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Jan 412:42 PM
UNIT 6 THE MUSCULAR
SYSTEM
Jan 412:43 PM
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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Jan 412:47 PM
II. Types of Muscle*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, Figure 8 look
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:
Jan 412:51 PM
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Jan 412:51 PM
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
Dec 217:14 AM
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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Jan 410:38 PM
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
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REVIEW:
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Jan 611:16 PM
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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Jan 79:21 AM
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
Dec 1910:06 AM
Motor Unit?
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Jan 198:15 AM
POLARIZED MUSCLE FIBER
RESTING MEMBRANE POTENTIAL
Jan 198:15 AM
POLARIZED MUSCLE FIBER
RESTING MEMBRANE POTENTIAL
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Jan 179:40 PM
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 the 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, 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
Jan 1710:12 PM
DEPOLARIZATION VS REPOLARIZATION
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DEPOLARIZATION VS REPOLARIZATION
Jan 1711:02 PM
Effects of Membrane Potential Changes
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Jan 179:40 PM
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– Ca2+ reabsorbed by SR– Na+/K+ pump restores ion concentrations– muscle cell relaxes and returns to original length
RELAXED SARCOMERE
CONTRACTED SARCOMERE
Role of:> Ca2+
> ATP
Jan 88:00 PM
REVIEW:
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Jan 1710:13 PM
NEUROMUSCULAR JUNCTION
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Local Depolarization
Depolarization Action Potential
Repolarization
Action Potential: Generation & Propagation
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Jan 1711:04 PM
Cross Bridge Cycle
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A. AllorNone Law:
> Muscle cells contract to their fullest extent when adequate action potential is present
> Degree of contraction (muscle) depends on:– speed of muscle contraction (frequency
of stimulation)– # of motor units stimulated (recruitment)
VI. Performance of Muscle Fibers
Jan 203:54 PM
VI. Performance of Muscle Fibers cont'd
B. Muscle Tone:> resting tension> some fibers contract in response to stretch receptors in
muscles– not enough tension to cause movement– helps firm the muscle
– inactivity leads to atrophy
C. Isotonic vs Isometric Contractions:> Isotonic
– tension > resistance– muscle tension remains constant & muscle shortens
> Isometric– tension < resistance – tension increases, muscle doesn't shorten
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Jan 2010:01 PM
VII. Energy Sources: ATP Supplies
A. Direct Phosphorylation:
> Creatine phosphate is coupled with ADP, then a phosphate is transferred to ADP, creating ATP
> 1520 second supply (stored ATP & CP reserves)
Jan 219:59 PM
VII. Energy Sources: ATP Supplies cont'd
B. Anaerobic Respiration (glycolysis):
> Glucose broken into pyruvic acid 2 ATP/glucose
> If not enough O2, pyruvic acid Lactic Acid
> provides energy at a very fast rate, but only for 3040 seconds
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Jan 2110:05 PM
VII. Energy Sources: ATP Supplies cont'd
C. Aerobic Respiration: with O2 during light activity & rest
> Glycolysis breaks glucose into pyruvic acid
> with O2 present, pyruvic acid enters mitochondria and Krebs cycle then to Electron Transport Chain (ETC)
> results in CO2, H2O, and 36 ATP per glucose
> provides much energy, but at slow rate
