Gross: 8:00 - 9:00Scribe: Ryan O’Neill

Friday, 27th 2009Proof: Strud Tutwiler

Dr. ZehrenPage1 of 7

NCC – neural crest cell

  1. Introduction [S1]: know the tables of this material in your syllabus! Know all of the derivatives!
  2. Pharyngeal Arches [S2]
  3. The pharyngeal arches are sometimes called branchial arches, but in humans are better referred to as pharyngeal because branchial means “gill.”
  4. Are paired bars of tissue that appear in the lateral wall of the pharynx on either side during the 4th week of development.
  5. Appear in a cranial-to-caudal sequence.
  6. There are 6 pharyngeal arches, but the last two are not very prominent, so they don’t make swellings on the outer surface of the embryo.
  7. The 5th pharyngeal arch is very rudimentary and sometimes disappears.
  8. These arches are externally separated by pharyngeal grooves, which are shallow indentations of the surface ectoderm.
  9. The stomodeum is the primitive oral cavity which will eventually communicate with the lumen of the pharynx
  10. There is a membrane separating the stomodeum (primitive oral cavity) from the lumen of the pharynx called the oral (buccal) pharyngeal membrane.
  11. ENDODERMAL PHARYNGEAL POUCHES [S3]
  12. If we look on the inside, you will see that the lumen of the pharynx is lined with endoderm and is continuous with the esophagus.
  13. There are laterally directed pouches called pharyngeal pouches that are lined with endoderm that extend out towards the surface of the embryo toward the pharyngeal grooves on the outside.
  14. At the level of C, we take a cross section and look down on the pharynx from above we will see the view from the next slide.
  15. COMPONENTS OF A PHARYNGEAL ARCH [S4]
  16. View: pharynx from above.
  17. Note: cranial end of the embryo, stomodeum, lumen of the pharynx, outer surface of the embryo, pharyngeal grooves and pharyngeal pouches.
  18. Where the ectoderm of the groove meets the endoderm of the pouch there is a little bit of mesenchyme in between and the 3 layers (ecto, endo and meso) form a membrane called the pharyngeal membrane which normally do not perforate in humans but in lower vertebrates they do perforate and this is where the gill slits are located.
  19. The pharyngeal arches are the bars of tissue that you see on each side.
  20. You can see in the numbering of these arches that the arch lies directly anterior to its corresponding pouch and groove.
  21. The first pharyngeal arch (sometimes called the “mandibular arch”) is directly anterior to the first pharyngeal pouch and groove.
  22. The second arch (sometimes called the “hyoid arch”) lies just anterior to its corresponding pouch and groove as well.
  23. Within each pharyngeal arch there are a number of structures that form:
  24. The core of the arch is the mesenchymal(the pink represents mesenchyme on this slide).
  25. However, it is not all mesodermal. On the board are the sources of pharyngeal mesenchyme
  26. Some are mesodermal
  27. Some are paraxial mesoderm – will form the pharyngeal arch muscles within each arch
  28. Within each arch there is a muscular mass that will give rise to various muscles in the head and neck. Those muscles can be traced all the way back to paraxial mesoderm
  29. Some are cartilaginous rudiments within each arch.
  30. The cartilages will either persist as cartilage or ossify to form other bony structures.
  31. The cartilages of the first 3 pharyngeal arches are formed from neural crest cells. Neural crest cells are ectodermal cells that migrate from the neural tube and give rise various different structures. Included among these are the pharyngeal arch cartilages of the first 3 arches.
  32. There is this stiffening bar of cartilage that form in each of these arches called the pharyngeal arch cartilage.
  33. In the case of the 4th and 6th arches, these cartilages don’t come from the neural crest cells, but come from lateral plate mesoderm.
  34. The mesenchyme of pharyngeal arch 1 (unlike the other arches) not only forms cartilage skeletal elements but some of this mesenchyme will ossify directly to form bone. These cartilages undergo endochondralossification to form certain bony elements.
