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1/2/2016

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Spinal Cord

The Nervous System

The Spinal Cord

• Continuation of CNS inferior to foramen

magnum

– Simpler than the brain

– Conducts impulses to and from brain

• Two way conduction pathway

– Reflex actions

The Spinal Cord

• Passes through vertebral canal

– Foramen magnum � L2

– Conus medullaris = tapered end of the cord

– Filum terminale = anchors the cord

– Cauda equina = bundle of lower spinal nerves

CervicalCervicalCervicalCervical

enlargementenlargementenlargementenlargement

Dura andDura andDura andDura and

arachnoidarachnoidarachnoidarachnoid

matermatermatermater

LumbarLumbarLumbarLumbar

enlargementenlargementenlargementenlargementConusConusConusConus

medullarismedullarismedullarismedullaris

CaudaCaudaCaudaCauda

equinaequinaequinaequina

FilumFilumFilumFilum

terminaleterminaleterminaleterminale


spinal nervesspinal nervesspinal nervesspinal nerves



SacralSacralSacralSacral


ThoracicThoracicThoracicThoracic


(a) The spinal cord and its nerve

roots, with the bony vertebral

arches removed. The dura mater

and arachnoid mater are cut

open and reflected laterally.

The Spinal Cord

• Spinal nerves

– 31 pairs

• Cervical and lumbar enlargements

– Nerves serving the upper & lower limbs emerge

here

Figure 12.29aFigure 12.29aFigure 12.29aFigure 12.29a


enlargementenlargementenlargementenlargement

Dura andDura andDura andDura and

arachnoidarachnoidarachnoidarachnoid

matermatermatermater


enlargementenlargementenlargementenlargementConusConusConusConus

medullarismedullarismedullarismedullaris

CaudaCaudaCaudaCauda

equinaequinaequinaequina

FilumFilumFilumFilum

terminaleterminaleterminaleterminale





SacralSacralSacralSacral


ThoracicThoracicThoracicThoracic


(a) The spinal cord and its nerve

roots, with the bony vertebral

arches removed. The dura mater

and arachnoid mater are cut

open and reflected laterally.

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The Spinal Cord

• Protection

– Bone

– Meninges

– CSF

• Spinal tap-inferior to L2 vertebra

Figure 12.30Figure 12.30Figure 12.30Figure 12.30

LigamentumLigamentumLigamentumLigamentumflavumflavumflavumflavum

SupraSupraSupraSupra----spinousspinousspinousspinousligamentligamentligamentligament

Lumbar punctureLumbar punctureLumbar punctureLumbar punctureneedle enteringneedle enteringneedle enteringneedle enteringsubarachnoidsubarachnoidsubarachnoidsubarachnoidspacespacespacespace

FilumFilumFilumFilumterminaleterminaleterminaleterminale

InterInterInterInter----vertebralvertebralvertebralvertebraldiscdiscdiscdisc

TTTT12121212

LLLL5555

Cauda equinaCauda equinaCauda equinaCauda equinain subarachnoidin subarachnoidin subarachnoidin subarachnoidspacespacespacespace

DuraDuraDuraDuramatermatermatermater

LLLL5555

LLLL4444

SSSS1111

ArachnoidArachnoidArachnoidArachnoidmattermattermattermatter

The Spinal Cord

• Cross section

– Central gray matter

– Cortex of white matter

Figure 12.31aFigure 12.31aFigure 12.31aFigure 12.31a

(a) Cross section of spinal cord and vertebra

Epidural spaceEpidural spaceEpidural spaceEpidural space(contains fat)(contains fat)(contains fat)(contains fat)

Pia materPia materPia materPia mater

SpinalSpinalSpinalSpinalmeninges meninges meninges meninges

ArachnoidArachnoidArachnoidArachnoidmater mater mater mater

Dura materDura materDura materDura mater

Bone ofBone ofBone ofBone ofvertebravertebravertebravertebra

Subdural spaceSubdural spaceSubdural spaceSubdural space

SubarachnoidSubarachnoidSubarachnoidSubarachnoidspacespacespacespace(contains CSF)(contains CSF)(contains CSF)(contains CSF)

