The document discusses different types of muscles in the human body and their strengths. It notes that the masseter muscle in the jaw is often considered the strongest based on its ability to exert force against a short lever arm. The quadriceps femoris and gluteus maximus muscles can exert the most force at their points of insertion. The uterus may be the strongest muscle by weight as it exerts significant force during childbirth. The heart performs the largest quantity of physical work over a lifetime compared to other muscles.

1. Muscle SystemMuscle System
Andrew McCaskill – Anatomy/Physiology -CHHS

2. “Muscular "strength" usually refers to the ability to exert a force
on an external object—for example, lifting a weight. By this
definition, the masseter or jaw muscle is the strongest. What
distinguishes the masseter is not anything special about the
muscle itself, but its advantage in working against a much shorter
lever arm than other muscles.
Interesting Facts: What is the strongest muscle in the
human body?
Depending on what definition of "strongest" is used, many different
muscles in the human body can be characterized as being the
"strongest”.
If "strength" refers to the force exerted by the muscle itself,
e.g., on the place where it inserts into a bone, then the
strongest muscles of the body are usually said to be the
quadriceps femoris or the gluteus maximus.
"Copyright 2003-2004 University of Washington. All rights reserved including all
photographs and images. No re-use, re-distribution or commercial use without prior
written permission of the authors and the University of Washington."
"Musculoskeletal Images are from the University of Washington "Musculoskeletal
Atlas: A Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan
Graney, Ph.D."

3. Again taking strength to mean only "force", then a shorter muscle will
be stronger "pound for pound" (i.e., by weight) than a longer muscle.
The uterus may be the strongest muscle by weight in the human body.
At the time when an infant is delivered, the human uterus weighs about
40 oz (1.1 kg). During childbirth, the uterus exerts 25 to 100 lbs (100 to
400 N) of downward force with each contraction.
The external muscles of the eye are conspicuously large and strong in relation
to the small size and weight of the eyeball. It is frequently said that they are
"the strongest muscles for the job they have to do" and are sometimes claimed
to be "100 times stronger than they need to be". Eye movements, however,
probably do "need" to be exceptionally fast.

4. The heart has a claim to being the
muscle that performs the largest
quantity of physical work in the
course of a lifetime. Estimates of the
power output of the human heart
range from 1 to 5 watts. This is
much less than the maximum power
output of other muscles; for
example, the quadriceps can
produce over 100 watts, but only for
a few minutes. The heart does its
work continuously over an entire
lifetime without pause, and thus
does "outwork" other muscles. An
output of one watt continuously for
seventy years yields a total work
output of 2 to 3 ×109 joules.
The tongue may possibly be
the strongest muscle at birth.

5. ““Muscular contraction is one of the mostMuscular contraction is one of the most
wonderful phenomena of the biologicalwonderful phenomena of the biological
kingdom. That a soft jelly should suddenlykingdom. That a soft jelly should suddenly
become hard, change its shape, and lift abecome hard, change its shape, and lift a
thousand times its weight, and that it shouldthousand times its weight, and that it should
be able to do so several times a second, isbe able to do so several times a second, is
little short of miraculous. Undoubtedly,little short of miraculous. Undoubtedly,
muscle is one of the most remarkable itemsmuscle is one of the most remarkable items
in nature’s curiosity shop. - Albert Szent-in nature’s curiosity shop. - Albert Szent-
Gyorgyi, 1937 Nobel Laureate in BiologyGyorgyi, 1937 Nobel Laureate in Biology

