06 Somites and Muscle Development
Summary
TLDREn esta sexta parte de la serie de revisiones en línea de Falcon, se discuten los somitas y el desarrollo muscular. Se explica que la mayoría de los músculos provienen de la mesodermo, pero hay excepciones como los músculos pupilares que son derivados de la ectodermo. Se describe el proceso de formación de los somitas alrededor de la semana 20 del desarrollo embrionario, su segregación en áreas ventral y dorsal y la influencia de señales como el sonic hedgehog. Se explora el desarrollo de los músculos del cuerpo, incluyendo los músculos cardiacos y su origen en la mesodermo esplacníco. Además, se mencionan condiciones como el síndrome de Poland y el síndrome de prune belly, que afectan el desarrollo muscular.
Takeaways
- 👶 Los músculos pupilares en un recién nacido pueden estar ausentes debido a la formación de la pupila por el ectodermo, en lugar del mesodermo.
- 🦵 La formación de los músculos comienza alrededor de la semana 20, con la formación de pares de somitas que se segregan en áreas ventrales y dorsales.
- 🧬 El proceso de formación de los somitas se ve influenciado por el gen sonic hedgehog.
- 🦴 Los somitas se dividen en el esclerotomo ventral, el dermotomo y el miotomo dorsal, que más tarde se separan en el dermotomo y el miotomo.
- 👂 Los músculos de la región del cuello se derivan de los somitas que permanecen sin segmentar y son los músculos faríngeos.
- 🩺 Los segmentos del cuerpo se derivan de un par de somitas y el mesodermo adjacente, formando segmentos que se desarrollan desde el craneal hacia el caudal.
- 🫁 El mesodermo intermedio forma un cordón de mesenchima que dará lugar al sistema urinario y genital.
- 🩸 El mesodermo lateral se divide en mesodermo esplancnico y somático, dando lugar a músculos lisos gastrointestinales y vasculares, respectivamente.
- 💪 Los músculos del corazón y los músculos lisos tienen dos fuentes: el mesodermo esplancnico y el somático.
- 👶 Un recién nacido con músculos de la espalda poco controlados puede ser debido a una falla en el crecimiento del nervio hacia los músculos, específicamente el divisiones axiales del miotomo.
- 🦾 Los músculos extensores de la columna vertebral se derivan de la división axial del miotomo.
Q & A
¿Cuál es la fuente del músculo pupilar en un recién nacido?
-El músculo pupilar proviene del ectodermo, lo cual es una excepción a la regla de que la mayoría de los músculos son formados por el mesodermo.
¿Cuándo comienza la formación de los somitos en el desarrollo embrionario?
-La formación de los somitos comienza alrededor de la semana 4, cuando se forman pares de somitos a medida que el nódulo primitivo regresa en dirección caudal.
¿Qué molécula de señalización es importante en la formación de los somitos?
-La molécula de señalización sonic hedgehog es crucial en la formación de los somitos, dirigiendo el proceso de agregación del mesenquima localizado.
¿Cómo se diferencian las áreas ventral y dorsal de los somitos?
-Los somitos se segregan en áreas ventrales mediales llamadas esclerotomas y áreas dorsales laterales denominadas dermotomas.
¿De qué manera los esclerotomas y dermotomas contribuyen al desarrollo muscular?
-Los esclerotomas y dermotomas se dispersan debido a las transformaciones epitelio-mesenquimales, formando parte de la musculatura del cuerpo.
¿Qué tipo de músculos se derivan del mesodermo neural en la región del cuello?
-El mesodermo neural en la región del cuello da lugar a los músculos branchiales o faríngeos, también conocidos como músculos somaíticos del cuello.
¿Cuál es la secuencia temporal en la formación de los segmentos del cuerpo?
-Los segmentos del cuerpo se desarrollan de manera craneofacial a caudal, comenzando con la formación de la cadena de mesenquima a los 19-20 días de desarrollo.
¿Cómo se relaciona el mesodermo lateral con la formación de los músculos del cuerpo?
-El mesodermo lateral se divide en mesodermo esplañocólico, que da lugar a los músculos liso gastrointestinales, y mesodermo somático, que da lugar a los músculos liso vasculares.
¿Qué tipo de células musculares se derivan del ectodermo neural?
-Las células musculares que se derivan del ectodermo neural incluyen los constrictores y dilatadores del ojo, como los músculos que controlan la pupila.
¿Qué músculo se desarrolla a partir de la división axial paralela de los dermotomas y cuál es su función?
