Download Skeletal Muscle Contraction

Chapter 8
Muscular System
8-1
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 Introduction:
A. The three types of muscle in the
body are
1. Skeletal
2. Smooth
3. Cardiac
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 Structure
of a Skeletal Muscle
A. Muscle is made of
-skeletal muscle tissue
-connective tissues
-nervous tissue
-blood
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B. Connective Tissue Coverings
1.
Fascia-fibrous connective tissue that
separates the individual muscles
2.
Tendons-bone to muscle connection
-fascia extends beyond muscle
to make this.
-connect to periosteum
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3.
Aponeuroses-connective tissue that
attaches muscle to muscle
-abdominal muscles, lumbar
vertebrae, palmar/plantar regions
4. Epimysium-wraps around entire
muscle; connective tissue
5.
Fascicles-individual muscle
compartments
6.
Perimysium-separates the fascicles
*wraps around each fascicle
7. Endomysium-covers each muscle cell
8.
Muscle cells-muscle fiber
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C. Skeletal Muscle Fibers
1.
Each muscle fiber is a single, long,
cylindrical muscle cell.
2.
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Sarcolemma-cell membrane
Sarcoplasm-cytoplasm with many
mitochondria and nuclei;
-has myofibrils.
-myofibrils are
separated into compartments
called sarcomeres that contain
thick filaments and thin
filaments.
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a.
b.
c.
Thick filaments of myofibrils
are made up of the protein
myosin.
Thin filaments of myofibrils
are made up of the protein
actin.
The organization of these
filaments produces striations.
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XVCI
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3.
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A sarcomere extends from Z line
to Z line.
a.
I bands
-light bands
-made up of actin
-anchored to Z lines
b.
A bands
-dark bands
-made up of overlapping
thick and thin filaments.
c.
In the center of A bands is an
H zone, consisting of myosin
filaments only.
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4.
Beneath the sarcolemma of a
muscle fiber lies the sarcoplasmic
reticulum (endoplasmic reticulum),
which is associated with transverse
(T) tubules (membrane channels)
- activate the muscle
contraction mechanism
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Muscle Strain?



Muscle fibers and
connective tissue are
flexible but they tear
Only few fibers-mild
Fascia tear and muscle
function loss-severe

Discolored and swollen
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8 - 18
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Nervous and muscular system:
1.
The site where the motor neuron
and muscle fiber meet
a.
The muscle fiber membrane
forms a motor end plate
-nuclei and mitochondria
are abundant.
b.
Neurotransmitters (chemicals)
are stored at the end of the
motor neuron
-these are released from
the motor neuron and
stimulate the muscle
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E.
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Motor Units
-motor neuron and the muscle fiber
it contracts
8.3 Skeletal Muscle Contractions
21
Bio 2
HW-TBA; test on Monday next
week
Agenda: Contraction of the muscle
1. Take out muscle contraction notes.
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Skeletal Muscle Contraction
2 events take place in a muscle
contraction
-shortening of sarcomeres
-pulling of the muscle against its
attachments.
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Myosin-thick filament
1. Crossbridges
projecting outward
Actin-thin filament
1. Globular protein
2. Binding sites for
myosin
3. Troponin and
tropomyosinproteins that block
binding sites of actin
-prevent myosin
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from
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sliding filament theory of muscle contraction
1. Myosin cross-bridges attach to binding site
on actin
2. Myosin pulls on actin
3. Myosin releases actin and attaches to next
binding site
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A8A
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How does ATP help?

