Download The Nervous System The Spinal Cord The Spinal Cord The Spinal

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The Spinal Cord
• Continuation of CNS inferior to foramen
magnum
The Nervous System
Spinal Cord
– Simpler than the brain
– Conducts impulses to and from brain
• Two way conduction pathway
– Reflex actions
The Spinal Cord
Cervical
enlargement
• 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
(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.
Dura and
arachnoid
mater
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Filum
terminale
Cervical
spinal nerves
Thoracic
spinal nerves
Lumbar
spinal nerves
Sacral
spinal nerves
The Spinal Cord
• Spinal nerves
– 31 pairs
• Cervical and lumbar enlargements
– Nerves serving the upper & lower limbs emerge
here
Cervical
enlargement
Dura and
arachnoid
mater
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Filum
terminale
(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.
Cervical
spinal nerves
Thoracic
spinal nerves
Lumbar
spinal nerves
Sacral
spinal nerves
Figure 12.29a
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T12
The Spinal Cord
Ligamentum
flavum
Lumbar puncture
needle entering
subarachnoid
space
L5
• Protection
– Bone
– Meninges
– CSF
L4
SupraSupraspinous
ligament
• Spinal tap-inferior to L2 vertebra
L5
Filum
terminale
S1
InterIntervertebral
disc
Arachnoid
matter
Dura
mater
Cauda equina
in subarachnoid
space
Figure 12.30
The Spinal Cord
Pia mater
Arachnoid
mater
Dura mater
Epidural space
(contains fat)
Subdural space
• Cross section
– Central gray matter
– Cortex of white matter
Subarachnoid
space
(contains CSF)
Spinal
meninges
Bone of
vertebra
Dorsal root
ganglion
Body
of vertebra
(a) Cross section of spinal cord and vertebra
Figure 12.31a
White
columns
Dorsal funiculus
Ventral funiculus
Lateral funiculus
Dorsal root
ganglion
Dorsal median sulcus
Gray
commissure
Dorsal horn
Gray
Ventral horn
matter
Lateral horn
Spinal nerve
Dorsal root
(fans out into
dorsal rootlets)
Ventral root
(derived from several
ventral rootlets)
Central canal
Ventral median
fissure
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)
Pia mater
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
Figure 12.31b
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The Spinal Cord
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
• White matter
Somatic
sensory
neuron
– Myelinated ascending (sensory) & descending
(motor) tracts
Visceral
sensory
neuron
• Also some transverse (commisural fibers)
Visceral
motor
neuron
– Tracts located in 3 white columns (funiculi) on each
side
Spinal nerve
Somatic
motor neuron
Ventral root
(motor)
Ventral horn
(motor neurons)
1. Dorsal (posterior)
2. Lateral
3. Ventral (anterior)
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32
White
columns
Dorsal funiculus
Ventral funiculus
Lateral funiculus
Dorsal root
ganglion
Dorsal median sulcus
Gray
commissure
Dorsal horn
Gray
Ventral horn
matter
Lateral horn
Spinal nerve
Central canal
The Spinal Cord
• Spinal tracts
– Run through the funiculi
– Multineural pathways
• Contain axons with similar destinations and functions
Dorsal root
(fans out into
dorsal rootlets)
Ventral median
fissure
Ventral root
(derived from several
ventral rootlets)
Pia mater
– Most decussate (cross over)
– Most exhibit somatotopy
– Pathways are paired symmetrically
Arachnoid mater
Spinal dura mater
(b) The spinal cord and its meningeal coverings
Figure 12.31b
Ventral
corticospinal
tract
Pyramids
Decussation
of pyramid
Lateral
corticospinal
tract
The Spinal Cord
Medulla oblongata
• Naming of tracts
– Many are named for origin and termination
– Example
Cervical spinal cord
• Anterior (ventral) spinothalamic tract
–
–
–
–
Skeletal
muscle
Origin = spinal cord
