Development Of The Muscular System Flashcards
Paraxial mesoderm
Somites become…
- myotome (muscle)
- Scleratome (axial skeleton)
- dermatome (dermis)
Intermediate mesoderm
Urogenital, becomes…
- Kidneys
- gonads
Lateral plate mesoderm
Connective tissue, like…
- blood
- lymph
- mesenteries
- cardiovascular
Somites line up along the neural fold, can be used to what?
Counting Somites can be used to determine the age of the embryo
Two parts of the Somite
- Dorsolateral»dermatome + myotome
2. Ventromedial»scleratome ( will migrate around notochord and neural tube.
Describe the two paths for bone development to the axial skeleton.
- Scleratome»mesenchyme»bone
- called intramembranous ossification
- flat bones of skull, many face bones, and clavicle - Scleratome»mesenchyme»hyaline cartilage»bone
- called endochondral ossification
- long bones, pelvis, pectoral girdle
Formation of the vertebral column
- Caudal dense portion fuses with cephalic loose portion of the Scleratome inferior to it
- neural tube sends nerves out between the newly formed vertebra and attach to myotome
- newly innervated muscle attach to vertebra above and below
What parts of the vertebral column are formed by which parts of the scleratome?
Caudal dense—forms superior body and spinous process
Cephalic loose—forms inferior vertebral body
Intervertebral discs have two parts.
What are they made from?
- Nucleus pulposus
- made of notochord
- notochord expands, degenerates, and globs up
- creates a mucoid substance - Annulus fibrosis
- fibrous tissue from the scleratome
- encircles the globs of degenerating nototchord
Formation of ribs
- scleratome cells that grow out from the costal processes of the thoracic vertebra
- costal cartilage also comes fro the scleratome
Formation of the sternum
- develops in the somatic lateral plate mesoderm
- sternal bars start as mesenchymal condensations
- sternal bars fuse together to become sternum
Cervical ribs
- contribute to thoracic outlet syndrome
- brachial plexus can become compressed leading to motor and sensory issues
Pectus cariatum
- sternum protrusion
- “pigeon chest”
- no deficits, only cosmetic
- boys more affected
- becomes more pronounced as puberty progresses
Pectus excavatum
- sternum depression
- “funnel chest”
- can compress and shift hear to the left
- complications include SOB, pain, fatigue, exercise intolerance
- on a spectrum, can be mild or severe.
Hox genes
Genes that control the body plan along the cranio-caudal axis
Gain of function of hox genes leads to what?
Caudalization
- changes in the combinatorial code, results in transformation of the vertebrae
- ex. If hox 6, which usually is for C6-T6, extends up pinto C4+ C5, those cervical vertebra will appear more thoracic
Loss of function of hox genes leads to what?
- cranialization
- changes in the combinatorial code, results in transformation of the vertebrae
- ex. If hox 5, which usually plans C3-T2, is deleted, all of those vertebrae will appear more cervical in nature.
The dorsolateral part of the paraxial mesodermal somite, becomes the dermatome and the myotome.
The myotome gives rise to two different structures, what are they and what do they become?
- Epimere
- give rise to epaxial muscles (true muscles of the back)
- innervated by dorsal rami - Hypomere
- hypaxial muscles (all other muscles)
- innervated by ventral rami
Epaxial muscles
- form extensor muscles of neck and vertebral column
Hypaxial muscles
- cervical myotome: scalene, prevertebral, genioohyoid, infrahyoid muscles
- thoracic myotome: lateral and ventral flexor muscles of the vertebral column (obliques, rectus abdominus)
- lumbar myotome: quadratus lumborum
Sacrococcygeal myotome: muscles of pelvic diaphragm
Poland syndrome
- complete or partial absence of pec major/ pec minor
- due to absence of migration of cells of hypomere into chest
- can also lead to absence of ribs 2-4
- often associated with syndactyly (fusion of digits)
Prune belly syndrome
- partial or complete absence of abdominal musculature
- primarily affect males
- associated with cryptochidism(failure of one or both testicles to descend) and malformation of urinary tract/bladder»> urethral obstruction
- caused by abnormal migration of hypomere cells.
