Back and Spinal Cord

ANAT 305 - Cross Sectional Anatomy

Prior to the union of the two vertebral arteries forming the basilar artery, it gives off three branches. What are these three branches?

1. Anterior spinal artery

2. posterior spinal artery 

3. posterior inferior cerebellar artery (PICA)

What are the two curvatures of the vertebral column

• Primary Curvatures

  • curve posteriorly: thoracic and sacral kyphosis

• Secondary curvatures

  • curve anteriorly: cervical and lumbar lordosis

What are the two muscles groupings of the back and their functions

• Extrinsic muscles

  • move the upper limbs and the ribs

• Intrinsic muscles

  • maintain posture and move the vertebral column

List the 5 extrinsic muscles

• Trapezius

• Latissimus dorsi

• Rhomboid major 

• Rhomboid minor

• Levator scapule

Trapezius Muscle

• Attachment

• Innervation

• Function

• attachment

  • occipital bone and spinous process of C7-T12 —> clavicle and acromion

• Innervation

  • CN XI (spinal accessory nerve)

• Function

  • elevates, retracts, rotates the scapula

Lattisimus Dorsi Muscle

• Attachment

• Function

• Attahcments: lower thoracic vertebrae, iliac crest, lower ribs —> intertubercular sulcus of humerus

• function: extends, adducts, medially rotates the humerus

Teres Major Muscle

• Attachment

• Function

• attachment: inferior angle of scapula —> intertubucular groove of the humerus

• function: extend adducts, medial rotates the humerus

  • called Lat jr as it does all the same movements

Levator scapulae

• attachment

• function

• attachment: transverse processes of the upper cervical vertebrae —> scapula

• function: elevate the scapula

What are the two intermediate groups of back muscles and what is their function

Serratus posterior inferior and superior

• Both are are attached from the vertebral column to the ribs

  • SPS: elevates ribs II-V

  • SPI: depress ribs IX-XII

What does the thoracolumbar fascia cover and connect with

it covers the deep muscles of the back/trunk and is continous with the deep fascia of the neck

What two back muscles have medial attachments that blend into the thoracolumbar fascia

latissimus dorsi

serratus posterior inferior

What are the erector spinae muscles

They are a group of three muscle columns situated along the vertebral column, responsible for extending and laterally flexing the spine.

• med to lat: spinalis, longissimus, ileocostalis

What are the two components of a vertebrae and what seperates the vertebral bodies of adjacent vertebrae?

The two components are the body and the arch.

The intervertebral discs separate the vertebral bodies of adjacent vertebrae.

What is the function of the vertebral pedicle

The vertebral pedicle connects the vertebral body to the vertebral arch

function of vertebral lamina

The vertebral lamina connects the spinous process to the transverse processes, providing structural support and protection to the spinal cord.

Spinous process of the vertebrae

is a bony projection on the posterior aspect of a vertebra, serving as an attachment point for muscles and ligaments

Transverse process of vertebrae

extends laterally from the vertebra's pedicle and lamina, serving as an attachment point for muscles and ligaments, and articulating with ribs in the thoracic region.

What is the major distinguishing feature of C1 (atlas)?

It lacks a vertebral body, which fuses onto the body of C2 during development to form the dens of C2.

What is the structural composition of the atlas (C1)?

the atlas is ring-shaped and composed of two lateral masses interconnected by anterior and posterior arches

How are the vertebral arches of the vertebrae aligned to form?

They align to form the lateral and posterior walls of the vertebral canal, which extends from C1 to S5 and contains the spinal cord, blood vessels, connective tissue, fat, and the proximal parts of the spinal nerves.

What extends from the region where a lamina meets a pedicle?

Transverse process

What forms the anterior and lateral walls of the vertebral canal?

• anterior wall = vertebral bodies, intervertebral discs

• lateral walls = vertebral arches and their ligaments

What are the three connective tissue membranes within the vertebral canal?

• Pia mater

  • inner most layer, adherent to the spinal cord

• arachnoid mater

  • middle layer: seperated from the pia by the subarachnoid space which contains the CSF

• dura mater

  • outermost thick layer: continous with the cranial dura and tapers as the filum terminale to attach to posterior coccyx

Do spinal nerve roots pierce the meninges when leaving the spinal cord?

No, as they exit through the intervertebral foramen, an extension of the dura mater surrounds each root, forming a protective sleeve that merges with the epineurium of the spinal nerve

What space is located between the walls of the vertebral canal (bony canal) and the dural sac (outermost membrane surrounding the spinal cord)?

The epidural space, containing fat and internal vertebral venous plexus

List the 9 layers that an LP needle/RT beam would pass through right at midline to hit CSF

• skin

• subcutaneous fat

• supraspinous ligament

• interspinous ligament

• ligamentum flavum

• epidural space

• dura mater

• subdural space

• arachnoid mater

the needle then enters the subarachoid space to collect CSF

List the 8 layers an LP needle/RT beam would pass through laterally to hit CSF

• skin

• subcutaneous fat

• Erector spinae muscles

• ligamentum flavum

• epidural space

• dura mater

• subdural space

• arachnoid mater

completely avoids the interspinous and supraspinous ligaments.