  35. Some of the bones in your body ossify directly from mesenchyme and don’t pass through a cartilaginous stage.
  36. Ex: The first pharyngeal arch has the mandible and maxilla that ossify directly from mesenchyme.
  37. The first arch is the only arch that has any membrane bones associated with it. These are also neural crest.
  38. A nerve also grows into each pharyngeal arch, either a cranial nerve or a branch of a cranial nerve.
  39. The nerve will innervate the muscles derived from that arch and the skin and mucosa related to that arch.
  40. In each pharyngeal arch there is an artery that develops—aortic arches. We will cover the various derivatives of what these arches develop into during development.
  41. MIGRATION OF NEURAL CREST CELLS INTO PHARYNGEAL ARCHES [S5]
  42. Shows an embryo and how the NCCs migrate from the neural tube down into the facial area and into the pharyngeal arches. The arrows indicate their migration.
  43. In the case of the first 3 arches these NCCs will form the cartilages of these arches and in the case of arch 1 some membrane bones. In the case of the 4th and 6th arch, the NCCs don’t form the cartilages, but they continue down and continue to heart development.
  44. Forget about arch #5 (which is not shown here) because it is so rudimentary.
  45. SCANNING EM OF EMBRYO (5TH WEEK) [S6]
  46. This is a natural human embryo from an anterior view.
  47. The eyes are laterally placed.
  48. The frontonasal prominence – forehead.
  49. This slit is the entrance into the stomodeum.
  50. The first pharyngeal arch gets bent into an upper and lower part.
  51. The upper bar is the maxillary prominence – goes on to form the maxilla
  52. The lower bar is the mandibular prominence – goes on to form the mandible
  53. Note: corresponding arches and grooves…you can’t see the pouches because they are on the inside.
  54. PHARYNGEAL ARCH CARTILAGES [S7]
  55. Let’s begin with the derivatives of the cartilages.
  56. This is an embryo of 5 weeks with color-coated arches.
  57. 1st arch:
  58. The first arch is bent to an upper maxillary and lower mandibular prominence.
  59. The cartilage of the first arch is likewise divided into 2 parts:
  60. The cartilage of the maxillary prominence - Palatopterygoquadrate = maxillary cartilage
  61. The maxillary cartilage will ossify to form the incus. This is one of its derivatives.
  62. The cartilage of the mandibular prominence - Meckel’s cartilage - will ossify to form the malleus and the sphenomandibular ligament, which runs from the spine of the sphenoid to the lingula of the mandible. During development some of the cartilage degenerates and the perichondrium around the cartilage persists as the spenomandibular ligament. It is really a remnant of the first arch cartilage (or the perichondrium of the first arch cartilage). The rest of the Meckel’s cartilage disappears.
  63. Remember, the first arch is the only arch that has membrane bones associated with it.
  64. The incus and malleus are endochondral bones. They are formed by ossification of either the maxillary or Meckel’s (mandibular) cartilage.
  65. The maxillary and mandibular processes have mesenchyme that ossifies directly as well.
  66. In the case of the upper, maxillary process the maxilla the zygomatic bone and the squamous temporal all are formed by direct ossification of the mesenchyme of the maxillary process.
  67. In the case of the mandible, this is a membrane bone formed by the ossification of mesenchyme surrounding Meckel’s cartilage, but not an ossification of Meckel’s cartilage itself.
  68. 2nd arch cartilage (Reichert’s cartilage) – shown in pink
  69. The upper end of this cartilage will ossify to form the third ear ossicle—the stapes.
  70. The lower end will form the styloid process of the skull, the stylohyoid ligament, the lesser horn of the hyoid and the upper part of the body of the hyoid. You can see all of these are right in a line with each other.
  71. 3rd arch cartilage
  72. Will form the lower part of the body of the hyoid and the greater horn.
  73. 4th and 6th cartilages
  74. Will form the cartilages of the larynx—thyroid and cricoid cartilage (as well as the erythroid cartilage, which we haven’t discussed yet).
  75. Epiglottis is an exception. It doesn’t come from an arch cartilage.
  76. Main point: laryngeal cartilages are from either arch 4 or 6.
  1. PHARYNGEAL ARCH MUSCLES [S8]
  2. Arch 1: the mandibular arch forms the muscles of mastication (masseter and temporalis, along with the pterygoid muscles which are not shown), as well as the mylohyoid muscle and the anterior belly of digastric.
