Dissector Answers - Back & Spinal Cord

Learning Objectives:

Upon completion of this session, the student will be able to:

1. Define the "anatomical position". Using the conventional anatomical terms, describe the body and the spatial relationships of its parts, for example dorsal/ventral, medial/lateral, proximal/distal, and superficial/deep.
2. Recognize and define the standard planes and sections used to describe parts of the body and the relationships of the various planes and sections to one another.
3. Describe the general structural plan of the body and the relationships of the layers, partitions and compartments one encounters when dissecting from superficial to deep in any particular region.
4. Demonstrate a cutaneous nerve and describe the pattern of cutaneous nerves on the back.
5. Identify, and give the general attachments of, nerve and blood supply to, and the general functions of the superficial back muscles.
6. Identify the bony prominences of the back and spine that may be palpated and used for reference to underlying structures.
7. Identify and give the function of the significant parts of a typical vertebra and associated ligaments.
8. Identify the specialized vertebrae.
9. Describe the spine, its curvatures, and vertebral column movements.
10. Identify the coverings and the supporting structures of the spinal cord. Give the point of the termination of the spinal cord and the dural sac.
11. Identify the terminal specialties of the cord, their relation to lumbar puncture, the nerve rootlets, and blood supply.
12. Describe the anatomy of the cord and vertebrae as related to fractures, dislocations, and possible cord injury.
13. Describe or illustrate the location and function of the basic somatic motor and sensory neurons on a cross section of the spinal cord.
14. Describe a typical spinal nerve, the somatic motor and sensory components found in any portion, and their distribution.
15. Describe conceptually how any region of the thoracic wall gets its blood supply and innervation.
16. Define and explain the significance of dermatomes.
17. Explain the difference between superficial and deep (true) back muscles.

Learning Objectives and Explanations:

1. Define the "anatomical position". Using the conventional anatomical terms, describe the body and the spatial relationships of its parts, for example dorsal/ventral, medial/lateral, proximal/distal, and superficial/deep. (W&B 3-4)

All anatomical descriptions are used in relation to the anatomical position, which refers to the body as standing erect with:

• head, eyes and toes pointed anteriorly (forward)
• upper limbs by the sides with palms facing anteriorly
• lower limbs together with toes directed anteriorly.

Terms of relationship in the anatomical position:

• Superficial, intermediate, deep: used in dissection to describe the position of one structure with respect to another (The investing fascia is superficial to the muscle.)
• Medial: indicates that a structure is nearer to the median plane (midpoint) of the body. Lateral: indicates that a structure is farther away from the median plane. (The eyes are lateral to the nose.)
• Posterior (dorsal): denotes the back surface of the body, or a structure nearer to the back. Anterior (ventral): denotes the front surface of the body, or a structure nearer to the front. (The sternum is anterior to the vertebral or spinal column.)
• Proximal, distal: relative terms that are used when contrasting positions with respect to the attachment/origin of the limb/structure. Proximal is nearer and distal is farther from the attachment/origin. (The wrist is distal to the elbow.)

2. Recognize and define the standard planes and sections used to describe parts of the body and the relationships of the various planes and sections to one another. (W&B 3-4)

Anatomical descriptions are based on four imaginary planes that pass through the body in the anatomical position:

• Median/sagittal/midsagittal plane: the vertical plane passing longitudinally through the body, dividing it into right and left halves.
• Parasagittal planes: vertical planes passing through the body parallel to and on the right or left side of the median plane.
• Coronal/frontal planes: vertical planes passing through the body perpendicular to the median plane, dividing it into anterior and posterior sections.
• Horizontal (transverse) planes: planes passing through the body at right angles to the median and coronal planes. It divides the body into superior and inferior parts. Views of this type are commonly called cross-sections.

