Spinal Cord: Structure, Pathways, Function, Injury

Posterior Column Syndrome - Friedrich's Ataxia

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~Anterior spinal artery syndrome - supplies ant. 2/3 of spinal cord ~abrupt onset ~ bilateral loss of pain and temp due to anoxic anterior commissure ~complete flaccid paralysis from damaged ventral horn LMN's at the injury (if at lower T's or upper C's --> flaccid paralysis in hands) ~really big one, MAYBE: lateral corticospinal tracts below the injury ~ maintained 2 point discriminative touch, vibration, proprio

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~Tabes Dorsalis - Tertiary Syphillis ~ Loss of 2 point discriminative touch, vibration, proprio

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Hemisection, Brown-Sequard Syndrome: Alternating signs ~ Ipsilateral UMN symptoms below the lesion (hyperreflexia) ~ Ipsilateral loss of 2 point discrimination, vibration, proprio ~ Contralateral loss of pain and temp 2 spinal segments below the lesion ~ Dont forget about the LMN tho in the ventral horn .. some hypotonia and areflexia ~ Rare, but highly tested. can happen from a stab wound that only gets half of the spinal segment

? Describe the symptoms

Syringomyelic syndrome --> usually affects cervical spinal cord segments ~ bilateral loss of pain and temp bc the anterior commissure is out. If only in one part of the cord --> cape and glove effect from loss in a few dermatomes ~ spreads ventral --> LMN deficits (weakness, wasting, fasiculations, atrophy, flaccid paralysis, hyporeflexia) ~spread far enough from the center --> lateral cortico-spinal tracts hits the medial UE 1st

? Describe the symptoms

~ Complete transection ~ early spinal shock produces areflexia ~muscle fasiculations and wasting (LMN) AT THE INJURY SITE, below LMN are fine (knee-jerk reflex) ~ bilateral paralysis below the level of transection - motor loss ~ loss of all GSA's (2 point discriminative touch, vibration, proprio, pain, temp) below level of transection ~ after weeks/months --> spasticity & hyper-reflexia (UMN)

? Describe the symptoms

~ Pain, temp, crude touch information on Aδ/C GSA fibers enter the dorsal aspect of the spinal segment at the lateral root entry zone --> travel rostrally for 2 segments through Lissauer's tract--> synapse on their secondary neuron on rexed laminae II/substantia gelatinosa (or I or V) of the dorsal horn --> crosses anterior white commissure --> joins the anterolateral system --> stays anterolateral the whole way to the VPL nucleus of the thalamus. synapses on the VPL nucleus and another neuron goes to the somatosensory cortex. There is a little bit of medial projection next to the VPL to allow for pain modulation to descend

Describe the Anterolateral system (spinothalamics) of the spinal cord

~ Upper motor neurons start in the cortex motor strip in the frontal lobe pre central sulcus--> travel caudally through internal capsule --> crus cerebri/cerebral peduncles of the midbrain --> through the pons ventrally (through the horizontal bulbus pons fibers) --> makes up the ventral medulla pyramids --> decusses at the pyramidal, motor decussation at the cervico-medullary junction --> becomes the lateral corticospinal tract --> proceeds caudally until it finds its LMN

Describe the Corticospinal-Pyramidal System (lateral corticospinal tract) of the spinal cord

2 point discriminative touch, vibration, proprioception travel on GSA fibers ( Aβ & Aα) --> say hello to their cell body in the DRG --> enter dorsal horn at the medial root entry zone-> bifurcate --> 1 (reflex via GSE's/LMN's) --> 1 travels rostrally through the dorsal columns (gracile or cuneate fasiculi)--> reaches lower.caudal medulla where the cuneate and gracile NUCLEI are --> synapse on secondary neuron in the cuneate nucleus --> info cross in a sensory decussation/internal arcuate fibers --> becomes the medial lemniscus pathway --> travels throughout the brainstem laterally towards the VPL nucleus of the thalamus on the contralateral side --> synapses on the VPL nucleus and another neuron goes to the somatosensory cortex

Describe the Dorsal Column Medial Lemniscus System (gracile-cuneate fasciculi) of the spinal cord

