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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)