Gross anatomy of spinal cord and its tracts

1. SPINAL CORD
Dr. Prabhakar Yadav
Assistant Professor
Department of Human Anatomy
B.P. Koirala Institute of Health

2. Length: 45 cm
Occupy: upper 2/3rd of vertebral canal.
Extent: Upper border of atlas to lower border of L1 vertebra or upper border
of vertebra L2.
Extent in fetus: Lower border of S2 vertebra
Extent in Infant: Lower border of L3 vertebra
Functions of spinal cord:
1. Transmission of information to & fro between body & brain.
2. Execution of simple reflexes.

3. External Features:
• 31 pairs of spinal nerves
• Cervical & Lumbar enlargements: are due to increased mass of motor
cells in the anterior grey horns of grey these spinal segments.
• Conus medullaris:
Fissures and sulci
• Anterior median fissure; anterolateral sulci:
• posterior median sulcus; Posterolateral sulci

4. Spinal segments: Portion of spinal cord which gives origin to rootlets
for a pair of spinal nerves is called spinal segment.
Cervical enlargement: In the region of C5–T1 spinal segments.
Nerves arising from these segments form brachial plexus.
Cervical enlargement lies opposite C3 to T1 vertebrae
Lumbar enlargement: In the region of L2–S3 spinal segments.
Nerves arising from these segments form lumbar plexus.
Lumbar enlargement lies opposite T9 to L1 vertebrae.

5. Spinal segments lie above their corresponding vertebral level due
to relative shortening of the spinal cord as compared to the
vertebral canal
Approximate vertebral levels of the spinal segments
 Usseful in determining the level of vertebral injury
Cauda equine: is a leash of lumbar (except L1), sacral & coccygeal
nerve roots that descend almost vertically downwards around
the filum terminale in the pool of CSF.

6. Filum terminale: is thread-like prolongation of pia mater beyond the conus
medullaris.
• 20 cm long; extends from tip of conus medullaris to the base of the coccyx.
• It pierces the dura matter & attach on the dorsum of first piece of coccyx.
• filum terminale internum is about 15 cm long ;lies within the dural sac.
• filum terminale externum is 5 cm long ; lies outside the dura mater.

7. Ligamenta denticulata:
• On each side between dorsal & ventral nerve roots, pia mater forms transparent bands- ligament denticulata.
• Lateral margin of each ligamentum denticulatum sends 21 teeth-like projections, which pass through
subarachnoid space & arachnoid mater & attach to on the inner surface of dural tube between the points of
emergence of two adjacent spinalnerves.
• First tooth is at the level of foramen magnum; last tooth lies between T12 & L1 spinal nerves.
• Ligamenta denticulata helps to anchor the spinal cord in the middle of the subarachnoid space.

8. Internal Structure
Spinal cord consists of: # Central mass of grey matter made up of nerve cells
# Peripheral mass of white matter made up of (myelinated )fibre tracts.
Grey matter is divided into symmetrical right and left- connected across midline by a transverse grey commissure.
Central canal of the cord passes through the center of the grey commissure.
Canal is surrounded by substantia gelatinosa centralis.

9. Grey matter is divided into a narrow elongated posterior horn (column) and broad anterior horn (column)
Posterior horn extends almost up to the surface of the cord but anterior horn falls short of it.
posterior horns are connected to the surface by a gelatinous substance called substantia gelatinosa
Thoracic segments & upper two lumbar segments (T1 to L2) possess lateral horn.

10. White Matter: Divided into three parts called columns:
1. Anterior white column (anterior funiculus): between anterior median fissure & anterior horn
2. Posterior white column (posterior Funiculus) : between posterior median septum & posterior horn
3. Lateral white column (lateral funiculus) : between anterior & posterior horns.
• Anterior white columns are joined together by white commissure that lies anterior to the grey commissure.
• Each white column is made up of tracts, which are either ascending (sensory) or descending (motor).
 In general # Posterior white column is sensory, anterior column is motor & lateral column is mixed.
# Ascending tracts are located towards the periphery & descending tracts towards the center

