Muscle Identification
Lecture Notes:
A.
Skeletal muscles produce movement by pulling on insertion bones across joints.
B.
Bones serve as levers and joints as fulcrums of these levers.
C.
Muscles that move a body part usually do not lie over that part, but proximal to it.

D.
Skeletal muscles almost always act in groups rather than singly--i.e. most movements produced by coordinated action of several muscles
1.
prime mover-- major muscle producing action
2.
synergists -- muscles that help produce an action
3. antagonists -- muscles that produce an opposite action as compared to the prime mover and synergists, must relax as prime mover and synergists contract.

E.
Hints on how to deduce actions:
1.
Start by making yourself familiar with the names, shapes, and general locations of the larger muscles.
2.
Try to deduce which bones the two ends of a muscle attach to from your knowledge of the shape and general location of the muscle.
3.
Make a guess as to which bones moves when the muscle shortens.
a.
insertion --the bone that is moved by the muscle b.
origin -- the bone that remains relatively stationary is its origin.

4.
Deduce a muscle's actions by applying the principle that its insertion moves toward its origin.
5.
To deduce which muscle produces a given action, start by inferring which is the insertion bone.

F.
Names:
1.
a.
b.
c.
action flexors --decrease the angle of a joint extensors -- increase the angle of a joint abductors -- move the bone away from midline d.
e.
adductors rotators
-- move the part toward the midline
-- cause a part to pivolt upon its axis f.
levators -- raise a part

g.
depressors --lower a part h.
i.
j.
k.
sphincters -- reduce the size of an opening tensors -- tense a part, that is, make it more rigid supinators -- turn the hand palm upward pronators -- turn the hand palm downward

2.
direction of its fibers a.
b.
c.
transverse oblique rectus
3.
a.
b.
location frontalis temporalis

4.
a.
b.
number of divisions composing a muscle biceps triceps
5.
a.
b.
its shape longus brevis
6.
points of attachment a. sternocleidomastoid

Frontalis
Orbicularis oculi
Nasalis
Zygomaticus
Orbicularis oris
Buccinator
Masseter
Epicranial aponeurosis
Temporalis
Occipitalis
Trapezius
Sternocleidomastoid

Sternocleidomastoid
Trapezius
Deltoid
Linea alba
Abdominal aponeurosis
External oblique
Pectoralis major
Serratus anterior
Latissimus dorsi
Internal oblique
Rectus abdominis
Transverse abdominis

Sternocleidomastoid
Trapezius
Deltoid
Latissimus dorsi
External oblique
Infraspinatus
Teres major
Lumbodorsal Fascia

Triceps brachii
Brachialis
Pronator teres
Flexor carpi ulnaris
Palmaris longus
Flexor carpi radialis
Biceps brachii
Brachioradialis

Biceps brachii
Brachioradialis
Extensor carpi radialis longus
Extensor carpi radialis brevis
Extensor digiorum
Deltoid
Triceps brachii
Brachialis
Anconeus
Extensor carpi ulnaris
Flexor carpi ulnaris

Iliopsoas
Pectineus
Adductor longus
Adductor magnus
Gracillis
Gastrocnemius
Soleus
Gluteus medius
Tensor fasciae latae
Sartorius
Vastus lateralis
Rectus femoris
Vastus medialis
Fibularis longus
Extensor digitorum longus
Tibialis anterior

Gracillis
Adductor magnus
Achilles tendon
Gluteus medius
Gluteus maximus
Tensor fasciae latae
Biceps femoris
Semitendinosus
Semimembranosus
Gastrocnemius
Soleus

Left thigh
Biceps femoris
Semitendinosus
Semimembranosus hamstrings adductors
Adductor magnus
Adductor longus
Adductor brevis anterior lateral quadriceps
Rectus femoris
Vastus laterialis
Vastus medialis
Vastus intermedius

Origins and Insertions
Masseter
Origin:_ zygomatic arch ______________________
Insertion:_ mandible _________________________
Action:_ closes jaw __________________________
Diaphragm
Origin:__ bottom of ribs _____________________
Insertion:__ central tendon __________________
Action:__ causes inspiration ________________
Deltoid
Origin:__ clavicle & scapula _________________
Insertion:___ humerus _________________________
Action:___ abducts arm ______________________