3. Describe the general structural plan of the body and the relationships of the layers, partitions and compartments one encounters when dissecting from superficial to deep in any particular region. (W&B 4-6)

Structural layers, from superficial to deep:

• Skin: made of epidermis and dermis. The epidermis is the thin, outer, impervious cellular layer. The dermis is the thicker, leather-like layer that gives skin its strength. In it are hair follicles, sweat glands, sebaceous glands (innervation and blood supply is through the subcutaneous tissue deep to skin). (Latin/Greek, epi = upon, attached to)
• Subcutaneous tissue or fat: also known as superficial fascia or hypodermis. A fascia is a covering, a sheet of connective tissue. (Latin, fascia = band)
• Deep or investing fascia: a denser connective tissue layer that "invests" the area like a stocking or sleeve. It binds groups of muscles together as a unit and has partitions between the muscles called intermuscular septa. The investing fascia is usually named regionally (e.g. thoracolumbar fascia). (Latin, septum = partition, wall)
• Muscular fascia: surrounds individual muscles directly
• Neurovascular bundle: veins, arteries, lymphatic vessels, and nerves often travel together in these bundles. They vary in size and do not always have all four elements. They often have branches that begin deep and travel superficially - supplying muscles, then subcutaneous tissue, and finally terminating in the skin.
• The deepest layer in limbs is the bone, while in the trunk the body cavities will be the deepest.

4. Demonstrate a cutaneous neurovascular bundle and describe patterns of cutaneous nerves on the back. (W&B 88-89, N 170, 177, 180, 192, 258, TG 1-12, 1-17)

Neurovascular bundles are collections of nerves, arteries, and veins running together. Veins are more easily found, because coagulated blood shows through their thin walls. Arteries will appear as small white tubular structures with dark veins stuck on their sides. Two veins, called venae commitantes, usually travel on either side of most smaller arteries. Nerves are usually white as well, but they do not have veins stuck to their sides like arteries have. Nerves often look striated or fasciculated, and they may have tortuous courses, meaning that their courses may "wiggle". This is a common feature for nerves, as opposed to vessels, because nerves are less elastic than vessels. They need some "give" built in to their courses, especially if they travel out to moveable structures. Think of an old-fashioned telephone receiver cord and that is the general idea. Related to the difference in the elasticity between blood vessels and nerves is a difference in branching patterns. Blood vessels tend to branch at angles that approach 90 degrees, while nerves branch much more gradually, by fanning out. There are notable exceptions, but they are very few and they can be explained by unusual situations.

The sensory nerves of the back all arise from the dorsal primary ramus of the associated spinal nerve. Above the mid-thorax, these terminal cutaneous branches can be found piercing the trapezius near the mid-line and traveling laterally from there to innervate the skin. Below the mid-thorax, the cutaneous branches pierce the muscles in an increasingly lateral position as you move inferiorly. (Latin, ramus = branch)

The cutaneous branches of dorsal primary rami only innervate skin from the back of the head to the upper buttocks, and as far laterally as the rib angles, approximately. The rest of the trunk, and all of the skin of the limbs, is supplied by branches of ventral primary rami of spinal nerves. The cutaneous nerves of the trunk are distributed segmentally to supply strips of skin, roughly following the direction of the ribs, called dermatomes.

5. Identify, and give the general attachments of, nerve and blood supply to, and the general functions of the superficial back muscles. (N 174, 424, TG 1-13)

Note: Muscles are typically described by their origin and insertion. The origin of a muscle is the point from which it acts - usually, but not always, this is more proximal in the limbs. The insertion of a muscle is the more moveable point - the part that is acted upon - usually, this is more distal in the limbs.

