Muscular System Flashcards
The muscular system develops from the ___, except for the muscles of the iris which develop fromt he ____
Mesoderm
Neuroectoderm
Myoblasts-embryonic muscle cells are derived from ___
Mesenchyme
Skeletal muscle: The myoblasts that form the skeletal msucles of the trunk are derived from the ___ in the ___ regions of the ___
Mesenchyme
Myotome
Somites
The limb muscles develop from __ precursor cells in the limb buds
Myogenic
Studies show that these cells originate from the ventral ___ of somites in response to molecular signals from nearby tissue
Dermomyotome
The myogenic precursor cells migrate into h limb buds, where they undergo ___ transformation
Epitheliomesenchymal
The first indication of ___ is the elongation of the nuclei and cell bodies of mesenchymal cells as they differentiate into myoblasts
Myogenesis
The primordial muscle cells soon fuse to form elongated , multinucleated, cylindrical structures-___
Myotubes
At the molecular level, these events are preceded by gene activation and expression of the ___ family of muscle specific basic helix-loop-helix transcription factors int he precursor myogenic cells. What are they
MyoD
MyoD, myogenin, Myf-5, MRF4)
What signalling molecules regulate the beginning of myogenesis and the induction of the myotome
Shh(from ventral neural tube)
Shh9from notochord)
Wnt, BMP4(from dorsal neural tube)
Wnt, BMP4(from overlying ectoderm)
Muscle growth results fromt he ongoing fusion of __ nd ___
Myoblasts and myotubes
____ develop in the cytoplasmof the myotubes during or after fusion of the myoblasts
Myofilaments
Soon after myofilaments develop, __ and other organelles characteristic of striated muscle cells develop
Myofibrils
As the myotubes differentiate, they become invested with external laminae, which segregate them from the surrounding CT
Ok
__ produce the perimysium and epimysium layers of the fibrous sheath
Fibroblasts
The endomysium is formed by the __ lamina which is derived from the muscle fiber and reticular fibers
External
Most skeletal muscles develop when
Before birth
And remaining by end of first year
The increase in the size of a muscle after the first year results from an increase int he diameter of the fibers because of the formation of more myofilaments
Muscle increase in length and width to grow the skeleton
Each myotome part of a somite divides into a dorsal __ __ and a ventral __ ___
Epaxial division
Hypoxia division
Each developing spinal nerve also divides and sends a branch to each division with the ____ ___ ___ supplying the epaxial division and the __ __ __ supplying the hypaxial division
Dorsal primary ramus
Ventral primary ramus
Some muscles, such as the __ __, remain segmentally arranged like the somites
Intercostal msucles
Most myoblasts migrate away from the myotome and form ___ ___
Nonsegmented msucles
What do the myoblasts from the epaxial divisions of the myotomes form
Segmental msucles of the main body axis
Extensor msucles of the neck and vertebral column
The embryonic extensor muscles that are derived from the sacral and coccygeal myotomes ___. What are their adult derivatives
Degenerate
Dorsal sacrococcygeal ligaments
Myoblasts from the hypaxial division of thecervical myotome form what
Scalene, prevertebral, geniohyoid, and infrahyoid
The myoblasts from the hypaxial divisions of the thoracic myotomes form what
Lateral and ventral flexor muscles of the vertebral column
The myoblasts from the hypaxial divisions of the lumbar myotomes form
Quadratus lumborum muscle
What else is derived from hypaxial division of myotomes
Muscles of limbs, intercostal msucles, abdominal msucles
The sacrococcygeal myotomes form what (still hypaxial
Muscles of pelvic diaphragm
And probably the striated msucles of the anus and sex organs
Myoblasts fromt he pharyngeal arches form what msucles
Muscles of mastication and facial expression as well as those of the pharynx and larynx.
What are the muscles of the pharyngeal arch innervated by
Pharyngeal arch nerves
The mesoderm oin the prechordal plate area is believed to give risk the three preotic myotomes from which myoblasts differentiate
Groups of myoblasts, each supplied by its own cranial nerve, form the extrinsic muscles of the eye
Cn3, 4, 6
Myoblasts from the occipital (postotic) myotomes form the ___ msucles whicha re innervated by the __ nerve
Tongue
Hypoglossal XII
The musculature of the limbs develops from myoblasts surrounding the developing ___
Bones
The precursor myogenic cells in the limb buds originate from the __
Somites
The precursor myogenic cells are first located int he __ part of the dermomyotome and they are ___
Ventral
Epithelial
After the epitheliomesenchymal transformation, the precursor myogenic cells migrate to where
The primordium of the limb
Some smooth muscle fibers differentiate from __ ___ surrounding the endoderm of the primordial gut and its derivatives
Splanchnic mesenchyme
The smooth muscle in the walls of many blood an lymphatic vessels arises from the ___ __
Somatic mesoderm
The muscles of the iris (sphincter and dilator pupillae) and the myoepithelial cells in the mammary and sweat glands are derived form the mesenchymal cells that originate from ___
Ectoderm
What is the first sign of smooth muscle differentiation
Development of elongated nuclei in spindle-shaped myoblasts
During early development, new myoblasts continue to differentiate from mesenchymal cells, but do not __; they remain ___
Fuse
Mononucleated
During later development, the division of existing myoblasts gradually replaces the differentiation of new myoblasts in the production of new smooth muscle tissue
Filamentous, but nonsacromeric, contractile elements develop in their cytoplasm and the external surface of each differential cell acquires a surrounding external lamina
As smooth muscle fibers develop into sheets or bundles, they receive autonomic innervation
Fibroblasts and muscle cells synthesize and lay down collagenous , elastic, and reticular fibers
The __ ___ ___ gives rise to the mesenchyme surrounding the developing heart tube
Lateral splanchnic mesoderm
Cardiac myoblasts are derived fromt he mesenchyme surrounding the developing heart tube by differentiation and growth of ___ cells, unlike striated skeletal muscle fibers, which develop by __ of cells
Single
Fusion
In development of cardiac muscles, the myoblasts adhere to each other as in developing skeletal muscle , but the intervening cell membranes do not ____. These areas of adhesions give rise to ___ ___
Disintegrate
Intercalated discs
Growth of cardiac muscle fibers results fromt he formation of new _____
Myofilaments
Late in the embryonic period, special bundles of muscle cells develop that have relatively few myofibrils and relatively larger diameters than typical cardiac muscle fibers
The cells develop from original trabeculated myocardium and have fast conducting gap junctions and form the conducting system of the heart (purkinje fibers)
Poland syndrome
Breast and nipple aplasia or hypoplasia, deficiencies of axillary hair and subcutaneous fat and shortened arms and fingers
Absence of the pectoralis major is often associated with ____
Syndactaly
Congenital torticollis
Sternocleidomastoid muscle injured at birth
Fixed rotation Nd tilting of the head because of concomitant muscle fibrosis, as well as shortening of the sternocleidomastoid muscle on one side
Causes of congenital torticollis
Birth trauma
Malpositioning in utero
Accessory soleus muscle
3% of population
Primordium of soleus may undergo early splitting to form an accessory soleus
