
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
Do you know your bones?
Types of joints in the appendicular skeleton
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
Vertebrate Skeletal Muscle
Vertebrate Skeletal Muscle
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
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
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Neural Control of Muscle Tension• Contraction of a whole muscle is graded
– Which means that we can voluntarily alter the extent and strength of its contraction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles – the number of fibers that contract – the rate at which muscle fibers are stimulated
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In a vertebrate skeletal muscle – Each branched muscle fiber is innervated by
only one motor neuron
• Each motor neuron – May synapse with multiple muscle fibers
Figure 49.34
Spinal cord
Nerve
Motor neuroncell body
Motorunit 1
Motorunit 2
Motor neuronaxon
Muscle
Tendon
Synaptic terminals
Muscle fibers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A motor unit – Consists of a single motor neuron and all the
muscle fibers it controls
• Recruitment of multiple motor neurons – Results in stronger contractions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A twitch – Results from a single action potential in a
motor neuron
• More rapidly delivered action potentials – Produce a graded contraction by summation
Figure 49.35
Action potential Pair of
action potentials
Series of action potentials at
high frequency
Time
Tens
ion
Singletwitch
Summation of two twitches
Tetanus
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• Tetanus is a state of smooth and sustained contraction – Produced when motor neurons deliver a volley
of action potentials
Types of Muscle Fibers“Slow-twitch” vs “Fast twitch?” white meat vs dark meat
muscle that needs energy for prolonged contraction/exercise needs more Oxygen = more myglobin, more pigment, darker
Skeletal muscle fibers are classified as slow oxidative, fast oxidative, and fast glycolytic
Based on their contraction speed and major pathway for producing ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Types of skeletal muscles
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Other Types of Muscle• Cardiac muscle, found only in the heart
– Consists of striated cells that are electrically connected by intercalated discs
– Can generate action potentials without neural input
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In smooth muscle, found mainly in the walls of hollow organs – The contractions are relatively slow and may
be initiated by the muscles themselves
• In addition, contractions may be caused by – Stimulation from neurons in the autonomic
nervous system