11. Nuclei of Spinal Cord
Anterior horn is motor in function
Lateral is visceral efferent & afferent in function and
Posterior is sensory in function.
Nuclei in Anterior Grey Horn (Column) :
Anterior horn is divided into a ventral part- head &
dorsal part- base.
Nuclei in anterior horn innervate skeletal muscles.
Cells in the anterior horn are arranged in 3 main groups:
Medial Group:
• Present throughout the length of the spinal cord
• Innervate axial muscle of the body (musculature of
neck & trunk)
• It is subdivided into ventromedial & dorsomedial
nucleus.
Lateral group:
• Peresent only in cervical & lumbosacral
enlargements
• Innervate the limb muscles.
• It is subdivided into 3 subgroups:
Anterolateral Nu: supply proximal musles of limbs
Posterolateral Nu: supply intermediate muscles
Post-posterolateral Nu: supply distal segments

12. Central group forms three definite nuclei:
1. Phrenic nucleus: present in cervical region (extending from C3 to C5 segments) innervates the diaphragm.
2. Nucleus of spinal root of accessory (XI cranial) nerve: present in the cervical region (extending from C1 to C5
segments) and giving origin to the spinal root of accessory nerve.
3. Lumbosacral nucleus: present in the lumbosacral region (extending from L2 to S3 segments). Its function is
unknown

13. Nuclei in Lateral Horn
• Intermediolateral nucleus:
- Extends form T1 to L2 segments of the cord
- Gives origin to preganglionic fibres of the sympathetic nervous system (thoracolumbar outflow) ,which leave the
cord along with anterior nerve roots.
• Intermediomedial nucleus
- Extends from S2 to S4 segments of the cord
- Gives origin to preganglionic fibres of parasympathetic nervous system (sacral outflow), which leave the cord along
with anterior nerve roots of the corresponding sacral nerves.

14. Nuclei in Posterior Grey Column:
(i) Posteromarginal nucleus:
• Thin layer of neurons caps the posterior horn.
• It receives some of incoming dorsal root fibres.
(ii) Substantia gelatinosa (of Rolando):
• Found at the tip of posterior horn through the entire extent
of spinal cord.
• Acts as a relay station for pain & temperature fibres
• Its axons give rise to lateral spinothalamic tract.
(iii) Nucleus proprius:
• Lies anterior to substantia gelatinosa throughout the extent
of cord.
• It receives the fibres from posterior white column that are
associated with the sense of position and movement
(proprioception), two-point discrimination, and vibration.

15. Nuclei in Posterior Grey Column:
(iv) Nucleus dorsalis (Clarke’s column/ Thoracic nucleus)
• occupies medial part of base of posterior horn extending
from C8 to L2/L3 segments.
• It is a relay nuclear column for reflex or unconscious
proprioceptive impulses to the cerebellum
• Its axons give rise to posterior spinocerebellar tract.
• It receives proprioceptive afferents (muscle and joint sense)
and exteroceptive afferents (touch and pressure from the
trunk and lower limb).
Visceral afferent nucleus:
• Located lateral to the nucleus dorsalis
• Extends from T1 to L2 and from S2 to S4 segments
• receives visceral afferents from the dorsal nerve roots

16. Laminar Organisation in Spinal Cord
In thick sections, spinal cord neurons appear to have laminar arrangement.
 Ten layers of neurons are recognized (Laminae of Rexed).
Laminae are numbered consecutively by Roman numerals, starting at the tip of the dorsal horn & moving ventrally
into ventral horn.
Laminae Corresponding grey column nuclei
I Posteromarginal nucleus
II Substantia gelatinosa
III & IV Nucleus proprius
V & VI Base of dorsal column
VII Nucleus dorsalis (Clarke's column) and intermediolateral &
intermediomedial nuclei of lateral horn
VIII & IX Medial and lateral groups of nuclei of anterior grey column
X Surrounds the central canal and composed of the grey
commissure and substantia gelatinosa centralis

17. Sensory Receptors
Peripheral endings of afferent fibres which receive impulses are known as receptors.
Functional classification:
(i) Exteroceptors: These respond to stimuli from external environment i.e. pain, temperature, touch & pressure.
(ii) Proprioceptors: These respond to stimuli in deeper tissues i.e. contraction of muscles, movements, position and
pressure related to joints.(These actions are perceived at unconscious level)
(iii) Interoceptors/Enteroceptors: These include receptor end-organs in the walls of viscera, gland, blood vessels and
specialised structures in the carotid sinus & carotid bodies.
(iv) Special sense receptors: These are concerned with vision, hearing, smell and taste.

