Asecending tract (Revision) by Dr.Rabia Inam Gandapore.ppt

Neuroanatomy

1. SENSORYSENSORY
(ASCENDING)(ASCENDING)
SPINAL SPINAL
TRACTS TRACTS
Dr. Rabia Inam Gandapore
Assistant Professor
Head of Department Anatomy
(Dentistry-BKCD)
B.D.S, M.Phil. Anatomy,
Dip.Implant, CHPE, CHR, Dip. Arts

2. OBJECTIVESOBJECTIVES
•By the end of the lecture, we will be able to:
•Distinguish between the different types of
ascending tracts.
•Locate the position of each tract.
•Identify the course of each of these tracts and
their function.
•Clinical correlation.
•Recent articles

3. 3
The White matter of the spinal cord consists of
Ascending and Descending Nerve Fibers.
It is divided into Dorsal, Lateral & Ventral Columns or Funiculi.

4. WHITE MATTER TRACTS
•Bundles or fasciculi of
fibers that occupy more
or less definite positions
in the white matter.

5. WHITE MATTER TRACTS
•They are classified into:
1- Short Tracts;
intersegmental or
propriospinal).
Fibers occupy narrow band
peripheral to the grey matter
(fasciculus proprius)
They interconnect adjacent or
distant spinal segments
And Permit intersegmental
coordination

6. 2-Long Tracts:
(a) Ascending (sensory or afferent).
(b) Descending (motor or efferent).
They serve to join the brain to the spinal cord.

7. Ascending Pathways
•For conscious perception:
Spinothalamic system
Medial Lemniscal system
•For unconscious perception:
Spinocerebellar
Spino-olivary
Spinotectal
Spinoreticular

8. Ascending Tracts;
•Carry impulses from pain, thermal, tactile, muscle and joint receptors to the
brain.
•Some of this information eventually reaches a conscious level (the cerebral
cortex),
•while some is destined for subconscious centers (e.g. the cerebellum).

9. •Pathways that
carry
information to a
conscious level
share certain
common
characteristics:
•There is a
sequence of
Three Neurones
between the
peripheral
receptors and
the cerebral
cortex.

10. The first-order neurone or primary
afferent neurone) enters the spinal
cord through the dorsal root of a
spinal nerve and its cell body lies in
the dorsal root ganglion.
The main fiber remains on the ipsilateral
side of the cord and terminates in synaptic
contact with the second neurone which
lies either in the spinal grey matter or in
the medulla oblongata of the brain stem.

11. •The axon of the second order
neurone crosses over
(decussates) to the opposite
side of the CNS and ascends to
the thalamus,thalamus, where it
terminates.
•The third-order neurone has
its cell body in the thalamus.thalamus.
•Its axon passes to the
somatosensory cortexsomatosensory cortex of the
parietal lobe of the cerebral
hemisphere.

13. •Three major pathways carry sensory information:
•Posterior column (Gracile & Cuneate fasciculi)
•Anterolateral pathway (Spinothalamic)
•Spinocerebellar pathway

14. Spinothalamic Tracts
•Located lateral and ventral to
the ventral horn.
•Carry impulses concerned
with; pain and thermal
sensations (Lateral tract)
and non- discriminative
touch and pressure
(Anterior tract).
•In brain stem, constitute the
spinal lemniscus.
•Information is sent to the
primary sensory cortex on
the opposite side of the body

15. Lateral Spinothalamic
Pain and Thermal receptor---
free nerve ending
Pain impulses travel in fast
conductive delta A-type
fibers (0.1sec)and slow
conducting C-type fibers
1.0sec.
Axons enter the spinal cord
through posterior root
ganglion.
Reach to the tip of posterior
column divide into ascending
and descending branches.
Posterolateral tract of
lissauer
Terminates first order neurons
in substantia gelatinosa of
posterior gray column (amino
acid glutamate, substance P.

16. Lateral Spinothalamic
Tract

•Second-order neurones, cross to the
opposite side in anterior gray column and
white commissures within one spinal
segment of the cord forms lateral
spinothalmic tract.
•It lies medial to anterior spinocerebellar
tract.

17. Lateral Spinothalamic Tract
•Upper cervical sgments
the sacral fibers are lateral
while cervical fibers are
medial.
•Medulla oblongata it lies
lateral between inferior
olivary nucleus and the
nucleus of trigeminal
nerve.
•Forms spinal lemniscus
with spinotectal tract.

