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Ch. 6
The Muscular
System
Case Study Investigation
You are selected for an internship at the National Space Biomedical
Research Institute in Houston, Texas. Part of your job is to monitor the
health of the astronauts for the National Aeronautics and Space
Administration (NASA) before, during, and after a space mission. By
chance, your time in the lab corresponds with the return of an American
astronaut from the International Space Station. She just spent 171 days
in the space station and is now getting back to her research studies on
earth. Unfortunately, it was discovered that she would
have to go through at least 3 weeks of physical therapy.
You learned from reading her physical health report
that she lost ____of her skeletal muscle mass. Most of
it occurred within the last 2 months of the mission in
space. The normal muscle loss during a space mission
is less than 20%. A majority of muscle atrophy results from disuse, yet
she followed all the exercise programs NASA requires. Your job is to
assist the research team in investigating her problem.
Determine the most likely cause of her accelerated loss of muscle mass.
Overview
Muscle cells are composed of
specialized
__________________that allow
them to change shape and shorten
or ____________________
Over half the body’s mass is
composed of muscle tissue, and over
90% of this muscle tissue is involved
in skeletal movement.
Muscles require glucose, oxygen,
calcium and electrolytes and
release metabolic wastes.
Chapter 6 – The Muscular System
Muscle
Three types of muscle are found in the human body:
a) __________________muscle
(slightly striated
& involuntary;
b) ____________
muscle
(striated &
voluntary)
c)_____________________muscle
(non-striated &
involuntary)
Musculature:
Gross Anatomy
2. ___________: rest of
the muscle (i.e. masseter)
3. ________________:
moveable bone the muscle
attaches to
(i.e. mandible)
1._______________: stationary
bone the muscle attaches to
(i.e. zygomatic arch)
Origin:
Scapula /
Humerus
Sacs of synovial fluid btwn
tendon & bone for lubrication
Body
Biceps
Brachii
Insertion:
Radius
_________________
attachs muscle
to bone
raises eyebrow
closes jaw
closes eyes
smile muscle
closes jaw
extends head / neck
closes lips
yes/no muscle
Muscles of the Trunk
deltoid
adducts
arm
flex trunk
abducts
arm
adducts
upper
arm
MUSCLES of the
ARM
flexes
elbow
extends
elbow
flexes forearm
pronates & supinates
flexes thigh +
lower leg
(middle quadricep)
Quadriceps
extend the leg
(lateral quadricep)
(medial quadricep)
Vastus intermedius
(inner quadricep)
plantar-flexes
ankles
dorsi-flexes ankles
plantar-flexes ankles
extends thigh
Hamstrings
flex the leg
adducts thigh
(middle hamstring)
(medial hamistring)
(lateral
hamstring
Basic Skeletal Muscle Function
1. Skeletal Movements = _______ on bone (relaxation / contraction)
_____________________=muscle
responsible for the movement
____________ = muscles that
help the prime mover
____________ = muscle that produces the opposite movement as prime mover
2. Posture / Muscle Tone: ______________weight
distribution and hold muscles in position
a. tonic contraction:
only a few muscles
contract at a time;
NO shortening and
NO movement
3. Regulate ____________________________
a. ______________________: bands of smooth muscle that prevent
outflow of fluids from hollow organs
4. Move substances within the body:
a. cardiac muscle – ________________________________
b. smooth muscle –moves food through digestive sys.
(__________________)
5. ___________ Production: when muscles contract they
produce heat
a. ________thermia – decrease in
body temp below normal
b. ______thermia – increase in
body temp above normal
Concept Check #1
1. What are muscles composed of that allow them to do their jobs?
2. What are 5 functions of the muscular system.
3. If I were to flex my elbow which muscle would be the prime
mover, synergist, and antagonist?
Concept Check #2
4. Give an example of how cardiac and smooth muscle move
substances within the body.
5. How does the origin and insertion of a muscle differ?
6. Research the origin and insertion for the following muscles:
Skeletal Muscle Structure
surrounds fassicles
surrounds each
surrounds entire
muscle
bundle of muscle cells
http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP13904 Muscle Structure Animation
Microcopic Muscle Cell Structure
 skeletal muscle cells are long, cylindrical cells covered with an
excitable (can transmit) membrane called the ________________
 proteins in sarcolemma _______________________________info
to muscle cells causing them to contract
 cytoskeleton of
muscle cells contain
myofilaments made
up of protein
a) thick: myosin
b) thin:
1) __________
2) ___________
3) _______________________
 contractile unit of muscle is called a ____________________
(thousands/muscle cell) which is surrounded by a sarcoplasmic reticulum
(stores/transports __________for contraction)
 Thick & thin
myofilaments
overlap within
sarcomere 
gives muscle its
______________
appearance &
carries out
contraction
 chains of
sarcomeres form
_______________
________________________ Chain Structure
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter42/animations.html# - Sarcomere shortening bio book animation
 1 sarcomere 
How Do Muscles Contract
 contraction occurs when sarcomeres shorten simultaneously
1. Nerve Stimulation at the neuromuscular junction (motor
neuron meets muscle fiber)
 Nerve cells release neurotransmitter __________________ which
binds to sarcolemma and allows ___________to cross membrane
 Flow of ions causes _______ to be released from SR; travels to
sarcomere and initiates contraction phase
http://www.galaxygoo.org/biochem/ne
o/nmj_flash.html
(basic neuromuscular
junction animation)
2. Muscle Contraction – takes place inside muscle cell
 Ca binds to _______________; moves it off the actin-binding
site on tropomyosin so myosin can ______________ to actin
 ________________ provides energy for myosin head to pull
thick m.f across thin m.f. (shortening Z-lines of sarcomere)
https://www.youtube.com/wat
ch?v=CepeYFvqmk4 - How a
muscle cell is signaled
https://www.youtube.com/wat
ch?v=jqy0i1KXUO4 - Crash
Course in Contraction
http://highered.mcgrawhill.com/sites/0072495855/student_view0/cha
pter10/animation__action_potentials_and_mu
scle_contraction.html - action potential and
muscle contraction
http://highered.mheducation.com/sites/0072495855/student_view
0/chapter10/animation__breakdown_of_atp_and_crossbridge_movement_during_muscle_contraction.html - good video
3. Muscle Relaxation
starts when neural
stimulation _________