-El músculo que se desarrolla a partir de la división axial paralela de los dermotomas es el extensor de la columna vertebral, encargado de ayudar en la extensión de la columna.
¿Cuál es la importancia del desarrollo de los músculos en la clínica, especialmente en la columna vertebral?
-El desarrollo de los músculos en la columna vertebral es crucial para el control y la movilidad. Un fallo en el crecimiento de los nervios hacia los músculos puede resultar en hipotonía, como en el síndrome de la síndrome de Poland o el síndrome de Prune Belly.
Outlines
🔬 Desarrollo de los músculos y somitas
Este párrafo explora el desarrollo de los músculos y somitas en la embriología. Se comienza discutiendo la formación de los músculos pupilares y se menciona que la mayoría de los músculos se forman a partir del mesoderma, pero hay excepciones como los músculos pupilares que provienen de la ectodermo. Se describe el proceso de formación de los somitas a partir de la semana 4 del desarrollo embrionario, incluyendo la segregación en áreas ventral y dorsal y la influencia de la señalización molecular, como el sonic hedgehog. También se discute la formación de los músculos del cuerpo, la región del cuello y las áreas corporales, así como las diferenciaciones de los somitas en músculos de la cabeza y el cuerpo. Se enfatiza la importancia de comprender estos procesos para los exámenes médicos como el USMLE step one.
💓 Desarrollo de los músculos cardíacos y suaves
En el segundo párrafo se aborda el desarrollo de los músculos cardíacos y suaves. Se explica que el músculo cardíaco se origina del mesoderma splánquico y se forma alrededor del tubo cardiaco primitivo. Se mencionan los dos orígenes de los músculos suaves: el mesoderma splánquico asociado con el intestino y el mesoderma somático asociado con los músculos periféricos y vasculares. Se plantea una pregunta sobre un bebé con músculos de espalda poco controlados, lo que conduce a una discusión sobre la organización de los somitas y su relación con los músculos extensores de la columna vertebral. Además, se habla sobre el desarrollo de las extremidades, su ossificación, y la importancia de la región ectodérmica apical (AER) en la elongación del bourgeon de la extremidad. Se destacan las diferencias entre el desarrollo de la extremidad superior e inferior y cómo esto afecta la distribución de los nervios y los músculos en el cuerpo adulto.
👶 Trastornos del desarrollo muscular
El tercer párrafo se centra en trastornos relacionados con el desarrollo de los músculos, como el síndrome de Poland y el síndrome de la vejiga de pruna. El síndrome de Poland se caracteriza por la ausencia de músculos y grasa subcutánea en un lado del cuerpo, comúnmente el pectoral. El síndrome de la vejiga de pruna se asocia con un abdomen distendido y una falta de músculos en la pared abdominal. También se discute la hipotonia, conocida como síndrome del bebé blando, que puede tener múltiples causas y se manifiesta en la falta de control muscular. Se presentan imágenes de adultos con distrofia miotónica y bebés con síndrome del bebé blando para ilustrar estos trastornos. El párrafo concluye con una mención al siguiente segmento que tratará sobre el desarrollo del esqueleto y la columna vertebral.
Mindmap
Keywords
💡Somites
💡Mesoderma
💡Ectodermo
💡Sonic Hedgehog
💡Músculos de la pared del cuerpo
💡Mesoderma lateral
💡Mioblastos
💡Músculo cardíaco
💡Músculo liso
💡Poland Syndrome
💡Hipotonía
Highlights
The pupillary muscles are an exception to the general rule of muscle development, as they are derived from ectoderm, not mesoderm.
Muscle formation begins at day 20 with pairs of somites forming as the primitive node regresses caudally.
Sonic hedgehog signaling plays a crucial role in mesenchyme aggregation during early muscle development.
Somites segregate into ventral-medial (sclerotome) and dorsal-lateral (dermomyotome) regions, which later develop into various muscle structures.
Sclerotomes and dermomyotomes undergo epithelial-mesenchymal transformation, driven by molecular signaling.
The pharyngeal muscles, originating in the head region, remain unsegmented, forming through somatic muscle differentiation.
Body wall muscles develop from specific segments of dermomyotomes and adjacent mesoderm, growing in cranial-caudal order.
The lateral plate mesoderm divides into splanchnic mesoderm (giving rise to GI smooth muscle) and somatic mesoderm (forming vascular smooth muscle).