Hamstrings:
Biceps femoris
Origin:___ ischium & femur __________________
Insertion:___ fibula and tibia ________________
Action:__ extends thigh & flexes knee _______
Semitendinosus
Origin:__ ischium _____________________________
Insertion:__ tibia ______________________________
Action:__ extends thigh & flexes knee ________
Semimembranosus
Origin:__ ischium _____________________________
Insertion:__ tibia ______________________________
Action:__ extends thigh & flexes knee ________

Quadriceps:
Rectus Femoris
Origin:___ iliac __________________________________
Insertion : __patella & tibia _____________________
Action:__ extends knee & flexes thigh _________
Vastus lateralis
Origin:___ femur _________________________________
Insertion:__ patella & tibia _____________________
Action:__ extends knee & flexes thigh _________
Vastus medialis
Origin:___ femur _________________________________
Insertion:__ patella & tibia _____________________
Action:__ extends knee & flexes thigh _________
Vastus intermedius
Origin:___ femur _________________________________
Insertion:__ patella & tibia _____________________
Action:__ extends knee & flexes thigh _________

Arm:

MUSCLE SYSTEM
LECTURE NOTES
22

I. The Muscle System:
23
A. functions:
1. movement by contraction
2. maintains posture
3. stabilizes joints
4. generates heat

B. review of muscle tissues:
24
1. smooth a. visceral b. nonstriated c. involuntary d. functions in slow , sustained, long-lasting wave-like contractions (tight-junctions)

25
2. cardiac a. heart b. striated c. involuntary d. functions in rapid, rhythmic contractions (intercalated discs)

26
3. striated a. skeletal muscle , makes up the skeletal system b. striated c. voluntary d. functions in rapid, strong contractions but tires easily

C. Gross structure: striated muscle
1. skeletal muscle organ composed of a. muscle fibers (cells) b. CT c. blood vessels d. nerve fibers
27

2. CT wrappings: a. endomysium - covers and surrounds the individual muscle fibers b. perimysium - bundles together several m.fibers into a unit called a fascicle (fasciculi).
c. epimysium - covers and surrounds the fascicles and unites the entire muscle organ.
d. deep fascia - binds muscles into functional groups and extends to wrap other structures as well.
28

29
Muscle Organ epimysium perimysium myofiber endomysium fascicle

3. attachments:
30 a. direct (fleshy) - the epimysium of the muscle is fused to the periosteum of a bone.
direct attachment

b. indirect - the epimysium of the muscle extends beyond the muscle into a tendon or an aponeurosis which then anchors the muscle to a bone. more common tendons
1) origin - stationary attachment
2) insertion - movable attachment
31

32
D. Microscopic structure
1. muscle cell = muscle fiber also known as a myofiber .
a. Myofibers are composed of smaller rod shaped units called myofibrils .
b. muscle fibers are contained by the cell membrane which is called the sarcolemma . c. myofibrils are surrounded by the fluid cytoplasm called sarcoplasm.

muscle fiber / myofiber sarcoplasm myofibril
33 sarcolemma

2. each muscle fiber is an elongated cell
(cylindrical) that is multi-nucleated with the nuclei found on the periphery of the fiber.
multi-nucleated cells peripheral nuclei
34

3. each muscle fiber contains numerous (100's-
1000's) myofibrils which contain the protein filaments that show distinct banding we call striations.
striations light & dark banding myofibrils
35

36 a. composed of 2 protein filaments--myofilaments

1) actin myofilament (actually composed of actin, tropomysin and troponin) (thin) a) troponin -prevents bonds between actin and myosin filaments.
b) tropomysin -provides a straight shape for the actin filament.
actin tropomysin troponin
37

2) myosin myofilament (thick) protein filaments
Myosin molecules have a rodlike tail ending in two round “ heads”. These are usually called
“cross bridges” because they will form a chemical bond with the actin myofilament.
38

39
3) structure of the striations; a) dark bands are called A-bands b) in the middle of the A-band is a lighter band --the H-band c) in the middle of the H-band there is a darker line known as the M-line .
d) on each side of the A-band there is a light band referred to as the I-band e) the I-band is crossed by a darker band; the Z-band or Z-line f) the area between 2 Z-lines composes a sarcomere ; the unit of structure and function

Z line sarcomere
M
Z line
40
I
H
A
I

41 b. during contraction the filaments (actin and myosin) slide over each other-shortening the muscle fiber.

