lec 4 - spinal cord gross anatomy and vasculature Flashcards
Cervical Region
8 spinal levels and 8 spinal nerves, but only 7 cervical vertebrae.
The nerves of the same number of the vertebrae exit above their respective vertebrae:
> C1-C7: exit superior to vertebral level
> C8: exits inferior to C7 vertebra
Thoracic region
12 spinal levels, 12 spinal nerves, and 12 vertebrae
all the thoracic spinal nerves to exit below their respective vertebral levels
L1-L5: exit inferior to vertebral level
Lumbar region
5 spinal levels, 5 spinal nerves, and 5 vertebrae
All lumbar spinal nerves exit below their respective vertebrae
L1-L5: exit inferior to vertebral level
Sacral region
5 spinal levels, 5 spinal nerves, and 5 vertebrae that are fused together to form the sacrum
Sacral spinal nerves exit below their respective vertebrae
S1-S5: exit via sacral foramina or sacral hiatus
S1-S4 ventral rami exit out of the anterior sacral foramina.
S1-S4 dorsal rami exit out of the posterior sacral foramina.
The S5 spinal nerve exits out of the sacral hiatus with the coccygeal spinal nerve
coccygeal region
1 spinal level, 1 spinal nerve, and 1-5 fused vertebrae to form the coccyx
The coccygeal spinal nerve exits with the 5th sacral spinal nerve through the sacral hiatus
Co1: exits via sacral hiatus
Spinal levels do not line up with vertebral levels =
due to differential growth during embryonic development
spinal cord finished development before the vertebral column because the nervous system is one of the first systems to develop
vertebral column continues to grow and develop after the spinal cord has finished development
vertebral column is longer than the spinal cord
Herniated Discs
Most common regions: cervical and lumbosacral
For cervical and lumbosacral disc herniations, the spinal nerve involved typically corresponds to the lower of the adjacent 2 vertebrae
Cervical nerve roots have a fairly horizontal pathway as they exit the intervertebral foramen =
posterior longitudinal ligament strengthens the central portion of the intervertebral disc
herniations typically occur laterally rather than centrally
usually involves the nerve root that corresponds to the lower vertebral bone of the herniated disc (e.g., C5-C6 disc herniation usually results in C6 radiculopathy)
Lumbar nerve roots must descend prior to exiting through the intervertebral foramen
As the nerve roots are about to exit, they move into the lateral recess of the spinal canal
posterolateral disc herniation in the lumbosacral region usually impinges nerve roots on their way to exit beneath the next lower vertebra, which correspond to the number of the nerve root involved (e.g., L5-S1 disc herniation usually results in S1 radiculopathy)
Cervical enlargement
C5-T1 spinal levels = brachial plexus
Lumbosacral enlargement
L1-S3 spinal levels = lumbosacral plexus
Conus medullaris
End of spinal cord
Occurs between vertebral levels L1-L2
Cauda equina
Collection of spinal nerve rootlets that extends beyond conus medullaris
Cauda Equina Syndrome (CES)
Impaired function of multiple nerve roots below L1 or L2
Depending on the level of injury, symptoms may include sensory and motor deficits in the lower limb, urinary incontinence, fecal incontinence, and sexual incontinence
Detecting and treating CES early is critical to avoid irreversible deficits
Common causes of CES include lumbar disc herniation, schwannoma, meningioma, meningitis, and trauma
Compression of the conus medullaris causes ___, which has similar symptoms
conus medullaris syndrome
Spinal nerve rootlets
Ventral rootlets: motor
Dorsal rootlets: sensory
The dorsal roots and rootlets carry ___ information into the ___ gray horn of the spinal cord
sensory
dorsal
(sensory pathway)
purely sensory input pathways transmitting information in only one direction (toward the spinal cord)
The ventral rootlets and roots carry ___ information out from the ___ gray horn of the spinal cord
motor
ventral
(motor pathway)
The ventral rootlets and roots are purely motor output pathways transmitting information in only direction (away from the spinal cord)
The dorsal and ventral roots converge to form the ___
spinal nerve (trunk)
= both a sensory and motor pathway (mixed nerve) carrying information in both directions (toward and away from the spinal cord)
Spinal nerve roots
Ventral roots: motor
Dorsal roots: sensory
Dorsal root ganglion
Spinal nerve (trunk)
Motor and sensory
dorsal ramus =
carries sensory and motor information to and from the intrinsic/deep/epaxial back muscles
both a sensory and motor pathway carrying information in both directions (toward and away from the spinal cord)
