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Spinal Cord Laminae & Histology

Notes

Spinal Cord Laminae & Histology

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Spinal Cord Overview: Anatomy & Histology

Summary

cross-section of the spinal cord: anatomic view

General Notes

Note the following:

  • The posterior and anterior orientation of our anatomical cross-section has the opposite orientation of radiographic view.
  • The central canal is mostly obliterated by the second decade of life.
  • See: Spinal Cord Photos

Key spinal cord anatomical structures

The gray matter horns

From posterior to anterior:

  • The posterior horn, which comprises sensory nuclei.
  • Intermediate zone, which comprises autonomic and spinocerebellar nuclei.
  • Anterior horn, which comprises motor nuclei.
  • We see that the gray matter horns form the shape of a butterfly.

White matter funiculi (aka columns)

  • The white matter of the spinal cord is segmented into the following funiculi (aka columns):

From posterior to anterior:

  • Posterior funiculus, which carries large proprioceptive sensory afferents for movement and position sensation.
  • Lateral funiculus, which carries large motor efferents (ie, the corticospinal tracts).
  • Anterior funiculus, which carries small, thermoceptive and nociceptive sensory afferents for pain and temperature sensation, respectively.
  • Fasciculus proprius, which comprises the collective bundle of interspinal rostro-caudal white matter projections; thus, it is also referred to as the spinospinal tract.

Rostro-caudal spinal cord levels

We'll pay attention to their relative amounts of white and gray matter.

Lumbosacral cord

  • Large gray matter horns, because of the large population of neurons required to innervate the lower limbs.
  • Small amount of white matter, because relatively few ascending fibers have joined the cord and relatively few descending fibers remain in it.

Thoracic cord

  • Small gray matter horns, because segmental thoracic innervation requires relatively few neurons.
  • Moderately large amount of white matter because of the many fibers relaying to and from the lumbosacral neurons.

Cervical cord

  • Large gray matter horns large because of the large population of neurons required to innervate the upper limbs.
  • Large amount of white matter because all descending and ascending fibers either pass through or terminate within it.

Spinal Cord Histology

Luxol fast blue stain turns the proteolipid of myelin blue, making it prominent.

  • We delineate the: posterior horn, intermediate zone, and anterior horn; posterior funiculus, lateral funiculus, and anterior funiculus; fasciculus proprius.

10 Rexed laminae

  • They constitute the functional categorization of neurons within the gray matter horns.

Here, we list some key lamnia nomenclature within their gray matter horns.

Posterior horn

From posterior to anterior:

  • Laminae I–VI, correspondingly, these are the sensory laminae.
    • Lamina I: the marginal nucleus (aka posteromarginal nucleus)
    • Lamina II: substantia gelatinosa, so-named because its lack of myelinated fibers gives it a gelatinous appearance on myelin staining.
  • As a simplification, laminae I and II (and also lamina V) receive small, poorly myelinated or unmyelinated fibers, which carry pain and temperature sensation.
  • Laminae III and IV comprise nucleus proprius
    • They receive large cutaneous sensory fibers. However, that the majority of large fibers do not synapse within the Rexed laminae at all but instead directly ascend the posterior columns.
  • Laminae V and VI
    • They receive descending motor fibers and assist in sensorimotor integration.

Intermediate zone

  • Lamina VII
    • Comprises the dorsal nucleus of Clarke (a key spinocerebellar nuclear column) and the intermediolateral cell column (a key autonomic nuclear column).

Anterior horn

  • Laminae VIII and IX, which are the motor laminae.
  • Lamina X surrounds the central canal.

Section of anterior spinal cord

Notes on Staining

  • In this slide, myelin is blue, because the Luxol fast blue stain turns the proteolipid of myelin blue.
  • Here, Cresyl violet staining stains the gray matter neurons and cell processes because the Nissl substance in the neurons has a high RNA content, which makes it basophilic, and turns in violet with this stain.

Histology

  • The anterior nerve roots stain blue from their myelin.
  • The prominent anterior median fissure is the deep longitudinal fissure along the anterior surface of the spinal cord.
  • The leptomeninges are the pia/arachnoid mater covering of the spinal cord.
  • The prominent anterior spinal artery lies in midline.

Histology of a motor neuron

See: Spinal Motor Neuron

  • Lies within the anterior horn of the spinal cord.
  • We note its cell body, nucleus, nucleolus (which is prominent), and a dendrite (a dendritic process), and its cone-shaped axon hillock, which connects the cell body to the base of the axon.

Axon hillock physiology

  • Membrane potentials from throughout the cell body spread to the axon hillock, and only if they depolarize it to its threshold will the axon fire an action potential; thus, this is the decision-making center of the neuron.

Related Tutorials

Histological Images

Histological images modified with permission from:

  • http://medsci.indiana.edu/a215/virtualscope/docs/chap6_3.htm
  • http://medsci.indiana.edu/c602web/602/c602web/toc.htm