Cardiac muscle arises from splanchnic mesoderm surrounding the primitive heart tube, eventually forming the heart muscle.
The apical ectodermal ridge (AER) drives limb bud elongation, playing a key role in limb formation during weeks 3-6.
Retinoic acid provides limb bud orientation along the medial-lateral plane.
Limb muscles are derived from somatic mesoderm and somites, with long bones forming via endochondral ossification.
Poland syndrome involves missing pectoralis muscles and sometimes ribs, with the right side more commonly affected.
Prune belly syndrome results in a lack of anterior and lateral abdominal muscles, leading to a wrinkled abdomen.
Hypotonia, also known as floppy baby syndrome, is associated with various conditions, including Down syndrome and myotonic dystrophy.
Transcripts
welcome to part 6 of the online Falcon
review series this time we're going to
discuss somites
and muscle development starting with a
question in a newborn infant the pupil
was found to lack its musculature which
of the following contribute to the
formation of the pupillary muscles the
answer we're looking for here is
ectoderm most muscles are mesoderm
formed but there are exceptions to this
rule and there's a few exceptions that
are important for the USMLE step one
that you be aware of let's move on and
start to discuss some of these other
exceptions as well as the primary
formation of the musculature of the body
is and it's organization so my formation
begins around a 20 where pairs of
somites will form as the primitive node
regresses caudal II this will be driven
in many places by sonic hedgehog
processes will begin with localized
mesenchyme aggregations which will form
so millimeters or preso mites
then the somites will segregate into
ventral medial areas called the sclera
tome and a dorsal lateral area termed
the dermal Maya tomes these dermal Maya
tomes will later separate into the
dermatome and the Maya tomes
independently the sclera tome and the
dermal Maya tomes will disperse due to
the epithelial mesenchymal
transformations that start to occur
driven by some of the signaling
molecules that will be present in the
tissues again and a really important one
that you be cued into for questions is
the sonic hedgehog the soma tamir's that
will form in the head region which
typically has seven pair will actually
remain unsegmented and that's where you
get the branchial merrick muscles or
pharyngeal muscles sorted from in the
head think of them though and just
generalize it as somatic muscle this is
ball
carry muscle so let's look at the body
wall segments all of the structures that
are derived from a single pair of dermal
Myatt ohms and the adjacent bob mesoderm
will form a body wall segment and the
body segments will be developing at
different times and again they'll start
from a cranial to caudal organization
the intermediate mesoderm will form a
chord of mesenchyme which will form
along the urogenital ridge around day 19
and 20 this it will give rise to the
urinary system and the genital system
which we'll discuss later then the
lateral plate needs a term which we were
introduced a little bit earlier we'll
start to form and then that will split
into two layers by the formation of the
intra embryonic Silom during the folding
near day 20 the layer of the lateral
plate mesoderm that's going to associate
with the endoderm is known as splanchnic
mesoderm which will typically give rise
to GI smooth muscle and the layer of the
lateral plate museum that's associated
with the ectoderm will be the somatic
music urn which will give rise to
vascular smooth muscles when you move
from ease of Durham to somite you're
going to have as we've seen earlier the
neural groove with the neural fold that
will start to rise up and invaginate and
then we have the paraxial Missa Durham
which is closest to the notochord and
that paraxial Missa Durham will form
condensations which will form the
somites and there'll be 42 to 44 of them
as I said they won't all be present at
one time and they'll develop from
cranial caudal then that intermediate
music erm and then finally the lateral
plate needs a term just as a reminder of
where these are the skeletal muscle
sources will have some exceptions to
predominantly being knees a term or so
might formed there's going to be some
neural ectoderm derivatives which will
include the constrictors and dilators of
the eye that we discussed in the
question
earlier and there'll be some acto dermal
derivatives which will be myoepithelial
cells such as the mammary glands and the
sweat glands
so from rostral coddle you can see the
pre otic Maya tones which will form in
around the ears the pharyngeal arch
musculature will come from the arch
associate mesoderm the occipital Maya
tones which will give rise to tongue
muscle the cervical Maya tones and the
thoracic and therefore lumbar Maya tones
will form the body so mites again all
together there should be 42 to 44 of
those when we look at the cardiac and
smooth muscle development the cardiac
muscle is an important source to
remember from where it came the
splanchnic needs a durham will give rise
to the EPI myocardial mantel which will
surround that primitive heart tube and
then this will form the Nizza derm of
the heart muscle itself the smooth
muscles within the body again have two
sources those splanchnic mesa Durham's
which will be associated with gut and
the somatic mesoderm
which will be associated with the
peripheral and the vasculature muscles
