Transcript The Dorsal Column-Medical Lemniscal System

The
Dorsal Column-Medial
Lemniscal System
Learning Module
Click to Begin
Used with permission of the
Academy of Neurologic
Physical Therapy
of the APTA
Do not duplicate without
acknowledging Learning
Activity author
Michael McKeough, PT, EdD
Contents
Overview
Introduction
Learning Objectives
Instructions
Legend
Read these Instructions!
Dorsal Column-Medical Lemniscal System
Fasciculus gracilis
Fasciculus cuneatus
Lesion lessons
Fasciculus gracilis lesion
Fasciculus cuneatus lesion
Dorsal column lesion
Medial lemniscus lesion
Internal capsule lesion
Patient Cases
Case 1
Case 2
Case 3
Contents DCML Lesions Patient Cases Exit
Overview
Introduction
Learning Objectives
Instructions
Legend
Contents DCML Lesions Patient Cases Exit
Introduction
• This module reviews the Dorsal Column-Medial Lemniscal System
(DCML).
• Module organization consists of three components. Overview
consists of this Introduction and the Learning Objectives. Contents
consists of Navigation Instructions, a Legend, Review of the normal
structure and function of the DCML, and 5 interactive lesion lessons.
Cases consists of Instructions and 3 interactive patient cases with
feedback.
• At the bottom of each page a navigation bar contains options to
move throughout the module.
• Material is presented at both the behavioral level and the
neuroanatomical level.
• The behavioral level is presented first and depicts a patient’s clinical
presentation.
• The neuroanatomical level depicts the detailed anatomy of first-order,
second-order and third-order neurons.
• The neuroanatomical level accounts for the patient’s behavioral
presentation on examination under normal and lesioned conditions.
Contents DCML Lesions Patient Cases Exit
Learning Objectives
After completing this module you should be able to:
1. describe, in detail, the structure and function of the
dorsal column-medial lemniscal system (fasciculus
gracilis and fasciculus cuneatus).
2. given a lesion, identify the signs and symptoms that
would be expected.
3. given a patient case (examination results and chief
complaint), identify the location of the lesion
causing the signs and symptoms .
4. correlate neurology information between the
behavioral and neuroanatomical levels.
Contents DCML Lesions Patient Cases Exit
Instructions
• This module contains 5 interactive lesion lessons with animation.
• Lesson lessons begin with a question about the symptoms
produced by that particular lesion.
• Clicking the answer button will reveal the answer to the question.
• Clicking the explanation button will lead to both behavioral and
neuroanatomical explanations of the lesion.
•
Each presentation is launched by clicking the animation button.
The same button serves to replay the animation if desired.
• Any of the 5 lessons may be accessed by simply clicking on the
lesion title on the Contents page.
• Please refer to the legend that defines the symbols used
throughout the module.
Contents DCML Lesions Patient Cases Exit
Legend
Mechanism of injury
First-order neuron
Lesion
Second-order neuron
Sensory stimulus
Light touch stimulus
Function intact
Function lost
Contents DCML Lesions Patient Cases Exit
Third-order neuron
Sensory impairment
The Dorsal ColumnMedial Lemniscal System
Discriminative touch, vibration,
and position information from the
body is conveyed by the dorsal
column-medial lemniscal system
(DCML). The DCML is a crossed
system. It originates from
mechano-receptors (sensory
receptors sensitive to
mechanical deformation) located
in the body wall and projects to
the contralateral cerebral
hemisphere via a three neuron
projection system. The DCML is
comprised of the fasciculus
gracilis and fasciculus cuneatus.
