ms anatomy: embryology of limbs

this lecture covered some basic ideas about the formation of limbs in an embryo. it covered: the structural development of limbs from somites, the formation of bones, formation of blood vessels, and some structural abnormalities.

somites are described as "paraxial mesodermal segments" that ultimately differentiate into three parts: sclerotome, which forms the spine and ribs, dermatome, which forms the dermal layer of the skin, and myotome, which forms the muscles of the back and limbs. the limb "bud" starts growing off of the lateral plate mesoderm, with migrating somatic cells contributing to its development as well. it grows outward, developing along the proximal-distal axis via FGF, spearheaded by the apical ectodermal ridge. the "zone of polarization activation" is what develops patterns in the caudal-cranial axis (such as the different sizes and shapes of the 5 fingers) via Shh. these two mechanisms feed off of each other in a positive feedback loop, where Shh from the ZPA promotes the FGF in the AER and vice versa, through intermediates called formin, gremlin, and bone morphogenetic protein.

the process of endochondrial ossification is then described briefly: mesenchymal cells condense and form "pre-cartilaginous aggregates". cartilage producing cells (chondroblasts) secrete BMP to promote growth and Ihh to promote BMP, another positive feedback mechanism. chondroblasts then secrete hyaline cartilage, and become chondroblasts that reside in empty pools called lacunae. hydroxyapetite, an inorganic calcium phosphate crystal, is then secreted and eventually kills off the chondrocytes via apoptosis. osteoblasts then secrete bone matrix and bone is formed. bone remodeling occurs through the balance of osteoblast (bone forming cells, formed from mesenchymally derived osteoprogenitor cells) and osteoclast (bone destroying cells, derived from fused mononuclear hemopoetic progenitor cells) activity on opposite ends of a surface of bone.

some facts about blood vessel development: angioblasts form vascular plexuses which form the aorta and cardinal veins. central artery distributes blood to marginal sinus, which becomes the basilic and cephalic veins. central artery becomes brachial and interossei arteries.

finally, some abnormalities of limb development: amelia is absence of limbs. meromelia is absence of limb segments. phocomelia is absence of proximal limb segments but normal distal segments. polydactylyl is extra digits. syndactylyl is webbed digits.

questions
1. what are somites made from and what induces them?
2. somites divide into...
3. what does the sclerotome become?
4. what does the dermatome become?
5. what does the myotome become?

6. describe the production of cartilage producing cells.
7. what do Wnt genes do?
8. where do the limb buds originate?
9. limb develops from both...
10. what is skeletal muscle formed from?
11. what is dermis formed from?
12. what is the epidermis formed from?
13. what are sensory neurons formed from?

14. what is the AER and what does it do?
15. what is the ZPA and what does it do?
16. what does the myotome form in the limbs?
17. describe the interaction between the AER and ZPA.
18. what are the signaling factors between the AER and ZPA?

19. describe the process of endochondral ossification.
20. what do cartilaginous cells secrete?
21. what is mineralization triggered by?
22. what are osteoblasts derived from?
23. epiphyseal plates expand...
24. achondroplasia is...
25. bone remodeled by...
26. osteoblasts are derived from...
27. osteoclasts are derived from...
28. osteoclasts are activated by...

29. amelia...
30. meromelia...
31. phocomelia...
32. polydactyly...
33. syndactyly...

34. angioblasts form...
35. central artery distributes...
36. marginal sinus becomes...
37. central artery becomes...

