جلسه ششم مسیرهای انتقال حسهای پیکری 1. 2 3 4 5

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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