4. Cross-Sectional Anatomy
• Two lengthwise grooves divide
cord into right and left halves
–Ventral (anterior) median fissure
–Dorsal (posterior) median sulcus
• Gray commissure—connects
masses of gray matter; encloses
central canal
5. Figure 12.31a
(a) Cross section of spinal cord and vertebra
Epidural space
(contains fat)
Pia mater
Spinal
meninges
Arachnoid
mater
Dura mater
Bone of
vertebra
Subdural space
Subarachnoid
space
(contains CSF)
Dorsal root
ganglion
Body
of vertebra
6. Figure 12.31b
(b) The spinal cord and its meningeal coverings
Dorsal funiculus
Dorsal median sulcus
Central canal
Ventral median
fissure
Pia mater
Arachnoid mater
Spinal dura mater
Gray
commissure
Dorsal horn Gray
matter
Lateral horn
Ventral horn
Ventral funiculus
Lateral funiculus
White
columns
Dorsal root
ganglion
Dorsal root
(fans out into
dorsal rootlets)
Ventral root
(derived from several
ventral rootlets)
Spinal nerve
8. White Matter
• Consists mostly of ascending
(sensory) and descending (motor)
tracts
• Transverse tracts (commissural
fibers) cross from one side to the
other
• Tracts are located in three white
columns
12. Spinal Nerves: Roots
• Each spinal nerve connects to
the spinal cord via two roots
• Ventral roots
–Contain motor (efferent) fibers
from the ventral horn motor
neurons
–Fibers innervate skeletal muscles
13. Spinal Nerves: Roots
• Dorsal roots
–Contain sensory (afferent) fibers
from sensory neurons in the dorsal
root ganglia
–Conduct impulses from peripheral
receptors
• Dorsal and ventral roots unite to
form spinal nerves
14. Figure 13.7 (a)
Dorsal root
ganglion
Gray matter
White matter
Ventral root
Dorsal root
Dorsal and
ventral rootlets
of spinal nerve
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Sympathetic trunk
ganglion
Spinal nerve
Rami communicantes
Anterior view showing spinal cord, associated nerves, and vertebrae.
The dorsal and ventral roots arise medially as rootlets and join
laterally to form the spinal nerve.
15. Spinal Nerves: Rami
• Each spinal nerve branches into
mixed rami
–Dorsal ramus
–Larger ventral ramus
–Meningeal branch
–Rami communicantes (autonomic
pathways) join to the ventral rami
in the thoracic region
16. Figure 13.7 (b)
Dorsal ramus
Ventral ramus
Intercostal nerve
Spinal nerve
Rami communicantes
Dorsal root
ganglion
Dorsal root
Ventral root
Sympathetic trunk
ganglion
Sternum
(b) Cross section of thorax showing the main roots and
branches of a spinal nerve.
Branches of intercostal
nerve
• Lateral cutaneous
• Anterior cutaneous
17. Cervical Plexus
• Formed by ventral rami of C1–C4
• Innervates skin and muscles of
the neck, ear, back of head, and
shoulders
• Phrenic nerve
–Major motor and sensory nerve of
the diaphragm (receives fibers
from C3–C5)
19. Brachial Plexus
• Formed by ventral rami of C5–C8
and T1 (and often C4 and T2)
• Major branches of this plexus:
–Roots—five ventral rami (C5–T1)
–Trunks—upper, middle, and lower
–Divisions—anterior and posterior
–Cords—lateral, medial, and
posterior
20. Figure 13.9 (a)
Upper
Middle Trunks
Lower
Roots (ventral rami):
Upper subscapular
Lower subscapular
Thoracodorsal
Medial cutaneous
nerves of the arm
and forearm
Long thoracic
Medial pectoral
Lateral pectoral
Nerve to
subclavius
Suprascapular
Dorsal scapular
Posterior
divisions
Anterior
divisions
Lateral
PosteriorCords
Medial
Axillary
Musculo-
cutaneous
Radial
Median
Ulnar
Posterior
divisions
Trunks Roots
C4
C5
C6
C7
C8
T1
(a) Roots (rami C5 – T1), trunks, divisions, and cords
22. Figure 13.9 (c)
Median nerve
Musculocutaneous nerve
Radial nerve
Humerus
Ulna
Ulnar nerve
Median nerve
Radius
Radial nerve (superficial branch)
Superficial branch of ulnar nerve
Dorsal branch of ulnar nerve
Digital branch of ulnar nerve
Muscular branch
Digital branch
(c) The major nerves of the upper limb
Axillary
nerve
Anterior
divisions
Posterior
divisions
Trunks Roots
23. Lumbar Plexus
• Arises from L1–L4
• Innervates the thigh, abdominal
wall, and psoas muscle
• Femoral nerve
• Obturator nerve
24. Figure 13.10
(a) Ventral rami and major branches
of the lumbar plexus
Iliohypogastric
L1
L2
L3
L4
L5
Ilioinguinal
Genitofemoral
Lateral femoral
cutaneous
Obturator
Femoral
Lumbosacral
trunk
Lateral femoral
cutaneous
Anterior femoral
cutaneous
Saphenous
Obturator
Iliohypogastric
Ilioinguinal
Femoral
Ventral rami
Ventral
rami:
(b) Distribution of the major nerves from
the lumbar plexus to the lower limb
25. Sacral Plexus
• Arises from L4–S4
• Serves the buttock, lower limb,
pelvic structures, and perineum
• Sciatic nerve
27. Figure 13.11 (b)
Superior gluteal
Inferior gluteal
Common fibular
Deep fibular
Superficial fibular
Plantar branches
Tibial
Sural (cut)
Posterior femoral
cutaneous
Pudendal
Sciatic
(b) Distribution of the major nerves from
the sacral plexus to the lower limb
