Post on 05-Jan-2016
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Ascending Sensory Pathways
Dorsal Column-Medial Lemniscus systemfine touch
position sense
Anterolateral systemtemperaturecoarse touch
pain
James Bisley (jbisley@mednet.ucla.edu)
Dorsal Column-Medial Lemniscus system
Conveys mechanosensory information from the periphery to the cortex
• Cutaneous Mechanoreceptors (fine touch)
• Proprioception & Kinesthesia (position)
Fine touch
receptor
afferent
PainTemperatureCoarse touch
Kinesthesia is the “awareness” of body position
and movement
Proprioception is the “sub-concious”
information used in the feed-back control of
posture and precise movements.
Position sense
Position sense information comes from:
Muscle spindles
Golgi tendon organs
Joint receptors
Cutaneous mechanoreceptive afferents
Efference copy
Position sense
Proprioceptors
Motor unit(controlled by efferent)
Muscle spindle
Golgi tendon organ
Joint receptor
Afferent fiber information
Fiber type Class Diameter
(μm)
Conduction Vel. (m/s)
Types of receptors
Aα Ia
Ib
13-20 80-120 Primary muscle spindle
Golgi tendon organ
Aβ II 6-12 35-75 Skin mechanoreceptors
Secondary muscle spindle
Aδ III 1-5 5-30 Coarse touch, temperature, and pain
C
(no myelin)
IV 0.2-1.5 0.5-2 Coarse touch, temperature, and pain
Dorsal Column-Medial Lemniscus system
Some terminology
We use the terms first, second and third order
neurons to describe the steps of the
pathway to cortex.
receptor
First orderneuron
Secondorder
neuron
Thirdorder
neuron
Dorsal Column-Medial Lemniscus system
Afferents have their cell bodies in the DORSAL
ROOT GANGLIA.
Called pseudo-unipolar neurons.
Dorsal Column-Medial Lemniscus system
The DRG axons enter through the dorsal horn of
the spinal cord
Spinal reflexes, Clarke’s Nucleus, etc
Dorsal Column-Medial Lemniscus system
Fibers that convey information from lower limbs and body (below
spinal segment T6) travel ipsilaterally along the GRACILE TRACT.
Dorsal Column-Medial Lemniscus system
Fibers that convey information from upper limbs and body (above
spinal segment T6) travel ipsilaterally along the CUNEATE TRACT.
GRACILE TRACT
There is a topographic representation of the body in the dorsal columns
Dorsal Column-Medial Lemniscus system
Fibers in the Gracile Tract have their first synapse in the GRACILE NUCLEUS.
Fibers in the Cuneate Tract have their first
synapse in the CUNEATE NUCLEUS.
Caudal medullaThere is a topographic representation of the body in the dorsal column nuclei
Dorsal Column-Medial Lemniscus system
Axons from the second order neurons form the INTERNAL ARCUATE FIBERS in the caudal
medulla, which decussates becoming the
contralateral MEDIAL LEMNISCUS.
Caudal medullaThere is a topographic representation of the body in the medial lemniscus
Dorsal Column-Medial Lemniscus system
The representation of the body shifts as the medial lemniscus runs rostrally.
Dorsal Column-Medial Lemniscus system
The axons of the second order neurons terminate
in the VENTRAL POSTERIOR LATERAL
NUCLEUS of the thalamus (VPL).
There is a topographic representation of the body in the VPL (lower extremities are lateral)
Dorsal Column-Medial Lemniscus systemG
raci
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un
eate
What about the face?
Dorsal Column-Medial Lemniscus system
Pseudo-unipolar neurons have their cell bodies in
the TRIGEMINAL GANGLION.
What about the face?
Mid-pons Except for Proprioception
Pseudo-unipolar neurons have their cell bodies in the
MESENCEPHALIC NUCLEUS inside the CNS.
Dorsal Column-Medial Lemniscus system
Pseudo-unipolar neurons have their cell bodies in
the TRIGEMINAL GANGLION.
