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Home , Anterior funiculus, Arachnoid mater, Cauda equina, Conus medullaris, Dura mater, Filum terminale

1/2/2016

The

• Continuation of CNS inferior to foramen magnum The – Simpler than the – Conducts impulses to and from brain • Two way conduction pathway Spinal Cord – Reflex actions

The Spinal Cord CervicalCervicalCervical CervicalCervicalCervical spinal • Passes through vertebral canal enlargement

– Foramen magnum ‰ L2 Dura andDuraand (a) The spinal cord and its arachnoid roots, with the bony vertebral ThoracicThoracicThoracic – = tapered end of the cord matermatermater arches removed. The spinal nerves and are cut – LumbarLumbarLumbar = anchors the cord open and reflected laterally. enlargement – = bundle of lower spinal nerves ConusConusConus medullaris LumbarLumbarLumbar CaudaCaudaCauda spinal nerves equinaequinaequina FilumFilumFilum terminale SacralSacralSacral spinal nerves

The Spinal Cord CervicalCervicalCervical CervicalCervicalCervical spinal nerves • Spinal nerves enlargement

– 31 pairs Dura andDuraand arachnoid ThoracicThoracicThoracic matermatermater • Cervical and lumbar enlargements spinal nerves – Nerves serving the upper & lower limbs emerge LumbarLumbarLumbar enlargement here ConusConusConus medullaris LumbarLumbarLumbar CaudaCaudaCauda spinal nerves equinaequinaequina FilumFilumFilum (a) The spinal cord and its nerve terminale SacralSacralSacral roots, with the bony vertebral spinal nerves arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.

Figure 12.29a

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T The Spinal Cord TT121212 Ligamentum flavumflavumflavum L • LL555 Protection needle entering subarachnoid – Bone spacespacespace LLL – 444 – CSF SupraSupraSupra-Supra --- spinousspinousspinous • Spinal tap-inferior to L2 vertebra ligament

LLL555 FilumFilumFilum terminale

SSS111 InterInterInter-Inter --- Cauda equina vertebral Arachnoid DuraDuraDura in subarachnoid discdiscdisc mattermattermatter matermatermater spacespacespace

Figure 12.30

The Spinal Cord

• Cross section (contains fat) Arachnoid Spinal mater SpinalSpinal – meninges Central gray matter Dura mater Subarachnoid – Cortex of spacespacespace Bone ofBoneof (contains CSF) vertebravertebravertebra

Dorsal root ganglionganglionganglion BodyBodyBody of vertebra

(a) Cross section of spinal cord and vertebra

Figure 12.31a

Dorsal median GrayGrayGray The Spinal Cord commissure Dorsal Dorsal horn WhiteWhiteWhite Ventral funiculus GrayGrayGray columns Ventral horn matter • Gray matter columns mattermatter Lateral horn – Dorsal root Site of & motor cell body ganglionganglionganglion – All neuron cell bodies in spinal gray matter are multipolar – Regions • Dorsal (posterior) horns Dorsal root • Ventral (anterior)horns (fans out into Ventral median dorsal rootlets) fissure • Lateral horns (only in thoracic and lumbar regions)

Ventral root (derived from several Pia mater ventral rootlets) Arachnoid mater Spinal dura mater

(b) The spinal cord and its meningeal coverings

Figure 12.31b

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Dorsal root (sensory) The Spinal Cord Dorsal root Dorsal horn (interneurons) SomaticSomaticSomatic • White matter sensorysensorysensory neuron – Myelinated ascending (sensory) & descending Visceral (motor) tracts sensory neuronneuronneuron • Also some transverse (commisural fibers) Visceral – Tracts located in 3 white columns (funiculi) on each motormotormotor Spinal nerve neuron Ventral horn side Ventral root (motor ) SomaticSomaticSomatic (motor) 1. Dorsal (posterior) 2. Lateral InterneuronsInterneurons receivingreceiving inputinput fromfrom somaticsomatic sensorysensory nneurons 3. Ventral (anterior) InterneuronsInterneurons receivingreceiving inputinput fromfrom visceralvisceral sensorysensory neurons

Visceral motor (autonomic) neurons

Somatic motor neurons Figure 12.32

Dorsal median sulcus The Spinal Cord GrayGrayGray commissure Dorsal funiculus Dorsal horn WhiteWhiteWhite Ventral funiculus GrayGrayGray columns Ventral horn matter columns Lateral funiculus mattermatter • Spinal tracts Lateral horn Dorsal root – ganglionganglionganglion Run through the funiculi – Spinal nerve Central canal Multineural pathways • Contain with similar destinations and functions Dorsal root (fans out into Ventral median – Most decussate (cross over) dorsal rootlets) fissure – Most exhibit somatotopy Ventral root (derived from several Pia mater – Pathways are paired symmetrically ventral rootlets) Arachnoid mater Spinal dura mater

(b) The spinal cord and its meningeal coverings

Figure 12.31b

Ventral corticospinal The Spinal Cord tract Medulla oblongata Pyramids • Naming of tracts Decussation of pyramid – Many are named for origin and termination Lateral corticospinal – Example Cervical spinal cord tract • Anterior (ventral) – Skeletal Origin = spinal cord muscle – Termination = – Location = – Ascending = must be sensory Lumbar spinal cord

