Myology
• Myology: The study of the anatomy, physiology
and related diseases of muscle is referred to
as myology.
• Muscle: The term “muscle” describes an organ
composed of either smooth muscle tissue,
skeletal muscle tissue, or cardiac muscle
tissue that is designed specifically to contract.
The contraction of muscle tissue can be used to
produce voluntary or involuntary movements of
various parts of the body.
Types of Muscle
• Three types of muscle exist within the
human body:
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Skeletal muscle
Cardiac Muscle
Smooth Muscle
Skeletal Muscle
• Skeletal Muscle Tissue: Skeletal muscle tissue is
primarily designed to exert forces on the bones of the
skeletal system and create movement. A skeletal
muscle cell results from the fusion of many myoblasts
into one single skeletal muscle cell. Its is for this reason
that skeletal muscle cells are multinucleated. Skeletal
muscle cells also appear striated under a microscope.
The internal architecture of the contractile proteins
causes the skeletal muscles to have alternating dark
colored and light colored bands. Skeletal muscle
tissue is also referred to as voluntary muscle
because it is used to exert forces upon the structures
within the body (especially the bones of the skeletal
system) and create consciously controlled voluntary
movements.
Cardiac Muscle
• Cardiac Muscle: Cardiac muscle tissue forms the
myocardium of the heart. It is an involuntary
form of striated muscle that is autorhythmic
(capable of initiating its own electro-chemical
impulses which are necessary to induce
contraction). Cardiac muscle cells contain
specialized areas of cell membrane known as
intercalated discs and are arranged as a
functional syncytium. The combination of these
two specializations helps it to experience 100%
recruitment of muscle cells upon stimulation to
contract.
Cardiac Muscle
Smooth Muscle
• Smooth Muscle Tissue: Smooth muscle
cells are nonstriated forms of
involuntary muscle. This type of muscle
can be found in the walls of blood vessels,
surrounding glands, in the walls of the
hollow organs in the skin, in the trachea
and attached to hair follicles (erector pili
muscle).
Histology of Muscle: Epimysium, Perimysium and Endomysium
MUSCLE
• Skeletal muscle is made of many individual cells
called MUSCLE FIBERS due to their elongated
shape.
• Each muscle fiber is surrounded by a connective
tissue called endomysium.
• A group of 10-100 muscle fibers surrounded by
perimysium is called a muscle fascicle.
• Group of muscle fascicles are surrounded by
epimysium will make the actual skeletal
muscle.
• The endomysium, perimysium and epimysium
extend throughout the muscle and join together
at the ends to form the tendons.
• Tendons are the inelastic CT fibers that attach
to the periosteum of the bone.
• A broad flat tendon is called an aponeurosis.
• Fascia is the term to describe sheet of fibrous
CT that exists beneath the skin and surrounds
the muscles and organs.
• Superficial fascia separates the skin from
muscle. It’s composed of areolar CT and
adipose tissue and allows for passage of blood
vessels, lymph vessels, nerves into and out of
muscle. It also insulates and protects the muscles.
• Deep fascia consists of dense irregular
arranges CT and lines the internal surface of
the body cavity, and limbs. Deep fascia holds
muscles of similar function together, allows
for free movement and allows for
transmission of nerves, blood vessels, and
lymphatic vessels.
• Muscle cells are stimulated to contract by
somatic motor neurons ( voluntary )
• Neurons make contact at the neuromuscular junction.
Neuromuscular/Myoneural Junction
Neuromuscular/Myoneural
Junction
• The individual muscle fibers have a cell membrane
known as the sarcolemma.
• The sarcolemma has thousands of transverse
invaginations called T-Tubules. They extend from
the sarcolemma to the center of each muscle fiber.
• T-Tubules transmit action potentials that are
needed for muscle contraction.
• The structural arrangement helps to insure that
the action potential required to stimulate the
muscle contraction will spread throughout the
muscle in a quick and uniform manner.
