CENTRAL NERVOUS SYSTEM
(THE SPINAL CORD)
SPINAL CORD:
- A cylindrical elongated part of the CNS that extends from the level of the foramen magnum to the level of the lower border of L1 or upper border of L2.
- ~ 45 cm. In males; ~ 42 cm. In females
LIMITS:
ROSTRAL: Foramen Magnum - arbitrarily divides the medulla oblongata and the spinal cord.
CAUDAL: Conus Medllaris - inferior end; conical (tapered) distal end
- Extends to the first segment of the coccyx as a thin strand, the Filum Terminale.
CAUDA EQUINA - "horse's tail"; compose of the filum terminale together with the rootlets of the lumbosacral plexus.
GROSS ANATOMY:
- Varies in diameter from about 1 cm to 1.5 cm
- Shape: from oval to round
- Thoracic region is the narrowest.
2 Gross Swellings or Enlargements: Corresponds to the origin of the nerves of the UE and LE.
1. Cervical Enlargement - C3 to T2 vertebral level.
- Where nerves of the brachial plexus arise.
2. Lumbar Enlargement - T9 to T12 vertebral level.
- Where nerves of the lumbosacral plexus arise.
EXTERNAL LONGITUDINAL DIVISIONS:
1. POSTERIOR (DORSAL) MEDIAN SULCUS - shallow
2. ANTERIOR (VENTRAL) MEDIAN FISSURE - deep
** Both mark the exact midsagittal plane of the spinal cord.
- Divides the cord into symmetric ® and (L) halves
Dorsolateral and Ventrolateral Sulci
- Mark the line of attachments of the DORSAL and VENTRAL NERVE ROOTS
TRANSVERSE SECTION: Shows a central core of gray matter surrounded by white matter.
I. GRAY MATTER - H-shaped or butterfly-shaped mass
- Consists of neuronal bodies, dendrites and their synapses and glial cells.
PROJECTIONS:
1. Anterior Gray Horn - Contains the cell bodies of somatic motor neurons and motor nuclei.
- Motor in function: sends general somatic efferent (GSE) axons into the ventral roots.
2. Lateral Gray Horn - intermediate gray horn present only in the thoracic, upper lumbar, and sacral segments of the spinal cord.
- Contains preganglionic cells of the ANS.
- Motor in Function: sends general visceral efferent (GVE) axons of the CNS into the ventral roots.
3. Posterior Gray Horn - contain somatic and autonomic sensory nuclei.
- Sensory in Function: receives general somatic afferent (GSA) and general visceral afferent (GVA) fibers.
II. WHITE MATTER - consists of bundles of nerve fibers (myelinated or unmyelinated) that course upward or downward.
- Organized into COLUMNS or FUNICULI and TRACTS (PATHWAYS)
A. COLUMNS or FUNICULI
1. DORSAL (POSTERIOR) COLUMN
- Column of white matter between the dorsal median sulcus and the dorsolateral sulcus.
- In the cervical and upper thoracic region, it is further subdivided by the DORSAL INTERMEDIATE SULCUS, into:
a. FASCICULUS GRACILIS - medial portion
b. FASCICULUS CUNEATUS - lateral portion
2. LATERAL COLUMN
- The mass of white matter between the dorsolateral and the ventrolateral sulci.
3. VENTRAL (ANTERIOR) COLUMN
- The mass of white matter between the ventrolateral sulcus and the ventral median fissure.
III. TRACTS (PATHWAYS)
- Group or bundles of myelinated fibers that either run upward (Ascending) or downward (Descending).
2 GROUPS:
A. ASCENDING TRACTS - Consist of nerve fibers that relay sensory information to the brain.
B. DESCENDING TRACTS - Composed of nerve fibers that relay motor instructions down from the brain.
IMPORTANT SENSORY TRACTS:
1. POSTERIOR COLUMN (FASCICULUS GRACILIS and CUNEATUS)
- For consious proprioception and other epicritic sensations such as stereognosis, barognosis, 2 pt. Discrimination, cutaneous tactile localization, graphesthesia, fine touch.
2. LATERAL SPINOTHALAMIC TRACT
- For pain and temperature.
3. ANTERIOR SPINOTHALAMIC TRACT
- For crude/ light/ simple/ low intensity touch and pressure.
4. SPINOCEREBELLAR TRACT
- For unconscious proprioception.
DESCENDING PATHWAYS OF THE SPINAL WHITE MATTER:
- The largest and most important of these tracts arises from the cerebral cortex.
CORTICOSPINAL TRACT (PYRAMIDAL TRACT) - Mediates voluntary contraction of skeletal muscles.
- Interruption of this tract results in weakness or paralysis of volitional movements.
DISTRIBUTION IN THE SPINAL CORD:
1. LATERAL CORTICOSPINAL TRACT - majority of the corticospinal fibers DECUSSATE at the cervicomedullary junction to descend in the contralateral lateral column.
- Thus, the lateral corticospinal tract consists of majority of crossed fibers and a minority of uncrossed fibers.
2. VENTRAL CORTICOSPINAL TRACT - A minority of fibers continue ipsilaterally into the ventral column as the ventral corticospinal tract.
CORTICOBULBAR TRACT - Related to movements of muscles of facial expression, mastication and tongue musculature.
CLINICAL SIGNIFICANCE OF THE DECUSSATION AND LATERAL CORTICOSPINAL TRACT: HEMIPLEGIA, PARAPLEGIA, AND QUADRIPLEGIA.
- Interruption of the pyramidal tract will paralyze voluntary movement on one side of the body, known as HEMIPLEGIA.
- The side of the hemiplegia depends on whether the lesion interrupts the pyramidal tract ROSTRAL or CAUDAL to the "cervicomedullary" decussation.
a. A lesion rostral to the decussation causes CONTRALATERAL HEMIPLEGIA.
** Certain Corticobulbar movements will also be paralyzed, most notably, voluntary movements of the lower part of the face.
b. A lesion caudal to the decussation causes IPSILATERAL HEMIPLEGIA; face is spared.
QUADRIPLEGIA - bilateral interruption of the corticospinal tract after the decussation if rostral to the "arms"
- Results to paralysis of both upper extremities and lower extremities.
PARAPLEGIA - if caudal to the arms.
- Results to paralysis of both lower extremities.
Anatomy and Physiology l Home
Home [ PROFCENTRAL ] Page
