Embryology of the Skeletal and Muscular Systems

Comprehensive vocabulary review flashcards covering embryonic bone and muscle morphogenesis, skeletal dysplasias, craniosynostosis syndromes, and congenital musculoskeletal abnormalities.

Somites

Segmented cuboidal blocks of paraxial mesoderm that appear during the third week of embryogenesis along the dorsolateral surface of the embryo, serving as the first part of the skeleton to develop.

Sclerotome

The ventromedial portion of a somite composed of loosely woven mesenchyme that differentiates to form the vertebrae and the ribs.

Dermomyotome

The dorsolateral region of a somite that splits into the dermatome, which forms fibroblasts of the skin, and the myotome, which gives rise to muscle-forming myoblasts.

Osteogenesis

The biological process of bone formation.

Intramembranous Ossification

Bone development where mesenchyme condenses within pre-existing membranous sheaths and directly ossifies into bone without the prior formation of a cartilage model, characteristic of skull flat bones.

Endochondral Ossification

Bone development wherein mesenchymal cells first create a cartilage model that is subsequently calcified and replaced by bone tissue, typical of limb and long bones.

Hyaline Cartilage

The most widely distributed cartilage type in the human body, commonly located at articular surfaces of joints and the junctions between ribs and sternum.

Fibrocartilage

A dense, fibrous cartilage type found in high-stress weight-bearing areas such as the intervertebral discs and the pubic symphysis.

Elastic Cartilage

A pliable, flexible cartilage type characterized by elasticity, exemplified by the cartilaginous framework of the external ear.

Diaphysis

The central shaft of a developing long bone containing the primary center of ossification.

Epiphysis

The extremity of a long bone that remains largely cartilaginous at birth and later develops secondary ossification centers at the growth plates.

Periosteum

A dense, vascular layer of connective tissue that encases the outer surfaces of bones (excluding joint articulations) to provide structural support.

Rickets

A metabolic bone disease resulting from deficient calcium, phosphorus, or vitamin D receptor defects, leading to disoriented chondrocytes at the growth plate, bowed limbs, and delayed fontanelle closure.

Hypophosphatemic Rickets

An X-linked dominant hereditary disorder characterized by inadequate blood phosphate levels and disrupted bone mineralization.

Synovial Joint

A specialized fluid-filled joint surrounded by a fibrous capsule and ligaments, whose internal synovial membrane secretes lubricating fluid to eliminate friction.

Nucleus Pulposus

The gelatinous central core of an intervertebral disc that originates from the expansion of embryonic notochord tissue between adjacent vertebrae.

Chordoma

A rare invasive neoplasm that arises from persistent remnants of embryonic notochord that failed to degenerate, typically developing in the nasopharyngeal or lumbosacral regions.

VACTERL Association

A congenital disorder linked to Notch pathway mutations featuring Vertebral anomalies, Anal atresia, Cardiac defects, Tracheoesophageal fistula, Esophageal atresia, Renal anomalies, and Limb defects.

Hemivertebra

A developmental failure of one lateral half of a vertebral body to form, recognized as the most common underlying cause of congenital scoliosis.

Klippel-Feil Syndrome

A vertebral developmental anomaly defined by congenital fusion of the cervical vertebrae, presenting clinically with a short neck, low posterior hairline, and restricted neck movement.

Myeloschisis

The most severe and lethal form of spina bifida, characterized by complete failure of neural tube closure leaving open, cleft neural arches and exposed neural tissue.

Pectus Excavatum

A congenital anterior chest wall deformity characterized by a concave depression of the lower sternum, accounting for approximately $90\%$ of thoracic wall defects.

Pectus Carinatum

An anterior chest deformity characterized by an outward protrusion of the sternum and costal cartilages, commonly referred to as pigeon chest.

Acrania

A lethal neural tube defect resulting from failure of the rostral neuropore to close during the fourth week, leading to complete absence of the calvaria, forebrain, and midbrain.

Microcephaly

A neurodevelopmental disorder wherein impaired central nervous system and brain growth leads to an abnormally small cranium and mental deficiency, with normal facial dimensions.

Craniosynostosis

The premature prenatal fusion of one or more cranial sutures, which forces compensatory skull enlargement and alters head shape.

Scaphocephaly

The most frequent form of craniosynostosis, caused by early closure of the sagittal suture, producing an elongated, narrow, wedge-shaped cranium.

Brachycephaly

A cranial anomaly resulting from the premature fusion of both coronal sutures, resulting in a short, wide skull with a high forehead and frontal bossing.

Apert Syndrome

An autosomal dominant craniosynostosis syndrome caused by FGFR2 mutations, marked by brachycephaly, proptosis, midface hypoplasia, and severe bony syndactyly of the hands and feet.

Crouzon Syndrome

An autosomal dominant craniosynostosis syndrome linked to FGFR2 and FGFR3 mutations, characterized by proptosis, midface hypoplasia, and premature suture fusion without limb involvement.

