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Notes – The Muscular
System part 2
Micro anatomy of a myofibril – Read & Study pgs 185-187
Skeletal muscle cells are multinucleate with the nuclei located just beneath the plasma
A. ____________________________________: specialized plasma membrane of a muscle
B. __________________________________________: cytoplasm of a muscle fiber
C. ______________________________: unique oxygen binding protein in a muscle
D. _______________________________ – long rod like organelles
1. ______% of cell volume
2. Run parallel the entire length of cell
3. Other organelles squeezed in between
4. A bands - ____________ bands
a. contain ________________ – lighter central area - visible only in relaxed fiber
5. I bands - _____________ bands
a. contain _________________________ at midpoint
6. Banding patterns/striations reveal the working structure
E. _____________________________ - region between 2 successive Z lines - contractile unit
1. actin, anchored to Z line/disc, contain _________________ and _______________ to
regulate myofilament attachment
2. _____________ with cross bridge heads - contain ATPases (enzymes split ATP)
F. _________________________________: form of smooth ER surrounding myofibrils
1. major function of SR: store ___________________ and release it on demand
2. at A-I junction, sarcolemma forms penetrating hollow tube called _____ tubule whose
function is to conduct stimulus deep into every ____________________________
End of Quiz #1 Material: Microanatomy of a Myofibril
Contraction of Muscle
I. Mechanism of contraction (on a cellular level) - Regulation of Contraction – how muscle
knows WHEN to contract – Read & Study pgs 187-190
A. Motor Unit
a. One motor neuron and ALL the muscle cells that it stimulates
b. Spread throughout muscle
c. Stimulation of one motor unit results in weak contraction of ENTIRE muscle
i. Since a motor unit is spread throughout the muscle & not clustered
together, it stimulation will activate cells scattered throughout the entire
ii. This causes a weak contraction of the entire muscle
iii. Muscles requiring fine control have small motor units that only activate a
few cells at a time.
B. Neuromuscular Junction
a. Each axon terminal forms junction with single muscle fiber
C. Synaptic cleft – fluid filled gap between nerve and muscle
a. Nerve and muscle do not make contact
b. Importance: prevent continuous stimulation
D. Transmission
a. Vesicles in axon terminal filled with neurotransmitter – chemical released by nerve
upon arrival of nerve impulse
b. The neurotransmitter for skeletal muscle is acetylcholine (ACh)
c. Neurotransmitter crosses synaptic cleft and attaches to receptors on the
d. Sarcolemma becomes temporarily permeable to sodium (Na+)
e. Na+ ions rush into muscle cell which reverses electrical conditions
f. Action potential is caused which moves along sarcolemma and down T tubules
deep into muscle fiber
g. Once initiated – action potential is unstoppable (all or none principle) resulting in
full contraction of that particular muscle fiber (cell)
E. Safeguards - When nerve stimulation stops:
a. Ach is destroyed by acetylcholinesterase (AChE) to prevent continued contraction
b. Substances such as certain organophosphates found in pesticides and fertilizers
destroy AChE causing convulsions
F. K+ ions leaves cell rapidly to restore electrical balance
G. Then Na-K pump restores ions to original positions for relaxation of muscle fiber
B. Sliding filament theory –see diagrams pages 190-191
1. The thin filaments slide past the thick filaments so that overlap increases
2. What causes the filaments to slide?
a. cross bridge attachment - Mysosin head has __________ energy configuration
and binds to actin binding site in the presence of Ca2+
b. power stroke — ATP provides energy to bend and pull actin filament toward
center of sarcomere – results in shortening of ~1% of the sarcomere
c. cross bridge detachment — ATP also provides energy causing cross bridge to
i. rigor mortis – ________________________________________________
d. "cocking" of the myosin heads — energy returns myosin head to upright high
energy configuration
C. role of ionic calcium in regulating muscle contraction — In the absence of ionic calcium,
the _________________________ (a regulatory protein) blocks the binding sites on the
actin so the filaments cannot attach to each other. When ionic calcium becomes present, it
is avidly bound by the ______________________ (another regulatory protein) which causes
the tropomyosin to change shape thus exposing the binding site allowing attachment of the
actin and myosin.