Muscle	Origin	Insertion	Action	Innervation	Artery	Notes
trapezius	medial third of the superior nuchal line, external occipital protuberance, ligamentum nuchae, spinous processes of vertebrae C7-T12	lateral third of the clavicle, medial side of the acromion and the upper crest of the scapular spine, tubercle of the scapular spine	elevates and depresses the scapula (depending on which part of the muscle contracts); rotates the scapula superiorly; retracts scapula	motor: spinal accessory (XI), proprioception: C3-C4	transverse cervical a.	named for its shape; trapezius is an example of a muscle that migrates during development from its level of origin (cervical) to its final position, pulling its nerve and artery along behind
latissimus dorsi	vertebral spines from T7 to the sacrum, posterior third of the iliac crest, lower 3 or 4 ribs, sometimes from the inferior angle of the scapula	floor of the intertubercular groove	extends the arm and rotates the arm medially	thoracodorsal nerve (C7,8) from the posterior cord of the brachial plexus	thoracodorsal a.	the inserting tendon twists so that fibers originating highest insert lowest
levator scapulae	transverse processes of C1-C4 vertebrae	medial border of the scapula from the superior angle to the spine	elevates the scapula	dorsal scapular nerve (C5); the upper part of the muscle receives branches of C3 & C4	dorsal scapular a.	levator scapulae is named for its action
rhomboideus major	spines of vertebrae T2-T5	medial border of the scapula inferior to the spine of the scapula	retracts, elevates and rotates the scapula inferiorly	dorsal scapular nerve (C5)	dorsal scapular a.	named for its shape
rhomboideus minor	inferior end of the ligamentum nuchae, spines of vertebrae C7 and T1	medial border of the scapula at the root of the spine of the scapula	retracts, elevates and rotates the scapula inferiorly	dorsal scapular nerve (C5)	dorsal scapular a	named for its shape

6. Identify the bony prominences of the back and spine that may be palpated and used for reference to underlying structures.

• Triangle of auscultation (W&B 90, N 152, TG 1-13): A triangular gap formed by the superior horizontal border of the latissimus dorsi, the medial border of the scapula, and the inferolateral border of the trapezius. This is a good place to examine posterior segments of the lungs with a stethoscope.
• Lumbar triangle (W&B 90, N 152, TG 1-13): Bordered medially by the latissimus dorsi, laterally by the external abdominal oblique, and inferiorly by the iliac crest. This point is vulnerable to abdominal hernia.
• Vertebra (spina) prominens (W&B 88, N 21, TG 1-01): This prominent vertebra at C7 is characterized by a long spinous process. It can be palpated and marks the location of the last cervical vertebra.
• Scapula (W&B 88, N 420, 421, TG 1-01): The spine of the scapula can be palpated medially at level T3.
• Iliac crest (crest of ilium) (W&B 88, N 486, TG 1-01): This important landmark can be palpated at level L4. It denotes superior border of the greater pelvic region.
• External occipital protuberance (inion) (W&B 88, N 4): A median projection located a little inferior to the bulging part of the posterior aspect of the head at the junction of the head and neck. Directly below this the spinous process of C2 can be palpated. C1 has no spinous process, and its small posterior tubercle is neither visible nor palpable. (Latin, occiput = against head)
• Nuchal groove (N 152, TG 1-01): The median area between C3 and C5 denotes the short bifid spinous processes of C3 through C5 vertebrae. (Latin, nucha = nape)
• Mastoid processes (N 4, TG 7-05, 7-06): These are prominences of the temporal bone posterior to the ear and the angle of the jaw on either side of the head. The transverse process of C1 may be felt by deep palpation between the mastoid processes. (Latin/Greek, mastoides = resembling a nipple)

7. Identify and give the function of the significant parts of a typical vertebra and associated ligaments. (W&B 339-344, N 154A, 154B, 155, TG 1-02, 1-03A, 1-03D, 1-05A, 1-05B, 1-05D, 1-08A, 1-08B, 1-10, 1-11A, 1-11B) )

