A flattened
cylinder tapering into a cone.
-
ventrally
grooved = anterior median fissure;
dorsal shallow groove = posterior median sulcus
Cord extends to S2
in fetus ¨ the dura remains attached here forever
more.
-
but cord
becomes relatively shorter: L3
at birth, bottom of L1
by adulthood.
Cervical
enlargement (C5-T1) for
brachial plexus (vertebrae C3-T1)
Lumbosacral
enlargement (L2-S3) for
lumbar & sacral plexi (vertebrae T9-L1)
See vertebral canal notes.
Anterior and posterior; unit in intervertebral foramina.
- stem from spinal cord in subarachnoid space as a series of rootlets (3-4 for each anterior root, several for each posterior root)
- form nerve roots, these evaginate dura on exit, separately, then unit to form mixed nerve root
Ganglion for posterior root lies in foramen, within dura evagination
Cord is short, so nerve roots slipe ever steeper down to evagination points; below L1 pass as cauda equina; pia filum terminale extends from conus medullaris among the nerve roots.
Grey matter centrally, surrounded by white matter.
Anterior median fissure and posterior median septum almost divide it into two halves
- grey commissure crosses midline, contains central canal (continuation of 4th ventricle, lined by ependyma
- a narrow white commissure lies anterior to grey.
Grey matter has anterior, lateral and posterior horns.
- anterior horns largest in cervical and lumbar, (cf posterior white columns largest in cervical).
- posterior horn reaches surface of cord
- more medial anterior horn cells = trunk muscles, lateral = limbs
- more ventral = proximal limbs; more dorsal = distal.
- Lateral horn is from T1-L2; preganglionic sympathetic. And S2-4.
Cells are arranged in laminae designated I-X
- V are spinothalamic
- IX alpha and gamma motor neurones
- VII, VIII interneurons.
White matter
3 destinations: opposite cerebral hemisphere via thalamus (conscious sensation); cerebellum (muscular); brainstem or cord (reflexes).
- first order in posterior root ganglia, second in spinal cord / brainstem, third in thalamus.
Corticospinal direct, go from motor centre to anterior horn cells / cranial nerves (UMNs) ¨ LMNs
Indirect extrapyramidal pass through eg red, reticular, subthalamic and substantia nigra nuclei
Posterior columns Ð gracile (medial) and cuneate (lateral) = light touch, vibration, proprioception and bladder / rectum fullness.
- fibres are added progressively laterally (so lowest are nearest midline; cuneate = thorax and upper limb; gracilis = perineum, lower limb, lower trunk.) Ie its laminated.
- end in medulla at nuclei of same name, then decussate to form medial lemniscus runs through brainstem to thalamus.
- Loss leads to loss of jt position, Romberg's +ve, arms out with eyes closed, walking in dark / balance problems ie Ôsensory ataxiaÕ & loss of vibration sense.
- 2 point discrimination (also tests cortex) and stereognostic sense will be lost also.
Anterolateral Ð pain, temp, crude touch, itch, tickle, orgasm & cerebellum for coordination.
- decussate on entry at their spinal level via interneurons.
- Is also laminated.
- 10% pass to thalamus, rest to brainstem reticular formation, third order then to cortex etc.
- tests are pain pinprick, temperature.
- In anterolateral cordotomy lateral tract is severed for chronic pain; lasts 2 yrs at most due to plasticity.
Anterior and Posterior Spinocerebellar tracts Ð unconscious proprioception
Lateral corticospinal Ð motor decussation at lower medulla
- 98% of neurons synapse with interneurons ¨ alpha, gamma motor neurons at ant horn.
- 55% concerned with upper limb; 20% for trunk; 25% for lower limb.
- Relatively unimportant few cross at their spinal cord level across anterior median fissure
Extrapyramidal:
i) lateral reticulospinal: medullary part of reticular formation ¨ lateral white column,
ii) medial reticulospinal: pontine reticular formation ¨ anterior white column
iii) lateral vestibulospinal: lateral vestibular nucleus of medulla ¨ down cord to anterior roots
- great importance for posture, balance.
Hypothalamospinal: links to sympathetic / parasympathetic cells; lies next to lateral horn.
LMN = flaccid paralysis
UMN = spastic, upgoing plantars, clonus (alpha neurons released from inhibition)
- rare lesions in the pyramid of medulla will cause flaccid paralysis
Cortical lesions affecting both sides are rare: the parasagittal meningioma may affect leg areas of both hemispheres.
Single anterior and right & left posterior arteries.
Anterior: lies in median anterior fissure.
- formed at foramen magnum by union of two anterior spinal branches, each from a vertebral artery above the foramen
- inconsistently runs whole course
- supplies anterior and lateral cord
Posterior: arise from posterior inferior cerebellar or vertebral artery above foramen magnum.
- usually double, forming long trunks through and behind posterior nerve rootlets.
- Scanty connections anastomose with the anterior artery
- Supplies posterior columns
Radicular arteries: crucial reinforcements to longitudinal trunks.
- embryologically arose segmentally and passed through intervertebral foramina to cord
- were derived from parent vessels appropriate to site: vertebral costocervical, posterior intercostal, lumbar, lateral sacral
- however most disappear ¨ variable number and site remain ¨ anterior and posterior arteries
- arteria radicularis magna is largest, from lower intercostal or upper lumbar on left (donÕt fuck with parent stems of major radicular arteries or supply to the cord impaired).
Anastomotic connections in pia also give little branches to some of cord
Spinal veins form a loose-knit plexus with anterior and posterior midline longitudinal veins and two more posterior veins: one behind each nerve root.
¨ internal vertebral venous plexus
¨ via external vertebral plexus ¨ appropriate segmental veins: vertebral / azygos, lumbar, lat sacral.
Complete transection:
All movement and sensation below is lost.
- paralysis flaccid at first; spastic after a few weeks
- bladder / rectal sphincter control lost, reflex emptying remains intact
- canÕt cough if lesion affects below T10 (need abdo / lower intercostal tone)
¨ check perianal skin to detect sparing / pinprick for anal reflex.
Paralysis / loss of touch / kinaesthetic below level of lesion on same side
- (lateral corticospinal & posterior column)
Loss of pain / temp on other side
- (crossed anterolateral tract)
Sudden hyperextension: ¨ loss of pain & temp and flaccid paralysis of upper limbs
- because anterior horn damage and interruption of more deeply placed cervical fibres
- lower limbs show spasticity if lumbar fibres of lateral corticospinal tract involved.
Posterior white columns remain intact
Rest of cord affected: motor and sensory except perhaps sacral sparing again.