D. SUMMARY: excitation-contraction coupling
1. Action potential "wave" travels along sarcolemma and deep into T tubules.
2. This triggers Ca2+ release from terminal cisternae of SR
3. Ca2+ binds to troponin — binding sites exposed.
4. Contraction: see sliding filament theory
5. Action potential ends, Ca2+ is taken back up into the SR
6. Tropomyosin blockage restored, contraction ends, muscle fiber relaxes.
II. Contraction of a Skeletal Muscle (on an organ level) - Know figure 6.8 page 192
All or none principle applies to the muscle cell NOT the whole muscle
A. Graded Muscle Responses - variations in degrees of muscle shortening produced in
2 ways:
a. By changing the frequency of muscle stimulation (recognize on diagram)
i. Single Muscle Twitch - differences in twitch responses due to differences
in metabolic properties and enzymes present in different muscles (useful for
ii. Treppe - staircase pattern on myogram recording
1. each succeeding contraction is strengthened
2. reflects sudden increased availability of calcium ions
3. heat increases efficiency of muscle’s enzyme systems basis of warm
up period for athletes
iii. Wave summation - impulses delivered in rapid succession will cause each
contraction to build onto the preceding contraction
iv. Tetanus - As this continues, the individual contractions become fused into a
smooth, sustained contraction called tetanus (usual manner of muscle
b. by changing the number of muscle cells being stimulated
Multiple Motor Unit Summation (Recruitment)
1. controls force of muscle contraction
2. larger # of motor units recruited = larger force of contraction
3. Weak or precise movements = few motor units
4. Type I first, then type IIa, then type IIb (will learn about later)
B. Isometric vs. isotonic contractions page 195
i. Isotonic (same ________________) contractions
1. Myofilaments are able to slide past each other during contractions
2. The muscle shortens & movement occurs
ii. Isometric (same ____________________) contractions
1. Tension in the muscles increases
2. The muscle does not shorten & no movement occurs – Resistance
3. Most movements involve both types of activity
Muscle metabolism - page 193-195
ATP is the only energy source that can be used directly to power muscle activity – it must
be generated continuously
Stored ATP in working muscles is depleted in ~ 6 seconds.
I. Three pathways that regenerate ATP for muscles
Direct phosphorylation of Anaerobic
Aerobic respiration
Creatine Phosphate
Glucose, fatty acids
High energy molecule
(only glycolysis
(resting/slowly contracting
found only in muscle fibers used)
muscles), amino acids (if no
glucose/fatty acids available)
Oxygen use
CP + ADP  creatine +
Glucose + oxygen
1 ATP per CP, creatine
2 ATP per
glucose, lactic
~36 ATP per glucose, CO2,
Duration of
____________ seconds
Brief maximum power
Weightlifting, diving,
More sustainedless vigorous as
O2 depletes
Endurance rather than power
activities: Marathon, jogging
Speed &
Very fast, very reversible,
easily replenished when
muscle are inactive
2 ½ x faster than
aerobic, not as
Slower, requires continuous
delivery of oxygen & nutrients
to muscle BUT most efficient
Muscle Fatigue & Oxygen Debt
I. 3 main factors affect your respiration type:
a. ______________________________________________________
b. ______________________________________________________
c. ______________________________________________________
II. Aerobic respiration
a. Is the most __________________ type of respiration – producing the most ATP
per glucose molecule
i. Glucose + oxygen produce 36-38 _________ + carbon dioxide + water
b. It is slower and requires ___________________ delivery of oxygen & nutrients to
the muscle
c. Duration of energy produced can be hours
i. This type of energy production is used for activities that require
______________________ rather than power
1. Jogging, marathon running, walking, etc
III. Anaerobic respiration
a. Circulatory and respiratory system cannot _____________oxygen as fast as
muscles are using it up.
