Neuroanatomy Draw It To Know It

8. Spinal Canal and Muscle–Nerve Physiology 129

Nerve Roots & Rami

■ Th e ventral root carries motor fi bers and the dorsal
root carries sensory fi bers.
■ Th e dorsal root ganglion lies within the intervertebral
foramen along the posterior nerve root; it houses the
cell bodies of sensory nerves.
■ Sensory cell bodies are pseudo-unipolar: they contain
a short axon with bipolar processes that pass both
centrally and peripherally.
■ Just distal to the dorsal root ganglion, the anterior
and posterior roots join to form a mixed spinal nerve,
which then separates into dorsal and ventral rami.

■ Dorsal rami innervate the paraspinal muscles and

provide sensory coverage to the back of the head and

posterior trunk.

■ Ventral rami provide motor and sensory innervation

to a widespread group of muscles and sensory areas,

including the anterior trunk and upper and lower

limbs.

■ Impulses travel up the white ramus (myelinated) to

the paravertebral sympathetic ganglion and then

down the gray ramus (unmyelinated) back to the

v e n t r a l r a m u s.

C2

T1

L1

Cervical

plexus

VERTEBRAESPINAL CORDVERTEBRAENERVES

Brachial

plexus

Lumbar

plexus

Sacral

plexus

Coccyx 1

(^23)
(^45)
S1
2
3
4
5
2 3 4 5 6 7 8 9
10
11
12
L1
C1 2
(^34)
(^56)
7
T1^8 S1
C7
1
8
76
5
4
3
2
32
4 5 6 7 8 9
10
11
(^121)
(^23)
(^4512)
L5
C8
I I
IIIII II
IV IVV
VIV VI
T1VII T1VII
II
III
IV
V
VI
VII
VIII
IX
X
XI
XI
X
IX
VIII
VII
VI
V
IV
III
XII
XII L1
L1 II
III
IV
V
II
III
IV
V
II
III
FIGURE 8-1 Segmental organization of the spinal canal and the peripheral nerves. Used with permission from Altman, Joseph, and Shirley A. Bayer.
Development of the Human Spinal Cord: An Interpretation Based on Experimental Studies in Animals. Oxford; New York: Oxford University Press, 2001.