Notes PPT

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
 Sarcolemma – specialized plasma
membrane of muscle fiber
 Cells are multinucleate
 Nuclei are just beneath the sarcolemma
 Sarcoplasm – cytoplasm of a muscle
Figure 6.3a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.9b
• 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
• 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
 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
Micro anatomy
• Banding patterns/striations reveal the
working structure of muscle fiber
Microscopic Anatomy of Skeletal
 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
Microscopic Anatomy of Skeletal
 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
Microscopic Anatomy of Skeletal
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
Twizzler analogy
Many packages of
Twizzlers = Fascicle
Find a Fascicle on your
Twizzler analogy 2
1 package of Twizzlers
Muscle fiber
The packaging =
Twizzler analogy 3
1 bundle of twizzlers =
Twizzler analogy 4
1 Twizzler strand =
Compare the Muscle Fiber to
Pull and Peel Twizzlers
How amazing is that?
• Sarcoplasmic
reticulum –
specialized smooth
• Function: Stores
ionic calcium &
releases it on
• Surrounds
• At junction of A
band and I band,
sarcolemma forms
hollow T-tubule to
conduct stimulus
deep into every
How muscle knows WHEN to
Mechanism of contraction on a
cellular level
Motor Unit
• One motor
neuron and ALL
the muscle cells
that it stimulates
• Spread
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
– Muscles requiring fine control have small
motor units that only activate a few cells at a
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
Figure 6.5b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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:
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.5b
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
 The Neuromuscular Junction
 video 2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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)
• Excitation-Contraction Coupling
• 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
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
(crossbridges) to
attach to binding
sites on the thin
 Myosin heads then
bind to the next site
of the thin filament
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.7
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 6.7
What causes the filaments to
• 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
Neuromuscular junction animation
Focus Questions:
What is the name of the stimulus that travels down the axon to the
muscle fiber?
An action potential
Does the terminal (end) of the axon enter the muscle fiber?
No. There is a gap between the two.
Does acetylcholine enter the muscle fiber?
What chemical does enter the muscle fiber, resulting in an action
potential through the muscle fiber?
Sliding Filament theory
Boat = Myosin (thick filament)
Oar = Myosin side arm
Water = Actin (thin filament)
Life ring = Calcium
1. ATP is bound to myosin side arm.
2. ATP cleaves into ADP + P (high energy)
Step 1 Action potential
1. A nerve action potential releases acetylcholine into
the synaptic cleft opening the Na+ channels.
2. Action potential spreads across sarcolemma
releasing Ca into sarcoplasma
Step 2 Myosin-actin binding
1. Ca binds to troponin.
2. A shape change in troponin moves tropomyocin out
of the way of actin binding site.
3. Actin and myosin bind using energy from cleaved
Step 3 Power Stroke
1. Side arm pivots so myosin and actin slide by each
other shortening the sarcomere.
2. ADP and P released (low energy)
Step 4 ATP Binding
Actin-myosin release
1. A different ATP molecule binds to active site.
2. Actin released
Step 5 ATP cleavage
1. Return to high energy state
2. Cycle will repeat if Ca still available.
Think it over
The boat (myosin) does not move far in one cycle, can a
muscle contraction occur with one cycle?
If a muscle is contracted what happens if a new molecule
of ATP is not available?
Muscle stays contracted- cramps
Why does rigor mortis occur? (Hint: What chemical is
no longer available to the body?)
ATP is not available to control Ca release so contractions
are continuous 6-8 hours after death. Body relaxes 16-24
hours as enzymes break down contractile structures.
Myofilament Contraction
Sarcomere summary
Sliding Filament Theory
Focus questions:
What happens to the length of the sarcomere
during a contraction?
The sarcomere shortens.
• Sarcomere Contraction
Sliding Filament Animation
animation 2
Focus Questions:
What chemical exposes the binding site for actin and myosin?
What is the source of energy for a contraction?
What is the name of the step in which the actin filament is
actively contracted?
What chemical must be present in order for the actin and myosin
filaments to separate?
Muscle contraction at the
macroscopic level
1. Place your fingers along the angle of your
jaw just in front of your ear. Grit your
teeth and fell what happens to the hardness
of the masseter muscle.
During muscle contraction the muscle
becomes ________________________.
2. With your thumb and little finger of one
hand, span the opposite arm’s bicep’s from
the elbow to as close to the shoulder as
possible. Bend the arm and observe the
change in the length of the muscle.
