Ivana Pavlinac Dodig, M.D., Ph.D.

1. Organization of the CNS2. Spinal cord3. Pathways of the spinal cord1. Long ascending tracts2. Long descending tracts

4. Spinal cord in cross sections

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Grey Matter = Cell Body

White Matter = Myelinated axon

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CortexNucleus (CNS)Ganglion (PNS); exception: Basal Ganglia

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Nerve (PNS)Tract (CNS)Fasciculus/Funiculus = group of fibers with common origin and destinationLemniscus = ribbon‐like fiber tractPeduncle = massive group of fibers (usually several tracts)

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Tracts are named with origin first, then destinationCorticobulbar tractCorticospinal tractSpinocerebellar tractMammilothalamic tract

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Spinal cord is SMALL!40‐45 cm long1 cmwide at widest pointDoes not extend all the way to the bottom of the spinal columnFrom foramenmagnum to  intervertebral disc (L1‐L2); continues as filum terminale (to sacral canal)

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Parscervicalis

Parsthoracica

Parslumbalis

Conus medullaris& filum terminale

Upper 2/3 of thevertebral column

Pattern of grey/white matter is reversed in the cordWhite matter tracts on outsideGrey matter on the insideStaining reverses this!!!

White matter (tracts of axons)

Grey matter(cell bodies)

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White matter ‐ funiculi:Dorsal (posterior)LateralVentral (anterior)

Gray matter – buterfly shaped – horns:AnteriorPosteriorIntermediolateral cell column (IML)

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Posterior (dorsal) hornIntermediate greyAnterior (ventral) horn

Laminar organisationRexed laminae

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Spinal cord is segmented anatomicallyInput and output occurs in groups of rootlets arranged in a series longitudinally along the cord

Dorsal rootlets = Input (carry sensory information)Ventral rootlets =Output (motor neurons)

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Dorsal and ventral roots

Common spinal nerve trunk (1‐2 mm)

Dorsal and ventral ramus

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31 pair of spinal nerves8 cervical (C1 ‐C8)12 Thoracic (T1 ‐T12)5 Lumbar (L1 ‐ L5)5 Sacral (S1 ‐ S5)1 Coccygeal

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The spinal cord is housed within the vertebral columnEach cord segment has a corresponding vertebra of the same name (e.g., C3)Spinal nerves enter/exit underneath their corresponding vertebral segment

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But wait! Something doesn’t add up!How can spinal nerves exit below their corresponding vertebral segment if the cord is only 40cm‐45cm long?Answer: Spinal nerves extend down to the appropriate vertebral segment forming the caudaequina

This means cord segments and vertebral segments don’t line up

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Each set of rootlets forms a spinal nerve that innervates a corresponding segment of 

the body

Area of the skin supplied by theright and left dorsal roots of a single spinal segment.

Overlapping areas!

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Cord is not of uniform thickness throughout its length. Why not?

Answer: Segments of the cord innervate parts of the body that differ in complexityThere are fewer white matter tracts lower in the cord. 

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2 enlargements:▪ Cervical (C5‐T1)▪ Lumbar (L1‐S2)

o C1‐C4 = plexus cervicaliso C5‐T1 = plexus brachialiso L1‐L4 = plexus lumbaliso L4‐S2 = plexus sacralis

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Cervical enlargementC5 - T1

Lumbar enlargementL1 – S2

Association

Projection 

Commissural

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Exteroceptive (from surface): touch, vibration, pain, temperature, localization

Proprioceptive (deep, protopathic): locomotorsystem (periost, tendon and muscle spindles, joints); mostly nonconscious!

