The spinal cord extends from the foramen magnum to the lower border of the first lumbar vertebra. It is covered by meninges and has a cylindrical shape. The spinal cord contains gray matter in an H-shape containing nerve cell bodies and white matter surrounding the gray matter containing myelinated nerve fibers. The spinal cord has 31 segments that correspond to 31 pairs of spinal nerves. It contains ascending tracts that carry sensory information to the brain and descending tracts that carry motor commands from the brain. The spinal cord plays a key role in motor and sensory functions through its connections with the brain and body.

1. Spinal Cord
by
Dr.Hafiz Muhammad Asad Ullah

2. Situation:
Spinal cord lies loosely in the vertebral canal. It extends
from foramen magnum where it is continuous with
medulla oblongata above, and up to the lower border of
first lumbar vertebra below.
Meninges:
Spinal cord is covered by sheaths called meninges, which
are membranous in nature. Meninges are dura mater, pia
mater and arachnoid mater. These coverings continue as
coverings of brain. Meninges are responsible for
protection and nourishment of the nervous tissues.
Shape and Length:
Spinal cord is cylindrical in shape. Length of the spinal
cord is about 45 cm in males and about 43 cm in females.

3. Enlargements:
Spinal cord has two spindle-shaped swellings,
namely cervical and lumbar enlargements. These
two portions of spinal cord innervate upper and
lower extremities respectively.
Segments:
Spinal cord is made up of 31 segments. In fact,
spinal cord is a continuous structure. Appearance of
the segment is by nerves arising from spinal cord,
which are called spinal nerve.
Spinal Nerves:
Segments of spinal cord correspond to 31 pairs of
spinal nerves in a symmetrical manner

4. Spinal segments/Spinal nerves:
1. Cervical segments/Cervical spinal nerves = 8
2. Thoracic segments/Thoracic spinal nerves = 12
3. Lumbar segments/Lumbar spinal nerves = 5
4. Sacral segments/Sacral spinal nerves = 5
5. Coccygeal segment/Coccygeal spinal nerves = 1
Total = 31

5. Nerve Roots:
Each spinal nerve is formed by an anterior
(ventral) root and a posterior (dorsal) root. Both
the roots on either side leave the spinal cord
and pass through the corresponding
intervertebral foramina (openings between
vertebrae).
Internal Structure of Spinal Cord:
Neural substance of spinal cord is divided into
inner gray matter and outer white matter

7. GRAY MATTER OF SPINAL CORD
Gray matter of spinal cord is the collection of
nerve cell bodies, dendrites and parts of axons.
It is placed centrally in the form of wings of the
butterfly and it resembles the letter ‘H’. Exactly
in the center of gray matter, there is a canal
called the spinal canal. Ventral and the dorsal
portions of each lateral half of gray matter are
called ventral (anterior) and dorsal (posterior)
gray horns respectively.

8. Organization of Neurons in Gray
Matter
Organization of neurons in the gray matter of spinal cord
is described as: 1. Nuclei or columns 2. Laminae or layers
NUCLEI:
Clusters of neurons are present in the form of nuclei or
cell columns in gray matter. e.g. Dorsal nucleus of Clarke
and Marginal nucleus.
LAMINAE:
Neurons of gray matter are distributed in laminae or
layers. Each lamina consists of neurons of different size
and shape. Laminae are also called Rexed laminae .They
are ten in number.

9. Laminae in Posterior Gray Horn:
Laminae I to VI constitute the posterior gray horn.
These laminae contain nuclei of sensory neurons,
which are concerned with sensory functions.
Laminae in Anterior Gray Horn:
Laminae VIII and IX form the anterior gray horn.
These laminae contain nuclei of motor neurons.
Intermediate Zone:
Laminae VII and X constitute the intermediate zone.
It contains the intermediolateral nuclues which
plays a role in the autonomic sensory and
motor functions.

10. WHITE MATTER OF SPINAL CORD
White matter of spinal cord surrounds the gray matter. It is formed by
the bundles of predominantly myelinated fibers. Anterior median
fissure and posterior median septum divide the entire mass of white
matter into two lateral halves. Each half of the white matter is divided
by the fibers of anterior and posterior nerve roots into three white
columns or funiculi:
I. Anterior or Ventral White Column. It is also called anterior or ventral
funiculus.
II. Lateral White Column Lateral white column is present between the
anterior nerve root and anterior gray horn on one side and posterior
nerve root and posterior gray horn on the other side. It is also called
lateral funiculus.
III. Posterior or Dorsal White Column Dorsal white column is situated
between the posterior nerve root and posterior gray horn on one side
and posterior median septum on the other side. It is also called
posterior or dorsal funiculus.

