TBL 2 Objectives

Question 1

Recall the origin and function of the bilateral somites

Answer 1

paraxial mesoderm forms block-like somites adjacent to the notochord and neural tube

• mesenchymal cells of the somites differentiate into fibroblasts that form the annulus fibrosis of IV discs and the dermis mainly associated with the vertebral column and thoracic wall
• mesenchymal cell-derived myoblasts form skeletal muscles associated with the spine and the thoracic wall
• mesenchymal cells also generate chondroblasts and osteoblasts that produce cartilage and bone, respectively
• chondroblasts and osteoblasts of the cervical, thoracic, lumbar, sacral, and coccygeal somites form the vertebrebral column

Question 2

Explain the questions for application of knowledge:

1. What casuses spina bifida occulta, the most common congenital anomaly of the vertebral column?
2. How does spina bifida cystica differ from spina bifida occulta?

Answer 2

1. Neural arches of L5 and/or S1 fail to develop normally and fuse posterior to the vertebral canal
2. Spina Bifida cystica is associated with herniation of meninges (meningocele) and/or herniation of the spinal cord (meningomyelocele)

Question 3

Summarize endochondral ossification (taken from 4th TBL)

Answer 3

The process by which hyaline cartilage replicas are replaced with bone

• formation of thin bony collars around diaphysis, separating chondrocytes from capillaries in the perichondrium
• osteoblasts, angiogenic capillaries, and macrophaes from the the bony collar enter diaphysis and replace eroded cartilage with trabecular bone that creates primary ossification center in the diaphysis
• transformation of primary osteons into mature osteons forms compact none that occupies the outer part of the diaphysis

Question 4

Describe the composition trabecular bone

Answer 4

i’ll do this later

Question 5

Define the axial skeleton

Answer 5

The axial skeleton includes the skull, vertebral column aka spine, ribs, and sternum

Question 6

Compare the vertebral body and vertebral arch

Answer 6

The 24 presacral vertebrae (7 cervical, 12 thoracic, 5 lumbar) consist of anterior vertebral bodies and posterior vertebral arches that create vertebral foramina to enclose the spinal cord, spinal nerve roots, and spinal ganglia. Continuity of the vertebral foramina creates the vertebral canal.

Question 7

Describe the intervertebral discs

Answer 7

IV discs consist of a nucleus pulposus (originally from the notochord), the gelatinous central mass that is surrounded by concentric layers of Type I collagen fibers forming the annulus fibrosis (originally from the paraxial mesodermal somites). The discs strongly attach adjacent vertebral bodies and their resilient deformability provides shock absorbers for the spine. IV discs make up 25% of the vertebral column, while vertebral bodies make up 75%.

Question 8

Define the location and function of the ligament flava

Answer 8

The ligament flava vertically interconnects the lamina of adjacent vertebrae, thus contributing to the posterior wall of the vertebral canal.

Question 9

Compare locations and functions of the anterior and posterior longitudinal ligaments

Answer 9

The anterior longitudinal ligament is a strong, broad fibrous band that covers and connects the anterolateral aspects of the vertebral bodies and IV discs. It prevents hyperextension of the vertebral column, maintaining stability of the joints between the vertebral bodies. It is the only ligament that limits extension; all others limit flexion.
The posterior longitudinal ligament is a narrow, weaker ligament that runs within the vertebral canal along the posterior side of the vertebral bodies. It is attached mainly to the IV discs and less so to the vertebral bodies. It resists hyperflexion of the vertebral column and helps prevent or redirect posterior herniation of the nucleus pulpous. Nociceptive (pain) nerve endings are located here as well.

Question 10

Distinguish the primary and secondary curvatures of the spine

Answer 10

At the fetal/newborn stage, only primary curvatures exist. Secondary curvatures form during infancy/childhood after an infant can lift his head and begins to walk. They are maintained by differences in thickness between anterior and posterior portions of the IV discs. 
Cervical: secondary
Thoracic: primary
Lumbar: secondary
Sacral: primary

Question 11

Define the origin, function, and fate of the notochord

Answer 11

During development, some mesodermal cells will migrate and invade the developing endoderm. These cells will form the notochord, a rigid rod of supporting mesoderm that induces formation of the axial skeleton and neural tube. The notochord is located immediately below the neural tube and ultimately forms the nucleus pulposus of the IV discs.