What about the face?
Except for Proprioception
Pseudo-unipolar neurons have their cell bodies in the
MESENCEPHALIC NUCLEUS inside the CNS.
Dorsal Column-Medial Lemniscus system
Axons project to second order neurons in the
PRINCIPAL (SENSORY) NUCLEUS OF THE
TRIGEMINAL COMPLEX in mid-pons.
What about the face?
Mid-pons
There is a topographic representation of the face in the principal (sensory) nucleus
Dorsal Column-Medial Lemniscus system
Axons of the second order neurons decussate
and join the TRIGEMINOTHALAMIC
TRACT (which runs adjacent to the medial
lemniscus).
What about the face?
Mid-pons
Dorsal Column-Medial Lemniscus system
The axons of the second order neurons terminate
in the VENTRAL POSTERIOR MEDIAL
NUCLEUS of the thalamus (VPM).
What about the face?
There is a topographic representation of the face in the VPM
Mid-pons
Mid-pons
Dorsal Column-Medial Lemniscus system
Neurons in the VP complex project to
PRIMARY SOMATIC-SENSORY CORTEX via the POSTERIOR LIMB of
the INTERNAL CAPSULE.
The whole body is represented in the ventral posterior complex.
Dorsal Column-Medial Lemniscus system
Neurons in the VP complex project to
PRIMARY SOMATIC-SENSORY CORTEX via the POSTERIOR LIMB of
the INTERNAL CAPSULE.
Dorsal Column-Medial Lemniscus system
Area 3aPrimarily proprioception
input
Area 3bPrimarily tactile input
Area 1Primarily tactile input, but
receptive fields usually cover several digits
Area 2Combination of tactile and
proprioception. Hand configuration & stimulus shape are both important
Dorsal Column-Medial Lemniscus systemThe whole body is represented in each area of SI
Owl Monkey
Dorsal Column-Medial Lemniscus system
The somatosensory homunculus
Anterolateral system
Conveys pain, temperature and coarse touch information from the periphery to the cortex
Fiber type Class Diameter
(μm)
Conduction Vel. (m/s)
Types of receptors
Aα Ia
Ib
13-20 80-120 Primary muscle spindle
Golgi tendon organ
Aβ II 6-12 35-75 Skin mechanoreceptors
Secondary muscle spindle
Aδ III 1-5 5-30 Coarse touch, temperature, and pain
C
(no myelin)
IV 0.2-1.5 0.5-2 Coarse touch, temperature, and pain
Central Pain Pathways:Sensory discriminative component
As with the tactile system, the cell bodies are
located in the DORSAL ROOT GANGLIA.
Pseudo-unipolar neurons.
Central Pain Pathways:Sensory discriminative component
The DRG axons enter through the dorsal horn of
the spinal cord
Upon entering, the axons branch into ascending
and decending collaterals forming the
DORSOLATERAL TRACT of LISSAUER.
Central Pain Pathways:Sensory discriminative component
The axons run up or down several spinal cord segments in Lassauer’s tract before synapsing in
the gray matter of the dorsal horn.
Central Pain Pathways:Sensory discriminative component
The second order neurons decussate
immediately and form the SPINOTHALAMIC TRACT (aka the
anterolateral tract).
anterior white commissure
Central Pain Pathways:Sensory discriminative component
The second order neurons decussate
immediately and form the SPINOTHALAMIC TRACT (aka the
anterolateral tract).
There is a topographic representation of the body in the spinothalamic tract anterior white commissure
Central Pain Pathways:Sensory discriminative component
The second order neurons decussate
immediately and form the SPINOTHALAMIC TRACT (aka the
anterolateral tract).
Central Pain Pathways:Sensory discriminative component
The second order neurons decussate
immediately and form the SPINOTHALAMIC TRACT (aka the
anterolateral tract).