12. TRACTS IN SPINAL CORD
Groups of nerve fibers passing through spinal cord are known as tracts of
the spinal cord. The spinal tracts are divided into two main groups. They
are: 1. Short tracts 2. Long tracts.
1.Short Tracts
Fibers of the short tracts connect different parts of spinal cord itself. Short
tracts are of two types:
i. Association or intrinsic tracts, which connect adjacent segments of
spinal cord on the same side
ii. Commissural tracts, which connect opposite halves of same
segment of spinal cord.
2. Long Tracts of spinal cord, which are also called projection tracts,
connect the spinal cord with other parts of central nervous system. Long
tracts are of two types:
i. Ascending tracts, which carry sensory impulses from the spinal cord to
brain
ii. Descending tracts, which carry motor impulses from brain to the spinal
cord.

13. ASCENDING TRACTS OF SPINAL CORD
Ascending tracts of spinal cord carry the
impulses of various sensations to the brain.
Pathway for each sensation is formed by two or
three groups of neurons, which are:
1. First order neurons
2. Second order neurons
3. Third order neurons.

14. First Order Neurons
First order neurons receive sensory impulses from the
receptors and send them to sensory neurons present in
the posterior gray horn of spinal cord through their fibers.
Nerve cell bodies of these neurons are located in the
posterior nerve root ganglion.
Second Order Neurons
Second order neurons are the sensory neurons present in
the posterior gray horn. Fibers from these neurons form
the ascending tracts of spinal cord. These fibers carry
sensory impulses from spinal cord to different brain areas
below cerebral cortex (subcortical areas) such as
thalamus. All the ascending tracts are formed by fibers of
second order neurons of the sensory pathways except the
ascending tracts in the posterior white funiculus, which
are formed by the fibers of first order neurons.

15. Third Order Neurons
Third order neurons are in the subcortical areas.
Fibers of these neurons carry the sensory
impulses from subcortical areas to cerebral
cortex.

16. Ascending Tracts of spinal cord
1. ANTERIOR SPINOTHALAMIC TRACT
Anterior spinothalamic tract is formed by the fibers of second
order neurons of the pathway for crude touch sensations.
Function: Anterior spinothalamic tract carries impulses of
crude touch (protopathic) sensation.
2. LATERAL SPINOTHALAMIC TRACT Lateral spinothalamic
tract is formed by the fibers from second order neurons of
the pathway for the sensations of pain and temperature .
Fibers of lateral spinothalamic tract carry impulses of pain
and temperature sensations.
Function: Fibers arising from this marginal nucleus transmit
impulses of fast pain sensation.

17. 3. VENTRAL SPINOCEREBELLAR TRACT
Ventral spinocerebellar tract is also known as
Gower tract, indirect spinocerebellar tract or
anterior spinocerebellar tract. It is constituted by
the fibers of second order neurons of the pathway
for subconscious kinesthetic sensation
Function: Ventral spinocerebellar tract carries the
impulses of sub conscious kinesthetic sensation
(proprioceptive pulses from muscles, tendons and
joints). Impulses of subconscious kinesthetic
sensation are also called non-sensory impulses.

18. 4. DORSAL SPINOCEREBELLAR TRACT
Dorsal spinocerebellar tract is otherwise called
Flechsig tract, direct spinocerebellar tract or
posterior spinocerebellar tract. Like the ventral
spinocerebellar tract, this tract is also constituted
by the second order neuron fibers of the pathway
for subconscious kinesthetic sensation.
Function : Along with ventral spinocerebellar tract,
the dorsal spinocerebellar tract carries the impulses
of subconscious kinesthetic sensation, which are
known as non-sensory impulses

19. 5. SPINOTECTAL TRACT
Spinotectal tract is considered as a component
of anterior spinothalamic tract. It is constituted
by the fibers of second order neurons.
Function: Spinotectal tract is concerned with
spinovisual reflex.
(Spinovisual reflex: involuntary postural
movements of the head in response to visual
and auditory stimuli).