Question 12

Periousteum and endosteum

Answer 12

Periosteum consists of Type 1 collagen fiber bundles covering an inner monolayer of osteoprogenitor cells. The outer fibrous layer is firmly anchored into the compact bone.
Endosteum: lines the surface of the medullary cavity.

Question 13

Vascularity of bone

Answer 13

Central canals in primary osteons enclose capillaries, then osteocytes produce spindle like processes that reside in bony canaliculi. The bony canaliculi connects to the central canal. Capillary filtrates in interstitial fluid of central canals. Volkmann canals join the central canals enabling periosteal arterioles to supply capillaries of the central canals

Question 14

Locations of trabecular bone and compact bone in mature bone

Answer 14

Trabecular bone remains in the core of developing bones while compact bone surrounds the trabecular bone.

Question 15

Bone remodeling

Answer 15

Interstitial lamellae forms during bone remodeling and represent the remnants of osteons after remodeling. It requires bony matrix resorption followed by deposition of new bone matrix. Osteoclasts are in charge of bone resorption and osteoblasts of the endosteum and periosteum create new bone matrix

Question 16

What causes this metabolic bone disease and why can it result in increased kyphosis?

Answer 16

• Metabolic bone disease is caused by a net demineralization of the bones which is caused by a disruption of the normal balance of calcium deposition and calcium resorption.
• This can lead to kyphosis because it causes compression fractures of the anterior vertebral bodies. This results in wedge like vertebrae in the thoracic region causing excessive curvature.

Question 17

Posterior and anterior horns and roots of the spinal cord

Answer 17

Anterior (ventral) and posterior (dorsal) horns constitute gray matter of the spinal. The horns contain nerve cell bodies. Cell bodies in the anterior horn form the anterior (motor) roots of spinal nerves and the posterior (sensory) roots of spinal nerves synapse with cell bodies in the posterior horn. Posterior and anterior roots are constitutes of white matter that surrounds the gray matter of the spinal cord. Neurons reside in the gray matter. The spinal nerves are formed by union of the anterior roots with sensory axons from the spinal ganglion; thus, all spinal nerves contain both sensory and motor axons

Question 18

Name the superficial and deep extrinsic shoulder muscles

Answer 18

Superficial: Trapezius and latissimus dorsi
Deep: Rhomboids and levator scapulae

Question 19

Relate proximal and distal muscle attachments to actions of the muscles

Answer 19

 Trapezius: proximally to the external occipital protuberance, superior nuchal line, nuchal ligament, spinous process C7-T12, distally to cavicle, acromion, scapular spine.
 Latissimus dorsi: proximally to spinous process T7-T12, distally intertubercular sulcus.
 Rhomboids: proximally to spinous process T2-T5, distally medial scapular border.
 Levator scapulae: proximally to tranverse processes of C1-C4, distally to the superior angle of scapula.

Question 20

Cite innervations and independent and synergistic actions of the muscles

Answer 20

Trapezius: Cranial nerve 11 (accessory), C3, C4. Elevates, depresses or retracts spine.
Latissimus dorsi: Thoracodorsal nerve (C6, C7, C8). Extends, adducts, medially rotates and raises body to arms when climbing.
Rhomboids: Dorsal scapular nerve (C4, C5). Retracts scapula.
Levator scapulae: Doral scapular nerve (C4,C5). Elevates scapula.

Question 21

Name the designated intrinsic back muscle and cite its innervation

Answer 21

Erector spinae, innervated by posterior rami of spinal nerves.

Question 22

Relate proximal and distal attachments of the intrinsic back muscle to its actions

Answer 22

proximally to the broad tendon arising from sacrum and iliac crest and inferior lumbar spinous processes, distally to the posterior aspects of thoracic and cervical ribs. Extends back, lateral movement of spine.

