Major ascending and descending tracts in the spinal cord

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Pain
Major ascending and
descending tracts in the
spinal cord
anterior column between the anterior horn and median fissure,
a lateral column between the anterior and posterior columns,
and a posterior column between the posterior horn and posterior
median sulcus. The posterior columns comprise a medial (fas­
ciculus gracilis) and lateral (fasciculus cuneatus) tract and these
convey sensory fibres subserving fine touch and proprioception
(Figure 1). The anterior columns are incompletely separated from
each other by the median fissure; the residual communication is
called the anterior commissure.
John Craven
The posterior column contains intersegmental fibres and
ascending fibres associated with light touch, pressure, vibration
and proprioception; their cell bodies lie in the dorsal root gan­
glia and the fibres pass to the gracile and cuneate nuclei in the
medulla.
Abstract
This article provides a synopsis of the anatomy of the spinal cord with
the emphasis on the position and function of the major tracts forming the
posterior, lateral and anterior columns of the white matter.
The lateral column
Peripherally placed ascending fibres
• The anterior and posterior spinocerebellar tracts are associ­
ated with unconscious proprioception. The cell bodies of the an­
terior tract lie in the opposite posterior horn and its fibres pass
to the cerebellum. The posterior tract has its cell bodies in the
thoracic nucleus of the same side and its fibres pass uncrossed to
the cerebellum.
• The dorsolateral fasciculus is a mixed bundle of fibres arising
in the dorsal root ganglia and the gelatinous substance before
ending in the posterior horn.
• The lateral spinothalamic tract subserves pain and temper­
ature. Its cell bodies lie in the opposite posterior horn and its
fibres pass in the anterior commissure before ascending to the
thalamus.
Intermediately placed, mainly descending fibres
• The fibres of the lateral corticospinal (crossed pyramidal) tract
originate from cell bodies in the cerebral motor cortex. On their
descent, the fibres cross in the medulla before ending by entering
the anterior horn to connect to motor cells.
Keywords ascending pathways; descending pathways; grey matter;
white matter
The adult spinal cord is about 45 cm long. It is cylindrical in shape
and has cervical and lumbar enlargements where the nerves sup­
plying the upper limb (C5–T1) and lower limb (L1–S3) originate.
The cord is shorter than the vertebral canal and thus the nerve
roots descend with increasing obliquity within the canal to reach
the appropriate intervertebral foramen. The cord has an anterior
median fissure and a posterior median sulcus; the rootlets of the
spinal nerves emerge from its side at anterolateral and postero­
lateral sulci. The cord contains grey matter, largely neuronal cell
bodies, and white matter, which contains the long ascending and
descending tracts.
Grey matter
The grey matter is arranged around the central canal and pro­
jects towards the anterolateral and posterolateral sulci to form
paired anterior and posterior horns (Figure 1). The anterior
horn contains mainly motor cells giving rise to the fibres of the
an­­terior roots and the posterior horn, mainly sensory cells sub­
serving touch, pain and temperature, the fibres of which enter
from the posterior roots. In the thoracic region and, to a lesser
extent, in the sacral region, there are lateral horns, which give
rise to preganglionic cells of the sympathetic nervous system. In
the thoracic region, a group of large cells, the thoracic nucleus,
lies at the base of the posterior horn. Grey matter contains large
numbers of inter-neurons, linking cells within a segment or
across adjacent segments, and these contribute to local reflex
arcs.
Cross-section of spinal cord showing ascending
pathways on right and descending pathways on left
Fasciculus cuneatus
Fasciculus gracilis
Posterior median sulcus
Spinocerebellar tracts
Posterior
Anterior
Lateral
corticospinal
tract
Rubrospinal
tract
White matter
Olivospinal
tract
Vestibulospinal tract
Tectospinal tract
White matter is divided, by the anterior and posterior horns and
emerging spinal rootlets, into three columns on each side: an
Anterior corticospinal tract
John Craven, FRCS, was formerly Consultant Surgeon at York Hospital,
York, UK. He is past chairman of the primary examiners of the Royal
College of Surgeons of England.
Lateral
spinothalamic
tract
Fasciculus
proprius
Anterior
spinothalamic tract
Anterior median fissure
Q1
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:1
Figure 1
© 2007 Elsevier Ltd. All rights reserved.
Pain
• The reticulospinal and rubrospinal tracts contain extrapyram­
idal motor fibres, which originate in the midbrain.
• Vestibulospinal, olivospinal, reticulospinal and tectospinal
tracts are of extrapyramidal fibres, which pass to the anterior
horn cells from brainstem nuclei.
• The anterior spinothalamic tract carries fibres subserving
touch. Its cells lie in the posterior horn of the opposite side and
its fibres ascend to the thalamus.
• In the fasciculus proprius, surrounding the grey matter, lie ­fibres
forming inter- and intra-segmental connections. These connections
form the basis of intersegmental reflexes in the spinal cord.
◆
The anterior column contains the following.
• The anterior corticospinal (uncrossed pyramidal) tract is a small
tract, the fibres of which originate in the cerebral motor cortex of
the same side and descend without medullary decussation. At their
destination the fibres cross horizontally, in the anterior commis­
sure, to synapse with cell bodies in the opposite anterior horn.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:1
© 2007 Elsevier Ltd. All rights reserved.
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