6. Muscle isMuscle is contractilecontractile
tissuetissue of the body and isof the body and is
derived from thederived from the
mesodermal layermesodermal layer ofof
embryonic germ cells. Itsembryonic germ cells. Its
function is to producefunction is to produce
forceforce and causeand cause motionmotion,,
either locomotion oreither locomotion or
movement within internalmovement within internal
organs.organs.
Much of muscle contraction occursMuch of muscle contraction occurs without conscious thoughtwithout conscious thought
(involuntary)(involuntary) and is necessary for survival, like theand is necessary for survival, like the contraction of thecontraction of the
heart, or peristalsisheart, or peristalsis (which pushes food through the digestive(which pushes food through the digestive
system).system). VoluntaryVoluntary muscle contraction is used to move the body, andmuscle contraction is used to move the body, and
can becan be finely controlled, like movements of the finger, or grossfinely controlled, like movements of the finger, or gross
movements like the quadriceps muscle of the thigh.movements like the quadriceps muscle of the thigh.
There areThere are
approximately 650approximately 650
skeletal muscles inskeletal muscles in
the human body.the human body.
Contrary to popularContrary to popular
belief, the number ofbelief, the number of
muscle fibersmuscle fibers
cannot be increasedcannot be increased
through exercise;through exercise;
instead the muscleinstead the muscle
cells simply getcells simply get
bigger.bigger.

7. Anatomy
Muscle is mainly composed of muscle
cells (myocyte but usually known as
“muscle fibers“, a single fiber can reach a
length of 30cm.). Within the cells are
myofibrils; myofibrils contain sarcomeres,
which are composed of actin and myosin.
Individual muscle fibres are surrounded
by endomysium. Muscle fibres are bound
together by perimysium into bundles
called fascicles; the bundles are then
grouped together to form muscle, which
is enclosed in a sheath of epimysium.
Muscle spindles are distributed
throughout the muscles and provide
sensory feedback information to the
central nervous system.
Neuromuscular
junction
1. Axon
2. Synaptical junction
3. Muscle fiber
4. Myofibrils

8. Myofibrils are cylindrical organelles, found within muscle cells. They are
bundles of filaments that run from one end of the cell to the other and are
attached to the cell surface membrane at each end.
The filaments of
myofibrils consist
of two types,
thick and thin.
1. Thin filaments
consist primarily
of the protein
actin.
2. Thick filaments
consist primarily
of the protein
myosin, held in
place by titin
filaments.

9. The filaments are organized into repeated subunits along the
length of the myofibril. These subunits are called sarcomeres. The
sarcomeric subunits of one myofibril are in nearly perfect
alignment with those of the myofibrils next to it. This alignment
gives rise to certain optical properties which cause the cell to
appear striped or striated. In smooth muscle cells, this alignment is
absent. Hence there are no apparent striations and the cells are
called smooth.
A muscle cell, from a biceps, may contain 100,000 sarcomeres.

10. Actin is a globular structural protein that polymerizes in
a helical fashion to form an actin filament. Actin is one
of the most abundant proteins in many eukaryotic cells.

11. Most myosin molecules
are composed of both a
head and a tail domain.
The head domain binds
the filamentous actin,
and uses ATP
hydrolysis to generate
force and to "walk"
along the filament
towards the (+) end .
Myosin are heavy
chains, possibly 2000
amino acids in length,
which constitute the
head and tail domains.

12. Titin, also known as
connectin, is a
protein that is
important in the
contraction of striated
muscle tissues.. The
protein limits the
range of motion of the
sarcomere in tension,
thus contributing to
the passive stiffness
of muscle.
Factoid: Titin is the largest known protein, consisting
of 26,926 amino acids. The protein's chemical formula
is C132983 H211861 N36149 O40883 S693.

13. Physiology
Muscular activity
accounts for much of
the body's energy
consumption. All
muscle cells produce
adenosine triphosphate
(ATP) molecules which
are used to power the
movement of the
myosin heads.
Adenosine 5'-triphosphate (ATP)
Within the voluntary skeletal muscles, the
glucose molecule is metabolized in a process
called glycolysis which produces two ATP
molecules in the process. Muscle cells also
contain globules of fat, which are used for
energy during aerobic exercise. The aerobic
energy systems take longer to produce the
ATP and reach peak efficiency, and requires
many more biochemical steps, but produces
significantly more ATP than anaerobic
glycolysis.
Cardiac muscle on the other
hand, can readily consume
any of the three
macronutrients (protein,
glucose and fat) without a
'warm up' period and always
extracts the maximum ATP
yield from any molecule
involved. The heart and liver
will also consume lactic acid
produced and excreted by
skeletal muscles during
exercise.

