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Chapter 9
Muscles and Muscle Tissue
Lecture 16
Marieb’s Human
Anatomy and Physiology
Marieb w Hoehn
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Lecture Overview
• Types, characteristics, functions of muscle
• Structure of skeletal muscle
• Mechanism of skeletal muscle fiber
contraction
• Energetics of skeletal muscle contraction
• Skeletal muscle performance
• Types of skeletal muscle contractions
• Comparison of skeletal muscle with
smooth muscle and cardiac muscle
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Muscular System
Review - Three Types of Muscle Tissues
Skeletal Muscle • usually attached
to bones
• under conscious
control (voluntary)
• striated
• multinucleated
Smooth Muscle • walls of most viscera,
blood vessels, skin
• not under conscious
control
• not striated
Cardiac Muscle • wall of heart
• not under
conscious control
• striated
• branched
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Functions of Muscle
• Provide stability and postural tone (skeletal)
– Fixed in place without movement
– Maintain posture in space
• Purposeful movement (skeletal)
– Perform tasks consciously, purposefully
• Regulate internal organ movement and
volume (mostly involuntary - smooth)
• Guard entrances/exits (digestive/urinary –
skeletal and smooth)
• Generation of heat (thermogenesis - skeletal)
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Characteristics of All Muscle Tissue
• Contractile
– Ability to shorten (if possible) with force;
exerts tension
– CANNOT forcibly lengthen
• Extensible (able to be stretched)
• Elastic (returns to resting length)
• Excitable (can respond electrical impulses)
• Conductive (transmits electrical impulses)
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Structure of a Skeletal Muscle –
Gross/Histological Level
• epimysium
(around muscle)
• perimysium
(around fascicles)
• endomysium
(around fibers, or
cells)
Alphabetical order of MUSCLE from largest to smallest: fascicle, fiber, fibril, and filament
Figure from: Hole’s Human A&P, 12th edition, 2010
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Skeletal Muscle Fiber (Cellular level)
Sarcoplasmic reticulum is like the ER of other cells; but it contains [Ca2+ ]
Transverse or T-tubules contain extracellular fluid ( [Na+], [K+])
Fully differentiated, specialized cell – its structures are given special names
Figure from: Saladin, Anatomy &
Physiology, McGraw Hill, 2007
• sarcolemma (plasma membrane)
• sarcoplasm (cytoplasm)
• sarcoplasmic reticulum (ER)
• transverse tubule (T-tubule)
• triad • cisternae of sarcoplasmic
reticulum (2)
• transverse, or T-tubule
• myofibril (1-2 µm diam.)
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Structure of the Sarcomere (Histological Level)
• I band
• A band
• H zone
• Z line
• M line
The sarcomere is the contractile unit of skeletal (and cardiac) muscle (~ 2µm long)
Figures From:
Marieb & Hoehn,
Human Anatomy &
Physiology, 9th ed.,
Pearson, 2013
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Structure of the Sarcomere
(Histological/Molecular Level)
‘A’ in A band
stands for
Anisotropic
(dArk)
‘I’ in I band
stands for
Isotropic (LIght)
Zones of non-overlap: I band (thin filaments), and H zone (thick filaments)
A sarcomere runs from Z line (disk) to Z line (disk) (From ‘Z’ to shining ‘Z’!)
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
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Preview of Skeletal
Muscle Contraction
Major steps:
1. Motor neuron firing
2. Depolarization (excitation)
of muscle cell
3. Release of Ca2+ from
sarcoplasmic reticulum
4. Shortening of sarcomeres
5. Shortening of muscle/CTs
and tension produced
Figure from: Martini, Anatomy & Physiology,
Prentice Hall, 2001 Physiology here we come!!
T Tubule
Sarcoplasmic
reticulum
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Grasping Physiological Concepts
• The steps in a physiological process give you the
‘when’, i.e. tell you when things happen and/or the
order in which they happen.
• For each step in a process, you should MUST ask
yourself the following questions - and be sure you get
answers!
– How? (How does it happen?)
– Why? (Why it happens and/or why it’s important?)
– What? (What happens?)
See Figures 9.7 and 9.8 in your textbook for excellent
overall summaries of the muscle contraction process
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Sliding Filament Theory
Theory used to
explain these
observations is
called the sliding
filament theory
…
Figure from: Hole’s Human A&P, 12th edition, 2010
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Myofilaments (Molecular Level)
Thin Filaments
• composed of
actin
• associated
with troponin
and
tropomyosin
Thick Filaments
• composed of
myosin
• cross-bridges
Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
The Sarcomere as a 3D Object…
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https://www.youtube.com/watch?v=-pg09F5V63U
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Mechanism of Sarcomere Contraction
When you
think myosin,
think mover:
1. Bind
2. Move
3. Detach
4. Reset
Ca2+ troponin
myosin actin
Figure from: Hole’s
Human A&P, 12th
edition, 2010
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Mechanism of Sarcomere Contraction
1. Bind
2. Move 3. Detach
4. Reset
What would
happen if ATP was
not present?