~ it stains the axons, so they are black, and all nuclei is unstaind/white

Describe the Wiegert stain

Golgi tendon organ measures tension. It lies near the junction of a tendon with a muscle. The reflex says that once you get too much tension, the muscle or attachment to the tendon will pop, so it lets go --> a "an inverse myotatic reflex --> only goes through an inhibition. 1b afferents activate an inhibitory motor neuron --> muscle relaxation

Describe the autogenic inhibition/inverse myotatic proprioceptive reflex

their cell body is in the ventral horn, they are heavily myelinated, they go to a SKM

Describe the course of GSE's/LMN's once they leave the spinal cord

~ their cell body is in the IMLCC, they leave the spinal nerve at the white communicating ramus where it meets its secondary neuron that heads out to autonomic territory

Describe the course of GVE's once they leave the spinal cord

travels towards the dorsal horn, says hello so its cell body in the DRG, enters the dorsal horn and bifurcates. 1 --> synapse on a GSE LMN for a reflex. 1 ---> ascends rostrally to the brain in the dorsal column medial lemniscus system

Describe the course of the exteroceptive (Aβ) and proprioceptive (Aα) GSA fibers on their way to the spinal cord.

Aδ/C fibers travel towards the dorsal horn, say hello to their cell body in the DRG, enter the dorsal horn, they travel rostrally for 2 segments, they synapse on a secondary neuron in the rexed lamenae II of the dorsal horn, crosses the anterior commissure to join the anterolateral system and ascend with the pan and temp info.

Describe the course of the nociceptive and thermal ending GSA fibers

~posterior spinal arteries come off of each PICA (posterior inferior cerebellar artery) or each vertebral artery. ~posterior spinal arteries supply the dorsal columns (cuneate and gracile fasiculi + nuclei) and dorsal horn

Describe the dorsal spinal cord blood supply

Flexor (withdrawal) reflex: ~ nociceptive receptors detect stimulus ~ involves Aδ/C GSA's of pain and temp --> synapses on inhibitory interneuron controlling the leg extensor/quadriceps femora (dont want to put more pressure on it) and excitatory interneurons controlling the flexors of the thigh and calf to pull away Crossed extension reflex: ~ Aδ/C GSA's of pain and temp cross the ant white commissure --> flexor inhibition and extensor excitement on contralateral leg

Describe the flexor and crossed extension reflex

~Aβ & Aα - heavily myelianted. Aα is faster ~Aδ - lightly myelianted --> slowly conducting ~ C - almost never myelinated

Describe the myelination differences within the GSA's

~ Starts in the medial brainstem (in pontine and medullary reticular formation) --> excitatorily synapses on upper limb extensors GSE's/LMN's in the ventral horn of the spinal cord. Overdrive of this tract? Locked out arms. Impt in respiration, bowel, and bladder

Describe the reticulospinal tract

~ UMN that starts in red nucleus in the gray matter of the midbrain at the level of the superior colliculus --> decusses immediately --> heads caudally next to lateral cortico-spinal tracts --> excitatorily synapses on upper limb flexors/biceps GSE's/LMN's in the ventral horn of the spinal cord. Overdrive of this tract? Locked in the curled arms position

Describe the rubrospinal tract

~ muscle spindles/stretch receptors detect stretch/length, the signal travels through 1a fibers to the dorsal horn, (bifurcation), synapses on an excitatory neuron that controls the extensor and synapses on an inhibitory inter-neuron to inhibit the flexor muscle

Describe the stretch (knee jerk) proprioceptive reflex

~peripheral nerve lesion ~Motor deficits: Paralysis/weakness in the muscle - loss of GSE. ~No GSA: Numbness - no (Aβ —> 2 point discrimination, touch, vibration,) (Aα —> proprioception), (Aδ —> pain or temp)

Describe the symptoms of Lesion 1

~lesion of the dorsal root no paralysis/weakness, but all sensory lost: Numbness - no (Aβ —> 2 point discrimination, touch, vibration,) (Aα —> proprioception), (Aδ/c —> pain or temp)

Describe the symptoms of Lesion 2

~ lesion of the ventral root GSE loss + maintained GSA. Flaccid paralysis --> LMN issue

Describe the symptoms of Lesion 3

~ lesion of LMN in the ventral horn --> hyporeflexia ~ pain and temp, proprioception, 2 pt discrim touch + vibraiton = fine ~ When you do a reflex exam, will they know that you hit them? Yes, the proprioception GSA's came into the dorsal horn, bifurcated, 1 went to the brain via the dorsal columns, but the one that is affected is the one that participates in the mono-synaptic reflex. What about pain and temp? Still functional, the red splotch is below area V of the rexed lamellae —> they should be able ascend just fine and then cross.