Pfeiffer Syndrome

A craniosynostosis condition associated with FGFR1, FGFR2, or FGFR3 mutations, frequently presenting with cloverleaf skull deformity, proptosis, and minor limb defects.

Saethre-Chotzen Syndrome

An autosomal dominant craniosynostosis disorder linked to mutations in the TWIST gene or FGFR3, presenting with coronal synostosis, ptosis, and syndactyly without severe visceral defects.

Apical Ectodermal Ridge

A specialized band of ectodermal tissue located at the distal rim of the embryonic limb bud that directs limb outgrowth and induces differentiation of the underlying mesenchyme.

Clavicle

The first bone in the human body to begin ossification, initially forming via intramembranous ossification before developing cartilaginous zones at both ends.

Rhizomelia

Disproportionate congenital shortening affecting the proximal segments of the limbs, specifically the humerus and femur.

Achondroplasia

An autosomal dominant form of dwarfism caused by a G380R mutation in FGFR3, characterized by rhizomelic limb shortening, macrocephaly, midface hypoplasia, and trident hands.

Thanatophoric Dysplasia

A lethal skeletal dysplasia caused by FGFR3 mutations, characterized by severe micromelia, telephone-receiver femurs, a narrow thoracic cage causing pulmonary hypoplasia, and cloverleaf skull.

Cretinism

A condition caused by untreated congenital hypothyroidism or maternal iodine deficiency, resulting in stunted skeletal growth and severe mental deficiency.

Poland Sequence

A congenital condition marked by unilateral hypoplasia or absence of the pectoralis major muscle (affecting the right side in over $75\%$ of cases), frequently accompanied by ipsilateral syndactyly.

Arthrogryposis

A heterogeneous disorder characterized by multiple congenital joint contractures affecting multiple limbs, typically secondary to oligohydramnios and restricted intrauterine fetal movement.

Torticollis

A congenital or birth-trauma neck deformity resulting from injury, hematoma, or fibrosis of the sternocleidomastoid muscle, producing ipsilateral head tilting and restricted rotation.

These Fibrous gaps allow the skull to change shape during the birthing process

Fontanelles are soft spots on an infant's skull that consist of fibrous connective tissue, allowing the bones to move and overlap during delivery.

The incidence rate of a birth which is 2-4x more common in girls than boys and always associated with Acrania. Very rarely associated with other defects.

1/1000

what causes rickets

Vitamin D deficiency and Phosphorous

How many pairs of true, false, and floating ribs are there?

7 true, 5 false, 2 floating ribs in the human skeleton.

Ossification that occurs in the mesenchyme within pre-existing membranous sheaths

Intramembranous ossification

Mesenchymal models are transformed into cartilage bone models which later become ossified during what process?

Endochondral Ossification is the process.

Name the 3 types of cartilage

Hyaline, elastic, and fibrocartilage.

T/F the absence/ variation of muscles is common and usually is clinically insignificant

True

The most severe type of NTD: Spinal cord in affected area is completely open causing a flattened mass of nerve tissue

Myeloschisis

The pectoral girdle, pelvic girdle, and limb bones are all part of the?

Appendicular skeleton

Absence of pectoralis major is the primary issue in what autosomal dominant condition

Poland syndrome

Unlike the skeletal muscles, which are formed from the myotome, cardiac and smooth muscles are formed from which region of the somites?

Splanchnic Mesoderm

Name 3 teratogens and a potential birth defect that they could cause?

Alcohol—Fetal alcohol Syndrome

Smoking—Cleft lip/palate

Seizure Medication —Open Neural Tube Defects

Thalidomide—Limb Reduction Defects

Which structures form the craniocaudal sequence for the embryo and are the origin of most of the axial skeleton and associated musculature?

Somites

What is a congenital heart defect associated with: Pulmonary stenosis, right ventricular Hypertrophy, Overriding aorta and ventricular septal defect

Tetralogy of Fallot

How many umbilical arteries/veins are there, and where do they originate from?

2 arteries from fetus, 1 vein from chorionic villi of placenta and returning to the fetus.

Advanced maternal age is associated with

increased risk of chromosomal abnormalities and pregnancy complications.

Advance paternal age is associated with

Single gene disorders, increased risk of conditions such as autism and schizophrenia.

A woman has one 15 year old boy with one partner, a set of twins 12 year old girls with another. With her first partner she had 2 miscarriages at 12 weeks, and a pregnancy that ended in fetal demise at 25 weeks. She’s also had one abortion <12 weeks. Notate her Pregnancy Hx.

G:6 P:4 SAB:2 TAB:1 L:3

Blank —- is an AD disorder characterized by abnormal facies including a small jaw, ear anomalies including hearing loss, ocular and ophthalmic defects and facial clefts

Treacher Collins syndrome

Two Notch Signaling Pathway Conditions

CHARGE and VACTERL

Names 3 features of VACTERL

Vertebral defects,

Anorectal malformations,

Cardiac anomalies

Esophageal Atresia

Limb defects

Describe all clinical features of CHARGE association

Craniofacial

Heart disease

Atresia Choanae

Retardation of Growth

Genital anomalies

Ear anomalies