18. Pons posterior part
Midbrain lies in tegmentum lateral
to medial lemniscus
Third order neuron in ventral
posterolateral nucleus of the
thalamus
Axons of third order neuron
pass through the posterior
limb of the internal capsule
and corona radiata
Crude pain and
temperature sensation
are appreciated.
Emotion reaction.
Reach somesthetic area in
the postcentral gyrus of the
cerebral corex.
Contralateral half of the
body represented as
inverted with hands and
mouth inferiorly

19. Anterior Spinothalamic
TractFunction:
•Carries crude touch & pressure to
thalamus and sensory cortex.
Neurones: 3 Neurones
•Neurone I:
Medium sized cells in the dorsal
root ganglia.
•Neurone II:
reach to tip of posterior gray
column. Divide into ascending and
descending branches. Travel to
distance of one or two segments of
spinal cord. Forms posterolateral
tract of lissauer. Terminate in
substantia gelatinosa group in
posterior gray column.

20. Cross to opposite side in the
anterior gray and white
commissures within several
spinal segments
Anterolateral white column
as anterior spinothalamic
tract.
Cervical fibers are medial
and sacral fibers are
lateral.
Medulla oblongata
forms spinal lemniscus
Posterior part of pons
and tegmentum of
midbrain
Ventral posterolateral
nucleus of the thalamus
Third order neuron pass
through the posterior limb
of internal capsule and
corona radiate
Somesthetic area in the
postcentral gyrus.

21.  Syringomyelia, (widening of the central canal)
leads to Loss of pain & temperature below the
level of the lesion because the spinothalamic axons
decussate to the opposite side of the cord by
passing through the ventral white commissure,
which lies ventral to the central canal of the cord,.

22. Dorsal Column
•Posterior Column:
•RECEPTORS. Meissner corpuscles,
pacinian corpuscles, muscle spindles,
tendon organs.
•Contains two tracts;
Fasciculus Gracilis (FG) &
Fasciculus Cuneatus (FC)
•Carry impulses concerned with
proprioception and
discriminative touch
from ipsilateral side of the body
•Contain the axons of primary afferent
neurons that have entered cord
through dorsal roots of spinal nerves
•FG contains fibers received at sacral,
lumbar and lower thoracic levels,
•FC contains fibers received at upper
thoracic and cervical levels

23. Medial Lemniscus
•Red:
–Gracilis
•Blue
–cuneatus
In posterior white column
fibers divide in ascending and
descending fiber
Descending fibers synapses
with cells of posterior gray horn
with internuncial neurons.
Also with anterior horn cells
Intersegmental
reflexes.

24. •Fibers ascend without interruption
where they terminate upon 2nd
order neurons in nucleus gracilis
and nucleus cuneatus
•The axons of the 2nd order neurons
decussate in the medulla as
internal arcuate fibers and ascend
through the brain stem as medial
lemniscus.
•The medial lemniscus terminates in
the ventral posterior nucleus of the
thalamus (3rd order neurons),
which project to the somatosensory
cortex (thalamocortical fibers).
After passing through posterior
limb of internal capsule. And
corona radiate.

25. Many of the fibers in the fasciculus cuneatus from
cervical and upper thoracic segments
Terminate on second order neuron of nucleus
cuneatus then enter the cerebellum
Inferior cerebellar peduncle of the same side
As cuneocerebellar tract or posterior external
arcuate fibers
Function:- convey information of
muscle joint sense to the cerebellum.

27. Spinocerebellar
Tracts
•The spinocerebellar system
consists of a sequence of only
two neurons;
•Neurone I:Large cells of dorsal
root ganglia.
•Neurone II: cells of the nucleus
dorsalis (Clark's nucleus.
•Two tracts: Dorsal &Ventral
•Located near the dorsolateral
and ventrolateral surfaces of
the cord
•Contain axons of the second
order neurons
•Carry information derived from
muscle spindles, Golgi tendon
organs and tectile receptors to
the cerebellum
•for the control of posture and
coordination of movements

28. Spinocerebellar Tracts

29. Posterior Spinocerebellar Tract
•Present only above level L3
•The cell bodies of 2nd
order neuron lie in Clark’s
column( nucleus dorsalis)
•Axons of 2nd order neuron
terminate ipsilaterally
(uncrossed) in the
cerebellar cortex by
entering through the
inferior cerebellar
peduncle.
•Posterior spinocerebellar
tract convey sensory
information to the same
side of the cerebellum

30. Ventral (Anterior)Spinocerebellar
Tract
•The cell bodies of 2nd order
neuron lie in base of the
dorsal horn of the lumbosacral
segments
•Axons of 2nd order neuron
cross to opposite side, ascend
as far as the midbrain, and
then make a sharp turn
caudally and enter the
superior cerebellar peduncle
•The fibers cross the midline
for a second time within the
cerebellum before terminating
in the cerebellar cortex
•Ventral spinocerebellar tract
convey sensory information to
the same side of the
cerebellum