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Types of Muscle
 Three types of muscle:
 Cardiac- found only in the heart

Striated, involuntary
 Smooth- surrounds tubular organs, such as intestines
and esophagus.

Non-striated, involuntary
 Skeletal- found attached to bones in the legs, back,
shoulders and elsewhere.

Striated, voluntary
Hyperplasia
 Individual muscle cells differentiate and divide before
birth in a process called Hyperplasia.
 The Hyperplastic process is complete before birth, so
an animal is born with all the muscle fibers it will ever
possess.
Hypertrophy
 After birth as an animals skeletal system lengthens,
muscles must also lengthen to keep up.
 Muscles must also grow in diameter as the animal
matures.
 Both of these types of postnatal (after birth) growth
are called Hypertrophy.
Hypertrophy
 Increase in bone length actually causes muscle cells to
lengthen at each end.
 This type of hypertrophy is called stretch-induced
hypertrophy.
 Muscle cells increase in width through exerciseinduced hypertrophy, thus increasing size of whole
muscle.
Muscles and Muscle Cells
 A single muscle cell is called a myofiber.
 Each myofiber is individually wrapped by a thin film of
connective tissue called the endomysium.
 Bundles of myofibers are wrapped by a connective
tissue sheath called perimysium.
 These bundles of myofibers make up whole muscles
that are wrapped by a connective tissue sheath called
epimysium.
Muscles and Muscle Cells
 All the connective tissues surrounding myofibers,
bundles of myofibers, and whole muscles consist of a
protein called collagen.
Arrangement of Whole Muscle
Sarcomere
 Each myofiber is divided into striped units called
sarcomeres.
 The sarcomere is a tiny segment of the myofiber that
shortens when muscles contract and elongate when
muscles relax.
 Z-lines define the beginning and end of a single
sarcomere.
Muscle Proteins
 Sarcomeres are predominately made of five muscle
proteins:
 Myosin
 Actin
 Troponin
 Tropomyosin
 Titin
Muscle Proteins
 The thicker filament represents myosin and is
referred to as the “A” band of the sarcomere.
 The thin filament represents the actin and is referred
to as the “I” band of the sarcomere.
 Troponin and tropomyosin help regulate muscle
contractions.
 Titin prevents overstretching of the muscle.
Review
Muscle Contractions
 As the sarcomere contracts, myosin stays stationary
and attachments located at the ends of the myosin
molecule, called “myosin feet”, pull the actin filaments
closer together.
 This shortens the area called the “H” zone and then
shortens the sarcomere.
Muscle Contractions/Relaxations
 Thousands of sarcomeres shortening in unison cause
the entire muscle to contract and shorten.
 When the muscle relaxes, each sarcomere resumes its
original position and the muscle resumes its normal
shape.
Allowing Muscle Contractions
 The mineral Calcium allows muscle contraction to
occur.
 Each myofiber is surrounded by a reservoir of calcium
called the sarcoplasmic reticulum (SR).
 When the muscle receives a message to contract from a
nerve, the SR releases calcium in to the myofiber.
 This causes the myosin feet to pull the actin filaments
together.
Allowing Muscle Contractions
 When the nervous impulse ends, calcium flows back
into the SR and the muscle relaxes.
 The relaxation process requires no energy; actin and
myosin molecules simply slide back to their original
positions.
Glucose or Glycogen
 The whole process of contraction is fueled by either
glucose or glycogen.
 Glucose is blood sugar, which can be obtained directly
from the blood stream.
 Glycogen is stored glucose found within the muscle.
 If the muscle runs out of its fuel, it goes into a state of
exhaustion called muscle fatigue.
Types of Muscle Cells
 Two main types of myofibers distinguished by color
and relative speed of contraction.
 Fast, white fibers
 Slow, red fibers
Fast, White Fibers
 Fibers are large in diameter and have few blood vessels
running through them.
 Use stored glycogen as their primary energy source.
 Large muscle groups consist of mostly fast, white
fibers.
 Ex.- Breast meat of poultry
 Anaerobic (no oxygen) exercise which is intense and
short-term tends to develop this type of muscle fiber.
Slow, Red Fibers
 Fibers have many blood vessels running through them
and are then red in appearance.
 Get most of their energy directly from glucose in the
blood stream.
 ex.- Drumsticks of poultry
 Aerobic (with Oxygen) exercise, which is long term
and less intense develops this type of muscle fiber.
Muscle Fibers in Large Animals
 The type of myofiber that predominates in an animals
is largely controlled by genetics and varies by muscle
group.
 Ex.- muscle fibers present in the loins of animals tend to
be fast, white fibers while muscle fibers present in the
legs of animals tend to be slow, red fibers.
Muscle Fibers in Large Animals
 Heavily muscled animals have more fast, white muscle
fibers, which are larger in diameter and take up more
space.
 Several intermediate types of myofibers also have
properties of both fast, white fibers and slow, red
fibers.
Turkey and Veal
 If an animal is subjected to stresses that favor a specific
fiber type, fibers have the ability to slowly transform
through the intermediate types toward the favored
muscle type.
 Wild turkeys have mostly slow, red fibers because they
have to run and fly away from predators.
 Issues with veal calf housing arose when calves were
kept in small pens to restrict movement to keep meat
color white and meat quality tender.
 These calves would have mostly fast, white fibers even in
legs.
Muscle to Meat
 When an animal is slaughtered, blood stops flowing to
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muscle tissue.
The energy supply of glucose is then cut off.
Nerve pathways are severed and impulses still reach
muscles.
Muscles cells continue to attempt contraction using
glycogen as an energy source.
This process produces lactic acid as a waste product of
anaerobic respiration.
Muscle to Meat
 The buildup of lactic acid cause the pH of the muscle
to decline.
 Normal pH in a myofiber is 7.0 (neutral)
 When the pH drops to around 5.5 muscles cease to use
glycogen.
 The sarcomeres stop moving and the muscle becomes
stiff.
 This state of muscle stiffness is called rigor mortis.
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Biology of Fat Development
 Fat = adipose tissue
 Fat cells = adipocytes
 Adipocytes are very large but that is due to being
almost entirely stored energy