• Vertebral body: the largest part of the vertebra, shaped like a short cylinder. Supports the spine and entire body.
• Vertebral arch: the ring of bone formed by the paired pedicles and paired laminae of the vertebrae. It connects the body with the transverse processes.
• Pedicle: part of the arch. This short, strong process extends posteriorly from the posterolateral surface of the vertebral body. It is paired and connects the body with the transverse process.
• Intervertebral notch: notches on the superior and inferior surface of the vertebral pedicle. The superior intervertebral notch of one vertebra combined with the inferior intervertebral notch of the adjacent vertebra forms the intervertebral foramen.
• Intervertebral foramen: opening between the pedicles of adjacent vertebra. It is the opening for the passage of the spinal nerves out from the spinal cord.
• Lamina: part of the arch. This broad flat plate of bone is located between the transverse process and the spinous process of the vertebra. It is paired. It gives attachment to the ligamenta flava, which span the intervals between the laminae of adjacent vertebrae.
• Transverse process: lateral process that extends from the junction of the pedicle and the lamina of the vertebra. It is the site for muscle attachment and rib articulation.
• Spinous process: posterior mid-line process arising from the junction of the two laminae of the vertebrae. The spinous processes are important sites of muscle attachment.
• Articular processes: processes that project inferiorly and superiorly from the junction of the lamina and pedicle of the vertebra. There are two superior and two inferior processes on each vertebra, and they articulate with adjacent vertebrae through synovial joints. Clinicians refer to these as "facet joints."
• Vertebral canal: the opening formed by the combination of the body and the vertebral arch. It contains the spinal cord, meninges, epidural fat, and the internal vertebral plexus of veins.
• Anterior longitudinal ligament: ligament that runs from superior to inferior along the anterior surface of the body of the vertebrae. It helps attach the bodies of the vertebrae to each other.
• Posterior longitudinal ligament: ligament that goes from superior to inferior along the posterior surfaces of all vertebral bodies, joining them together. It is broader at the discs and narrower at the bodies, giving it a scalloped edge. It is located in the vertebral canal but it is NOT penetrated by the needle during spinal tap.
• Ligamenta flava: ligaments formed predominantly by elastic fibers which join the laminae of adjacent vertebrae. These are paired and are penetrated by a needle during a spinal tap. (Latin, flavus = yellow)
• Intervertebral disc: fibrocartilaginous disc between adjacent vertebral bodies which are important shock absorbers and give the spine flexibility. The discs are composed of two parts:
  • Anulus fibrosus: outer fibrous rim. (Latin, anulus = ring)
  • Nucleus pulposus: pulpy mass located inside the anulus.

8. Identify the specialized vertebrae. (W&B 343, N 17, 18, TG 1-03A, 1-03C, 1-08A)

• Atlas (C1): has no vertebral body, only anterior and posterior arches, and it articulates with the odontoid process of C2. (Think of Atlas supporting the weight of the world on his shoulders.)
• Axis (C2): dens (odontoid process) projects superiorly from its body and articulates with the anterior arch of the atlas. There is no rotation of the skull with respect to the atlas, so the first moveable joint in the spinal column is the C1-C2 joint - the "axis" of rotation if you will.
• Vertebra prominens (C7): also called "spina prominens". Although the two terms are used interchangeably, one is most often referring to the spinous process of C7. It is long and non-bifid, and is palpable through the skin at the nape of the neck.

9. Describe the spine, its curvatures and vertebral column movement. (W&B 344-345, N 153, TG 1-02)

• The spine extends from the skull to the apex of the coccyx and forms the skeleton of the neck, and back and the main part of the axial skeleton. It consists of 33 vertebrae arranged in five regions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal. (One professor suggests thinking of times of the day that you eat, i.e. 7am, 12pm, and 5pm.)
• Motion only occurs among 24 vertebrae: 7 cervical, 12 thoracic, and 5 lumbar. The sacral and coccygeal vertebrae are usually fused. (Latin/Greek, coccyx = cuckoo's beak. Latin, os sacrum = holy bone)
• Possible movements of the spinal column:
  • Flexion (touching your toes)
  • Extension (bending backwards)
  • Lateral bending
  • Rotation (either of head and neck only, or of the entire torso)
• Four curvatures of the spine are apparent in adults:
  • Cervical: secondary curvature - concave posteriorly
  • Thoracic: primary curvature - concave anteriorly
  • Lumbar: secondary curvature - concave posteriorly
  • Sacral: primary curvature - concave anteriorly

10. Identify the coverings and the supporting structures of the spinal cord. Give the point of the termination of the spinal cord and the dural sac. (W&B 350-353, N 160, 161, 169, TG 1-18, 1-19, 1-20)