18. Lumber puncture:
Spinal anesthesia:
Epidural anesthesia:

19. Blood supply of spinal cord
3 longitudional arteries:
a. 1 Anterior spinal artery- Anterior median fissure
b. 2 posterior spinal arteries- posterolateral sulcus
• Arteria vasocorona - arterial plexus; +nt in pia
mater- send branches to substance of spinal cord.

20. Anterior spinal artery:
• arise near termination of vertebral
artery
• arteries of 2 sides unite to form single
anterior spinal artey – Supply anterior
2/3 of spinal cord and also medulla
Posterior spinal artery:
br. of posterior inferior cerebellar artery
or br of vertebral artery- supply
posterior 1/3 of spinal cord.

21. Blood from the vertebral arteries reaches
only up to the cervical segments of the cord.
Segmental Spinal Arteries:
branches of vertebral, ascending cervical,
deep cervical, intercostal, lumbar and sacral
arteries enter the vertebral canal through
intervertebral foramen.
Anterior and Posterior radicular arteries
that accompany the anterior and posterior
nerve roots to the spinal cord & anastomose
with anterior and posterior spinal arteries

22. Posterior spinal arteries - small in the
upper thoracic region.
If segmental or radicular arteries in this
region is occluded--
First three thoracic segments of the spinal
cord are particularly vulnerable to
ischemia.
Feeder arteries great anterior medullary
artery of Adamkiewicz,:
arises from the aorta in the lower thoracic
or upper lumbar vertebral levels;
it is unilateral and, (left side).
major source of blood to the lower two-
thirds of the spinal cord

23. Veins of the Spinal Cord
1. /2. anteromedian and posteromedian
channels
3-6. anterolateral and posterolateral
channels that are paired
venous vasocorona
radicular veins that open into epidural or
internal vertebral plexus and through it
into various segmental veins.
communicate superiorly with the veins of
the brain and the venous sinuses.

24. Tract:
A collection of nerve fibres that connects two masses of grey matter within the
central nervous system, (which have same origin, course and termination) is called
a tract. They are sometimes referred to as fasciculi (= bundles) ; or lemnisci (=
ribbons).
Tracts are named after the masses of grey matter connected by them.

25. Descending (motor) tracts Ascending (sensory) tracts
# Ascending tracts are located towards the periphery & descending tracts towards the center

26. Descending tracts: conduct impulses from brain to the spinal cord
A. Pyramidal or cortlcospinal tract: Descends from cerebral cortex to the spinal cord.
1.Lateral corticospinaj tract -lies in the lateral funiculus.
2.Anterior corticospinal tract - lies in anterior funiculus.
B. Extrapyramidal tracts. These are:
1. Rubrospinal tract 2. Medial reticulospinal tracts 3. Lateral reticulospinal tracts. 4. Olivospinal tract.
5. Vestibulospinal tract 6.Tectospinal tract.

27. Ascending tracts: conduct the impulses from the periphery to the brain through the cord.
Important ascending tracts fall into the following three types:
1. Those concerned with pain & temperature sensations and crude touch- lateral & anterior spi-nothalamic tracts.
2. Those concerned with fine touch & conscious proprioceptive sensations- fasciculus gracilis & fasciculus cuneatus.
3. Those concerned with unconscious proprioception & muscular coordination- anterior & posterior
spinocerebellar tracts.

28. Ascending Tracts: 1.Lateral spinothalamic tract 2.Anterior spinothalamic tract
3.Fasciculus gracilis (medially) 4.Fasciculus cuneatus (laterally)
5.Dorsal or posterior spinocerebellar tracts. 6.Ventral or anterior spinocerebellar tract
7.Spino-olivary tract. 8.Spinotectal tract.

