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Chapter 8 – Muscular System
I. IntroductionA. All movements require muscles to
contract using ATP (chemical energy)- moving blood, urine, & sweat- producing heat to warm the body
B. Three types of muscle exist - skeletal, smooth, & cardiac
C. Each muscle is an organ made of blood & tissues (muscle, connective, & nervous)
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II. Connective TissueA. A layer of fibrous connective tissue
called fascia surrounds & separates each muscle
- it extends beyond muscles to form tendons that are fused to the periosteum of bones Pg. 170
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B. There are 3 layers of connective tissue within each muscle
1. epimysium: closely surrounds a skeletal
muscle2. perimysium: separates muscle
into bundles called fascicles
3. endomysium: surrounds each muscle fiber (cell)
* This arrangement allows parts to move independently
Pg. 170
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III. Structure of a Muscle Fiber (cell)
A. Cell Membrane = SarcolemmaB. Cytoplasm = Sarcoplasm, containing:
1. many nuclei & mitochondria2. thin proteins called myofibrils,
which are responsible for muscle contraction
a) thin one is actinb) thick one is myosin
Pg. 171
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C. Sarcoplasmic Reticulum – channels surrounding each myofibril that transport chemicals
D. Transverse (T) Tubules – channels that pass through the core of a muscle fiber to transport calcium & ATP
* SR & T-tubules activate muscle contraction when the fiber is stimulated
Pg. 171
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IV. Types of MuscleA. Smooth
1. involuntary muscles lining organs (stomach, bladder, uterus, blood vessels)
2. do peristalsis (wavelike contractions) to move substances through the lumen these muscles surround
3. fibers are slower to contract & relax, but resistant to fatigue
Pg. 107-108
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B. Cardiac
1. involuntary muscle of the heart2. doesn’t fatigue3. have striations & intercalated
disks – join cells & transmit contraction from cell to cell
Pg. 107-108
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C. Skeletal1. voluntary muscles used for
movement that are attached to bones
2. do fatigue3. have striations
Pg. 107-108
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V. Skeletal Muscles of the Human Body
A. Muscles attach to bones at 2 sites1. Origin = immovable end of a
muscle2. Insertion = movable end of a
muscle
* Contraction always occurs to move point of insertion towards point of origin *
B. Interaction of Skeletal Muscles1. Of a group of muscles, the one
doing the majority of the work is the prime mover or agonist
2. Assisting muscles are called synergists
3. Muscles that resist the action of the prime mover are antagonists
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C. Skeletal Muscles to know (pgs: 184-185)
FaceFrontalis – lifts eyebrows
Orbicularis oris – moves lipsZygomaticus – “smile” muscle; lifts cheeks
Masseter – chewing muscleorbicularis oculi – moves skin around eyes
NeckSternocleidomastoid – turns neck/head
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TrunkTrapezius – raises arm, scapula
Latissimus dorsi – adducts arm, pulls shoulder ↓Pectoralis major – adducts arm, pulls arm
across chest, rotates humerusRectus abdominis – flexes abdominal wall
External oblique – “ ”
Upper ExtremitiesDeltoid – abducts arm
Biceps brachii – flexes forearm, rotates hand laterally
Triceps brachii – extends forearm
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Lower Extremities - Upper LegGluteus maximus – extends thigh
Gluteus medius – abducts & rotates thighSartorius – “ ”
Gracilis – adducts thighRectus femoris – extends leg at knee
Vastus medialis & lateralis – “ ”Biceps femoris – flexes leg
Lower LegTibialis anterior – dorsiflexion
Soleus – plantar flexionGastrocnemius – plantar flexion & flexion of leg at
knee
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VI. Muscles & The Nervous System
A. Neuromuscular Junction - site where a motor neuron (nerve cell) and a muscle fiber meet
1. The end of the muscle fiber forms a motor end plate
2. The motor neuron stores chemicals called neurotransmitters
Pg. 172
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B. Motor Units 1. are 1 motor neuron and the 2-3
muscle fibers it controls
2. when stimulated, the muscle fibers of the motor unit contract all at once (an “All or None Response”)
Pg. 172
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C. Actin & Myosin create Striation Patterns in a Sarcomere:
1. I bands – light bands composed of actin
attached to Z lines- Sarcomere = area
from Z line to Z line2. A bands – dark bands w/
both actin & myosin- H zone of only
myosin w/ an M line in the middle
- M line holds myosin in place
Pg. 171
Pg. 170Letters Origin
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D. Contraction - the pulling of a muscle against its attachments
1. ATP is needed from mitochondria
2. The neurotransmitter, acetylcholine, is released at
the neuromuscular junction3. Calcium (Ca) ions
are released into muscle fibers thru T tubules
4. ACTIN and MYOSIN slide togetherPg. 175
Sarcomere animation
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E. Relaxation – the lengthening of a muscle from its point of origin
1. Acetylcholine is decomposed by Acetylcholinesterase
(ATP needed)
2. Calcium ions leave muscle fiber thru T-tubules
3. ACTIN and MYOSIN slide apart
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VII. FatigueA. During rest or moderate activity,
enough O2 is present in muscle cells to do aerobic respiration
B. Oxygen debt develops during strenuous exercise - Muscles lose their ability to contract & become fatigued
C. Lactic acid (feeling of pain or of muscles burning) builds up as an end product of anaerobic respiration
1. A muscle cramp occurs due to a lack of ATP required to get rid of calcium ions so muscle fibers can relax
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D. “Repaying” oxygen debt may take several hours
E. Factors that may lead to muscle fatigue:
- Accumulation of lactic acid- Loss/decrease in blood supply (less
O2)
- Loss of acetylcholine supply- Malnutrition (lack of glucose)- Respiratory problems (less O2)
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VIII. Muscle ConditionsA. Muscle Tone - achieved by sustained
contraction within muscles, & is needed for normal posture
1. Slow Fibers – fatigue-resistant muscle fibers
use (distance running, swimming) develop more mitochondria
2. Fast Fibers forceful exercise (weight lifting) causes muscles to contract more new actin and myosin develop, increasing the diameter of muscle fiber muscle enlarges (no new fiber made)
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B. Muscle Use & Disuse1. Muscular Atrophy
Decrease in size & strength of muscles due to disuse (accidents)
less mitochondria, actin, & myosin
2. Muscular Hypertrophy – enlarged muscles due
to increased overuse
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C. Muscle Injuries
1. Mild Strain – few fibers injured, fascia intact, little loss of function
2. Severe Strain – many fibers & fascia torn, loss of function, pain,
discoloration, swelling of tissues
3. Tetanic Contraction – sustained, forceful contraction that
lacks relaxation (i.e.-tetanus bacteria, drugs)
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D. Rigor Mortis – muscle contraction at time of death
muscles run out of ATP & Ca can’t be removed
constant state of contraction after 72 hrs
Actin and Myosin remain linked until muscle cells decompose
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Study Analogy
1. Take 9 pencils (muscle fibers) 2. Wrap each pencil in lined paper
(endomysium)
3. Take 3 pencils in a bundle (a fascicle) and wrap them in colored paper (perimysium)
4. Then take all the bundles and wrap them in gift wrap (epimysium)
5. Wrap all of it in brown paper (fascia)
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