Dorsal rootDorsal rootDorsal rootDorsal rootganglionganglionganglionganglion

BodyBodyBodyBodyof vertebraof vertebraof vertebraof vertebra

Figure 12.31bFigure 12.31bFigure 12.31bFigure 12.31b

(b) The spinal cord and its meningeal coverings

Dorsal funiculusDorsal funiculusDorsal funiculusDorsal funiculus

Dorsal median sulcusDorsal median sulcusDorsal median sulcusDorsal median sulcus

Central canalCentral canalCentral canalCentral canal

Ventral medianVentral medianVentral medianVentral medianfissure fissure fissure fissure


Arachnoid materArachnoid materArachnoid materArachnoid mater

Spinal dura materSpinal dura materSpinal dura materSpinal dura mater

GrayGrayGrayGraycommissure commissure commissure commissure

Dorsal hornDorsal hornDorsal hornDorsal horn GrayGrayGrayGraymattermattermattermatter

Lateral hornLateral hornLateral hornLateral horn

Ventral hornVentral hornVentral hornVentral hornVentral funiculusVentral funiculusVentral funiculusVentral funiculus

Lateral funiculusLateral funiculusLateral funiculusLateral funiculus

WhiteWhiteWhiteWhitecolumnscolumnscolumnscolumns


Dorsal rootDorsal rootDorsal rootDorsal root(fans out into (fans out into (fans out into (fans out into dorsal rootlets)dorsal rootlets)dorsal rootlets)dorsal rootlets)

Ventral rootVentral rootVentral rootVentral root(derived from several(derived from several(derived from several(derived from severalventral rootlets)ventral rootlets)ventral rootlets)ventral rootlets)

Spinal nerveSpinal nerveSpinal nerveSpinal nerve

The Spinal Cord

• Gray matter

– Site of interneurons & motor neuron cell body synapses

– All neuron cell bodies in spinal gray matter are multipolar

– Regions

• Dorsal (posterior) horns

• Ventral (anterior)horns

• Lateral horns (only in thoracic and lumbar regions)

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Figure 12.32Figure 12.32Figure 12.32Figure 12.32

SomaticSomaticSomaticSomaticsensorysensorysensorysensoryneuron neuron neuron neuron

Dorsal root (sensory)Dorsal root (sensory)Dorsal root (sensory)Dorsal root (sensory)

Dorsal root ganglionDorsal root ganglionDorsal root ganglionDorsal root ganglion

VisceralVisceralVisceralVisceralsensory sensory sensory sensory neuronneuronneuronneuron

SomaticSomaticSomaticSomaticmotor neuron motor neuron motor neuron motor neuron


Ventral rootVentral rootVentral rootVentral root(motor) (motor) (motor) (motor)

Ventral hornVentral hornVentral hornVentral horn(motor neurons)(motor neurons)(motor neurons)(motor neurons)

Dorsal horn (interneurons)Dorsal horn (interneurons)Dorsal horn (interneurons)Dorsal horn (interneurons)

VisceralVisceralVisceralVisceralmotormotormotormotorneuron neuron neuron neuron

Interneurons receiving input from somatic sensory neuronsInterneurons receiving input from somatic sensory neuronsInterneurons receiving input from somatic sensory neuronsInterneurons receiving input from somatic sensory neurons

Interneurons receiving input from visceral sensory neuronsInterneurons receiving input from visceral sensory neuronsInterneurons receiving input from visceral sensory neuronsInterneurons receiving input from visceral sensory neurons

Visceral motor (autonomic) neuronsVisceral motor (autonomic) neuronsVisceral motor (autonomic) neuronsVisceral motor (autonomic) neurons

Somatic motor neuronsSomatic motor neuronsSomatic motor neuronsSomatic motor neurons

The Spinal Cord

• White matter

– Myelinated ascending (sensory) & descending (motor) tracts

• Also some transverse (commisural fibers)