Myofibrils
• Within the muscle fiber cells, their exists thread like
structures called MYOFIBRILS. They are the actual
contractile element of the skeletal muscle.
• They are 2 microns wide and run the entire length of
the muscle. It is the striation of the myofibrils that
make them look striated.
• A fluid filled system of membranous sacs known as
the sarcoplasmic reticulum surrounds each
myofibril. This area stores the CALCIUM. Calcium is
need for a muscle to contract.
Microscopic anatomy cont.
• Dilated portions of the sarcoplasmic
reticulum known as the terminal
cisternae lie up against each side of the T
tubule.
• Two terminal cisternae & the T tubule= the
triad.
• The triad is the highway for the action
potential to travel.
Microscopic anatomy cont.
• Myofibrils are composed of microfilaments some
thin and some thick. They are arranged into
basic contractile units called sarcomere.
• The Sarcomere is compose of three things:
• 1) regulatory proteins – tropomyosin &
troponin. ( on & off switch )
• 2) contractile proteins- Actin & Myosin
• 3) structural proteins- titin, dystrophin, nebulin,
myomesin, connectin: Deal with alignment,
stabilization, elasticity, extensibility
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Actin: Forms the THIN filament.
Composed of 3 proteins
1) actin F & G (G=Binding site)
2) tropomyosin
3) troponin
• Tropomyosin molecule extends the entire length of the
actin and covers the myosin binding sites.
• Troponin holds the tropomyosin over the binding site on
the G protein until it’s time for contraction. It’s the lock
that keeps the active site inaccessible.
• It can expose the binding sites when calcium is
released. CALCIUM is the Key to the lock
Actin, Troponin and
Tropomyosin
Actin
• The backbone of the actin filament is a double stranded
“F” actin protein which is wound into a double helix.
Each “F” actin protein is composed of two “G” actin
proteins. The myosin binding sites are located on the
individual “G” actin proteins. The tropomyosin
molecule extends down the length of the actin molecule
and covers the myosin binding sites. Another protein
known as troponin attaches to the tropomyosin. The
troponin holds the tropomyosin in place over the myosin
binding sites on the “G” actin proteins until it is time for
the muscle to contract.
Myosin
• Myosin forms the thick filament of the myofibril and is
composed of six polypeptide chains. There are two
heavy polypeptide chains which are arranged
longitudinally and form the double helix of the tail of the
myosin molecule. The other end of these heavy myosin
polypeptide chains are folded into a globular protein
known as the myosin head. The myosin heads are
attached to a cross bridge of myosin that allows the
head to hang off the double stranded myosin filament.
These cross bridges contain two hinges that function in
the actual contractile process. The four light polypeptide
chains are incorporated into the myosin head, and help
control the function of the head during muscle
contraction.
• Myosin: forms the thick
filament composed of 6
polypeptide chains.
• Tails, 2 hinges, head.
• See picture on next page
Myosin: Cross Bridges and
Heads
White meat-vs-Dark meat
• Dark meat in chicken is found in the thigh
and white meat found in the breast.
• More myoglobin in legs then in wings.
• White= Fast twitch fibers. Little myoglobin,
less mitochondria. So these are used for
POWER and SPEED for short duration
only. They fatigue easily because of lactic
acid build up.
• Red= Slow twitch fibers- increased
myoglobin, increased mitochondria, used
for endurance and postural muscles of
back and calf.
Functions of ATP in muscle
• Energizes muscle for the power stroke
• Disconnects myosin cross bridge from the binding
site on G protein of actin
• Energizes the calcium pump
• ATP= Adenine, Ribose sugar & 3 phosphates
• Potential energy is released when the terminal
high energy bond is broken by a hydrolytic
enzyme.
• As ATP supply is low there are 3 place that can
supply it. ATP demands on contracting muscle are
enormous. ATP is generated at the same rate it is
being used.
