Inha University Hospital Professor Yoon SH Spinal Cord Anatomy Inha University Hospital Professor Yoon SH

Spinal Cord Anatomy Spinal cord is covered by pia, arachnoid, and dura Cord suspended in dural sheath by denticulate ligament on each side Attached along lateral surface of cord midway between dorsal and ventral roots

Spinal cord anatomy Cord is enlarged in cervical (C4-T1) and lumbosacral regions (L2-S3) Cord contains grey matter, white matter tracts, and central canal Central canal lined by ependyma

Spinal cord anatomy Gray matter Dorsal root entry zone White matter Vascular anatomy

Cross-section of the spinal cord with laminae of Rexed . From G. Paxinos & C. Watson

Lamina of Rexed Gray matter of spinal cord divided into ventral (anterior) and posterior (dorsal) horns Posterior horn contains laminae 1-6 Lamina 1 gives origin to the pathway relaying information about pain to the thalamus Lamina 2 and 3 (substantia gelatinosa) functions in regulating afferent input to the spinal cord.

Lamina of Rexed Lamina 4 projects to the lateral cervical nucleus, the posterior column nuclei, and the thalamus (spinothalamic tract) Lamina 5 and 6 receives proprioceptive input AND sensory information relayed by lamina 4. These are the sites of origin of ascending projections to higher centres. From T1 to L3 is Clarke’s column, which is within lamina 6 and contains projections to the cerebellum via the dorsal spinocerebellar tract

Lamina of Rexed Anterior horn: Lamina 9 contains motor neurons supplying the limbs and lamina 9M contains motor neurons supplying the trunk and neck. 9M is medial to 9. Is further subdivided into flexor and extensors (flexors are dorsal) and into distal and proximal (distal is more lateral).

Lamina of Rexed Laminae 7 and 8 contain interneurons involved in motor control and motor neurons that project to brain. Lamina 8 is highly related to lamina 9M, and participates in movements of muscles in the head and neck. Lamina 7 is related to lamina 9 and participates in limb muscle movement Lamina 8 and 9M are highly developed in high cervical and thoracic segments controlling neck and trunk, whereas laminae 7 and 9 are highly developed in the spinal enlargements controlling the arms and legs

Lamina of Rexed Intermediolateral cell column is present in thoracic and sacral segments, and is not considered part of the anterior or posterior horn Contains neurons of origin of pre-ganglionic autonomic fibres Lamina 10 surrounds central canal, and contains neurons that project to the opposite side of the cord.

White matter Divided into dorsal, lateral and ventral funiculi Dorsal funiculus mostly comprised of ascending fibres whose bodies are located in dorsal root ganglia Fibres are ipsilateral Proprioception and fine discrimination (note that vibration is carried in both dorsal and lateral funiculi)

White matter – dorsal funiculus Fasciculus gracilis medial to fasciculus cuneatus F. gracilis from lower limbs and cuneatus from upper limbs Note that lowest segmental innervation is most medial in gracilis and highest innervation is most lateral in cuneatus Nucleus gracilis and cuneatus in medulla There are descending fibres in dorsal funiculus which modify sensory input to the cord

White matter – lateral funiculus Dorsolateral and lateral parts (fasciculi) Dorsolateral contains lateral corticospinal tract (axons from contralateral frontal and parietal lobes); frontal fibres end in ventral horn Lower limbs are lateral in tract and head is medial Distal muscles are posterior to proximal muscles Rubrospinal tract (from contralateral red nucleus) is rudimentary in humans; involved in increasing flexor tone

Lateral funiculus Raphespinal tract in dorsal part of lateral funiculus; modifies painful stimuli from dorsal horn; fibres may begin in reticular formation of medulla Hypothalamospinal tract arises from paraventricular nucleus of hypothalamus and end in pre-ganglionic autonomic segments T1-L3 and S2-S4

Lateral funiculus spinocervical tract ascends and terminates in lateral cervical nucleus, which is rudimentary in humans (significance is unknown) Dorsal spinocerebellar tract is present above L3; arises from Clarkes column and terminates in ipsilateral cerebellum; forms part of pathway of conscious proprioception from lower limb

Lateral funiculus Ventrolateral fasciculus Spinothalamic tract has its nuclei in lamina 4,5,6 mostly. Axons cross midline in ventral white commissure and traverse the ventral horn End in thalamus Collateral branches to reticular formation Pain and thermal sensations Fibres from lower limb are most superficial and from upper limb are deepest