Describe the symptoms of Lesion 4

~ 1st of all, these are LMN's waiting to be stimulated by UMN's ~from medial to lateral: trunk, shoulder, arm, forearm, hand ~from ventral to dorsal: extensor --> flexor

Describe the topographical organization of laminae #IX

~ Aorta --> subclavian --> vertebral. ~Both vertebral arteries join at the medulla-pons junction to form the basilar artery which continues rostrally, ventral to the pons. ~Just before merging to form the basilar artery, a branch comes off of each vertebral artery to form the anterior spinal artery (ASA), which heads caudally through the anterior median fissure of the ventral spinal cord. ~ASA supplies much of the ventral horn and ventral dorsal horn, and the lateral corticospinal tract

Describe the ventral spinal cord blood supply

UMN's getting info from vestibular system —> mostly handling head, neck, postural movements. Vestibular system is telling you where everything is in space, so it connects to these tracts for response. UMN control of extensors for posture, balance, involuntary. TRUNK

Describe the vestibulospinal tract

This is the Nissl stain which stains cell bodies - the cell bodies are dark and the axons are unstained

Describe this staining

originate in the ventral horn

LMN's of the spinal cord?

~ 1st affects the legs because they are lateral Starts to press in further? then begin to see arm signs

Lateral mass on the ATL system of the spinal cord?

Loss of bilateral 2 point discriminative touch, vibration, proprioception of everywhere under the lesion

Lesion A?

~ Cervical ~Left UMN symptoms - corticospinals

Lesion B?

~ left sided UMN signs (spastic paralysis, hyper-reflexia after a week or two)

Lesion B?

~ Syringomyelia ~ Lack of pin prick sensation around the ring and index fingers in both hands ~2/5 weakness in both arms

Lesion C?

this is a thoracic segment! ~ Loss of proprioception in the right leg only - dorsal columns ~ increased reflexes on the right side- corticospinals

Lesion E?

~loss of right sided/contralateral pin prick

Lesion E?

~ alpha and gamma motor neurons of rexed laminae IX of the ventral horn, includes the axons in spinal or peripheral nerves

Lower motor neuron lesions involve?

all have significant behavioral responsibilities, especially clinically: ~ rubrospinal tract ~vestibulospinal tract ~ reticulospinal tract

Name real quick the other motor pathways of the spinal cord other than lateral corticospinal

~ Spinal trigeminal nucleus

Name the continuation of rexed lamninae II/substantia gelatinosa from the spinal cord into the brain stem

~ ascending sensory: dorsal column medial lemniscus, anterolateral system/spinothalamic tract ~ descending motor: - Lateral: cortico-spinal tract, rubrospinal tract - Medial: vestibulospinal tracts, reticulospinal tracts

Name the major ascending and descending pathways

1. Dorsal Column Medial Lemniscus System (gracile-cuneate fasciculi) 2. Anterolateral system (spinothalamics) 3. Corticospinal-pyramidal system (Lateral cortico-spinal tracts)

Name the major pathways of the spinal cord

the portion of the GSA bifurcation that stays local ~ stretch (knee jerk) reflex ~ autogenic inhibition

Name the proprioception reflexes

~ (Aβ) 2 point discrimination, vibration exteroceptive endings ~ (Aα/1a, 1b)) - proprioceptive endings muscle spindles/stretch receptors, golgi tendon displacement ~ Nociceptive and thermal endings exteroceptive endings (Aδ/C) - pain and temp

Name the types of GSA fibers and the information they carry to the spinal cord

~ somatosensory cortex ~ just posterior

The destination of the anterolateral and dorsal column medial lemniscus pathway, ___________, where is it located in regards to the central sulcus?

lower motor neurons, they're located in the ventral horn. this is where motor output occurs

The higher number laminae (spinal cord nuclei) contain _______________.

