Muscular System

Function– Locomotion– Posture– Protection– Heat production

Muscle Classification

Skeletal Muscle– Attached to skeleton– Striated– Muscle fiber = Muscle cell

Multinucleate Myofibrils are striated cylinders within myofiber

Skeletal Muscle

Myofilaments are proteins within the myofibrils that result in contraction – Actin – thin & has a receptor site for myosin– Myosin – thick & has a receptor site for actin

and ATP– Contraction – Myosin heads attach to actin and

with ATP perform a Power Stroke

Skeletal Muscle

SarcomereThe distance from Z line to Z lineThe basic unit of contractionSarcomere gets smaller as Power Stroke

occurs

Key Points

Why is the sarcomere the functional unit of contraction?

Why does the power stroke result in contraction?

What would happen to contraction if you ran out of ATP?

Motor Neurons

Skeletal muscle cannot contract without stimulation from a motor neuron

Motor Unit = The motor neuron plus the myofiber(s) it innervates

Key Points

Why would a spinal cord injury result in paralysis?

Somatic Muscles

All of the body’s skeletal muscles except the branchiomeric muscles

VoluntaryBody wall & Appendage muscles

– Trunk and Tail– Hypobranchial– Tongue– Extrinsic Eyeball

Somatic Muscles

Myotome derivatives primarilySome from hypomere

Key Points

What is a myotome?

Somatic Muscles

Orient the body in the environment

Somatic Muscles

Red Fibers– More blood supply for aerobic metabolism– Myoglobin for oxygen storage– Fatigue resistant– Fish for cruising long distances, tetrapods for

posture

Somatic Muscles

White fibers– Less blood supply; geared for anaerobic

metabolism– Fatiguable– Fish for spurts of swimming– Tetrapods for sprints

Key Points

Why is the breast meat of the goose dark, but the breast meat of the chicken is white?

Cardiac Muscle

Striated with intercalated disksInvoluntaryLateral plate mesoderm (hypomere) in

origin

Smooth Muscle

Involuntary Lateral plate mesoderm in origin Regulates internal environment Innervated by Autonomic Nervous System Found in the wall of tubes and hollow organs Intrinsic Eye muscles Erectors of feathers and hairs

Key Points

Besides those mentioned, give a specific example of where might you find smooth muscle?

Gross features of skeletal muscle

Origin, insertionTendonAponeurosisFascia

Muscle shapes

Skeletal Muscle Actions

Flex/ExtendAdduct/AbductLevator/DepressorProtract/RetractConstrictor/DilatorRotator

Skeletal Muscle Actions

Supinator/PronatorTensor (taut)

Skeletal Muscle Actions

Agonist – primary moverAntagonist – opposes primary moverSynergist – helps primary mover

Development & Phylogeny

PositionEmbryologyNerve supply

Development

Dorsal Mesoderm – Epimere – Somite– Myotome– Sclerotome & Dermatome

Lateral plate Mesoderm – Hypomere– Somatic – body wall muscles– Splanchnic – smooth muscle of viscera

AXIAL MUSCLES

TrunkTailHypobranchialTongueExtrinsic Eye

Axial Muscles

Metamerism as in myomeres

Axial Muscles

AgnathansSimpleSegments (myomeres)Myotome derivatives

Axial Muscles – Jawed Fish

Horizontal or Lateral SeptumEpaxial Muscles

– From myotomes in embryology– Innervated from dorsal rami of spinal nerves– Extend spine & some lateral bending– Extrinsic eye muscles (innervated by cranial

nerves)– Epibranchial muscles

Axial Muscles – Jawed Fish

Hypaxial MusclesFrom Myotomes

– Innervated by ventral rami of spinal nerves– Ventroflex and lateral bending

Hypaxial Muscles – Jawed fish

Hypobranchial musclesLocated on floor of pharynx, pectoral girdle

to jawAre hypaxial muscles that migrated forwardFunction in respiration & feedingE.g. Coracomandibularis, Coracohyoid

Axial Muscles - Tetrapods

Epaxial trunk musclesDorsal muscles from skull to tailDorsalis trunci in amphibiansLongissimus – long dominant spine

extensor in amniotesIliocostalis – most lateral epaxial spine

muscle important in reptiles

Epaxial Muscles

See Vertebrate Muscles page

Epaxial Muscles in Tetrapods

Trends Decreased except in neckFewer myosepta

Axial Muscles - Tetrapods

Hypaxial MusclesTend to form sling-like sheetsLateral muscles support & compress body

wallObliquesTransversusIntercostals in amniotes only

Hypaxial Muscles - Tetrapods

Rectus abdominis – ventroflexes and compresses abdomen

Diaphragm – unique to mammals for breathing

Hypaxial Muscles in tetrapods

See Vertebrate Muscles page

Hypobranchial and Tongue Muscles - tetrapods

Function – stabilizes hyoid and larynxE.g. geniohyoid, sternohyoid, sternothyroid,

thyrohyoid

Hypobranchial & Tongue muscles in tetrapods

Tongue musclesLingu-; Gloss-Anchors to hyoidE.g. lingualis, styloglossus

Hypobranchial & Tongue muscles in Tetrapods

See Vertebrate Muscles page

Extrinsic Eye muscles in tetrapods

VoluntaryObliques – rotates eye along its transverse

axisRectus – up, down, left, rightRetractor in some

Extrinsic Eye muscles

See Vertebrate Muscles Page