20. 6. FASCICULUS DORSOLATERALIS
Fasciculus dorsolateralis is otherwise called tract
of Lissauer. It is considered as a component of
lateral spinothalamic tract. And, it is constituted
by the fibers of first order neurons.
Function
Fibers of the dorsolateral fasciculus carry
impulses of pain and thermal sensations.

21. 7. SPINORETICULAR TRACT
Spinoreticular tract is formed by the fibers of
second order neurons.
Function: Fibers of the spinoreticular tract are the
components of ascending reticular activating
system and are concerned with consciousness and
awareness.
Reticular activating system: It comprises of a set of
connected nuclei in the brains of that is responsible
for regulating wakefulness and sleep-wake
transitions.

22. 8. SPINO-OLIVARY TRACT
Spino-olivary tract is situated in anterolateral
part of white column. The fibers terminate in
olivary nucleus of medulla oblongata, from here,
the neurons project into cerebellum.
Function: This tract is concerned with
proprioception.

23. 9. SPINOVESTIBULAR TRACT
Spinovestibular tract is situated in the lateral white
column of the spinal cord. Fibers of this tract arise
from all the segments of spinal cord.
Function: This tract is concerned with
proprioception.
10. FASCICULUS GRACILIS (TRACT OF GOLL)
11. FASCICULUS CUNEATUS (TRACT OF BURDACH)
Fasciculus gracilis and fasciculus cuneatus are
together called ascending posterior column tracts.
These tracts are formed by the fibers of first order
neurons of sensory pathways.

24. Functions
These tracts convey impulses of following sensations:
i. Fine (epicritic) tactile sensation
ii. Tactile localization (ability to locate the area of skin where the
tactile stimulus is applied with closed eyes)
iii. Tactile discrimination or two point discrimination (ability to
recognize the two stimuli applied over the skin simultaneously with
closed eyes)
iv. Sensation of vibration (ability to perceive the vibrations from a
vibrating tuning fork placed over bony prominence conducted to deep
tissues through skin). It is the synthetic sense produced by
combination of touch and pressure sensations.
v. Conscious kinesthetic sensation (sensation or awareness of
various muscular activities in different parts of the body)
vi. Stereognosis (ability to recognize the known objects by touch with
closed eyes). It is also a synthetic sense produced by combination of
touch and pressure sensations.

25. 12. COMMA TRACT OF SCHULTZE
Comma tract of Schultze is also called fasciculus
interfascicularis. It is situated in between tracts of Goll and
Burdach. This tract is formed by the short descending fibers,
arising from the medial division of posterior nerve root.
These fibers are also considered as the descending
branches of the tracts of Goll and Burdach.
Function
Function of this tract is to establish intersegmental
communications and to form short reflex arc.

26. DESCENDING TRACTS OF SPINAL
CORD
Descending tracts of the spinal cord are formed
by motor nerve fibers arising from brain and
descend into the spinal cord. These tracts carry
motor impulses from brain to spinal cord.
Descending tracts of spinal cord are of two
types:
A. Pyramidal tracts
B. Extrapyramidal tracts

27. PYRAMIDAL TRACTS
Pyramidal tracts are the descending tracts concerned with
voluntary motor activities of the body. These tracts are
classified as corticobulbar and corticospinal tracts.
The corticobulbar (or corticonuclear) tract is a two
neuron motor pathway connecting the motor cortex to
the medullary pyramids, and is primarily involved in carrying
the motor function of the cranial nerves.
Corticospinal tracts connect the motor cortex to the spinal
cord. There are two corticospinal tracts, the anterior
corticospinal tract and lateral corticospinal tract. While
running from cerebral cortex towards spinal cord, the fibers of
these two tracts give the appearance of a pyramid on the
upper part of anterior surface of medulla oblongata hence the
name pyramidal tract.
In the medulla, 90% of the nerve fibers on each side
will decussate, or cross over to the other side, these exert
contralateral control.

28. EXTRAPYRAMIDAL TRACTS
Descending tracts of spinal cord other than
pyramidal tracts are called extrapyramidal
tracts. These are concerned with involuntary
motor activities. Extrapyramidal tracts are
chiefly found in the reticular formation of
the brainstem, and target neurons in the spinal
cord involved in reflexes, locomotion, complex
movements, and postural control.

29. Cross section of spinal cord.