Muscular System Function – Locomotion – Posture – Protection – Heat production
Dec 16, 2015
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
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
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
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
Skeletal Muscle Actions
Flex/ExtendAdduct/AbductLevator/DepressorProtract/RetractConstrictor/DilatorRotator
Skeletal Muscle Actions
Agonist – primary moverAntagonist – opposes primary moverSynergist – helps primary mover
Development
Dorsal Mesoderm – Epimere – Somite– Myotome– Sclerotome & Dermatome
Lateral plate Mesoderm – Hypomere– Somatic – body wall muscles– Splanchnic – smooth muscle of viscera
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
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
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
Extrinsic Eye muscles in tetrapods
VoluntaryObliques – rotates eye along its transverse
axisRectus – up, down, left, rightRetractor in some