29. Pyramidal or Corticospinal Tract:
Origin: Tract is formed by axons of pyramidal cells (of Betz) lying in
primary motor area (area 4) with some axon of cells in premotor area
(area 6) of cerebral cortex.
Course: corona radiate, internal capsule, midbrain, pons & pyramids of
medulla oblongata.
80% of fibres cross to opposite side -pyramidal decussation.
Fibres that have crossed enter lateral white column & descend as lateral
corticospinal tract.
Termination: by synapsing through internuncial neurons with anterior
horn cells.
20% of fibres that do not cross enter anterior white column to form
anterior corticospinal tract.
The fibres of this tract also cross at appropriate levels through the
anterior white commissure at the level of their termination & terminate
by synapsing through internuncual neuron with anterior horn cell.

30. • Because of medullary decussation of corticospinal fibres the cerebral
cortex of one side controls the muscles of the opposite half of the
body.
• Pyramidal tract also includes corticobulbar/corticonuclear fibres
which descend to brainstem, cross to the opposite side & terminate
by synapsing with nerve cells of brainstem nuclei of the cranial
nerves

31. Functional Significance
(i) Cerebral cortex controls voluntary movements of opposite half of
body through anterior horn cells.
(ii) Influence of this tract is supposed to be facilitatory for flexors and
inhibitory for extensors(Controls conscious skilled movements
especially of hands )
Clinical Correlation
Lesions of pyramidal tract (i.e. upper motor neuron (UMN) lesions)
result in the loss of voluntary movements in the opposite half of the
body below the level of the lesion.
The muscles are not actually paralyzed but the control of upper motor
neurons and the lower motor neurons (LMN) supplying muscles is lost.
As a result LMNs become hyperactive and the tone of muscles is
increased leading to spastic paralysis.

32. Extrapyramidal Tracts
1. Rubrospinal tract: is formed by axons of red nucleus.
• Fibres cross with the fibres of the opposite side in the tegmentum of
midbrain -constituting ventral tegmental decussation.
• Tract descends through the pons, medulla & enters lateral white column.
• Fibres terminate by synapsing through internuncial neurons with anterior
horn cells.
 Rubrospinal tract facilitates the activity of the flexor muscles and inhibits
the activity of the extensor or anti-gravity muscles.
Function: Unconscious coordination of movements (Controls muscle tone &
synergy)

33. 2. Medial (pontine) reticulospinal tract:
• is formed by fibres from reticular formation in pons.
• Tract descends to the cervical segments only.
• It lies in the anterior white column.
• It has uncrossed fibres.
3. Lateral ( Medullary) reticulospinal tract:
• is formed by fibres from reticular formation in medulla.
• Tract descend upto thoracic segments of spinal cord.
• It lies in the anterolateral white column
• It has both crossed and uncrossed fibres.
 Both tracts terminate by synapsing with the neurons in
laminae VII of anterior gray columns of spinal cord.

34. The tracts have either facilitate or inhibit influence on
motor neurons.
Medial reticulospinal tract:
has inhibitory influence on motor neurons to the skeletal
mucles
Lateral reticulospinal tract:
has facilitatory influence on motor neurons to the skeletal
mucles
Reticulospinal tracts influence voluntary movements and
reflex activity

35. Tectospinal Tract:
• Arise from nerve cells in superior colliculus of midbrain.
• Most of the fibers cross the midline forming dorsal tegmental
decussation
• Descend through pons, medulla & anterior white column.
• Fibres terminate by synapsing through internuncial neurons
with anterior horn cells in the upper cervical segments
Function: concerned with reflex postural movements in response
to visual stimuli.