• Dura mater: outermost covering membrane. This is tough, pierced by spinal nerves, and anchored inferiorly to coccyx as the filum terminale (externum). It extends through the intervertebral foramina and along the dorsal and ventral nerve roots to a point distal to the spinal ganglia, forming dural root sleeves. The dural sac proper ends at the level of S2, and is anchored inferiorly to the coccyx by the coccygeal ligament, or filum terminale (externum). (Latin, dura mater = tough mother)
• Arachnoid mater: delicate membrane made of fibrous and elastic tissue that lines the dural sac and the dural root sleeves. The arachnoid mater encloses the CSF-filled subarachnoid space containing the spinal cord, spinal nerve roots, and spinal ganglia. It is held against the dura but separable from it. In a lumbar spinal puncture, the arachnoid is pierced. NO subdural space exists between dura and arachnoid, it is only a POTENTIAL space.
• Subarachnoid space: contains cerebrospinal fluid. Below L2 it contains the cauda equina.
• Pia mater: innermost covering membrane of the spinal cord. The pia mater closely follows entire spinal cord and directly covers the roots of spinal nerves and the spinal blood vessels. Inferior to the conus medullaris, the pia continues as the filum terminale. (Latin, pia mater = delicate mother)
  • Denticulate ligaments: specializations of pia mater. These ligaments form a longitudinal shelf separating dorsal and ventral rootlets. Also, by extending laterally from cord and attaching to the dura by way of 21 pairs of denticulations, they suspend the spinal cord in the subarachnoid space.

11. Identify the terminal specialties of the cord, their relation to lumbar puncture, the nerve rootlets, and blood supply. (W&B 350-353, N 160, 161, TG 1-11, 1-18, 1-20)

• Conus medullaris: located at L2. This is the tapered termination of the spinal cord proper.
• Filum terminale: continuation of the pia mater inferior to the conus medullaris. It descends all the way to the coccyx, anchoring the spinal cord.
• Cauda equina: the collection of nerve roots coming from the end of the spinal cord, within the lumbar cistern, traveling to the vertebral foramina inferior to the conus medullaris. (Latin, cauda equina = horse's tail)
• A lumbar puncture is done either above or below L4 in the region of the cauda equina.
• Blood supply follows along with the nerve rootlets themselves.

12. Describe the anatomy of the cord and vertebrae as related to fractures, dislocations, and possible cord injury.

• Herniation (N 161, 162, TG 1-11, 1-18, 1-20): Focal protrusion of disc material secondary to rupture of anulus fibrosus. This most commonly occurs in the lumbar region, and can result in compression of spinal nerves (which usually leads to the clinical presentation).
• Dislocation of vertebrae: Like any other dislocation, this is a case of the bone slipping out of place, most commonly in the cervical region. The spinal canal is relatively small and these injuries very often result in damage to the spinal cord.
• Fracture of the dens: Due to the relative strength of the ligaments in the region compared to the dens, stress often results in its fracture. In effect, it is "the first thing to go".
• Cord injuries: The spinal cord can be injured in various ways, all of which are extremely serious and can result in significant impairment of function.

13. Describe or illustrate the location and function of the basic somatic motor and sensory neurons on a cross section of the spinal cord. (W&B 353-355, N 169, 170)

A cross-section of the spinal cord will show a butterfly-shaped area of gray matter surrounded by white matter. The butterfly has four "horns", two dorsal and two ventral. Sensory neurons originate in the dorsal horns and make up the dorsal roots, but their cell bodies are in the dorsal root ganglia, outside of the spinal cord. Motor neurons have their cell bodies within the spinal cord, in the ventral horn. (The ventral horn is "fatter", since those cell bodies take up space!) They unite to form the ventral roots. Distal to the dorsal root ganglia, the roots unite, forming the spinal nerve. The nerve quickly splits into two branches, or ventral and dorsal rami, which carry both sensory and motor fibers. (Latin, ramus = branch)