Lateral to medial: leg, trunk, arm

Topographic map of when the lateral cortico-spinal tracts cross the crus cerebri?

~ descending pathways and cells of origin ~ Green dot UMN lesion of the lateral cortical spinal tract in the spinal cord

Upper motor neuron lesions involve?

There's a little bit of input by the Aβ's (exteroceptive GSA's) —> stimulate the activity of inhibitory inter-neruons on the C fibers. THIS Y WE RUB WHEN WE HIT SOMETHING TO REDUCE PAIN ********** pattern, not labelled line

What are Aβ fibers doing in the Rexed laminae II? (Dr. Whim's lecture)

a bundle of nerve fibers enclosed in a sheath of connective tissue, or forming one of the main tracts of white matter in the spinal cord.

What are funiculi?

The center of the cord to be able to cross.

What does the crossed extension reflex test probe?

~ GSE/LMN's - motor to skeletal muscle. cell body is in the ventral horn ~ GVE - controls viscera for lower cervical and thoracic (C8/T1-L1) , cell body is in the IMLCC

What functional components of the spinal cord lead out of the ventral horn/IMLCC?

~ GSA (2 pt discriminative touch, vibration, proprioception, pain and temp) ~GVA (visceral sensation) ~ they all say hello to their cell bodies in the dorsal root ganglion

What functional components of the spinal cord lead to the dorsal horn?

hereditary chiari malformation - causes a big cyst/fluid in the spinal cord

What is notable in causing syringomyelia?

~ bone. it is like blinding

What is notable on a CT?

~ this is the thoracic spinal segment ~ IMLCC's (from T1-L2) ~ Dorsal thoracic nuclei of clarke/posterior thoracic nucleus (relevant to prop. to the cerebellum in block 2) --> cell bodies of this nucleus send their axons to form the ipsilateral posterior spinocerebellar tract

What is notably here in this level of the spinal cord?

rexed laminae I, II, V Aδ - I, II, V C - I, II

What spinal cord nuclei do Aδ/C fibers target?

Ipsilateral - it doesnt cross until the brainstem. It precedes the cross

Where does a Dorsal Column Medial Lemniscus System (gracile-cuneate fasciculi) deficit of the spinal cord present?

~ipsilaterally - it has ALREADY crossed in the caudal medulla ~hemiplegia (paralysis) below the lesion --> all the lower motor neurons are left un-innervated --> hyperreflexia

Where does a Lateral Cortco-spinal tract deficit of the spinal cord present? How does the lesion present?

~ Contralateral ~ Lesions of the anterolateral tract produce a contralateral deficit in pain and temperature sensation 2 segments below. The reason is because this tract is carrying contralateral information, so if it is affected, the side of the body that its carrying information for is affected, not where its currently at/.

Where does an Anterolateral system (spinothalamics) of the spinal cord deficit of the spinal cord present?

~arm - lateral cortico-spinal tract --> voluntary ~ axial/trunk - reticulo and vestibulospinal --> involuntary

Where does the rexed laminae IX get its UMN's from?

~between pia and arachnoid mater. CSF flows through here ~from outer to inner it goes: DAP

Where is the subarachnoid space?

Cervical spinal cord ~ Cuneate fasiculi have been wedged in laterally --> above T6

Where is this? Explain

Lumbar region - gracile fasiculus is bigger than it was in the sacral region, dorsal horns are skinnier

Where is this? Explain

Sacral region - all cell bodies, pair of gracile fasiculli visible dorsally (it's tiny bc there isn't a lot of ascending info yet --> stained black bc its axons). substantia gelatinosa and ventral horns are huge. lots of input and output, but not alot of info passing by in the fasiculi yet

Where is this? Explain

Thoracic region - horns are tiny. mostly ascending and descending info going by in the white matter. little input and output in the thoracic regions --> lots of info in the fasiculi. mostly visceral info, this is why you see the IMLCC's appear. ~ dorsal nucleus of Clarke (rexed laminae VII of dorsal horn) --> ipsilateral posterior spinocerebellar tract

Where is this? Explain

~ cervico-medullary junction ~ starting to lose spinal cord definitions. substania gelatinosa is becoming the spinal trigeminal nucleus

Where is this? Explain

~ 1,3,4

Which of these lesions are lower motor neuron lesions?

