Download Document

DISCRIMINATIVE TOUCH, VIBRATORY SENSE, AND
CONSCIOUS MUSCLE JOINT SENSE
(Dorsal column-medial leminiscus tract/system)
Lufukuja G.
1
Dorsal column-medial lemniscus
tract/system
• This pathway transmits information from mechanoreceptors
and proprioceptors.
Lufukuja G.
2
Dorsal column…
• First order neurons from the periphery enter the spinal cord through
the dorsal root. The main axons ascend the spinal cord in the
ipsilateral dorsal column and end in the dorsal column nuclei in the
medulla oblongata where they synapse with second-order neurons.
Lufukuja G.
3
Dorsal column …
• The axons enter the spinal cord from the posterior root
ganglion and pass directly to the posterior white column
of the same side.
• Here, the fibers divide into long ascending and short
descending branches. The descending branches pass down
a variable number of segments, giving off collateral
branches that synapse with cells in the posterior gray
horn, with internuncial neurons, and with anterior horn
cells. It is clear that these short descending fibers are
involved with intersegmental reflexes
Lufukuja G.
4
Dorsal column …
• If the primary axon enters below spinal level T6, the axon
travels in the fasciculus gracilis, the medial part of the
column. If the axon enters above level T6, then it travels
in the fasciculus cuneatus, which is lateral to the fasiculus
gracilis.
Lufukuja G.
5
Lufukuja G.
6
5/24/2017
G.LUFUKUJA
7
Dorsal column-medial leminiscus
• The fibers of the fasciculus
….gracilis and fasciculus cuneatus
ascend ipsilaterally and terminate by synapsing on the
second-order neurons in the nuclei gracilis and cuneatus of
the medulla oblongata
Lufukuja G.
8
•
Dorsal column-medial leminiscus
tract/system
The axons of the second-order neurons, called the internal
arcuate fibers, sweep anteromedially around the central
gray matter and cross the median plane, decussating with
the corresponding fibers of the opposite side in the sensory
decussation. The fibers then ascend as a single compact
bundle, the medial lemniscus, through the medulla
oblongata, the pons, and the midbrain.
Lufukuja G.
9
Lufukuja G.
10
Lufukuja G.
11
Lufukuja G.
12
Medial lemniscus tract/system
• Secondary axons from the medial lemniscus finally
terminate in the ventral posterolateral nucleus (VPL) of the
thalamus, where they synapse with tertiary neurons. From
there, tertiary neurons ascend via the posterior limb of the
internal capsule, and end in the primary somatosensory
cortex.
Lufukuja G.
13
MUSCLE JOINT SENSE PATHWAYS
TO THE CEREBELLUM
(Spinocerebellar tracts )
Lufukuja G.
14
Lufukuja G.
15
Spinocerebellar tract…
• The spinocerebellar tract is a
set
of
axonal
fibers
originating in the spinal cord
and terminating in the
ipsilateral cerebellum.
• This tract conveys information
to the cerebellum about limb
and
joint
position
(proprioception).
Lufukuja G.
16
Spinocerebellar tract…
• This is important for the cerebellum to integrate neuronal
inputs from the cerebral cortex with activities in the peripheral
and for body balance
• Proprioceptive information is obtained by Golgi tendon organs
and muscle spindles.
• Golgi tendon organs consist of a fibrous capsule enclosing
tendon fasciculi and bare nerve endings that respond to
tension in the tendon by causing action potentials
• Muscle spindle fibres are complicated systems of tension
monitoring nerve endings within muscles which result in
information being carried via larger and faster neurons
Lufukuja G.
17
Lufukuja G.
18
Dorsal S-C tract…
• The secondary neuronal axons (dorsal spinocerebella
tract) continue to ascend ipsilaterally and then pass
into the cerebellum via the inferior cerebellar
peduncle.
• The second-order neurons from the dorsal nucleus of
Clarke form the dorsal spinocerebellar tract; secondorder neurons from the lateral cuneate nucleus form
the cuneocerebellar tract. Both tracts remain on the
ipsilateral side of the spinal cord, ascending via the
inferior cerebellar peduncle to terminate in the
paleocerebellar cortex
Lufukuja G.
19