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)
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The Spinal Cord
• Ascending Pathways
– Consist of two or three neurons
The Spinal Cord
• Ascending Pathways
– 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
• First order
• Second order
• Third order
– Examples
• Posterior (dorsal) column
– Receptor to medulla
• Spinothalamic tract
– Receptor to spinal cord
The Spinal Cord
• Ascending Pathways
– Second-order neurons
• Interneurons
• Cell bodies in dorsal horn of spinal cord
• Synapse with third-order neuron
The Spinal Cord
• Ascending Pathways
– Third-order neurons
• Interneurons
• Cell bodies in thalamus
– Examples
– Examples
• Posterior (dorsal) column
– Thalamus to cortex
• Posterior (dorsal) column
• Spinothalamic tract
– Medulla to thalamus (decussates in medulla)
– Thalamus to cortex
• Spinothalamic tract
– Spinal cord to thalamus (decussates in spinal cord)
The Spinal Cord
• Ascending pathways
– Two pathways transmit somatosensory information
to the sensory cortex via the thalamus
Posterior (dorsal) column
•
–
Fine touch, proprioception, vibration
Spinothalamic pathways
•
–
Crude touch, temperature, pain
Ascending tracts
Dorsal
white
column
Fasciculus gracilis
Fasciculus cuneatus
Dorsal
spinocerebellar
tract
Ventral
spinocerebellar
tract
Lateral
spinothalamic tract
Ventral (anterior)
spinothalamic
tract
Descending tracts
Ventral white
commissure
Lateral
reticulospinal tract
Lateral
corticospinal tract
Rubrospinal
tract
Medial
reticulospinal
tract
Ventral corticospinal
tract
Vestibulospinal tract
Tectospinal tract
Figure 12.33
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Lateral
spinothalamic
tract (axons of
second-order
neurons)
Primary
somatosensory
cortex
Axons of third-order
neurons
Thalamus
Medulla oblongata
Pain receptors
Cerebrum
Midbrain
Cervical spinal cord
Axons of first-order
neurons
Temperature
receptors
Lumbar spinal cord
Cerebellum
Pons
(b) Spinothalamic pathway
(b) Spinothalamic pathway
Figure 12.34b (1 of 2)
Figure 12.34b (2 of 2)
Dorsal
spinocerebellar
tract (axons of
second-order
neurons)
Medial lemniscus (tract)
(axons of second-order neurons)
Nucleus gracilis
Nucleus cuneatus
Primary
somatosensory
cortex
Axons of third-order
neurons
Thalamus
Medulla oblongata
Fasciculus cuneatus
(axon of first-order sensory neuron)
Cerebrum
Joint stretch
receptor
(proprioceptor)
Cervical spinal cord
Fasciculus gracilis
(axon of first-order sensory neuron)
Axon of
first-order
neuron
Muscle spindle
(proprioceptor)
Midbrain
Lumbar spinal cord
Cerebellum
Pons
Touch
receptor
(a) Spinocerebellar
pathway
(a) Spinocerebellar
pathway
Dorsal (posterior)
column
Dorsal (posterior)
column
Figure 12.34a (2 of 2)
Figure 12.34a (1 of 2)
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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Pyramidal cells
(upper motor
neurons)
Primary motor cortex
Internal capsule
Ventral
corticospinal
tract
Medulla oblongata
Pyramids
Decussation
of pyramid
Lateral
corticospinal
tract
Cerebrum
Cervical spinal cord
Skeletal
muscle
Midbrain
Cerebral
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)
The Spinal Cord
Figure 12.35a (2 of 2)
An extrapyramidal
pathway
Extrapyramidal (indirect) tracts
Various CNS regions (avoiding pyramids) to cord
Impulses regarding unconscious motor control
Posture and balance
Involve two neurons:
Cerebrum
Red nucleus
Midbrain
1. Upper motor neurons (1st order)
Subcortex or pons (decussate) to cord
2. Lower motor neurons (2nd order)
Cerebellum
Spinal cord to muscle
Innervate skeletal muscles (involuntary)
Pons
(b)
Rubrospinal tract
Figure 12.35b (1 of 2)
The Spinal Cord
Rubrospinal tract
• 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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