Interoceptive: from visceral system; mostlynonconscious! Base for proper function of theautonomic reflexes, homeostasis, neuroendocrinesystem

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Tractus spinothalamicus

Tractus spinocerebelaris

Fasciculus gracilis and cuneatus

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1. Direct pathway (pain, temperature, simple tactilesensations)▪ Neospinothalamic tract

2. Indirect pathways (affective, autonomic, endocrine, motor, and arousal components of pain, and simple tactile sensations)▪ Paleospinothalamic▪ Spinoreticular▪ Spinomesencephalic tracts

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Dorsal rootganglion

Dorsal rootDorsal horn (nucleus

proprius)

Lateral whitecolumn

Neuron I Neuron II

Tractusneospinothalamicus

Ventralposterolateral

nucleus of thalamus

Neuron III

Capsula internaPostcentral

gyrus (area 3,1,2)

Receptors in skin

Anterior whitecommissure

Neurons located in the dorsal horn and intermediate gray matterAscend contralaterally and ipsilaterallySynapses in reticular formationProject in midline and intralaminar thalamicnuclei – diffuse projections to the cortex and limbic regions (cingulate gyrus)

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Neurons located in the dorsal horn and intermediate gray matterAscend contralaterally and ipsilaterallySynapses in medullary and pontine reticularformationProject in midline and intralaminar thalamicnuclei – diffuse projections to the cerebralcortex

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Neurons located in the dorsal horn and intermediate gray matterAscend to themidbrain (PAG)Descending projections to the spinal cord toinhibit pain sensations

Transmission to the amygdala viaparabrachial nuclei?

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Neospinothalamic tract

Neospinothalamic tract – anesthesia, thermoanesthesia, loss of simple tactile sensations

Neospinothalamic tract – somatotopic organization

Sacral sparing – damage to the neospinothalamictract leaves intact the pain, temperature, and simple tactile sensations in sacral dermatomes(lesion in the gray matter first affects thoracic and cervical fibers due to somatotopic organization of neospinothalamic tract)

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Tactile sense: vibration, deep touch, two‐point discriminationKinesthetic sense: position and movement

Sacral and lumbar part = medial  fasciculus gracilis (Goll’s fascicle)

Toracal and cervical part = lateral  fasciculus cuneatus (Burdach’s 

fascicle)

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Dorsal rootganglion

Dorsal root Dorsal horn

Ipsilateraldorsal columns

Neuron I Neuron II

Fasciculusgracilis and cuneatus

Nucl. gracilisand cuneatus

Neuron III

Postcentralgyrus (area

3,1,2)

Receptors in dermis; 

proprioceptors

Mediallemniscus

Ventral posterolateralnucleus of thalamus

Capsulainterna

Dorsal (posterior) columns

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Tractus spinocerebellaris anterior – informationabout whole limb movement and posturaladjustments (lower limb)

Tractus spinocerebellaris rostralis – upper limb

Tractus spinocerebellaris posterior – status of individual muscles and groups of muscles + tractus cuneocerebellaris

All enter cerebellum ipsilaterally!!!33

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Dorsal rootganglion

Dorsal root Dorsal horn

Lateralfuniculus

Neuron I Neuron II

Tractusspinocerebellaris

anterior

Superior cerebellarpeduncle

Cerebellum(anterior lobe)

Receptors in tendons

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Dorsal rootganglion

Dorsal root Dorsal horn

Lateralfuniculus

Neuron I Neuron II

Tractusspinocerebellaris

rostralis

Inferior cerebellarpeduncle

Cerebellum(anterior lobe)

Receptors in tendons

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Dorsal rootganglion

Dorsal rootDorsal horn

(nucl. dorsalis of Clarke)

Lateralfuniculus

Neuron I Neuron II

Tractusspinocerebellaris

posterior

Inferior cerebellar peduncle(restiform body)

Cerebellum(anterior lobe)

Receptors in joints, tendonsand muscles

Nonconscious proprioception of upper limb

Rostral to C8 (no nucl. dors. of Clarke)

Ipsilaterally in the fasciculus cuneatus 

Neuron II = accessory cuneate nucleus

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Tractusneospinothalamicus

Tractusspinocerebelaris

Fasciculus gracilis et cuneatus

Neuron I Dorsal root ganglion

Neuron IIDorsal horn

(nucleus proprius)

Dorsal horn(nucl. dorsalis

Clarke)

Nucl. gracilis et cuneatus

Neuron III thalamus thalamus

Function Pain and  temperatureNonconsciousproprioception

Discriminative touchand kinesthesia

Corticospinal tractRubrospinal tract

Tectospinal tractVestibulospinal tractReticulospinal tract

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Flexor motor system, fine movements of the limbs

Antigravity muscles, posture, and balance

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Homunculus – precentral gyrus Primary motor cortex

