export_spinal cord Flashcards
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
- Anterior median fissure
- Posterior median sulcus
- Posterolateral sulci
- 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.
- Anterior funiculus:
- Lateral funiculus
- 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?
- 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
Unknown
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.
What is the dorsal nucleus of Clarke
- Lies in the 7th layer of Rexed and extends from C8 to L2.
- Sends fibers to the ipsilateral dorsal spinocerebellar tract.
What is the central cervical nucleus?
It extends from C1-C4 and sends crossed fibers to the cerebellum and inferior vestibular nucleus.
What is the intermediolateral cell column
This is the medial part of layer 7 of Rexed and extends the entire length of the cords with visceral input.
It sends sympathetic fibers along with the ventral roots via white rami communicantes (parasympathetics arise from S2-S4)
Where is the 8th layer of Rexed located
At the base of the anterior horn.
The 9th layer of Rexed contains what type of neurons
Alpha and gamma neurons
Medial nuclear group - axial muscle control.
Lateral nuclear group - appendicular muscle control
Ventral group - controls extensors
Dorsal group - controls flexors
What is the function of the 10th layer of Rexed.
Unknown.
It is the gray matter found surrounding the central canal of the spinal cord.
What fibers run in the medial bundle of the dorsal root
Large myelinated fibers to the posterior columns or medial posterior horn from the encapsulated receptors such as to the Golgi tendon organs, muscle spindles, Pacinian corpuscles and Meissner’s corpuscles. [The fancy receptors]
What fibers run in the lateral bundle of the dorsal roots
Thin non-myelinated fibers which convey crude touch, pain and temperature from free nerve endings.
Main neurotransmitter used by spinal and cranial sensory ganglia is
Glutamate
What are the ascending tracts in the spinal cord
- Posterior columns
- Anterior spinothalamic tract
- Lateral spinothalamic tract
- Spinotectal tract
- Dorsal spinocerebellar tract
- Ventral spinocerebellar tract
- Cuneocerebellar tract
- Rostral spinocerebellar tract
- Spinoolivary tract
- Spinoreticular tract
Features of the posterior columns of the spinal cord
Convey touch, vibration and proprioception. That being said most lower limb group 1 afferents (1a muscle spindles/1b Golgi tendon organs) go to Clarke’s column and the dorsal spinocerebellar tract not the fasciculus gracilis and posterior columns.
Lower limb fibers are medial
Features of the anterior spinothalamic tract
Conveys mostly light touch. Fibers originate from layers 1, 4, and 5, cross in the anterior commissure and then terminate in the reticular formation, periaqueductal gray, VPL and intralaminar thalamic nucleus.
Lower limb fibers are lateral.
Features of the lateral spinothalamic tract of the spinal cord
Conveys pain and temperature. Fibers originate from layers 1, 4, and 5 cross to the contralateral lateral spinothalamic tract and ascend to the reticular formation and thalamic VPL.
Features of the spinotectal tract
Convey pain stimuli.
These fibers originate from layers 1 and 5, cross to the anterolateral spinal cord where they terminate in the superior colliculus and periaqueductal gray.
Features of the dorsal spinocerebellar tract
Conveys touch, pressure and proprioception from the lower limbs.
Type 1a, 1b and II fibers from the Golgi tendon organs and muscle spindles go to Clarke’s nucleus, then ascend in the ipsilateral dorsal spinocerebellar tract and then terminate in the cerebellar vermis via the ICP.
Features of the ventral spinocerebellar tract
Covey lower limb posture and coordination information. Type 1b fibers from the Golgi tendon organs go to the 5th, 6th and 7th layers where they sample efferent copies of motor commands. They then cross to the contralateral ventral spinocerebellar tract, and cross again to enter the anterior vermis via the SCP.
Features of the cuneocerebellar tract
It conveys touch, pressure and proprioception from the upper limbs. = upper limb equivalent of the dorsal spinocerebellar tract .
Type 1a and 1b fibers travel in the fasciculus cuneatus to the accessory cuneate nucleus in the medulla and ascend in the cuneocerebellar tract and terminate in lobule 5 of the cerebellum via the ICP.
Features of the rostral spinocerebellar tract
Upper limb equivalent of the ventral spinocerebellar tract.
Conveys upper limb posture and coordination information, in addition to providing efferent copies.
Enter the cerebellum via the ICP.
Features of the spinoolivary tract.
Conveys cutaneous and group 1b receptor impulses from the DRG to the posterior columns then to the cuneatus and gracilis nuclei followed by the accessory olivary nucleus where they then synapse in the contralateral anterior lobe of the cerebellum.
Features of the spinoreticular tract
Modulates motor, sensory, behavior, and awareness.