answers
1. made from paraxial mesoderm segments, induced by hox genes.
2. sclerotome, dermatome, myotome.
3. vertebrae and ribs
4. dermis
5. muscles of back and limbs
6. Shh from notochord and neural tube induce Pax (1,9) genes, which converted somitic cells into chondroblasts.
7. influence the conversion of dorsal somitic cells into dermatome and myotome.
8. lateral plate mesoderm.
9. local limb bud tissue, as well as migrating tissue from somites.
10. migrating mesoderm cells from myotome differentiate into muscle (following tendons during migration)
11. dermatomal cells
12. ectoderm
13. neural crest cells.
14. apical ectodermal ridge, forms bones along the proximal-distal axis via FGF.
15. forms bones along the cranial-caudal axis via Shh.
16. dorsal-ventral compartment muscles via Wnt.
17. the two centers have a positive feedback system where FGF from the AER maintains Shh expression at the ZPA and Shh in turn activates FGF in AER.
18. formin, gremlin, bone morphogenetic protein (BMP)

19. mesenchymal cells in center of limb condense into "pre-cartilaginous aggregates". chondroblasts form hyaline cartilage matrix. chondroblasts enlarge and form lacunae. hydroxyapetite deposits on partitions between lacunae. cartilage cells die by apoptosis. capillaries vascularize calcified cartilage. osteoblasts deposit bone matrix which replaces cartilage.
20. BMP to promote growth and Ihh to promote production of BMP
21. local secretion of alkaline phosphatase.
22. mesenchymally derived osteoprogenitor cells.
23. with growth hormone
24. premature ossification of epiphyseal plates
25. selective deposition and resorption of bone from opposing surfaces, depending on relative activity of osteoblasts and osteoclasts.
26. osteoprogenitor cells
27. "fused mononuclear hemopoietic progenitor cells"
28. cytokine signaling.

29. absence of limbs
30. absence of limb segments
31. absence of proximal end of limb with normal distal end
32. extra digits
33. webbed digits

34. vascular plexus with aorta and cardinal veins
35. blood through capillaries into marginal sinus
36. cephalic and basilic veins
37. brachial and interosseus arteries

MS anatomy: deep back and neck

this lecture covered the anatomy of the spine as well as the muscles of the deep back, head, and neck. the spine is made of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and a sacrum at the bottom which is made up of 5 fused vertebrae. notable differences between the three vertebral sections: cervical vertebrae have short, split spines, while thoracic vertebrae have long, downward sloping ones. lumbar vertebrae have extra processes next to the transverse processes called mamillary processes. range of movement is wide for cervical and lumbar sections but narrow for thoracic. the spine has two opposite curves, called kyphotic and lordotic. the sacrum and the thoracic spine are kyphotic, folding the body inwards, while the the lumbar and cervical spine have the lordotic curve which has the opposite shape.

some unique features about the top two vertebrae, the atlas (C1) and axis (C2). the atlas lacks a vertebral body and just has anterior and posterior arch. resting in the anterior arch, secured by the transverse ligament, is an upward protrusion from C2, called the "dens" of the axis, which is actually the fusion of the vertebral bodies of C1 and C2. the dens and the atlas form the atlanto-axis pivot joint and allow for rotational movement of the head. the joint between the atlas and the occiput is called the atlanto-occipital joint and is stabilized by a host of muscles that attach to the occiput around it (more to come) as well as the atlanto occipital membrane, a ligament that spans from the posterior occiput to the spinous process of C1. the joint itself is between the superior articular facets of the atlas and the condyles of the occiput.

we then look at the muscles of the back, neck, and head, starting with the muscles of the deep back. these include the erector spinae, the superficial and larger group of back muscles that span from the sacrum to the base of the skull. these include the spinalis, the longissimus, and the iliocostalis. the transversospinalis are a deeper and more intricate set of back muscles that lie in the groove between the transverse and spinous processes-- originating from transverse processes, inserting into spinous processes. the semispinalis covers the upper 1/3 of the spine and each muscle group has a span of 5-8 vertebrae, the multifidus is prominent near the sacrum and spans 3-4 vertebrae a piece, and the rotatores go all along the spine and cover 1-2 vertebrae each. in general, the erector spinae (the larger muscles) are more involved in extension and the transverospinalis muscles (smaller muscles) are more involved in lateral flexion and rotation.