14. Describe a typical spinal nerve, the somatic motor and sensory components found in any portion, and their distribution. (W&B 9-10, N 169, 170, TG 1-17)

• Parts (proximal to distal):
  • Roots: dorsal and ventral. Roots are made of several rootlets
  • Spinal nerve: where the two roots come together briefly
  • Primary rami: dorsal and ventral. These are the first branches off the spinal nerve.
  • Cutaneous branches: posterior, lateral and anterior.
• Functional components:
  • Sensory: Afferent, either somatic or visceral.
  • Motor: Efferent, either somatic or visceral.
    • Somatic motor: to voluntary muscle.
    • Visceral motor (autonomic): to involuntary muscle and glands.
  • White ramus communicans: connection between sympathetic trunk and ventral primary ramus. These are only found between T1 and L2. (More on these later.)
  • Gray ramus communicans: connection between sympathetic trunk and ventral primary ramus. Found in all spinal nerves (31 pairs). (More on these later.)

15. Describe conceptually how any region of the thoracic wall gets its blood supply and innervation. (W&B 364-368, N 180, 258, TG 1-17)

Both the nerves and the arteries are segmented along vertical axis of the thorax. The intercostal nerves come from the spinal nerves. The arteries are mostly segmental branches of the aorta. The veins, arteries, and nerves run in a groove under each rib with the veins most superior and the nerves most inferior (VAN). Each also gives off a smaller collateral branch that runs on top of the rib below.

16. Define and explain the significance of dermatomes. (W&B 123, 581 (limbs), N 164, TG 1-23A, 1-23B)

One dermatome is the region innervated by one spinal nerve. They typically overlap, with one nerve covering its own dermatome as well as half of the one above and below it.

17. Explain the difference between superficial and true back muscles. (W&B 89-93,335-338, N 174, 179, TG 1-12, 1-13, 1-14, 1-15)

• Superficial back muscles control upper limb movements as well as aid in respiration. They mostly receive their nerve supply from the ventral rami of cervical nerves. These include the:
  • Trapezius: innervated by the accessory nerve (CN XI).
  • Latissimus dorsi: innervated by thoracodorsal nerve, made from branches of ventral primary rami of C7 & C8.
  • Rhomboideus major & minor: innervated by dorsal scapular nerve, a branch of the VPR of C5.
  • Levator scapulae: innervated by dorsal scapular nerve and branches of the VPR's of C3 & C4.
  • Serratus posterior (superior and inferior): innervated by intercostal nerves, first four and last four respectively. (Latin, serratus = to saw)
• Deep or true back muscles specifically act on the vertebral column, producing its movements and maintaining posture. They are innervated by dorsal rami of spinal nerves. The fascia covering them constitutes the thoracolumbar fascia.

Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless. Surface Anatomy of the Back - Surface Markings of the Back - The Muscles Connecting the Upper Extremity to the Vertebral Column - The Accessory NerveThe Vertebral Column - General Characteristics of a Vertebra - The Cervical Vertebrae - The Thoracic Vertebrae -The Lumbar Vertebrae - The Sacral and Coccygeal Vertebrae - The Vertebral Column as a Whole - The Deep Muscles of the Back - The Spinal Cord - The Meninges of the Brain and Spinal Cord - The Spinal Nerves

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Questions and Answers:

1. What are the names of the nerves that innervate the subcutaneous tissue and skin?

The cutaneous branches of the dorsal rami innervate the subcutaneous tissue and skin of the back. Their origin are the spinal nerves running from C3 to the coccyx. These innervate the "intrinsic" (deep) muscles of the back and the overlying skin, but not the muscles in between. It is important to remember that the extrinsic or superficial muscles of the back (latissimus dorsi, trapezius, etc.) are not innervated by the dorsal rami but by branches off of the ventral primary rami of spinal nerves. (Do not confuse rami with roots here... while branches of the dorsal primary rami supply motor function to the deep back muscles and sensory function to the skin, sensory nerves arise from the dorsal root and motor nerves arise from the ventral root.) (N 180, 258, TG 1-12, 1-17)

2. What is the function of the investing fascia?

The investing fascia (deep fascia) invests the muscles and associated tendons up to their attachment to bone and is itself attached to the periosteum of the bones. Parts of it are named for the muscle being invested. For example, the thoracolumbar fascia encloses the deep muscles of the back in the thoracic and lumbar regions. Furthermore, groups of muscles with similar functions may be contained in a common compartment formed by the investing fascia. These fascial compartments often contain or direct the spread of an infection or a tumor.

