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The spinal cord extends from which levels

The foramen magnum to the 1st or 2nd lumbar vertebrae


The distal portion of the spinal cord is known as the 

Conus medullaris. - Extends to the end of the spinal canal at 3 months gestation, L3 at birth and L1/2 in adults.

The long nerve roots which extend past the conus medullaris are known the as cauda equina.


What is the filum terminale

The filum terminale consists of the pia from the conus medullaris, the rest of the ependymal cells, glia and fat. It extends from the thecal sac through to S2. It will eventually form the coccygeal ligament that attaches to the posterior coccyx. 


How many pairs of nerve roots lie at each level?

8 cervical
12 thoracic

5 lumbar

5 sacral

1 coccygeal


Where do the nerve roots exit?

Nerve roots exit through the intervertebral foramina


Where does the C1 nerve root exit

The C1 nerve root exits between the occiput and the atlas.


Where do cervical roots exit in general. 

Cervical roots generally exit ABOVE their respective pedicle with the exception of the C8 root which exits between C7 and T1. 


What is the sensory dermatome of C1

There is no sensory dermatome for C1. C1 has no dorsal root. 


What is the organization of sensory fibers in the posterior nerve roots

Pain and temperature fibers lie laterally

Posterior column proprioceptive fibers lie medially.


What are the four fissures/sulci associated with the spinal cord

1. Anterior median fissure
2. Posterior median sulcus

3. Posterolateral sulci

4. Posterior intermediate sulci


What is the relationship of the anterior median fissure to the spinal cord

The anterior median fissure extends deeply to near the gray commissure. 


What is the relationship of the posterior median sulcus to the spinal cord

The posterior median sulcus extends down to the posterior median septum


What is the relationship of the posterolateral sulci to the spinal cord

These two folds are located near the dorsal root entry zones - DREZ


What is the relationship of the posterior intermediate sulci to the spinal cord

The posterior intermediate sulci separate the fasciculus gracilis from the fasciculus cuneatus


What are the three paired funiculi of the spinal cord. 

1. Anterior funiculus:
2. Lateral funiculus

3. Posterior funiculus


Features of the anterior funiculus of the spinal cord

This funiculus extends from the anterior median fissure to the ventral root.

It contains ascending fibers from the spinal gray matter and descending fibers from the brainstem and cortex.


Features of the lateral funiculus of the spinal cord

The lateral funiculus lies between the ventral and dorsal roots.

It contains ascending fibers from the spinal gray and descending fibers from the brainstem and cortex.


Features of the posterior funiculus of the spinal cord

The posterior funiculus of the spinal cord extends from the posterior horn to the posterior median septum.

It is the largest funiculi and is mainly composed of ascending fibers from the dorsal root ganglion.

In the cervical and upper thoracic spinal cord it is divided by the posterior intermediate septum.


What is the central gray of the spinal cord. 

This is the butterfly shaped region of the spinal cord. The two lateral portions are connected by the gray commissure
The posterior horns extend out more to the surface than the anterior horns.


General features of the cervical spinal cord

It is oval shaped.

The fasciculus gracilis lies medially and the fasciculus cuneatus lies laterally.


General features of the thoracic spinal cord.

It contains less gray matter.
There is no fasciculus cuneatus at the lower levels.

The lateral horns of the thoracic spinal cord contain intermediolateral cell column.

The dorsal nucleus of Clarke lies at the base of the dorsal horn and extends throughout the thoracic cord. It is especially large at T10 through L2.


General features of the lumbar spinal cord

The lumbar spinal cord is nearly circular and contains less white matter than seen in the cervical cord. 


What are Rexed's layers/laminae

These are the layers of the gray matter in the spinal cord.

Note there is no layer 6 between T4-L2.


Features of Rexed layer/lamina 1

Lies at the top of the dorsal horn and contains the posteromarginal nucleus.
It receives input from the DRG and layer II.

DRG axons ascend or descend over layer I in Lissauer's tract before synapsing.

Mainly pain and temperature

Neurotransmitters include substance P, enkephalin, 5HT and somatostatin.


Features of the second layer of Rexed

Aka the substantia gelatinosa.
Input: posterior columns, dorsolateral and lateral funiculi with C fibers/slow pain.

Modulates sensation via layers III and IV.

Neurotransmitter: substance P.


The 1st and 2nd layers of Rexed contain a large amount of what neurotransmitter and receptor.

Susbtance P

Opiate receptors


Layers 1 and 2 of Rexed output to where?

1. To the ventral and lateral horns: reflexes

2. Rostrally to facilitate sensory transmission


Features of the third and fourth layers of Rexed

This region is also known as the nucleus proprius. It contains interneurons which convey low intensity stimuli to the thalamus. 


What is the function of the 5th layer of Rexed



Features of the 7th layer of Rexed

Aka the zona intermedia, it is located between the anterior and posterior horns of the spinal cord and includes the lateral horns.

Key structures in the 7th layer of Rexed include the dorsal nucleus of Clarke; central cervical nucleus and the intermediolateral cell column.