Neurology sheet # 3
Date: 24/2/2011
Today we are going to talk about:
Lamina of Rexed.
Ascending Tracts.
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Lamina of Rexed:
Lamina I :Posteromarginal nucleus.
Lamina II: Substantia gelatinosa=> Found throughout the spinal cord.
Lamina III, IV: Nucleus proprius=> Also found throughout the spinal cord, it’s the
largest nucleus.
Lamina V,VI: Clark’s column( Nucleus Dorsalis ). C8-L3( not L3 vertebra, but spinal
cord segmest).
Lamina VII: Intermediate grey:


Interomediolateral column: Inside the Lateral horn, therefore, It
contains autonomic neurons.
*Sympathetic fibers=> T1-L2
*Parasympathetic fibers=> S2-S4
Interomediomedial column.
Lamina VIII: Interneurons.
Lamina IX: Anterior Horn ( motor cells ) :


Alpha cells : Large cells( multi- polar), supply the skeletal muscles.
Gamma cells: Smaller cells.
Lamina X: Grey Commissure.
Ascending Tracts:
Carries sensory information from the periphery towards the brain for integration,
and is composed of multiple neurons( 3 neurons), Information travels from 1st- 2nd3rd neuron then finally entering the sensory center inside the brain.
Modality: pain, temperature, pressure, and touch.
Receptor: *Exteroceptor=> Receptors transferring sensory information from the
exterior: outside the body.
*Proprioceptor=> Receptors transferring sensory information from the interior :
inside the body.
We said previously that there are 3 neurons: To transfer the sensory information
from the periphery to the brain:
-Primary Neuron: Dorsal root ganglion( Sensory ganglion)…. Transferring of
information always begin from there(Fixed).
-Secondary Neuron: Spinal cord or Brain Stem According to the type of the tract(
Changeable).
-Tertiary Neurons: Thalamus ( Ventral Posteriolateral Nucleus) . Fixed.
-Termination: Primary sensory center(S1) inside the Cerebral Cortex.
*Types of ascending tracts:
- Posterior white column.( Medial Lemniscal pathway).
- Spinothalamic Tract.
- Spinoreticular tract.
- Spinocerebellar Tract.
- Spino-olivary Tract.
- Spinotectal Tract.
*Spinothalamic Tract:
- its name means that it begins from spinal cord and terminates inside thalamus.
Two types:
a. Anterior spinothalamic: Modality=> Carrying Light touch, and pressure
information.
b. Lateral spinothalamic: Modality=> Carrying pain and temperature.

-
Receptor:
Free nerve ending.
Primary Neuron => Dorsal root ganglion.
Secondary Neuron=> Dorsal horn ( inside the spinal cord).
Tertiary neuron=> Thalamus.

Termination : Primary sensory center (S1).
Steps of spinothalamic tract:
1) First order neuron in the dorsal root ganglia.
2) First synapse between the axon of the dorsal root ganglion and the cell body
of the secondary neurons inside the dorsal horn specifically inside lamina II:
Substantia Gelatinosa .
3) The secondary neuron crosses to the other side passing through the grey
commissure reaching the anteriolateral side white matter of the spinal cord.
4) Reaching the Thalamus and make the second synapse.
5) Finally reaching the primary sensory area ( S1) to make the third synapse.
*To sum up: The spinothalamic tract has 3 synapses:
1st=> between the dorsal root ganglion And the secondary neurons inside the dorsal
horn (substantia gelatinosa).
2nd=> inside the thalamus.
3rd=> Axons of thalamus synapse with the cell body of the neurons in the primary
sensory area.
*Note=> There is no synapse in the anteriolateral side of white matter.
* Injury or cutting on the right side of the spinothalamic tract will lead to loss of
sensation below the site of lesion on the left side.WHY???????? Because the tract
begins at the right side then crosses to the left side and vise versa.
Note=> When moving upwards through the spinal cord the number of axons of the
spinothalamic tract will increase medially reaching the maximum number within the
cervical region.
Pain:
Slow Pain
FAST PAIN ( Acute pain)
Duration:
1 second : Long
Fibers:
C- fibers.
A delta fibers.
Diameter:
Small
Larger
Pain:
Diffuse
Well localized
# Of Synapses:
Site:
Large #
0.1 second :Short
Small #
Tissues
Skin.
Emotional.
Less emotional.
Dull, Boring
Sharp, Pricking
Blocked by Morphine
Not blocked by Morphine.
*posterior White column:
Modality=>
1)
Discriminative touch
sensation( Including: Vibration)/ Known also as: Two point discrimination:
meaning when two stimuli are effect at the same time the body will still be
able to exactly recognize the site of the stimuli even if they were too close
together.
2)
Conscious
proprioception ( Position sensation)
*Proprioception=> sensation from the muscles, or joints, or tendons…. And
the sensation finally reaches the brain.
Receptor=> Most receptors except free nerve endings, WHY????
Because free nerve endings are found in skin not in muscles. Instead of free nerve
endings there are:



Joint receptor.
Muscle spindle.
Tendon Organ : same
as muscle spindle but inside the tendon.
-Primary neuron: Dorsal root ganglion.
-Secondary Neuron: Dorsal column nuclei: two types of nuclei:
1)
Gracillis
2)
Cuneatus
And both nuclei are found in medulla oblongata( Brain Stem).
-Tertiary Neuron: Thalamus.
-Termination: Primary sensory area ( S1).
*Steps of this tract:
Sensory information enters through the dorsal root ganglia then passing through the
posterior white column, but does not enter the grey matter because there is no
synapse, because the secondary neurons are found in Medulla oblongata.
Reaching the medulla, the two nuclei(Gracillis and Cuneatus) will synapse then
crossing to the other side.
On the other side moving towards the thalamus( Tertiary neuron).
Finally.. Reaching the primary sensory center( S1).
…………………………..Done
by: Yasmin Alsayeh………………………………………