14. Contraction of a muscle fiber. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (
www.sinauer.com) and WH Freeman (www.whfreeman.com)
Physiological steps of
muscle contraction
AnimAtion 1
Animation 2

15. there Are three type of muscle:

16. Skeletal muscleSkeletal muscle or "voluntary muscle" is anchored by
tendons to bone and is used to affect skeletal movement such as
locomotion and in maintaining posture. An average adult male is
made up of 40-50% of skeletal muscle and an average adult
female is made up of 30-40%.
There are two types of fibers for skeletal muscles: Type I and
Type II. Type I fibers appear reddish. They are good for
endurance and are slow to tire because they use oxidative
metabolism (movements act for a long time but not very fast).
Type II fibers are whitish; they are used for short bursts of
speed and power, use anaerobic metabolism, and are
therefore quicker to tire (act quickly, but not for a very long
time.).

17. Muscles are normally arranged in
opposition so that as one group of
muscles contract, another group 'relaxes'
or lengthens, this is called antagonism.
How skeletal
muscle works
Antagonism means that it
is impossible to stimulate
the contraction of two
antagonistic muscles at
any one time. In the
example of throwing a ball,
the biceps contracts to pull
the arm upward and create
force, while the triceps
muscle in the back relaxes
in preparation for the
throwing action.

18. Skeletal muscles
usually have one end
(the "origin") attached
to a relatively
stationary bone, (such
as the scapula) and the
other end (the
"insertion") is attached
across a joint, to
another bone (such as
the humerus).
"Copyright 2003-2004 University of Washington. All rights reserved including all
photographs and images. No re-use, re-distribution or commercial use without prior
written permission of the authors and the University of Washington."
"Musculoskeletal Images are from the University of Washington "Musculoskeletal
Atlas: A Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan
Graney, Ph.D."

19. Cardiac muscle is anatomically different in that the muscle
fibers are typically branched like a tree branch, and connect to
other cardiac muscle fibers through intercalated disks. Cardiac
muscle is a type of involuntary, striated muscle found exclusively
within the heart. Its function is to “pump" blood through the
circulatory system by contracting.

20. Intercalated Discs
Under light microscopy, intercalated discs appear as thin, typically
dark-staining lines dividing adjacent cardiac muscle cells. The
intercalated discs run perpendicular to the direction of muscle
fibers.
Unlike skeletal muscle, which contracts in response to
nerve stimulation, cardiac muscle is myogenic, meaning that
it is self-excitable stimulating contraction without an
electrical impulse coming from the central nervous system.
This inherent contractile activity is heavily regulated by the
autonomic nervous system. If synchronization of cardiac
muscle contraction is disrupted for some reason (for
example, in a heart attack), uncoordinated contraction
known as fibrillation can result.

21. Nuclei (Differences)
Cardiac muscle can be distinguished from skeletal muscle
because cardiac muscle nuclei are centrally located among the
myofibrils, unlike the peripheral nuclei of skeletal muscle.
A unique aspect of cardiac muscle is the number of nuclei
found inside the cell. Skeletal muscle cells are multinucleated
from the fusion of muscle cells, whereas smooth muscle cells
are strictly mononucleated, and cardiac muscle cells are
predominantly mononucleated in humans.

22. Smooth muscle
or "involuntary
muscle" is found
within the walls of
organs and
structures such as
the esophagus,
stomach, intestines,
bronchi, uterus,
urethra, bladder, and
blood vessels, and
unlike skeletal
muscle, smooth
muscle is not under
conscious control.