During muscle contraction the muscle
___________________ in length.
3. Wrap a string around your extended upper
arm and determine the circumference.
Clench your fist tightly and flex your arm to
contract the muscle.
During muscle contraction the diameter of the
muscle _____________________.
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.28
Developmental Aspects
• Progresses superior to inferior direction
– Baby can lift head before walking
• Progresses proximal to distal
– Baby can move arm before grasping
– This is due to the way that neural
pathways are built in your brain.
Men vs. women
Women’s skeletal muscles make up 36 %
of body weight
Men’s is 42 % due to effects of
Muscle strength per unit mass is equal
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.
Aerobic vs. Anaerobic
• 3 main factors affect your respiration type:
– Your nutrition
– Your respiratory efficiency
– Your cardiovascular fitness
– The type of respiration that is happening depends
on what is going on in a particular muscle at a
particular time. You will have some muscles
doing aerobic and others doing anaerobic AT THE
Aerobic Respiration
• Is the most efficient type of respiration –
producing the most ATP per glucose
– Glucose + oxygen produce 36-38 ATP +
carbon dioxide + water
• It is slower and requires continuous delivery
of oxygen & nutrients to the muscle
Aerobic Respiration
• Duration of energy produced can be hours
• This type of energy production is used for
activities that require endurance rather than
– Jogging, marathon running, walking, etc
Anaerobic Respiration
• Muscle uses up oxygen faster than
circulatory and respiratory systems can
deliver it
• Glucose gets converted to lactic acid in that
• Lactic acid will get converted to pyruvic
acid and enter aerobic mechanism when
oxygen becomes available
Anaerobic Respiration
Circulatory and respiratory system cannot
deliver oxygen as fast as muscles are
using it up.
This 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
• Liver must reconvert the pyruvic acid
produced to glucose or glycogen
• ALL of these processes require oxygen
Oxygen Debt
The amount of oxygen that must be taken into
the body to provide for these restorative
The difference between amount of oxygen needed for
totally aerobic respiration during muscle activity
AND the amount that is actually used.
All nonaerobic sources of ATP used during muscle
activity contribute to this debt
Oxygen Debt
Repaid by rapid, deep breathing
(hyperventilation) triggered by change in pH
from lactic acid) after exertion is ended
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 circulatory and respiratory systems.
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
Things like smoking, poor nutrition, too much
sugar, etc. decreases your efficiency
Muscle Strain
• Commonly called a “pulled muscle”
• Is excessive stretching & possible tearing of
muscle due to overuse/abuse
• Injured muscle becomes painful & inflamed
• Treatment: adjacent joints are usually
Muscle Strain
• Factors contributing
– Degree of stretch (more flexible at a joint the
less likely you are to strain a muscle than
someone who’s “tight”
– Speed of stretch
• A bruise or bleeding within a muscle
• Caused by impact to muscle
• When already injured muscle is repeatedly
struck, a more serious condition, myositis
ossificans, can develop
Myositis Ossificans
• Involves formation of a calcium mass with
the muscle over a period of 3-4 weeks
• After 6-7 weeks the mass usually begins to
dissolve and is reabsorbed by the body.
• In rare cases, a bony lesion can remain in
the m
Muscle Cramps
• Moderate to severe muscle spasms that
cause pain
• Possible causes
– Electrolyte imbalance
– Ca, Mg or K deficiency
– dehydration
(Delayed Onset Muscle Soreness)
• Follows participation in a long or strenuous
• Soreness begins 24-72 hours after activity
• Involves multiple microscopic tears in
muscle tissue & causes inflammation, pain,
swelling & stiffness
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
• 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
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
Muscle Disorders
• Charley horse – officially a trauma induced
tearing of muscles followed by bleeding into
the tissues (NOT just a cramp)
Halux valgus – permanent displacement of the
great toe – caused by wearing pointy toed shoes
Duchenne Muscular Dystrophy
• Page 194
• Genetic – affects primarily males – X linked
• Dystrophin protein not produced correctly –
leads to muscle fiber degeneration & atrophy
• Progresses from extremities upward
• Generally do not live beyond young adulthood
Myasthenia gravis
• Probably autoimmune
• Shortage of neurotransmitter receptors in
• Muscles not stimulated properly & grow
progressively weaker
• Death occurs when respiratory muscles fail
to function
Drooping of
Myasthenia Gravis
eyelid called

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