Cycle repeats about 5 times/sec
Each power stroke shortens sarcomere by about 1%
So, each second the sarcomere shortens by about 5%
…
Figure from: Hole’s Human A&P, 12th edition, 2010
See Textbook Figure 9.12 (Focus – Cross Bridge Cycle)
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Neuromuscular Junction
• site where axon and
muscle fiber
communicate
• motor neuron
• motor end plate
• synaptic cleft
• synaptic vesicles
• neurotransmitters
The
neurotransmitter for
initiating skeletal
muscle contraction is
acetylcholine (ACh)
Figures from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
SR
Ca2+
Ca2+
Ca2+ Ca2+ Ca2+
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Stimulus for Contraction: Depolarization
• nerve impulse causes release of
acetylcholine (ACh) from
synaptic vesicles
• ACh binds to acetylcholine
receptors on motor end plate
• generates a muscle impulse
• muscle impulse eventually
reaches sarcoplasmic reticulum
(via T tubules) and Ca2+ is
released
• acetylcholine is destroyed by
the enzyme acetylcholinesterase
(AChE)
Linking of nerve stimulation with muscle contraction is called
excitation-contraction coupling (See Fig 9.11 in textbook)
Figure from:
Martini,
Anatomy &
Physiology,
Prentice Hall,
2001
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Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Summary of Skeletal Muscle Contraction
Contraction Relaxation
See Textbook Figure 9.12 (Focus – Cross Bridge Cycle)
- Bind (Ca, myosin)
- Move
- Detach
- Reset
5. Contraction
Cycle begins
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Modes of ATP Synthesis During Exercise
Continual shift from one energy source to another
rather than an abrupt change
Muscle stores enough ATP for about 4-6 seconds worth of contraction, but is
the only energy source used directly by muscle. So, how is energy provided for
prolonged contraction?
Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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Energy Sources for Contraction
Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
myoglobin stores extra oxygen so it can rapidly supply
muscle when needed
(Creatine-P)
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Oxygen Debt (Excess Post Exercise O2 Consumption – EPOC)
• when oxygen is not available
• glycolysis continues
• pyruvic acid converted to
lactic acid (WHY?)
• liver converts lactic acid to
glucose
(The Cori Cycle)
EPOC - amount of extra oxygen needed by liver to convert lactic
acid to glucose, resynthesize creatine-P, make new glycogen, and
replace O2 removed from myoglobin.
Figure from: Hole’s
Human A&P, 12th edition,
2010
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Muscle Fatigue
• Inability to maintain force of contraction although
muscle is receiving stimulus to contract
• Commonly caused by
• decreased blood flow
• ion imbalances
• accumulation of lactic acid
• relative (not total) decrease in ATP availability
• decrease in stored ACh
• Cramp – sustained, involuntary contraction
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Length-Tension Relationship
Maximum tension in striated muscle can only be generated when there
is optimal (80-100%) overlap between myosin and actin filaments
Figures From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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Muscular Responses
Threshold Stimulus
• minimal strength required to cause contraction in an
isolated muscle fiber
Record of a Muscle
Contraction = myogram
• latent period
• period of contraction
• period of relaxation
• refractory period
• all-or-none response
An individual muscle fiber (cell) is either “on” or “off” and
produces maximum tension at that resting length for a given
frequency of stimulation
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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Treppe, Wave Summation, and Tetanus
• Treppe, Wave Summation, and Tetanus
– all involve increases in tension generated in a muscle fiber
after more frequent re-stimulation
• The difference among them is WHEN the muscle
fiber receives the second, and subsequent,
stimulations:
– Treppe – stimulation immediately AFTER a muscle cell
has relaxed completely.