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Fasciculus gracilis
Fasciculus cuneatus
Stimulus
First-order neuron
Second-order neuron
Third-order neuron
Contents DCML Lesions Patient Cases Exit
Primary sensory cortex
Thalamus
Nucleus Gracilis
Fasciculus Gracilis:
Behavioral Description
Fasciculus gracilis
gracilis: light touch,
vibration, and position sense
from the contralateral leg and
lower trunk
Fasciculus Gracilis
Consists of a 3-neuron
projection system extending
from receptors in the periphery
to the primary somatosensory
cortex (Click neuroanatomical
explanation)
Click to animate
Neuroanatomical Explanation
Stimulus
First-order neuron
Second-order neuron
Third-order neuron
Contents DCML Lesions Patient Cases Exit
Fasciculus cuneatus
Fasciculus Gracilis:
Neuroanatomical Description
First-order neurons
Cell body: dorsal root ganglion (DRG)
Distal axon: innervates mechanoreceptors in
leg and lower trunk via peripheral nerves
Proximal axon: enter dorsal column (fasciculus
gracilis), ascend ipsilaterally and terminate in
the nucleus gracilis
Second-order neurons
Cell body: nucleus gracilis
Axon: decussates in the medulla and projects
to the contralateral thalamus (ventral
posterior lateral nucleus, VPL) via the medial
lemniscus
Third-order neurons
Cell body: VPL of thalamus
Axon: ascends via the posterior limb of the
internal capsule and terminates in the primary
somatosensory cortex
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
DRG
Fasciculus cuneatus
Primary sensory cortex
Thalamus
Fasciculus Cuneatus:
Behavioral Description
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus cuneatus: light
touch, vibration, and position
sense from the contralateral
arm and upper trunk
Consists of a 3-neuron
projection system extending
from receptors in the
periphery to the primary
somatosensory cortex (Click
neuroanatomical explanation)
Click to animate
Neuroanatomical Explanation
Stimulus
First-order neuron
Second-order neuron
Third-order neuron
Contents DCML Lesions Patient Cases Exit
Fasciculus Cuneatus:
Neuroanatomical Description
First-order neurons
Cell body: dorsal root ganglion (DRG)
Distal axon: innervates mechanoreceptors in
arm and upper trunk via peripheral nerves
Proximal axon: enter dorsal column (fasciculus
cuneatus), ascend ipsilaterally and terminate
in the nucleus cuneatus
Second-order neurons
Cell body: nucleus cuneatus
Axon: decussates in the medulla and projects
to the contralateral thalamus (ventral
posterior lateral nucleus, VPL) via the medial
lemniscus
Third-order neurons
Cell body: VPL of thalamus
Axon: ascends via the posterior limb of the
internal capsule and terminates in the primary
somatosensory cortex
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
DRG
Lesion Lessons
Fasciculus gracilis lesion
Fasciculus cuneatus lesion
Dorsal column lesion
Medial lemniscus lesion
Internal capsule lesion
Contents DCML Lesions Patient Cases Exit
Lesion of the left fasciculus gracilis
at T8 produces what impairment?
Click for answer
Damage to the left fasciculus gracilis at T8 causes
the absence of light touch, vibration, and position
sensation in the left leg and lower left trunk. Only
the fasciculus gracilis exists below T6.
Click for explanation
Contents DCML Lesions Patient Cases Exit
Lesion of the fasciculus
gracilis on the left:
Behavioral Explanation
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Sensory impairment:
absence of light touch,
vibration, and position
sensation in the left
leg and lower left
trunk.
Click to animate
Sensory impairment:
left leg and lower
left trunk.
Neuroanatomical Explanation
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the fasciculus gracilis
on the left: Neuroanatomical
Explanation
Because the tract has not
yet decussated, impairment
is ipsilateral to the lesion.
Lesion of first-order neurons
interrupts ascending
information so light touch,
vibration, and position
sensation is impaired in the
left leg and lower left trunk.
Receptors and reflex
connections below the
lesion level remain intact.
Click to animate
Behavioral Explanation
Contents DCML Lesions Patient Cases Exit
Lesion of the left fasciculus
cuneatus at C3 produces what
impairment?
Click for answer
Damage to the left fasciculus cuneatus at C3 causes
the absence of light touch, vibration, and position
sensation in the left arm and upper left trunk.
Click for explanation
Contents DCML Lesions Patient Cases Exit
Lesion of the
fasciculus cuneatus
on the left: Behavioral
Explanation
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Sensory impairment:
absence of light
touch, vibration, and
position sensation in
the left arm and
upper left trunk.
Click to animate
Sensory impairment:
left arm and upper
left trunk.
Neuroanatomical Explanation
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the fasciculus cuneatus
on the left: Neuroanatomical
Explanation
Because the tract has not
yet decussated, impairment
is ipsilateral to the lesion.
Lesion of first-order neurons
interrupts ascending
information so light touch,
vibration, and position
sensation is impaired in the
left arm and upper left trunk.
Receptors and reflex
connections below the lesion
level remain intact.
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
Lesion of the left dorsal columns
at T2 produces what impairment?
Click for answer
Damage to the left dorsal columns at T2 causes the
absence of light touch, vibration, and position
sensation in the left side of the body below the lesion
level (trunk, arm, and leg).
Click for explanation
Contents DCML Lesions Patient Cases Exit
Lesion of the dorsal
columns on the left:
Behavioral Explanation
Sensory impairment:
absence of light touch,
vibration, and position
sensation in the left
side of the body below
the lesion level (trunk,
arm, and leg).
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Click to animate
Neuroanatomical Explanation
Sensory impairment:
left side of the body,
below the lesion
level.
