1. Muscular System
• Function
– Locomotion
– Posture
– Protection
– Heat production

2. • Vertebrate muscles:
• striated vs. smooth
• voluntary vs. involuntary
• skeletal vs. non-skeletal
•
Skeletal muscle (left) & Smooth muscle
(right)

3. Muscle Classification
• Skeletal Muscle
– Attached to skeleton
– Striated
– Muscle fiber = Muscle cell
• Multinucleate
• Myofibrils are striated cylinders within myofiber
• Non-skeletal muscle = muscles not attached to the
skeleton; most are smooth & involuntary

4. • 1 - Skeletal, striated, voluntary muscles
– axial
• body wall & tail
• hypobranchial & tongue
• extrinsic eyeball muscles
– appendicular
– branchiomeric (homologous to the branchial/
pharyngeal muscles from fishes to mammals,
striated muscles, innervated by cranial nerves)
– integumentary

5. • 2 - Non-skeletal, smooth, chiefly
involuntary muscles
–muscles of tubes, vessels, & hollow
organs
–intrinsic eyeball muscles
–erectors of feathers & hair
• 3 - Cardiac muscle
• 4 - Electric organs

6. • Skeletal muscles have muscular & tendinous
portions:
• Muscle - consists of skeletal muscle cells
(which, in turn, consist of myofibrils and
myofilaments)
• Tendons - extensions of a muscle's tough
connective tissue sheath (fascia & epimysium)
that anchor a muscle to its origin & insertion

8. –Origin = site of attachment that is
relatively fixed
–Insertion = site of attachment that is
normally displaced by contraction of
the muscle

9. •Names of skeletal muscles are based on:
•direction of fibers (e.g., oblique(
•location or position (e.g., superficial(
•number of divisions (e.g., triceps(
•shape (e.g., deltoid(
•origin and/or insertion (e.g., iliocostalis(
•action (e.g., levator scapulae(
•size (e.g., major(
•or some combination of these

13. Skeletal Muscle
• Myofilaments are proteins that result in
contraction within the myofibrils
–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

17. Skeletal Muscle
•Sarcomere
•The distance from Z line to Z line
•The basic unit of contraction
•Sarcomere gets smaller as Power Stroke
occurs

18. 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?

19. Motor Neurons
• Skeletal muscle cannot contract without
stimulation from a motor neuron
• Motor Unit = The motor neuron plus the
myofiber(s) it innervates

21. Key Points
• Why would a spinal cord injury result in
paralysis?

22. 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

23. Somatic Muscles
• Myotome derivatives primarily
• Some from hypomere

24. Key Points
• What is a myotome?

26. Somatic Muscles
• Orient the body in the environment

27. Somatic Muscles
• Red Fibers
– More blood supply for aerobic metabolism
– Myoglobin for oxygen storage
– Fatigue resistant
– Fish for cruising long distances, tetrapods for
posture

28. Somatic Muscles
• White fibers
– Less blood supply; geared for anaerobic
metabolism
– Fatiguable
– Fish for spurts of swimming
– Tetrapods for sprints

29. Key Points
• Why is the breast meat of the goose dark, but
the breast meat of the chicken is white?

30. Cardiac Muscle
• Striated with intercalated disks
• Involuntary
• Lateral plate mesoderm (hypomere) in origin

32. 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

34. Key Points
• Besides those mentioned, give a specific
example of where might you find smooth
muscle?

35. Gross features of skeletal muscle
• Origin, insertion
• Tendon
• Aponeurosis
• Fascia

38. Muscle shapes

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

41. Skeletal Muscle Actions
• Supinator/Pronator
• Tensor (taut)

42. Skeletal Muscle Actions
• Agonist – primary mover
• Antagonist – opposes primary mover
• Synergist – helps primary mover