3. Between some muscles there is loose fascia, fat and connective tissue. What is the function of this fascia?

Loose fascia and fat are located throughout the body at sites which require padding or mobility, where friction is a concern, or where blood vessels and/or nerves require padding.

4. Why do nerves, arteries, and veins branch in different manners?

Nerves, arteries, and veins all have different embryological origins, different anatomical sources, different targets, and obviously different functions. But, just like different people travel on the same interstate highway to go to different places, nerves, arteries, and veins can start somewhere, jump into a neurovascular bundle in order to travel a distance, then jump off to reach their destination.

5. Where do nerves C3 and C4 (branching off of anterior primary rami of spinal nerves) combine to form the subtrapezial plexus?

C3, C4, and the accessory nerve (CN XI) combine at the C5 level to form the subtrapezial plexus. Together they innervate the trapezius muscle. The accessory nerve carries the motor fibers, while C3 and C4 carry the proprioceptive sensory fibers. (N 127, 177, TG 1-13)

6. What is the thoracolumbar fascia (aponeurosis)?

The thoracolumbar fascia is an extensive fascial sheet that splits into anterior and posterior layers, thereby enclosing the deep back muscles. It is thin and transparent where it covers the thoracic parts of the deep muscles but is thick and strong in the lumbar region. The lumbar part of the thoracolumbar fascia, extending between the 12th rib superiorly and the iliac crest inferiorly, is a point of origin for the internal oblique and transverse abdominal muscles. (N 174, 179, TG 1-13)

7. In reference to latissimus dorsi: How are the costal attachments of the muscle related to adjacent muscles? Is there an attachment to the scapula?

The serratus posterior inferior and serratus anterior muscles lie deep to the latissimus dorsi, attaching to the costal surfaces. At the mid-scapular plane, however, between the 9th and 12th rib, there is also attachment of the latissimus dorsi to the ribs. Additionally, the latissimus dorsi often has a small attachment to the inferior angle of the scapula. (N 174, TG 1-13)

8. What is the coccygeal ligament?

At the level of termination of the dura sac, S2, the dura continues below as the coccygeal ligament (or filum terminale externum) to attach to the coccyx. (N 160, TG 1-20)

9. What do the lateral continuities of the dura mater cover at and distal to the intervertebral foramen?

They cover the dorsal root ganglia and spinal nerves, eventually blending with the epineurium of the spinal nerves and their dorsal and ventral primary rami. (N 173, TG 1-19)

10a. What does the subarachnoid space usually contain?

The subarachnoid space usually contains cerebrospinal fluid (CSF). (N 169A, 169B, TG 1-19, 1-20)

10b. With what is the subarachnoid space continuous?

The subarachnoid space surrounding the spinal cord is continuous with the subarachnoid space surrounding the brain. This means that it is also continuous with the ventricular system within the brain, where CSF is produced. (N 109, TG 7-50)

11a. Where does the filum terminale lie?

The filum terminale (internum) extends inferiorly from the conus medullaris, as part of the cauda equina in the lumbar cistern, to become enclosed within the coccygeal ligament (or filum terminale externum). (N 160A, 160B, 161, TG 1-18, 1-20)

11b. Where does the filum terminale attach?

