DEVELOPMENT OF THE MUSCULOSKELETAL SYSTEM Flashcards
Types of Muscle Cell (Myocyte)
Skeletal or striated or voluntary myocyte
Smooth or visceral or involuntary myocyte
Cardiac myocyte
comprises 40 – 45 % of the total body weight.
➢ Long and cylindrical w/ many nuclei located at the periphery of the cell
Skeletal or striated or voluntary myocyte
is found in the walls of tubular and visceral
organs.
➢ Spindle-shaped w/ one nucleus located in the middle of the cell
Smooth or visceral or involuntary myocyte
comprises the myocardium of the heart.
➢ Branched w/ many nuclei located in the middle of the cell.
Cardiac myocyte
Mesodermal cells of myotome of each somite/somitomere separate from dermatome and
sclerotome, and elongate to spindle-shaped that synthesize myosin and actin and
appear striated. Several myoblasts fuse to form multinucleated myotubes
myoblasts
The myotubes, with
nuclei that migrate peripherally, present cross striations, and are now called .
skeletal myocytes
After birth, the myocytes interact with motor nerves and differentiate into .
fast-twitch, slow-twitch
or intermediate myocytes
Muscle development requires
innervations
Also, muscles and tendons must be stretched by growing bone) in order to grow proper lengths
under
tension(
Each anatomic muscle is
practically allocated a special number of myoblasts that is determined by the time of birth.
Thereafter, muscle cell growth is due solely to
cellular hypertrophy.
Epimere becomes
epaxial muscles
the hypomere becomes the
hypaxial muscles
by delamination forms mesenchymal cells that elongate to
form myoblasts.
Splanchnic mesoderm
for smooth muscles of blood vessels
Somatic mesoderm
for smooth muscles of the iris.
Ectoderm (neural ectoderm of optic cup)
that surrounds the epithelium of a structure or organ for other
smooth muscles.
mesenchyme
Cardiac muscle cells are joined together by intercellular
connections called
intercalated discs.
Types of Connective Tissues
- Loose connective tissue - mesenchymal, mucoid, areolar adipose tissue, etc.
- Dense connective tissue - tendons, ligaments.
- Cartilage
- Bone
Mesenchymal cells from mesoderm (somite) or in case of head, from ectoderm (neural
crest) become stellate or spindle-shaped and are now termed .
fibroblasts
There are two types of fibers secreted by fibroblasts:
collagenous and elastic.
Blood vessels and osteogenic cells invade the calcified cartilage and form the
periosteal
bud
The bone trabeculae interconnect to form .
cancellous bone
is made possible through the epiphyseal plate, a plate of
cartilage between the diaphysis and epiphysis where the cartilage is continuously
formed and replaced during the growing years of the animal
Growth in length of long bone
occurs by deposition of additional layers of bone
substance on the bone surface by osteoblasts in the periosteum of diaphysis and
destruction of bone and cartilage by osteoclasts and chondroclasts, respectively, in
the central portion of diaphysis to create a marrow canal or marrow cavity.
Growth in diameter of long bone
Addition of layers of bone matrix reduces the intertrabecular spaces and the cancellous
bone in the diaphysis is converted into a
compact bone
Osteocytes present cytoplasmic processes that radiate into the matrix through tiny bone
channels called
canaliculi
The intertrabecular spaces are occupied by blood-forming cells
(red bone marrow) and are also called
marrow spaces
Common Malformations of the Vertebra
Alignment Defects
Scoliosis
Kyphosis
Lordosis
Torticolis or wry neck
Spina bifida
Rachischisis
Spina bifida occulta
- lateral deviation of vertebral column
Scoliosis
- sagittal deviation of vertebral column in a fixed position
Kyphosis
- sagittal deviation of vertebral column in a fixed extended position
Lordosis
- abnormal twisting of the cervical vertebral column
Torticolis or wry neck
- absence of vertebral arch (failure of vertebral arch to form dorsally
over the vertebral foramen).
Spina bifida
– spina bifida of several adjacent vertebrae
Rachischisis
- spina bifida covered by skin and subcutis
Spina bifida occulta
- does not ossify
Nasal capsule
- ethmoid and bone around the pituitary gland
Prechordal cartilage
- base of occipital bone
Parachordal cartilage
- temporal bone
Otic capsule
develops from outward growth of ectomesenchymal tissue located rostral to the
cranium and pharynx.
Face
Malformations of the Face
Cheiloschisis
Palatoschisis
Branchial cyst (
Heterotropic polyodontia -
- cleft lip caused by failure of fusion of medial nasal and maxillary
processes.
Cheiloschisis
- cleft palate caused by failure of medial palatine processes to fuse
Palatoschisis
(no opening)
Branchial cyst
(opening to exterior)
branchial sinus
(openings to interior and exterior).
branchial fistula
- (dentigerous cyst, ‘ear teeth’). Primordia of enamel organs
escape to the exterior and develop tooth structures anchored on the parietal bone or
base of the ear.
Heterotropic polyodontia
Types of Limb Malformations
Limb Reduction
Limb Duplication
Limb and Joint Deformities
Type of Limb Reduction
Achondroplasia (dwarfism; Dachshund)
Amelia
Meroromelia
Acromelia
Hemimelia
Micromelia
Phocomelia
Syndactyly
Brachydactyly
Ectrodactyly
inherited; systemic premature
ossification of physes of extremeties
Achondroplasia (dwarfism; Dachshund) -
- complete absence of a limb.
Amelia
- absence of a part of a limb.
Meroromelia
– complete absence of limb.
Acromelia
– absence of half or one or more segments of a limb
Hemimelia
- reduced size of a limb.
Micromelia
- absence of one or more proximal segments, a consequence of
pregnant women taking thalidomide in the late 1950’s
Phocomelia
- fused digits.
Syndactyly
- shortened or stumpy digits
Brachydactyly
- absence of one or more digits
Ectrodactyly
Type of Limb Duplication
Polydactyly
Bimelia
Notomelia (noto=back
- presence of one or more extra digits. This is common in pig and cat
Limb Duplication
- one or more extra digits
Polydactyly
- partial or complete duplication of one limb
Bimelia
- limb growing from the back of the animal.
Notomelia (noto=back)
Type of Limb and Joint Deformities
Arthrogryposis
Hip Dysplasia
Ankylosis
- crooked limb. Gr. gryposis=crooked) - can results from
malformed joints, denervation, abnormal muscle tension, or impaired
mobility in utero.
Arthrogryposis
- abnormal maturation of the hip joint that results in formation
of a shadow acetabulum and flattened femoral head.
Hip Dysplasia
- permanent fixation of a joint caused by immobility of the fetus in
utero.
Ankylosis
