TBL 2 - Vertebral Column, Osteogenesis, Spinal Cord, Extrinsic Shoulder Muscles, and Intrinsic Back Muscles

Question 1

What does the axial skeleton include?

Answer 1

Skull, vertebral column, ribs, and sternum

Question 2

What is spondylolysis and what is the consequence?

Answer 2

Fracture of a vertebra between its superior and inferior articular processes (pars interarticularis). Consequence is dislocation between the two vertebrae.

Question 3

What is the nucleus pulposus and annulus fibrosis and what function does the resulting structure serve?

Answer 3

Form the IV disc. The central mass is the nucleus pulposus and the annulus fibrosis is the concentric Type I collagen that surrounds it. Deformability of this provides shock absorption.

Question 4

Where do spinal nerves emerge from the vertebral canal?

Answer 4

The intervertebral foramina

Question 5

Which clinical conditions might require a laminectomy and how is a laminectomy surgically performed?

Answer 5

A laminectomy is where a spinous process and its lamina are removed by transecting the vertebrate at the pedicles. They are used to relieve pressure on the spinal cord or nerve roots in cases of a tumor, herniated disc, or bony hypertrophy

Question 6

How does stenosis affect the lumbar portion of the vertebral canal and the lumbar spinal nerves?

Answer 6

Stenosis is the narrowing of the vertebral foramen. The foramina decrease in size as one goes down the spine even though the nerves increase in size. Narrowing in the lumbar region can compress the nerve roots in the inferior vertebral canal.

Question 7

What does the ligamenta flava do?

Answer 7

Connects the laminae vertically to close the posterior wall of the vertebral canal

Question 8

Describe the anterior and posterior longitudinal ligaments

Answer 8

Anterior - covers anterior surface of vertebral bodies and IV discs. Limits extension of column by maintaining stability
Posterior - posterior surface of the vertebral bodies, attaches to IV discs. Somewhat weaker but it prevents posterior herniation of the nucleus pulposus and contains many pain nerves

Question 9

Describe primary and secondary curvatures of the spine and how secondary curvature is maintained.

Answer 9

Primary - concave anteriorly like ( and develop from the fetal position.
Secondary - concave posteriorly like ) and develop due to differences in anterior and posterior portions of IV discs. They form after an infant can lift its head and walk

Question 10

Why do herniations of the nucleus pulposus usually protrude posterolaterally?

Answer 10

Annulus fibrosis is thin here and there is no support from the anterior or posterior longitudinal ligaments so degeneration of AF leads to the nucleus pulposus getting pushed posterolaterally

Question 11

What are primary causes of excessive kyphosis and lordosis? How does scoliosis differ in appearance from excessive kyphosis?

Answer 11

Excessive kyphosis - humpback - caused by erosion due to osteoporosis of the anterior part of vertebrae. There is an increase in thoracic curvature
Lordosis - hollow back - where there is anterior tilting of the pelvis due to weakened anterolateral abdominal muscles
Scoliosis - curved back - lateral curvature with rotation of the vertebrae. The spinous processes turn toward the cavity of abnormal curvature

Question 12

Describe formation of notochord and what it becomes

Answer 12

Migrating mesodermal cells that invade the developing endoderm detach to form the notochord. Ultimately becomes the nucleus pulposus of the IV discs

Question 13

What is the precursor to the annulus fibrosis and dermis associated with the vertebral column and thoracic wall during the prenatal period

Answer 13

Mesenchymal cells of somites differentiate into fibroblasts that form the annulus fibrosis and dermis.

Question 14

During the embryonic period, what forms the skeletal muscles associated with the spine and thoracic wall?

Answer 14

Mesenchymal cell-derived myoblasts

Question 15

From where do the chondroblasts and osteoblasts of the cervical, thoracic, lumbar, sacral, and coccygeal somites come from?

Answer 15

Mesenchymal cells

Question 16

What causes spina bifida occulta, the most common congenital anomaly of the vertebral column?

Answer 16

Neural arches of L5 and/or S1 do not develop properly and fuse posterior to the vertebral canal

Question 17

How does spina bifida cystica differ from spina bifida occulta?

Answer 17

In spina bifida cystica, one or more arches do not develop at all causing more severe problems than in occulta

Question 18

Describe the process and the cartilage at the beginning of osteogenesis.