36. Vestibulospinal Tract:
• vestibular nucleus lying at pontomedullary junction.
• vestibular nuclei receive afferent fibers from inner ear
through the vestibular nerve and from the cerebellum.
• Neurons of the lateral vestibular nucleus give rise to the
axons that form the vestibulospinal tract.
• Tract descends uncrossed through medulla & through the
length of the spinal cord in the anterior white column.
• Fibers terminate by synapsing with internuncial neurons of
the anterior gray column of the spinal cord
Inner ear & cerebellum, by means of this tract, facilitate the
activity of the extensor muscles & inhibit the activity of the
flexor muscles in association with the maintenance of balance
Function: Unconscious maintenance of posture & balance

37. Olivospinal Tract:
• Arise from the inferior olivary nucleus in medulla
• Descend in the lateral white column.
• Influence the activity of the motor neurons in the anterior
gray column.
• There is now considerable doubt that it exists

38. Ascending Tracts
For the sensory pathways
• Cell bodies of first-order sensory neurons lie in the dorsal root
ganglia which has pseudounipolar cells.
• Peripheral process forms sensory fibres of peripheral nerves which
carry various types of sensations.
• Central process enter spinal cord through dorsal nerve root &
terminate either by synapsing with cells in posterior grey column of
spinal cord or at higher level in the medulla oblongata with the cells
of nucleus gracilis and nucleus cuneatus.
• After relay in the nuclei second neuron fibres start & ascend to
either thalamus or cerebellum.
• Cerebellum finally recieves second neurons fibres.
• From thalamus third- order neuron fibres are projected to the
sensory areas in the cerebral cortex

40. Lateral spinothalamic tract:
• Carries the sensation of pain & temperature.
• First order neuron fibres start in the dorsal root
ganglia.
• These relay by synapsing with neurons lying in grey
matter of lamina II and III.
• Pain fibres relay in Lamina II (substantia gelatinosa)
• Second order neuron fibres cross immediately to
opposite side close to the central canal and ascend as
tract in the lateral white column of spinal cord.
Anterior spinothalamic tract:
• carries the sensation of crude touch & pressure, tickle
& itch.
• First order neuron fibres start in the dorsal root
ganglia.
• These relay by synapsing with neruons lying in the grey
matter of lamina III & IV (nucleus proprius)
• Second order neuron fibres ascend for 1-2 segments
and cross to opposite side in the white commissure &
ascend as a tract in the anterior white column of spinal
cord.

41. • Second order neuron terminate in ventral posterolateral
nucleus (VPL) of the thalamus
• Axons of the third order sensory neurons project to the
primary sensory cortex of the cerebral hemisphere
• Anterior and lateral spinothalamic tracts carry sensations
from the opposite half of body.

42. Anterior & lateral spinothalamic tracts lie in continuity with each other in the anterolateral white column of spinal
cord.
Sensations of pain , temperature , touch & pressure, are lying lateral to medial. Pressure sensations are medial most
near the anterior median fissure.
Sacral, lumbar, thoracic and cervical fibres are situated in layers in theses tract from superficial to deep
(somatotrophic organization).
P
Pr To
T

43. Clinical Correlation
• Fibres of lateral spinothalamic tract carry pain and temperature sensations— pain fibres being lateral to the
temperature.
The pain fibres are very superficial in the lateral white column of the cord in the cervical region. Therefore,
cordotomy can be performed safely at this level to relieve pain in the opposite half of the body.
• Damage of anterior spinothalamic tract leads to loss of crude touch and pressure on the opposite of the body
below the level of the lesion.

44. Clinical Correlation
Syringomyelia:
It is the condition in which there is dilatation of central
canal of spinal cord usually beginning in cervical region.
Decussating fibresfor pain and temperature in the grey
commissure are interrupted.
This leads to bilateral loss of pain and temperature in the
affected region.
But touch and proprioception is present. Thus patient has
dissociation of sensory loss.
Usually the patient gets severe infections in the fingers
due to uncared cuts and bruises.