Somatic motor neurons (lower motor neurons) (a) Pyramidal (lateral and ventral corticospinal) pathways

Figure 12.35a (2 of 2)

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The Spinal Cord The Spinal Cord

• Ascending Pathways • Ascending Pathways – Consist of two or three neurons – First-order neurons • • First order Cell bodies in ganglia (dorsal root or cranial) • Carry impulses from sensory receptors in muscle and skin • Second order to spinal cord and brain • Third order • with second-order neurons – Examples • Posterior (dorsal) column – Receptor to medulla • Spinothalamic tract – Receptor to spinal cord

The Spinal Cord The Spinal Cord

• Ascending Pathways • Ascending Pathways – Second-order neurons – Third-order neurons • Interneurons • Interneurons • Cell bodies in dorsal horn of spinal cord • Cell bodies in thalamus • Synapse with third-order neuron – Examples – Examples • Posterior (dorsal) column • Posterior (dorsal) column – Thalamus to cortex – Medulla to thalamus (decussates in medulla) • Spinothalamic tract • Spinothalamic tract – Thalamus to cortex – Spinal cord to thalamus (decussates in spinal cord)

The Spinal Cord Ascending tracts Descending tracts

Fasciculus gracilis Ventral white Dorsal • Ascending pathways Fasciculus cuneatus commissure white column Lateral – Two pathways transmit somatosensory information reticulospinal tract to the sensory cortex via the thalamus Dorsal Lateral spinocerebellar corticospinal tract • Posterior (dorsal) column tract – Fine touch, proprioception, vibration Ventral • Spinothalamic pathways spinocerebellar Medial tract reticulospinal – Crude touch, temperature, Lateral tract spinothalamic tract Ventral corticospinal Ventral (anterior) tract spinothalamic tract

Figure 12.33

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Lateral Primary spinothalamic somatosensory tract (axons of second-order cortex neurons) Axons of third-order Medulla oblongata neurons Thalamus

Pain receptors

Midbrain

Cervical spinal cord Axons of first-order neurons Temperature Lumbar spinal cord receptors

Pons

(b) Spinothalamic pathway (b) Spinothalamic pathway

Figure 12.34b (1 of 2) Figure 12.34b (2 of 2)

Dorsal Medial (tract) Primary spinocerebellar (axons of second-order neurons) somatosensory tract (axons of Nucleus gracilis second-order Nucleus cuneatus cortex neurons) Axons of third-order Medulla oblongata neurons Fasciculus cuneatus Thalamus ( of first-order )

Cerebrum

Joint stretch receptor Axon of (proprioceptor) first-order Cervical spinal cord neuron Fasciculus gracilis (axon of first-order sensory neuron) (proprioceptor) Lumbar spinal cord Cerebellum

Pons Touch receptor (a) Spinocerebellar Dorsal (posterior) (a) Spinocerebellar Dorsal (posterior) pathway column pathway column

Figure 12.34a (2 of 2) Figure 12.34a (1 of 2)

The Spinal Cord The Spinal Cord

• Descending pathways & tracts ó – Deliver efferent impulses from the brain to the ó From primary to cord spinal cord (and from there to an effector muscle or ó Involve two neurons: glad) 1. Upper motor neurons (1 st order) 1. Direct pathways = pyramidal tracts – Cortex to cord (decussate in pyramids of the medulla or in the 2. Indirect pathways (extrapyramidal) = all others cord) 2. Lower motor neurons (2 nd order) – Spinal cord to muscle – Innervate skeletal muscles (voluntary)

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Pyramidal cells Ventral (upper motor corticospinal neurons) tract Medulla oblongata Pyramids Decussation Cerebrum of pyramid Lateral corticospinal tract Cervical spinal cord

Midbrain Skeletal Cerebral muscle peduncle

Cerebellum Lumbar spinal cord

Pons Somatic motor neurons (lower motor neurons) (a) Pyramidal (lateral and ventral corticospinal) pathways (a) Pyramidal (lateral and ventral corticospinal) pathways

Figure 12.35a (1 of 2) Figure 12.35a (2 of 2)

The Spinal Cord An extrapyramidal pathway óExtrapyramidal (indirect) tracts

ó Various CNS regions (avoiding pyramids) to cord Cerebrum ó Impulses regarding unconscious motor control

ó Posture and balance

ó Involve two neurons: Midbrain 1. Upper motor neurons (1 st order) ˜ Subcortex or pons (decussate) to cord nd 2. Lower motor neurons (2 order) Cerebellum ˜ Spinal cord to muscle ˜ Innervate skeletal muscles (involuntary) Pons

(b) Rubrospinal tract

Figure 12.35b (1 of 2)

Rubrospinal tract The Spinal Cord

• Motor neuron damage Medulla oblongata – Damage to LMN • Flaccid paralysis – Nerve impulses do not reach the affected muscles – Cannot move voluntarily or involuntarily – Muscles atrophy Cervical spinal cord – Damage to UMN • Spastic paralysis – Spinal motor neurons remain intact – Reflex activity continues (involuntary movement) – No voluntary muscle control

(b) Rubrospinal tract

Figure 12.35b (2 of 2)

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