‫جلسه ششم‬
‫مسیرهای انتقال حسهای پیکری‬
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Primary Afferent Nerves
• Receive information from receptors
– Project to CNS
• Parallel pathways
– touch & proprioception & …(DCML)
– pain & temperature & …(Anterolateral System)
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Somatosensory Pathways
• Touch & Proprioception
– Dorsal Column-Medial Lemniscal pathway (DCML)
• Pain and Temperature – Anterolateral (Spinothalamic) system
• Trigeminal pathway
– face & neck
– cranial nerve V, also others ~
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Anatomical Divisions
• Dorsal Column-Medial Lemniscal System
• Fine discriminative touch, vibration, limb position,
kinesthesia & deep pressure
– Position sense
• Proprioception - Awareness of limb position
• Kinesthesia - Awareness of limb movement
• Anterolateral System
• Pain, temperature and diffuse touch
• Lateral spinothalamic tract
• Anterior spinothalamic tract
Somatosensory System(1)
Dorsal Column – Medial Lemniscus
Thalamocortical Pathways
Three neuron Organization
• 1st Order
– Dorsal Root Ganglion
• 2nd Order
– Enter CNS at spinal cord or brainstem
– Project to opposite side crossing midline to thalamus
• 3rd Order
– Thalamus neurons which project to cortex
Schematic representation of the main mechanosensory
pathways (Part 1)
Dorsal Column-Medial Lemniscal System
• Important for skilled movements
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–
–
–
Stereognosis - Fine touch discrimination
Graphesthesia - Recognizing numbers written on body
Two and multiple point touch
Deep touch
• Receptors
– Meissner’s and Pacinian Corpuscles
• Encapsulated end receptors
• Highly sensitive and adaptable
– Muscle Spindle Organs
• Kinesthesia
• Proprioception
Discriminative Touch
multipolar
Cerebral Cortex
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Thalmus
2
1
Unipolar nerve
Brainstem
S1
Thalamus - VP
Touch
Dorsal Column-Medial
Lemniscal pathway
Medial lemniscus
Medulla
Dorsal Column
DRG
R
Spinal Cord
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Neural Pathways
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•
•
•
Neural Pathways
Fasciculus Gracilis
Fasciculus Cuneatus
Path
Mediate discriminative
Touch from different
Body areas; follow
three-neuron
organization
– Spinal Ganglion (1)
– Gracilis or Cuneatus Nucleus (2)
– Through Medial Lemniscus to Thalamus (2)
– Thalamus to Cortex (3)
Levels of Reception
• Fasciculus Gracilis
– Sacral to Midthoracic Level
– Lower Body
• Fasciculus Cuneatus
– Above Midthoracic Level
– Upper Body
Dorsal Column- Medial Lemniscal System
• In the PNS/Spine
Pacinian corpuscle
Cervical
Fasciculus
cuneatus
Thoracic
Fasciculus
gracilis
Meissner’s corpuscle
Lumbar
Sacral
Dorsal Column-Medial Lemniscal System
Pons and Medulla
Nucleus gracilis (lower
body)
Nucleus cuneatus (upper body)
Medulla
Decussation
Dorsal Column- Medial Lemniscal System
• MidbrainCortex
Homunculus
Thalamus
Midbrain
Medial lemniscus
Dorsal Column Pathways & Medial Lemniscus
• Discriminative Touch
•
Pressure
•
Vibratory Sensation
•
Fine Discrimination
– Two-Point Tactile Test
•
Proprioception (conscious)
– Sense of movement & position
(eg: is your toe up or down?);
Muscle Spindles, GTOs & Joint
Receptors
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Nucleus Cuneatus
Nucleus Gracilis
Dorsal Column Pathways/
Fasciculus Cuneatus
• Input from the upper
extremity, down to the
level of T5 passes into the
Fasciculus Cuneatus.
• Somatotopic Organization:
Input from the arm
(Fasciculus Cuneatus) is
lateral to input from the leg
(Fasciculus Gracilis)
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Dorsal Column Pathways/
Fasciculus Gracilis
• Input from the lower
extremity, up to the level of
T6 passes into the
Fasciculus Gracilis of the
dorsal funiculus.