let's ask another question an infant
which is born with poorly controlled
muscles of the back who is likely due to
a failure of the nerve to grow into the
muscles appropriately which muscle
forming structure gives rise to the
extensors of the vertebral column and
for this answer we're looking for e the
F axial division of the Maya tone and
this question is calling up your your
memory of the organization of those
somites as they distribute into
different body segments so if we go back
and look at the limb buds and their
ossification forms remember that the
upper limb will push out from the hand
plate and the lower limb will push out
from a caudal limb bud and these will
rotate in opposite directions the limb
bud will have associated somatic
mesoderm and
Semitic Nisa turn the somatic means a
dream arising from the lateral plate and
the Semitic Nisa Durham are being
myoblast from the body so might there's
going to be bones blood vessels and
they're going to come from somatic
mesoderm
and then the muscles of the limbs
themselves will come from the so might
the critical period remember for limb
development is going to be through three
to the end of fifth week or sixth week
and this is when teratogen involvement
is going to be the most crucial remember
some of the key words for the
development of the limb but is going to
be the AER or the apical ectodermal
ridge and this is going to be the
driving force which will induce them as
in kind and cause the elongation of the
limb bud the retinoic acid that's
associated with limb bud development
will give it orientation in the in the
medial lateral plane the long bones of
the limbs are going to be formed by
endochondral ossification except for the
clavicle which is the one of formed by
the intramembranous ossification and
that usually happens around the seventh
week so this is one bone associated with
a limb that has a late development
period now we're looking at the division
of the muscles and Maya tomes as they
distribute into the limbs themselves and
this understanding will help be
important for the distribution of nerves
the distribution of dermatomes and Maya
tomes
it's the epic Co Maya tome that will be
associated with the dorm dorsal ramus
and the true back muscles as well as the
skin overlying them whereas all of the
ventral Ram I will give rise to the hype
axial muscle and those will give supply
to the dermatomes and the Maya tomes of
all of the other muscles around the body
and the limb when you break that down
the F axial are going to be interviewed
by dorsal primary
spinal nerve and the high-back seal will
be innervated by the ventral primary
rear smile nurse that's an important
concept to remember because it applies
to a lot of the understanding that will
come with the brachial plexus and the
lumbosacral plexus later on on another
division importance is that the extensor
muscles tend to be from dorsal
development and the flexor muscles tend
to be from the more ventral development
however the rotation of the limbs that
put them on opposite sides in the adult
form therefore it's important to
remember for the understanding of the
lemon general that the upper limb is
essentially the same as a lower limb
except they're at 180 degrees of
rotational difference so the thumb which
in anatomical position is lateral
therefore has the big toe in the
anatomical position being medial let's
look at some problems that you should be
familiar with for the clinic that deal
with the development of muscles one
problem that you should be familiar with
is a couple of disorders that have or
involve missing muscles Poland syndrome
for one is a deficit or deficiency of
the subcutaneous fat and the muscles on
one side of the body typically more
often it will be the right side than the
left but they're not really sure why
this is but the pectoralis muscle the
sternum sometimes ribs and some hand
muscles are oftentimes missing when
Poland syndrome
the most common thing missing would be
the pectoralis major and minor when you
look at prune belly syndrome there's
oftentimes a wrinkly distended abdomen
because of a lack of the anterior
abdominal wall and lateral abdominal
wall muscles and here's the examples
seen off to the side of a Poland
syndrome where there's only unilateral
breast development because of the
subcutaneous fat involvement and the
muscle underlying the pectoralis major
is missing so you can see a deficit and
then the prune belly where you can see
that rippled abdominal wall of an infant
other condition affected by muscle
development is hypotonia which is also
known as floppy baby syndrome this can
have a lot of underlying causes which
can include anything from Down syndrome
or achondroplasia to myotonic dystrophy
here are some examples of those where
you can see an adult with myotonic
dystrophy notice the thin flat facial
effect you can see also the infants on
the sides there are two infants there
with floppy baby syndrome which are
going to be a result of dystonia that
concludes the sixth segment where we've
given you a little bit of a basic
understanding from the development from
the muscle standpoint of the body we'll
talk a lot more about muscles as we get
into the adult formations but those
principles will assist you in
understanding some of the developmental
questions on the USMLE step one the next
segment will be segment seven and we'll
discuss the skeleton and the vertebral
development
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