the muscular system chapter 6. skeletal muscle bundles of striped muscle cells attaches to bone...
TRANSCRIPT
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The Muscular System
Chapter 6
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Skeletal Muscle
• Bundles of striped
muscle cells
• Attaches to bone
• Often works in
opposition
bicepstriceps
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Tendons Attach Muscle to Bone
muscle
tendon
bursae
synovialcavity
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Human Skeletal MusclesTRICEPS BRACHII
PECTORALIS MAJOR
SERRATUS ANTERIOR
EXTERNAL OBLIQUE
RECTUS ABDOMINUS
ADDUCTOR LONGUS
SARTORIUS
QUADRICEPS FEMORIS
TIBIALIS ANTERIOR
BICEPS BRACHII
DELTOID
TRAPEZIUS
LATISSIMUS DORSI
GLUTEUS MAXIMUS
BICEPS FEMORIS
GASTROCNEMIUS
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Skeletal Muscle Structure
• A muscle is made
up of muscle cells
• A muscle fiber is a
single muscle cell
• Each fiber contains
many myofibrils
myofibril
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Sarcomere
Z band Z band Z band
sarcomere sarcomeresarcomere sarcomere
A myofibril is made up of thick and thin filaments arranged in sarcomeres
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Muscle Microfilaments
Thin filaments• Like two strands of
pearls twisted together
• Pearls are actin
• Other proteins in grooves in filament
Thick filaments• Composed of myosin
• Each myosin molecule has tail and a double head
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Sliding-Filament Model
• Myosin heads attach to actin filaments
• Myosin heads tilt toward the sarcomere center, pulling actin with them
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Sliding-Filament Model
Sarcomere shortens because the actin filaments are pulled inward, toward the sarcomere center
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Contraction Requires Energy
• Muscle cells require huge amounts of
ATP energy to power contraction
• The cells have only a very small store of
ATP
• Three pathways supply ATP to power
muscle contraction
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ATP for Contraction
Pathway 1DEPHOSPHORYLATIONCREATINE PHOSPHATE
Pathway 2AEROBIC RESPIRATION
Pathway 3GLYCOLYSIS ALONE
creatine
oxygenglucose from bloodstream andfrom glycogen break down in cells
ADP + Pi
Relaxation
Contraction
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Nervous System Controls Contraction
• Signals from nervous system travel along spinal cord, down a motor neuron
• Endings of motor neuron synapse on a muscle cell at a neuromuscular junction
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Role of Calcium in Contraction
• T tubules in the sarcoplasmic reticulum relay signal
• Calcium ions are released
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Troponin and Tropomyosin
• Lie in groove in actin filament
• When muscle is relaxed, tropomyosin blocks myosin binding site
• When troponin binds calcium ions, it changes shape and moves tropomyosin
• Cross-bridge formation and contraction can now proceed
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Muscle Tension
• Is mechanical force a contracting muscle
exerts on an object
• For a muscle to shorten, muscle tension
must exceed the load that opposes it
• The load may be the weight of an object
or gravity’s pull on the muscle
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Two Main Types of Contraction
• Isotonic contraction
– Muscle visibly shortens; moves a load
– Tension remains constant as the muscle
changes length
• Isometric contraction
– Muscle does not change length
– Tension is insufficient to move load
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Motor Unit
• One neuron and all the muscle cells that form junctions with its endings
• When a motor neuron is stimulated, all the muscle cells it supplies are activated to contract simultaneously
• Each muscle consists of many motor units
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Twitches and
Tetanus
peak
relaxation
stimulus contraction starts
time
number of stimuli per second
number of stimuli per second
tetaniccontraction
repeated stimulationtwitch
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Two Types of Skeletal Muscle
• Slow, or red, muscle– Many capillaries,
high myoglobin– Contracts fairly
slowly– Can sustain
contraction
• Fast, or white, muscle– Fewer capillaries,
less myoglobin– Contracts quickly– Cannot sustain
contraction
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Muscle Fatigue
• An inability to maintain muscle tension
• Occurs after a period of tetanic contraction
• Different types of muscle show different fatigue patterns