The pharyngeal arches, also known as visceral arches'','' are transient structures seen in the

embryonic development In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s and other

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s, that are recognisable precursors for many structures. In

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

, the arches support the gills and are known as the branchial arches, or gill arches. In the

human embryo Human embryonic development or human embryogenesis is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of deve ...

, the arches are first seen during the fourth week of development. They appear as a series of outpouchings of

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical ...

on both sides of the developing

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

. The vasculature of the pharyngeal arches are the aortic arches that arise from the aortic sac.

Structure

s and other

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

, the pharyngeal arches are derived from all three

germ layers A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce tw ...

(the primary layers of cells that form during

Neural crest cells The neural crest is a ridge-like structure that is formed transiently between the epidermal ectoderm and neural plate during vertebrate development. Neural crest cells originate from this structure through the epithelial-mesenchymal transition, an ...

enter these arches where they contribute to features of the skull and facial skeleton such as bone and cartilage. However, the existence of pharyngeal structures before neural crest cells evolved is indicated by the existence of neural crest-independent mechanisms of pharyngeal arch development. The first, most anterior

pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are transient structures seen in the Animal embryonic development, embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, t ...

gives rise to the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

. The second arch becomes the hyoid and jaw support. In fish, the other posterior arches contribute to the branchial skeleton, which support the gills; in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus. The genetic and developmental basis of pharyngeal arch development is well characterized. It has been shown that Hox genes and other developmental genes such as '' DLX'' are important for patterning the anterior/posterior and dorsal/ventral axes of the branchial arches. Some fish species have a second set of jaws in their throat, known as pharyngeal jaws, which develop using the same genetic pathways involved in oral jaw formation. During

, a series of pharyngeal arch pairs form. These project forward from the back of the embryo toward the front of the face and neck. Each arch develops its own artery, nerve that controls a distinct muscle group, and skeletal tissue. The arches are numbered from 1 to 6, with 1 being the arch closest to the head of the embryo, and arch 5 existing only transiently. These grow and join in the ventral midline. The first arch, as the first to form, separates the mouth pit or stomodeum from the

pericardium The pericardium (: pericardia), also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong inelastic connective tissue (fibrous pericardium), ...

. By differential growth the neck elongates and new arches form, so the pharynx has six arches ultimately. Each pharyngeal arch has a cartilaginous stick, a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

component that differentiates from the cartilaginous tissue, an artery, and a cranial nerve. Each of these is surrounded by mesenchyme. Arches do not develop simultaneously but instead possess a "staggered" development. Pharyngeal pouches form on the endodermal side between the arches, and pharyngeal grooves (or clefts) form from the lateral ectodermal surface of the

neck The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Addition ...

region to separate the arches. In fish, the pouches line up with the clefts, and these thin segments become

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s. In mammals the endoderm and

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the o ...

not only remain intact but also continue to be separated by a

layer. The development of the pharyngeal arches provides a useful landmark with which to establish the precise stage of embryonic development. Their formation and development corresponds to Carnegie stages 10 to 16 in

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

, and Hamburger–Hamilton stages 14 to 28 in the

chicken The chicken (''Gallus gallus domesticus'') is a domesticated subspecies of the red junglefowl (''Gallus gallus''), originally native to Southeast Asia. It was first domesticated around 8,000 years ago and is now one of the most common and w ...

. Although there are six pharyngeal arches, in humans the fifth arch exists only transiently during

embryogenesis An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male ...

First arch

The first pharyngeal arch, also mandibular arch (corresponding to the first branchial arch of fish), is the first of six pharyngeal arches that develops during the fourth week of development.William J. Larsen (2001). Human embryology. Edinburgh: Churchill Livingstone. It is located between the stomodeum and the first pharyngeal groove.

Processes

This arch divides into a maxillary process and a mandibular process, giving rise to structures including the

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s of the lower two-thirds of the face and the jaw. The maxillary process becomes the maxilla (or upper jaw, although there are large differences among animals), and palate while the mandibular process becomes the

or lower jaw. This arch also gives rise to the muscles of mastication.