42
1) there are " cross bridges " that reach from the myosin to the actin in order for the sliding to occur cross bridges

4. T-system - a system of tubules that extend transversely into the sarcoplasm, they enter the sarcoplasm at the level of the z-line. T- tubules are part of the sarcolemma and allow the for communication to occur with the inside of the cell.
T-tubules
43

44
Z lines
5. SR-sarcoplasmic reticulum --another system of tubules, separate from the Ttubules and differs from it in that the tubules of the sarcoplasmic reticulum run parallel to the muscle fiber and end in closed sacs at the ends of the sarcomere, above and below each Zline. Ca ++ ions are held in the SR.
SR

a. triad - the term applies to a triplelayered structure of a
T-tubule sandwiched between sacs of the sarcoplasmic reticulum ; close association allows for communication from one part of the fiber to another.
triad
45

E. Functioning:
1. sliding filament theory of contraction; a. individual sarcomeres shorten and the distance between 2 Z lines decreases.
b. myosin and actin filaments do not change length but slide over one another.
c. in a relaxed sarcomere, actin and myosin overlap just slightly .
46

d. in a contracted sarcomere, actin and myosin overlap a greater amount
1) the I-band decrease
2) the H-band decreases
3) the A band remains unchanged in length and increases in volume.
I H
A
I H A
47

e. Contraction mechanics:
1) Myosin will form cross bridges with actin only after Ca ++ ions have been released by the SR . The Ca ++ ions allow the formation of cross bridges by bonding with troponin . This rolls tropomyosin out of the way allowing myosin to bond with the binding site on actin forming the cross bridges .
48

49
2) Cross bridges form

50
3) The myosin heads flex and pull the actin myofilament toward the center of the sarcomeres.

51
4) Cross bridges then detach .

52
5) Myosin heads return to their “relaxed” position.

53
6) The process of forming cross bridges, flexing, detaching, relaxing, continues over and over for as long as the stimulus to contract continues.

F. Control of contraction:
1. A skeletal muscle is activated by its specific motor nerve when stimulated. a. Nerves make contact with muscle fibers with specialized nerve endings called neuromuscluar junctions . telodendrites
1) telodendrites (axonal endings) from nerves make close contact with the sarcolemma of the myofiber.
neuromuscular junctions
54

2) The membranes of the neuron are separated from the sarcolemma by a tiny space called the synaptic cleft.
3) the telodendrites have may synaptic vesicles
(sacs) which contain a chemical neurotransmitter called acetylcholine .
synaptic vesicles nerve ending (telodendrite) synaptic cleft
55 myofiber sarcolemma acetylcholine
4) when the nerve sends a stimulus to the myofiber, the synaptic vesicles release the neurotransmitter, which diffuses across the synaptic cleft and to the sarcolemma of the myofiber.

b. This stimulates the sarcolemma by producing electro-chemical reactions.
1) the sarcolemma in a relaxed myofiber is polarized . It has a
+ charge on the outside of its membrane separated from a charge on the inside. The difference in charge is controlled by the permeability of the membrane. K+ ions are permeable and enter the cell while Na+ ions are not easily permeable and are pumped out by the membrane. This produces a large number of Na+ ions building up around the outside of the cell producing a + charged membrane on the outer side. Even though there are K+ ion inside, there are other ions that are inside, the inner side of the membrane remains - in charge.
56

57
Na +
Na +
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_
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+ + + + + + + + + + + + + + + + + + + + + + + +
_
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Na + Na + Na +
Na + polarized membrane

58
2) when acetylcholine is released, it changes the permeability of the sarcolemma. Now, the Na+ ions come rushing in and the K+ ions rush out . This causes a flip-flop of the charges and depolarizes the sarcolemma. If the stimulus is large enough then depolarization will be self-propagating and move along the entire membrane of the myofiber.
This is known as an action potential .

