Transcript Pseudo-unipolar neurons

Ascending Sensory Pathways
Dorsal Column-Medial Lemniscus system
fine touch
position sense
Anterolateral system
temperature
coarse touch
pain
James Bisley ([email protected])
Dorsal Column-Medial Lemniscus system
Conveys mechanosensory information from
the periphery to the cortex
• Cutaneous Mechanoreceptors (fine touch)
• Proprioception & Kinesthesia (position)
Fine touch
Pain
Temperature
Coarse touch
receptor
afferent
Position sense
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
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.
First order
neuron
receptor
Second
order
neuron
Third
order
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.
There is a topographic representation of the
body in the dorsal column nuclei
Caudal medulla
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.
There is a topographic representation of the
body in the medial lemniscus
Caudal medulla
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 system
Gracile
Cuneate
What about the face?
Dorsal Column-Medial Lemniscus system
What about the face?
Pseudo-unipolar neurons
have their cell bodies in
the TRIGEMINAL
GANGLION.
Mid-pons
Except for
Proprioception
Pseudo-unipolar neurons
have their cell bodies in the
MESENCEPHALIC
NUCLEUS inside the CNS.
Dorsal Column-Medial Lemniscus system
What about the face?
Pseudo-unipolar neurons
have their cell bodies in
the TRIGEMINAL
GANGLION.
Except for
Proprioception
Pseudo-unipolar neurons
have their cell bodies in the
MESENCEPHALIC
NUCLEUS inside the CNS.
Dorsal Column-Medial Lemniscus system
What about the face?
Axons project to second
order neurons in the
PRINCIPAL (SENSORY)
NUCLEUS OF THE
TRIGEMINAL COMPLEX
in mid-pons.
Mid-pons
There is a topographic representation of
the face in the principal (sensory) nucleus
Dorsal Column-Medial Lemniscus system
What about the face?
Axons of the second
order neurons decussate
and join the
TRIGEMINOTHALAMIC
TRACT (which runs
adjacent to the medial
lemniscus).
Mid-pons
Dorsal Column-Medial Lemniscus system
What about the face?
The axons of the second
order neurons terminate
in the VENTRAL
POSTERIOR MEDIAL
NUCLEUS of the
thalamus (VPM).
Mid-pons
There is a topographic representation of the
face in the VPM
Dorsal Column-Medial Lemniscus system
Neurons in the VP
complex project to
PRIMARY SOMATICSENSORY CORTEX via
the POSTERIOR LIMB of
the INTERNAL
CAPSULE.
Mid-pons
The whole body is represented in
the ventral posterior complex.
Dorsal Column-Medial Lemniscus system
Neurons in the VP
complex project to
PRIMARY SOMATICSENSORY CORTEX via
the POSTERIOR LIMB of
the INTERNAL
CAPSULE.
Dorsal Column-Medial Lemniscus system
Area 3a
Primarily proprioception
input
Area 3b
Primarily tactile input
Area 1
Primarily tactile input, but
receptive fields usually
cover several digits
Area 2
Combination of tactile and
proprioception. Hand
configuration & stimulus
shape are both important
Dorsal Column-Medial Lemniscus system
The 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.
There is a topographic representation of the
Just like the tactile system
body in the VPL (lower extremities are lateral)
Some simple differences between the pathways
Dorsal column
Anterolateral
X
X
Test the pathway
Test the pathway
Light touch
Pain
Vibration
Temperature
2-point discrimination
Coarse touch
Sense of position
Central Pain Pathways:
Sensory discriminative component
What about the face?
Anterolateral tract
Pseudo-unipolar neurons
have their cell bodies in
the TRIGEMINAL
GANGLION and ganglia
associated with nerves
VII (Facial), IX (Glossopharyngeal) & X (Vagus).
Central Pain Pathways:
Sensory discriminative component
Anterolateral tract
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
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
Anterolateral tract
There is a topographic representation of the
face in the VPM
Axons from the second
order neurons terminate
in the VENTRAL
POSTERIOR MEDIAL
NUCLEUS (VPM) of the
Thalamus.
Central Pain Pathways:
Sensory discriminative component
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 SOMATICSENSORY CORTEX.
Central Pain Pathways:
Sensory discriminative component
Cortex
localization of pain
Sub-cortical
perception of pain
Paleospinothalamic
pathways
suffering component of
pain (reduced by
benzodiazepines)
Central Pain Pathways:
Descending Control of Pain
The same holds true for
the pars caudalis of the
spinal nucleus of the
trigeminal complex
Stimulation of PAG results in analgesia.
Central Pain Pathways:
Descending Control of Pain
In the dorsal horn or the pars caudalis
Opioids play a role in the descending control of pain
Endogenous opioid
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