Neuraxial Overview/Anatomy Flashcards
How many bones are in the spinal column (in each section)?
33 total
-7 Cervical
-12 Thoracic
-5 Lumbar
-5 Sacral (fused)
-4 Coccygeal
Describe how the angle of the spinous process changes as you move from cervical/thoracic down to lumbar.
-Cervical & Thoracic Spinous Processes point caudal
-Lumbar spinous processes point more posteriorly
What type of joints are the 2 facet joints between each vertebrae?
Synovial (movement)
How many pairs of spinal nerves are there?
31
-Mixed nerves: Motor, sensory, and ANS nerve fibers
Which vertebrae form the Atlanto-Axial Joint?
-C1 (Atlas)
-C2 (Axis)
Allow for side to side movement
How do spinal nerves exit the spinal column?
Via intervertebral foramina and sacral foramen.
When does the spinal cord stop in adults?
-L1
-10% of people at L2 (1% of the population it extends to L2-L3)
When does the spinal cord stop in a child/infant?
L3
What is the Conus Medullaris?
Where the spinal cord tapers to an end. This gives off large rootlets that are free flowing in CSF (Cauda Equina)
What does the Cauda Equina terminate into?
The Filum Terminale, which extends down and anchors lower sacrum.
What are the Bulbous Portions of the Spinal Cord?
-Consist of more gray matter.
-Cervical enlargement: C5-T1, anterior motor, upper limb muscles
-Lumbar enlargement: L2-S3, lower limb muscles
What is Pia Mater?
Thin, delicate vascular membrane that covers the spinal cord and as far laterally as the intervertebral foramen.
-Terminates inferiorly as the filum terminale
-Has projections that help connect it to Arachnoid Mater as well as Dura Mater.
What is between the Pia Mater and Arachnoid Mater?
CSF
What is Arachnoid Mater?
Non-vascular, delicate, impermeable membrane.
-Separated from the Pia Mater by the Subarachnoid space (filled with CSF)
-Continuous throughout the brain, cord, and ends in the Filum Terminale
What is Dura Mater?
A dense, fibrous sheath that encloses the spinal cord and extends throughout the brain and ends at the Filum Terminale.
-Thickest of the meninges
-Overlies the brainstem
-Covers the outer periosteal layer (cranium) and the Meningeal layer
-Forms a fold called the Falx Cerebri that separates the Cerebral Hemispheres
-Covers the nerve roots
-Is continuous with the connective tissue surrounding each spinal nerve (epineurium) as it goes through the intervertebral foramen.
When your spinal needle penetrates the _____, you will feel a distinct pop!
Dura
What separates the inner surface of the Dura and the Arachnoid Space?
Subdural Space (potential space)
What occurs if you inject anesthesia within the Subdural Space?
-Delayed Block (10-25 minutes)
-Very Dangerous High Block!!!
The lateral gray horn of T1-L2 contains Corticospinal Tracts for what motor neurons?
Sympathetic Motor Neurons (SNS)
The lateral gray horn of S2-S4 contains Corticospinal Tracts for what neurons?
Parasympathetic - pre & post ganglionic, splenic, descending colon
Where are Cranial Parasympathetic nerves derived from?
Fibers of the Vagus Nerve
-This is important because the Cranial parasympathetic fibers are outside of a spinal and will not be affected by it.
Why is it important that the Cranial Parasympathetic nerves are derived from fibers of the Vagus Nerve?
-Vagus parasympathetic nerve fibers lie outside of the Subarachnoid space
-They are little affected by the Spinal or Epidural anesthesia.
-Cranial PNS fibers enter the abdomen with Vagus nerve.
-Ex: Retractor on Mesentery during surgery - pt can have vagal response (N/V, bradycardia, hypotension, pain).
What can you do to combat the vagal response from stimulation of the mesentery during surgery?
Surgeon can block the Vagus Nerve as it enters the abdomen, or can add GETA.
What are the 4 things (nuclei?) contained in the Posterior Gray Column?
1) Substantia Gelatinosa
2) Nucleus Proprius
3) Nucelus Dorsalis
4) Visceral Afferent Nucleus
What is the Substantia Gelatinosa?
-Where afferent nerves from the dorsal roots (pain, temperature, and crude touch via the Spinothalamic tract) synapse
-Contains Opioid receptors
What do neuraxial opioids do?
