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Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
The Muscular System
part 2
Muscle Physiology
Modified by J. Kalinowski 1/2015
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Microscopic Anatomy of Skeletal
Muscle
 Sarcolemma – specialized plasma
membrane of muscle fiber
 Cells are multinucleate
 Nuclei are just beneath the sarcolemma
 Sarcoplasm – cytoplasm of a muscle
fiber
Figure 6.3a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.9b
Myoglobin
• Myoglobin is a common protein, which has
the ability to store oxygen in muscle cells.
The myoglobin has a high level of red
pigment, so the more myoglobin the meat
has, the redder it will be. The terms “red
meat” and “white meat” are actually an
indicator for the level of myoglobin.
Myoglobin Amounts
Myoglobin
• This protein is also the main reason that the
red meat turns darker while you’re cooking
it. During the heating process, iron atoms of
the myoglobin lose electrons and they move
up to a higher oxidation level. Thus, the
meat turns from pinkish-red to brown.
Microscopic Anatomy of Skeletal Muscle
 Myofibril - Long rod like organelles
comprising 80% of cell volume
 Running parallel the entire length of the cells
the myofibrils are aligned to give distinct
bands
 A band = dark band
Contains lighter central H Zone
visible only in relaxed fiber
 I band = light band
Contains Z disc/line at midpoint
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Micro anatomy
• Banding patterns/striations reveal the
working structure of muscle fiber
Microscopic Anatomy of Skeletal
Muscle
 Sarcomere
 Region of myofibril
 Contractile unit of a muscle fiber
 Region between 2 successive Z discs
Figure 6.3b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Microscopic Anatomy of Skeletal
Muscle
 Organization of the sarcomere
 Thin filaments = actin filaments
 Contain troponin & tropomyosin to regulate
attachment of myofilaments to each other
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Microscopic Anatomy of Skeletal
Muscle
Thick filaments = myosin filaments
 Composed of the protein myosin with
cross bridge heads
 Heads contain ATPase enzymes to split
ATP & release energy for contraction
Figure 6.3c
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Sarcoplasmic
Reticulum
• Sarcoplasmic
reticulum –
specialized smooth
endoplasmic
reticulum
• Function: Stores
ionic calcium &
releases it on
demand
Sarcoplasmic
Reticulum
• Surrounds
myofibrils
• At junction of A
band and I band,
sarcolemma forms
hollow T-tubule to
conduct stimulus
deep into every
sarcomere
Study all your info and
diagrams!
END OF QUIZ #1 MATERIAL
How muscle knows WHEN to
contract
Mechanism of contraction on a
cellular level
Motor Unit
• One motor
neuron and ALL
the muscle cells
that it stimulates
• Spread
throughout
muscle
Explanation - then see next slide!
• Stimulation of one motor unit results in
weak contraction of ENTIRE muscle
– Since a motor unit is spread throughout the
muscle & not clustered together, it stimulation
will activate cells scattered throughout the
entire muscle
– This causes a weak contraction of the entire
muscle
– Muscles requiring fine control have small
motor units that only activate a few cells at a
time.
Figure 6.4a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.14
Nerve Stimulus to Muscles
 Neuromuscular
junctions –
association site
of nerve and
muscle
Figure 6.5b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Nerve Stimulus to Muscles
 Each axon terminal
forms junction with
single muscle fiber
 Synaptic cleft – fluid
filled gap between
nerve and muscle
 Nerve and muscle do
not make contact
 Importance:
prevent
continuous
stimulation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.5b
Slide
Transmission – know the steps
 Vesicles in axon terminal filled with
neurotransmitter – chemical released by
nerve upon arrival of nerve impulse
 The neurotransmitter for skeletal muscle is
acetylcholine (ACh)
 Neurotransmitter crosses synaptic cleft
and attaches to receptors on the
sarcolemma
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Transmission – know the steps
• Sarcolemma becomes temporarily
permeable to sodium (Na+)
• Na+ ions rush into muscle cell which
reverses electrical conditions
• Action potential is caused which moves
along sarcolemma and down T tubules
deep into muscle fiber
• Once initiated – action potential is
unstoppable (all or none principle)
resulting in full contraction of that
particular muscle fiber (cell)
Safeguard
• When nerve stimulation stops:
–Ach is destroyed by
acetylcholinesterase (AChE) to
prevent continued contraction
–Substances such as certain
organophosphates found in
pesticides and fertilizers destroy
AChE causing convulsions
End of stimulation
• K+ ions leaves cell rapidly to
restore electrical balance
• Then Na-K pump restores ions
to original positions for
relaxation of muscle fiber
• Use your diagram to study!
