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 Sarcomere The distance from Z line to Z line The basic unit of contraction Sarcomere 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 Voluntary Body wall & Appendage muscles Trunk and Tail Hypobranchial Tongue Extrinsic Eyeball

Somatic Muscles Myotome derivatives primarily Some 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 disks Involuntary Lateral 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, insertion Tendon Aponeurosis Fascia

Muscle shapes

Skeletal Muscle Actions Flex/Extend Adduct/Abduct Levator/Depressor Protract/Retract Constrictor/Dilator Rotator

Skeletal Muscle Actions Supinator/Pronator Tensor (taut)

Skeletal Muscle Actions Agonist – primary mover Antagonist – opposes primary mover Synergist – helps primary mover

Development & Phylogeny Position Embryology Nerve supply

Development Dorsal Mesoderm – Epimere – Somite Myotome Sclerotome & Dermatome Lateral plate Mesoderm – Hypomere Somatic – body wall muscles Splanchnic – smooth muscle of viscera

AXIAL MUSCLES Trunk Tail Hypobranchial Tongue Extrinsic Eye

Axial Muscles Metamerism as in myomeres

Axial Muscles Agnathans Simple Segments (myomeres) Myotome derivatives

Axial Muscles – Jawed Fish Horizontal or Lateral Septum Epaxial 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 Muscles From Myotomes Innervated by ventral rami of spinal nerves Ventroflex and lateral bending

Hypaxial Muscles – Jawed fish Hypobranchial muscles Located on floor of pharynx, pectoral girdle to jaw Are hypaxial muscles that migrated forward Function in respiration & feeding E.g. Coracomandibularis, Coracohyoid

Axial Muscles - Tetrapods Epaxial trunk muscles Dorsal muscles from skull to tail Dorsalis trunci in amphibians Longissimus – long dominant spine extensor in amniotes Iliocostalis – most lateral epaxial spine muscle important in reptiles

Epaxial Muscles See Vertebrate Muscles page

Epaxial Muscles in Tetrapods Trends Decreased except in neck Fewer myosepta

Axial Muscles - Tetrapods Hypaxial Muscles Tend to form sling-like sheets Lateral muscles support & compress body wall Obliques Transversus Intercostals 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 larynx E.g. geniohyoid, sternohyoid, sternothyroid, thyrohyoid

Hypobranchial & Tongue muscles in tetrapods Lingu-; Gloss- Anchors to hyoid E.g. lingualis, styloglossus

Hypobranchial & Tongue muscles in Tetrapods See Vertebrate Muscles page

Extrinsic Eye muscles in tetrapods Voluntary Obliques – rotates eye along its transverse axis Rectus – up, down, left, right Retractor in some

Extrinsic Eye muscles See Vertebrate Muscles Page