skeletal muscle development of fetus embryonic growth

Skeletal muscle formation of fetus, embryology

1. Skeletal&muscular system Presented by : Rashad jaber, Maria haj, Shahba Mahmood, Arian radmehr

2. Introduction The skeletal system develops from mesenchyme, which is Mesodermal in Origin. Mesenchyme or the embryonic Connective Tissue migrate to form : Chondroblasts Osteoblasts Fibroblasts

3. Development of the Skeletal System Source of Origin: Paraxial Mesoderm Lateral plate Mesoderm Neural Crest Cells Paraxial mesoderm forms a segmented series of tissue blocks on each side of the neural tube, the 'Somites'. These somites differentiate into a; Sclerotome, (ventromedial part)  Dermomyotome , (dorsolateral part )

4. The skeletal m. starts after gastrulation

5. The skeleton : The skeletal m. divided into two parts : Axial skeleton Appendicular skeleton

6. Origins of the Axial & Appendicular Skeleton The mesenchyme in the paraxial mesoderm will transform into Osteoblasts that will form the bony elements of the vertebral column (e.g. body, transverse process, spinous process etc). The mesenchyme in the somatopleuric mesoderm will transform into osteoblasts that will form the Pelvic & Pectoral girdles and also the bones of upper & lower limbs.

7. Ossification Bone develops through two types of ossifications: Membranous Ossification, in which mesenchymal tissues will directly convert into bone ,eg flat bones of the skull. Endochondral Ossification, in which mesenchymal tissues first give rise to hyaline cartilaginous model of the bone and then, the osteoblasts convert them into the bone, eg Long bones, Vertebra.

8. Formation of Axial Skeleton

9. Development of the skull The Neurocranium; is the upper and and back part of the skul which forms a protective case around the brain . The Viscerocranium; the skeleton of the face

10. Neurorocranium Membranous neurocranium Formed by intramembranous ossification Mesenchymal cells are derived from neural crest and paraxial mesoderm Cells then encircle the brain and form most of the flat bones of the skull

11. Neurocranium The cartilaginous neurocranium (chondrocranium) Formed by a combination of mesodermal sclerotome and neural crest cells Cartilage are form around the brain beginning at the notochord Parachordal cartilage and the occipital sclerotomes fused to form the base of occipital bone While the sphenoid and ethmoidal bones are formed from the hypophysial cartilage and the trabeculae cranii All these pieces of bones fuse with each other to form a strong base of the skull, expect for the openings via which the cranial nerves leaves the skull

12. Viscerocranium Membranous Viscerocranium Dorsal portion Undergoes intramembranous ossification and gives rise to the maxilla, the zygomatic bone, the squamous temporal bones, the vomer and the palatine bone Ventral portion c ontains the Meckel's cartilage This region become surrounded by mesenchymal cells that condenses and ossifies by membranous ossification to form the mandible

13. Viscerocranium Chondral Viscerocranium Dorsal portion Forms the malleus and incus (Meckel's cartilage) Forms the stapes and the styloid process (Reichert's cartilage) Ventral portion Ossifies and forms the lesser cornu and the upper body of the hyoid bone Forms the greater cornu and lower body of the hyoid bone

14. Craniofacial Defects and Skeletal Dysplasias 1- Cranioschisis 2- Croniosynostosis Clinical correlations:

15. Hypochondroplasia Thanatophoric dysplasia Achondroplasia (ACH) Generalized Skeletal Dysplasia Cleidocranial dysostosis Clinical correlations:

16. Clinical correlations: Acromegaly caused by congenital hyperpituitarism and excessive production of growth hormone. Microcephaly abnormality in which the brain fails to grow and the skull fails to expand

17. Vertebra The vertebral column and ribs develop from the sclerotome compartments of the somite's, and the sternum is derived from mesoderm in the ventral body wall. A definitive vertebra is formed by condensation of the caudal half of one sclerotome and fusion with the cranial half of the subiacent sclerotome.

18. A typical vertebra consists of a vertebral arch and foramen (through which the spinal cord passes), a body, transverse processes, and usually spinous process. During the fourth week, sclerotome cells migrate medially and surrounds the notochord. The mesenchyme then extends backward on either side of the neural tube and surrounds it.

