General Organization of the Spinal Cord Flashcards
Where is the cervical enlargement found?
C4-T1
Why does the cervical enlargement occur?
To accomodate for innervation of the upper extremities via the brachial plexus
What occurs in the diameter of the chord in the thoracic segment?
The cord narrows
Where is the lumbosacral enlargement found?
L2-S3
Why does the lumbosacral enlargement occur?
To accomodate for innervation of the lower extremities
Where does the conus medullaris occur?
L1 or L2
Is the ventral median fissure continuous?
Yes
Is the dorsal median fissure continuous?
Yes
Is the ventral lateral sulcous paired and continuous?
Yes, both paired and continuous
What is important about the ventral lateral sulci?
Zone of ventral rootlets of spinal nerves
Is the ventral lateral sulcous paired and continuous?
Yes, both paired and continuous
What is important about the dorsal lateral sulci?
Zone of dorsal rootlets of spinal nerves
Is the dorsal intermediate sulcous paired and continuous?
Paired but not continuous
Where is the dorsal intermediate sulci found?
Along cord segments T6 and above
Where is the dorsal intermediate sulci positioned?
Between the dorsal median sulcus and a dorsal lateral sulcus
What is the white matter of spinal cord?
It is distributed peripherally surround the gray matter
What fibers does the white matter of spinal cord contain?
Both ascending and descending fibers
What are the three divisions of white matter areas in the spinal cord?
Posterior (Dorsal) funiculi or columns
Lateral funiculi or columns
Anterior (Ventral) funiculi or columns
What are the borders of the posterior funiculus?
Bordered by the dorsal median sulcus and a dorsal lateral sulcus
Is the posterior funiculus paired and continuous along the entire cord?
Yes, it is both paired and continuous
What type of fibers primarily make up the posterior funiculi?
Ascending fibers or Sensory
What are the borders of the lateral funiculi?
Bordered by a dorsal lateral sulcus and a ventral lateral sulcus
Is the lateral funiculus paired?
Yes, it is paired
What type of fibers primarily make up the lateral funiculi?
Includes both ascending and descending fibers (sensory and motor)
What are the borders of the anterior funiculi?
Bordered by the ventral median fissure and a ventral lateral sulcus
Is the anterior funiculus paired?
Yes, it is paired
What type of fibers primarily make up the anterior funiculi?
Includes both ascending and descending fibers (sensory and motor)
What is a fasciculus or tract?
organized groups of axons/fibers that are anatomically (have a similar origin, course, termination) or functionally within each funiculus
What are the three types of fasciculi pathways?
Ascending pathway
Descending pathway
Fiber pathways to extert control over autonomic/visceral function
What are the functions of the ascending pathways of the fasciculi?
Ascending or sensory pathways carry information to higher centers of the CNS
What are the functions of the descending pathways of the fasciculi?
Descending or motor pathways help mediate (voluntary) motor activity
What is the dorsal lateral tract also called?
Lissauer’s tract
Where is Lissauer’s tract located?
At the dorsal lateral sulcuz zone directly off of the gray matter dorsal horn
What fibers makes up Lissauer’s tract?
Ascending and descending fibers that travel short distances along the cord (1-2 segments up or down)
Is the fasciculus gracillis paired and continuous through the entire cord?
Yes it is both continuous and paired
Where is the fasciculus gracilis found below T6?
Between the dorsal median sulcus and the dorsal lateral sulcus
Where is the fasciculus gracilis found above T6?
Between the dorsal median sulcus and the dorsal intermediate sulcus
What fibers makes up fasciculous gracilis?
Major ascending pathways (sensory)
What is the function of fasciculus gracilis?
Relay lower body sensation up the spinal cord
Is the fasciculus cuneatus paired and continuous throughout the entire cord?
It is paired but not continuous throughout the entire cord
Where is the fasciculus cuneatus located?
Positioned between the dorsal intermediate sulcus and the dorsal lateral sulcus in the dorsal funiculus
Starting at which cord segment is the fasciculus cuneatus present?
T6 and above
What is the spinothalamic tract also known as?
the anterolateral system
Is the spinothalamic tract paired and continuous along the entire cord?
Yes, it is both paired and continuous
WHere is the spinothalamic tract located?
Located in the anterolateral part of the white matter
What fibers makes up the spinothalamic tract?
Major ascending pathway
What is the anterior white commissure?
Decussating (crossing) fibers that contribute to the spinothalamic tract
What is the gray matter of the spinal cord?
Distributed within the central part of the cord in an H-shaped or butterfly pattern.
What are the components of the gray matter of the spinal cord?
Posterior (dorsal) horns
Anterior (ventral) horns
Intermediate zone
Lateral horn
What types of neurons are found in the posterior horn?
primarily sensory neurons
What types of neurons are found in the anterior horn?
Primarily motor neurons
What is the intermediate zone of gray matter?
Gray matter that extends from one side, across midline, to the opposite side
What does the intermediate zone of gray matter contain?
The gray commissure that surround the central canal
What is the function of the central canal?
Connects the spinal canal with the IV ventricle
What types of neurons are found in the intermediate zone of gray matter?
Sensory neurons and interneurons
In which spinal cord are lateral horns found?