Answer 18

Chondroblasts produce avascular cartilaginous replicas of the bones. The cartilage consists of the cells in lacunae with a non calcified matrix surrounding by periochondrium. The hyaline cartilage is made of Type II collagen and is translucent and glassy in appearance. O2 and nutrients diffuse from capillaries in the perichondrium into the matrix

Question 19

First step of endochondrial ossification

Answer 19

Capillaries invade the cartilaginous matrix.

Question 20

What follows the capillary invasion of the first step of endochondrial ossification?

Answer 20

Osteoprogenitor cells and macrophages follow the capillary. Multiple macrophages fuse to form osteoclasts which phagocytize the cartilaginous matrix.

Question 21

What do osteoblasts do during endochondrial ossification and what are osteocytes in this process?

Answer 21

Osteoblasts produce Type I collagen that traps the osteoblasts in the lacunae. The trapped cells are osteocytes and they deposit hydroxyapatite crystals on the collage fibers aligning them in parallel rows.

Question 22

What is the name for the layer of osteoblasts that covers the bone and why is it important?

Answer 22

Endosteum - important for continued bone maturation

Question 23

What is the periosteum

Answer 23

Type I collagen fibers that cover a monolayer of osteoprogenitor cells. Surrounds compact bone that forms around the peripheral of the trabecular

Question 24

What is the first step of the transformation from trabecular bone into compact bone

Answer 24

Primary osteons, the oval shaped trabecular bone adjacent to the already formed peripheral compact bone, have inner surfaces lined by endosteum. Interstitial fluid separates the osteons from the centrally positioned capillaries (and sensory nerves)

Question 25

Once the primary osteon forms, how does it transition to a secondary osteon?

Answer 25

Endosteal osteoblasts produce the bony matrix with concentric rows of lacunae separated by parallel mineralized fibers. This encloses the central capillaries (and sensory nerves) forming the secondary osteons.

Question 26

Describe the secondary osteons and what the canaliculi are and its importance

Answer 26

Central canals enclosing the capillaries. Canals are lined by endosteum and the concentric dotted lines are osteocyte-filled lacunae created by the inward deposition of the mineralized fibers.
Canaliculi are little canals from the central canal to each lacunae to provide the osteocytes with capillary filtrates allowing for active maintenance of the bone

Question 27

What is a Volkmann canal and its importance

Answer 27

A perpendicular canal to the central canal allowing the capillaries to extend from the periosteum into the central canals

Question 28

In what direction are osteons oriented relative to the bone and what resides between the osteons and describe it.

Answer 28

Parallel to the longitudinal axis and the interstitial lamellae reside between the osteons. Interstitial lamellae are remnants of osteons after bone remodeling from physical stresses and more

Question 29

How to trabecular osteocytes access bone marrow capillaries after compact bone has formed?

Answer 29

Canaliculi connect the lacunae to the surface of the trabeculae giving the trabecular osteocytes access to filtrates from the bone marrow capillaries.

Question 30

What causes osteoporosis, a metabolic bone disease, and why can it result in increased kyphosis?

Answer 30

Net demineralization of bones so the balance between deposition and resorption is upset. Kyphosis is caused by the weakening of the vertebral bodies at the core.

Question 31

Are the horns gray or white matter and what resides there?

Answer 31

Gray and neurons

Question 32

Are the roots of spinal nerves gray or white matter?

Answer 32

White

Question 33

What constitutes the anterior roots of spinal nerves

Answer 33

Motor axons

Question 34

What constitutes the posterior roots of spinal nerves and where do they synapse

Answer 34

Sensory axons that synapse with neurons in the posterior horn (gray matter). Information comes into the spinal cord

Question 35

Spinal nerves are formed by the union of what?

Answer 35

Anterior roots and sensory axons from the spinal ganglion. They contain both motor and sensory axons.

Question 36

How many of each type of vertebrate bones are there?

Answer 36

7 Cervix, 12 Thoracic, 5 Lumbar, 5 Sacral, 4 Coccyx

Question 37

How many nerves of each type of spinal nerve exist?

Answer 37

8 pairs of cervical
12 pairs of thoracic
4 pairs of lumbar
5 pairs of sacral

Question 38

What and where is the conus modullaris?

