Download Skeletal Muscles

Muscle Physiology
Chapter 11
Connective Tissue Components
• Muscle cell = muscle fiber
• Endomysium – covers muscle fiber
• Perimysium – binds groups of muscle fibers
(fasicles)
• Epimysium – covers the entire muscle
• Tendon – fibrous tissue that connects muscle
to bone
• Aponeurosis – broad, flat sheet of connective
tissue
• Fascia – fibrous CT surrounding muscle and
tendon
General Function of Muscles
• Movement
– Excitability
– Contractility
– extensibility
• Heat Production
• Posture
Overview of Muscle Cell
•
•
•
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Muscle cell = muscle fiber
Sarcolemma = plasma membrane
Sarcoplasm = cytoplasm
Sarcoplasmic reticulum (SR) = network of
tubules and sacs
• Multi-nucleated, multiple mitochondrion
• Bundles of myofibrils extend lengthwise & fill
sarcoplasm
– Composed of thick and thin myofilaments
Sarcomere
• Contractile unit of a muscle fiber
• each myofibril consists of many sarcomeres
• Z line
– Anchors thin filaments
– Boundary of sarcomere
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•
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M line – anchors thick filaments
A band: segment of thick & thin filaments
I band: segment of thin filaments
H zone: where thin and thick filaments will
not overlap (only thick)
Sarcomere cont…
• Elastic filaments – connect thick
filaments to Z line
• T (transverse) tubules – allows impulses
traveling along sarcolemma to move
deeper within the cell
• Triad – t tubule sandwiched between
sacs of the SR
– Allows impulses traveling along a t tubule to
stimulate sacs of the SR
Myofilaments
• Myofibrils – made up of 1000s of thin
and thick myofilaments
• Thin filaments
– Actin
– Tropomyosin
– Troponin
• Thick filaments
– myosin
Muscle Excitation
• Nerve impulse reaches the end of a
motor neuron  releases acetylcholine
(Ach)
• Ach diffuses across the neuromuscular
junction and binds with the receptors on
the motor endplate
Muscle Contraction
• Impulses travel along the sarcolemma 
t tubules  sacs of SR
• Ca2+ is released into the sarcoplasm 
binds with troponin on thin
myofilaments
• Tropomyosin shift to expose actin’s
active site
• Energized myosin heads bind with
actin’s active site and pulls thin filament
towards center of sarcomere
– Requires ATP
Muscle Relaxation
• Nerve impulse is complete  Ca2+ is
pumped back into the sacs of the SR
• Ca2+ is stripped from the troponin 
tropomyosin covers the actin’s active
site
• Myosin heads can no longer bind with
actin  muscle fiber returns to its
resting length
http://www.sci.sdsu.edu/movies/actin_myosin_gif.html
Rigor Mortis
• “stiffness of death”
• SR releases excess Ca2+  myosin heads
bind with actin’s active sites 
contraction of myofilaments
• Lack of ATP after death causes cross
bridges to “stick”
http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter9/
Sliding Filament Theory
In fully
contracted
muscle:
• H zone
disappears
• I band
narrows
• A band
remains the
same
Energy for Contractions
• Hydrolysis (breakdown) of ATP
– ATP  ADP (breaking high energy bond
btwn 2nd and 3rd phosphate groups)
• ATP binds  myosin head moves to
resting position (11-7A)
• Breakdown of ATP allow myosin head to
bind with actin and perform “power
stroke” (11-7B-D)
• ATP binds to return myosin head back
to resting position
Alternate Source of Energy
• ATP must be
continually resynthesized
• Breakdown of
creatinephosphate (CP)
provides energy
for ATP resynthesis
• Catabolism of food
provides energy
for ATP and CP
synthesis
Oxygen & Glucose
• O2 and glucose are the starting
materials for cellular respiration
(process that makes ATP)
• During rest oxygen is stored in
myoglobin
–
–
–
Supplies muscle fibers with oxygen during period of exercise
High amounts of myoglobin = red fibers = slow twitch fibers
Low levels of myoglobin = white fibers = fast twitch fibers
Aerobic vs. Anaerobic Respiration
• Aerobic Respiration
– Oxygen-requiring process
– Produces maximum amount of ATP from one
glucose molecule
• Anaerobic Respiration
– Does not require oxygen
– Short-term, rapid process to re-synthesize
ATP
– Produces lactic acid
– Burning/soreness in muscles
Heat Production
• Some energy from catabolic processes
is lost as heat
• Muscle release massive amts of heat
• Thermoreceptors sense decrease in
body temp  hypothalamus integrates
information  signal sent to skeletal
muscle to contract  shivering 
homeostatic balance is maintained
Motor Unit
• Motor unit = motor neuron + muscle
fibers it attaches to
• Motor neurons can innervate few to
100s of muscle fibers
• A lower number of muscle fibers within
a motor unit = more precise movement
– Ex: hand vs abdomen
http://natchem.files.wordpress.com/2009/11/motor-unit-lg.jpg
Isotonic vs Isometric
Contractions
• Isotonic – tension remains the same;
length of the muscle changes
– Concentric contraction: muscle shortens
(contracts)
– Eccentric contraction : muscle lengthens
• Isometric – tension changes; length of
the muscle remains the same
– Myosin heads unable to move thin filaments
– Static tension
Smooth Muscle Contractions
• Small tapered cell w/ single nuclei
• No t-tubules; loosely organized SR
• No sarcomeres
– Contract to shorter lengths
– Myofilaments crisscross (balled up
appearance when contracted)
• Calcium binds to calmodulin
http://www.cytochemistry.net/microanatomy/muscle/smooth1.jpg
Smooth Muscle Tissue Types
1. Visceral
– Gap junctions connect smooth muscle fibers
into sheets
– Forms inner muscular layer of hollow
structures
– Exhibits autorhythmicity
• Peristalsis, excretion of urine, childbirth, mixing
of stomach contents
2. Multiunit
– Composed of many single-cell units
– Ex: arrector pili muscles, lines blood vessels