The filum terminale attaches to the coccyx . (N 159, TG 1-18, 1-20)

12. What are the relations of the denticulations and the denticulate ligament to the roots of spinal nerves?

The denticulations separate the dorsal and ventral roots by lying between them. (N 169, TG 1-19)

13. How many denticulations are there?

There are 21 denticulations. (N 169, TG 1-18)

14. Where do the denticulations attach?

They pierce the arachnoid mater to attach to the inner surface of the dura mater. (N 169, TG 1-19)

15. At what vertebral level is the conus medullaris?

The conus medullaris is at L1-2. (N 160A, 160B, 161, TG 1-18, 1-20)

16. Note posterior and anterior spinal arteries. What are their sources?

The spinal arteries arise within the skull. Anterior spinal arteries are branches of the vertebral arteries and posterior spinal arteries are branches of the posterior inferior cerebellar arteries. (N 171, 172A172B, TG 1-21, 7-56A, 7-56B)

17. What reinforces the spinal arteries?

Aorta or vertebral aa. --> segmental aa. --> posterior branch --> spinal branches --> radicular branches --> anterior and posterior spinal arteries via anastomoses. (N 171, TG 1-21)

18. What are radicular arteries?

Radicular arteries are branches of spinal branches of segmental arteries that run along the dorsal and ventral spinal nerve roots. (N 171, 172A172B, TG 1-19, 1-20, 1-21)

19. Are all radicular arteries the same?

Most radicular arteries are small, but there is often a rather large radicular artery, the great radicular artery, that may be found in the lower thoracic or upper lumbar levels, usually on the left side. The great radicular artery represents a major blood supply for the lower spinal cord. (N 171, 172A172B, TG 1-19, 1-20, 1-21)

20. What is the source for radicular arteries?

Radicular arteries arise from vertebral arteries in neck, segmental arteries (intercostal & lumbar), and lateral sacral arteries in the pelvis. (N 171, 172A172B, TG 1-19, 1-20, 1-21)

21. Observe arrangement of gray matter and white matter of the cord. What is their significance?

Gray matter is located on the inside of the spinal cord and makes up the "butterfly." It is composed of cell bodies and has dorsal, ventral and lateral horns. White matter, located on the outside of the "butterfly", is made up of myelinated nerve tracks. (W&B 33, N 169)

22. After exposing the posterior longitudinal ligament in cervical and lumbar regions, can you see the intervertebral discs?

You can not see the discs very well. The posterior longitudinal ligament spreads laterally at each disc to attach to it. (N 158, TG 1-11)

23. What is the significance of the attachment of the posterior longitudinal ligament to the discs?

The attachment of the posterior longitudinal ligament to the intervertebral disc helps to reinforce the posterior aspect of the anulus fibrosus. However, because the ligament thins laterally, most disc herniations occur in a posterolateral direction. (N 158, TG 1-11)

24. Where is the dura mater in relation to the intervertebral foramen?

Within the intervertebral foramen, attached to the periosteum surrounding it. (N 173, TG 1-18, 1-19, 1-20)

25. Examine dorsal and ventral rootlets as they emerge from the cord. How is the segmental pattern created?

Rootlets coalesce as they enter the dural sleeve, lateral to their exit from the cord, thereby forming segmental roots. (N 169)

26. What is a root?

The roots are nerves which leave the gray matter through ventral or dorsal horns and unite to become the spinal nerve. (N 169, TG 1-17, 1-19)

27. What is the functional difference between dorsal and ventral roots?

Ventral roots carry motor fibers, both somatic and visceral. Dorsal roots carry sensory fibers. (N 169, TG 1-17)

28. Trace the roots to the point of union to form the spinal nerve. Are they in separate sheaths before uniting?

No, the spinal nerve roots are usually contained within a common sleeve of dura mater. (N 169, TG 1-17)

29. Where is the dorsal root ganglion?

The dorsal root ganglion is located in the intervertebral foramen on the dorsal root. There is one ganglion per spinal nerve. (N 169, 180, TG 1-17, 1-19)

30. What is the extent of the dura mater, arachnoid mater, and pia mater on the spinal nerves?

The pia mater fuses with the arachnoid mater at the spinal nerve, while the dura mater still provides a covering. (N 169, TG 1-17, 1-19)