copyright © 2010 pearson education, inc. spinal cord location begins at the foramen magnum solid...

Copyright © 2010 Pearson Education, Inc.

Spinal Cord

• Location

• Begins at the foramen magnum

• Solid cord ends around L1 vertebra

• Filum terminal below that

• Functions

• Provides two-way communication to and from the brain

• Contains spinal reflex centers


Spinal Cord: Protection

• Bone, meninges, and CSF

• Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater

• CSF in subarachnoid space

Copyright © 2010 Pearson Education, Inc. Figure 12.30

Ligamentumflavum

Supra-spinousligament

Lumbar punctureneedle enteringsubarachnoidspace

Filumterminale

Inter-vertebraldisc

T12

L5

Cauda equinain subarachnoidspace

Duramater

L5

L4

S1

Arachnoidmatter

Lumbar puncture

Copyright © 2010 Pearson Education, Inc. Figure 12.29a

Cervicalenlargement

Lumbarenlargement

Caudaequina

Filumterminale

Cervicalspinal nerves

Lumbarspinal nerves

Sacralspinal nerves

Thoracicspinal nerves

Posterior (dorsal) view of spinal cord

Overlying structures (muscle, bone, etc) have been removed


Spinal Cord

• Spinal nerves

• 31 pairs

• Cervical and lumbar enlargements

• The nerves serving the upper and lower limbs emerge here

• Cauda equina

• The collection of nerve roots at the inferior end of the vertebral canal

Copyright © 2010 Pearson Education, Inc. Figure 12.31a

(a) Cross section of spinal cord and vertebra

Epidural space(contains fat)

Pia mater

Spinalmeninges

Arachnoidmater Dura mater

Bone ofvertebra

Subdural space

Subarachnoidspace(contains CSF)

Dorsal rootganglion

Bodyof vertebra

Cross-Sectional Anatomy

Copyright © 2010 Pearson Education, Inc. Figure 12.31b

(b) The spinal cord and its meningeal coverings

Dorsal funiculus

Dorsal median sulcus

Central canal

Ventral medianfissure

Pia mater

Arachnoid mater

Spinal dura mater

Graycommissure Dorsal horn Gray

matterLateral hornVentral horn

Ventral funiculusLateral funiculus

Whitecolumns

Dorsal rootganglion

Dorsal root(fans out into dorsal rootlets)

Ventral root(derived from severalventral rootlets)

Spinal nerve



Gray Matter

• Dorsal horns—interneurons that receive somatic and visceral sensory input

• Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots

• Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons

• Dorsal root (spinal) gangia—contain cell bodies of sensory neurons


Somaticsensoryneuron

Dorsal root (sensory)

Dorsal root ganglion

Visceralsensory neuron

Somaticmotor neuron

Spinal nerve

Ventral root(motor)

Ventral horn(motor neurons)

Dorsal horn (interneurons)

Visceralmotorneuron

Interneurons receiving input from somatic sensory neurons

Interneurons receiving input from visceral sensory neurons

Visceral motor (autonomic) neurons

Somatic motor neurons



White Matter

• Consists mostly of ascending (sensory) and descending (motor) tracts

• Transverse tracts (commissural fibers) cross from one side to the other

• Tracts are located in three white columns (funiculi on each side—dorsal (posterior), lateral, and ventral (anterior)

• Each spinal tract is composed of axons with similar functions


Pathway Generalizations

• Pathways decussate (cross over)

• Most consist of two or three neurons (a relay)

• Most exhibit somatotopy (precise spatial relationships)

• Pathways are paired symmetrically (one on each side of the spinal cord or brain)