Na+ and K+
ion levels
completely
recover

SR retrieves
most of its Ca

Myosin heads
release actin

Troponin ________
actin-binding
site on
tropomyosin
https://www.youtube.com/
watch?v=mO6a9UZmtag –
rigor mortis animation
________________ muscle stiffness caused by ___________________ out
of SR into sarcomere after death
Creatine phosphate, glycogen, & myoglobin (red chemical)  all serve as
______________________________reserves for muscle contraction
Types of Skeletal Muscle Fibers
unique muscle composition is genetically determined
https://www.23andme.com/health/Muscle-Performance/ - 23 and Me genetic testing
Feature
Slow Red Twitch Fibers
(Type I)
Fast White Twitch Fibers
(Type IIb)
Size
Smallest
largest
Mitochondria
large amount
(get ATP through aerobic
processes)
small amount
(get ATP through anaerobic
processes)
Color
red
(high myoglobin content)
white
(low myoglobin content)
Speed of
Contractions
Slow
Fast
Resistance to
Fatigue
High (very fatigue resistant)
Low (not fatigue resistant)
Activities
Maintaining posture,
endurance activities (i.e.
marathon runners)
Rapid, intense movements of short
duraction (i.e. sprinters, throwing a
ball or weight lifting)
Muscle: soleus
Muscle: gastrocnemius / vastus lateralis
Concept Check #3
7. List the three membranes of muscle in order from superficial to
deep then explain how they each differ.
8. What is the name given to the membrane that surrounds a muscle
cell and why is it important?
9. Why is the sarcoplasmic reticulum that surrounds the sarcolemma
so important?
Concept Check #4
10. Draw a picture of a sarcomere and label the two different
myofilaments and explain how it relates to the sliding filament theory.
11. Why is Ca necessary for starting a muscle contraction.
Skeletal Muscle Action
 skeletal muscle structure responds to the amount of work it must do
1. irregular use or lack of ________________________________________causes
 a loss of sarcomere proteins
 decrease in muscle strength
 decrease in muscle size = _________________________
2. regular use & increased ________________________causes
 increase in muscle strength
 increase in muscle size = _________________________
 Increased blood flow = enlarges muscle diameter = muscle strength
 Heavy muscle use = sarcomere density = muscle diameter
 Some ppl can increase sarcomere density and strength w/o a significant increase in
diameter……genetic differences and variations in blood flow
Skeletal Muscle Action
 shortening of the muscle brings the insertion closer to the origin
 ___________________________- minimal level of stimulus
required to cause a fiber to contract
 muscle cells are controlled by different motor units with different
threshold levels so not all muscles contract at the same time
 ____________________________– a fiber contracts completely or
not at all; It’s the difference in picking up 1 textbook or 25
textbooks.
http://study.com/academy/lesson/how-motor-unit-summation-develops-muscle-tension.html - study. Com (partial)
Skeletal Muscle Action
 muscles can be categorized by the effect it has on joint
motion
• abductor – muscles that move a bone ________ from
the midline (deltoid, gluteus maximus)
• adductor – muscles that move a bone ____________
to the midline (gracilis, pectoralis major)
• ________________ – muscles that increase the angle
of a joint (tricep, quadriceps)
• _________________– muscles that decrease the
angle of a joint (bicep, hamstrings)
• sphincter – muscles that _____________ the size of
an opening (esophogeal sphincter, rectal spincter)
Skeletal Muscle Action
 isotonic contractions: when a muscle is ________________
shortening or lengthening
ex. lifting weights
 isometric contractions: ____________________but muscle
is contracted and ________________is building ex. pushing
against an
immovable object
Fatigue
 during muscular exercise:
 b.v. in muscles _____________ & blood flow and
O2 delivery ____________________
 muscle ______________occurs after extended or
strong muscle contractions and _______________can’t
supply muscle fibers fast enough
 oxygen _____________ – amount of O2 taken in to
“pay back” resting metabolic conditions
 if O2 is unavailable, _____________is converted
into ______which helps break down glucose for energy
 production of lactic acid in the body causes soreness
Aging and Pathology of the Skeletal System
• many disorders of the musculature are due to interactions with the
skeletal and nervous systems
Strains vs. Sprains
strains – _______________ the muscle’s force on joints and tendons
 pain and swelling of fascia, joints, ligaments, and tendons
 nerves signal pain when stretched or swollen (stiff)
sprains – more severe; sudden or violent ________
on a joint/muscle
 tearing of ligament, muscle, or tendon and
damage to nearby blood vessels
 requires time for tissue and protein replacement
 To keep swelling down apply _______1st
followed by continuous _____________ to
speed healing
• ___________________ – related to sprains; direct hit(s) to a
muscle
Myopathy / Neuromuscular disorders

