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The Spinal Cord

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1/2/2016 The Spinal Cord • Continuation of CNS inferior to foramen magnum The Nervous System – Simpler than the brain – Conducts impulses to and from brain • Two way conduction pathway Spinal Cord – Reflex actions The Spinal Cord CCeerrvviiccaallCervical CCeerrvviiccaallCervical spinal nerves • Passes through vertebral canal enlargement – Foramen magnum L2 DDuurraaDura aannddand (a) The spinal cord and its nerve arachnoid roots, with the bony vertebral TThhoorraacciiccThoracic – Conus medullaris = tapered end of the cord mmaatteerrmater arches removed. The dura mater spinal nerves and arachnoid mater are cut – LLuummbbaarrLumbar Filum terminale = anchors the cord open and reflected laterally. enlargement – Cauda equina = bundle of lower spinal nerves CCoonnuussConus medullaris LLuummbbaarrLumbar CCaauuddaaCauda spinal nerves eeqquuiinnaaequina FFiilluummFilum terminale SSaaccrraallSacral spinal nerves The Spinal Cord CCeerrvviiccaallCervical CCeerrvviiccaallCervical spinal nerves • Spinal nerves enlargement – 31 pairs DDuurraaDura aannddand arachnoid TThhoorraacciiccThoracic mmaatteerrmater • Cervical and lumbar enlargements spinal nerves – Nerves serving the upper & lower limbs emerge LLuummbbaarrLumbar enlargement here CCoonnuussConus medullaris LLuummbbaarrLumbar CCaauuddaaCauda spinal nerves eeqquuiinnaaequina FFiilluummFilum (a) The spinal cord and its nerve terminale SSaaccrraallSacral roots, with the bony vertebral spinal nerves arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Figure 12.29a 1 1/2/2016 T The Spinal Cord TT121212 Ligamentum flavumflavumflavum L • LL555 Lumbar puncture Protection needle entering subarachnoid – Bone spacespacespace LLL – Meninges 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 • Epidural space Pia mater Cross section (contains fat) Arachnoid Spinal mater SpinalSpinal – Subdural space meninges Central gray matter Dura mater Subarachnoid – Cortex of white matter 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 sulcus GrayGrayGray The Spinal Cord commissure Dorsal funiculus Dorsal horn WhiteWhiteWhite Ventral funiculus GrayGrayGray columns Ventral horn matter • Gray matter columns Lateral funiculus mattermatter Lateral horn – Dorsal root Site of interneurons & motor neuron cell body synapses ganglionganglionganglion – All neuron cell bodies in spinal gray matter are multipolar Spinal nerve Central canal – 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 2 1/2/2016 Dorsal root (sensory) The Spinal Cord Dorsal root ganglion 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 neurons) SomaticSomaticSomatic (motor) 1. Dorsal (posterior) motor neuron 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 axons 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) spinothalamic tract – Skeletal Origin = spinal cord muscle – Termination = thalamus – Location = anterior funiculus – 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) 3 1/2/2016 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 • Synapse 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 Rubrospinal tract – Fine touch, proprioception, vibration Ventral • Spinothalamic pathways spinocerebellar Medial tract reticulospinal – Crude touch, temperature, pain Lateral tract spinothalamic tract Ventral corticospinal Ventral (anterior) tract spinothalamic Vestibulospinal tract Tectospinal tract tract Figure 12.33 4 1/2/2016 Lateral Primary spinothalamic somatosensory tract (axons of second-order cortex neurons) Axons of third-order Medulla oblongata neurons Thalamus Pain receptors Cerebrum Midbrain Cervical spinal cord Axons of first-order neurons Temperature Lumbar spinal cord receptors Cerebellum Pons (b) Spinothalamic pathway (b) Spinothalamic pathway Figure 12.34b (1 of 2) Figure 12.34b (2 of 2) Dorsal Medial lemniscus (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 (axon of first-order sensory neuron) Cerebrum Joint stretch receptor Midbrain Axon of (proprioceptor) first-order Cervical spinal cord neuron Fasciculus gracilis Muscle spindle (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 Pyramidal Tracts – Deliver efferent impulses from the brain to the From primary motor cortex to cord spinal cord (and from there to an effector muscle or 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) 5 1/2/2016 Pyramidal cells Ventral (upper motor Primary motor cortex corticospinal neurons) tract Medulla oblongata Internal capsule 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 Extrapyramidal (indirect) tracts Various CNS regions (avoiding pyramids) to cord Cerebrum Impulses regarding unconscious motor control Posture and balance Red nucleus 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) 6.
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