Answer 38

Inferior end of the spinal cord below lumbar enlargement. It is between L1 and L2 in adults and is between L3 and L4 at birth until age 5

Question 39

What is the cauda equina?

Answer 39

The long roots of the lumbar and sacral spinal nerves that result from the elongation of the spine and erect posture.

Question 40

What is the dural sac, where does it end, and what lines it in the cervical region

Answer 40

The dural sac is the termination end of the dura mater beyond the length of the spinal cord. Ends at S2 and is lined by the arachnoid in the cervical region

Question 41

What are the dura and arachnoid of spinal meninges composed of and what causes the arachnoid to press against the inner surface of the dura?

Answer 41

Dura - dense connective tissue
Arachnoid - loose connective tissue
CSF fills the subarachnoid space and causes the arachnoid to press against the inner surface of the dura.

Question 42

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

Answer 42

Many diseases affect the chemical or cellular composition of the CSF or cause blood to enter the CSF, all of which are diagnostic. The procedure should be done below the conus medullaris so newborns should have it at a lower vertebrate than adults.

Question 43

What is the filum terminale

Answer 43

It is an extension of the pia mater (which lines the outside of the white matter of the spinal cord) and pierces the end of the dural sac to anchor it to the coccyx

Question 44

What part of the spinal cord to the anterior and posterior spinal arteries supply?

Answer 44

The superior part of the cord

Question 45

What artery supplies 2/3rds of the spinal cord

Answer 45

The great anterior segmental medullary artery

Question 46

How to the segmental medullary arteries (anterior and posterior) enter the spine?

Answer 46

They arise from arteries adjacent to the spine and end via the IV foramina

Question 47

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

Answer 47

Anything that obstructs blood to the spine will cause spinal cord ischemia (inadequate blood supply). The consequence is paralysis inferior to the level of impaired blood supply and neuron cell death.

Question 48

Trace where the veins of the spinal cord drain.

Answer 48

They drain into the vertebral venous plexus in the epidural space between the dura and periosteum of the vertebral canal. Small branches of the venous plexus traverse the intervertebral foramina to empty into the trunk and neck.

Question 49

What is the role of muscle tone and when is it absence?

Answer 49

Firmness and stability of joints and posture. Ensures muscles are ready to respond to stimuli. Absent during deep sleep, or anasthesia or if nerve lesions cause paralysis.

Question 50

Superficial extrinsic shoulder muscles and their proximal and distal attachments and function

Answer 50

Trapezius - C7-T12 vertebrae to scapula and clavicle, lifts the scapula and rotates it to lift limb. When the scapula is protracted, it is retracted by the trapezius like pulling an object toward you
Latissimus dorsi - inferior 6 thoracic vertebrae (T7-T12) to medial side of humerus, adductor of limb like climbing

Question 51

Deep extrinsic shoulder muscles and their proximal and distal attachments and function

Answer 51

levator scapulae - C1-C4 to the superior angle of the scapula, acts synergistically with the trapezius to elevate scapula
rhomboids - C7-T5 to the medial border of the scapula, holds the scapula against the posterior thoracic wall

Question 52

What does the spinal accessory nerve innervate

Answer 52

Trapezius

Question 53

What doe the thoracodorsal nerve innervate?

Answer 53

Latissimus dorsi

Question 54

What is the visible clinical manifestation in patients with ipsilateral trapezius muscle weakness?

Answer 54

Weakness when shoulders shrugged against resistance

Question 55

Why is the use of crutches difficult by an adult with latissimus dorsi weakness, and how would the weakness affect a 1-year old infant?

Answer 55

Crutch would push shoulder superiorly and the lats would not be able to push down. Weakness in the lats would prevent an infant from climbing to a standing position

Question 56

What does the dorsal scapular nerve innervate and what is its spinal origin?

Answer 56

The levator scapulae and rhomboids

C4, C5

Question 57

The intrinsic back muscle and its proximal and distal attachments and unilateral and bilateral function

Answer 57

Erector spinae - sacrum to the posterior aspects of the ribs, thoracic and cervical vertebrae
Unilateral - laterally flexes spinal column
Bilateral - extends column and head

Question 58

What is innervated by the posterior rami of spinal nerves

Answer 58

Erector spinae and skin of the back