• The Neuromuscular Junction
Sliding Filament Theory
HOW a muscle contracts
Sliding Filament Theory
• The thin filaments
slide past the thick
filaments so the
overlap increases
• This shortens the
muscle fiber and
thus the entire
muscle
The Sliding Filament Theory
 Activation by nerve
causes myosin
heads
(crossbridges) to
attach to binding
sites on the thin
filament
 Myosin heads then
bind to the next site
of the thin filament
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.7
Slide
The Sliding Filament Theory of
Muscle Contraction
 This continued
action causes a
sliding of the myosin
along the actin
 The result is that the
muscle is shortened
(contracted)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.7
Slide
What causes the filaments to
slide?
• Cross bridge
attachment: in
presence of Ca ions,
high energy myosin
cross bridge binds to
actin binding site
• Power Stroke:
energy from ATP is
used to bend cross
bridge and pull actin
toward center of
sarcomere
• 1% shortening for
each power stroke
What causes the filaments to
slide?
• Cross bridge
detachment: ATP
also provides energy
to detach cross
bridge
• rigor mortis on next
slide
• “Cocking” of myosin
head: energy
returns myosin head
to high energy
configuration to
prepare for next
attachment
Cross
Transmission
Contraction
Bridge
Cross Bridge Cycling
Rigor Mortis –stiffness of death
• Muscles begin to
stiffen within 4 hours
after death
– Face, hand, feet, rest of
body
– Intensity depends on
muscle mass
• Peak rigidity occurs
12 to 48 hours
• Gradually disappears
over next 36-48 hours
in cool climates
• 9-12 hours in hot
• Dead cells unable to
exclude Ca ions so Ca
ions come out of SR
and promote cross
bridge binding
Rigor Mortis
• ATP synthesis stops
shortly after breathing
stops
– Exhaustion before
death accelerates rigor
since ATP has been
depleted
• Cross bridge
detachment impossible
• Actin & myosin
become irreversible
cross linked producing
stiffening of dead
muscle
• Gradual disappearance
results from
breakdown of
biological molecules
The Role of Ionic Calcium
• Tropomyosin (regulatory protein) normally
block binding sites on actin molecule so
myosin cannot attach to actin
• When ionic Ca becomes available (released
from SR), Ca binds to troponin (another
regulatory protein
• Troponin “pulls” tropomysosin off of the
binding site by causing it to change shape
• This allows attachment of cross bridges
Excitation Contraction Coupling
Excitation Contraction coupling
• Study diagram & YouTube animations provided
• Action potential "wave" travels along sarcolemma
and deep into T tubules.
• This triggers Ca2+ release from terminal cisternae
of SR
• Ca2+ binds to troponin — binding sites exposed.
• Contraction: see sliding filament theory
• Action potential ends, Ca2+ is taken back up into
the SR
• Tropomyosin blockage restored, contraction ends,
muscle fiber relaxes.
Contraction of a Skeletal Muscle
 “All or none” principle applies only to
each muscle fiber, NOT the whole
muscle
 Within a skeletal muscle, not all fibers
may be stimulated during the same
interval
 Different combinations of muscle fiber
contractions may give differing
responses
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.19
Use your Quiz Review and the
Manipulatives provided to study!!!
END OF QUIZ #2 MATERIAL
Graded Muscle Responses
 Graded responses – different
degrees of skeletal muscle
shortening,
 Produced in 2 ways
 By changing the frequency of muscle
stimulation (Be able to recognize the
diagrams & basic facts)
 By changing the # of muscle cells
being stimulated
Changing Frequency of Muscle
Stimulation
- recognize diagrams &
underlined info
Types of Graded Responses
 Twitch
 Response of muscle to single action
potential
 Not a normal muscle function
 Metabolic properties & enzymes present in
muscles cause different twitch responses
 Useful for diagnostics
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
6.20a
Types of Graded Responses
• Treppe
– Response that occurs when frequency &
strength of stimulus held constant.
– Staircase pattern on myogram recording
– Each successive contraction is stronger than the
previous one
– Reflects increased availability of Ca2+ ions
– Heat also increases efficiency of enzymes in
muscle
– Another good reason to warm up !!!!! (along
with thinning out your synovial fluid)
Treppe
Types of Graded Responses
 Wave Summation
 Impulses in rapid succession (increasing
the frequency) cause contractions to
build on one another
 The muscle does not completely
return to a resting state (not able to fully
relax)
 The effects are added and show as
unfused tetanus until the frequency is such
that it becomes fused tetanus (smooth)
Figure 6.9a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
6.20b
Types of Graded Responses
 Fused Tetanus
 No evidence of relaxation before the
following contractions
 The result is a sustained muscle contraction
– usual manner of muscle contraction
Figure 6.9a, b
Figure 6.9c,d
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
6.21b
CHANGING NUMBER OF
MUSCLE CELLS BEING
STIMULATED
- RECOGNIZE DIAGRAMS &
UNDERLINED INFO
Multiple Motor Unit Summation –
aka. Recruitment
 increasing the strength of the stimulus
therefore increasing the number of
motor neurons firing to gain more
muscle force.
