Chapter 6: Contraction of Skeletal Muscle Flashcards
how many percent of the body is skeletal muscle
40%
how many percent is smooth
and cardiac muscle in the body?
10%
The sarcolemma consists of a true cell membrane, called
the?
plasma membrane
outer coat made
up of a thin layer of polysaccharidematerial that
contains numerous thin collagen fibrils
plasma membrane
turn collect into bundles to form the muscle tendons thatthen insert into the bones.
tendon fibers
Each muscle fiber contains
several hundredto several thousand
myofibrils
Each myofibril is composed
of about?
1500 myosin filaments and 3000 actin filaments
The light
bands contain only actin filaments and are called?
I bands
dark bands contain
myosin filaments
ends of the actin filaments where they
overlap the myosin, and are called?
A bands
the small projections from the sides of the
myosin filaments
cross-bridges
ends of the
actin filaments are attached to a so-called?
Z-discs
composed of
filamentous proteins different from the actin and
myosin filaments
Z disc
The portion of the myofibril (or of the whole
muscle fiber) that lies between two successive Z
discs is called a?
sarcomere
at
this length the muscle is capable of generating its greatest force of contraction called
sarcoplasm
sarcoplasm surrounding the myofibrils
of each muscle fiber is an extensive reticulum called the ?
sarcoplasmic reticulum
This
reticulum has a special organization that is extremely important in controlling muscle contraction
sarcoplasmic reticulum
achieved by a large number of filamentous molecules
of a protein called?
titin
acts on a local area of the
musclefiber membrane to open multiple
“acetylcholine-gated
”cation channels through
protein molecules floating inthe membrane
acetylcholine
initiate attractive forces
between the actin and myosin filaments, causing them to slide along side each other, which is
the contractile process
calcium ions
the Z discs have been
pulled bythe actin filaments up to the ends of
the myosin filaments. Thus, muscle contraction
occurs by a
sliding filament mechanism
what causes the actin filaments to slide
inward among the myosin filaments?
caused by forces generated by interaction of the
cross-bridges from the myosin filaments with the
actin filaments.
The backbone of
the actin filament is a double-stranded
F-actin protein molecule
Each strand of the double F-actin helix is
composed of polymerized
G actin molecules
the active sites on the actinfilaments
with which the cross-bridges of the myosin filaments interact to cause muscle contraction
ADP molecules
Attached to one end of each tropomyosin
molecule is a
troponin
The actin filament also contains another protein
tropomyosin
Attached intermittently along the sides of the
tropomyosin molecules are still other protein
molecules called
troponin
has a strong affinity for actin
troponin I
subunits for tropomyosin
troponin T
subunits for tropomyosin
troponin T
subunits for calcium ions
troponin C
The new alignment of forces causes the
head to tilt toward thearm and to drag the actin
filament along with it
power stroke
the greater the amount of work performed by the muscle, the greater the amount of ATP that is cleaved
fenn effect
the increase in tension that occurs during contraction
active tension
contracts rapidly when it contracts against no load—to a state of full contraction in
about 0.1 second for the average muscle
skeletal muscle
When a muscle contracts against a load, it performs
work
The second important source of energy, which
is used to reconstitute both ATP and phosphocreatine
glycolysis
third and final source of energy. means combining
oxygen with theend products of glycolysis and
with various other cellular foodstuffs to liberate
ATP
oxidative metabolism
3 sources of energy for muscle contractions
- phosphocreatine
- glycolysis
- oxidative metabolism
what do you call of muscle contraction when the muscle does not
shorten during contraction
isometric
when it does
shorten but thetension on the muscle remains constant
throughout the contraction
isotonic
Muscles that react rapidly,
including anterior tibialis
fast muscle fibers
muscles such as soleus that respond slowly but
with prolonged contraction
slow fibers
Slow Fibers (Type 1, Red Muscle)
(1) Smaller fibers
(2)Also innervated by smaller nerve fibers
(3) More
extensive blood vessel system and capillaries to supply
extra amount of oxygen
(4) Greatly increased numbers of mitochondria,also to support high levels of oxidative metabolism
(5) Fiber Contain large amounts of
myoglobin, an iron-containing protein similar to hemoglobin in red blood cells
The
myoglobin gives the slow muscle a reddish appearance
andthe name?
red muscle
Fast Fibers (Type II, White Muscle)
(1) Large fibers
for great strength of contraction
(2) Extensive sarcoplasmic reticulum for rapid release of calcium ions to
initiate contraction
(3) Large amounts of glycolytic
enzymes for rapid release of energy by the glycolytic
process
(4) Less extensive blood supply because oxidative metabolism is of secondary importance
(5) Fewer
mitochondria, also because oxidative metabolism is
secondary
A deficit of red myoglobin in fast muscle
gives it the name
white muscle
All the
muscle fibers innervated bya single nerve fiber are called a
motor unit
means the adding together
of individual twitch contractions to increase the
intensity ofoverall muscle contraction
summation
Summation occurs in two ways;
✓ multiple fiber summation
✓ frequency summation
increasing the number
of motor units contracting simultaneously
multiple fiber summation
increasing the frequency of contraction
frequency summation
frequency summation can lead to?
tetanization
When the frequency reaches acritical level, the successive contractions eventually become
so rapid that they fuse together and the whole muscle
contraction appears to be completely smooth and continuous
tetanization
the strength of contractionincreases to a plateau, a phenomenon called the?
staircase effect or treppe
Even when muscles are at
rest, a certain amount of tautness usually remains.
This is called?
muscle tone
study of different types of
muscles, lever systems, and their movements is called?
kinesiology
total mass of a muscle increases
muscle hypertrophy
total mass of a muscle decrease
muscle atrophy
causing enlargement of
the individual muscle fibers
simple fiber hypertrophy
occurs to a much
greater extent when themuscle is loaded during the
contractile process
hypertrophy
The pathway that appears to account
for much of the protein degradation in a muscle undergoing atrophy is the
ATP dependent ubiquitin-
proteasome pathway
increase in fiber number
fiber hyperplasia
fibrous tissue that replaces the muscle fibers during denervation atrophy also has a tendency to continueshortening for many months, which is called
contracture
causes large
motor units
macromotor units
muscles of the body go
into a state of contracture called? that is,
the muscles contract and become rigid
rigor mortis