Ascending tracts Descending tracts

Fasciculus gracilisDorsalwhitecolumn

Fasciculus cuneatus

Dorsalspinocerebellar tract

Lateralspinothalamic tract

Ventral spinothalamictract

Ventral whitecommissure

Lateralcorticospinal tract

Lateralreticulospinal tract

Ventral corticospinaltract

Medialreticulospinal tract

Rubrospinaltract

Vestibulospinal tractTectospinal tract

Ventralspinocerebellartract


Ascending Pathways

• Consist of three neurons

• First-order neuron

• Conducts impulses from cutaneous receptors and proprioceptors

• Branches diffusely as it enters the spinal cord or medulla

• Synapses with second-order neuron


Ascending Pathways

• Second-order neuron

• Interneuron

• Cell body in dorsal horn of spinal cord or medullary nuclei

• Axons extend to thalamus or cerebellum


Ascending Pathways

• Third-order neuron

• Interneuron

• Cell body in thalamus

• Axon extends to somatosensory cortex


Ascending Pathways

• Two pathways transmit somatosensory information to the sensory cortex via the thalamus

• Dorsal column pathways

• Spinothalamic pathways

• (Skip spinocerebellar)


Dorsal Column Pathways (somatosensory)

• Transmit input to the somatosensory cortex for discriminative touch and vibrations

• Composed of the paired fasciculus cuneatus and fasciculus gracilis in the spinal cord and the medial lemniscus in the brain (medulla to thalamus)

Copyright © 2010 Pearson Education, Inc. Figure 12.34a (2 of 2)

Medulla oblongataFasciculus cuneatus(axon of first-order sensory neuron)

Fasciculus gracilis(axon of first-order sensory neuron)

Axon offirst-orderneuronMuscle spindle(proprioceptor)

Joint stretchreceptor(proprioceptor)

Cervical spinal cord

Touchreceptor

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

Dorsalspinocerebellartract (axons ofsecond-orderneurons)

Nucleus gracilisNucleus cuneatus

Lumbar spinal cord

(a) Spinocerebellarpathway

Dorsal column pathway

(skip spinocerebellar)

Dorsal column pathway (somatosensory)


Primarysomatosensorycortex

Axons of third-orderneurons

Thalamus

Cerebrum

Midbrain

Cerebellum

Pons

(a) Spinocerebellarpathway

Dorsal column–mediallemniscal pathway

Dorsal column pathway (somatosensory)


Spinothalamic Pathway (somatosensory)

• Spinothalamic tracts

• Transmit pain, temperature, and coarse touch impulses within the lateral spinothalamic tract

Copyright © 2010 Pearson Education, Inc. Figure 12.34b (2 of 2)

Axons of first-orderneurons

Temperaturereceptors

Lateralspinothalamictract (axons ofsecond-orderneurons)

Pain receptors

Medulla oblongata


Lumbar spinal cord

(b) Spinothalamic pathway

Spinothalamic pathway (somatosensory)

Copyright © 2010 Pearson Education, Inc. Figure 12.34b (1 of 2)

Primarysomatosensorycortex

Axons of third-orderneurons

Thalamus

Cerebrum

Midbrain

Cerebellum

Pons

(b) Spinothalamic pathway

Spinothalamic pathway (somatosensory)


Descending Pathways and Tracts

• Deliver efferent impulses from the brain to the spinal cord

• Direct pathways—pyramidal tracts

• Indirect pathways—all others


Descending Pathways and Tracts

• Involve two neurons:

1. Upper motor neurons

• Pyramidal cells in primary motor cortex

2. Lower motor neurons

• Ventral horn motor neurons

• Innervate skeletal muscles


The Direct (Pyramidal) System (corticospinal)

• Impulses from pyramidal neurons in the precentral gyri pass through the pyramidal (corticospinal) tracts

• Axons synapse with interneurons or ventral horn motor neurons

• The direct pathway regulates fast and fine (skilled) movements


Primary motor cortex

Internal capsule

Cerebralpeduncle

Midbrain

Cerebellum

Cerebrum

Pons

Pyramidal cells(upper motor neurons)

Pyramidal (corticospinal) pathways


Medulla oblongata


Skeletalmuscle

Pyramids

Decussationof pyramidLateralcorticospinaltract

Ventralcorticospinaltract

Lumbar spinal cord

Somatic motor neurons(lower motor neurons)

Pyramidal (corticospinal) pathways

copyright © 2010 pearson education, inc. spinal cord location begins at the foramen magnum solid...

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