Download Sensory Pathways (Ascending Tracts)

Sensory Pathways
(Ascending Tracts)
Dr Ayman G. Abu-Tabanja
First order neuron:
Located in posterior root ganglion
Second order neuron:
Give an axon that cross Medline and ascend to
higher level of the CNS
Third order neuron:
Located in the thalamus, send axons to sensory
region of cerebral cortex
Some afferent pathways send branches to:
1. Reticular formation: activate cerebral cortex and
maintain wakefulness
2. Motor neurons: reflex muscular activity
Lateral Spinothalamic Tract
This tract Conducts Pain and
Temperature
• Second order neurons give axons that cross
medline through anterior gray and white
commissures within one spinal segment
• Fibers ascend as Lateral spinothalamic
tract
• In brainstem, the tract ascends through
spinal lemniscus
• Spinal lemniscus: bundle of fibers that
contain lateral spinothalamic tract, anterior
spinothalamic tract, Spinotectal tract
Anterior Spinothalamic Tract
This tract conducts light (crude)
touch and pressure pathways
Second order neurons give axons
that cross medline through anterior
gray and white commissures within
several segments
Fibers ascend as anterior
spinothalamic tract
In brainstem, the tract ascends
through spinal lemniscus
Posterior white column Tracts
Conducts:
Descriminative touch
Vibratory sense
Conscious muscle joint sense
First order neurons: send axons that
pass directly to posterior white column
Most of these axons ascend upward as
bundles known as:
1. Fasciculus gracilis:
present in all spinal cord segments
Contain axons from sacral, lumbar and
lower thoracic
2. Fasciculus cuneatus:
Present in upper thoracic and all
cervical segments
• Axons will synapse with 2nd order
neurons located in:
Nucleus gracilis
Nucleus cuneatus
Axons of 2nd order neurons cross midline
Crossing axons are called :
Internal arcuate fibers
Axons ascend in a bundle known as
Medial lemniscus to synapse with
3rd order neurons in thalamus
Posterior Spinocerebellar Tract
Anterior Spinocerebellar Tract
Cuneocerebellar Tract
These tracts conduct:
Muscle joint sense to the
cerebellum
Posterior spinocerebellar tract
Axons of second order neurons ascend
within the lateral white column on the
same side
Axons enter through inferior cerebellar
Peduncle to reach cerebellar cortex
Anterior spinocerebellar
tract:
Most Axons of second order neurons
Cross medline and ascend within
the lateral white column of opposite side
Axons enter through Superior Cerebellar
Peduncle to reach cerebellar cortex
Cuneocerebellar Tract:
Originate from nucleus cuneatus
Enter cerebellum through
Inferior cerebellar peduncle
on the same side
The fibers of this tract is called:
Posterior external arcuate fibers
Loss of all motor and sensory functions
Bilateral LMN Lesion
Bilateral UMN lesion
Bladder and bowel functions are not controlled
Bilateral LMN Lesion
Bilateral UMN lesion
Loss of pain, temperature and light touch sensations
Bilateral LMN Lesion
Bilateral UMN lesion
( (Sacral sparing
Loss of sensations !!!!!?
Ipsilateral LMN Lesion
Ipsilateral UMN lesion
Contralateral Loss of pain & temperature sensations