Lateral funiculus Ventral spinocerebellar tract arises from dorsal horn and border cells of ventral horn of lumbosacral cord Crossed fibres Ascends to midbrain, enters superior cerebellar peduncle, and decussates again, and enters cerebellar cortex Concerned with proprioception

Lateral funiculus Spinotectal tract fibres from same part as spinothalamic tract end in superior colliculus and reticular formation (fibres are crossed Spinoreticular tract originates in laminae 4-8 ends in reticular formation; is important in perception of pain and other modalities originating in internal organs

Lateral funiculus Spino-olivary tract has uncertain role in humans Ventrolateral fasciculus also contains descending medullary reticulospinal tract, which controls motor activities that do not require conscious effort

Ventral funiculus Ventral corticospinal tract contains uncrossed fibres Vestibulospinal tract is uncrossed pathway from the lateral vestibular nucleus of medulla; axons terminate in lamina 8 Mediates reflexes of equilibrium

Ventral funiculus Pontine reticulospinal tract Medial longitudinal fasciculus (only in cord to upper cervical levels) is involved in movements of head required for equilibrium Tectospinal tract from contralateral superior colliculus

Fasciculus proprius Present in all funiculi immediately adjacent to gray matter Contains propriospinal fibres which connect different segmental levels of gray matter Ascend and descend variable lengths and provide functional equivalent of interneurons

Dorsal root entry zone Each dorsal root branches into 6-8 rootlets Axons segregated into two divisions within each rootlet: lateral and medial Lateral contains unmyelinated (type C) fibres and enters dorsolateral tract of Lissauer Medial contains larger, myelinated axons, and enter white matter medial to dorsal horn

Vascular anatomy - Arterial Cord is supplied by multiple radicular arteries, which form the anterior and posterior spinal artery Radicular arteries arise from adjacent arteries at each vertebral segment Pass through intervertebral foramina to supply nerve roots, but most do not reach the cord Larger radicular arteries which also supply cord are called radiculomedullary arteries

Vascular anatomy - arterial Anterior spinal artery originates in upper cervical region, from anterior spinal branches of vertebral artery. 6-10 anterior radicular arteries contribute to it throughout its length. Supplies anterior two thirds of cord, via central branches and penetrating branches of pial plexus

Vascular anatomy – arterial territories Cervical and first two thoracic segments of cord are supplied by radicular a. that arise from subclavian a. or branches thereof High degree of variability mid-dorsal region of cord (T3-T7) is supplied from radicular a. accompanying T4 or T5 root T8 to conus supplied by artery of Adamkiewicz

Vascular anatomy - Adamkiewicz Arises from left sided lumbar (segmental) artery in 80% 85% reaches cord between T9-L2; 15% between T3-T8 (in these cases it is supplemented by a radicular artery arising more inferiorly) Has large anterior and small posterior branch Anterior branch ascends, then gives off a small ascending branch and larger descending branch Descending branch goes inferior (to conus) and makes an anastomotic loop with posterior spinal a.

Vascular anatomy – arterial Cauda equina also supplied by branches from lumbar, iliolumbar, and lateral and median sacral a.

Vascular anatomy – posterior spinal artery Paired arteries Run along posterolateral cord Sometimes discontinuous Originates from verterbral artery Has contribution from 10-23 posterior radicular a. Supplies posterior one third of cord

Vascular anatomy Anterior spinal a. gives off central branches and branches to pial plexus Central branches run in anterior median fissure and supply central cord Pial plexus is formed from both anterior and posterior spinal a. Give penetrating branches which supply outer cord Some overlap between supply of central and pial branches

Vascular anatomy - venous Internal and external vertebral venous plexuses Form rings around each vertebra Freely anastomose with each other

Vascular anatomy - venous External plexus has anterior part (anterior to vertebral body) and posterior part (over posterior elements including laminae and spinous processes) Anterior and posterior parts freely anastomose

Vascular anatomy - venous Internal plexus: anterior part is on each side of PLL, posterior to vertebral body; posterior part is interior to ligamentum flavum Vertebral body drained by basivertebral veins which enter anterior external plexus

Vascular anatomy - venous Veins of cord mirror related arteries in distribution Venules drain into anterior and posterior veins, which drain into two median longitudinal veins, and into anterolateral and posterolateral longitudinal veins lying adjacent to the nerve roots Radicular veins join branches from internal plexus forming intervertebral veins (have valves), which exit intervertebral foramina and join their respective segmental veins