Embryology of the muscular system.22.pptx

Embryology lecture notes
Development of the heart
2nd week of development
3rd week of development

1. Embryology of the muscular system D. Ndhlovu

2. Expected learning outcomes When you have completed this section, you should be able to Describe the Development of Skeletal Muscles Myogenesis (muscle formation) of skeletal muscle Development of Skeletal Muscles in Different Regions of the Body 2. Describe the Development of Smooth (Involuntary) Muscles Myogenesis of the Smooth Muscle 3. Describe the Development of Cardiac Muscle Myogenesis of the Cardiac Muscle 4. Clinical correlation

3. All muscles of the body develop from mesoderm except muscles of iris, arrector pili of skin, and myoepithelial cells of glands, which develop from ectoderm Muscles are classified into 3 types: skeletal (striated action voluntary ) smooth (unstriated action involuntary ) Cardiac (striated action involuntary)

4. 1. skeletal muscles mostly develop from somites (paraxial mesoderm) 2. smooth muscles mostly develop from splanchnic intraembryonic mesoderm 3. cardiac muscle develops from splanchnic intraembryonic mesoderm surrounding developing heart tube

5. Development of Skeletal Muscles skeletal muscles of axial skeleton, body wall, limbs, and head develop from somites and somitomeres that extend from occipital to sacral region somite differentiates into two distinct zones: sclerotome and dermomyotome Sclerotome forms bones of axial skeleton dermomyotome consists of two components: a deeper part called myotome and a superficial part called dermatome Myotome forms muscular tissue dermatome forms dermis of skin

6. Muscles of eyeball (extraocular muscles) develop from preotic myotomes muscles of tongue from occipital myotomes muscles of limbs from myotomes present in upper and lower limb bud regions muscles of the body wall from myotomes in the trunk region

7. Myogenesis (muscle formation) of skeletal muscle: develop from mesenchyme derived from myotomal mesoderm mesenchymal cells differentiate into primordial muscle cells called myoblasts differentiation includes elongation of cell and its nucleus myoblasts fuse with each other end-to-end to form an elongated multinucleated cylindrical syncytial cell called myotube myotubes synthesize actin , myosin, and other muscle proteins proteins aggregate to form myofilaments and myofibrils

8. the myotubes are called muscle fibers A number of these muscle fibers are bound together by connective tissue to form individual muscles which secondarily get attached to skeletal elements During myogenesis myofilaments and myofibrils develop in the cytoplasm of muscle fibers All the skeletal muscles develop by birth Mitotic activity of myoblasts ceases after birth All the muscle fibers that an individual is destined to have are formed by birth

9. Development of Skeletal Muscles in Different Regions of the Body the skeletal muscles are divided into following groups: ● Muscles of the body wall (trunk) ● Muscles of head and neck ● Extraocular muscles ● Muscles of tongue ● Muscles of limbs

10. Muscles of the Body Wall derived from myotomes (somites) of the trunk region Each myotome is supplied by a single spinal nerve Each myotome divides into 2 parts: smaller dorsal part called epaxial part ( epimere ) larger ventral part called hypaxial part ( hypomere ) muscles derived from epimere are supplied by dorsal ramus of spinal nerve muscles derived from hypomere are supplied by ventral ramus of spinal nerve

11. epimeres of myotomes form extensor muscles of the vertebral column (e.g., erector spinae) hypomeres of myotomes extend ventrolaterally along the somatopleuric layer of celomic cavity form following muscles of the body wall 1. form 3 layers of muscles in the thorax- external intercostal, internal intercostal, and intercostal intimus (transversus thoracis) 2. In the abdomen also they form three layers of muscles external oblique, internal oblique, and transversus abdominis

12. 3. In the neck, they form longus colli, longus capitis, and scalene muscles scalene muscles in the neck represent intercostal muscles each side of midline on the ventral aspect of body, 3 primitive muscles of the body wall fuse to form the longitudinal column of muscle This longitudinal column of muscle in humans is represented by: (a) Rectus abdominis in abdomen (b) Rectus sternalis in thorax (present sometimes only) (c) Infrahyoid muscles in the neck

13. Muscles of Head and Neck 1. Extraocular muscles (extrinsic muscles) of eyeball develop from 3 preotic myotomes that are arranged around developing eye muscles (extrinsic muscles) of eyeball These myotomes are innervated by 3rd, 4th, and 6th cranial nerves hence the extraocular muscles are supplied by 3rd, 4th, and 6th cranial nerves 3rd cranial nerve (supplies inferior oblique, levator palpebrae superioris and medial, superior and inferior recti) 4th cranial nerve (supplies superior oblique) 6th cranial nerve (supplies lateral rectus)

14. 2. Muscles of tongue: develop from occipital somites(4 in number) occipital myotomes are innervated by precervical nerves that fuse to form composite hypoglossal nerve When the tongue develops in floor of pharynx the occipital myotomes migrate forward along epipericardial ridge , invade substance of the developing tongue form all intrinsic and extrinsic muscles of the tongue except palatoglossus