Myosin has an enzyme ATPase
 Breaks down ATP into ADP
 This releases energy for the muscle cell to
use.
• This energy causes myosin crossbridge to
cock its head to attach actin.
 ADP will be made back into ATP through cell
respiration
 After one pull, another ATP attaches on for the
myosin to release actin.
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How does a muscle know to contract?
1.
Neuron neurotransmitter
-acetylcholine
-triggers a stimulus to the
muscle
2.
Protein receptors in the motor end
plate detect the neurotransmitters.
-impulse spreads over
sacrolemma
-travel through tranverse
tubules and into the
sarcoplasmic reticulum.
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3.
4.
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sarcoplasmic reticulum releases
calcium to the sarcoplasm
Calcium
-moves troponin and tropomyosin
-actin binding sites are exposed so
myosin crossbidges can attach
-myosin pulls on actin to shorten
sarcomere
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8 - 32
Relaxation
-After the nervous impulse has been
received, acetylcholinesterase (enzyme)
rapidly decomposes the acetylcholine.
-Then, calcium is returned to the
sarcoplasmic reticulum, and the
linkages between myosin and actin are
broken.
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Energy Sources for Contraction
1. ATP is needed
-adenosine triphosphate
-limited supply so constantly must be
made through cellular respiration
2. Creatine phosphate
-quick back up energy supply
-can change ADP into ATP
3. Creatine Phosphokinase
-creates creatine phosphate
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Oxygen Supply and Cellular Respiration
Cell Respiration
Glucose + oxygen= ATP and carbon dioxide + water
-muscles need a lot of oxygen to create the
most ATP
-hemoglobin carries oxygen to muscles
-pigment called myoglobin stores oxygen in
muscle tissue
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
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Oxygen Debt
-rest or moderate activity-oxygen supply
is good
-oxygen deficiency occurs
-lactic acid is made
-travels to liver
-liver has oxygen debt
-amount of oxygen needs for the liver
to change lactic acid into glucose and
regain the original amount of ATP and
creatine phosphate
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Muscle Fatigue
1. When a muscle loses its ability to contract
during strenuous exercise, it is referred to as
fatigue.
2. Muscle fatigue usually arises from the
accumulation of lactic acid in the muscle.
-A lowered pH as a result of accumulated
lactic acid prevents the muscle from
contracting.
3. A muscle cramp occurs due to a lack of ATP
required to return calcium ions back to the
sarcoplasmic reticulum so muscle fibers can
relax.
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Section 8.4
Notes
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 Muscular Responses
A.
One method of studying muscle
function is to remove a single fiber
and connect it to a device that
records its responses to electrical
stimulation.
B.
Threshold Stimulus
1.
A muscle fiber remains
unresponsive to stimulation
unless the stimulus is of a
certain strength, called the
threshold stimulus.
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C. All-or-None Response
1.
When a muscle fiber contracts, it
contracts to its full extent (all-ornone response); it cannot contract
partially.
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D. Recording a Muscular Contraction
1. A myogram is the recording of an
electrically stimulated muscle
contraction.
2. A single, short contraction involving
only a few motor units is referred to
as a twitch.
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3. The time delay
between when the
stimulus is applied and
when the muscle contracts
is called the latent period,
which is less than 0.01
second.
4. The latent period is
followed by a period of
contraction and a period of
relaxation.
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Types of muscle contraction



Concentric (shorten)
 Lifting weights
 Any action that causes the muscle to overcome the
resistance of an object
Eccentric (lengthen)
 Returning the muscle to standard position
 Bicep lengthens as you lower it from the curled
position
 Normal everyday activities
Isometric (stays the same)
 Carry an object in front of you
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Summation
-muscle receives several
stimuli arrives at the
muscle before the end of
the relaxation phase
If the sustained contraction
lacks any relaxation, it is
called a tetanic contraction.
*action potentials are so
rapid
*Ca can’t be reclaimed by
SR
*occurs in most muscle
movements
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Recruitment of Motor Units
1.
An increase in the number of
activated motor units within a
muscle at higher intensities of
stimulation is called recruitment.
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G. Sustained Contractions
1. Summation and recruitment
together can produce a sustained
contraction of increasing strength.
2. Muscle tone is achieved by a
continuous state of sustained
contraction of motor units within a
muscle.
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8.5-8.6 Notes
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Muscle fibers continued


Red fibers
 Low glycogen
 High myoglobin and capillaries
 High mitochondria
 Take 3 times longer to contract after stimulation
 Have oxygen reserves so uses more
 Can’t use a lot of force, but can do small amounts
for a long time
Intermediate fibers-both red and white fibers
 Look more like red fibers but can sustain activity
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longer
Would you like white meat or
dark meat?
White meat-fast muscle fibers
 Little myoglobin and capillaries
 Mitochondria is low; have a lot of
glycogen
 Use a lot of ATP in a short time; after 10
seconds, use lactic acid fermentation up
to 3 minutes
 Used for short activities
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 Dark meat-red muscle fibers