What is an imporant landmark to perform the LP

The spinous process of L4 vertebrae

• aligns with the intercristal plane (a line drawn between iliac crests)

identifies the L4-5 intervertebral space, which is ideal site for performing LP

How does an epidural anesthetic work?

a needle is inserted through the skin, supraspinous ligament, interspinous ligament and ligamenta flava into the epidural space, which contains fat and connective tissue around the dura mater, where it numbs the exiting nerve roots and can partly diffuse into the subarachnoid space.

where do the vertebral arteries travel in the spinal column?

The vertebral arterties pass through the transverse foramina of C6 to C1, then enter the skull via the foramen magnum, where they join to form the basilar artery

Where do the spinal nerves exit the vertebral canal?

spinal nerves exit laterally through the intervertebral foramen which is formed between adjacent vertebrae

Why are some posterior regions of the vertebral arches clinically important?

In the lumbar region, gaps between the laminae and spinous process widen from L1-L5, allowing easier acces to the vertebral canal for procedures like LPs or epidurals

What 6 ligaments reinforce the vertebral column

• anterior longitudinal ligaments

• posterior longitudunal ligaments

• ligamenta flava

• interspinous ligaments

• supraspinous ligaments

• ligamentum nuchae

Where does the anterior longitudinal ligament lie

runs along the anterior surface of the vertebral bodies from the base of the skull to the sacrum, attaching to both vertebral bodies and discs

where does the posterior longitudinal ligament lie?

runs along the posterior surface of the vertebral bodies, lining the anterior wall of the vertebral canal

Ligamenta Flava

Connects the laminae of adjacent vertebrae, forming part of the posterior wall of the vertebral canal; helps maintain upright posture and assists in returning the spine to neutral after flexion.

What are the supraspinous ligament and ligamentum nuchae?

The supraspinous ligament connects the tips of spinous processes from C7 to the sacrum. From C7 to the skull, it is thicker and called the ligamentum nuchae.

What two reasons are a laminactomy performed

• A prolapsed intervertebral disc

• If there is spinal fusion or additional bony growths

Where does the spinal cord start and end?

Extends from the foramen magnum to L1-L2 in adults (L2-3 in children) at the conus medullaris

• filum terminale = CT filament extending from tip of conus medullaris

Is the spinal cord uniform in diameter along its length?

No, there is a cervical enlargement (C5-T1), and a lumbosacral enlargement (L1-S3)

Where does the spinal cord receive it’s arterial supply

from longitudinal arteries (anterior and posterior spinal aa.) and segmental spinal arteries entering at each vertebral level

where do segmental spinal arteries enter the vertebral canal?

Via the intervertebral foramina at every vertebral level.

what three places do segmental spinal arteries originate

• Vertebral and deep cervical arteries in the neck

• Posterior intercostal arteries in the thorax

• Lumbar arteries in the abdomen

what arteries do segmental spinal arteries give rise to?

Radicular and medullary arteries that supply the spinal cord.

What is the anterior spinal artery and where does it originate?

A single artery formed in the cranial cavity by the union of two branches from the vertebral arteries; runs along the anterior midline of the spinal cord.

What are the posterior spinal arteries and where do they originate?

Two arteries originating from the posterior inferior cerebellar arteries (branches of the vertebral arteries) in the cranial cavity; descend along the posterior aspect of the spinal cord.

What are the anterior and posterior spinal arteries reinforced by?

Segmental medullary arteries

In what space are the main longitudinal veins of the spinal cord located

in the subarachnoid space running along the cord

what veins are associated with the nerve roots

radicular veins

• two pairs of veins on each side, bracketing the connecton of the anterior and posterior roots

what midline venous channels exist in the spinal cord?

one anterior channel and one posterior channel

what do the spinal cord veins drain into?

the internal vertebral venous plexus in the epidural space, which connects segmental veins into larger systems (like the azygos)

How is each spinal nerve connected to the spinal cord?

posterior (dorsal) root : contains sensory neuron processes

DRG: cluster of sensory neuron cell bodies at the distal end of the posterior root in the intervertebral foramen

ventral root: contains motor fibers carrying signals away from the CNS

what is a spinal segment

a region of the spinal cord that gives rise to a pair of posterior and anterior rootlets which join to form a single spinal nerve

What do the divisions of a spinal nerve form?

• Posterior (dorsal) rami: innervate intrinsic back muscles and skin of the back.

• Anterior (ventral) rami: innervate most other skeletal muscles (limbs and trunk) and most remaining areas of skin.

Why is it relevant that the vertebral venous (internal) plexus is valveless?

• Allows bidirectional blood flow, influenced by gravity, body position, and pressure changes.

• Provides a low-resistance pathway for cancer cells or infections to spread to the pelvis and abdomen.

Lumbar Cistern

Fluid-filled space in the lower part of the vertebral column located within the thecal sac containing CSF and nerve roots of caudal equina and filum terminale

Extends from L1-L2 to S2

Where does the dural sac end?

S2

Where does the conus medullaris start?

L1-L2

What does the filum terminale internum and externum contain?

Filum terminale internum: pia mater and collagen

Will pierce the dura at S2 and take a sleeve of dura mater with it

Filum terminale externum: dura mater around and attaches to the coccyx

Where does the arachnoid mater end?

S2

What are the contents in the epidural space?

-Epidural fat

-internal vertebral venous plexus

-spinal nerves