19. Extensions of this mesenchyme also take place laterally forming transverse processes, and ventrally in the body wall, forming ribs. Mesenchymal cells from the sclerotomes, also migrate cranially to surround the notochord, where they form the intervertebral disc. As development progresses, the notochord degenerates and disappears. Between the vertebrae, the notochord expands to form the gelatinous center of the intervertebral disc - the nucleus pulposus. This nucleus is later surrounded by circularly arranged fires that form the anulus fibrosus. The anulus fibrosus and nucleus pulposus together constitute the intervertebral disc.

20. VERTEBRAE AND THE VERTEBRAL COLUMN Spinal nerves lie near the intervertebral discs and leave the vertebral column through the intervertebral foramina

21. VERTEBRAE AND THE VERTEBRAL COLUMN Two primary curves of the spine are established: thoracic and sacral curvatures Later, two secondary curves are established: 1.cervical curvature- child learns to hold up his or her head 2.lumbar curvature- child learns to walk

22. Vertebral defects 22 Scoliosis Klippel-Feil syndrome

23. Spina bifida

24. Ribs and Sternum Ribs are formed from the ventral extensions of the sclerotomic mesenchyme that form the vertebral arches. The Sternum is formed from the two sternal bars on either side of the midline.

25. Formation of Limbs The bones of the limbs, including the bones of the shoulder and pelvic girdles, are formed from mesenchyme of the limb buds. With the exception of the clavicle (which is a membrane bone), they are all formed by endochondral ossification.

26. The limb buds are paddle-shaped outgrowths that arise from the side wall of the embryo at the beginning of the 2nd month of intrauterine life . Each bud is a mass of mesenchyme covered by ectoderm. The mesenchyme of limb buds is derived from the parietal layer of the lateral plate mesoderm. This mesenchyme gives rise to bones, connective tissue and some blood vessels. The muscles of the limbs are derived from myotomes of somites which migrate into the limbs.

27. Muscular System Development The formation of the muscular system begins about 4Th week of embryonic development. The beginning cells are called Myoblasts Most of the muscular system develops from the mesodermal germ layer Except some smooth muscle tissues (pupil, sweat glands and mammary gland differentiate from ectoderm)

28. Skeletal muscles are derived from paraxial mesoderm, this forms; Somites from the occipital to the sacral regions Somitomeres in the head Smooth muscles differentiate from splanchnic mesoderm surrounding the gut and its derivatives. Cardiac muscles are derived from splanchnic mesoderm surrounding the heart tube

29. Striated Skeletal Musculature Musculature of the head, axial skeleton and body wall are formed by Somites and somitomeres From the occipital region caudally, somites form and differentiate into; Sclerotome Dermatome Two muscle-forming regions One in the dorsolateral region of the somite provides progenitor cells for limb and body wall musculature (hypomeric) The other in the dorsalmedial region forms the myotome (epimeric musculature

30. Patterning of Muscles  Patterns of muscle formation are controlled by connective tissue into which myoblasts migrate In the head region these connective tissues are derived from neural crest cells; in cervical and occipital regions they differentiate from somitic mesoderm; and In the body wall and limbs they originate from somatic mesoderm

31. Derivatives of Precursor Muscle Cells By the end of the 5th week prospective muscle cells are collected into two parts:  Epimere (small dorsal portion) - innervated by the dorsal primary ramus Hypomere (larger ventral part) - innervated by the ventral primary ramus Myoblasts of the epimeres form the extensor muscles of the vertebral column, and those of the hypomeres give rise to muscles of the limbs and body wall

32. Myoblasts from cervical hypomeres form the scalene, geniohyoid, and prevertebral muscles. Those from thoracic segments split into three layers, which in the thorax are represented by:- External Intercostal Internal Intercostal Innermost Intercostal In the abdominal wall these three muscle layers consist of the external oblique, the internal oblique, and the transversus abdominis muscles.

33. Myoblasts from the hypoblast of lumbar segments form the quadrates lumborum muscle Those from sacral and coccygeal regions form the pelvic diaphragm and striated muscles of the anus. A ventral longitudinal column arises at the ventral tip of the hypomeres. This column is represented by the rectus abdominis muscle and the infrahyoid musculature

34. Head Musculature  All voluntary muscles of the head region are derived from paraxial mesoderm ( somitomeres and somites ); Including muscle of the tongue, eye (except that of the iris, which is derived from optic cup ectoderm), and that associated with the pharyngeal (visceral) arches. Patterns of muscle formation in the head are directed by connective tissue elements (Neural crest cells)

35. Trunk musculature 1. Trunk musculature is derived from myotomes in the trunk region. Each myotome partitions into a dorsal epimere and a ventral hypomere . a. Epimere - develops into the extensor muscles of the neck and vertebral column (erector spinae). ii. The epimere is innervated by dorsal rami of spinal nerves. b. Hypomere- develops into the scalene, prevertebral, geniohyoid, infrahyoid,intercostal , abdominal muscles, lateral and ventral flexors of the vertebral column, quadratus lumborum, and pelvic diaphragm. ii. The hypomere is innervated by ventral rami of spinal nerves .

