BIO 210 LabInstructor: Dr. Rebecca Clarke

Chapter 13: The Spinal Cord and Spinal Nerves

Spinal CordStructurally and functionally integrated

with brainOccupies upper two-thirds of vertebral

column (adult: 1.5 ft long, 0.5 in. wide)Ends between vertebrae L1 and L2

Figure 13-2

Gross Anatomy of the Spinal Cord

Divided into 4 regions (like vertebrae):Cervical (C)Thoracic (T)Lumbar (L)Sacral (S)

31 Pairs of spinal nervesNamed for regionsCervical numbered

for vertebra belowRest numbered for

vertebra above

Figure 13-2

Gross Anatomy of the Spinal Cord: Distal End

Conus medullaris (medullary cone):Conical structure at T-L

junctionFilum terminale

(terminal filum):Thin strand of fibrous

tissue at end of conus medullaris

Cauda equina (“horse tail”):Bundle of elongated nerve

roots extending below conus medullaris (L2-S5)

Note: After age 4, vertebral column continues to elongate but spinal cord does not therefore roots elongate)

Figure 13–5a

Sectional Anatomy of the Spinal Cord

Posterior median sulcus: Groove on posterior side

Anterior median fissure: Deeper, wider groove on anterior side

Gray matter covered by thick layer of white matter

Figure 13–5a

Sectional Anatomy of the Spinal Cord: Gray Matter

Neuron cell bodies, neuroglia, unmyelinated axons

H- or butterfly-shape with horns (projections)Gray commissure – where axons connect R/L

sidesCentral canal in middle; contains CSF

Figure 13–5a

Sectional Anatomy of the Spinal Cord: Gray Matter

Cell bodies organized in nuclei in horns of gray matter:Somatic and visceralSensory (dorsal) and motor (ventral)

Figure 13–5a

Sectional Anatomy of the Spinal Cord: White Matter

Spinal tracts (bundles of myelinated axons) arranged in columns

Have similar distribution as nuclei in gray matterRelay same type of info (sensory or motor) in same

direction (ascending or descending) to brain

Figure 13-2

Gross Anatomy of a Spinal Nerve

Forms 2 branches on each side of spinal cord:Dorsal root:

Contains axons of sensory (afferent) neurons coming from receptors

Ventral root:Contains axons of motor

(efferent) neurons going to effectors

Dorsal root ganglion:Contains cell bodies of

sensory neurons

Mixed NervesCarry both sensory (afferent) and motor

(efferent) fibersSpinal nerves are mixed nerves

Spinal Nerves and Plexuses

Spinal Nerves and Plexuses

Nerve PlexusComplex interwoven network of nerve

fibers of adjacent spinal nervesFormed during developmentNerves arising at a plexus:

Are mixed nerves (like spinal nerves)Control skeletal muscles of neck, upper torso,

limbs

Figure 13–9

4 Major Nerve PlexusesCervical plexus

Neck, thoracic cavity, diaphragm

Phrenic nerveBrachial

Shoulder/pectoral girdle and upper limbs

Radial and ulnar nerves Lumbar

Pelvic girdle and lower limbs Femoral nerve

Sacral Pelvic girdle and lower limbs Sciatic nerve

Brachial Plexus

Meninges

Specialized, protective membranesSeparate, isolate, protect soft tissue of:

Spinal cord from bones of vertebra (spinal meninges)

Brain from bones of skull (cranial meninges)Spinal meninges continuous with cranial

meningesHave 3 layers:

Dura (“hard”) mater – outermost coveringArachnoid mater – middle layerPia (“delicate”) mater – innermost layer

Figure 13–3

Gross Anatomy of Spinal Cord and Meninges

Spinal cord located in vertebral foramenEpidural space

Between vertebra and dura materContains loose connective tissue, blood vessels,

adipose tissueEpidural block

Injection of anestheticUsed to control pain

Figure 13–3

Gross Anatomy of Spinal Cord and Meninges

Dura materArachnoid materSubarachnoid space

Between arachnoid membrane and pia materFilled with CSF

Acts as shock absorber Carries dissolved gases, nutrients, chemical messengers, waste

productsSpinal tap

Withdrawal of CSF for diagnostic purposes when CNS infection suspected, for back pain, headaches, disc problems, etc.

Pia mater

MeningitisMeningitis:

Viral or bacterial infection of meninges

Figure 16–5

Sympathetic Chain Ganglia

String of ganglia alongside spinal cord

Sympathetic Chain Ganglia

Figure 16–4a