Muscular System Flashcards
myogenic cells are influenced by what?
signalling factors in neural tube, notochord and ectoderm
Where are myogenic cells derived from?
paraxial mesoderm
Myotubes develop as what fuse?
myoblasts
How are myofibers formed?
from myofibrils which are produced in myotubes
Do fibroblasts develop from this mesenchyme?
yes - produce CT of mm
When does most skeletal mm develop?
prior to birth
What is Epaxial division?
extensors of the neck and back
innervated by dorsal 1* ramus of each spinal n.
What is hypaxial division?
cervicals = scalenes, prevert, geniohyoid, infrahyoids, upper limb mm.
thoracics= intercostals, abd. obliques, rectus abdominis
lumbars = QL, iliopsoas, some lower limb mm
sacral = pelvic diaphragm, sphincters, some lower limb mm
- innverated by ventral 1* ramus of spinal n.
How are myotome fibers oriented originally?
craniocaudally
Can a myotome split?
yes - drags n with it and forms 2 separate mm
how are non segmental trunk mm formed?
derived from myotomes at multiple levels that fuse together
What happens when a mm degenerates?
forms CT sheets or aponeurosis
What does splanchnic mesoderm of smooth mm. give rise to?
mm layers in gut derivatives
What does somatic mesoderm of smooth mm give rise to?
tunica media of blood vessels and lymphatics
What is special about smooth mm?
- cells differentiate but dont fuse together
- form sheets or bundles of cells
- acquire autonomic innervation
- produce collagen and elastic fibers
What does splanchnic mesoderm of cardiac mm give rise to?
cardiac myoblasts
What forms when cardiac myocytes come in contact?
intercalated discs
What are some skeletal mm anomalies?
- variation in form, position and/or attachment
- accessory mm develop occasionally
- absence of one or more mm
- more common bilaterally
What is arthrogyroposis multiplex congenital?
- congenital stiffness of 1+ joints
- due to hypoplasia of assoc. mm.
- mm replaced by fat and fibrous CT
What is torticollis?
unilateral shortening of SCM
- head lat. flex and look up and away from affected side
myofibers die and replaced by fibrous CT