inability of the nervous system to communicate properly to muscles
1. ________________________ myopathies – group of neuromuscular
diseases caused by genetic abnormalities of the mitochondria; muscles can’t
produce ________________ from food; muscles become easily cramped
2. __________________________(2 types – 1st non-hereditary;
2nd hereditary) – caused by damage to soft tissues @ muscle;
bone growing within muscle tissue; pain during contraction
3. muscular __________________- involves ______________
weakness in the voluntary muscles; inability of nervous system
to stimulate muscle action; results in atrophy and wasting
Affect of _____________________on Muscles
 ______________ body’s ability to produce muscle
 prevent muscle breakdown &
________________________time
 resemble chemical structure of
___________________________
 {T} directs the body to produce
more or ________________ male
characteristics (like increased
muscle mass, etc)
Aging of the Muscular System
 ___________________ (natural muscle loss due to aging process)
 _____________________(muscle loss usually associated with AIDS, cancer,
starvation, anorexia, bulimia); slower form reduces bodies ability to rebuild
muscle structure
 decrease in neural stimulation -> ____________________
 malnutrition / undernutrition  decrease in carbs and proteins 
_______________________and nutrients for repair and maintenance
 decline in _____________________and insulin-like growth factor
–1 (IGF-1); needed for muscle cell growth, maintenance, & repair
 physical therapies 
1) artificial up-regulation with electrical ____________causes
muscles to retain protein)
2) muscle ________________________
Concept Check #5
12. List 2 things that can happen when muscles are used irregularly.
Regularly?
13. How do hypertrophy and hypotrophy (atrophy) differ?
14. Do all the muscle fibers (cells) in my arm contract when I pick up
a pencil? Use the terms threshold stimulus and all or none theory
in your explanation.
Concept Check #8
15. How do strains, sprains, and contusions differ?
16. Name and describe 2 different types of myopathies.
17. What is cachexia in terms of muscle aging.
18. Describe 4 factors that contribute to muscle aging.
Case Study Investigation
 Selected for an internship at National Space Biomedical Research Ins.
 Required to monitor astronauts for NASA before, during, and after a
space mission.
 American astronaut spent 171 days in the space stations has to go
through 3 weeks of physical therapy.
 She lost 30% of her skeletal muscle even after following all the
exercise programs NASA required. The average is less than 20%.
Questions:
1. Why did the American lose 30% of her skeletal muscle after her
mission to space? Be specific.
2. She lost 10% more than the average astronaut. What else associated
with her mission could have contributed to the American’s muscle
loss?