the muscles that aid in movement of the head can be divided into three sections: suboccipital muscles, anterior neck muscles, and lateral neck muscles. suboccipital muscles include the rectus capitis posterior major and minor, and the inferior and superior oblique. for these muscles, when a muscle is oriented vertically, it is involved in extension, and when it is oriented diagonally or horizontally, it is involved in rotation. the anterior neck muscles include the rectus capitis anterior and longus colli and capitis. the lateral neck muscles are the scalenes and SCM. the suboccipital muscles are innervated by the posterior rami of C1, the anterior neck muscles are innervated by C1-4, and the lateral neck muscles are innervated by C2,3 and cranial nerve XI.


questions

vertebrae anatomy
1. spinous process is formed by...
2. transverse process is formed by...
3. mamillary processes...
4. vertebral canal is formed by...
5. zygapophyseal/facet joint is formed by...
6. what are the primary and secondary curves of the spine called?

cervical, thoracic, lumbar vertebrae:
7. body...
8. spines...
9. costotransverse foramen...
10. range of movement...
11. movements...

12. 5 sacral foramen fuse after...
13. sacral foarmina convey...
14. sacral promontory is...
15. what are the sacral crests and what are they made from?
16. sacral canal ends at...
17. what is the coccyx?

18. what is the sacralization of L5?
19. what is the lumbarization of S1?
20. what type of joint is the intervertebral joint?
21. describe the composition of the intervertebral joint.
22. what are the ligaments that support the intervertebral joints?
23. what is a herniated disc?
24. what type of joint is the facet joint?
25. supraspinous ligament...
26. interspinous ligament...
27. ligamentum flavum...

28. what are the anatomical features of C1?
29. what is unique about C2?
30. what is the atlanto-axis joint?
31. what is the transverse ligament?
32. alar and apical ligaments...
33. what is the atlanto-occipital joint and what movement does it allow?
34. what is the atlanto-occipital membrane penetrated by?

deep back muscles
35. what are the erector spinae muscles and where do they originate from?
36. spinalis...
37. longissimus...
38. iliocostalis...
39. what are the transverospinalis muscles?
40. semispinalis...
41. semispinalis capitis is...
42. multifidus...
43. rotatores...
44. what is the splenius and where do the two types attach?
45. describe the difference in action between the long and short deep back muscles.
46. what are deep back muscles innervated by?

suboccipital muscles- origins, insertions, actions
47. inferior oblique...
48. superior oblique...
49. rectus capitis posterior major...
50. rectus capitis posterior minor...
51. which nerve innervates the suboccipital muscles?

anterior neck muscles
52. rectus capitis anterior and lateralis...
53. longus colli and capitis...
54. which nerve innervates the anterior neck muscles?

lateral neck muscles
55. anterior scalenes...
56. posterior scalenes...
57. SCM...

58. flexion of head is mainly due to which muscles?
59. extension of head is mainly due to which muscles?

answers

1. fusion of two pedicles.
2. fusion of pedicles and laminae.
3. are on lumbar vertebrae and can be confused with transverse processes.
4. column of vertebral foramen and houses the spinal cord.
5. joining of superior and inferior articular facets.
6. primary = kyphotic in the thoracic spine and sacrum. secondary = lordotic in the cervical and lumbar spine.

7. oblong, heart shaped, oblong
8. short / bifid, long / downward sloping, intermediate / horizontal
9. transverse foramen, costotransverse, no foramen
10. wide, narrow, wide
11. flex/extend/abduct/some rotation, rotation, flex/extend/abduct/some rotation

12. 20 years
13. anterior and posterior rami of sacral nerves
14. prominent body of S1
15. median crest made from fused SP's, lateral crest from fused TVP's.
16. sacral hiatus
17. 4 small fused vertebrae at the bottom of the sacrum which serve as the origin for pelvic muscles and ligaments.

