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Muscular System
Chapter 8
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Homework
Read Chapter 8 pages 170-204
– Do Part A Q1-24 page 203
– Do Part B Q1-23 pages 203-4
– Do Part C page 204
– Parts A-C Due NLT 4/8/11 (Friday)
Chapter 8 Packet Due: 4/11/11
(Monday)
– Exercises #18-22
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I. Muscle Types
A. Skeletal Muscle
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B. Smooth Muscle
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C. Cardiac Muscle
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II. Skeletal Muscle
A. Skeletal muscle is composed of
muscle tissue, nervous tissue, blood,
and connective tissues
B. Fascia: layers of connective tissue
that cover the muscle
– May connect via tendons to the
periosteum of bone
– OR may connect to coverings of
neighboring muscles via aponeuroses
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C. Epimysium closely surrounds the
muscle (connective tissue)
D. Perimysium seperates muscle
tissue into small compartments
(connective tissue)
– Fascicles: bundles of muscle fibers in
the perimysium
C. Endomysium: covers each
individual muscle fiber (connective
tissue)
D. Figure 8.1: pg 172 text (next
slide)
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Skeletal Muscle
Fig 8.1
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E. Skeletal Muscle Fibers
– A single cell that contracts in response to
stimulation and then relaxes when the
stimulation ends
Sarcolemma – muscle cell membrane
Sarcoplasm – muscle cell cytoplasm
– Contains many mitochondria and nuclei
– Myofibrils in sarcolemma: contain 2 main
proteins, creating striations (note: there are other proteins)
1. myosin: thick
2. actin: thin
– Within sarcoplasm: sarcoplasmic reticulum
(like ER) and transverse tubules activate
muscle contraction when stimulated
Fluid filled channels that connect to the outside of the
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fiber
F. Motor neurons: nerve cells that
connect to the muscle cells
G. neuromuscular junction:
connection between the motor
neuron and the muscle fiber
H. Neurotransmitters: chemicals
released from the neuron to induce a
response in the muscle fiber
I. Motor unit: one neuron connects
to many muscle fibers
simultaneously enabling unified
contraction of all fibers
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III. Muscle Contraction
A. Actin and myosin slide past each
other causing a contraction
B. Structure:
– 1. actin is composed of a double helix
– 2. myosin contains extensions called
cross bridges
C. Sliding filament model
– Cross bridges pull on actin contracting
the muscle
– The cross bridge then releases and
binds with a section further down
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D. ATPase: enzyme that releases energy
for the myosin to latch to actin and pull
E. Acetylecholine: neurotransmitter that
stimulates skeletal muscle tissue
F. Muscle relaxation: occurs due to
decomposition of acetylcholine via
catalysts known as cholinesterases
– Cholinesterase inhibitors can be found in some
insecticides, Serin & VX neurotoxin gases,
some snake toxins
– Causes the action of acetlyecholine to keep
muscles contracting
– Tetanus toxin is not a cholinesterase inhibitor
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G. Energy requirement– mostly from
ATP (adenosine triphosphate)
– Creatine phosphate: enzyme catalyzing
rxn of ADP (adenosine diphosphate) to ATP
– O2 is necessary for the production of
ATP
-muscle cells can store some O2 (in
myoglobin) making it unnecessary for a
continuous supply of oxygen during
contraction but this reserve is not
endless
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H. muscle fatigue: a muscle that has lost
the ability to contract due to overuse, loss
of blood supply, lack of acetyocholine, or
most likely from the build up lactic acid
from anaerobic respiration
– Cramp: sustained involuntary contraction
– Rigor mortis – condition in which muscle fibers
contract ~72h post-mortem; caused by
increase in sarcolemma to Ca++ permeability
causing decrease in ATP in muscle fibers; cells
contract and remain so until the cells begin to
decompose
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I. Muscles are a major source of heat
production
– Excess heat removed via blood supply
J. Recruitment: increase in motor units
being activated
– This causes the entire muscle to contract with
maximal tension
– Twitches – small motor units easily stimulated;
often low stimulus cause muscle contraction of
small muscle groups
– Muscle tone – term applied to small sustained
muscle contractions when muscle is at rest;
responsible for maintaining posture
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IV. Smooth Muscle
A. lack striations because of less
developed sarcoplasmic reticulum
B. Slower to contract/relax (than
skeletal); able to maintain more forceful
contraction with same amt of ATP; able to
change length w/o changing tautness (so
as the stomach & intestines fill, strength is
not lost)
C. Two types:
– 1. Multiunit smooth muscle: muscle fibers are
separate; found in blood vessel walls and iris
of the eye
– 2. Visceral smooth muscle: sheets of spindleshaped cells; found in walls of hollow organs
Stimulation of one muscle stimulates the adjacent
muscles to cause rhythmic contractions thru the
entire organ; peristalsis is term applied to this
rhythmic muscle movement of digestive tract
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V. Cardiac Muscle
A. Found only in the heart
B. Striated cells form 3-D networks
C. When one portion of the muscle is
stimulated the impulse carries across to
other fibers; intercalated discs aid in the
transmission of impulses
D. Self-exciting & rhythmic; necessary to
carry out the primary function of heart –
to beat.
E. Pacemaker - the sinoatrial (SA) node or
sinus node; a small mass of specialized
cells in the top of the heart's right atrium
(upper chamber); makes the electrical
impulses that cause the heart to beat.
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VI. Muscle Movement
A. Origin: immovable end of the muscle
B. Insertion: movable end of the muscle
– When muscle contracts, its insertion is pulled
toward its origin
C. Prime mover: the muscle that provides
most of the movement
– Called the agonist
D. Synergists: the muscles that contract
and assist the prime mover
E. Antagonist: resist a prime mover’s
actions and causes movement in the
opposite direction
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