Development_of_the_Musculoskeletal_System_Corrected.pptx

Development of the Musculoskeletal System Dr. Taylor Polvadore Objectives 1. Describe the three different types of cells that will arise from a somite and their relationship to the spinal nerve 2. Describe the development of components of the axial and appendicular skeleton 3. Desc...

Development of the Musculoskeletal System Dr. Taylor Polvadore Objectives 1. Describe the three different types of cells that will arise from a somite and their relationship to the spinal nerve 2. Describe the development of components of the axial and appendicular skeleton 3. Describe development of the limbs from limb bud formation through development of the digits * * Week 5, 35 - 38 days Origin of Skeletal Tissue Paraxial mesoderm (somites) will form posterior skull, vertebral column, ribs Parietal lateral plate mesoderm will form the sternum and appendicular skeleton Neural crest cells will form the craniofacial skeleton  Somites * * Remember the Somites Segmental paraxial mesoderm on either side of neural tube * * * * * * * * * * (Sadler, 2024) Somites Differentiate Epithelization Ventro-medial cells become mesenchymal and form sclerotome (tendon, ligament, and bone) Signal comes from notochord and floor plate of the neural tube Dorso-lateral cells form the dermomyotome, a germinal epithelium e o m t yo m ato rm De (Sadler, 2024)  e m Somites Differentiate at om yo to e rm D Dermamyotome contributes to Ventro-lateral edge and dorso- medial edge again become mesenchymal and form the myotome (muscle) Dermis of the back Note: dermatomes of the skin are not equivalent to the future dermal portion of the dermomyotome (Sadler, 2024)  Innervation of Somites Each somite initiates the growth of one spinal nerve The tissues that form from that one somite (bone, muscle, connective tissue, dermis) will maintain innervation from that original spinal nerve Results in a segmental pattern of adult innervation to skin and muscle (Akbarnia et al., 2010) Innervation of Somites Each somite initiates the growth of one spinal nerve The tissues that form from that one somite (bone, muscle, connective tissue, dermis) will maintain innervation from that original spinal nerve Results in a segmental pattern of adult innervation to skin and muscle Innervation of Somites Each somite will divide (anatomically) into: Epimere: Dorsal ramus Intrinsic bones, muscle, connective tissue of the back Hypomere: Ventral ramus Muscles and connective tissue of the rest of the trunk and limbs (Akbarnia et al., 2010)  Axial and Appendicular Skeleton Axial Skeleton: Vertebrae (Sadler, 2024) Vertebrae: Resegmentation 1. Sclerotome cells organize around the neural tube 2. The cells then split into cranial and caudal halves 3. The caudal half of one sclerotome fuses to the cranial half of the sclerotome below 4. These cells then undergo ossification to form the vertebra (Schoenwolf et al., 2014) Vertebrae: Resegmentation Notochord: disappears from interior of sclerotomal masses differentiating into vertebra precursors and becomes the nucleus pulposus (Sadler, 2024) Clinical Correlation: Congenital Scoliosis Cause: one half of vertebra does not form = (Carlson, 2014) hemivertebra. This causes the column to https://radiopaedia.org/cases/congenital-scoliosis-4 curve laterally (scoliosis). Rib may be missing in area of hemivertebra (but it may also shift down one level; so you may still count 12 ribs) (Sister Wives, 2017) Clinical Correlation: Klippel-Feil Syndrome Cause: process of resegmentation is incomplete and original sclerotomes remain attached Results in fused vertebrae (Shoaib, 2021) Most often occurs in cervical region The classic clinical triad = short neck, low hairline, and restricted neck motion (Carlson, 2014) Axial Skeleton: Formation of Ribs Scleratomes make 12 thoracic vertebral elements These are made up of 3 embryonic primordia (Cochard, 2012) Centrum or body Neural arch Costal process In thoracic region = 12 sets of ribs (Farina et al., 2021) Extra Ribs (Aly et al., 2016)  Axial Skeleton: Sternum The sternum is the only portion of the axial skeleton derived from parietal lateral plate mesoderm (Kumarasamy and Agrawal, 2011) Sternal Foramen (Schoenwolf et al., 2014) Clinical Correlation: Ribs and Sternum When ribs overgrow the sternum: Pectus excavatum Depressed sternum that is sunken posteriorly Pectus carinatum Flattening of the chest bilaterally with an anteriorly projecting sternum Causes abnormal protrusive development of sternum Appendicular Skeleton: Limbs Derived from parietal (somatic) lateral plate