Spinal Cord and Segments

Describe the internal anatomy of the spinal cord

Grey matter - dorsal, lateral, ventral horns.

White matter - Fasciculi (fasicles/tracts), funiculi (regions)

What are “horns”

profiles of columns of cell bodies. Groups of cell bodies called “nuclei”.

what is the function of horns

Dorsal - sensory input from spinal nerve

Lateral- only in thoracolumbar regions, contains cell bodies of SNS and interneurons.

Ventral - Motor output to ventral root

Describe external anatomy of spinal cord

• Intumescences and plexi (enlargements)

• Conus medullaris, Terminal end of the spinal cord

• Cauda equina, ‘Tail of horse’

• Spinal nerve, Root and ganglia

Describe how the embryonic spinal cord develops and segregate to form adult structures.

• Alar and basal plates develop into symmetrical halves with a ventral median fissure.

• Mantle → grey matter

• Marginal → white matter

• Central canal remains as part of CSF circulatory system

Describe how the PNS develops and segregates to form adult structures

Neuroblasts in basal plate → (lower) motor neurones

Neuroblasts in neural crest → spinal ganglia → sensory neurones

Neural crest cells → autonomic ganglia.

Preganglionic fibres from lateral horn → autonomic ganglia

Describe a generic spinal cords input / output

Sensory neurone - spinal ganglion - ventral horn

dorsal horn - dorsal root ganglion - motor neurone

Describe a generic spinal cord segment

sections of the spinal cord defined by the pairs of spinal nerves that exit the cord, with each segment corresponding to a specific region of the spine (cervical, thoracic, lumbar, sacral, and coccygeal

discuss the variations between segments in different regions.

Cervical - 8 segments, has brachial plexus

Thoracic - 13 segments

Lumbar - 7 segments, lumbosacral plexus

Sacral - 3 segments, lumbosacral plexus

Caudal / Coccygeal - 5 segments

Describe the locations and functional significance of the spinal intumescences.

• Intumescence: Subtle enlargements of the spinal cord

• Cervical [C6-T2] - Thoracic limbs

• Lumbosacral [L4-S3] - Pelvic limbs

• Plexi: Dorsal and ventral branches of spinal nerves connect with neighbours to form continuous dorsal and ventral networks.

C6-T2 - Brachial plexus • L4-S3 - lumbosacral plexus

what is a funiculi

A region containing different bundles of nerve fibres/axons.

what is a fasciculi

: A bundle of the same anatomical nerve fibres/axons that make up a tract. • A funiculus contains multiple fasciculi.