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ششم جلسه
انتقال مسیرهایپیکری حسهای
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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– 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
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Cerebral Cortex
Thalmus
Brainstem
Unipolar nerve
multipolar
Touch
RSpinal Cord
Thalamus - VP
Medulla
S1
R
Dorsal Column
DRG
Medial lemniscus
Dorsal Column-Medial Lemniscal pathway
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Neural Pathways
• Neural Pathways• Fasciculus Gracilis• Fasciculus Cuneatus• Path– Spinal Ganglion (1)– Gracilis or Cuneatus Nucleus (2)– Through Medial Lemniscus to Thalamus (2)– Thalamus to Cortex (3)
Mediate discriminativeTouch from differentBody areas; follow three-neuron organization
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
Meissner’s corpuscle
Cervical
Thoracic
Lumbar
Sacral
Fasciculus gracilis
Fasciculuscuneatus
Dorsal Column-Medial Lemniscal System
Pons and Medulla
Medulla
Nucleus gracilis (lower body)
Nucleus cuneatus (upper body)
Decussation
Dorsal Column- Medial Lemniscal System
• Midbrain-Cortex
MidbrainMedial lemniscus
Thalamus
Homunculus
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)
• Nucleus Cuneatus & Gracilis
• Fasciculus Cuneatus • Fasciculus Gracilis • Dorsal Root Ganglia
Synapses and Crosses – now as the Medial Lemniscus
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VPL & VPM
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Schematic representation of the main mechanosensory pathways (Part 2)
Pain and Temperature
• Anterolateral System
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Cerebral Cortex
Thalmus
Brainstem/spinal cord
The Anterolateral System
SubstantiaGelatinosa
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Dorsal
Ventral
dorsal columns
Spinal Cord
lateral columns
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Schematic representation of the main mechanosensory pathways
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To Cerebellum(1)
• 1-Direct PathwaysA) Posterior(dorsal) Spinocerebellar Tract
B) Cuneocerebellar Tract
C) Anterior(ventral) Spinocerebellar Tract
D) Rostrospinocerebellar Tract
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To Cerebellum(2)
2- Indirect PathwaysA) Spinocervicocerebellar TractB) 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
• 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
• 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. Origin - VPL2. Course – Posterior limb of internal capsule3. Laterality - Uncrossed4. Topographical Organization - yes5. Destination – Primary somatosensory cortex, areas
1, 2, 36. Function – DC- ML functions7. 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 LESION60
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Brown-Sequard syndrome
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