43. Development & Phylogeny
• Position
• Embryology
• Nerve supply

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

46. AXIAL MUSCLES
• Trunk
• Tail
• Hypobranchial
• Tongue
• Extrinsic Eye

47. • Axial Muscles:
• include the skeletal muscles of the trunk & tail
• extend forward beneath the pharynx as
hypobranchial muscles & muscles of the tongue
• are present in orbits as extrinsic eyeball muscles
(check slide 27 in this powerpoint presentation)
• are metameric (most evident in fish and aquatic
amphibians where the axial muscles are used in
locomotion; in other tetrapods, metamerism is
obscured due to presence of paired appendages
responsible for locomotion on land)
• are segmental because of their embryonic origin;
arise from segmental mesodermal somites

49. •Trunk & tail muscles of fish:
•Axial musculature consists of a series
of segments (myomeres) separated by
myosepta
–Myosepta serve as origins & insertions
for segmented muscles
•Myomeres are divided into dorsal &
ventral masses by a horizontal septum
that extends between the transverse
processes of the vertebrae

50. •Epaxials = above the septum
•Hypaxials = below the septum

51. • Trunk & tail muscles of tetrapods
• Tetrapods, like fish, have epaxial & hypaxial masses, & these
retain some evidence of metamerism even in the highest
tetrapods.
• Modifications:
• 1 - epaxials are elongated bundles that extend through many
body segments & that are located below the expanded
appendicular muscles required to operate the limbs
• 2 - hypaxials of the abdomen have no myosepta & form broad
sheets of muscle
• 3 - hypaxials are oriented into oblique, rectus, & transverse
bundles

52. • Epaxials of tetrapods:
• lie along vertebral column dorsal to transverse
processes & lateral to neural arches
• extend from base of the skull to tip of the tail

53. •Hypaxials of tetrapods:
•1-Muscles of lateral body wall:
–oblique (external & internal), transverse, &
rectus muscles
•2-Muscles that form longitudinal bands
in roof of body cavity (subvertebral
muscles(

55. Rectus muscles:
•weakly developed in most fish; 'stronger'
in tetrapods
•support ventral body wall & aid in arching
the back
•in mammals - rectus abdominis (typically
extends from the anterior end of the
sternum to the pelvic girdle)

57. Appendicular muscles - move fins or
limbs
•Extrinsic - originate on axial skeleton or
fascia or trunk & insert on girdles or limbs
•Intrinsic - originate on girdle or proximal
skeletal elements of appendage & insert on
more distal elements

58. Branchiomeric muscles:
1 - associated with the pharyngeal
arches
2 - series of skeletal & smooth
muscles
3 - adductors, constrictors, & levators
operate jaws plus successive gill
arches

59. Integumentary muscles:
Extrinsic integumentary muscles (e.g., platysma)
•originate (usually) on the skeleton & insert on the
underside of the dermis
•striated
•move skin of amniotes
Intrinsic integumentary muscles (arrector pili muscles)
•entirely within the dermis
•found in birds & mammals
mostly smooth muscles

60. Axial Muscles
•Metamerism as in myomeres

62. Axial Muscles
•Agnathans
•Simple
•Segments (myomeres(
•Myotome derivatives

63. 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

66. Axial Muscles – Jawed Fish
•Hypaxial Muscles
•From Myotomes
–Innervated by ventral rami of spinal nerves
–Ventroflex and lateral bending

68. 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

70. 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

73. Epaxial Muscles
•See Vertebrate Muscles page

74. Epaxial Muscles in Tetrapods
• Trends
• Decreased except in neck
• Fewer myosepta

75. Axial Muscles - Tetrapods
• Hypaxial Muscles
• Tend to form sling-like sheets
• Lateral muscles support & compress body wall
• Obliques
• Transversus
• Intercostals in amniotes only

77. Hypaxial Muscles - Tetrapods
• Rectus abdominis – ventroflexes and
compresses abdomen
• Diaphragm – unique to mammals for
breathing

79. Hypaxial Muscles in tetrapods
•See Vertebrate Muscles page

80. Hypobranchial and Tongue Muscles -
tetrapods
• Function – stabilizes hyoid and larynx
• E.g. geniohyoid, sternohyoid, sternothyroid,
thyrohyoid

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

83. Hypobranchial & Tongue muscles in
Tetrapods
• See Vertebrate Muscles page

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

86. Extrinsic Eye muscles
• See Vertebrate Muscles Page