Meckel's cartilage

Meckel's cartilage forms in the

of the mandibular process and eventually regresses to form the

incus The ''incus'' (: incudes) or anvil in the ear is one of three small bones (ossicles) in the middle ear. The incus receives vibrations from the malleus, to which it is connected laterally, and transmits these to the stapes medially. The incus i ...

and malleus of the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles (malleus, incus, and stapes), which transfer the vibrations ...

, the anterior ligament of the malleus and the sphenomandibular ligament. The

or lower jaw forms by perichondral

ossification Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in t ...

using Meckel's cartilage as a 'template', but the maxillary does ''not'' arise from direct ossification of Meckel's cartilage.

Derivatives

The skeletal elements and muscles are derived from mesoderm of the pharyngeal arches. Skeletal * malleus and

of the

* maxilla and

* spine of sphenoid bone * sphenomandibular ligament * palatine bone * squamous part of temporal bone * anterior ligament of malleus Muscles * muscles of mastication (chewing) ** masseter ** medial and lateral pterygoid muscles ** temporalis * mylohyoid muscle * digastric muscle, anterior belly * tensor veli palatini muscle * tensor tympani muscle Other

Mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

and glands of the anterior two thirds of the tongue are derived from

and endoderm of the arch.

Nerve supply

The mandibular and maxillary branches of the

trigeminal nerve In neuroanatomy, the trigeminal nerve (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...

(CN V) innervate the structures derived from the corresponding processes of the first arch. In some lower animals, each arch is supplied by two cranial nerves. The nerve of the arch itself runs along the cranial side of the arch and is called post-trematic nerve of the arch. Each arch also receives a branch from the nerve of the succeeding arch called the pre-trematic nerve which runs along the caudal border of the arch. In human embryo, a double innervation is seen only in the first pharyngeal arch. The mandibular nerve is the post-trematic nerve of the first arch and

chorda tympani Chorda tympani is a branch of the facial nerve that carries gustatory (taste) sensory innervation from the front of the tongue and parasympathetic ( secretomotor) innervation to the submandibular and sublingual salivary glands. Chorda tymp ...

(branch of facial nerve) is the pre-trematic nerve. This double innervation is reflected in the nerve supply of anterior two-thirds of

tongue The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

which is derived from the first arch.

Blood supply

The artery of the first arch is the first aortic arch,McMinn, R., 1994. ''Last's anatomy: Regional and applied (9th ed).'' which partially persists as the

maxillary artery The maxillary artery (eg, internal maxillary artery) supplies deep structures of the face. It branches from the external carotid artery just deep to the neck of the mandible. Structure The maxillary artery, the larger of the two terminal branches ...

Second arch

The second pharyngeal arch or hyoid arch, is the second of fifth pharyngeal arches that develops in fetal life during the fourth week of development and assists in forming the side and front of the

Reichert's cartilage

Cartilage in the second pharyngeal arch is referred to as Reichert's cartilage and contributes to many structures in the fully developed adult.Sudhir, Sant, 2008.''Embryology for Medical Students 2nd edition'' In contrast to the Meckel's cartilage of the first pharyngeal arch it does not constitute a continuous element, and instead is composed of two distinct cartilaginous segments joined by a faint layer of mesenchyme. Dorsal ends of Reichert's cartilage ossify during development to form the stapes of the

before being incorporated into the middle ear cavity, while the ventral portion ossifies to form the lesser cornu and upper part of the body of the hyoid bone. Caudal to what will eventually become the stapes, Reichert's cartilage also forms the styloid process of the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

. The cartilage between the hyoid bone and styloid process will not remain as development continues, but its perichondrium will eventually form the stylohyoid ligament.

Derivatives

Skeletal From the cartilage of the second arch arises * Stapes, * Temporal styloid process, * Stylohyoid ligament, and * Lesser cornu of the hyoid bone. Muscles *

Facial muscles The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, alth ...

