Spinal cord Gross anatomy with Clinical Anatomy

1. CONTENTS
1. INTRODUCTION
2. GENERAL FEATURES
3. MENINGEAL COVERINGS
4. ENLARGEMENTS
5. EXTERNAL FEATURES
6. INTERNAL STRUCTURE
7. SPINAL NERVES
8. TRACTS OF SPINAL CORD
9. BLOOD SUPPLY
10. APPLIED ANATOMY

2. INTRODUCTION
 The spinal cord is the long cylindrical lower part of central
nervous system.
 It is the main pathway for information connecting the brain
and peripheral nervous system.
 It occupies upper two-thirds of vertebral canal.
 It is surrounded by the three meninges.
 It give rise to 31 pairs of spinal nerves .
 It retains the basic structural pattern.

3. GENERAL FEATURES
DIMENSIONS :
 The spinal cord is 18 inches or 45 cm in an adult male and 42 cm in an
adult female.
 The weight of spinal cord is 30 g.
LOCATION :
 In an adult it extends from upper border of atlas vertebra to the lower
border of L1 vertebra .
 In new-born , it extends up to L3 vertebra.
 Superiorly , it is continuous with the medulla oblongata .
 Inferiorly , it terminates as conus medullaris.

4.  Segment or part of spinal cord to which a pair of dorsal nerve roots and a
pair of ventral nerve roots is attached is called a spinal segment.
 As the spinal cord (45cm) is much shorter than the length of the vertebral
column (65cm) , the spinal segments do not lie opposite to the
corresponding vertebrae.
 A vertebral spine is always lower than the corresponding spinal segment .
 The level of spinal segment with their vertebral level is sown in the table
below:
Vertebral levels Spinal segments
C1-C7 C1-C8
T1-T6 T1-T8
T7-T9 T9-T12
T10-T11 L1-L5
T12- L1 S1-S5 and Co1

5. General features of spinal cord

6. MENINGEAL COVERINGS
 The spinal cord is surrounded by three meninges .
 Outermost – Dura mater , middle one – Arachnoid mater and innermost- Pia
mater
 The space between dura mater and arachnoid mater is called subdural space.
 The arachnoid and pia maters are separated by subarachnoid space which
contains CSF. The CSF is withdrawn from the subarachnoid space during
lumbar puncture.
 The spinal cord is enclosed only by the meningeal layer of dura mater .
 The space between the meningeal layer and endosteum of the vertebral canal
is called epidural space, where epidural anaesthesia can be given.

7. Modifications of spinal pia mater
1. Ligamentum denticulatum:
21 pairs of teeth – like projections , fuse laterally with arachnoid and dura maters,
Highest process attaches superior to foramen magnum
Keeps the spinal cord in position
2. Linea splendens :
Thickening seen at the anteromedian sulcus in the lower part of the spinal cord.
3. The filum terminale :
20 cm long
After leaving through sacral hiatus ends by getting attached to the periosteun of
dorsal surface of first segment of coccyx.
It consists of two parts : Filum termnale internum – 15 cm ( upper part)
Filum terminale externum – 5 cm ( lower part)

8. coverings and spaces in spinal cord

10. Enlargements
1. Cervical enlargement for supply of upper limb muscles :
This extends from C4 to T1 spinal segments with maximum diameter of
38mm at level of C6.
2. Lumbar enlargement for supply of muscles of lower limb :
It extends from level of L2 to S3 segments with maximum diameter of
35mm at the level of S1 segment.
CAUDA EQUINA : Dorsal and ventral roots of right and left sides of L2 –L5 ,
S1-S5 and Co1 nerves lie almost vertically around filum terminale . These
are called cauda equina as these resemble a horse’s tail.

11. External features
 Anteriorly , the spinal cord reveals a deep anterior median fissure
lodging the anterior spinal artery.
 Posterior median sulcus is a thin longitudinal groove from which a
septum runs in the depth of spinal cord.
 Each half is subdivided into – anterior , lateral and posterior regions by
anterolateral and posterolateral sulci.
 Ventral or motor nerve roots emerge from the anterolateral sulcus.
 Dorsal or sensory nerve roots enter spinal cord from posterolateral
sulcus.