b. leads to ____________ buildup - when oxygen is again available – lactic acid
is converted to pyruvic acid and oxidized
c. For muscle to be restored to resting state:
1. Oxygen stores must be replenished
2. Lactic acid converted to _____________ acid
3. __________________ stores replaced
4. ATP & creatine phosphate reserves replenished
5. Liver must reconvert the pyruvic acid produced to glucose or
6. ALL of these processes require _______
d. Oxygen debt is the ________________ amount of oxygen that must be taken
into the body to provide for these restorative processes
1. Difference between amount of oxygen needed for totally aerobic
respiration during muscle activity AND the amount that is actually
e. All ____________________ sources of ATP used during muscle activity
contribute to this debt
f. Repaid by rapid, deep breathing (__________________________ - triggered
by change in pH from lactic acid) after exertion is ended
g. Breathing pure oxygen does not help recovery time – oxygen has to have time
to get to the muscles that require it. There are limitations due to your
______________________ and __________________________ systems.
h. Athlete: ______% greater rate and efficiency of oxygen use than normal
i. Marathon runner: ______% greater
1. Working your muscles, heart, lungs, etc out on a regular basis
increases your efficiency
2. Things like smoking, poor nutrition, too much sugar, etc. decreases
your efficiency
B. muscle fatigue
1. physiological
a. unable to contract even though stimulated
b. can be caused by _____________ acid buildup, lack of oxygen in
muscle cells to produce ATP, ionic imbalances (Na-K pump)(active
c. when no ATP is available, ___________________ will occur (no ATP =
no cross bridge release)
2. psychological — voluntarily discontinuing activity
Muscle Fiber Types
1. ________________, ______________________ and ____________________ of muscle
contraction are affected by several factors. A main factor is fiber type:
a. Types of muscle fibers are ______________________ determined. Muscles are a
mixture of fibers but different muscles will have different ratios of the types.
b. See page 166 in G-W book – What Research Tells Us
2. Fiber Types: See Chart
a. Fast twitch fatigable muscle (White meat)
b. Slow twitch fatigue resistant (Dark meat)
i. Discuss why chicken/turkey breast meat is white meat while dove/duck
breast meat is dark meat.
A. Developmental aspects
1. Muscular development reflects neuromuscular coordination
2. Progresses from _____________________ & from ________________________
a. Due to the way that neural pathways are developed in your brain. See
examples on page 194 of Marieb book.
3. Men vs. women
a. Women’s skeletal muscles make up _____% of body weight while Men’s is
b. Muscle strength per unit mass is _____________
c. Men typically have greater muscle mass due to _____________________
B. Muscular Strength, Power, and Endurance
a. See pages 168-169 in G-W book
b. Be able to calculate Muscle force as shown in figure 5.13 (you will be provided
with the formula.
Muscle Disorders
a. Muscle Strain – Factors contributing to are:
i. Degree of stretch
ii. Speed of stretch
iii. Read about the grades of strains on pages 182-183 of G-W book.
b. Contusions
c. Myositis ossificans
d. Muscle cramp
f. _________________________________ – a twisting of the neck which causes
rotation and tilting of the head to one side – caused by injury to one of the
g. _________________________________ – Strain or stretching of
________________ muscles (magnus, longus, brevis)
h. __________________________________ – paralysis of anterior muscles in lower
leg – caused by injury to the ________________________ nerve
i. __________________________________ – inflammation of the
______________________ muscle group of the lower leg (& the periosteum they
pull on)– caused by trauma or strain – usually felt on the ____________ &/or
____________ borders of the tibia
j. _________________________________________ Muscular Dystrophy – pg 194
i. Genetic – affects primarily males – X linked trait
ii. _______________________ protein not produced correctly – leads to
muscle fiber degeneration & _______________________
iii. Progresses from extremities upward
iv. Generally do not live beyond young adulthood
Building Muscle Mass
In order to work a muscle effectively & to minimize risk of injury, there are factors that must be
considered. Number of reps and amount of weight depends on purpose of exercise (building vs.
1. Type of joint involved in motions
2. Direction of muscle fibers (contained in fascicle)
3. Anatomy of the muscle
4. Angles of body parts