intrinsic/deep/epaxial back muscles are derived from the epimere of the somite, which the dorsal ramus migrated into during embryonic development
innervates the skin overlying the intrinsic/deep/epaxial back muscles (the skin overlying the vertebral column)
ventral ramus =
carries sensory and motor information to and from the rest of the trunk and limb muscles
both a sensory and motor pathway carrying information in both directions (toward and away from the spinal cord)
Communicating rami = Connection to sympathetic trunk
Dermatomes
portion of skin innervated by a single spinal level
Sensory region of skin innervated by a single nerve root
C1 spinal segment does not have a dermatome
Trigeminal nerve (CN V) provides sensory innervation to the face
Notice in the chest that the C5 dermatome meets up with the T1 dermatome
This is because the C6, C7, and C8 dermatomes get pulled into the upper limbs
There is overlap in areas of the body that are supplied by specific dermatomal levels
injury to one spinal level often does not cause complete lack of sensation in that dermatome
it often leads to decreased sensation in that dermatome
pinprick test is a good test for dermatomal level integrity because it is more precise and activates smaller nerve fibers
Dermatomes vs. Cutaneous Fields
dermatomes are the sensory distribution of single spinal levels
cutaneous fields are the sensory distribution of peripheral nerves
Myotomes
group of muscles innervated by a single spinal nerve root
PNS Plexuses
cervical plexus
brachial plexus
lumbosacral plexus
Cervical plexus:
formed by cervical ventral rami (C1-C4)
Provides sensory and motor innervation to the neck and part of the head
Brachial plexus:
formed by cervical and thoracic ventral rami (C5-C8 and T1)
Provides sensory and motor innervation to the upper limb
Lumbosacral plexus:
formed by lumbar, sacral, and coccygeal ventral rami (L1-L5, S1-S5, and Co1)
Provides sensory and motor innervation to the lower limb and part of the pelvis
Somatic division
Target/effector: skeletal muscle
1 motor neuron pathway
Cell body in CNS
Autonomic division
Target/effector: smooth muscle, cardiac muscle, and glands
2 motor neuron pathway
Preganglionic (presynaptic) neuron = Cell body in CNS
Postganglionic (postsynaptic) neuron = Cell body in PNS
Somatic motor neuron cell bodies are located in the ventral horn of the spinal cord =
Follow spinal nerve anatomy to effector (skeletal muscle)
Somatic/general sensory neurons have receptors in skeletal muscle, skin, hair, nails, some mucosa, etc. =
Follow spinal nerve anatomy to dorsal horn of spinal cord
Cell bodies located in the dorsal root ganglion
Autonomic Nervous System
In general, the sympathetic and parasympathetic divisions of the ANS target the same organs, but they typically have opposing actions/effects
The ANS targets involuntary muscle (cardiac and smooth muscle) in viscera, thus the sympathetic and parasympathetic divisions modulate the activity of these viscera
Sympathetic division
Origin: thoracolumbar (T1-L2/L3) spinal levels
sympathetic neurons:
Sympathetic preganglionic neurons
> Arise in the lateral horn of the spinal cord at T1-L2/L3
> Release acetylcholine (ACh)
Sympathetic postganglionic neurons
> Arise in sympathetic trunk ganglia or collateral ganglia
> Most release norepinephrine (NE), some release ACh
Sympathetic trunk/chain
Located on either side of vertebral column from cervical to sacral regions
Transmits preganglionic and postganglionic sympathetic fibers
Sympathetic trunk/chain (paravertebral) ganglia
Swellings on sympathetic trunk
Motor ganglia: synapse location for preganglionic and postganglionic sympathetic fibers
The swellings/ganglia on the sympathetic trunk/chain is formed from the postganglionic sympathetic neuron cell bodies
Parasympathetic division
Origin: craniosacral
Cranial nerve nuclei in the brainstem and in the sacral spinal cord (S2-S4)
Parasympathetic neurons:
Parasympathetic preganglionic neurons
> Arise from cranial nerve nuclei in the brainstem and from the lateral horn of the spinal cord at S2-S4
> Release ACh
Parasympathetic postganglionic neurons
> Arise in the wall of the organ (in terminal ganglia)
> Release ACh
Gray matter of the spinal cord
Internal
Neuronal cell bodies and synapses
The gray matter is at the center of the spinal cord, surrounded by white matter (the gray matter resembles the shape of a butterfly).
The gray matter is where synapses occur in the spinal cord (integration of information).
White matter of the spinal cord
External
Neuronal axons
The white matter allows information to travel up and down the spinal cord and from right to left in the spinal cord.
