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Chapter 7: Muscles
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Overview
• The word muscle can refer to an organ or a tissue
• Muscles
– Make up 40-50% of body weight
– Can contract on conscious command
– Are responsible for movement
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Functions of Muscles
• Muscles convert chemical energy into mechanical force:
– Move body parts
– Maintain body posture and stabilize joints
– Adjust the volume of hollow structure (e.g., bladder)
– Move substances within the body (e.g., pump blood)
– Produce heat
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Three Types of Muscle
Skeletal
Cardiac
Smooth
Other names Somatic
Myocardial
Visceral
Striated
Yes
Yes
No
Contraction
Quick
Quick
Slow
Voluntary
Yes; some
involuntary
(reflexive)
No
No
Subject to
fatigue
Yes
No
No
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Three Types of Muscle (cont’d)
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Remember This!
• Adult muscle stem cells are called satellite cells;
they produce myoblasts, which fuse to form skeletal
muscle fibers.
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Structure of Skeletal Muscle
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Motor Units
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Steps in Muscular Contraction
• An electrical signal in the somatic motor neuron
• A chemical signal (acetylcholine) in the synapse
• An electrical signal in the sarcolemma
• A chemical signal (calcium) in the sarcoplasm
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Chemical Synapses
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Myofibrils and Myofilaments
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Myofibrils and Myofilaments (cont’d)
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Remember This!
• During muscle contraction
– sarcomeres and myofibrils shorten
– myofilaments do not change in length
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Thick and Thin Filaments
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Remember This!
Levels of Skeletal Muscle Organization
• Muscle
• Fascicle (bundle of muscle fibers)
• Muscle fiber (muscle cell)
• Myofibril (bundle of myofilaments)
• Myofilament (stands of contractile proteins)
• Contractile protein
smallest
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Muscle Contraction
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Muscle Contraction and Relaxation
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Muscle Contraction and Relaxation (cont’d)
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Muscle Relaxation
• Relaxation is the reverse of contraction
– Acetylcholine release stops
– Nicotinic receptor channels close and sarcolemma
repolarizes
– SR calcium channels close; Ca2+ ions taken into SR
– Tropomyosin covers binding sites
– Myosin no longer binds actin; sarcomere returns
to resting length
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Muscle Energy Production
• ATP stores energy in chemical bond used by muscles
ATP + H2O  ADP + H2O + PO4 + Energy
• Glycolosis is the fastest method of generating ATP from
nutrients.
• Mitochondria generate ATP from glucose and fatty acid
molecules.
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Muscle Energy Production (cont’d)
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Remember This!
• ATP binding causes the cross-bridge to release. The
energy from ATP cleavage is necessary for the power
stroke.
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Aerobic vs. Anaerobic Muscle Function
Aerobic muscle function
Anaerobic muscle function
Mitochondria provide ATP
Glycolitic fibers provide quick
energy kick
Oxygen is required
Oxygen is not required
Jogging = endurance activity
Lactic acid leads to fatigue
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Remember This!
• The terms anaerobic metabolism and glycolysis are
often used synonymously, but erroneously.
Glycolysis is the necessary first step in both aerobic
metabolism and anaerobic metabolism.
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Muscle Fiber Types
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Muscle Energy Metabolism
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Muscle Fatigue
• Muscle fatigue: loss of the ability to respond to nerve
stimulation after vigorous exercise
– Peripheral
– Central
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Mechanics of Muscle Contraction
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Mechanics of Muscle Contraction (cont’d)
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Remember This!
• In an everyday contraction at a given fiber length,
contraction of individual muscle fibers is all-or-none, as
the fiber contracts in incomplete tetanus.
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Mechanics of Muscle Contraction
• The force an individual muscle exerts depends on
– The force exerted by each contracting fiber
– The number of motor units contracting
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Types of Contractions
• Isotonic contraction: dynamic shortening of muscle
tissue that maintains constant force; e.g., chewing food
• Concentric contraction: myofilaments slide;
sarcomeres, fibers, muscles shorten; movement occurs;
e.g., biceps curl
• Eccentric contraction: myosin heads grab actin
filaments to slow movement; e.g., lowering weight
• Isometric contraction: force is generated and muscle
tenses, but myofibrils do not slide and length is
unchanged; e.g., maintaining upright body posture
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Types of Contractions (cont’d)
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Remember This!
• The thing common to all muscle contraction is force,
not movement.
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Smooth Muscle vs. Skeletal Muscle
Smooth Muscles
Skeletal Muscles
• Have short, plump cells
• Have long, thin cells (fibers)
• Built on intermediate
filaments
• Built in bundles; have lengthtension relationship
• Connected by dense bodies
• Anchored by Z disc
• Layered in sheets, so can
stretch in many directions
• Have striations
• Ca++ ions come through cell
membrane and regulate
myosin, not actin
• Ca++ ions come from SR and
T-tubules; control access to
binding sites
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Remember This!
• Intermediate filaments form the scaffolding of a
smooth muscle cell, and myofilaments contract the
cell.
• The myosin heads are regulated in smooth muscle;
the binding sites on actin molecules are regulated in
skeletal muscle.
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Smooth Muscle
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Smooth Muscle Regulation
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Origin and Insertion
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Superficial Muscles, Anterior View
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Superficial Muscles, Posterior View
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Muscles of Facial Expression
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Muscles Controlling the Jaw and Moving
the Head
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Muscles Controlling the Jaw and Moving
the Head (cont’d)
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Muscles of the Thorax
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Muscles of the Thorax (cont’d)
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Muscles of the Thorax (cont’d)
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Muscles of the Perineum
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Muscles that Move and Stabilize the
Pectoral Girdle
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Muscles that Move the Arm (Humerus) at
the Shoulder Joint
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Muscles that Move the Arm (Humerus) at
the Shoulder Joint (cont’d)
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Muscles that Move the Forearm, Hand,
and Fingers
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Muscles that Move the Forearm, Hand,
and Fingers (cont’d)
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Muscles that Move the Forearm, Hand,
and Fingers (cont’d)
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Muscles that Move the Thigh and Leg
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Muscles that Move the Thigh and Leg
(cont’d)
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Muscles that Move the Thigh and Leg,
(cont’d)
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Muscles that Move the Foot and Toes
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Muscles that Move the Foot and Toes
(cont’d)
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Muscles that Move the Foot and Toes
(cont’d)
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