45.  Fine touch, pressure, tactile localisation, tactile
discrimination, stereognosis, sense of vibration are carried
by fasciculus gracilis & fasciculus cuneatus.
Fasciculus gracilis (tract of Goll):
It commences at caudal limit of spinal cord & is composed of
first order neuron fibres from central process of dorsal root
ganglia
They run directly upwards in the posterior column of white
matter of spinal cord.
As the tract ascends, it receives accession from each dorsal
root.
The fibres which enter in the coccygeal & lower sacral region
are thrust medially by fibres which enter at higher levels.
Fasciculus gracilis which contains fibres derived from lower
thoracic, lumbar, sacral & coccygeal segments of spinal cord
occupies the medial part of posterior column & is separated
from fasciculus cuneatus by postero-intermediate septum

46. Fasciculus cuneatus (tract of Burdach):
It commences in mid-thoracic region. It derives its fibres from
upper thoracic arid cervical segments.
Both fasciculi contain first order neuron fibres from central
process of dorsal root ganglia & end by synapsing with neurons
in nucleus gracilis & nucleus cuneatus, from where second
neuron fibres take origin.
Axons of second order sensory neurons curve ventromedially
around the central grey mtter of the medulla as internal
arcuate fibres to undergo decussation.
Fibres after crossing midline turn upwards as a flat tract called
medial lemniscus which courses upwards to terminate in the
ventral posterolateral nucleus (VPL) nucleus of the thalamus.
The third order sensory neurons from thalamus project into the
cerebral cortex of the cerebral hemisphere.
This pathway carrying conscious proprioceptive sensations is
termed ‘dorsal column—medial lemniscus-pathway’.

47. Tabes dorsalis
It is a syphilitic degenerative lesion of the posterior white columns &
posterior nerve roots
• characterised by impairment of proprioceptive sensibility.
• Patient loses the sense of tactile discrimination, vibration,
passive movement and appreciation of posture.
• patient becomes ataxic, particularly if he closes his eyes, because
he has lost his position sense for which he can partially
compensate by visual knowledge of his spatial relationship
(Romberg's sign).

48. • Reflex proprioceptive sensations are carried by dorsal &
ventral spinocerebellar tracts.
• spinocerebellar tracts convey to the cerebellum both
unconscious proprioceptive impulses arising in Golgi tendon
organ and muscle spindle essential for the control of posture
& exteroceptive (touch)
Dorsal or posterior spinocerebellar tract:
- It begins at the level of 2nd/ 3rd lumbar segment of spinal
cord.
-First order neuron fibres are central processes of dorsal root
ganglia. These relay in the dorsal nucleus (thoracic or Clark's
column).
-second order neuron fibres form dorsal spinocerebellar tract.
-This uncrossed tract ascends in lateral column of white matter of
spinal cord.
-It ascends to the level of medulla oblongata where its fibres pass
through inferior cerebellar peduncle & terminate in the ipsilat-
eral cerebellar cortex.

49. Ventral or anterior spinocerebellar tract:
• First neuron fibres are central processes of dorsal root ganglia.
• Second neuron fibres are derived from the large cells of
posterior grey column (laminae V, VI) in the lumbar and sacral
segments.
• majority of the axons of the second-order neurons cross to the
opposite side and ascend as anterior spinocerebellar tract in
the contralateral white column; the minority of the axons
ascend as the anterior spinocerebellar tract in the lateral white
column of the same side.
• The fibers, having ascended through the medulla oblongata
and pons, enter the cerebellum through the superior cerebellar
peduncle and terminate in the cerebellar cortex.
• Those fibers that crossed over to the opposite side in the spinal
cord cross back within the cerebellum

50. • Functionally, both spinocerebellar tracts control the coordination & movements of muscles controlling posture of
the body.
• Anterior tract conveys muscle and joint information from both upper and lower limbs
Posterior tract receives information from trunk and lower limbs
• posterior tract is concerned with fine movements, whereas anterior tract is concerned with gross movements of
the limb as a whole.
spino-olivary and spinotectal tracts are responsible for visual and proprioceptive reflexes.

51. Hemisection of the spinal cord (Brown-Sequard syndrome)
-Ipsilateral upper motor neuron type of (spastic) paralysis below the level
of hemisection (due to involvement of pyramidal tract).
– Ipsilateral loss of proprioceptive sensations (sense of position, posture,
passive movement and vibrations) and fine ouch/discrimination (due to
involvement of posterior columns).
– Contralateral loss of pain and temperature sensations below the level
of lesion (due to involvement of spinothalamic tract).

52. Poliomyelitis : It is a viral disease which involves anterior horn
cells leading to flaccid paralysis of the affected segments. It is
lower motor neuron paralysis