Download Muscular System

Muscular System
Classification
Red vs. White
 Somatic vs. Visceral

– Move bones or cartilages vs. organs,
vessels, and ducts.
Voluntary vs. Involuntary
 Skeletal – Cardiac - Smooth

Cell Structure
As in other cells
 Sarcolemma

– Cell membrane of muscle cells

Sarcoplasmic reticulum
– Smooth endoplasmic reticulum

Multinucleate
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Skeletal muscle
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Endomysium
Perimysium
Epimysium
Fascicle
Motor end plate
Transverse tubules

Banding Pattern
 Actin
 Myosin
Cardiac
Cardiac muscle
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Only in the heart.
Mononucleate
Banded
Relatively short
Branched
Intercalated disks
connect cells

Waves of
contraction spread
by intercalated
disks.
 Initiated by nerves
or intrinsically.
Smooth
Smooth muscle
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Lack striations
Associated with
visceral functions
Not under voluntary
control
Contractions are
slow and sustained.
Mononucleate

Nerves innervate all
cells.
 Hormones may
excite or inhibit
contractions
Structure

Skeletal muscle has a belly, and is attached
at each end to bone.
 Attachment is via tendons, which are
extensions of the endomysium, perimysium,
and epimysium.
 Tendons can be rope like or sheet like
(aponeurosis).
 Sheets of connective tissue are the fascia.
Tendons

Can be long
permitting efficient
location of muscle.
 Require little
maintenance or
energy – little
circulation.
How Muscle Works

Nerve depolarizes sarcolemma at the motor
end plate.
 Depolarization wave spreads over entire
muscle via the sarcolemma and transverse
tubules.
 Actin and myosin filaments interact to shorten
sarcomere.
 Muscle can only shorten, to move the load.
Tension Length
Curve for
Skeletal
Muscle.
Some Generalizations

Red vs. White muscle
– Red muscle tends to have a greater
concentration of myoglobin, and is
therefore resistant to fatigue.
– White fibers contain less myoglobin, and
less circulation, and are therefore more
susceptible to fatigue – but they contract
faster.
– Compare the distribution of fibers in
various species of birds and fish.
Some Generalizations

Tonic and Twitch Fibers
– Tonic fibers contract slowly, produce low
force, but can sustain a contraction for a
long time (associated with posture), and
are common in amphibians and reptiles.
– Twitch fibers contract rapidly and are found
in somatic muscles of all vertebrates.
• Slow twitch – relative slow contraction, resistant
to fatigue.
• Fast twitch – relative fast contraction,
susceptible to fatigue.
Fast and Slow ‘Twitch’ Fibers
Some Observations
Fiber types or observable histologically.
So, it is possible to learn something
about the locomotion of an animal
based on its fine anatomy.
 Fibers are recruited depending on load
and time. This has something to say
about how athletes train.

Force Generation
Total force generated by muscle is
function of active contraction (actin and
myosin) as well as elastic component
derived from the tendons and
connective tissue.
 Multiple muscles w/ varying origins
move the same load: Why?

– Differences in maximum active tension.