– Tracts located in 3 white columns (funiculi) on each side

1. Dorsal (posterior)

2. Lateral

3. Ventral (anterior)

Figure 12.31bFigure 12.31bFigure 12.31bFigure 12.31b

(b) The spinal cord and its meningeal coverings

Dorsal funiculusDorsal funiculusDorsal funiculusDorsal funiculus

Dorsal median sulcusDorsal median sulcusDorsal median sulcusDorsal median sulcus

Central canalCentral canalCentral canalCentral canal

Ventral medianVentral medianVentral medianVentral medianfissure fissure fissure fissure


Arachnoid materArachnoid materArachnoid materArachnoid mater

Spinal dura materSpinal dura materSpinal dura materSpinal dura mater

GrayGrayGrayGraycommissure commissure commissure commissure

Dorsal hornDorsal hornDorsal hornDorsal horn GrayGrayGrayGraymattermattermattermatter

Lateral hornLateral hornLateral hornLateral horn

Ventral hornVentral hornVentral hornVentral hornVentral funiculusVentral funiculusVentral funiculusVentral funiculus

Lateral funiculusLateral funiculusLateral funiculusLateral funiculus

WhiteWhiteWhiteWhitecolumnscolumnscolumnscolumns


Dorsal rootDorsal rootDorsal rootDorsal root(fans out into (fans out into (fans out into (fans out into dorsal rootlets)dorsal rootlets)dorsal rootlets)dorsal rootlets)

Ventral rootVentral rootVentral rootVentral root(derived from several(derived from several(derived from several(derived from severalventral rootlets)ventral rootlets)ventral rootlets)ventral rootlets)


The Spinal Cord

• Spinal tracts

– Run through the funiculi

– Multineural pathways

• Contain axons with similar destinations and functions

– Most decussate (cross over)

– Most exhibit somatotopy

– Pathways are paired symmetrically

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

Medulla oblongataMedulla oblongataMedulla oblongataMedulla oblongata

Cervical spinal cordCervical spinal cordCervical spinal cordCervical spinal cord

SkeletalSkeletalSkeletalSkeletal

muscle muscle muscle muscle

PyramidsPyramidsPyramidsPyramids

DecussationDecussationDecussationDecussation

of pyramidof pyramidof pyramidof pyramidLateral

corticospinal

tract

Ventral

corticospinal

tract

Lumbar spinal cordLumbar spinal cordLumbar spinal cordLumbar spinal cord

Somatic motor neuronsSomatic motor neuronsSomatic motor neuronsSomatic motor neurons(lower motor neurons)(lower motor neurons)(lower motor neurons)(lower motor neurons)

(a) Pyramidal (lateral and ventral corticospinal) pathways

The Spinal Cord

• Naming of tracts

– Many are named for origin and termination

– Example

• Anterior (ventral) spinothalamic tract

– Origin = spinal cord

– Termination = thalamus

– Location = anterior funiculus

– Ascending = must be sensory

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The Spinal Cord

• Ascending Pathways

– Consist of two or three neurons

• First order

• Second order

• Third order

The Spinal Cord


– First-order neurons

• Cell bodies in ganglia (dorsal root or cranial)

• Carry impulses from sensory receptors in muscle and skin to spinal cord and brain

• Synapse with second-order neurons

– Examples

• Posterior (dorsal) column

– Receptor to medulla

• Spinothalamic tract

– Receptor to spinal cord

The Spinal Cord


– Second-order neurons

• Interneurons

• Cell bodies in dorsal horn of spinal cord

• Synapse with third-order neuron

– Examples


– Medulla to thalamus (decussates in medulla)


– Spinal cord to thalamus (decussates in spinal cord)