23. Function of smooth muscleFunction of smooth muscle
The contractile function of this muscle,The contractile function of this muscle,
to a large extent determines the functionto a large extent determines the function
of the organ. Often smooth muscleof the organ. Often smooth muscle
containing tissue arecontaining tissue are very elasticvery elastic so theso the
tissue can be stretched and still maintaintissue can be stretched and still maintain
its function. Smooth muscle mayits function. Smooth muscle may
contractcontract spontaneouslyspontaneously or be induced byor be induced by
a number ofa number of physiochemical agentsphysiochemical agents..
Smooth muscle contractsSmooth muscle contracts slowlyslowly andand
may maintain the contraction formay maintain the contraction for
prolonged periods in blood vessels (andprolonged periods in blood vessels (and
sphincters). Smooth muscle in thesphincters). Smooth muscle in the
digestive tract contracts in a rhythmicdigestive tract contracts in a rhythmic
peristalticperistaltic fashion.fashion.

24. Nervous control
The peripheral nervous system
is responsible for conveying
commands to the muscles and
glands, and is ultimately
responsible for voluntary
movement. Nerves move
muscles in response to
voluntary and autonomic
(involuntary) signals from the
brain.

25. Disease
There are many diseases and conditions which cause a
decrease in muscle mass, known as atrophy.
During aging, there is a
gradual decrease in the
ability to maintain skeletal
muscle function and mass.
This condition is called
sarcopenia. In addition,
there are other diseases
which may be caused by
structural defects in the
muscle (the dystrophies), or
by inflammatory reactions
in the body directed against
muscle (the myopathies).
Neuromuscular diseases are
those that affect the muscles
and/or their nervous control.
In general, problems with
nervous control can cause
paralysis, depending on the
location and nature of the
problem. A large proportion
of neurological disorders
leads to problems with
movement, ranging from
cerebrovascular accident
(stroke) and Parkinson’s
disease to Creutzfeldt-Jakob
disease.

26. Muscle Origin Insertion Action
Epicranius (2 parts:
frontal and
occipital)
Occipital
bone
Skin and
muscles
around the eye
Raises eyebrow
Orbicularis oculi Maxilla and
Frontal Bones
Skin around
eye
Closes eye (wink/blink)
Orbicularis oris Muscles near
mouth
Skin of lips Closes and protrudes lips
(kissing)
Muscles of
facial
expression

27. Muscle Origin Insertion Action
Zygomaticus Zygomatic
bone
Orbicularis oris Raises corner of mouth
(smiling effect)
Platysma Upper Chest mandible Draws mouth downward
(frowning effect)
Muscles of facial expression…continued

28. Muscle Origin Insertion Action
Masseter Zygomatic
arch
mandible Closes jaw
Temporalis Temporal
bone
Coronoid
process of
mandible
Closes jaw
Muscles of Mastication

29. Muscle Origin Insertion Action
Sternocleidomastoid Sternum and
clavicle
Mastoid
process of
temporal
Pulls head to one side
(tilts head), raises sternum
(shoulder shrug)
Splenius capitus Cervical and
thoracic
vertebrae
Mastoid
process of
temporal
Rotates head
Muscles that move the Head

30. Muscle Origin Insertion Action
Trapezius Occipital bone
and cervical and
thoracic
vertebrae
Clavicle and
Scapula
Raises arm and rotates
scapula
Pectoralis minor Ends of upper
ribs
Coracoid
process of
scapula
Raises ribs and pulls
scapula downward
"Copyright 2003-2004 University of Washington. All rights reserved
including all photographs and images. No re-use, re-distribution or
commercial use without prior written permission of the authors and
the University of Washington."
"Musculoskeletal Images are from the University of Washington
"Musculoskeletal Atlas: A Musculoskeletal Atlas of the Human Body"
by Carol Teitz, M.D. and Dan Graney, Ph.D."
Muscles of
the
pectoral
girdle

31. Muscle Origin Insertion Action
Pectoralis Major Clavicle, sternum Humerus Pulls arm anterioraly and
across chest
Latissimus dorsi Sacrum, thoracic
and lumbar
vertebrae
Humerus,
intertubercular
groove
Extends and adducts arm
Deltoid Acromion
process, clavicle
humerus Abducts arm
Subscapularis Scapula, anterior
surface
Lesser tubercle of
humerus
Rotates arm medially
Muscles that Move arM
"Copyright 2003-2004
University of Washington. All
rights reserved including all
photographs and images. No
re-use, re-distribution or
commercial use without prior
written permission of the
authors and the University of
Washington."
"Musculoskeletal Images are
from the University of
Washington "Musculoskeletal
Atlas: A Musculoskeletal Atlas
of the Human Body" by Carol
Teitz, M.D. and Dan Graney,
Ph.D."

