Post on 31-May-2015
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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