  3. In addition there are still 2 more muscles that come from arch 1:
  4. tensor palati (soft palate) and tensor tympani (middle ear)
  5. Arch 2: the main muscles are the muscles of the facial expression, along with the posterior belly of the digastric and the stylohyoid, as well as the stapedius muscle (middle ear, attaches to the stapes – also from arch 2)
  6. Arch 3: forms only one muscle: the stylopharyngeus – muscle of pharynx that elevates the pharynx
  7. Arch 4:All of the other muscles of the pharynx come from arch 4!
  8. In addition the muscles of the soft palate (other than the tensor palati) come from arch 4!
  9. Most of the muscles of the pharynx and soft palate come from arch 4.
  10. One other muscle comes from arch 4: the cricothyroid
  11. Arch 6: all of the other intrinsic muscles of the larynx (other than the cricothyroid) as well as the upper striated fibers of the esophagus.
  12. PHARYNGEAL ARCH NERVES [S9]
  13. Each arch has a cranial nerve or a branch of the cranial nerve associated with it.
  14. The 1st arch – CN V (trigeminal)
  15. V1 does not relate to the first pharyngeal arch in humans, only V2 and V3 are associated with arch 1!
  16. (V2 – lime green, V3 – dark green)
  17. V2 – the maxillary nerve – supplies the maxillary prominence
  18. V3 – the mandibular nerve – supplies the mandibular prominence
  19. V3 is the only motor part of the trigeminal and innervates all of the muscles of arch 1
  20. The 2nd arch – CN VII (facial)
  21. Supplies every muscle derived from arch 2.
  22. The 3rd arch – CN IX (glossopharyngeal)
  23. Supplies the only muscle of that arch—stylopharyngeus
  24. The 4th arch – CN X (vagus)
  25. More specifically, the pharyngeal branch of the vagus nerve supplies all of the muscles from the pharynx
  26. Also the external branch of the superior laryngeal nerve innervates the cricothyroid muscle, which is derived from arch 4 as well.
  27. The 6th arch - recurrent laryngeal nerve –all of the intrinsic muscles of the larynx other than the cricothyroid and the upper esophagus.
  28. These nerves that supply these arches have a motor to muscles and sensory to skin and mucosa!
  29. The lower diagram shows the mucosal distribution of the pharyngeal arch nerves.
  30. V2 – supplies the mucosa of the maxillary prominence, nasal cavity and palate
  31. V3 – sensory distribution in terms of mucosa is associated with the anterior 2/3 of the tongue and floor of the mouth
  32. VII (facial) – may supply some of the palate, it has taste fibers in it so there may be some taste buds on the palate supplied by VII and also via the chorda tympani, which supplies the taste buds on the anterior 2/3 of the tongue
  33. IX (glossopharyngeal) – mucosa of the pharynx, including the posterior 1/3 of the tongue
  34. X (vagus) – gets the lining of the larynx
  35. All of these nerves have sensory distributions to all of the parts of the mucosa
  36. CN V – takes over most of the cutaneous innervation of the head.
  37. V1, 2, 3 innervate most of the skin of the face.
  38. The cutaneous distribution of 7, 9 and 10 is restricted to a small area in the region of the ear.
  39. PHARYNGEAL ARCH ARTERIES (AORTIC ARCHES) [S10]
  40. Picture of an embryo in the 4th week of development still attached to the yolk sac.
  41. The aortic arches, much like the pharyngeal arches, appear in a cranial-to-caudal sequence.
  42. There are 6 pairs of aortic arches that form (but not all at the same time) and run from the aortic sac (structure in the floor of the pharynx) that run dorsally and communicate above the aortic arches with a vessel on either side called the dorsal aorta.
  43. In the region of the pharynx the dorsal aorta is a paired vessel, one on each side. These dorsal aortae extend anteriorly into the head region to supply the head end of the embryo.
  44. Behind the pharynx these paired dorsal aorta unite to form a single, unpaired vessel.
  45. Branches off the unpaired dorsal aorta will supply the more caudal parts of the embryo.
  46. Aortic sac (ventral) that is connected to paired dorsal aortae by these 6 pairs of aortic arches.
  47. We will talk about how these aortic arches get transformed into various vessels in the adult. Some disappear.
  48. TRANSFORMATION OF AORTIC ARCHES (VENTRAL VIEW) [S11]
  49. Ventral view of the aortic arch.
  50. Note: aortic sac, paired dorsal aortae and unpaired dorsal aorta
  51. Orient yourself with the left and right sides as if you are looking straight on at the embryo.
  52. At 6 weeks, aortic arch 1, 2 and 5 have disappeared. The only significant derivative of the first aortic arch is the maxillary artery (not shown). Know this!