mesoderm (Sadler, 2024) Skeletal Muscle Source Somites are the source of ALL skeletal muscle All striated muscle of the body wall and limbs is derived from somites (Sadler, 2024)  Skeletal Muscle Source Muscles derived from epimere are called epaxial muscles Intrinsic back muscles Muscles derived from hypomere are called hypaxial muscles All skeletal muscle except intrinsic back muscles (Sadler, 2024) Skeletal Muscle Source Lateral somitic frontier: Well-defined border between each somite and the parietal lateral plate mesoderm Primaxial domain: contains only somite- derived cells Abaxial domain: Parietal lateral plate mesoderm together with somite cells that have migrated across the lateral somitic frontier See Langman’s Medical Embryology Table 11.1 Lateral somatic frontier  Hypaxial/Epaxial vs Primaxial/Abaxial Lateral somatic frontier (Sefton & Kardon, 2019) Limb Buds Limb buds The upper limbs develop slightly in advance of the lower limbs Week 4: The upper limb bud appears in the lower cervical region Week 5: The lower limb bud (Moore, 2013) appears in the lower lumbar region Each limb bud consists of an outer ectodermal cap and an inner mesodermal core Week 5, 35 - 38 days  Apical Ectoderm Ridge (AER) Signal molecule (FGF-10) from mesoderm signals to overlying ectoderm Signal molecule (FGF-8) from ectoderm signals back to mesoderm to proliferate and maintain FGF10 expression (Sadler, 2024) FGF-8 expression is evident before growth of the limb bud, and becomes isolated to a thin strip of ectoderm on each limb bud: apical ectoderm ridge (AER) Limb Axes Proximal/Distal Axis Dorsal/Ventral Axis The AER sends a distal signal The dorsal side has Lmx-1 (homeobox gene) The ventral side blocks the Lmx-1 so that it cannot be expressed. Therefore, there is no signal on the ventral side (Schoenwolf et al., 2014) Cranial/Caudal Axis Zone of polarizing activity (ZPA) Located in the mesenchyme of caudal area of the limb bud Produces a “caudal” signal via (Schoenwolf et al., 2014) Sonic hedgehog (SHH) Morphogenetic gradient High SHH: the pinky side Low SHH: the thumb side (Schoenwolf et al., 2014) Differentiation of Limb Bones Limb bones originate in a proximal to distal fashion 1. Stylopod (proximal): humerus and femur 2. Zeugopod (intermediate): radius/ulna and tibia/fibula 3. Autopod (distal): carpals, metacarpals, phalanges, tarsals, metatarsals Limb bones are endochondral ossification (bone is formed from a cartilage base) (Sadler, 2024) Limb Patterning: Digital Rays Week 5: flattened hand and foot plates (Moore, 2013) Week 6: 5 rays appear in each hand and foot Digital rays form from apoptotic cell death along AER; stimulates growth of 5 different regions (fingers/toes) Week 8: Discreet, completely separated digits form from the 5 rays of each hand and foot (Sadler, 2024) Limb Rotation Upper Limb: Rotates 90° laterally Extensor muscles on lateral and posterior surface and the thumbs is lateral Lower Limb: Rotates 90° medially Extensor muscles on the anterior surface and the big toe medially Dorsal becomes anterior (dorsal surface of foot) Rotation isn’t finished until you’re walking (Schoenwolf et al., 2014) Dermatomes Segmental regions of skin mainly supplied by a single spinal nerve (sensory) The limb rotation causes the originally straight segmental pattern of lower limb innervation to twist into a spiral Umbilicus = T10 Limb Innervation: Sensory (cutaneous) (Moore, 2013) Radial Arrangement of Upper Limb Dermatome Innervation Limb Innervation: Motor Longitudinal Arrangement of Upper Limb Myotomal Innervation  Clinical Correlation: Limb Defects Cause: defect in the signaling from the apical ectodermal ridge 1. Amelia = complete absence of a limb 2. Meromelia = partial absence of a limb 3. Phocomelia = absence of long bones of limb 3 2 1 (Chawla & Marwah, 2014) (Mesfin et al., 2022) (Teko et al., 2022) Clinical Correlation: Limb Defects Brachydactyly (Jamsheer, 2016) Shortened digits Cause: insufficient AER-induced proliferation of mesoderm Syndactyly Fused digits www.rebeccasyumd.com/ Cause: insufficient apoptotic cell death syndactyly.html) between digital rays (Mujalda et al., 2023) Polydactyly (https:// Extra digits Cause: additional sites of apoptotic cell death Clinical Correlation: Limb Defects Ectrodactyly Missing digit www.independent.co.uk Cause: missing site of apoptotic cell death. Cleft foot (or hand); lobster claw anomaly Ectrodactyly of the third digit Syndactyly of digits 1/2 and 4/5 (Singh, 2021) Hand Hand Feet Questions? Physical Office: 332 Zoom office: https://burrell-edu.zoom.us/j/4259144314 [email protected]