University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

157

Pages:

2
Author:

Mariam A.

Positional changes of the cord        In the 3rd month of development, spinal cord extends the entire length of the embryo, and spinal nerves pass through the intervertebral foramina at level of origin. With age, the vertebral column and dura lengthen more rapidly than the neural tube, and the terminal end of the spinal cord gradually shifts to a higher level. o 24th week at S1  birth at L3  adult at L1. As a result of this disproportionate growth, spinal nerves run obliquely from their segment of origin in the spinal cord to the corresponding level of the vertebral column. Dura remains attached to the vertebral column at the coccygeal level. o Adult dural sac and subarachnoid space extends to S2. At the conus medullaris (end of cord), an extension of the pia mater passes caudally, goes through the dura (which provides covering for S2) and extends to the first coccygeal vertebra. This structure is the filum terminale, and it marks the regression of the spinal cord. Nerve fibres below the spinal cord make up the cauda eqauina. Lumbar puncture has needle inserted at the lower lumbar (L4 – L5), avoiding the lower end of the cord. Clinical correlation: spina bifida  Neural tube defects is caused by failure of fusion of one or more vertebral arches in developing vertebrae around the 4th week.  It affects tissue overlying the cord: skin, muscle, vertebral arch and meninges.  There are different types with different severity. o Occulta: L5 – S1; dimple, hair tuff, birthmark, etc. o With meningocele. o With meningomyelocele: referred to spina bifida cystica (same with above). o With myeloschsis: most severe.   Associated with hyperthermia, valproic acid, increased levels of vitamin A and decreased levels of folate. High prevalence in North China (1 every 200). Brain stem  Direct connection to spinal cord, with similar organisation.  At 5th week, rapid brain growth causes ventral bending, forming the midbrain and cervical flexures.  Unequal growth between flexures produces pontine flexure that causes thinning of roof.  Sulcus limitans extends only to rostral midbrain flexure. Brain  Rhombencephalon (hindbrain): myelencephalon and metencephalon.  Mesencephalon (midbrain):  Prosencephalon (forebrain): diencephalon and telencephalon.