18. total or partial fusion of L5 to sacrum.
19. total or partial separation of S1 from sacrum.
20. symphysis joint.
21. outer layer is fibrous CT called annulus fibrosus, gelatinous center called nucleus pulposus.
22. anterior and posterior longitudinal ligaments.
23. when pressure between the vertebrae causes the nucleus pulposa to herniate out of the annulus fibrosus and potentially compress spinal nerves against the articular processes.
24. synovial joint.
25. joins tips of vertebral spines
26. spans between vertebral spines
27. elastic CT helps extend vertebral column

28. the "atlas" has an anterior and posterior arch and no vertebral body.
29. the "axis" has an upward protrusion called the "dens" which is the fusion of the bodies of the atlas and axis.
30. the joint that is formed by the dens and the anterior arch of the atlas which allows for the rotation of the head.
31. anchors the dens to the anterior arch.
32. anchor dens to margin of foramen magnum and limits rotational movement.
33. joint between the occipital condyles of the head and the superior articular facets of the atlas. permits flexion and extension of head.
34. C1, vertebral artery.

35. iliac crest and sacrum.
36. interconnects thoracic spinous processes.
37. runs along costovertebral region, also has a capitis portion.
38. goes from iliac crest to ribs.
39. semispinalis, multifidus, rotatores- muscles that span from sacrum to base of skull. lie within groove between transverse and spinous processes and go from TP's to SP's.
40. semispinalis spans 5-8 vertebrae, are in the upper 1/2 of vertebral column.
41. strongest extensor of the skull.
42. spans 3-4 vertebrae, thickest over sacrum
43. span 1-2 vertebrae throughout spine.

44. muscle that goes from spinous processes to TP's or to skull. capitis attaches to mastoid process, cervicis attaches to TP's.
45. long deep back muscles more extension, short deep back muscles more rotation and lateral flexion.
46. posterior rami of spinal nerves.

47. O: spine of axis I: TP of axis A: rotate
48. O: TP of axis I: occiput A: extend
49. O: spine of axis I: occiput A: extend and rotate
50. O: posterior tubercle of atlas I: occiput A: extend
51. posterior ramus of C1

52. O: TP of atlas I: occiput A: flexion and lateral flexion and stabilization of altantoocciptal joint.
53. O: body and TP's of cervical vertebrae I: same, plus occiput A: flexion
54. C1-4

55. O: upper TP's I: 1st rib A: flexion of head, raise ribs N: lower cervical nerves
56. O: upper TP's I: 2nd rib A: flexion of head, raise ribs N: lower cervical nerves
57. O: manubrium, clavicle I: mastoid process A: flexion, lateral flexion, rotation, raise ribs N: motor-spinal accessory (cranial nerve XI), C2,3

58. SCM, rectus capitis anterior, longus capitis / colli
59. trapezius, rectus capitis posterior, superior oblique

musculoskeletal anatomy: blood vessels of upper limb

this lecture covered some basics in the structure of veins and arteries in upper limbs, as well as an extra slide about breast tissue. first it describes the major vein structure: the subclavian artery passes through the scalenes and becomes the axillary artery, which turns into the brachial artery below the teres major, until it bifurcates into the radial and ulnar artery in the forearm. on the backside, the major arteries in the scapular region which branch off of the axillary artery: the dorsal scapular artery is near the medial border of the scapula, the suprascapular artery is near the supra and infraspinous fossa, and the circumflex artery is near the medial triangular space. some possibilities for blockage or compression are looked at-- if the axillary artery is blocked, then flow can be shunted downstream via "reverse flow through the circumflex". thoracic outlet syndrome, or neurovascular compression syndrome, is a compression of the brachial plexus nerves and blood vessels that can occur either at the space between the scalenes, the costoclavicular space, or the pectoralis minor. cervical rib disorder is an extra rib growing off of C7 which can cause a similar sort of compression.