36. LIMB MUSCULATURE 1. Limb musculature is derived from myotomes ( somites ) in the upper limb bud region and lower limb bud region. 2. This mesoderm migrates into the limb bud and forms a posterior condensation and an anterior condensation . a. Posterior condensation- develops into the extensor and supinator musculature of the upper limb and the extensor and abductor musculature of the lower limb. b. Anterior condensation- develops into the flexor and pronator musculature of the upper limb and the flexor and adductor musculature of the lower limb.

37. SKELETAL MUSCLE AND TENDONS During differentiation, precursor cells, the myoblasts , fuse and form long, multinucleated muscle fibers. Myofibrils soon appear in the cytoplasm, and by the end of the third month , cross-striations, typical of skeletal muscle, appear. A similar process occurs in the seven somitomeres in the head region rostral to the occipital somites . However, somitomeres never segregate into recognizable regions of sclerotome and dermomyotome segments prior to differentiation. Tendons for the attachment of muscles to bones are derived from sclerotome cells lying adjacent to myotomes at the anterior and posterior borders of somites . The transcription factor SCLERAXIS regulates development of tendons.

38. Striated muscle development

39. smooth muscle development The smooth muscle of the gut and cardiac muscle forms from splanchnic mesoderm , whereas the smooth muscle contributing to blood vessels and hair follicles arises locally within the mesoderm . Smooth muscle can also form from neural crest cells . For example, the iris and ciliary muscles are derived from cranial neural crest cells , as is the smooth muscle of the dermis of the head and neck.

40. SMOOTH MUSCLE Smooth muscle for the dorsal aorta and large arteries is derived from lateral plate mesoderm and neural crest cells . In the coronary arteries, smooth muscle originates from proepicardial cells and neural crest cells (proximal segments). Smooth muscle in the wall of the gut and gut derivatives is derived from the visceral layer of lateral plate mesoderm that surrounds these structures. Only the sphincter and dilator muscles of the pupil and muscle tissue in the mammary and sweat glands are derived from ectoderm . Serum response factor (SRF) is a transcription factor responsible for smooth muscle cell differentiation. This factor is upregulated by growth factors through kinase phosphorylation pathways. Myocardin and myocardin -related transcription factors (MRTFs) then act as coactivators to enhance the activity of Serum response factor , thereby initiating the genetic cascade responsible for smooth muscle development.

41. CARDIAC MUSCLE Cardiac muscle develops from visceral mesoderm surrounds the endocardium of the primitive heart tube and becomes the myocardium. Myoblasts adhere to one another by special attachments that later develop into intercalated discs . Myofibrils develop as in skeletal muscle, but myoblasts do not fuse. During later development, a few special bundles of muscle cells with irregularly distributed myofibrils become visible. These bundles, Purkinje fibers, form the conducting system of the heart.

42. Prune belly syndrome

43. Poland syndrome

44. Congenital torticollis

45. Duchenne muscular dystrophy (DMD)

46. Question #1 The lumbar curvature of the spinal cord – Is pathological and can interrupt the child's development Develops as the child learns to walk Is one of the primary curves of the spine Develops as child learns to hold up his or her head

47. spina bifida can be prevented by: This condition is a severe congenital disease it can not be prevented The mother should drink a glass of wine every day to provide anti- oxidants to the baby during pregnancy folic acid supplementation prior to conception by a-fetoprotein supplementation prior to conception Question #2

48. Question #3 Somites differentiate into : Sclerotome Myotome Dermatome All of the above

49. Congenital torticollis affecting which muscle : Pectoralis major Supraspinatos Sternocleidomastiod Thyrohiod Question #4

50. Question #5 Posterior condensation of the limbs develops into : the flexor muscles Pronator musculature Extensors and supinator muscles Adductor muscles