Central Pain Pathways:Sensory discriminative component
The second order neurons decussate
immediately and form the SPINOTHALAMIC TRACT (aka the
anterolateral tract).
Central Pain Pathways:Sensory discriminative component
The second order neurons decussate
immediately and form the SPINOTHALAMIC TRACT (aka the
anterolateral tract).
Central Pain Pathways:Sensory discriminative component
Neurons in the spinothalamic tract
terminate in the VENTRAL POSTERIOR
LATERAL NUCLEUS (VPL) of the Thalamus.
Just like the tactile systemThere is a topographic representation of the
body in the VPL (lower extremities are lateral)
Some simple differences between the pathways
Test the pathway
Light touch
Vibration
2-point discrimination
Sense of position
Dorsal column Anterolateral
X
X
Test the pathway
Pain
Temperature
Coarse touch
Central Pain Pathways:Sensory discriminative component
What about the face?
Pseudo-unipolar neurons have their cell bodies in
the TRIGEMINAL GANGLION and ganglia associated with nerves VII (Facial), IX (Glosso-
pharyngeal) & X (Vagus).
Anterolateral tract
Central Pain Pathways:Sensory discriminative component
After entering the brain stem, the fibers descend
in the SPINAL TRIGEMINAL TRACT to the medulla, where they synapse onto neurons in the SPINAL NUCLEUS of
the TRIGEMINAL COMPLEX (primarily the
pars caudalis).
There is a topographic representation of the head
in the pars caudalis
Anterolateral tract
Central Pain Pathways:Sensory discriminative component
Axons from the second order neurons decussate immediately and then join
the ascending anterolateral tract in the
brain stem.
Central Pain Pathways:Sensory discriminative component
Axons from the second order neurons terminate
in the VENTRAL POSTERIOR MEDIAL
NUCLEUS (VPM) of the Thalamus.
There is a topographic representation of the face in the VPM
Anterolateral tract
The whole body & all somatic senses are
represented in the ventral posterior complex.
Neurons in the VP complex carrying pain information project to
PRIMARY and SECONDARY SOMATIC-
SENSORY CORTEX.
Central Pain Pathways:Sensory discriminative component
Central Pain Pathways:Sensory discriminative component
Cortex
localization of pain
Sub-corticalperception of pain
Paleospinothalamic pathways
suffering component of pain (reduced by benzodiazepines)
Central Pain Pathways:Descending Control of Pain
Stimulation of PAG results in analgesia.
The same holds true for the pars caudalis of the
spinal nucleus of the trigeminal complex
Central Pain Pathways:Descending Control of Pain
Endogenous opioid
Opioids play a role in the descending control of pain
In the dorsal horn or the pars caudalis
Central Pain Pathways:Local Control of Pain
Interaction between dorsal column and anterolateral systems regulates pain perception. This is why rubbing a wound after
sharp pain helps a bit.
Cutaneous mechanoreceptor
Cutaneous nociceptor
Stimulation of dorsal columns can antidromically
induce analgesia
Central Pain Pathways:Local & Descending Control of Pain
What you should know
Aα and Aβ fibers excite interneurons that reduce the transmission of pain
information
Descending fibers excite interneurons that reduce the transmission of pain
information
Dorsal Column-Medial Lemniscus system
• Information content• Fine touch, vibration and sense of position
• The path to cortex• Locations & projections of 1st, 2nd & 3rd order neurons
• Where decussation occurs
• Differences between DRG inputs & Vth nerve inputs
• Basic arrangement of topography throughout the system
• The organization of somatosensory cortex• 4 areas
• Basic arrangement of topography
Anterolateral system
• Information content• Coarse touch, temperature & pain
• The path to cortex• Locations & projections of 1st, 2nd & 3rd order neurons
• Where decussation occurs
• Differences between DRG inputs & Vth nerve inputs
• Basic arrangement of topography throughout the system
• The path from cortex• Main areas involved in descending control of pain
• 2 ways that pain can be modulated in dorsal horn