 Muscle force depends upon the number
of fibers stimulated
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.22
Multiple Motor Unit Summation –
aka. Recruitment
 Larger # of Motor units recruited =
larger force of contraction
 Weak or precise movements = few in #
of motor units (also small motor units)
 Recruitment of fiber types:
 Type I first, then type IIa, then type IIb
(will learn about later)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.22
Multiple
Motor Unit
Summation
Types of Muscle Contractions
 Isotonic (same tension) contractions
 Myofilaments are able to slide past each
other during contractions
 The muscle shortens & movement occurs
 Isometric (same length) contractions
 Tension in the muscles increases
 The muscle does not shorten & no
movement occurs
 Most movements involve both types of
activity
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.28
Muscle Metabolism
 ATP is the ONLY energy source used to
power muscles
 Must be generated continuously
 Only 4-6 seconds worth of ATP is stored by
muscles
 After this initial time, other pathways
must be utilized to produce ATP
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.23
Instructions
• Please read the following slides carefully!
• You are responsible for filling in the chart
BUT also for knowing all the info already
typed into the chart.
• You need to be able compare/contrast the 3
main pathways that the muscles have to
generate ATP
Direct Phosphorylation of CP
 Muscle cells contain creatine
phosphate (CP)
 CP is a high-energy
molecule found only in
muscle fibers
 After ATP is depleted, ADP is
left
 CP transfers energy to ADP,
to regenerate ATP
 CP supplies are exhausted in
about 15-20 seconds
 CREATINE
SUPPLEMENTATION
Figure 6.10a
Slide 6.24
Direct Phosphorylation
• Used for activities that require brief yet
massive power surges
• Weightlifting, sprinting, diving, etc.
• VERY fast since CP is already in the
muscle
• Very reversible SO is easily & quickly
replenished when muscles are inactive
Anaerobic Respiration
 Glycolysis with lactic
acid fermentation
 Reaction that breaks
down glucose without
oxygen
 Glucose is broken down
to pyruvic acid to
produce 2 ATP
 Pyruvic acid is
converted to lactic acid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10b
Slide
Anaerobic Respiration
 This reaction is used for
activities that are more
sustained.
 Duration of energy
production is 30-60
seconds
 Activities become
less vigorous as the
O2 depletes and
anaerobic respiration
must be used.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10b
Slide
Anaerobic Respiration
 Anaerobic respiration is
2 ½ times faster that
aerobic respiration so
can be utilized quickly
by the muscle.
 BUT, it is very inefficient
- Huge amounts of
glucose are needed to
produce small amounts
of ATP
 Lactic acid produces
muscle fatigue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10b
Slide
Aerobic Respiration
 Series of metabolic
pathways that occur in the
mitochondria
 Resting/slowly contracting
muscles use glucose or
fatty acids - Glucose is
broken down to carbon
dioxide and water,
releasing energy
 If these are not available –
amino acids may be used
but produce wastes that
can change body pH
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.10c
Slide 6.25
Aerobic Respiration
• Glucose + oxygen are required produce 3638 ATP + carbon dioxide + water
• Duration of energy produced can be hours
• This type of energy production is used for
activities that require endurance rather than
power
– Jogging, marathon running, walking, etc
Summary
DONE WITH CHART – STUDY
THE INFO CONTAINED IN IT
Muscle Fatigue & Oxygen Debt
Cellular Respiration
• 3 main factors affect your
cellular respiration type:
–Your nutrition
–Your respiratory efficiency
–Your cardiovascular fitness
Aerobic Respiration
• Is the most efficient type of
respiration – producing the most
ATP per glucose molecule (36-38
ATP /1 glucose)
• It is slower and requires continuous
delivery of oxygen & nutrients to
the muscle
• Used for endurance activities
Anaerobic Respiration
•
•
Circulatory and respiratory system cannot
deliver oxygen as fast as muscles are
using it up.
leads to lactic acid buildup - when oxygen
is again available – lactic acid is converted
to pyruvic acid and oxidized
Anaerobic Respiration
•
For muscle to be restored to resting state:
• Oxygen stores must be replenished
• Lactic acid converted to pyruvic acid
• Glycogen stores replaced
• ATP & creatine phosphate reserves
replenished
• Liver must reconvert the lactic acid
produced to glucose or glycogen
• ALL of these processes require oxygen
Oxygen Debt
•
•
Oxygen debt is the extra amount of
oxygen that must be taken into the body to
provide for these restorative processes
Difference between amount of oxygen
needed for totally aerobic respiration
during muscle activity and the amount that
is actually used.