59
Na +
+ + + + + + + + + + + + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
K +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ + + + + + + + + + + + + + + + + + + + + + + + polarized membrane

60
Na +
Na +
+ + + + - - - - - - - - - - + + + + + + + + + +
- - - - + - + - + - + - + - + - + - + - - - - - - - - - - -
K +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ + + + + + + + + + + + + + + + + + + + + + + + depolarization of the membrane

61 neuromuscular junction
Na +
Na +
Na +
- + - + - + - + - + - + - + - + - + + + + + +
- + - + - + - + - + - + - + - + - + - + - + - - - - - - -
K + K +
K +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ + + + + + + + + + + + + + + + + + + + + + + + depolarization of the membrane

62
Na +
Na +
Na +
Na +
- + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
K + K +
K + K +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ + + + + + + + + + + + + + + + + + + + + + + + depolarization of the membrane

63
Na +
Na +
Na +
Na +
Na +
Na +
- + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
K +
K + K +
K +
K +
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ + + + + + + + + + + + + + + + + + + + + + + +
Na +
Na +
Na +
Na + depolarization of the membrane

64
Na +
Na +
Na +
Na +
Na +
Na +
- + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
K +
K + K +
K +
K +
K +
- + - + - + - + - + - - - - - - - - - - + - + - + - + - +
K +
- + - + - + - + - + + + + + + + + - + - + - + - + - +
Na +
Na +
Na +
Na +
Na +
Na + depolarization of the membrane

65
Na +
Na +
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Na +
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- + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
K +
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- + - + - + - + - + - + - + - + - + - + - + - + - + - +
Na +
Na +
Na +
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Na + Na +
Na +
Na + depolarization of the membrane

66
Na +
Na +
Na +
Na +
Na +
Na +
- + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
K +
K + K +
K +
K +
K +
K + K +
K +
- + - + - + - + - + - + - + - + - +- + - + - + - + - +
K +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
Na +
Na +
Na +
Na +
Na + Na +
Na +
Na + depolarization of the membrane

67
K +
K +
K +
K +
K +
K + K + K +
- + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
Na +
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- + - + - + - + - + - + - + - + - +- + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
K +
K +
K +
K + depolarized membrane
K +

68
- + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - +
- + - + - + - + - + - + - + - + - +- + - + - + - + - +
- + - + - + - + - + - + - + - + - + - + - + - + - + - + depolarized membrane

c. As an action potential moves along the sarcolemma, it will travel down the T-tubules into the interior of the cell.
1) As the action potential moves through the triads it stimulates the SR to release Ca++ ions into the sarcoplasm.
Ca ++ bonds to troponin , which had prevented actin from bonding with myosin. With the barrier between actin and myosin gone, the cross bridges form between actin and myosin and the sliding of the filaments takes place
(contraction occurs).
69

d. Immediately following contraction, the nerve ending releases a second chemical which counteracts the transmitter substance. (This is an enzyme; usually cholinesterase ) and reverses the electro-chemical reactions.
1) The sarcolemma quickly recovers and pumps the Na+ ions out re-establishing a polarized membrane and everything reverses bringing the myofiber back to a relaxed state.
70

71
2. Muscle fibers function on the all or none principle. a. They either contract all the way or they do not contract at all depending on the amount of the stimulus.
1) if the stimulus is too small, only a local disturbance occurs and the cell does not contract
2) if the stimulus is large enough, the entire cell contracts.

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3. Muscle organs function on a graded strength response. This allows variations in the degree of movement produced by the muscle. Two ways are involved: a. increasing the rapidity of stimulations & b. increasing the number of motor units contracting.

1) a motor unit is a nerve-muscle functional unit.
A motor nerve has many telodendrite endings, each which makes contact with a myofiber. When that nerve sends a stimulus, all of the myofibers it makes contact with will contract. So it works as a unit . The average motor unit contains about 150 myofibers. A muscle organ is composed of hundreds of motor units which are spread throughout the muscle. By stimulating a single motor unit, a weak contraction of the entire muscle occurs. By stimulating hundreds of motor units, a very strong contraction can occur.
73

74 one motor unit

75 another motor unit

76
2 motor units

77
5 motor units

G. Anatomy of a Contractions:
1. myogram - a graph showing the response of a muscle during contraction.
1.2
1
0.8
0.6
0.4
0.2
0 latent contraction relaxation recovery
78 start of stimulation