• The first order neuron
enters the cord & ascends
without either synapsing or
crossing to the opposite
side.
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Dorsal Column Pathways & Medial Lemniscus
• Cerebral Cortex
• VPL Thalamus (Synapses
again here)
Synapses
and Crosses –
now as the
Medial
Lemniscus
• Nucleus Cuneatus &
Gracilis
• Fasciculus Cuneatus
• Fasciculus Gracilis
• Dorsal Root Ganglia
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VPL & VPM
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Schematic representation of the main mechanosensory pathways (Part 2)
Pain and Temperature
• Anterolateral System
Cerebral Cortex
3
2
1
Thalmus
Brainstem/spinal cord
The Anterolateral System
Substantia
Gelatinosa
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Spinal Cord
dorsal columns
Dorsal
lateral columns
Ventral
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Schematic representation of the main mechanosensory pathways
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To Cerebellum(1)
• 1-Direct Pathways
A) Posterior(dorsal) Spinocerebellar Tract
B) Cuneocerebellar Tract
C) Anterior(ventral) Spinocerebellar Tract
D) Rostrospinocerebellar Tract
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To Cerebellum(2)
2- Indirect Pathways
A) Spinocervicocerebellar Tract
B) Spinoolivocerebellar Tract
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Dorsal Spinocerebellar Tract
• Mediates
unconscious
proprioception
• Lower limbs and
middle regions of
body to to bilateral
cerebellum
• Spinal ganglion to
nucleus dorsalis of
Clark at third
lumbar segment
• Do not cross and
enter ipsilateral
cerebellar
hemisphere
Dorsal Spinocerebellar Tract
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1. ORIGIN: Clarke’s nucleus in the thoracic spinal cord
2. COURSE: lateral columns of the spinal cord. Inferior cerebellar
peduncle.
3. LATERALITY: Uncrossed
4. TOPOGRAPHICAL ORGANIZATION: Lower limbs only.
5. DESTINATION: Cerebellar cortex and deep nucleus (not shown).
Terminations are mossy fibers.
6. FUNCTION: Information about muscle stretch and contraction.
7. DYSFUNCTION: Possible ataxia from loss of input to cerebellum.
Dorsal spinocerebellar tract travels in lateral column to the
cerebellum
Dorsal spinocerebellar tract travels in lateral column to the
cerebellum
Cuneocerebellar Tract
• Mediates upper limbs and neck
• Uncrossed fibers to ipsilateral external
cuneate nucleus to cerebellum
• Clinical Considerations
– Romberg used to determine some function
– Difficult to test clinically
Ventral Spinocerebellar Tract
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•
•
Mediates unconscious
proprioception
Lower limbs to
bilateral cerebellum
Sacral and Lumbar
levels through
ventrolateral
Spinocerebellar tract
to opposite cerebellar
hemisphere
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Thalamocortical Pathway
1.
2.
3.
4.
5.
Origin - VPL
Course – Posterior limb of internal capsule
Laterality - Uncrossed
Topographical Organization - yes
Destination – Primary somatosensory cortex, areas
1, 2, 3
6. Function – DC- ML functions
7. Dysfunction – Loss of somatic sensations
The Brown- Sequard Syndrome
• CHARACTERISTIC PATTERN OF SENSORY LOSS DUE TO
LOCALIZED DAMAGE ON ONE SIDE OF SPINE
• USUALLY ACCOMPANIED BY MOTOR LOSS AS WELL
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Lesion on Right Half of Spinal Cord
• LOSS OF PAIN SENSATION ON LEFT SIDE BELOW LESION
• LOSS OF TOUCH AND VIBRATION ON RIGHT SIDE
BELOW LESION
• LOSS OF BOTH ON RIGHT SIDE AT SAME LEVEL
• NO LOSS ABOVE LESION
• LOSS OF MOTOR ON RIGHT SIDE BELOW LESION
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Brown-Sequard syndrome
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