Spinal cord

The spinal cord provides a crucial information conduit, connecting the brain with most of the body.

It is the target of a number of disease processes, some of which (eg, spinal cord compression) are treatable but rapidly progressive if not treated.

Failure to diagnose some disorders of the spinal cord, such as spinal cord compression, can be catastrophic and may relegate the patient to a lifetime of paralysis.

A knowledge of the architecture of the spinal cord and its coverings, and of the fiber tracts and cell groups that comprise it, is essential.

The sensory component of each spinal nerve is distributed to a dermatome, a well-defined segmental portion of the skin

in many patients there is no C1 dorsal root, there is no C1 dermatome

when a C1 dermatome does exist as an anatomic variant, it covers a small area in the central part of the neck, close to the occiput

dermatomes for C5, C6, C7, C8, and T1 are confined to the arm

C4 and T2 dermatomes are contiguous over the anterior trunk.

thumb, middle finger, and fifth digit are within the C6, C7, and C8 dermatomes, respectively

Nipple-T4 Umbilicus – T 10

The territories of dermatomes tend to overlap, making it difficult to determine the absence of a single segmental innervation on the basis of sensory testing

Myotomes

myotome refers to the skeletal musculature innervated by motor axons in a given spinal root

Most muscles are innervated by motor axons that arise from several adjacent spinal roots.

Nevertheless, lesions of a single spinal root, in many cases, can cause weakness and atrophy of a muscle

Segment-Pointer Muscles.

Root Muscle

C5 C5 C6 C7 L3, L4 L5 S1

Deltoid Biceps Brachioradialis Triceps Quadriceps

femoris Extensor hallucis

longus Gastrocnemius

Rexed’s laminae

Rexed's laminae

Lamina I This thin marginal layer contains

neurons that respond to noxious stimuli [pain, temperature] and send axons to the contralateral spinothalamic tract.

Lamina II- substantia gelatinosa made up of small neurons, some of

which respond to noxious stimuli. Substance P, a neuropeptide

involved in pathways mediating sensibility to pain, is found in high concentrations in laminas I and II.

Laminas III and IV[nucleus proprius]

Their main input is from fibers that convey position and light touch sense.

Lamina Vcontains cells that respond to both

noxious and visceral afferent stimuli.

Lamina VI deepest layer ,contains neurons that

respond to mechanical signals from joints and skin.

Lamina VII

contains the cells of the dorsal nucleus (Clarke's column) medially as well as a large portion of the ventral gray column.

Clarke's column contains cells that give rise to the posterior spinocerebellar tract.

also contains the intermediolateral nucleus (or intermediolateral cell column) in thoracic and upper lumbar regions.

Preganglionic sympathetic fibers project from cells in this nucleus, via the ventral roots and white rami communicantes, to sympathetic ganglia.

Laminas VIII and IX

represent motor neuron groups in the medial and lateral portions of the ventral gray column

The medial portion (also termed the medial motor neuron column) contains the LMNs that innervate axial musculature

The lateral motor neuron column contains LMNs for the distal muscles of the arm and leg

flexor muscles are innervated by motor neurons located close to the central canal

extensor muscles are innervated by motor neurons located more peripherally

Lamina X

represents the small neurons around the central canal or its remnants.

White Matter

composed of myelinated and unmyelinated nerve fibers.

The fast-conducting myelinated fibers form bundles (fasciculi) that ascend or descend for varying distances

Fiber bundles with a common function are called tracts

The lateral and ventral white columns contain tracts that are not well delimited and may overlap in their cross sectional areas

the dorsal column tracts are sharply defined by glial septa

Location of tracts

Descending tracts in the Spinal Cord. Lateral

corticospinal (pyramidal) tract

Fine motor function (controls distal musculature) Modulation of sensory functions

Anterior corticospinal tract

Vestibulospinal tract

Gross and postural motor function (proximal and axial musculature

Postural reflexes

Rubrospinal Reticulospinal

Motor function Modulation of

sensory transmission (especially pain) Modulation of spinal reflexes

Descending autonomic

Tectospinal Medial

longitudinal fasciculus

Modulation of autonomic functions

Reflex head turning

Coordination of head and eye movements

Ascending tracts

Dorsal column system

Spinothalamic tracts

Fine touch, proprioception, two-point discrimination

Sharp pain, temperature, crude touch

Dorsal spinocerebellar tract

Ventral spinocerebellar

Movement and position mechanisms

Movement and position mechanisms