32. Muscle Origin Insertion Action
Biceps brachii Coracoid process
of scapula
Radial tuberosity
and ulna
Flexes forearm at elbow and
rotates hand laterally
Triceps brachii Lateral and medial
surfaces of
humerus/scapula
Olecranon process
of ulna
Extends forearm at elbow
Supinator Lateral epicondyle
of humerus and
ulna
Medial surface of
radius
Rotates arm laterally (supinates
arm)
Pronator teres Medial epicondyle
of humerus and
ulna
Lateral surface of
radius
Rotates arm medially (pronates
arm)
Muscles that Move the forearM!
"Copyright 2003-2004 University of Washington. All rights reserved including all photographs and images. No re-use, re-distribution or commercial use without prior written permission of the authors
and the University of Washington."
"Musculoskeletal Images are from the University of Washington "Musculoskeletal Atlas: A Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan Graney, Ph.D."

33. Muscle Origin Insertion Action
Flexor carpi radialis Medial epicondyle
of humerus
Base of 2nd
and 3rd
metacarpals
Flexes and abducts wrist
Flexor carpi ulnaris Medial epicondyle Carpal and
metacarpal bones
Flexes and adducts wrist
Extensor digitorum Lateral epicondyle
of humerus
Posterior surface
of phalanges in
fingers 2-5
Extends fingers
Muscles that Move the hand!
"Copyright 2003-2004
University of Washington. All
rights reserved including all
photographs and images. No
re-use, re-distribution or
commercial use without prior
written permission of the
authors and the University of
Washington."
"Musculoskeletal Images are
from the University of
Washington "Musculoskeletal
Atlas: A Musculoskeletal Atlas
of the Human Body" by Carol
Teitz, M.D. and Dan Graney,
Ph.D."

34. Muscle Origin Insertion Action
External Oblique lower ribs ilium Tenses abdominal wall
Transversus
abdominis
Lower ribs,
lumbar vertebrae
Crest of the pubis Tenses abdominal wall and
compresses abdominal
contents
Serratus anterior Outer surface of
ribs
scapula Pulls scapula downward
Rectus abdominus Crest of Pubis Xiphoid Process
of sternum
Tenses abdominal wall and
compresses abdominal
contents
Muscles of the AbdoMinAl WAll

35. Muscle Origin Insertion Action
Psoas major Transverse
processes of
lumbar vertebrae
Lesser trochanter
of femur
Flexes Thigh
Gluteus Maximus Sacrum, coccyx,
and posterior
surface of ilium
Posterior surface
of femur
Extends Thigh
Gluteus minimus Lateral surface of
ilium
Greater trochanter
of femur
Abducts and rotates thigh
medially
Muscles thAt Move the thigh:
"Copyright 2003-2004 University of Washington. All rights reserved including all photographs and images. No re-use, re-distribution or commercial use without prior written permission of the authors
and the University of Washington."Musculoskeletal Images are from the University of Washington "Musculoskeletal Atlas: A Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan
Graney, Ph.D."

36. Gracilis pubis Medial surface
of tibia
Adducts thigh, flexes and
rotates lower limb
medially
Adductor Magnus Ischium Medial surface
of femur
Adducts, extends, and
rotates thigh laterally
"Copyright 2003-2004 University of Washington. All rights reserved including all photographs and images. No re-use, re-distribution or commercial use without prior written permission of the authors
and the University of Washington."Musculoskeletal Images are from the University of Washington "Musculoskeletal Atlas: A Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan
Graney, Ph.D."