Question 23

What is the result of an injury to the thoracodorsal nerve?

What muscle is weak when you can’t shrug your shoulders against resistance?

Answer 23

Injure throacodorsal nerve = cant lift body with arms/ use axillary crutches.
Trapezius weakness = cant shrug shoulders against resistance.

Question 24

Cite the number of segmental spinal nerves

Answer 24

31:

cervical: 8
thoracic: 12
lumbar: 5
sacral: 5
coccygeal: 1

Question 25

Compare location of conus medullaris in neonates and adults

Answer 25

neonates: btwn vertebrae L3/4
adults: btwn L1/2

Question 26

Describe the cauda equina

Answer 26

(cauda - “tail” ; equina - “horse”)
the cauda equina is the bushy “tail” of spinal nerve roots that extend out of the conus medullaris (the end of the spinal cord) and coursing within the lumbar cistern of CSF to reach their distal targets of innervation.

Question 27

Define the meningeal layers and the location of CSF

Answer 27

Meningeal layers surround, support, and protect the spinal cord and spinal nerve roots.

From the inside out (deep to superficial):

PIA MATER – directly encases the spinal cord. Transparent- very thin; only 2-3 cell layers.
[sub-arachnoid space – CSF]
ARACHNOID MATER: loose connective tissue
DURA MATER: dense connective tissue
[epidural space – filled w fat and vessels]
[vertebral body]

The CSF is contained within the sub-arachnoid space, where it pushes the arachnoid against the inner surface of the dura. The CSF continues inside the lumbar cistern, the cavity enclosed by dural sac after conus medullaris (dural sac ends at S2)

Question 28

Describe the filum terminale

Answer 28

made of vestiges of neural, connective, and neuroglial tissues, covered by pia mater.

proximal end arises from the tip of the conus medullaris (at this point it is the filium terminale internum)

descends among spinal roots in the cauda equina
as the filum terminale perforates the inferior end of the dural sac, it gains a layer of dura and continues through the sacral hiatus (filum terminale externum).

distal end attaches to dorsum of coccyx

it is a “pial extension,” like denticulate ligaments

Question 29

Summarize the arterial supply and venous drainage of the spinal cord

Answer 29

ARTERIAL SUPPLY

The superior spinal cord is supplied by:
1 anterior spinal artery
2 posterior spinal arteries

The inferior spinal cord is supplied by:
anterior and posterior segmental medullary arteries.
The segmental medullary arteries arise from the arteries adjacent to the vertebral column, and enter the spine via IV foramina. The largest is the great anterior segmental medullary artery of Adamkiewicz, which supplies about 2/3 of the spinal cord.

VENOUS DRAINAGE

The veins of the spinal cord joins the internal vertebral plexus in the epidural space (btwn the dura and the periosteum of the vertebral canal). The plexus veins drain via the IV foramina into anterior and posterior external vertebral venous plexuses. These course along the vertebral column and empty into the veins of the trunk and neck.

Question 30

Why is obstructive disease of the great anterior segmental artery of Adamkiewicz associated with spinal cord ischemia, and what is the clinical consequence?

Answer 30

This artery supplies 2/3 of the spinal cord, so circulatory impairment of the spinal cord will arise if it is narrowed (for example, by obstructive artery disease). The clinical consequence of spinal cord ischemia is muscle weakness and paralysis. First, the axons from the site of ischemia will die, leading to the death of their cell bodies distal to the site.

Question 31

Why is lumbar spinal puncture an important diagnostic tool? Why would different vertebral levels be used in newborn infants and adults?

Answer 31

The LP withdraws CSF from the lumbar cistern. CSF may be altered or have different chemical concentrations in CNS diseases such as meningitis, so looking at it is a useful diagnostic. You can also very easily tell if there is blood in the CSF.

In adults, the LP is done between L3/L4, or L4/L5, so as to steer clear of the spinal cord (which should end at the conus medullaris around L1/2). In newborn infants, the conus medullaris extends to L3/L4 until the age of 5, when vertebral column development and erect posture have come into play.