Anatomy and localization of spinal cord disorders Author Andrew Eisen, MD, FRCPC Section Editor Michael J Aminoff, MD, DSc Deputy Editor Janet L Wilterdink, MD All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Nov 2015. | This topic last updated: Nov 18, 2015. INTRODUCTION — Because it is the primary pathway of communication between the brain and peripheral nervous system, diseases that affect the spinal cord are clinically eloquent. Many of these disease processes have a predilection for targeting specific areas or tracts within the spinal cord. As a result, knowledge of spinal cord anatomy and recognition of typical common spinal cord syndromes are useful in the evaluation of a patient with a myelopathy and can allow for a more directed diagnostic evaluation. The anatomy of the spinal cord and its vascular supply and clinical features of common spinal cord syndromes will be reviewed here. Diseases that affect the spinal cord are discussed separately. (See "Disorders affecting the spinal cord".) SPINAL CORD ANATOMY — There are 31 spinal cord segments, each with a pair of ventral (anterior) and dorsal (posterior) spinal nerve roots, which mediate motor and sensory function, respectively. The ventral and dorsal nerve roots combine on each side to form the spinal nerves as they exit from the vertebral column through the neuroforamina (figure 1). Longitudinal organization — The spinal cord is divided longitudinally into four regions: the cervical, thoracic, lumbar, and sacral cord. The spinal cord extends from the base of the skull and terminates near the lower margin of the first lumbar vertebral body (L1). Below that level, the spinal canal contains the lumbar, sacral, and coccygeal spinal nerve roots that comprise the cauda equina. Because the spinal cord is shorter than the vertebral column, vertebral and spinal cord segmental levels are not necessarily the same. The C1 through C8 spinal cord segments lie between the C1 through C7 vertebral levels. The T1 through T12 cord segments lie between T1 through T8. The five lumbar cord segments are situated at the T9 through T11 vertebral levels, and the S1 through S5 segments lie between T12 to L1. The C1 through C7 nerve roots emerge above their respective vertebrae; the C8 nerve root emerges between the C7 and T1 vertebral bodies. The remaining nerve roots emerge below their respective vertebrae (figure 2). Cervical cord — The first cervical vertebra (the atlas) and the second cervical vertebra (the axis), upon which the atlas pivots, support the head at the atlanto-occiput junction. The interface between the first and second vertebra is called the atlanto-axis junction. Cervical spinal segments innervate the skin and musculature of the upper extremity and diaphragm (figure 3 and figure 4): ●C3 through C5 innervate the diaphragm, the chief muscle of inspiration, via the phrenic nerve ●C4 through C7 innervate the shoulder and arm musculature ●C6 through C8 innervate the forearm extensors and flexors ●C8 through T1 innervate the hand musculature
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Anatomy and localization of spinal cord disorders Author Andrew Eisen, MD, FRCPC Section Editor Michael J Aminoff, MD, DSc Deputy Editor Janet L Wilterdink, MD All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Nov 2015. | This topic last updated: Nov 18, 2015.
INTRODUCTION — Because it is the primary pathway of communication between the brain and
peripheral nervous system, diseases that affect the spinal cord are clinically eloquent. Many of
these disease processes have a predilection for targeting specific areas or tracts within the spinal
cord. As a result, knowledge of spinal cord anatomy and recognition of typical common spinal
cord syndromes are useful in the evaluation of a patient with a myelopathy and can allow for a
more directed diagnostic evaluation.
The anatomy of the spinal cord and its vascular supply and clinical features of common spinal
cord syndromes will be reviewed here. Diseases that affect the spinal cord are discussed
separately. (See "Disorders affecting the spinal cord".)
SPINAL CORD ANATOMY — There are 31 spinal cord segments, each with a pair of ventral
(anterior) and dorsal (posterior) spinal nerve roots, which mediate motor and sensory function,
respectively. The ventral and dorsal nerve roots combine on each side to form the spinal nerves
as they exit from the vertebral column through the neuroforamina (figure 1).
Longitudinal organization — The spinal cord is divided longitudinally into four regions: the
cervical, thoracic, lumbar, and sacral cord. The spinal cord extends from the base of the skull and
terminates near the lower margin of the first lumbar vertebral body (L1). Below that level, the
spinal canal contains the lumbar, sacral, and coccygeal spinal nerve roots that comprise the
cauda equina.
Because the spinal cord is shorter than the vertebral column, vertebral and spinal cord segmental
levels are not necessarily the same. The C1 through C8 spinal cord segments lie between the C1
through C7 vertebral levels. The T1 through T12 cord segments lie between T1 through T8. The
five lumbar cord segments are situated at the T9 through T11 vertebral levels, and the S1 through
S5 segments lie between T12 to L1. The C1 through C7 nerve roots emerge above their
respective vertebrae; the C8 nerve root emerges between the C7 and T1 vertebral bodies. The
remaining nerve roots emerge below their respective vertebrae (figure 2).
Cervical cord — The first cervical vertebra (the atlas) and the second cervical vertebra (the axis),
upon which the atlas pivots, support the head at the atlanto-occiput junction. The interface
between the first and second vertebra is called the atlanto-axis junction.
Cervical spinal segments innervate the skin and musculature of the upper extremity and
diaphragm (figure 3 and figure 4):
●C3 through C5 innervate the diaphragm, the chief muscle of inspiration, via the phrenic
nerve
●C4 through C7 innervate the shoulder and arm musculature
●C6 through C8 innervate the forearm extensors and flexors
Longitudinal organization of spinal cord, spinal nerves, and
vertebrae
Nerve roots and peripheral nerves corresponding to the
principal movements of the upper extremity
The letters labeling the movements form a spiral down the extremity. The nerve
roots and peripheral nerves corresponding to each movement are listed below. Figure
redrawn with permission from Gelb, DJ. The Neurologic Examination.
Cervical dermatomes
Schematic representation of the cervical and T1 dermatomes. There is no C1
dermatome. Patients with nerve root syndromes may have pain, paresthesias, and
diminished sensation in the dermatome of the nerve that is involved.
Nerve roots and peripheral nerves corresponding to the
principal movements of the lower extremity
The letters labeling the movements proceed in order from proximal to distal down the
front of the limb, and then repeat from proximal to distal down the back of the limb.
The nerve roots and peripheral nerves corresponding to each movement are listed
below.
Lumbosacral dermatomes
Schematic representation of the lumbosacral dermatomes. Patients with sciatica may
have pain, paresthesias, and diminished sensation in the dermatome of the nerve root
that is involved.
Major white matter tracts of the spinal cord
Cross section of the spinal cord demonstrating arterial blood
supply
Spinal cord syndromes
Location of lesion in dorsal cord syndrome
Location of lesion in ventral cord syndrome
Location of lesion in Brown-Sequard syndrome
Location of lesion in central cord syndrome
Important causes of spinal cord dysfunction*
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