37. Muscle Origin Insertion Action
Sartorius Iliac spine Medial surface of
tibia
Flexes leg and rotates leg
medially
Biceps femoris* Ischium Head of fibula and
lateral condyle of
tibia
Flexes leg, extends thigh
Semitendinosus* Ischium Medial surface of
tibia
Flexes leg, extends thigh
Semimembranosus* Ischium Medial condyle of
tibia
Flexes leg, extends thigh
Muscles thAt
Move the leg:
* MAkes up
hAMstring group
"Copyright 2003-2004 University of Washington. All rights reserved including all photographs and images. No re-use, re-distribution or commercial use without prior written permission of the authors
and the University of Washington."Musculoskeletal Images are from the University of Washington "Musculoskeletal Atlas: A Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan
Graney, Ph.D."

38. Muscle Origin Insertion Action
Rectus
femoris*
Spine of
ilium and
acetabulum
Patella
(continues
to tibial
tuberosity)
Extends leg at knee
Vastus
lateralis*
Greater
trochanter
Patella
(continues
to tibial
tuberosity)
Extends leg at knee
Vastus
medialis*
Medial
surface of
femur
Patella
(continues
to tibial
tuberosity)
Extends leg at knee
Vastus
intermedius*
Lateral
surface of
femur
Patella
(continues
to tibial
tuberosity)
Extends leg at knee
Muscles thAt Move the leg:
continued * QuAdriceps group
"Copyright 2003-2004 University of Washington. All rights reserved including all photographs and images. No re-use, re-distribution or commercial use without prior written permission of the authors
and the University of Washington."Musculoskeletal Images are from the University of Washington "Musculoskeletal Atlas: A Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan
Graney, Ph.D."

39. Muscle Origin Insertion Action
Tibialis anterior Lateral condyle
of tibia
Cuneiform and
first metatarsal
Inversion of foot
Extensor digitorum
longus
Lateral condyle
of tibia and fibula
Dorsal surface of
2nd
and 3rd
phalanges
Extension of toes
Flexor Digitorum
longus
Posterior surface
of tibia
Distal phalanges
of four lateral
toes
Flexes four lateral toes
Muscles thAt
Move the
Ankle, foot,
And toes.
"Copyright 2003-2004 University of Washington. All rights
reserved including all photographs and images. No re-use, re-
distribution or commercial use without prior written permission
of the authors and the University of
Washington."Musculoskeletal Images are from the University
of Washington "Musculoskeletal Atlas: A Musculoskeletal
Atlas of the Human Body" by Carol Teitz, M.D. and Dan
Graney, Ph.D."

40. Gastrocnemius Lateral and
medial
condyles of
femur
calcaneus Flexes foot
and knee
Soleus Head and
shaft of
fibula and
posterior
surface of
tibia
calcaneus Flexes foot
"Copyright 2003-2004 University of Washington. All rights reserved including all photographs and images. No re-use,
re-distribution or commercial use without prior written permission of the authors and the University of
Washington."Musculoskeletal Images are from the University of Washington "Musculoskeletal Atlas: A
Musculoskeletal Atlas of the Human Body" by Carol Teitz, M.D. and Dan Graney, Ph.D."

41. conclusion: Muscle As A coMprehensive unit!
With close to 700
separate muscles
tightly interwoven
throughout the
human body, much
of those attached to
specific bone
projections with
unique types of
locomotion, it is
easy to see the
complexity of these
two interacting and
mutually dependent
systems.
In short, skeletal muscle and
the skeletal system show an
amazing example of two
systems interacting together
with a measure of
sophistication that has
amazed the most gifted of
minds and has left them
speechless. In modern
terminology, these two
systems show irreducible
complexity (WPP) in that one
system alone would cease to
function and/or provide little to
no overall function to human
body.
In 1543, Vesalius published the seven-volume
De humani corporis fabrica (On the fabric of
the human body), a groundbreaking work of
human anatomy. The work emphasized the
priority of dissection and what has come to be
called the "anatomical" view of the body —
seeing human internal functioning as an
essentially corporeal structure filled with
organs arranged in three-dimensional space.

42. http://www.artlex.com/Art
Lex/e/images/ecorche_c
ontemp.chart.lg.jpg