* Occipitofrontalis muscle * Platysma * Stylohyoid muscle *Posterior belly of digastric muscle * Stapedius muscle *Auricular muscles

Nerve supply

Facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

(CN VII)

Blood supply

The artery of the second arch is the second aortic arch, which gives origin to the stapedial artery in some mammals but atrophies in most humans.

Muscles derived from the pharyngeal arches

Pharyngeal muscles or Branchial muscles are striated muscles of the head and neck. Unlike skeletal muscles that developmentally come from somites, pharyngeal muscles are developmentally formed from the pharyngeal arches. Most of the skeletal musculature supplied by the cranial nerves ( special visceral efferent) is pharyngeal. Exceptions include, but are not limited to, the

extraocular muscles The extraocular muscles, or extrinsic ocular muscles, are the seven extrinsic muscles of the eye in human eye, humans and other animals. Six of the extraocular muscles, the four recti muscles, and the superior oblique muscle, superior and inferior ...

and some of the muscles of the tongue. These exceptions receive general somatic efferent innervation.

First arch

All of the pharyngeal muscles that come from the first pharyngeal arch are innervated by the mandibular divisions of the

. These muscles include all the muscles of mastication, the anterior belly of the digastric, the mylohyoid, tensor tympani, and tensor veli palatini.

Second arch

All of the pharyngeal muscles of the second pharyngeal arch are innervated by the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

. These muscles include the muscles of facial expression, the posterior belly of the digastric, the stylohyoid muscle, the auricular muscle and the stapedius muscle of the middle ear.

Third arch

There is only one muscle of the third pharyngeal arch, the stylopharyngeus. The stylopharyngeus and other structures from the third pharyngeal arch are all innervated by the

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper Medulla oblongata, medulla, just anterior (closer to the nose) to t ...

Fourth and sixth arches

All the pharyngeal muscles of the fourth and sixth arches are innervated by the superior laryngeal and the recurrent laryngeal branches of the

vagus nerve The vagus nerve, also known as the tenth cranial nerve (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibe ...

. These muscles include all the muscles of the palate (exception of the tensor veli palatini which is innervated by the

), all the muscles of the pharynx (except stylopharyngeus which is innervated by the

), and all the muscles of the larynx.

In humans

It has been proposed that the five arches in amniotes numbered 1–4 and 6, be re-named as simply 1–5. The fifth arch is seen to be a transient structure and becomes the sixth arch, (the fifth being absent). More is known about the fate of the first arch than the remaining four. The first three contribute to structures above the larynx, whereas the last two contribute to the

larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...

and

trachea The trachea (: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from ...

. The recurrent laryngeal nerves are produced from the nerve of arch 5, and the laryngeal cartilages from arches 4 and 5. The superior laryngeal branch of the vagus nerve arises from arch 4. Its arteries, which project between the nerves of the fourth and fifth arches, become the left-side arch of the aorta and the right subclavian artery. On the right side, the artery of arch 5 is obliterated while, on the left side, the artery persists as the ductus arteriosus; circulatory changes immediately following birth cause the vessel to close down, leaving a remnant, the ligamentum arteriosum. During growth, these arteries descend into their ultimate positions in the chest, creating the elongated recurrent paths.

Terminology

It has been proposed that the arches be re-named simply as 1–5. The argument is the existence of the fifth arch (and pouch), held to be a transient structure in the embryo.

Additional images

File:Gray41.png, Schematic of developing

with first (mandibular), second (hyoid), pharyngeal arches and third arches labelled

References

External links

* {{Authority control Vertebrate anatomy Pharyngeal arches Animal developmental biology Otorhinolaryngology Embryology

Structure

First arch

Processes

Meckel's cartilage

Derivatives

Nerve supply

Blood supply

Second arch

Reichert's cartilage

Derivatives

Nerve supply

Blood supply

Muscles derived from the pharyngeal arches

First arch

Second arch

Third arch

Fourth and sixth arches

In humans

Terminology

Additional images

See also

References

External links