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

SkeletalSkeletal

Skeletal muscle Endomysium Perimysium Epimysium Fascicle Motor end plate Transverse tubules Banding Pattern Actin Myosin

Cardiac

Cardiac muscle 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 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.