Positional Changes Of The Spinal Cord Figure 123

A. At week 8, the spinal cord extends the entire length of the vertebral canal as spinal nerves exit the intervertebral foramina near their level of origin. This condition does not persist owing to the disproportionate growth of the vertebral column during the fetal period.

Table 12-1

Neural Tube Vesicles and Their Adult Derivatives

Table 12-1

Neural Tube Vesicles and Their Adult Derivatives

Primary Vesicles

Secondary Vesicles

Adult Derivatives

Prosencephalon

Telencephalon Diencephalon

Cerebral hemispheres, caudate, putamen: amygdaloid, claustrum, lamina terminalis, olfactory bulbs, hippocampus

Epithalamus, subthalamus, thalamus, hypothalamus, mamillary bodies, neurohypophysis, pineal gland, globus pallidus, retina, iris, ciliary body, optic nerve (CNII), optic chiasm, optic tract

Mesencephalon

Mesencephalon

Midbrain

Rhombencephalon

r Metencephalon 1 Mylencephalon

Pons, cerebellum Medulla

Fetal Conus Medullaris

Body of vertebra nr

S, nerve root

Fetal Conus Medullaris

Figure 12-3. The end of the spinal cord (conns medullaris) is shown in relation to the vertebral column and meninges. (A) Week 8. (B) Week 24. (C) Newborn. (D) Adult. As the vertebral column grows, nerve roots (especially those of the lumbar and sacral segments) are elongated to form the cauda equina. The SI nerve root is shown as an example. (Modified from Moore KL and Persaud TVN: The Developing Human, 6th ed. Philadelphia, WB Saunders, 1998, p 459.)

B. At birth, the end of the spinal cord (conus medullaris) extends to the L3 vertebral level.

C. In adults, the end of the spinal cord (conus medullaris) extends to the L1-L2 interspace.

D. The collection of dorsal and ventral nerve roots that descend below the conus medullaris is called the cauda equina.

E. An extension of the pia mater forms the filum terminale, which anchors the spinal cord to the coccyx.

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