2. muscle twitch - a response to a single brief stimulus; may be divided into 4 intervals; a. latent period--this is the interval following stimulation, before contraction begins. This is the time required for stimulation, energy production, travel of impulse, chemical processes, and the beginning of contraction. No response is seen on a myogram. b. the contraction period directly follows the latent period.
The dark bands increase slightly in volume while the volume of the light band decreases during the contraction period. The shorten of the sarcomeres occurs.
79

c. The relaxation period is the reversal of the process of contraction. It involves definite chemical changes within the muscle as the cell returns to its original length.
d. The recovery period is the short period of time required for the cell to recover from these changes, this would involve restoring ATP , Ca ++ , K + , Na + , etc.
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81
1.2
1
0.8
0.6
0.4
0.2
0 latent contraction relaxation recovery start of stimulation

H. Types of contractions-
1. Muscle twitch-the response of a muscle to a single brief threshold stimulus. The muscle contracts quickly and then relaxes.
2. wave summation - where a second contraction begins before the first contraction is complete. the second contraction builds on the first producing a larger contraction.
3. tetanus - smooth sustained contractions, normal movements, caused by continuous stimulation of a muscle.
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3. treppe - staircase effect- contractions become stronger as the muscle is worked, warm up period for athletes

4. muscle tone - a slight contracted state, keeps the muscles firm, healthy, ready to respond to stimulation, stabilizes joints and maintain posture.
5. isotonic contractions- normal movements in which the muscles shorten when producing movements.
6. isometric contractions- contraction of muscles and the increase of tension but little or no movement occurs.
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85
I. Energy for Contraction:
1. Energy which is released from ATP does the work of rotating the cross bridges (chemical bonds created between actin and myosin) to a different angle. As the cross bridges flex, they move the thin filaments to which they are attached in toward the center of the sarcomeres. This necessarily shortens the sarcomere and the myofibrils.
2. Muscle fatigue - occurs when the ATP production is not fast enough, our muscles can not contract.

3. Oxygen debt - occurs when our bodies can not supply enough oxygen to maintain aerobic respiration. We then use backup anaerobic respiration to produce some ATP. But to restore the body back to its normal condition, oxygen will be required so we called it an oxygen debt.
4. Muscle contraction requires a large amount of energy. ATP is the original source of energy for muscle contraction.
However, there is very little ATP stored in muscle tissue.
Muscle activity of any duration quickly uses up the supply of stored ATP. There are at least 3 ways our bodies have to produce ATP energy.
86

a. During rest and for light to moderate energy demands,
ATP is supplied by aerobic cellular respiration from the mitochondria . When an adequate supply of oxygen is present, glucose molecules are completely metabolized releasing sufficient energy for muscle activity. This is the body's preferred way of producing its energy. It produces the most ATP units per glucose molecule as compared to the other 2 backup methods. For each glucose molecule,
36 ATP units are released and available for work.
1) glucose + O
2
_________ > energy + CO
2
+ H
2
O
ADP 36 ATP
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b. However, if the muscle activity is strenuous , energy from cellular respiration will be too slow to meet the need for energy. The muscle tissue contains a back-up compound, creatine phosphate (CP) that is rich in energy too. This compound releases a phosphate group to resynthesize ATP from ADP. This produces ATP molecules so that muscle contraction can continue for a short time.
1) CP + ADP __________ > ATP + C
2) Later, when there is enough O
2
, the reverse reaction occurs, producing more CP as stored energy.
3) C + ATP __________ > CP + ADP
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c. As the level of CP decreases, and additional energy is required, there is another compound, a starch, glycogen that can release energy for muscle activity. Glycogen is stored in muscle tissue. Glycogen can be converted directly into lactic acid and release energy in the process. This is done without O
2 and is called anaerobic respiration or lactic acid fermentation. The lactic acid will cause muscle fatigue and an oxygen debt will be created in the body.
1) glycogen ____________ > lactic acid + 2 ATP units
2) When the body has had time to reduce its activity to a less strenuous pace and oxygen is again plentiful, the lactic acid will be removed by the blood , taken to the liver and with the aid of more energy, reconverted into glycogen where it will be stored again in the muscle.
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