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Muscles
The Muscular System Functions

Body Movement

Maintenance of Position

Respiration / organ volume

Production of Body Heat
(Thermogensis)

Movement of substances
(construction of organ and
vessels)

Heart Beat
Characteristics of Skeletal Muscle

Contractility


Excitability


Muscles need to be stimulated before contracting
Extensibility


A muscle’s ability to shorten and generate force to do
useful work at the expense of cellular energy.
The way muscles can be stretched without damage
Elasticity


Muscle’s return to their original length and shape after
contracting
Conductivity – conducts action / potential along
plasma membrane
Skeletal muscle picture
 Striated,
multinucleated and voluntary
Skeletal Muscle

Each skeletal muscle fiber is a single cell
containing numerous myofibrils
 Myofibrils are composed of actin and myosin
myofilaments
 Myofibrils are joined end to end to form
sarcomeres
 Muscle fibers are organized into fasciculi and
fasciculi are organized into muscles by
associated connected tissue.
Myofibrils
Sacomere
Myofilaments
Connective tissue components
 Endomysium
– separating individual
muscle fibers
 Perimysium – surround borders of 10 –
100 fibers (fascicles)
 Epimysium – outlines the whole muscle
 Deep fascia – dense irregular tissue, holds
muscles together, separating into
functional groups.
Smooth Muscles
Smooth muscle is nonstriated (striped),
uninucleated, and involuntary. Visceral
organs (alimentary canal)
Cardiac Muscle
*Cardiac: striated, uninucleated, branches,
interculated discs, involuntary
Both Cardiac and Smooth muscle are under
involuntary control and is influenced by
hormones, such as epinephrine.
Innervation of a Motor Unit and
Muscle Fiber
Muscle fiber
is innervated
by one single motor
neuron
This neuron
motors more than
one muscle fiber.
There may
be 500 to
1,000 muscle
fibers per neuron
Neuroelectrical factors

Potassium ions (K+) are greater inside the
muscle cell than outside, whereas sodium ions
(Na+) are greater outside than inside
 The inside of cell is negatively charged
electrically, whereas outside is positively
charged
 (Neuromuscular junction) Nerve impulse
reaching the neuromuscular junction causes and
axon ending to release the neurotransmitter
acetylcholine.
Neuronelectical factor con’t

This makes cell membrane permeable to Na+.
They rush in creating an electrical potential. K+
begins to move out to restore resting potential
(Not as Na+ comes in)
 This causes muscles to generate its own
impulse called the action potential
 The sarcoplasm reticulum then release Ca++
into the fluids surrounding myofibrils.
 Ca++ stops the action of the inhibitor substance
troponin and tropomysin (which keep actin and
myosin apart), causing contractile process to
occur
Chemical factors




Ca++ combines loosely with myosin to form activated
myosin.
Activated myosin reacts with ATP, attached to the
myosin, and releases energy from the ATP to form
actomyosin
Myosin filaments have cross bridges that now connect
with the actin and pull the actin filaments in among the
myosin filament
A sliding process occurs: The width of the A bands
remain constant, but Z lines move closer. By now the
sodium – potassium pump has kicked in to restore the
resting potential. Ca++ gets reabsorbed and contraction
ceases
Energy sources: ATP
 Glycolysis:
glucose to pyruvic acid, net
gain of 8 ATP if O2 present, if no O2 then
lactic acid (burn in muscles) forms with net
gain of 2 ATP
 Krebs’ citric acid cycle: pyruvic to
CO2+H2O+30 ATP (28 ATP + 2 GTP)
 Phosphocreatine in muscle cells: used in
sprinting
 Free fatty acid: fatty acids + H2O + ATP
Muscle Terms

Twitch


Threshold


A very small detectable sensation
All-or-none response


A sudden uncontrollable muscle spasm
A muscle will respond to stimulation completely or not
at all
Lag phase

The interval of time between stimulus and
contractions
Muscle Terms (Cont.)

Contraction phase


Relaxation phase


The phase of decreased tension after all or none
Tetanus


Tension rises to a peak
Calcium ions cause spasmodic / sustained
contractions
Recruitment

Patterns and corresponding change of muscle
patterns, increase number of motor units activated
Muscle Anatomy Terms

Tendon


Origin


Explains where the muscle begins
Insertion


The head of the muscle, where it is located, stationary bone
Head


Tough fibers that connect muscle to bony structures; wide flat
sheet called aponeurosis
Muscle’s relationship with other muscles, moveable bone
Belly



The fleshy part of the contracting muscle
Resistance – force opposes movement
Effort – force exerted to achieve movement
Anatomy of Skeletal Muscle

A single skeletal muscle, such
as the triceps muscle, is
attached at its origin to a large
area of bone; in this case, the
humerus. At its other end, the
insertion, it tapers into a
glistening white tendon which,
in this case, is attached to the
ulna, one of the bones of the
lower arm.
Terms
 Prime

mover
Muscle that contracts (pulls) mainly by itself
 Antagonist

A muscle that works opposite of another,
relaxing muscle
 Synergists
Muscles working together
REMEMBER: muscles only pull

Naming skeletal muscles







A. Direction of muscle fiber to midline
B. Location – structure near muscle is found
C. Relative SIZE of muscle
D. NUMBER of origins (tendons)
E. SHAPE of Muscles
F. Origin and insertion sites
G. Action – same as in joints. 2 new are
Sphincter – decrease size of opening, Tensor –
make body more rigid
Isometric / Isotonic
Muscle Contraction

Isotonic contractions


Tension on a muscle stays the same but the muscle
shortens so things can be lifted, joints moves
Isometric contractions
This is when the muscle does not shorten when
contracting. This can happen when pushing on a wall
or something else that will not move.
TONE
 This is a constant state of partial contraction
maintained in a muscle

Muscle disorder
 Symptoms:
Paralysis, weakness,
degeneration or atrophy, pain, spasms
 Causes: Muscular tissue, Vascular system
feeding muscle cells, nervous system
connections, connective tissue
surrounding cell bundles (fascicles)
Types of disorders
Fibromyalgia – muscle pain
 Myasthenia gravis- muscle tiring / weakness,
acetylcholine receptor destruction
 Muscular dystrophy- inherited, males, muscles
degenerate
 Hernia – myocele – muscle breaks through sheath,
Inguinal – bowel through abdominal muscle
 Myoclonus – spasm / twitching of muscle, singultus –
hiccup (myoclonus of diaphragm)
 Botox – paralyze the muscle that causes wrinkles.
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