Oxygen Debt
•
•
All nonaerobic sources of ATP used
during muscle activity contribute to this
debt
Repaid by rapid, deep breathing (triggered
by change in pH from lactic acid) after
exertion is ended
Oxygen
• Breathing pure oxygen does not help to
repay this debt in the short term!
• Oxygen must have some time to get to the
muscles.
• There are limitations due to your
circulatory/cardiovascular system and your
respiratory system.
• Supplemental Oxygen
Efficiency of Oxygen Use
•
•
•
Athlete: ~10 % greater rate and efficiency
of oxygen use than normal person
Marathon runner: ~45 % greater
Working your muscles, heart, lungs, etc
out on a regular basis increases your
efficiency
–
Things like smoking, poor nutrition, too much
sugar, etc. decreases your efficiency
Physiological Fatigue
 When a muscle is fatigued, it is unable to
contract EVEN when stimulated
 The common reasons for muscle fatigue are:
 Lactic acid buildup
 Lack of oxygen in muscle
 Ionic imbalance
 Contractures will occur when no ATP is
available (no cross bridge detachment)
 Example: writer’s cramp
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
Psychological Fatigue
 Psychological fatigue is voluntarily
discontinuing activity when you start to
“feel tired”
 May be caused by a decrease in the
amount of available ATP
Types of fibers
• Force, velocity, and duration of muscle
contraction are affected by several factors.
• A main factor is fiber type
• Muscle fiber types (and ratios) are
genetically determined.
• Muscles are a mixture of fibers but different
muscles will have different ratios of types.
• Article: Fiber types in Mammalian Skeletal
Muscle
Fiber Types
There are now 4 types proposed as
indicated in article on previous slide.
White vs. Dark meat
MISCELLANEOUS
Developmental Aspects
• Muscular development reflects
neuromuscular coordination
• Due to the way neural pathways
are developed in your brain
• Pg 194 of Marieb book
Developmental Aspects
• Progresses superior to inferior
direction
– Baby can lift head before walking
• Progresses proximal to distal
– Baby can move arm before grasping
object
Men vs. women
•
•
•
Women’s skeletal muscles make up 36 %
of body weight
Men’s is 42 % due to effects of
testosterone
Muscle strength per unit mass is equal
MUSCLE STRENGTH, POWER,
& ENDURANCE
See pages 168-169 in G-W book
• Write the definitions of strength, power, &
endurance in your notes.
• Be able to calculate the Muscle force as
shown in Figure 5.13 when provided the
formula
• Read & follow the example calculation.
• Calculate the Fm in the “Now you try” last
paragraph – show all your work so you can
check your calculation! You will have to do
this on your test.
MUSCLE DISORDERS
Muscle Strain
• Factors that contribute to muscle strain are:
– Degree of stretch
– Speed of stretch
• Read about the grades of strains on pages
182-183 of G-W book
• Also fill in the basic information for
contusions, myositis ossificans, muscle
cramps, & DOMS
Disorders
Read about anabolic steroids on page
180 of Marieb book
Muscle Disorders
• Torticollis – a twisting of the neck which causes
rotation and tilting of the head to one side –
caused by injury to one of the sternocleidomastoid
muscles
• Pulled groin muscles – Strain or stretching of
adductor muscles (magnus, longus, brevis)
• Foot drop – paralysis of anterior muscles in lower
leg – caused by injury to the peroneal nerve
Torticollis
Muscle disorders
• Shin splints –
inflammation of the
anterior muscle group
of the lower leg (& the
periosteum they pull
on)– caused by trauma
or strain – usually felt
on the medial &/or
anterior borders of the
tibia
Duchenne Muscular Dystrophy
• Page 194
• Genetic – affects primarily males – X linked
trait
• Dystrophin protein not produced correctly –
leads to muscle fiber degeneration & atrophy
• Progresses from extremities upward
• Generally do not live beyond young adulthood
KNOW THIS: Muscle Disuse
• When a muscle is completely immobilized
from:
– Enforced bed rest
– Loss of neural stimulation
– Injury
• Degeneration and loss of muscle mass
begins
– Can decrease at a rate of 5% per day
KNOW THIS: Disuse Atrophy
• Flaccid
– Muscle loses tone and becomes soft and flabby
• Atrophy
– Loss of muscle mass
– Replaced by fibrous CT making muscle rehabilitation
impossible
– May be delayed by electrical stimulation
• When muscle is totally deprived of neural
stimulation:
– Paralyzed muscle may ultimately atrophy to ¼ of
original mass
Building Muscle Mass
•
•
•
•
Type of joint involved in motions
Direction of muscle fibers (contained in fascicle)
Anatomy of the muscle
Angles of body parts
• In order to work a muscle effectively & to
minimize risk of injury, the above factors must be
considered. Number of reps and amount of weight
depends on purpose of exercise (building vs.
toning).
•