Spinal Cord and Spinal Nerves Lab
Spinal Cord
• Spinal nerves– 31 pairs
• Cervical and lumbar enlargements• Cauda equina
Figure 12.29a
Cervicalenlargement
Dura andarachnoidmater
LumbarenlargementConusmedullarisCaudaequina
Filumterminale
Cervicalspinal nerves
Lumbarspinal nerves
Sacralspinal nerves
Thoracicspinal nerves
(a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.
Spinal Cord
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
Figure 12.31a
(a) Cross section of spinal cord and vertebra
Epidural space(contains fat)
Pia mater
Spinalmeninges
Arachnoidmater Dura mater
Bone ofvertebra
Subdural space
Subarachnoidspace(contains CSF)
Dorsal rootganglion
Bodyof vertebra
Figure 12.31b
(b) The spinal cord and its meningeal coverings
Dorsal funiculus
Dorsal median sulcus
Central canal
Ventral medianfissure
Pia mater
Arachnoid mater
Spinal dura mater
Graycommissure Dorsal horn Gray
matterLateral hornVentral horn
Ventral funiculusLateral funiculus
Whitecolumns
Dorsal rootganglion
Dorsal root(fans out into dorsal rootlets)
Ventral root(derived from severalventral rootlets)
Spinal nerve
Gray Matter
• Dorsal horns• Ventral horns• Lateral horns (only in thoracic
and lumbar regions) • Dorsal root (spinal) ganglia
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
Figure 12.33
Ascending tracts Descending tracts
Fasciculus gracilisDorsalwhitecolumn
Fasciculus cuneatus
Dorsalspinocerebellar tract
Lateralspinothalamic tract
Ventral spinothalamictract
Ventral whitecommissure
Lateralcorticospinal tract
Lateralreticulospinal tract
Ventral corticospinaltract
Medialreticulospinal tract
Rubrospinaltract
Vestibulospinal tractTectospinal tract
Ventralspinocerebellartract
Spinal Nerves
• 31 pairs of mixed nerves– 8 cervical (C1–C8)
– 12 thoracic (T1–T12)
– 5 Lumbar (L1–L5)
– 5 Sacral (S1–S5)
– 1 Coccygeal (C0)
Figure 13.6
CervicalnervesC1 – C8
ThoracicnervesT1 – T12
LumbarnervesL1 – L5
Sacral nervesS1 – S5
Coccygeal nerve Co1
Cervical plexus
Intercostalnerves
Cervicalenlargement
Lumbarenlargement
Cauda equina
Brachial plexus
Lumbar plexus
Sacral plexus
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
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
Figure 13.7 (a)
Dorsal rootganglion
Gray matterWhite matterVentral rootDorsal root
Dorsal andventral rootlets of spinal nerve
Dorsal ramusof spinal nerveVentral ramusof spinal nerve
Sympathetic trunkganglion
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.
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
Figure 13.7 (b)
Dorsal ramus
Ventral ramus
Intercostal nerve
Spinal nerve
Rami communicantes
Dorsal rootganglion Dorsal rootVentral root
Sympathetic trunkganglion
Sternum
(b) Cross section of thorax showing the main roots and branches of a spinal nerve.
Branches of intercostalnerve
• Lateral cutaneous• Anterior cutaneous
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)
Figure 13.8
Hypoglossalnerve (XII)
C1
C2
C3
C4
C5
Segmentalbranches
Lesser occipitalnerveGreater auricularnerve
Ansa cervicalis
Phrenic nerve
Supraclavicularnerves
Accessory nerve (XI)
Transversecervical nerve
Ventralrami:
Ventral rami
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
Figure 13.9 (a)
Upper
Middle Trunks
Lower
Roots (ventral rami):
Upper subscapular
Lower subscapular
Thoracodorsal
Medial cutaneousnerves of the armand forearm
Long thoracic
Medial pectoral
Lateral pectoral
Nerve tosubclaviusSuprascapular
Dorsal scapular
Posteriordivisions
Anteriordivisions
Lateral
PosteriorCords
Medial
Axillary
Musculo-cutaneousRadial
Median
Ulnar
Posteriordivisions
Trunks Roots
C4
C5
C6
C7
C8
T1
(a) Roots (rami C5 – T1), trunks, divisions, and cords
Brachial Plexus: Nerves
• Axillary • Musculocutaneous • Median• Ulnar• Radial
Figure 13.9 (c)
Median nerve
Musculocutaneous nerve
Radial nerveHumerus
Ulna
Ulnar nerveMedian nerve
Radius
Radial nerve (superficial branch)
Superficial branch of ulnar nerveDorsal branch of ulnar nerve
Digital branch of ulnar nerveMuscular branchDigital branch
(c) The major nerves of the upper limb
Axillarynerve
Anteriordivisions
Posteriordivisions
Trunks Roots
Lumbar Plexus
• Arises from L1–L4
• Innervates the thigh, abdominal wall, and psoas muscle
• Femoral nerve • Obturator nerve
Figure 13.10
(a) Ventral rami and major branches of the lumbar plexus
Iliohypogastric
L1
L2
L3
L4
L5
Ilioinguinal
Genitofemoral
Lateral femoralcutaneous
Obturator
Femoral
Lumbosacraltrunk
Lateral femoralcutaneous
Anterior femoralcutaneousSaphenous
Obturator
IliohypogastricIlioinguinalFemoral
Ventral rami Ventralrami:
(b) Distribution of the major nerves from the lumbar plexus to the lower limb
Sacral Plexus
• Arises from L4–S4
• Serves the buttock, lower limb, pelvic structures, and perineum
• Sciatic nerve
Figure 13.11 (a)
SuperiorglutealLumbosacraltrunkInferiorgluteal
CommonfibularTibialPosteriorfemoralcutaneousPudendal
Sciatic
Ventral rami and major branches of the sacral plexus
L4
L5
S1
S2
S3
S4
S5
Co1
Ventral rami Ventral rami:
Figure 13.11 (b)
Superior gluteal
Inferior gluteal
Common fibular
Deep fibular
Superficial fibular
Plantar branches
Tibial
Sural (cut)
Posterior femoralcutaneous
Pudendal
Sciatic
(b) Distribution of the major nerves from the sacral plexus to the lower limb