15. Extrinsic muscles of the tongue: genioglossus , hyoglossus, styloglossus and palatoglossus Intrinsic muscles of the tongue: Superior longitudinal, Inferior longitudinal, transverse and vertical hypoglossal nerves supply all the intrinsic and extrinsic muscles of the tongue except palatoglossus which is supplied by the vagus nerve which is not a muscle of the tongue but that of a palate

16. 3. Muscles of pharyngeal arches: Develop from mesoderm of pharyngeal arches derived from somatomeres muscles derived from mesoderm of pharyngeal arches are muscles of mastication, facial expression, pharynx, and larynx Muscles are innervated by nerves of the respective pharyngeal arches

17. Muscles of Limbs develop from myotomes present in the upper and lower limb bud regions mesoderm derived from these myotomes migrates into the limb bud during the fifth week forms anterior and posterior condensations anterior condensation of mesoderm gives rise:- to flexor and pronator muscles of the upper limb and extensor , adductor and dorsiflexors muscles of the lower limb posterior condensation of mesoderm gives rise:- to extensor and supinator muscles of the upper limb and flexor , abductor and plantar flexors muscles of the lower limb

18. As the limb buds are formed various spinal nerves enter into the mesenchyme first they enter as isolated dorsal and ventral divisions of ventral primary rami soon these divisions unite to form large dorsal and ventral nerves radial nerve, which supplies to the extensor muscle, is formed by the union of dorsal divisions ulnar and median nerves, which supply the flexor muscles, are formed by the union of ventral divisions

19. upper limb bud lies opposite the lower five cervical and upper two thoracic (C4,5,6,7,8, and T1,2) segments lower limb lies opposite the lower four lumbar and upper two sacral (L1,2,3,4,5, and S1,2) segments the muscles of upper limb are innervated by lower five cervical and upper two thoracic segments the muscles of lower limb are supplied by lower four lumbar and upper two sacral spinal segments

20. Development of Smooth (Involuntary) Muscles 1. The smooth muscle in the wall of digestive and respiratory tracts develops mainly from splanchnic mesoderm surrounding primordia of digestive and respiratory tracts 2. The smooth muscle in the wall of most of the blood and lymph vessels develops in situ from surrounding splanchnic mesoderm somatic mesoderm may also form smooth muscle in the wall of many blood and lymph vessels 3. Muscles of iris ( sphincter and dilator pupillae ), arrector pili muscles of skin, and myoepithelial cells of sweat and mammary glands develop from mesenchymal cells derived from ectoderm muscles of iris develop from ectoderm of the optic cup

21. Myogenesis of the Smooth Muscle mesenchymal cells differentiate into the myoblasts myoblasts become spindle shaped and their nuclei become oval myoblasts do not fuse with each other as in skeletal muscle muscle fibers of smooth muscle remain mononucleated contractile elements develop in the cytoplasm of the muscle fiber but are nonsarcomeric

22. Development of Cardiac Muscle cardiac muscle develops from myoepicardial mantle, which is formed by thickening of splanchnic mesoderm surrounding the developing heart tube Myogenesis of the Cardiac Muscle cardiac muscle fibers develop from differentiation and growth of single myoblasts growth of cardiac muscle fibers occurs due to formation of new myofilaments and myofibrils cardiac muscle fibers elongate and give rise to numerous side branches

23. side branches as well as ends of one cardiac muscle fiber adhere to side branches and ends of other cardiac muscle fibers, but the intervening cell membranes persists (i.e., they do not disintegrate) sites of adhesion of the cell membranes between cardiac muscle fibers persist as intercalated discs cardiac muscle does not form true syncytium myofibrils around the central nucleus of the cardiac muscle fibers present cross striated appearance

24. Late in the embryonic period some myoblasts develop cardiac muscle fibers that have relatively few myofibrils and diameters than the typical cardiac muscles fibers These atypical cardiac muscle fibers form bundles called Purkinje fibers, which form conducting system of the heart

25. Clinical Correlation 1. Duchenne muscular dystrophy (DMD): a hereditary disease of skeletal muscles that usually affects males occurs due to mutation of a gene responsible for the formation of protein (dystrophin) on the inner surface of sarcolemma of muscle fibers skeletal muscle becomes progressively weak from early childhood and by adulthood the person becomes practically immobile

26. 2. Congenital anomalies of the skeletal muscles (a) Partial or complete absence of one or more muscles: It is a rather common phenomenon best examples is partial or complete absence of pectoralis major muscle other examples are palmaris longus, serratus anterior, and quadratus femoris

27. (b) Congenital torticollis: It is congenital shortening of the sternocleidomastoid muscle, which occurs due to excessive stretching of this muscle during delivery excessive stretching causes hemorrhage in the muscle and subsequent shortening due to fibrosis

28. 1. What is Duchenne muscular dystrophy ? Give its embryological basis and discuss its clinical presentation Discuss the molecular regulation of development of muscle