The spinal cord has a cylindrical shape and is surrounded by three layers of meninges. It contains gray matter in an H-shape with nerve cell groups, and white matter divided into columns containing ascending, descending, and intersegmental tracts. The gray matter consists of nerve cells that project into the anterior and posterior nerve roots. The white matter contains myelinated fibers that transmit sensory information ascending to the brain and motor commands descending from the brain.
3. Gross Appearance
Cylindrical in shape
Foramen magnum L1/L2 (adult)
L3 (newborn)
Occupies upper ⅔ of vertebral canal
Surrounded by 3 layers of meniges :
dura mater
arachnoid mater
pia mater
CSF in subarachnoid space
4. Enlargements: cervical & lumbar
Conus medullaris
Filum termniale
Anterior median fissure
Posterior median sulcus
31 pairs of spinal nerves attached to it
by the anterior roots & posterior roots
6. Gray Matter
H-shaped pillar with anterior & posterior gray horns
United by gray commissure containing the central canal
Lateral gray column (horn) present in thoracic & upper
lumbar segments
Amount of gray matter related to the amount of muscle
innervated
Consists of nerve cells, neuroglia, blood vessels
Nerve cells in the anterior gray columns
Large & multipolar
Axons pass out in the anterior nerve roots as α-efferents
Smaller nerve cells are multipolar
Axons pass out in anterior roots as ɣ-efferents
7. Nerve cells in the posterior gray columns
4 nerve cell groups
Substantia gelatinosa
situated at the apex
throughout the length of spinal cord
composed mainly of Golgi Type II neurons
Nucleus proprius
anterior to substantia gelatinosa
present throughout the whole length of spinal cord
main bulk of cells in posterior gray column
8. Nucleus dorsalis (Clark’s column)
base of posterior column
C8 – L3 / L4
associated with proprioceptive endings (neuromuscular spindles & tendon
spindles)
Visceral afferent nucleus
lateral to nucleus dorsalis
T1 – L3
receives visceral afferent info
9. Nerve cells in the lateral gray columns
Formed by the intermediolateral group of cells
T1 – L2 / L3
Cells give rise to preganglionic sympathetic fibres
In S2, S3, S4; they give rise to preganglionic parasympathetic fibres
The gray commissure & central canal
connects the gray on each side
central canal in the centre
posterior gray commissure
anterior gray commissure
central canal present throughout
superiorly continuous with the central canal of medulla oblongata
inferiorly, expands as terminal ventricle
terminates within the root of filum terminale
10. White Matter
Divided into
anterior white column
lateral white column
posterior white column
Consists of nerve fibres, neuroglia, blood vessels
White due to myelinated fibres
TRACTS
Ascending
Descending
Intersegmental
11. Ascending Tracts
Fibres that ascend from spinal cord to higher centres
Conduct afferent information which may or may not reach
consciousness
Information may be
exteroceptive (pain, Tº, touch)
Lateral spinothalamic tract
Pain & temp pathways
1st-order neurons
Pain conducted by δ A-type fibres & C-type fibres
2nd-order neurons
decussate to the opposite side
3rd-order neurons
ends in sensory area in postcentral gyrus
Anterior spinothalamic tracts
Light (crude) touch & pressure pathways
12. Posterior spinocerebellar tract
Muscle joint sense pathways to cerebellum
Unconscious proprioception
Muscle joint info from muscle spindles, GTO, joint receptors of the trunk
& lower limbs
Info is used by the cerebellum in the coordination of movements &
maintenance of posture
Anterior spinocerebellar tract
Majority of 2nd-order neurons cross to the opposite side
Enter cerebellum through superior cerebellar peduncle
Info from trunk, upper & lower limbs
Also carries info from skin & subcut tissue
13. Descending Tracts
Lower motor neurons
Upper motor neurons
Corticospinal tracts
concerned with voluntary, discrete, skilled movements
Meninges
Dura mater
Arachnoid mater
Pia mater
15. Dura mater
Dense, strong fibrous membrane
Encloses the spinal cord & cauda equina
Separated from wall of vertebral canal by the extradural space
Arachnoid mater
Delicate impermeable membrane
Lies between pia and dura mater
Separated from pia mater by subarachnoid space
Pia mater
Vascular membrane
Closely covers spinal cord
Thickened on either side between nerve roots to form the
ligamentum denticulatum