1 UNIT 6 THE MUSCULAR SYSTEM I. Functions of Muscular System A. 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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UNIT 6 THE MUSCULAR SYSTEM - Badger Anatomy & Physiology€¦ · UNIT 6 THE MUSCULAR SYSTEM I. Functions of Muscular System A. Produces Movement –Internal vs. External «locomotion
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UNIT 6 THE MUSCULAR
SYSTEM
I. Functions of Muscular SystemA. Produces Movement
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