~gray matter - ventral and dorsal horns, represents cell bodies ~white matter - everything else, represents myelinated axons

White matter vs. gray matter on the spinal cord

Cape effect of Syringomyelia

Who dis?

Complete cervical transection

Who dis?

Complete cervical transection Blue - 2 pt discrim, vibration, proprio loss Green - pain and temp loss Red - motor loss

Who dis?

Hemisection of Thoracic Spinal Cord - Brown Sequard

Who dis?

Hemisection of Thoracic Spinal Cord - Brown Sequard. Blue - 2 pt discrim, vibration, proprio loss Green - pain and temp loss Red - motor loss

Who dis?

Syringomyelia

Who dis?

~ ipsilaterally (info crosses in the brainstem) ~contralaterally (info crosses in the cord)

Within the spinal cord, the dorsal medial column info travels rostrally ________, but the anterolateral system info travels __________

~ Anatomical : ventral horns are down and the dorsal horns are up ~ Clinical: feet towards you. Ventral is at the top and dorsal is at the bottom

Anatomical versus Clinical orientation?

~A-alpha fiber from the proprioceptive stretch receptor bifurcates and sends input *within* the spinal segment to the lower motor neurons as part of the stretch reflex. So, while its axon headed rostral was transected, its local 'return' input to the dorsal horn in the L3 segment is working just fine. So, this reflex will be hyperreflexive. ~The L3 three segment is below the injury. Only things at the injury or passing through the injury are affected. Segments below still have local segmental circuitry. They're hyperreflexive because the UMNs aren't connected anymore to limit the reflex (or to move the joint voluntarily).

How does cervical transection cause hyper-reflexia in the knee jerk reflex ?

~ through spinal reflexes

How to probe the level and location of a spinal cord injury?

~ sensory ~ motor ~ reflex ~ integrative

Just state real quick the functions of the spinal cord

~Spintothalamic ~ Spinoreticular

Notable fibers of the anterolateral system?

~Below T6 - pair of fasiculus gracilis ~above T6 - additional of lateral pair of fasiculus cuneatus = 2 pairs = 4 dorsal columns for the dorsal column medial lemniscus pathway

Somato-topic arrangement in the dorsal columns?

Input from the Aδ/C fibers into laminae I, II, V of the dorsal horn. A.K.A Rexed laminae - numbered throughout the grey matter ~ Posteromarginal nucleus --> I ~. Substantia Gelatinosa II - continues as the spinal trigeminal nucleus in the brainstem ~Nucleus Proprius (III-V) ~ Dorsal nu. or Clarke (VII) ~ IMLCC (VII) - GVE preganglionic sympathetic neurons at T1-L2 ~ Medial and lateral motor nulcei/LMN's - Ventral horn! (IX)

Spinal Cord Nuclei?

~ Cervical - sideways oval ~ Thoracic - super skinny dorsal horns ~Lumbar - The most "normal" ~Sacral really chunky ventral and dorsal horns

Spinal cord segment shapes at the different levels:

~ flaccid paralysis ~ hypotonia ~ areflexia ~ muscle wasting ( no stimulation of the muscle by the UMN) ~ muscle fasiculations, fibrillations

State the lower motor neuron signs (brainstem and spinal cord)

~loss of inhibitory modulation of motor pathways ~ Spastic paralysis of affected muscles (unable to move limb, but it is in a weird position - running ungoverned by the upper motor neuron) ~ Hyper-reflexia after initial arreflexia (ungoverned by UMN) ~ Hypertonia/stiffness ~ Babinksi sign (inverted plantar reflex, dorsiflexion of great toe) ~ Spasticity (when you move it fast, there will be resistance/quick locking --> clasped knife release)

State the upper motor neuron signs/pyramidal tract signs

T2 - CSF is white T1 - CSF is dark/black

T2 vs T1 MRI?