The spinal cord

 
1) It’s cylindrical shape
2) Starts : At the foramen magnum in the skull
3) Ends
1. Adult : Lower border of the 1^st lumbar vertebra (L 1)
2. Young child : upper border of the 3^rd lumbar vertebra (L 3)
4) Inferiorly
1. Tapers off into the conus medullaris (It’s a prolongation of the pia mater)
2. Filum terminale descends & attach to the posterior surface of the coccyx
5) Anteriorly : Anterior median fissure (Deep longitudinal fissure)
6) Posteriorly : Posterior median sulcus
7) Coverings
1. 3 meninges (Dura, Arachnoid & Pia mater)
2. CSF in the sub arachnoid space
8.) It has 2 fusiform enlargements
1. Cervical enlargement : Gives origin to brachial plexus
2. Lumbar enlargement : Gives rise to lumbosacral plexus
9) There are 31 pairs of spinal nerves attached by the:
1. Motor roots (Anterior)
2. Sensory roots (Posterior)
10) Each posterior nerve root has a posterior root ganglion (Gives rise to peripheral & central nerve fibers)

Spinal cord – Nerve supply

Vertebral spines	Cord segments
C-1	C-1
C-6	C-7
T-4	T-6
T-10	L-1
T-12 to L-1	S-1

Body landmark	Dermatome
Back of head	C-2
Shoulder	C-4
Thumb	C-6
Middle finger	C-7
Small finger	C-8
Nipple	T-4, T-5
Umbilicus	T-10
Inguinal region	L-1
Big toe	L-4, L-5
Small toe	S-1
Genitalia and perianal region	S-4, S-5

Structure of the spinal cord : (Grey matter: Inner core & White matter: Outer covering)
Transverse section of the spinal cord
Gray matter ( click image to enlarge )

White Matter ( click image to enlarge )

Comparison of structural details of different regions of the spinal cord

Region	Shape	White matter	Grey matter
Anterior column	Posterior column	Lateral column
Cervical	Oval	FC & FG are present	MG : Neck muscles LG : UL muscles CG : Accessory (C1 – 5) & phrenic nucleus (C3,4 & 5)	SG, NP are present ND is absent	Absent
Thoracic	Round	FC (T1 – T6) & FG are present	MG : Trunk muscles	SG,NP,ND & VAN are present	Present Gives rise to PGS fibers
Lumbar	Round to oval	FC is absent FG is present	MG : LL muscles CG : Lumbosacral nerve	SG,NP,ND (L1 -4) & VAN are present	Present (L1 – L3) Gives rise to PGS fibers
Sacral	Round	MG : Lower limb & perineal muscles	SG & NP are present ND is absent	Absent Group of cells present at S2 – S4 for PS outflow

Index

White matter	FC : Fasciculus cuneatus FG : Fasciculus gracilis
Lateral grey column	PGS : Preganglionic sympathetic PS : Parasympathetic
Posterior grey column	SG : Substantia gelatinosa group NP : Nucleus proprius ND : Nucleus dorsalis (Clark’s column) VAN : Visceral afferent nucleus
Anterior grey column	MG : Medial group of cells LG : lateral group of cells CG : Central group of cells

Central canal
1) Superiorly (Open) : Opens into the cavity of the 4^th ventricle
2) Inferiorly (Closed) : In the conus medullaris, it expands to form the terminal ventricle & terminates below within the root of filum terminale
3) It’s filled with CSF
4) It’s lined by ciliated columnar epithelium (Ependyma)
Blood supply of the spinal cord
A. Arterial supply : Supplied by 3 small arteries + feeder arteries

	Posterior spinal arteries	Anterior spinal artery
Origin	Directly : Vertebral arteries inside the skull Indirectly : Posterior inferior cerebellar arteries	Formed by the union of 2 arteries, which are arising from the vertebral artery inside the skull
Position	Descends on the posterior surface of the spinal cord (Closed to the posterior nerve roots)	Descends on the anterior surface of the spinal cord with in the anterior median fissure
Supply	Posterior 1/3 of the spinal cord	Anterior 2/3 of the spinal cord
Special points	They are small in the upper thoracic region	It’s small in the upper & lower thoracic segments of the spinal cord
Risk of ischemia	T1,T2 & T3 segments are vulnerable to undergo ischemia if the segmental or radicular arteries are occluded	T4 & L1 segments are vulnerable to undergo ischemia if the segmental or radicular arteries are occluded

Segmental spinal arteries 1) ASA & PSA arteries are reinforced by segmental arteries, which enter the vertebral canal through the inter vertebral foramina 2) These arteries are branches of arteries outside the vertebral column (Deep cervical, Intercostal & Lumbar arteries) 3) Segmental arteries give rise to anterior & posterior radicular arteries

Feeder arteries
1) Enter the vertebral arteries & anastomose with the ASA & PSA
2) The most important feeder artery is the Great anterior medullar artery of Adamkiewicz
1. It arises from the aorta at lower thoracic or upper lumbar vertebral levels
2. Unilateral
3. In the left side of most people
4. Major source of blood to the lower 2/3 of the spinal cord
B. Veins of the spinal cord
1) Drains mainly into the veins of the brain & the venous sinuses via 6 tortuous longitudinal channels
2) Finally drain into the internal vertebral venous plexus