we then look at some of the major veins in the arms: the cephalic vein runs up the anterolateral forearm, up the bicep, between the deltoid and the pectoralis major, and drains into the subclavian vein. the basilic vein runs on the anteromedial side of the forearm and up the medial side of the arm, converging into the deep veins into the axillary vein. the medial cubital vein interconnects these two veins in the cubital fossa, which is a space in the upper forearm made from the borders of the pronator teres, brachioradialis, and the line between the two epicondyles. the cubital fossa also contains the median and radial nerves, superficial veins, brachial artery, and the tendon of the biceps. venae comitantes are veins that surround and hug major arteries and provide an alternate pathway for venous blood to return to the heart. being closer to the center of the body, they play a pivotal role in the regulation of body temperature, where blood is shunted to them in order to converse body heat (and shunted to the superficial veins to lower body temperature).

finally, some completely random facts about mammary glands. they are organized in 15-20 lobes, and are basically modified sweat glands embedded in adipose tissue. lactiferous ducts collect milk into lactiferous sinuses and cooper's ligaments anchor the breast to deep fascia. lymph channels from the breast carry lymph to four different locations: the opposite breast, the axilla, parasternal nodes, abdominal nodes.


questions
1. describe the arteries of the upper limb, going from the subclavian down to the radial and ulnar.
2. what are the arteries that circulate around the scapula and where are they?
3. if the axillary artery is occluded...
4. what is neurovascular compression syndrome?
5. what is a cervical rib?
6. what is the deep palmar arch?
7. describe the path of the ulnar artery in the hand.
8. palmar and dorsal arches branch into...
9. nerves and blood vessels run...

10. what are the veins that venipuncture can be performed in?
11. where does the cephalic vein run? where does it drain into?
12. where does the basilic vein run? where does it converge?
13. where does the medial cubital vein run?
14. what are venae comitantes?
15. how is body temperature regulated with superficial vs. deep veins?
16. what is the cubital fossa made of and what are the structures within it?

17. describe mammary glands.
18. lactiferous ducts...
19. suspensory (Cooper's) ligaments...
20. where do lymph channels carry lymph from the breast to?

answers
1. the subclavian artery runs between the middle and anterior scalene muscles and turns into the axillary artery, from the scalenes until the lower part of the teres major muscle. from there it turns into the brachial artery, up to the point of bifurcation into the radial and ulnar artery.
2. the dorsal scapular artery (vertebral border of scapula), suprascapular artery (supra, infraspinous fossa), and circumflex scapular artery (medial triangular space).
3. blood is shunted to the distal axillary artery by reverse flow through the circumflex artery.
4. compression of the brachial plexus and blood vessels, possible in three places: between scalenes, costoclavicular, and pectoralis minor.
5. an extra rib from the 7th vertebrae, can cause compression of the brachial plexus or arteries as well.
6. the portion of the radial artery that passes through the anatomical snuffbox and around the first metacarpal to enter the palm.
7. the ulnar artery goes through the tunnel of guyon (the space between the pisiform and hook of hamate), then forms the "superficial palmar arch".
8. metacarpal, common, and proper digital arteries paralleling the cutaneous nerves.
9. along the sides of digits.

10. cephalic, basilic, medial cubital
11. anterolateral forearm, over biceps, between deltoid and pectoralis major. drains into subclavian vein in clavipectoral triangle.
12. anteromedial forearm, penetrates medial side of arm. converges into deep veins to form axillary vein.
13. between the cephalic and basilic veins.in the cubital fossa.
14. veins that run accompany major arteries and provide an alternate means of venous return to the heart and aid in thermoregulation.
15. to lower body temperature, blood is shunted to superficial veins. to raise body temperature, blood is shunted to venae comitantes.
16. made of space between pronator teres, brachioradialis, line between two epicondyles. contains: superficial veins, median and radial nervees, brachial artery, biceps tendon.

17. 15-20 lobes, modified sweat glands embedded in adipose tissue.
18. drain milk into lactiferous sinuses.
19. support breast from deep fascia.
20. pectoral nodes in axilla, opposite breast, parasternal nodes, abdominal nodes.