Cellular respiration
• The process by which a living cell converts
the chemical bond energy of the energy
nutrients into chemical bond energy as ATP.
It’s divided into Anaerobic & aerobic.
• Anaerobic- Requires NO OXYGEN, and occurs
in the cytoplasm of the cell and is known as
GLYCOLYIS. ( GlucosePyruvic acid)
• Aerobic- Requires OXYGEN and occurs in the
mitochondria. Citric Acid cycle ( kreb cycle)
Cellular Respiration
The Citric Acid (Kreb’s) Cycle
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BIOTIN
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9) OXALOACETIC acid
PYRUVIC ACID
I
PANTOTHENIC ACID
I ---> CO2
B5
I
I
ACETYL CoA
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1)
CITRIC ACID
2)
ISOCITRIC acid
3) OXALOSUCCINIC ACID
8) MALIC ACID
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4) ALPHA KETOGLUTARIC ACID
7) FUMARIC ACID
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5) SUCCINYL COA
6) SUCCINIC ACID
Glycolysis
• After glucose enters the cell it must be phosphorylated to
prevent it form leaving the cell and to prepare it for
cellular respiration.
• When glucose is phosphorylated, it’s referred to as
glucose- 6 – phosphate. It can’t leave the cell, and the
glucose bonds become unstable and allowed to be
broken down easier during cellular respiration.
• Glucose + 2 ADP +2PO42 pyruvic acid +2ATP + 4H
• During exercise the body is operating at an oxygen
debt, therefore it is the predominant source of ATP
production during physical exertion. An enzyme known
as lactic dehydrogenase will convert pyruvic acid 
lactic acid when oxygen levels are low. (soreness)
When O2 is normal it converts it back and pyruvic acid
will be used for Krebs
• The Pyruvic acid produced by anaerobic process of
glycolyis will enter the kreb cycle.
• pyruvic acid acetyl CoA 1.citric acid 2.isocitric
acid3.oxalosuccinic acid 4.alpha ketoglutamic
acid5.succinyl CoA 6.succinic acid 7.fumaric
acid 8.malic acid 9.oxaloacetic acid acetyl CoA
BIOTIN
Pyruvic acid  oxaloacetic acid
Glucose is needed to make pyruvic acid, so low carb
diets will lead to the break down of muscle and
organ proteins into amino acids. 50% will be
converted into glucose the remainder will be broken
into kreb cycle intermediates.
• At rest a muscle produces more ATP than it needs.
So ATP transfers energy to CREATINE(a small
molecule assembled from fragments of amino acids)
• ATP + Creatine  ADP + Creatine Phosphate (CP).
• During each contraction, myosin head breaks
down ATP producing ADP and a phosphate
group. The energy stored in CP is used to recharge
ADP back to ATP in a reversible reaction.
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CPK
• ADP + Creatine phosphate  ATP + Creatine
• CPK crosses the cell membrane and is released into
the bloodstream with muscle damage.
Types of Contraction
• Isotonic contraction- 1. Concentric and 2.Eccentric.
• Concentric- muscle tension exceeds the resistance and
the muscles shortens. ( origin and insertion approximate
each other) ( positive or acceleration contraction)
• Eccentric- Peak tension is less than the load and the
muscle elongates. The origin and insertion move apart
fro one another. ( the negative or deceleration)
• Isometric- tension never exceeds the resistance. No
change in joint angle
Muscles continued
• Origin- Usually more proximal and the part USUALLY is
stationary.
• Insertion- Usually more distal and the part USUALLY
moves.
• Agonist- The main muscle that provides the motion
• Synergist- a Muscle that assists the agonist
• Antagonist- opposes the agonist.
• Innervation- The nerve supply to a muscle. Muscles of
the upper extremity innervated by the brachial plexus
C5-T1. Muscles of the lower extremity innervated by the
lumbar plexus L1-L4 & sacral plexus L4-S4