Gray Matter of the Spinal Cord - Dorsal horn
Present at all spinal levels
Somatic sensory and visceral sensory
Gray Matter of the Spinal Cord - Ventral horn
Present at all spinal levels
Somatic motor
Gray Matter of the Spinal Cord - Lateral/Intermediate horn
Present at T1-L2/L3 (sympathetic) and S2-S4 (parasympathetic) spinal levels
Autonomic/visceral motor
Dorsal gray commissure:
connects right and left dorsal horns
Dorsal to central canal
Ventral gray commissure:
connects right and left ventral horns
Ventral to central canal
Dorsal Root Entry Zone
where sensory neurons enter the spinal cord
Medial DREZ:
where large, myelinated sensory neurons carrying somatosensation and proprioception enter the spinal cord
Afferents from mechanoreceptors
Lateral DREZ/Lissauer’s tract:
where small unmyelinated or lightly myelinated sensory neurons carrying pain enter the spinal cord
Afferents from nociceptors, thermoreceptors, and viscera
Gray Matter Nuclei
DORSAL HORN:
1) Postero(marginal) zone/ nucleus
2) Substantia gelatinosa
3) Nucleus proprius
4) Column of Clarke/Clarke’s nucleus/nucleus dorsalis
LATERAL HORN:
5) Intermediolateral cell column (IMLCC)/lateral horn
VENTRAL HORN:
6) Motor nuclei
Postero(marginal) zone/ nucleus
location: dorsal horn of all spinal levels
function: pain and temp
synapses: primary afferent fibers conveying pain and temp synpases with 2nd order neuron dendrites
inputs/projections: 2nd order neurons with their dendrites in this nucleus project into the contralateral anterolateral system/spinothalamic tracts
Substantia gelatinosa
location: dorsal horn of all spinal levels
function: pain modulation
synapses: primary afferent fibers conveying pain and temp synapse with dendrites of 2nd order neuron whose cell bodies are in the nucleus proprius - cell bodies are interneurons that release enkephalin
inputs/projections: dendrites of the 2nd order neurons with their cell bodies in the nucleus proprius, project into contralateral anterolateral system/spinothalamic tracts - enkephalinergic interneurons that modulate pain
Nucleus proprius
location: dorsal horn of all spinal levels
function: pain and temperature
synapses: nucleus contains 2nd order neuron cell bodies whose dendrites extend into the substania gelatinosa to synapse with primary afferent fibers conveying pain and temp
inputs/projections: 2nd order neurons with their cell bodies in this nucleus project into the contralateral anterolateral system/spinothalamic tracts
Column of Clarke/Clarke’s nucleus/nucleus dorsalis
location: dorsal horn of C8-L3 spinal levels
function: proprioception (unconscious)
synapses: primary afferent fibers conveying proprioception synapse with 2nd order neuron cell bodies
inputs/projections: 2nd order neurons with their cell bodies in this nucleus project into the ipsilateral dorsal spinocerebellar tract
Intermediolateral cell column (IMLCC)/lateral horn
location: T1-L2/L3 and S2-S4 spinal levels
function: autonomic motor
synapses: contains cell bodies of preganglionic sympathetic neurons at T1-L2/L3 and preganglionic parasympathetic neurons at S2-S4
inputs/projections: receives input from descending pathways from the brainstem and diencephalon
Motor nuclei
location: ventral horn of all spinal levels
function: somatic motor
synapses: contains lower motor neuron cell bodies for skeletal muscle contraction
inputs/projections: receives input from spinal reflexes and descending motor pathways
Ventral horn topography and lower motor neuron (LMN) organization
Medial LMNs innervate proximal/axial muscles
Lateral LMNs innervate distal limb muscles
Ventral LMNs innervate extensor muscles
Dorsal LMNs innervate flexor muscles
White Matter of the Spinal Cord
Dorsal column/funiculus
Ventral column/funiculus
Lateral column/funiculus
Dorsal column/funiculus =
Contains ascending sensory tracts/ fasciculi
Ventral column/funiculus =
Contains mostly descending motor tracts/fasciculi
Lateral column/funiculus =
Contains ascending sensory and descending motor tracts/fasciculi
Sulci of the Spinal Cord
Dorsal median sulcus/fissure
Dorsal intermediate sulcus
Dorsolateral sulcus
Ventral median sulcus/fissure
Ventrolateral sulcus
All of these sulci run longitudinally on the external surface of the spinal cord
The posterior/dorsal median fissure/sulcus is at the midline and separates the ___
right and left dorsal columns
there is one dorsal median sulcus
The posterior/dorsal intermediate sulcus/fissure is ___ to the dorsal median sulcus
There are two dorsal intermediate sulci (right and left). Each sulcus separates the dorsal column into two tracts:
lateral
gracile tract and cuneate tract
The posterolateral (dorsolateral) sulcus/fissure is lateral to the __ sulcus and is in the region of the ____
dorsal intermediate
dorsal root entry zone
There are two dorsolateral sulci (right and left). The posterior spinal arteries travel in each of the dorsolateral sulci.
The ventrolateral (anterolateral) sulcus/fissure is lateral to the ____ and is the exit point for the ventral rootlets as they leave the ventral horn
ventral median sulcus
There are two ventrolateral sulci (right and left)
Blood Supply of the Spinal Cord
> Posterior spinal arteries
Anterior spinal artery
Posterior spinal arteries =
2 posterior spinal arteries in dorsolateral sulci
Supply posterior 1/3 of spinal cord = Dorsal horns and dorsal columns
Anterior spinal artery =
1 anterior spinal artery in ventral median fissure
Supplies anterior 2/3 of spinal cord = Ventral and lateral horns and ventral and lateral columns
Venous Drainage of the Spinal Cord
The internal and external vertebral venous plexuses drain blood from the spinal cord and vertebral column
The external vertebral venous plexus is in the epidural space
The internal vertebral venous plexus is in the subarachnoid space