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*Smooth Muscle Fibers
*elongated
*tapered ends
*no striations
*underdeveloped
*Visceral smooth muscle-sheets of muscle
*walls of hollow organs
*fibers stimulate one another
*show rhythmicity (peristalsis)
* multiunit smooth muscle
*blood vessels and eye iris
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*fibers are separate and not sheets
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Smooth Muscle Contraction
*similar mechanism to skeletal muscle
*acetylcholine and norepinephrine
stimulate and inhibit muscle contraction
*hormones can also stimulate and inhibit
contraction
*slower to contract and relax than skeletal
*can contract longer using the same amount
of ATP
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Cardiac Muscle
*contraction mechanism similar
*has extra calcium
*contract for longer periods
* self-exciting and rhythmic
*whole structure contracts as a unit.
*intercalated disks
-membrane junctions that joins cells and
transmit the contraction from one cell to
the next
*makes the signal travel fast
*do not need neural stimulation like
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skeletal;
have pacemaker
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Skeletal Muscle Actions
*origin-immovable end
*insertion-movable end
*contraction-pulls the insertion toward the
origin
*Muscle names based on: size, shape, location,
action, number of attachments, or direction
of its fibers
*prime mover-the main worker
*synergist-helpers
*antagonist-opposing muscles
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B.
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Muscles of Facial Expression
1.
Muscles of facial expression
attach to underlying bones
and overlying connective
tissue of skin, and are
responsible for the variety of
facial expressions possible in
the human face.
2.
Major muscles include the
epicranius, orbicularis oculi,
orbicularis oris, buccinator,
and zygomatigus.
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C.
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Muscles of Mastication
1.
Chewing movements include
up and down as well as sideto-side grinding motions of
muscles attached to the skull
and lower jaw.
2.
Chewing muscles include
masseter and temporalis.
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D. Muscles that Move the Head
1. Paired muscles in the neck and back
flex, extend, and turn the head.
2. Major muscles include
sternocleidomastoid, splenius
capitis, and semispinalis capitis.
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E. Muscles that Move the Pectoral
Girdle
1. The chest and shoulder muscles
move the scapula.
2. Major muscles include the
trapezius, rhomboideus major,
levator scapulae, serratus anterior,
and pectoralis minor.
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F. Muscles that Move the Arm
1.
Muscles connect the arm to the
pectoral girdle, ribs, and vertebral
column, making the arm freely
movable.
2.
Flexors include the
coracobrachialis and pectoralis
major.
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3.
4.
5.
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Extensors include the teres major
and latissimus dorsi.
Abductors include the
supraspinatus and the deltoid.
Rotators are the subscapularis,
infraspinatus, and teres minor.
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G.
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Muscles that Move the Forearm
1.
These muscles arise from the
humerus or pectoral girdle
and connect to the ulna and
radius.
2.
Flexors are the biceps brachii,
the brachialis, and the
brachioradialis.
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3.
4.
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An extensor is the triceps brachii
muscle.
Rotators include the supinator,
pronator teres, and pronator
quadratus.
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H. Muscles that Move the Wrist, Hand, and
Fingers
1.
Movements of the hand are caused
by muscles originating from the
distal zumerus, and the radius and
ulna.
2.
Flexors include the flexor carpi
radialis, flexor carpi ulnaris, palmaris
longus, and flexor digitorum
profundus.
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3.
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Extensors include the extensor carpi
radialis longus, extensor carpi
radialis brevis, extensor carpi
ulnaris, and extensor digitorum.
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I. Muscles of the Abdominal Wall
1.
This group of muscles connects the
rib cage and vertebral column to the
pelvic girdle.
a.
A band of tough connective
tissue, the linea alba,
extending from the xiphoid
process to the symphysis
pubis, serves as an
attachment for certain
abdominal wall muscles.
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2.
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These four muscles include:
external oblique, internal oblique,
transverse abdominis, and rectus
abdominis.
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J. Muscles of the Pelvic Outlet
1.
The superficial urogenital diaphragm
fills the space within the pubic arch,
and the deeper pelvic diaphragm
forms the floor of the pelvic cavity.
2.
Pelvic diaphragm includes the
levator ani.
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3. Urogenital diaphragm: includes the
superficial transversus, perinei,
bulbospongiosus, and
ischiocavernosus.
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K. Muscles that Move the Thigh
1.
The muscles that move the thigh
are attached to the femur and to
the pelvic girdle.
2.
Anterior group includes the
psoas major and iliacus.
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3.
4.
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Posterior group is made up
of the gluteus maximus, gluteus
medius, gluteus minimus, and
tensor fasciae latae.
Thigh adductors include the
adductor longus, adductor magnus,
and gracilis.
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L. Muscles that Move the Leg
1.
This group connects the tibia or
fibula to the femur or pelvic girdle.
2.
Flexors are the biceps femoris,
semitendinosus semimembranosus,
and sartorius.
3.
An extensor is the quadruceps
femoris group made up of four
parts: rectus femoris, vastus
lateralis, vastus medialis, and vastus
intermedius.
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M. Muscles that Move the Ankle, Foot, and
Toes
1. Muscles that move the foot are
attached to the femur, fibula, or
tibia, and move the foot upward,
downward, or in a turning
motion.
2. Dorsal flexors include the tibialis
anterior, peroneus tertius, and
extensor digitorum longus.
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3.
4.
5.
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Plantar flexors are the
gastrocnemius soleus, and flexor
digitorum longus.
An invertor is the tibialis posterior.
An evertor is the peroneus longus.