-Inhibit the release of excitatory neurotransmitters (Substance P, Glutamate)
-Inhibit afferent neural transmission to the brain from peripheral nerves
What is the Nucleus Proprius?
Ascending pathways for general sensation, pain, temperature, and tactile sensation
What is the Nucleus Dorsalis?
Only in the cervical and lower lumbar regions
-Project to Cerebellum for Proprioception
What is the Visceral Afferent Nucleus?
Receives visceral information
Where does the action for Neuraxial Blocks primarily occur?
On the nerve roots
What does the Posterior Primary Rami innervate?
-Lateral Branch: motor to Muscle
-Medial Branch: sensation to skin
What does the Anterior Primary Rami innervate?
-Cervical Plexus (C1-C4)
-Brachial Plexus (C5-T1)
-Lumbosacral Plexus (L1-S4)
-Coccygeal Plexus (S4-S5, 1st Coccygeal)
What is the White Matter?
The external portion of the cord.
-Axons have myelin (lipid/protein - makes it white)
-Cluster of axons forms the “Tracts”
-Has Ascending Pathways (Sensory) and Descending Pathways (Motor)
What are the 3 components of the Ascending Pathways (White Matter- Sensory)?
1) Tract of Lissauer
2) Posterior White Columns
3) Ant/Posterior Spinocerebellar Tracts
What are the 4 components of the Descending Pathways (White Matter- Motor)?
1) Corticospinal Tracts
2) Reticulospinal Tracts
3) Vestibulospinal Tracts
4) Rubrospinal Tracts
What is the Tract of Lissauer?
-Part of the pain pathway
-Have sensation, then jump 1-2 vertebral levels, then cross at the spinothalamic tract and then enter the posterior gray horn
What are the Posterior White Columns?
-Fascicularis Gracilis (Legs) and Fascicularis Cuneatus (arms)
-Touch, discriminate touch, vibration, conscious muscle joint sense, proprioception
What is the function of the Ant/Posterior Spinocerebellar Tracts?
Carries proprioception info to the Cerebellum
What are the Corticospinal Tracts?
-Lateral and Anterior
-Gross motor movement
-Fine motor, voluntary
What are the Reticulospinal Tracts?
-Awake and voluntary movement
-Reflexes
-Works by getting constant stimulation from body. When you block afferent impulses, they have less stimulation, so patient gets sleepy/somnolent.
What are the Vestibulospinal Tracts?
-Balance traverses the inner ear and cerebellum via this tract
-Facilitates extensor muscles
-Inhibits flexor muscles to maintain balance
What are the Rubrospinal Tracts?
Alpha motor neurons that facilitate flexor muscles
How does blockade of dorsal roots compare to blockade of ventral root?
-Dorsal: Somatic/visceral, sensory
-Ventral: Autonomic, Motor
What are the 3 ways the Spinal Cord receives blood supply?
1) Posterior Spinal Arteries
2) Anterior Spinal Artery (singular)
3) Artery of Adamkiewicz (Arteria radicularis magna)
What are the Posterior Spinal Arteries?
-Derived from the cerebral arterial system
-Rich supply of collateral flow from the Subclavian, Intercostal Lumbar, and Sacral arteries
-Supplies Posterior 1/3 of the cord; has contributions from radicular arteries
-Descend on each side of the cord and increase in blood supply as they go down from radicular arteries that feed into it
What is the Anterior Spinal Artery?
-A single artery that is derived from both Vertebral arteries and transverses down the midline of the cord in the Anterior Median Fissure
-Has contributions from radicular arteries
-As it moves down, gets smaller
-Becomes extremely small in the mid to lower thoracic region
-Can be problematic if radicular arteries are occluded (feeder arteries)
-Supplies 2/3 of the Anterior Cord
What is the Artery of Adamkiewicz (Arteria Radicularis Magna)?
The most important radicular artery from a single segmental branch of the aorta.
-Supplies nearly all of the flow to the lower thoracic and lumbar segments (Lower 1/3 of Anterior cord)
-Injury to this artery = increased risk for ischemia.
What causes Anterior Spinal Artery Syndrome?
Damage, ischemia, hypoperfusion, or occlusion to the Artery of Adamkiewicz.
What are the S/Sx of Anterior Spinal Artery Syndrome?
