Spinal Cord and Nerve Roots

Question 1

PNS

Answer 1

• consists of cranial nerves and spinal nerves, which link CNS to peripheral tissues
• neurons contributing to PNS are partly contained in CNS
• 12 cranial nerves
• 31 pairs spinal nerves

Question 2

Spinal Cord Characteristics

Answer 2

• extends from foramen magnum to level of disc between L1 and L2
• distal end is conus medularis
• filum terminale tethers it down
• 2 enlargements: cervical C5-T1 and lumbar L1-S3

Question 3

Features of Spinal Cord

Answer 3

• anterior median fissure: anterior surface
• posterior median sulcus: posterior surface
• posterolateral sulcus: each side of posterior surface where posterior rootlets of spinal cord enter cord
• central canal surrounded by gray matter and white matter

Question 4

Spinal Cord Arteries

Answer 4

• longitudinal arteries: anterior spinal and 2 posterior spinal arteries
• segmental spinal arteries: anterior and posterior radicular arteries supply anterior and posterior roots and segmental medullary arteries reinforce longitudinal vessels

Question 5

Spinal Cord Veins

Answer 5

• 2 pairs of veins on each side of posterior and anterior roots to cord
• anterior spinal vein: parallels anterior median fissure
• posterior spinal vein: parallels posterior median sulcus
• internal vertebral plexus

Question 6

Spinal Cord Meninges

Answer 6

• epidural space separates vertebral canal from spinal dural mater
• spinal dura mater is outermost layer
• arachnoid matter ends at S2 and is below dura mater
• subarachnoid space is between arachnoid and pia mater, contains CSF, and ends at St
• pia mater is firmly attached to spinal cord and is a denticulate ligament

Question 7

Arrangement of Structures in the Vertebral Canal

Answer 7

• anteriorly: bodies of vertebrae, IVDs, posterior longitudinal ligament
• laterally: pedicles, intervertebral foramina
• posteriorly: laminae, ligamentum flavum

Question 8

Spinal Nerves

Answer 8

• posterior (dorsal) root
• anterior (ventral) root
• branches: posterior dorsal ramus-innervate only intrinsic back muscles; anterior ventral ramus-innervate most other skeletal muscles and areas of the skin and forms all major plexuses
• so the nerve consists of sensory, motor, and autonomic signals between the cord and the body
• the roots carry only sensory or motor messages
• the rami carry both sensory and motor messages
• the dorsal root ganglion is a group of cell bodies that…
• SAME DAVE
• dorsal ramus is smaller than ventral
• have 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal

Question 9

Conus Medullaris Syndrome

Answer 9

• deficits occur as result of lesion in sacral region

- compression/trauma at level of conus medullaris

Question 10

Cauda Equina Syndrome

Answer 10

• impaired function in multiple nerve roots below L1 and L2

- compression at cauda equina roots

Question 11

Naming the Spinal Nerve

Answer 11

• cervical region the spinal nerves come out above the named vertebrae
• in every other region (thoracic, lumbar, sacral, coccygeal) they come out below the named vertebrae

Question 12

Dermatomes

Answer 12

• one spinal nerve innervates the dermatome, myotome, and sclerotome (bone) from one somite
• so a dermatome is the area of skin innervated by a particular spinal nerve
• sharp lines on diagrams give false impression of boundaries
• sensory terminals overlap considerably

Question 13

Shingles

Answer 13

• herpes zoster
• virus remains in primary sensory neurons (usually in 1 dermatome on one side) dormant but viable
• virus may revive decades later wreaking havoc with somatosensory system
• agonizing pain for months or years
• constant burning, sometimes stabbing
• skin becomes inflamed and blistered, then scaly (very sensitive to stimuli)
• usually reactivates only in one DRG

Question 14

Myotomes

Answer 14

• group of skeletal muscles innervated by a particular spinal nerve
• usually functionally related