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the dorsal columns on
the left: Neuroanatomical
Explanation
Because the lesion involves
first-order neurons that
have not yet decussated,
impairment is ipsilateral to
the lesion. Because both
gracilis and cuneatus are
damaged, light touch,
vibration, and position
sensation is impaired in the
left trunk, leg and arm
below the lesion level.
Receptors and reflex
connections below the
lesion level remain intact.
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
Lesion of the right medial lemniscus
produces what impairment?
Click for answer
Damage to the right medial lemniscus causes the
absence of light touch, vibration, and position
sensation in the entire left side of the body from the
neck down.
Click for explanation
Contents DCML Lesions Patient Cases Exit
Lesion of the medial
lemniscus on the right:
Behavioral Explanation
Sensory impairment:
absence of light touch,
vibration, and position
sensation in the entire
left side of the body from
the neck down.
Click to animate
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Sensory impairment:
the entire left body,
from the neck down.
Neuroanatomical Explanation
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the medial lemniscus
on the right: Neuroanatomical
Explanation
Because the lesion involves
second-order neurons that
have already decussated,
impairment is contralateral
to the lesion. The medial
lemniscus conveys light
touch, vibration, and
position sensation from the
entire left trunk, leg and
arm below the neck.
Sensation from the face is
unaffected because it is
conveyed via cranial
nerves.
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
Lesion of the right internal
capsule or primary
somatosensory cortex
produces what impairment?
Click for answer
Damage to the right internal capsule or primary
somatosensory cortex causes the absence of light
touch, vibration, and position sensation in the entire
left side of the body including the face.
Click for explanation
Contents DCML Lesions Patient Cases Exit
Lesion of the internal
capsule or primary
somatosensory cortex
on the right: Behavioral
Explanation
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Sensory impairment: absence
of light touch, vibration, and
position sensation in the entire
left side of the body including
the face.
Click to animate
Sensory impairment:
the entire left body,
including the face.
Neuroanatomical Explanation
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the internal
capsule or primary
somatosensory cortex on
the right:
Neuroanatomical
Explanation
Because the lesion
involves third-order
neurons that have
decussated, impairment is
contralateral to the
lesion. The internal
capsule conveys light
touch, vibration, and
position sensation from
the entire left side of the
body, trunk, leg, arm and
face.
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
Patient Cases
Read these instructions!
Patient Case 1
Patient Case 2
Patient Case 3
Contents DCML Lesions Patient Cases Exit
Case Instructions
• These patient cases are intended to facilitate the integration and
clinical application of information about the DCML by coupling
the findings on examination and patient interview with their
neuroanatomical correlates.
• Each case begins with the patient’s chief complaint and
significant examination findings. Then, the question is asked,
Damage to what system(s) is causing this patient’s problems?
Clicking the Answer button will reveal the answer and clicking
the Show lesion button will reveal the neuroanatomic lesion
along with the patient’s behavioral impairments.
• Cases are presented from two perspectives. What lesion would
account for a given set of examination results and patient
history? For a given lesion, what signs and symptoms would be
expected on examination?
• Click on a Case number to begin the exercise.
Contents DCML Lesions Patient Cases Exit
Case 1 Clumsiness and difficulty grasping
with the left hand
A left handed patient complains of “clumsiness” of her left arm and hand due
to uncertainty of the limb’s position in space. She frequently fails to grasp or
drops object with her left hand. Strength and AROM are WNL in all four
extremities. Light touch, two-point discrimination, proprioception, and vibration
sense are intact in the right upper extremity but absent in all dermatomes
below the C3 dermatome in the left upper extremity. She is able to distinguish
sharp from dull WNL in all four extremities and trunk, bilaterally.
Damage to what system(s) is causing this patient’s problems?
Answer
Lesion of the left fasciculus cuneatus at approximately C3.
Lateral corticospinal tracts are intact, bilaterally: strength and AROM are WNL
in all four extremities.
Lateral spinothalamic tracts are intact, bilaterally: sharp/ dull is WNL.
Fasciculus gracilis is intact, bilaterally: light touch, two-point discrimination,
proprioception, and vibration are WNL in bilateral lower extremities.
Fasciculus cuneatus is absent on the left: light touch, two-point discrimination,
proprioception (limb position in space), and vibration are absent in all
dermatomes below C3 on the left but intact on the right upper extremity.
Contents DCML Lesions Patient Cases Exit
Show lesion
Lesion of the
fasciculus cuneatus
on the left: Behavioral
Explanation
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Sensory impairment:
absence of light
touch, vibration, and
position sensation in
the left arm and
upper left trunk.