-Flaccid paralysis
-Variable loss of sensation of pain and temperature at and below the level of injury.
-Preservation of proprioception and light touch
When does Anterior Spinal Artery Syndrome occur?
-Most common in Aortic Surgery with prolonged cross clamping or direct injury
-Risk factors: Atherosclerosis, prolonged hypotension, embolic issues.
Motor paralysis is due to disruption of what?
Motor paralysis = disruption of cord at the Corticospinal Tract. (!)
Loss of pain and temp at and below injury is due to the disruption of what?
Loss of pain and temp at and below injury = disruption of spinothalamic tract.
Why are proprioception and vibratory sensation retained with ASA syndrome?
Intact dorsal columns
What is unique to a Partial Complex injury (Anterior Spinal Artery Syndrome)?
-Posterior cord can remain intact
-Sensory fascicularis gracilis intact as well as proprioception
What is the Anterior Longitudinal Ligament (ALL)?
-A continuous band running down the anterior surface of the vertebral column from the skull to sacrum.
-Holds the vertebrae together firmly, while allowing some movement
-Tapers inferior to superior.
-More likely to have a cervical disc herniation ANTERIORLY (ACDF)
What is the Posterior Longitudinal Ligament (PLL)?
-A continuous band running down the posterior surface of the vertebral column from the skull to sacrum.
-Holds the vertebrae together firmly, while allowing some movement
-Tapers superior to inferior.
-More likely to have posterior lumbar herniation (Lumbar Lami & Discectomy)
What is the Supraspinous Ligament?
The most superificial
-Runs between adjacent spines
-Thickest/broadest in Lumbar Region
What is the Interspinous Ligament?
-Thin ligament
-Connects the adjacent spines
-Fills in between the Ligamentum Flavum and the Supraspinous Ligaments
What is the Ligamentum Flavum?
-Elastic fibers and membranous material
-Thinnest in cervical region
-Thickest in lumbar region
-Attaches to the anterior and inferior aspect of the Lamina below
-Blends laterally with the joint capsule between the articular processes and fuses posteriorly with the interspinous ligament.
-Does contain small vessels from the vertebral plexuses (can have blood tinge in syringe)
-Normally lies 3-4 cm from the spinous process in the lumbar region
Why do we care that the Ligamentum Flavum is two halves that are fused in the middle?
-We rely on the LOR technique, and most epidurals are done medially
-In very rare cases, the ligament does not fuse midline (usually occurs at L1-L2)
What is important to know with NA anesthesia and the elderly?
-Ligamentum Flavum can become calcified
-Disc height may diminish (decreasing interspace)
Where is the Epidural Space located?
Between the periosteal lining of the canal and the dura.
-Extends from the base of the skull to the level of the sacral hiatus (S4)
What are the borders of the Epidural Space?
Anterior: Posterior Longitudinal Ligament (PLL)
Posterior: Ligamentum Flavum & Vertebral Pedicles
Lateral: Intervertebral Foramen
Runs from the Foramen Magnum to the Sacral Hiatus (last sacral opening)
What is the usual distance of Ligamentum Flavum to Dura?
-Smallest where cord is present (Upper lumbar, thoracic, and cervical). Around 3-4 mm
-After cord ends (L2), can be 5-7 mm
What is the normal distance from skin to epidural?
Usually 4-5 cm
-Can be 2-9 cm depending on patient size
What is contained in the Epidural Space?
-Fatty tissue with bands of connective tissue that may hold the fatty globules together (this can divert catheter direction or obstruct flow of LA)
What is the pressure in the Epidural Space?
Slightly negative pressure: -1 to -7 cmH2O (except in the sacral area)
What is the widest and narrowest part of the Epidural Space?
-Widest: L2 (5-6 mm)
-Narrowest: C5 (1-1.5 mm)
Where is the Subarachnoid Space (Intrathecal Space) located?
Between the Pia Mater and the Arachnoid Mater
Where is CSF produced?
Choroid Plexus in the ventricles in the brain (2 lateral ventricles & 3rd ventricle)
Where does CSF get absorbed?
Arachnoid Villi
How much CSF is produced per day?
21 mL/hour or 500 mL/day
-150 mL present at any given time, with 30-80 mL of that in the spinal subarachnoid space
What is the specific gravity of CSF?
1.003 - 1.009
-Isobaric
-Contains trace amounts of glucose and protein