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Capsulainterna

Cruscerebri

Pyramids

Anterior horn*

Neuron I(upper

motoneuron) Tractuscorticospinalislateralis (90%)

Ventral root

Neuron II(lower

motoneuron)

Spinal nerve

Precentral gyrus(area 4)

Tractuscorticospinalisanterior (10%)

Coronaradiata

90% fibers cross at pyramidal decussation →lateral funicle (tractus corticospinalis lateralis) → apendicular muscles

10% fibers descend ipsilaterally (tractus corticospinalis anterior) and cross at lower motoneuron → axial muscles

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Lower motor neuron paralysis:

•loss of voluntary movement,

•flaccid paralysis, 

•loss of muscle tone, 

•atrophy of muscles, 

•loss of all reflexes

Upper motor neuron paralysis: 

•loss of voluntary movement, 

•spasticity, 

•increased deep tendon reflexes, 

•loss of superficial reflexes, 

•Babinski sign

monoplegia

hemiplegia

diplegia

paraplegia

quadriplegia(tetraplegia)

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Tractus corticospinalis

Neuron I(upper motoneuron)

Precentral gyrus (area 4)

Neuron II(lower motoneuron)

Spinal cord: anterior horn

*Plexus brachialis: C5-Th1Plexus lumbosacralis: L1-S5

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Reflex arc – spinal segment: Aferent neuronInterneuron = Renshaw’s cellEferent neuronEfector (muscle)

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Motor response to afferent stimulation

Automatic reactions – fast response to pain and noxious stimuli

Tractus rubrospinalis Tractus tectospinalis Tractus vestibulospinalis (medialis and lateralis)Tractus reticulospinalis Fasciculus longitudinalis medialis

Fasciculi proprii – intrinsic reflex mechanisms of the spinal cord

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Nucleusruber

Interneurons

Ventral horn

Ventral tegmentaldecussation

Inferior olive

Sensorimotorcortex

• Facilitation of flexor motor neurons• Inhibition of extensor motor neurons

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Upper cervicalsegments

Colliculussuperior

• Aid in directing head movements in response to auditory and visual stimuli

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InterneuronsMotor neurons

Extensormuscles

Vestibularapparatus

Nucl. vestibularislateralis

Cerebellum

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• Facilitation of ipsilateral extensor muscles• Maintaining upright posture and balance

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• Adjustment of head position in response to changes in posture (i.e. while walking)

Ventral hornNucl. vestibularis

medialis

Motor functionsMedullary (lateral) reticulospinal tract – supressesextensor spinal reflexesPontine (medial) reticulospinal tract – facilitatesextensor spinal reflexes

Autonomic functions (ventrolateral medulla – IML of thoracolumbar cord)Modulation of pain (enkephalinergic)

Midbrain PAG → nucl. raphe magnus→ dorsal horninterneurons→ spinothalamic system

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MLFIpsilateral upper cervical

motor neurons

Colliculussuperior

Nucl. vestibularismedialis

Reticularformation

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• Mainly ascending fibers!!!• Head position control in response to excitation by the labyrinth

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Anterior median fissure

Anterior white commisure

Posterior median sulcus

Posterior intermediate sulcus

Tract ofLissauer

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Segments of the spinal cord have a similar organization, but vary in appearance. Always know where you are in the cord (i.e., cervical, thoracic, lumbar, sacral) 

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Cervical cord is wide, flat, almost oval in appearance. 

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Cervical

Cervical Enlargement

What’s different about the cervical enlargement?

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Less white matter than cervicalRounder appearanceLess prominent ventral horns than cervical enlargement

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Less white matter than thoracicRounder appearanceLarger ventral horns, especially in lumbar enlargement

Lumbar

Lumbar Enlargement

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Not much white matterMostly grey, although not much of that either

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IML = T1‐L2

Clarke’s nucleus = C8‐L3

Fasciculus cuneatus = above T6

Corticospinal tractVoluntary movement

Dorsal columnsDiscriminative touchConscious proprioception

Spinocerebellar tract (dorsal and ventral)Unconscious proprioception

Spinothalamic tractPain/temperature

Corticospinal tracts

Dorsal Columns

Spinothalamic tracts

Spinocerebellar tracts

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