Lecture 13: Axial And Branchiomeric Musculature

Question 1

Describe the 3 skeletal muscle divisions

Answer 1

Skeletal muscles can, for convenience, be divided into three groups:

• Axial:
• Derived directly from myotome portions of somites
• Demonstrate a segmental arrangement (metamerism)
• Innervated by spinal nerves
• Branchiomeric:
• Formed from embryonic mesenchyme associated with pharyngeal arches
• Demonstrate a segmental arrangement
• Innervated by cranial nerves
• Appendicular:
• Formed from body wall or limb bud mesenchyme
• Innervated by spinal nerves

Question 2

Describe axial musculature

Answer 2

Musculature of the vertebrate body wall and tail makes up the axial musculature.

• Axial musculature is derived from the embryonic somites (myomeres) and is metameric.
• Metamerismis evident in fishes and in urodeles.
• In most tetrapods the metamerism is not as evident.
• Axial musculature is divided into epaxial and hypaxial musculature.
• Epaxial musculature is innervated by dorsal rami of spinal nerves.
• Hypaxial musculature is innervated by ventral rami of spinal nerves.
• In amniotes hypaxial muscles ventral to the transverse processes (subvertebral) or organized into longitudinal bundles.
• In craniates, hypaxial muscles extend into the pharynx as hypobranchial muscles and, in amniotes, extend forward into the tongue.
• The mammalian diaphragm and cremaster muscles are hypaxial muscles.

Question 3

Describe the muscles located in the eyeball

Answer 3

• These muscles in sharks and other craniates arise originate from three pairs of preotic somitomeres and are innervated by cranial nerves III, IV, and VI.

Question 4

Describe the two groups that appendicular muscles are divided into

Answer 4

Appendicular muscles are divided into extrinsic and intrinsic groups:

• Extrinsic appendicular muscles originate from the axial skeleton and insert on the girdle or limb.
• Appendicular muscles in fishes are mostly extrinsic.
• Extrinsic muscles of tetrapods develop in one of two ways:
• • They may develop within the embryonic wall and spread to the limb.
• • They may develop in the limb and spread to the to the axial skeleton.
• Intrinsic appendicular muscles originate from the girdle or proximal limb and insert more distally.
• Intrinsic muscles in tetrapods develop within the limb.

Question 5

Describe branchiomeric muscles

Answer 5

• Branchiomeric muscles develop from the branchial arches.
• Muscles derived from the first branchial arch (mandibular arch) open and close the jaws.
• • Muscles of the first arch are innervated by the fifth cranial nerve.
• Muscles derived from the second branchial arch (hyoid arch) attach to the hyoid skeleton, lower jaw, and operculum in fishes.
• • Muscles of the second arch are innervated by the seventh cranial nerve.
• • The sphincter colli of lower tetrapods spreads over the head of amniotes to become the platysma and muscles of facial expression.
• Muscles derived from the remaining arches operate gills in fishes and take on new functions in tetrapods.
• • Muscles of the remaining arches are innervated by cranial nerves nine and ten.
• • The cucullaris of fishes and urodeles gives rise to the trapezius and sternocleidomastoid of amniotes.

Question 6

Describe the trunk muscles of fish

Answer 6

• Fish depend primarily on powerful movements of the trunk and/or tail for locomotion (people generally don’t eat fish fins).
• Trunk muscles of fish are the axial muscles.
• • These muscles are derived from somitic myotomes and exhibit a segmental arrangement.
• • In gnathostomes they are typically divided into epaxial (more dorsal) and hypaxial (more ventral) muscles.
• • Segments that make up the axial musculature are called myomeres.
• • The number of myomeres corresponds with the number of vertebrae but the spatial arrangement of the myomeres alternates with that of the vertebrae.

Question 7

Describe the myomeres of fish

Answer 7

• A lateral view of a typical myomere in a gnathostome fish resembles the letter “W.”
• The open (top) end of the “W” faces craniad.
• Sideways, the “W” is split into an upper portion (part of the epaxial musculature) and a lower portion (part of the hypaxial musculature).
• • The epaxialand hypaxialparts are separated from each other by a fibrous tissue partition: The horizontal septum is Not present in cyclostomes
• Individual myomeres are separated from each other by vertical connective tissue partitions: the Transverse septa

See slide 10

Question 8

Reference card

Answer 8

Make an image flashcard of slide 11 and review slide 12

And 13 and 15 and 16 and 32 (plus any i skipped between there)

Question 9

Describe axial musculature in amphibians

Answer 9

• Reduction in epaxial musculature:
• Still somewhat prominent in urodeles as dorsalis truncus.
• Useful in flexing body axis for swimming.
• Division of hypaxial muscles into layers.
• Increase in mass and complexity of limb muscles.
• Review slide 14 SAT

Question 10

Describe axial muscles in reptiles and mammals

Answer 10

• Dorsalis truncus subdivided into three longitudinal columns:
• Transversospinalis (or spinalis).
• Longissimus dorsi.
• Iliocostalis.
• Epaxial muscles reduced in turtles. (Because why would a turtle need much back muscle?)
• Hypaxial muscles divided into three layers as in amphibians.
• Those in thoracic area are interrupted by ribs. (Intercostal muscles…or spare ribs)
• See Slide 16

Question 11

Describe the hypaxial muscles in reptiles and mammals

Answer 11

Hypaxial muscles:

• Same as in Necturus in abdominal region.
• In thoracic region:
• External oblique: External intercostals
• Internal oblique: Internal intercostals
• Transversus: Subcostals
• see slide 18

Question 12

Describe the arrangement of back muscles (three groups)

Answer 12

1. Superficial (Extrinsic)
2. Intermediate (Extrinsic)
3. Deep (Intrinsic)

See Slides 22-25

Question 13

Describe the superficial back muscle group

Answer 13

• Connect limb to axial skeleton.
• Innervated by ventral (anterior) rami or CN XI.
• Include: Trapezius, Latissimus dorsi, Levator scapulae, Rhomboideus major, and Rhomboideus minor

Question 14

Describe the intermediate back muscle group

Answer 14

• Respiratory muscles.
• Innervated by ventral (anterior) rami.
  Serratus posterior group: Serratus posterior superior, and Serratus posterior inferior

Question 15

Describe the Deep Back Muscle Group

Answer 15

• True intrinsic muscles of the back are innervated by dorsal (posterior) rami.
• Three sub-groups:
• • Superficial: Splenius capitis and Splenius cervicis
• • Intermediate: Iliocostalis, Longissimus Spinalis
• • Deep: Semispinalis, Multifidus, and Rotatores

Question 16

Describe superficial intrinsic muscles

Answer 16

• Superficial intrinsic muscles make up the spinotransversalis system:
• Muscles run laterally and upward to attach to transverse processes and skull.
• Two parts: Splenius capitis & Splenius cervicis

Question 17

Describe intermediate intrinsic muscles

Answer 17

• Intermediate intrinsic muscles make up the sacrospinalis system:
• These muscles collectively form the erector spinae group
• These muscles run longitudinally upward and attach to transverse processes, ribs, and spinous processes.
• The erector spinae group forms three longitudinal bundles:
• Iliocostalis, Longissimus, and Spinalis

Question 18

Describe deep intrinsic muscles

Answer 18

Deep intrinsic muscles make up the transversospinalis system:

• Muscles run laterally and insert medially.
• Muscles run from transverse processes to transverse processes.
• This group of muscles includes:
• • Semispinalis, Multifidus, Rotatore

Question 19

Describe extrinsic eye muscles

Answer 19

• Six extrinsic eye muscles are associated with each eye ball.
• These muscles are derived from three pairs of anterior somites.
• Therefore, three pairs of cranial nerves innervate these muscles:
  1. Trochlear nerve (CN IV): Innervates superior oblique muscle.
  2. Abducensnerve (CN VI): Innervates lateral rectus muscle.
  3. Oculomotor nerve (CN III): Innervates remaining four muscles: Inferior rectus, Medial rectus, Inferior rectus, Inferior oblique

Question 20

Describe the branchiomeric musculature of sharks

Answer 20

• Muscles of the gill arch region arise from the embryonic mesenchyme instead of somites.
• More anterior ones are striated.
• More posterior ones are smooth.
  – Transition reflects change from vigorous movements required for feeding and gill function to slower, sustained movements required for transport of food along gut tract.
• Each set is associated with a gill arch.
  See Slides 30-33

Question 21

Describe in broader terms branchiomeric musculature

Answer 21

• During embryonic development muscles may migrate considerable distances in different vertebrates.
• Migration usually occurs after the muscle has been innervated, and the nerve is dragged along with the muscle during migration.
• In all vertebrates, specific cranial nerves are associated with each of the gill arches.

Question 22

Describe the 3+ Branchiomeric Gill Arches

Answer 22

1. Gill arch I (mandibular): Innervated by CN V: (trigeminal nerve).
2. Gill arch II (hyoid): Innervated by CN VII: (facial nerve).
3. Gill arch III: Innervated by CN IX: (glossopharyngeal nerve).

*4ish. Remaining gill arches: Innervated by CN X:(vagus nerve).

See Slide 35

Question 23

Describe the nonmamallian temporomandibular condition joint

Answer 23

• Articulation occurs between quadrate bone (associated with upper jaw) and articular bone (associated with lower jaw)

Question 24

Describe the mammalian condition of the temporomandibular joint

Answer 24

• Synovial joint with an articular disk.
• Articular surfaces are the temporal bone and the mandibular condyle.
• Fate of articular and quadrate bones (both derivatives of Meckel’s cartilage):
• • Quadrate bone moves into middle ear and becomes the incus.
• • Articular bone moves into middle ear and becomes the malleus.
• • Note that the stapes is present in lower vertebrates as the only middle ear bone and is derived from pharyngeal arch II.

I’m suspecting some heavy NTK questioning here.

Question 25

Reference Card

Answer 25

Slide 37 is totally ntk, but will take a minute or two to organize it into flashcards.

As is Slide 39

Question 26

Describe the muscularity of mastications

Answer 26

• All innervated by mandibular branch of CN V.
• Masseter:
- Zygomatic bone to lateral surface of
ramus and coronoid process
- Elevates and protracts mandible
• Temporalis:
- Temporal fossa and fascia to coronoid
process
- Elevates and retracts mandible
• Lateral pterygoid:
- Lateral pterygoid plate and sphenoid to
front of mandible and TMJ
- Protracts mandible; depresses chin
(bilateral; grinding (unilateral)
• Medial pterygoid:
- Lateral pterygoid plate and maxilla to
medial surface of mandible near
angle
- Elevates, protracts, grinding
(unilateral)
- See Slides 42-45