Click to animate
Sensory impairment:
left arm and upper
left trunk.
Neuroanatomical Explanation
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the fasciculus cuneatus
on the left: Neuroanatomical
Explanation
Because the tract has not
yet decussated, impairment
is ipsilateral to the lesion.
Lesion of first-order neurons
interrupts ascending
information so light touch,
vibration, and position
sensation is impaired in the
left arm and upper left trunk.
Receptors and reflex
connections below the lesion
level remain intact.
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
Case 2: Numbness and tingling on the left side of the body
Following a brainstem stroke, the patient complains of numbness and tingling
on the left side of the body. Sharp/dull and temperature sensation is unimpaired,
throughout. 2 point discrimination on the fingertips are: 5 mm on the right and
15 mm on the left. In the absence of vision, the patient is able to identify
common objects in the right hand but not the left and able to reproduce limb
positions with the right lower extremity but not the left. Light touch and vibration
sensation are WNL on the right but absent on the left side of the body. Pain and
temperature as well as light touch, vibration and position sense are intact on
both sides of the face. Strength and AROM are WNL in all four extremities.
Damage
what
system(s)
is causing
patient’s problems?
Answer
Lesion oftothe
medial
lemniscus
on thethis
right.
Lateral corticospinal tracts are intact, bilaterally: strength and AROM are WNL
in all four extremities.
Lateral spinothalamic tracts are intact, bilaterally: sharp/ dull is WNL.
Fasciculus gracilis is intact, bilaterally: light touch, two-point discrimination,
proprioception, and vibration are WNL in bilateral lower extremities.
Fasciculus cuneatus is absent on the left: light touch, two-point discrimination,
proprioception (limb position in space), and vibration are absent in all
dermatomes below C3 on the left but intact on the right upper extremity.
Contents DCML Lesions Patient Cases Exit
Show lesion
Lesion of the medial
lemniscus on the right:
Behavioral Explanation
Sensory impairment:
absence of light touch,
vibration, and position
sensation in the entire
left side of the body from
the neck down.
Click to animate
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Sensory impairment:
the entire left body,
from the neck down.
Neuroanatomical Explanation
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the medial lemniscus
on the right: Neuroanatomical
Explanation
Because the lesion involves
second-order neurons that
have already decussated,
impairment is contralateral
to the lesion. The medial
lemniscus conveys light
touch, vibration, and
position sensation from the
entire left trunk, leg and
arm below the neck.
Sensation from the face is
unaffected because it is
conveyed via cranial
nerves.
Behavioral Explanation
Click to animate
Contents DCML Lesions Patient Cases Exit
Case 3: Multiple Sclerosis
A 34 year-old Caucasian female with a six year history of Multiple Sclerosis
(exacerbating-remitting) has reported to the emergency room complaining of
severe symptoms. A magnetic resonance image (MRI) of her spine shows a
visible plaque, not seen in previous images, at the level of T10. The plaque
involves the entire dorsal column on the left.
What signs and symptoms would be expected from this lesion?
Answer
Lesion of the left dorsal column at T10 would impair (in the case of a large
lesion possibly obliterate) light touch, vibration, and position sensation in the
left leg and lower left trunk. Only the fasciculus gracilis exists below T6.
Because she has the exacerbating-remitting type of MS, her previous
symptoms will remain. If the DCML is the only system affected by this most
recent exacerbation, the functions controlled by the corticospinal tract
(voluntary movement) and lateral spinothalamic tract (pain and temperature
sensation) would remain as before.
Contents DCML Lesions Patient Cases Exit
Show lesion
Lesion of the fasciculus
gracilis on the left:
Behavioral Explanation
Primary sensory cortex
Thalamus
Nucleus Gracilis
Nucleus Cuneatus
Fasciculus Cuneatus
Fasciculus Gracilis
Sensory impairment:
absence of light touch,
vibration, and position
sensation in the left
leg and lower left
trunk.
Click to animate
Sensory impairment:
left leg and lower
left trunk.
Neuroanatomical Explanation
Lesion
Lost function
Impairment
Contents DCML Lesions Patient Cases Exit
Lesion of the fasciculus gracilis
on the left: Neuroanatomical
Explanation
Because the tract has not
yet decussated, impairment
is ipsilateral to the lesion.
Lesion of first-order neurons
interrupts ascending
information so light touch,
vibration, and position
sensation is impaired in the
left leg and lower left trunk.
Receptors and reflex
connections below the
lesion level remain intact.
Click to animate
Behavioral Explanation
Contents DCML Lesions Patient Cases Exit
The End
D. Michael McKeough, PT, EdD
 2015