Extends only from T1 to L2 cord segments
Where are lateral horns found in a cross section of a spinal cord between T1 and L2?
Positioned in the lateral part of the intermediate zone
What neurons make up the lateral horn?
Preganglionic sympathetic neurons
What is the trend of white matter as you go from lumbar/sacral cord segments to cervical cord segments?
1) Lumbar/sacral: lowest number of axons/fibers
2) Thoracic: Volume of white matter increasingly more than lumbar region
3) Cervical: Volume of white matter is the highest
What is the trend of gray matter as you go from lumbar/sacral cord segments to cervical cord segments?
1) Lumbar/sacral: number of neurons high because of lower extremity innervation
2) Thoracic: volume of gray matter is low because of no extremity innervation
3) Cervical: Volume of gray matter is high because of upper extremity innervation
What part is only found in thoracic cord levels?
Lateral horn
What part is only found in the cervical cord segments?
Fasciculus cuneatus
What are dorsal root ganglion also known as?
spinal nerve ganglion
What type of neurons are dorsal root ganglion?
pseudounipolar neurons
What is the difference between a peripheral and central process?
Peripheral process = from sensory receptor to DRG
Central process = From DRG to CNS
What are axonal collateral branches?
Branches that span off of axons
What are decussating fibers?
Fibers that cross from one side to the other
What are interneurons also known as?
Internuncials
What are interneurons?
small neuron that makes synaption connections locally (travel short distances)
What are longitudinal columns of neurons of the gray matter along the cord known as?
laminae of rexed
How many laminae or columns are found in the spinal cord gray matter?
Ten laminae (I-X)
Where is lamina I found?
Thin layer located at tip of dorsal horn
What is the function of lamina I?
1) Receive incoming dorsal root fibers
2) Project some axons to contralateral spinothalmic tract
What is lamina II also known as?
Substantia gelatinosa
What is the function of lamina II?
receive dorsal root fibers and descending fibers
What are interneurons found in lamina II important for?
modification of pain pathways
Where do the axons of the lamina II synapse?
The axons of these neurons synapse on neurons of other laminae in adjacent cord segments
What is the function of lamina IV?
Receive input from the dorsal root fibers
What is important about the neurons of lamina IV?
The tract cells (neurons) contribute fibers to the contralateral spinothalmic tract
Where are laminae V and VI found?
Located at the base of the dorsal horn
What is the function of laminae V and VI ?
receives dorsal root fibers and much input from descending fibers
Do laminae V and VI contain interneurons?
Yes, some neurons are interneurons
What is the relationship between laminae V and VI and the spinothalmic tract?
laminae V and VI include tract cells that contriubte to the contralateral spinothalmic tract
Where is lamina VII found?
Largest area comprising the intermediate zone and part of the ventral horn
Does laminae VII contain interneurons?
Yes, Some neurons are interneurons
What are the 4 nuclear cell columns included in the lamina VII?
1) Intermediolateral nucleus
2) Intermediomedial nucleus
3) Nucleus Dorsalis
4) Sacral autonomic nucleus
What nucleus makes up the lateral horn?
Intermediolateral nucleus
In which cord segments is the intermediolateral nucleus found?
T1-L2
What is the function of the intermediolateral nucleus?
Preganglionic sympathetic neurons
What is the nucleus dorsalis also known as?
Clarke’s nucleus
What cord segments is the nucleus dorsalis found?
C8-L3
What do the axons of the nucleus dorsalis make up?
The axons from these neurons form the dorsal spinaocerebellar tract
What cord segments are the sacral autonomic nucleus found?
S2-4
What is the function of the sacral autonomic nucleus?
Preganglionic parasympathetic neurons
Where is lamina IX found?
Multiple cell columns embedded in laminae VII or VIII
How are lamina IX neuron colums distributed?
Medial to Lateral
What is the function of the lamina IX?
Functions as interneurons
What type of Neuron (motor or sensory) are found in lamina IX?
Most are the motor neurons of the ventral horn
How do Lamina IX axons exit the cord?
Exit the cord via the ventral roots of spinal nerves
What do the lamina IX innervate?
Skeletal muscle cells
What skeletal muscles do the medially positioned lamina IX cell columns innervate?
Axial skeleton/trunk
What skeletal muscles do the more laterally positioned lamina IX cell columns innervate?
Extremity muscles
What are the two special motor nuclei of lamina IX?
Phrenic nucleus
Spinal Accessory nucleus
In which cord segments is the phrenic nucleus found?
C3-C5
In which cord segments is the spinal accessory nucleus found?
C1-C5
What is the function of the phrenic nucleus?
Motor innervation to diaphragm
What is the function of the spinal accessory nucleus?
Motor innervation to trapezius and SCM muscles
Where is lamina X found?
Area of gray commissure
What type of neurons are found in lamina X?
Mostly interneurons
Which laminae do dorsal rootlets terminate in?
I-VI
Which laminae make up the dorsal horn?
I-VI
What are lamina II neurons also known as?
substantia gelatinosa
What are important about lamina II neurons?
Important interneurons that can modify pain pathways
What do the tract cells that contribute axons to the spinothalamic tract reside primarily?
Laminae IV and V-VI
Which lamina are the motor neurons of the ventral horn?
Lamina IX neurons
