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1
UNIT 6 THE MUSCULAR
SYSTEM
I. Functions of Muscular SystemA. Produces Movement
– Internal vs. External« locomotion & manipulation« circulate blood & maintain
blood pressure« move fluids, food, baby
B. Maintaining Posture
C. Stabilizing Joints– tendons span across joint
D. Generation of Heat– ATP ADP + P + Energy
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II. Types of Muscle (Review)*Muscle cells are also called muscle fibers
myo-mys-sarco-
SHAPE Elongated cylinder shape Spindle shape
Cylinder shape w/ branching ends, intercalated disks
NUCLEUS Multinucleated Single Single
APPEARANCE Striated, nonbranching
Nonstriated, arranged in sheets/layers
Striated, Branched ends
CONTROLVoluntary (reflex also), by nervous system
Involuntary, nervous system, hormones
Involuntary, nervous system, hormones
CONTRACTIONSlowRapid, Great force, Tire easily
Slow sustained contractions
Sustained steady rate, can increase
SKELETAL SMOOTH CARDIAC
Key Words:
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III. Gross Anatomy: Skeletal MuscleA. Connective Tissue Protection
– Muscle fibers are fragile– Protected by...
« Surrounded by connective tissue« Bundled together
B. Organization– Endomysium: Delicate connective
tissue sheath around individual muscle fibers
– Perimysium: Coarser membrane wrapped around several fibers (Fasicle)« Fasicle: Bundle of fibers
– Epimysium: Very tough layer surrounding many fasicles making up entire muscle« Blends together at end to form
» Tendons: cordlike» Aponeuroses: sheetlike
*Tendons & Aponeuroses attach muscle to bones, cartilage, or other connective tissue
III. Gross Anatomy: Skeletal Muscle cont'd
> Origin: site of attachment on a fixed bone
> Insertion: site of attachment on a bone that moves
> Action: function
– ex.
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IV. Microscopic Anatomy: Skeletal Muscle
A. Sarcolemma:– plasma membrane of muscle fiber
B. Myofibril:– organelles that fill up muscle fiber that are made up of smaller units called myofilaments
C. Myofilaments:– protein filaments that are responsible for the contraction (shortening) of muscle fiber/cell« Myosin: thick filament w/ projections« Actin: thin filament
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IV. Microscopic Anatomy: Skeletal Muscle cont'd
D. Sarcoplasmic Reticulum:– smooth ER that surrounds myofibril– stores & releases Ca2+ on demand
E. TTubules:– extensions of sarcolemma that penetrate into cell– passes by each myofibril, conducts impulse– ensures each myofibril contracts at same time
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IV. Microscopic Anatomy: Skeletal Muscle cont'd
F. Sarcomere:– tiny contractile unit linked together making up myofibril– one sarcomere goes from zline to zline– gives muscle banded appearance
« ABand: appear dark because thick Myosin filaments overlap with thin Actin filaments» except for small space in middle (HZone)
« IBand: appear light because only thin actin
MYOFIBRIL
REVIEW:
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Sliding Filament Model:• Actin slides past myosin causing shortening of muscle fiber
• Contracted Sarcomere:> I bands shorten
> Z lines move closer together
> H zone disappears
> Successive A bands move closer together
> A bands stay same length
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V. Muscle Stimulation & Contraction
A. Terms:> Neurotransmitter: chemical released from axonal
terminals
> Acetylcholine (ACh): neurotransmitter for muscle contractions
> Action Potential: electrical current caused by changes in ion concentration across a membrane
> Contractility: ability to shorten/contract
> Irritability: ability to receive and respond to a stimulus
> Neuron: nerve cell
> Motor Unit: motor neuron & all cells it stimulates
> Neuromuscular Junction: nervemuscle junction
> Synaptic Cleft: gap between axonal terminal and sarcolemma
Motor Unit> Motor neuron and
all muscle fibers it stimulates
Neuromuscular Junction
Leave space (~1/3 to 1/2 page) to draw a motor unit
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Motor Unit> Motor neuron
and all muscle fibers it stimulates
Neuromuscular Junction
POLARIZED MUSCLE FIBER (will add to...)
RESTING MEMBRANE POTENTIAL
V. Muscle Stimulation & Contraction cont'd
B. Contraction Intro:
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POLARIZED MUSCLE FIBER
RESTING MEMBRANE POTENTIAL
V. Muscle Stimulation & Contraction cont'd
B. Contraction Intro:
NEUROMUSCULAR JUNCTION
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V. Muscle Stimulation & Contraction
B. Contraction:
> Nerve impulse– AP reaches axon terminal– Ca2+ voltagegated channels open & Ca2+ diffuses in
> Acetylcholine is released from axonal terminal & diffuses across synaptic cleft– Attaches to sarcolemma (receptors on chemicallygated ion channels)
> Sarcolemma becomes permeable to Na+ (leads to change in membrane voltage) – As Na+ diffuses into the cell, local depolarization occurs
« Opening Na+ voltagegated channels along sarcolemma– Depolarization can lead to an ACTION POTENTIAL
« Membrane voltage must reach threshold to generate an AP
– K+ diffuses out, repolarization wave occurs
(Depolarization Action Potential)
(Repolarization)
« Due to a certain change in membrane potential» Na+ voltagegated channels close» K+ voltagegated channels open
« Repolarization only restores electrical conditions
DEPOLARIZATION VS REPOLARIZATION
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DEPOLARIZATION VS REPOLARIZATION
Effects of Membrane Potential Changes
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V. Muscle Stimulation & Contraction cont'd
B. Contraction cont'd:
> As AP travels along sarcolemma & Ttubules:– Calcium ions are released from the sarcoplasmic reticulum
> Ca2+ allows myosin heads to attach to actin filaments (forming cross bridges)– Sliding Filament Model
> When action potential ends:– ACh broken down by Acetylcholinesterase– Ca2+ reabsorbed by SR (via active transport)– Na+/K+ pump restores ion concentrations– Muscle cell relaxes and returns to original length
RELAXED SARCOMERE
CONTRACTED SARCOMERE
Role of:> Ca2+
> ATP
REVIEW:
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Local Depolarization
Depolarization Action Potential
Repolarization
Action Potential: Generation & Propagation
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Cross Bridge Cycle