The Spinal Cord


– Third-order neurons

• Interneurons

• Cell bodies in thalamus

– Examples


– Thalamus to cortex


– Thalamus to cortex

The Spinal Cord

• Ascending pathways

– Two pathways transmit somatosensory information

to the sensory cortex via the thalamus


– Fine touch, proprioception, vibration

• Spinothalamic pathways

– Crude touch, temperature, pain

Figure 12.33

Ascending tracts Descending tracts

Fasciculus gracilisDorsalwhitecolumn

Fasciculus cuneatus

Dorsalspinocerebellar tract

Lateralspinothalamic tract

Ventral (anterior)

spinothalamictract

Ventral whitecommissure

Lateralcorticospinal tract

Lateralreticulospinal tract

Ventral corticospinaltract

Medialreticulospinal tract

Rubrospinaltract

Vestibulospinal tract

Tectospinal tract

Ventralspinocerebellartract

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Figure 12.34b (2 of 2)

Axons of first-order

neurons

Temperature

receptors

Lateralspinothalamictract (axons ofsecond-orderneurons)

Pain receptors

Medulla oblongata

Cervical spinal cord

Lumbar spinal cord

(b) Spinothalamic pathway


Primary

somatosensory

cortex

Axons of third-order

neuronsThalamus

Cerebrum

Midbrain

Cerebellum

Pons

(b) Spinothalamic pathway

Figure 12.34a (2 of 2)

Medulla oblongata

Fasciculus cuneatus

(axon of first-order sensory neuron)

Fasciculus gracilis

(axon of first-order sensory neuron)

Axon of

first-order

neuron

Muscle spindle(proprioceptor)

Joint stretchreceptor(proprioceptor)


Touch

receptor

Medial lemniscus (tract)(axons of second-order neurons)

Dorsalspinocerebellartract (axons ofsecond-orderneurons)

Nucleus gracilisNucleus cuneatus

Lumbar spinal cord

(a) Spinocerebellarpathway

Dorsal (posterior)

column


Primary

somatosensory

cortexAxons of third-order

neurons

Thalamus

Cerebrum

Midbrain

Cerebellum

Pons

(a) Spinocerebellarpathway

Dorsal (posterior)

column

The Spinal Cord

• Descending pathways & tracts

– Deliver efferent impulses from the brain to the

spinal cord (and from there to an effector muscle or

glad)

1. Direct pathways = pyramidal tracts

2. Indirect pathways (extrapyramidal) = all others

The Spinal Cord

� Pyramidal Tracts

� From primary motor cortex to cord

� Involve two neurons:

1. Upper motor neurons (1st order)

– Cortex to cord (decussate in pyramids of the medulla or in the

cord)

2. Lower motor neurons (2nd order)

– Spinal cord to muscle

– Innervate skeletal muscles (voluntary)

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Primary motor cortex

Internal capsule

Cerebral

peduncle

Midbrain

Cerebellum

Cerebrum

Pons

(a)

Pyramidal cells

(upper motor

neurons)

Pyramidal (lateral and ventral corticospinal) pathways


Medulla oblongata


Skeletal

muscle

Pyramids

Decussation

of pyramidLateral

corticospinal

tract

Ventral

corticospinal

tract

Lumbar spinal cord

Somatic motor neurons(lower motor neurons)

(a) Pyramidal (lateral and ventral corticospinal) pathways

The Spinal Cord

�Extrapyramidal (indirect) tracts

� Various CNS regions (avoiding pyramids) to cord

� Impulses regarding unconscious motor control

� Posture and balance

� Involve two neurons:

1. Upper motor neurons (1st order)

� Subcortex or pons (decussate) to cord

2. Lower motor neurons (2nd order)

� Spinal cord to muscle

� Innervate skeletal muscles (involuntary)


Midbrain

Cerebellum

Cerebrum

Red nucleus

Pons

Rubrospinal tract(b)

An extrapyramidal

pathway


Medulla oblongata


Rubrospinal tract

Rubrospinal tract(b)

The Spinal Cord

• Motor neuron damage

– Damage to LMN

• Flaccid paralysis

– Nerve impulses do not reach the affected muscles

– Cannot move voluntarily or involuntarily

– Muscles atrophy

– Damage to UMN

• Spastic paralysis

– Spinal motor neurons remain intact

– Reflex activity continues (involuntary movement)

– No voluntary muscle control

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