Project to the reticular formation in the medulla ipsilaterally and the pons and midbrain bilaterally.
What are the descending tracts in the spinal cord
- Corticospinal tract
- Tectospinal tract
- Rubrospinal tract
- Vestibulospinal tract
- Pontine reticulospinal tract
- Medullary reticulospinal tract
- Medial longitudinal fasciculus
- Descending autonomic pathways
Features of the corticospinal tract
Conveys voluntary skilled movements.
Fibers originate from Betz cells, Area 4, premotor area and post-central areas. These fibers go through the pyramid to the spinomedullary junction where they enter either the lateral, anterior or anterolateral corticospinal tract.
Features of the lateral corticospinal tract
Crossed motor fibers which travel in the posterolateral funiculus which enter the intermediate gray to to laminas 4,5,6, and 7.
Represent 90% of the fibers from the medullary pyramids.
Neurotransmitters are glutamate and aspartate.
Features of the anterior corticospinal tract.
10% of the fibers from the medullary pyramids. Run ipsilaterally but cross in the anterior white commissure to enter lamina 7.
Features of the tectospinal tract.
Conveys reflex posture movements in response to visual and possibly auditory stimuli.
Fibers from the superior colliculi cross in the midbrain to join the MLF at the medulla and travel in the anterior funiculus to the cervical levels C1-C4 and synapse in laminas 6,7, and 8.
Features of the rubrospinal tract
Involved in the maintenance of flexor tone.
Fibers from the red nucleus cross in the ventral tegmentum, travel anteriorly and partially intermingle with the corticospinal tract as they terminate in laminas 5,6, and 7.
Features of the vestibulospinal tract
The vestibulospinal tract is involved in maintaining extensor tone.
Fibers from the lateral vestibulospinal nucleus travel ipsilaterally within the entire length of the cord in the anterior portion of the lateral funiculus to laminas 7,8, and 9.
Features of the pontine reticulospinal tract
Involved in the maintenance of extensor tone especially in the antigravity muscles.
Fibers from the medial pons travel ipsilaterally in medial anterior funiculus near the MLF and go to laminas 7 and 8.
Both the vestibulospinal and pontine reticulospinal tracts are involved in maintaining…..
Extensor tone.
Note that the former - vestibulospinal - has somatotopic organization.
Features of the medullary reticulospinal tract
Involved in the inhibition of extensor tone.
Fibers from the medial reticular formation of the medulla especially the nucleus reticularis gigantocellularis travel in the anterior portion of the lateral funiculus to lamina 7 throughout the cord.
There is substantial cortical input to this system.
Features of the descending autonomic pathways in the spinal cord
Travel from the hypothalamus, Edinger-Westphal nucleus, locus ceruleus, and solitary nucleus travel in the lateral funiculus to the intermediolateral cell column in the thoracic, lumbar and sacral spine for sympathetic and parasympathetic control.
What are the flexor tracts in the spinal cord
Lateral/medullary reticulospinal tract
Rubrospinal tract - upper limbs only
What are the extensor tracts
Medial and lateral vestibulospinal tracts
Medial/pontine reticulospinal tract
Damage to the anterior lobe of the cerebellum does what?
Removes tonic inhibition of the lateral vestibular nucleus resulting in increased extension.
What are the normal AP diameters of the spine
C1-2: 15mm
C3-T12: 12mm
L1-5: 15-20mm
What are the normal AP diameters of the spine
C1-2: 15mm
C3-T12: 12mm
L1-5: 15-20mm
Uncovertebral joints
Extends between the lateral uncinate processes of the cervical vertebrae
Zygapophyseal joints
From the facets, innervated by the fibers of the medial branch of the posterior spinal rami. Medially these joints are only covered by ligamentum flavum.
Hemifacets are found where?
Transverse processes of T1-T10. For the costovertebral joints.
Anterior longitudinal ligament
Extends from the basiocciput to S1 and is adherent to the vertebral bodies.
Posterior longitudinal ligament
Extends from the C1 to S1. The PLL merges rostrally with the dura. Adherent to the annulus only - not the vertebral bodies. Fat and veins lie in between the PLL and the vertebral bodies.
Transverse atlantal ligament
Extends between the tubercles of the lateral masses of atlas and holds the dens against the anterior arch. The superior and inferior cruciate ligaments emerge from the transverse ligament.
The superior and inferior cruciate ligaments
Connect transverse ligaments to the posterior basion (S CL) and posterior body of the axis (I CL) respectively.
Apical and alar ligaments
Apical: extends from the tip of the dens to the basion
Alar: The two alar ligamens extend from the dens to the lateral margins of the foramen magnum
The spinal cord is connected to the dura by
Extension of the pia known as the dentate ligaments.
