71 INNERVATION OF THE FEMALE REPRODUCTIVE ORGANS

10



SPINAL CORD



õổáồđõổáồđõổáồđ10.1



Cytoarchitecture of the Spinal Cord Gray Matter



õổáồđõổáồđõổáồđ10.2



Spinal Cord Levels: Cervical, Thoracic, Lumbar, and Sacral



õổáồđõổáồđõổáồđ10.3



Spinal Cord Levels: Cervical, Thoracic, Lumbar, and Sacral (Continued)



õổáồđõổáồđõổáồđ10.4



Spinal Cord Levels: Cervical, Thoracic, Lumbar, and Sacral (Continued)



õổáồđõổáồđõổáồđ10.5



Spinal Cord Levels: Cervical, Thoracic, Lumbar, and Sacral (Continued)



õổáồđõổáồđõổáồđ10.6



Spinal Cord Levels: Cervical, Thoracic, Lumbar, and Sacral (Continued)



õổáồđõổáồđõổáồđ10.7



Spinal Cord Lower Motor Neuron Organization and Control



õổáồđõổáồđõổáồđ10.8



Spinal Somatic Reflex Pathways



õổáồđõổáồđõổáồđ10.9



Muscle and Joint Receptors and Muscle Spindles



10.10



The Muscle Stretch Reflex and Its Central Control via Gamma Motor

�Neurons



207



2

208



Regional Neuroscience



Nuclear cell columns



Laminae of Rexed



Nucleus posterior marginalis (marginal zone)

Substantia gelatinosa (lamina II)

Nucleus proprius of posterior horn

Nucleus dorsalis; Clarke‘s column (T1- L3)

II



Lateral basal nucleus



III

IV



Spinal reticular zone

Intermediolateral cell column;

sympathetic preganglionic neurons

(T1-L2)



V

VI

X



Intermediomedial cell column;

parasympathetic preganglionic

neurons (S2-4)



VII

IX



VIII



Flexors

Motor neurons of limbs

(cervical and lumbar

enlargements of cord)



I



IX



IX



Extensors

Distal part of limb

Proximal part of limb



Motor neurons of trunk and neck (C1-3 and T2-12)



10.1  CYTOARCHITECTURE OF THE SPINAL

CORD GRAY MATTER

The spinal cord gray matter is located centrally in the interior

of the spinal cord in a butterfly pattern. The gray matter is

subdivided into three horns: (1) the dorsal horn, a site of major sensory processing; (2) the intermediate gray with a lateral

horn, a site where preganglionic sympathetic (thoracolumbar) and parasympathetic (sacral) neurons reside and where

interneuronal processing occurs; and (3) the ventral horn, a

site where lower motor neurons (LMNs) reside and where

converging reflex and descending control of LMNs occurs.

Neuronal cell groups appear homogeneous in some regions of

gray matter, intermixed with a presence of some discrete nuclei (e.g., Clarke’s nucleus, substantia gelatinosa). Laminae of

Rexed, an alternative system of cytoarchitectural classification

established in the 1950s, subdivides the spinal cord gray matter

into ten laminae. This system is used extensively for the dorsal

horn and the intermediate gray, laminae I–VII, particularly in

conjunction with anatomical details of nociceptive processing and for some reflex and cerebellar processing. Although

these laminae have distinctive characteristics at each segmental level, they show some similarities across segmental levels.

The absolute amount of spinal cord gray is more extensive in

the cervical and lumbosacral enlargements of the spinal cord,



which �correspond to zones associated with limb innervation,

than it is in upper cervical, thoracic, and sacral regions.



CLINICAL POINT

Classical descriptions of secondary sensory processing in the spinal

cord describe neurons of lamina I (marginal zone) and lamina V of the

dorsal horn as cells of origin for crossed projections into the spinothalamic/anterolateral system for the processing of pain and temperature

sensation (protopathic modalities). Primary sensory large-diameter

axons, carrying information about fine discriminative touch, vibratory sensation, and joint position sense (epicritic modalities), enter

through the dorsal root entry zone and travel rostrally into the dorsal

column system, bypassing synapses in the spinal cord; these axons terminate in their secondary sensory nuclei, gracilis and cuneatus, in the

caudal medulla. According to this scheme, pure dorsal column lesions

should result in the total loss of epicritic sensation on the ipsilateral

side of the body below the level of the lesion. However, such lesions

result in diminution of these epicritic sensations or in the inability to

discriminate vibratory sensations of different frequencies, but not in

the total loss of these modalities. Only with additional damage to the

dorsolateral part of the lateral funiculus is the profound loss of epi�

critic sensation observed. This is because additional dorsal horn neurons receive primary sensory input related to epicritic sensation and

send ipsilateral projections into the dorsolateral funiculus, providing

additional contributions to lemniscal processing of fine discriminative

modalities.