  53. 2nd and 5th arches have no adult derivatives as far as aortic derivatives are concerned.
  54. 3rd aortic arch (paired) - persists and you can see the external carotid artery that is growing out.
  55. The proximal portion of the 3rd aortic arch will become the common carotid artery.
  56. The distal part will become the beginning (proximal) portion of the internal carotid artery.
  57. The remainder of the internal carotid artery (which will go to the head) is formed by either the left or right dorsal aorta.
  58. 4th aortic arch (paired) - forms a proximal portion on the right side that will become the right subclavian artery
  59. On the left side the 4th aortic arch will form a small portion of the arch of the aorta.
  60. 6th aortic arch (paired)
  61. The proximal most parts of the 6th aortic arch on each side will form the proximal parts of the pulmonary arteries going to the lungs.
  62. The more distal part on the right side disappears.
  63. The more distal part on the left side persists and becomes a vessel called the ductus arteriosis
  64. This is important because it means during development your lungs are not functioning as respiratory organs, so there is no need to send unoxygenated blood to the lungs via the pulmonary arteries because it is going to come back to the heart unoxygenated. So a shunt develops called the ductus arteriosis is important because it shunts pass the pulmonary arteries and bypasses the lungs and directly into the aortic arch. The blood is oxygenated in the placenta.
  65. Ductus arteriosis = formed from the left side of the distal part of the 6th aortic arch!
  66. TRANSFORMATION OF AORTIC ARCHES (VENTRAL VIEW) [S12]
  67. Note the diagram on the right: 6 month infant
  68. The proximal parts of the 3rd pair of aortic arches on each side have formed the common carotid arteries.
  69. The more distal part has formed the proximal portion of the internal carotid artery.
  70. The dorsal aortae have formed the remainder of the internal carotid.
  71. Notice the external carotids do not develop as a transformation of an aortic arch.
  72. They just develop as an outgrowth of the aortic arch.
  73. The 4th arch forms a little of the right subclavian artery and some of the aortic arch.
  74. The 6th arch forms the proximal part of the pulmonary artery on each side.
  75. On the left side. the ductus arteriosis becomes non-functional at birth and becomes the ligamentum arteriosum, which connects the base of the left pulmonary artery with the concavity of the aortic arch.
  76. RELATION OF RECURRENT LARYNGEAL NERVE TO AORTIC ARCHES[S13]
  77. The recurrent laryngeal nerves supply the 6th pharyngeal arch and they are branches of the vagus nerve.
  78. Note the right and left vagus nerves descending into the thorax from the neck. They give off a recurrent laryngeal branch, which goes to the 6th arch.
  79. The 6th aortic arches are both completely present at this point.
  80. The heart (which begins its development in the pharyngeal region) starts to descend during development and drags the aortic arches with it and as a result the laryngeal nerves get hooked around the distal part of the 6th aortic arch and dragged down and then have to recur around the distal part of the 6th aortic arch on each side, but with further development the right 6th aortic arch the distal part disappears. There is nothing left for that nerve to loop around.
  81. The 5th aortic arch never formed, so the right recurrent laryngeal nerve ends up looping around the 4th aortic arch, which becomes part of the right subclavian artery.
  82. RELATION OF RECURRENT LARYNGEAL NERVES IN A CHILD [S14]
  83. On the left side, it loops around the distal part of the 6th aortic arch, which becomes the ductus arteriosus and at birth becomes the ligamentum arteriosum.
  84. In the adult, the left recurrent laryngeal nerve is found looping around the ligamentum arteriosum.
  85. Then both nerves ascend into the neck between the esophagus and trachea.
  86. PHARYNGEAL POUCHES, GROOVES & MEMBRANES [S15, S16]
  87. Skipped initially, then came back- Horizontal sections through the pharynx.
  88. Note the pouches, arches and grooves on the outside.
  89. The first pouch grows out laterally and termed the tubotympanic recess for a while because it forms the auditory tube and the tympanic (middle ear) cavity.