– Wave Summation – Stimulation BEFORE a muscle fiber is
relaxed completely
• Incomplete (unfused) tetanus – partial relaxation between stimuli
• Complete (fused) tetanus – NO relaxation between stimuli
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Treppe, Wave Summation, and Tetanus
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Wave (Temporal)
Summation Treppe
(10-20/sec)
Incomplete
Tetanus
(20-30/sec)
Complete
Tetanus
(>50/sec)
Little/no
relaxation
period
Tetany is a sustained contraction of skeletal muscle
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Motor Unit
• single motor neuron plus all muscle fibers controlled by
that motor neuron
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013
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Recruitment of Motor Units
• recruitment - increase in the number of motor
units activated to perform a task
• whole muscle composed of many motor units
• as intensity of stimulation increases,
recruitment of motor units continues, from
smallest to largest, until all motor units are
activated
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Sustained Contractions
• smaller motor units recruited first
• larger motor units recruited later
• produces smooth movements
• muscle tone – continuous state of partial contraction
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Types of Contractions
• isotonic – muscle contracts and
changes length
• concentric – shortening contraction
• isometric – muscle “contracts” but does not change length
• eccentric – lengthening
contraction
Figure from:
Hole’s Human
A&P, 12th edition,
2010
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Types of Skeletal Muscle Fibers
Slow Oxidative
(SO)
(REDSOX)
Fast Oxidative-
Glycolytic (FOG)
Fast Glycolytic
(FG)
Alternate name
Slow-Twitch
Type I
Fast-Twitch
Type II-A
Fast-Twitch
Type II-B
Myoglobin (color)
+++ (red)
++ (pink-red)
+ (white)
Metabolism
Oxidative
(aerobic)
Oxidative and
Glycolytic
Glycolytic
(anaerobic)
Strength
Small diameter,
least powerful
Intermediate
diameter/strength
Greatest diameter,
most powerful
Fatigue resistance High Moderate Low
Capillary blood
supply
Dense
Intermediate
Sparse
All fibers in any given motor unit are of the same type
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Types of Skeletal Muscle Fibers
All fibers in any given motor unit are of the same type
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Smooth Muscle Fibers
Compared to skeletal muscle fibers
• shorter
• single nucleus
• elongated with tapering ends
• myofilaments organized
differently
• no sarcomeres, so no striations
• lack transverse tubules
• sarcoplasmic reticula not well
developed
• exhibit stress-relaxation
response (adapt to new stretch
state and relax)
Figure from: Martini, Anatomy &
Physiology, Prentice Hall, 2001
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Types of Smooth Muscle
Single-unit (unitary)
smooth muscle
• visceral smooth muscle
• sheets of muscle fibers
that function as a group,
i.e., a single unit
• fibers held together by
gap junctions
• exhibit rhythmicity
• exhibit peristalsis
• walls of most hollow
organs, blood vessels,
respiratory/urinary/
reproductive tracts
Multiunit Smooth Muscle
• fibers function
separately, i.e., as
multiple independent
units
• muscles of eye,
piloerector muscles,
walls of large blood
vessels
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Smooth Muscle Contraction
• Resembles skeletal muscle contraction
• interaction between actin and myosin
• both use calcium and ATP
• both depend on impulses
• Different from skeletal muscle contraction
• smooth muscle lacks troponin
• smooth muscle depends on calmodulin
• two neurotransmitters affect smooth muscle
• acetylcholine and norepinephrine
• hormones affect smooth muscle
• have gap junctions
• stretching can trigger smooth muscle contraction (but briefly,
then relaxation again occurs)
• smooth muscle slower to contract and relax
• smooth muscle more resistant to fatigue
• smooth muscle can undergo hyperplasia, e.g., uterus
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Cardiac Muscle
• only in the heart
• muscle fibers joined together by
intercalated discs
• fibers branch
• network of fibers contracts as a
unit (gap junctions)
• self-exciting and rhythmic
• longer refractory period than
skeletal muscle (slower contract.)
• cannot be tetanized
• fatigue resistant
• has sarcomeres
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
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Review
• Three types of muscle tissue
– Skeletal
– Cardiac
– Smooth
• Muscle tissue is…
– Contractile
– Extensible
– Elastic
– Conductive
– Excitable
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Review
• Functions of muscle tissue
– Provide stability and postural tone
– Purposeful movement
– Regulate internal organ movement and volume
– Guard entrances/exits
– Generation of heat
• Muscle fiber anatomy
– Actin filaments, tropomyosin, troponin
– Myosin filaments
– Sarcomere
– Bands and zones
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Review
• Muscle contraction
– Sliding filament theory
– Contraction cycle (Bind, Move, Detach, Release)
– Role of ATP, creatine
– Metabolic requirements of skeletal muscle
– Stimulation at neuromuscular junction
• Muscular responses
– Threshold stimulus
– Twitch – latent period, refractory period
– All or none response
– Treppe, Wave summation, and tetanus
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Review
• Muscular responses
– Recruitment
– Muscle tone
– Types of muscle contractions
• Isometric
• Isotonic
• Concentric
• Eccentric
• Fast and slow twitch muscle fibers
– Slow Oxidative (Type I) (think: REDSOX)
– Fast Oxidative-glycolytic (Type II-A)
– Fast Glycolytic (Type II-B)