Anatomy TBL 3

3 types of muscle tissue

1. skeletal

2. cardiac

3. smooth

what is the germ layer origin of skeletal muscle?

paraxial mesoderm (myotomes)

what is the germ layer origin of cardiac muscle?

viceral/splanchnic lateral plate mesoderm

what is the germ layer origin of smooth muscle?

multiple sources

• visceral/splanchnic lateral plate mesoderm

• NCC: large arteries and coronary arteries of heart

what is the exception of the germ layer origins of smooth muscle?

pupillary, mammary gland and sweat glands come from ECTODERM

• do not come from mesoderm like most other smooth muscle

• glands come from invagination in surface ectoderm

• pupillary muscles come from neural ectoderm of the optic cup

skeletal muscle formation in week 5

myoblast cells fuse to form myotubes

skeletal muscle formation by end of 3rd month

myofibrils and striations form

tendon formation

tendons = NOT muscle

• from sclerotome

¾ of tissue types are formed from what embryologically?

MESODERM

• all except for nervous

mesoderm divides into separate areas on each side of the embryo

• axial

• paraxial

• intermediate

• lateral plate

axial mesoderm

not bilateral- at midline

• becomes notochord

paraxial mesoderm

• paired

• form somitomeres first → commit to cellular pathway

• compacted somitomeres → somites

intermediate mesoderm

lateral plate mesoderm

• somatic (parietal)

• visceral (splanchnic)

somatic (parietal) lateral plate mesoderm

visceral (splanchnic) lateral plate mesoderm

embryonic folding will do what?

bring ectoderm and amniotic cavity around entire embryo

• endoderm folds into tube

humans are coelomates

have body cavities

somitomeres

formed from paraxial mesoderm

• commit to cellular pathway

somites

week 3-4

• 42-44 pairs

• used to stage development

• 7 cranial unnumbered and do not become somites, remain somitomeres

how does a somite form

paraxial mesoderm → somitomere → somite

3 regions of somite

week 4-5

• sclerotome

• myotome

• dermatome

sclerotome

myotome

dermatome

eye muscle somitomere source

where is the somitomere source of pharyngeal arch muscles?

CN I-IV

what is the somitomere source of occipital myotomes

where is the somitomere source for cervical myotomes?

C1-T1

where is the somitomere source of thoracic myotomes?

T1 and below

mesenchymal condensation of limb bud

limb axis

epithelial ridge

role of somites

formation of a myotome and the somitic frontier

which cells migrate ventrally?

ventrolateral and dorsomedial cells of the somite migrate ventrally

which cells migrate to the lateral somitic frontier

some cells of the ventrolateral group migrate to the lateral somitic frontier into the parietal lateral plate mesoderm

lateral somitic frontier

separates the somite from the parietal lateral plate mesoderm

primaxial domain [separated by lateral somatic fronteir] abaxial domain

primaxial domain

• myotome cells from somite

• around the neural tube

• neural tube and notochord give developmental signals for muscle formation

primaxial domain: dermis from where?

dermatome

primaxial domain produces what?

• scalenes

• intercostals

• rhomboids

• levator scapulae

• latissimus dorsi

abaxial domain

• migrated somitic ventrolateral cells

• lateral plate mesoderm gives developmental signals for muscle formation

abaxial domain: dermis from where?

lateral plate mesoderm

abaxial domain produces what?

• pectoralis major and minor

• abdominal muscles (all 4)

• distal upper limb muscles

• all lower limb muscles

epaxial

above the axis

hypaxial

below the axis

epaxial muscles

• innervated by dorsal rami of spinal nerves

• intrinsic back muscles

hypaxial muscles

• innervated by ventral rami of spinal nerves

• body wall and limb muscles

myotomes receive innervation from where?

spinal nerves of the same segment of their somitic origin

upper limb is associated with which myotomes?

C5-T1 myotomes

lower limb is associated with which myotomes?

L4-S3 myotomes

dorsal and ventral muscle masses form in each limb

• dorsal = extensors

• ventral = flexors

for limb and girdle muscles, what happens when original location changes?

limb rotation

myogenic cells

myogenic cells that form muscles migrate to pharyngeal arches first

• from cranial somites and somitomeres

• use neural crest cells to guide cells to arches

head and neck muscle innervation

cranial nerves form connection with muscle in arches, prior to migration out of arches

arch 1 is innervated by:

CN V

arch 2 is innervated by:

CN VII

arch 3 is innervated by:

CN IX

arch 4/6 is innervated by:

CN X

pharyngeal arch muscles

1-2: muscles to open jaw and middle ear muscles

1-4: tongue

arch 1

muscle of mastication

arch 2

muscle of facial expression

arch 3

stylopharyngeus muscle

arch 4/6

muscle of soft palate, pharynx, larynx

germ layer origin of cardiac muscle

splanchnic lateral plate mesoderm

myoblasts do not fuse…

instead form special junctions called intercalated discs

what is the germ layer origin of smooth muscle in large arteries

lateral plate mesoderm and NCC

what is the germ layer origin of smooth muscle in coronary arteries

proepicardial cells and NCC

what is the germ layer origin of smooth muscle in gut wall and derivatives

splanchnic lateral plate mesoderm

what is the germ layer origin of smooth muscle in pupil/mammary gland/sweat glands

ectoderm