12. External features with enlargement

13. Internal structure
In a transverse section of a segment of spinal cord :
 White matter, i.e. nerve fibres , lies outside .
 Grey matter lies inside.
 In the centre of grey matter there is the central canal containing
cerebrospinal fluid ( CSF).
 The canal is lined by single layer of ependymal cells.
 The grey matter is in the form of ‘H’ with a grey commissure joining the
grey matter of right and left sides .

14.  Grey matter comprises of one posterior horn and one anterior horn on each side
in the entire extent of the cord .
 Only in T1-L2 and S2-S4 segments ,there is an additional lateral horn for the
supply of the viscera. This horn is a part of autonomic nervous system.
DORSAL HORN:
 Found at all spinal cord levels
 Comprised of sensory neurons
VENTRAL HORN:
 Comprised of motor neurons
 That innervate skeletal muscle
 Shape and size of the horns differ in different segments due to functional
reasons.

15. Shape of horns in different segments of spinal cord
Segments of
spinal cord
Posterior horn Lateral horn Anterior horn
Cervical , oval shape Slender Absent Narrow in 1-3 segments
Broad in C4 –C8 segments
for supply of upper limbs
Thoracic , circular
shape
Slender Present for
thoracolumbar
outflow
Slender in T2-T12
segments , broad in T1
segment
Lumbar , circular
shape
Bulbous Present only in
lumbar 1 and 2
segments
Bulbous for supply of
lower limbs
Sacral , circular but
smaller
Thick Group of cells in
sacral 2-4
segments for
Bulbous for supply of
lower limbs

16. Structure of the spinal cord

17. spinal nerves
 Spinal nerves arise in pairs .
 There are 31 pairs of spinal nerves as 8 cervical ,12 thoracic, 5 lumbar , 5
sacral and 1 coccygeal.
 Each spinal nerve arises by a series of six to eight dorsal and ventral nerve
rootlets.
 These rootlets unite in or near the intervertebral foramen to form the
spinal nerve.
BRANCHES :
 Dorsal Ramus – It supplies the dorsal one-third of the body wall. They do
not supply the limbs.
 Ventral Ramus-It supplies the ventral two-thirds of the body wall including
the limbs.

18. TRACTS OF THE SPINAL CORD
 A collection of nerve fibres that connects two masses of grey matter within the
central nervous system is called a tract .
 Tracts may be ascending (sensory) or descending (motor) .
 They are usually named after the masses of grey matter connected by them.
 Some tracts are called fasciculi or leminsci.
 Descending tracts are of two types :
 PYRAMIDAL or CORTICOSPINAL Tracts ( lateral and anterior)
EXTRAPYRAMIDAL Tracts – rubrospinal , medial reticulospinal , lateral reticulospinal ,
olivospinal , vestibulospinal and tectospinal.
 Ascending tracts – lateral spinothalamic , anterior spinothalamic , fasciculus gracilis ,
fasciculus cuneatus , posterior spinocerebellar , anterior spinocerebral, spino –
olivary and spinotectal.

22. Tracts of spinal cord

23. Blood supply
 The vertebral arteries are the main source of blood to the spinal
cord .
 The following arteries branch from the vertebral arteries to
directly supply the spinal cord :
1. One anterior spinal artery
2. Two posterior spinal arteries
3. Anterior and posterior radicular arteries
4. Arterial vasocorona – anastomose between
the spinal arteries

24. Applied anatomy
 Cauda equina syndrome – Damage to cauda equina results into :
Lower motor neuron type of paralysis due to compression of ventral nerve roots
Root pain due to involvement of dorsal nerve roots
Bladder and bowel movement is delayed
 Poliomyelitis – Viral disease involving anterior horn cells leading to flaccid
paralysis of affected segments . It is a lower motor neuron paralysis
If upper cervical segments affected , it may be fatal because of the involvement of
C4 segment which supplies the diaphragm through phrenic nerve.

25. Applied anatomy
 Lumbar puncture – In a child , done at level of L4 Vertebra as spinal
cord extends till L3 vertebra at birth. In an adult , done at level of L3
Vertebra as spinal cord ascends till level of L1 vertebra.
 Conus medullaris syndrome – Due to injury to S2-S4 segments of spinal
cord
Features are : Anaesthesia in perineum
Involvement of bladder and bowel is early
Sexual functions are affected

26. Applied anatomy
 Tabes dorsalis – Occurs during tertiary stage of syphills.
Degenerative lesions of dorsal nerve roots and of posterior white
columns
Its feature is several pain in lower limbs and the lower limbs are
mainly affected..

27. Applied anatomy