Spinal Cord



Second cervical level



209



Fasciculus gracilis

Fasciculus cuneatus



Dorsolateral fasciculus (Lissauer's zone)

Substantia gelatinosa



Dorsal spinocerebellar tract



Nucleus proprius



Rostral spinocerebellar tract

Lateral corticospinal tract

Rubrospinal tract



Spinal accessory nucleus



Ventral spinocerebellar tract

Anterolateral system (Spinothalamic

tract and spinoreticular tract)



Anterior horn



Lateral (medullary) reticulospinal tract

Lateral vestibulospinal tract

Medial (pontine) reticulospinal tract

Anterior corticospinal tract



Anterior white commissure

Medial longitudinal fasciculus (with medial vestibulospinal

tract, interstitiospinal tract, and tectospinal tract)



Seventh cervical level



Descending monoamine axons

(noradrenergic, serotonergic)

Descending fibers from hypothalamus

and brain stem to spinal cord



Fasciculus gracilis

Fasciculus cuneatus



Dorsolateral fasciculus (Lissauer's zone)

I



Dorsal spinocerebellar tract



Marginal zone

Substantia gelatinosa



II

III



Nucleus proprius



IV



Rostral spinocerebellar tract



V



Lateral corticospinal tract



VI



Rubrospinal tract



Intermediate gray



VII

Ventral spinocerebellar tract

Anterolateral system (Spinothalamic

tract and spinoreticular tract)



IX



X

Lower motor neurons

in anterior horn



IX

VIII



Lateral (medullary) reticulospinal tract

Lateral vestibulospinal tract

Medial (pontine) reticulospinal tract



10.2  SPINAL CORD LEVELS: CERVICAL,

�THORACIC, LUMBAR, AND SACRAL

The organization of the gray matter into laminae of Rexed is

retained throughout the spinal cord. The dorsal and ventral

horns are larger and wider at levels of the cervical and lumbosacral enlargements. The lateral horn is present from L1 to T2.

Some nuclei are found only in circumscribed regions, such as

the intermediolateral cell column with preganglionic sympathetic neurons (T1–L2 lateral horn); Clarke’s nucleus (C8–L2);

and the parasympathetic preganglionic nucleus (S2–S4). The



Anterior white commissure

Medial longitudinal fasciculus

Anterior corticospinal tract



white matter increases in absolute amount from caudal to rostral. The dorsal columns contain only fasciculus gracilis below T6; fasciculus cuneatus is added laterally above T6. The

spinothalamic/spinoreticular anterolateral system increases

from caudal to rostral. The descending upper motor neuron

(UMN) pathways diminish from rostral to caudal. The lateral

corticospinal pathway loses more than half of its axons as they

synapse in the cervical segments; this tract then diminishes in

size as it extends caudally.



210



Regional Neuroscience



Second thoracic level



Fasciculus gracilis

Fasciculus cuneatus



Dorsolateral fasciculus (Lissauer's zone)



Dorsal spinocerebellar tract

Marginal zone

Lateral corticospinal tract



Substantia gelatinosa

Nucleus proprius



Rubrospinal tract



Nucleus dorsalis of Clarke

Lateral horn



Ventral spinocerebellar tract



Intermediolateral cell column



Anterolateral system

(Spinothalamic tract and

spinoreticular tract)



Lower motor neurons

in anterior horn



Lateral (medullary) reticulospinal tract

Lateral vestibulospinal tract



Anterior white commissure

Medial longitudinal fasciculus



Medial (pontine) reticulospinal tract



Anterior corticospinal tract



Eighth thoracic level



Fasciculus gracilis



Dorsolateral fasciculus (Lissauer's zone)



Dorsal spinocerebellar tract



I



Lateral corticospinal tract



II

III

IV



Rubrospinal tract



VI



Marginal zone

Substantia gelatinosa

Nucleus proprius



V



Nucleus dorsalis of Clarke



VII

Ventral spinocerebellar tract

Anterolateral system

(Spinothalamic tract and

spinoreticular tract)



Descending monoamine axons

(noradrenergic, serotonergic)

Descending fibers from hypothalamus

and brain stem to spinal cord



Lateral horn



X



IX



Intermediolateral cell column

Lower motor neurons

in anterior horn



VIII



Lateral (medullary) reticulospinal tract

Lateral vestibulospinal tract



Anterior white commissure

Medial longitudinal fasciculus



Medial (pontine) reticulospinal tract



Anterior corticospinal tract



10.3  SPINAL CORD LEVELS: Â�CERVICAL, Â�THORACIC,

LUMBAR, AND SACRAL (­continued)

CLINICAL POINT

Damage to the lateral funiculus of the cervical spinal cord caused by

demyelination, trauma, ischemia, or other causes can lead to disruption of (1) the descending lateral corticospinal tract and rubrospinal

tract, resulting in ipsilateral spastic (long-term result) hemiplegia

below the level of the lesion; and (2) the descending axons from the

hypothalamus to the preganglionic sympathetic neurons in the intermediolateral cell column at the T1 and T2 segments of the cord. These

preganglionic neurons supply the superior cervical ganglion, which

provides postganglionic noradrenergic sympathetic innervation to the

ipsilateral head. Disruption of these descending axons in the lateral

funiculus or at any point distal in the sympathetic pathway can result



in Horner’s syndrome, which consists of ipsilateral ptosis (because of

effects on the superior tarsal muscle), miosis (because of effects on the

pupillary dilator muscle), and anhidrosis (less sweat gland activity).

Trauma that damages one entire side of the spinal cord at the cervical level produces the same symptoms (ipsilateral spastic paralysis

with brisk reflexes, and ipsilateral Horner’s syndrome) and also causes

(1) flaccid paralysis of ipsilateral muscles innervated by LMNs damaged by the trauma; (2) loss of epicritic sensation (fine discriminative

touch, vibratory sensation, joint position sense) ipsilaterally below the

level of the trauma because of damage to the dorsal column and dorsolateral funiculus axons; and (3) loss of pain and temperature sensation contralaterally below the level of the lesion because of damage to

the anterolateral system (spinothalamic/spinoreticular system). This

collection of neurological deficits resulting from a hemisection lesion

to the spinal cord is called a Brown-Séquard lesion.