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Primary Afferent Nerves Receive information from receptors Project to CNS Parallel pathways touch & proprioception & …(DCML) pain & temperature & …(Anterolateral System)

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 ~ 9

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) neuro4e-fig-09-08-1r.jpg

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 Cerebral Cortex 3 Thalmus 2 1 Brainstem multipolar Cerebral Cortex 3 Thalmus 2 1 Brainstem Unipolar nerve

Touch S1 R R Spinal Cord Dorsal Column-Medial Lemniscal pathway Thalamus - VP Medial lemniscus Medulla Dorsal Column R DRG R Spinal Cord

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 discriminative Touch from different Body areas; follow three-neuron organization

Levels of Reception Fasciculus Gracilis Fasciculus Cuneatus 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 Thoracic Lumbar Sacral Fasciculus cuneatus Fasciculus gracilis Meissner’s corpuscle

Dorsal Column-Medial Lemniscal System Pons and Medulla Nucleus gracilis (lower body) Nucleus cuneatus (upper body) Medulla Decussation

Dorsal Column- Medial Lemniscal System Midbrain-Cortex 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

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)

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.

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

VPL & VPM

Schematic representation of the main mechanosensory pathways (Part 2) neuro4e-fig-09-08-2r.jpg

Pain and Temperature Anterolateral System Cerebral Cortex 3 Thalmus 2 1 Brainstem/spinal cord

The Anterolateral System Substantia Gelatinosa

Spinal Cord dorsal columns Dorsal Ventral lateral columns

Schematic representation of the main mechanosensory pathways neuro4e-fig-09-08-0.jpg

To Cerebellum(1) 1-Direct Pathways A) Posterior(dorsal) Spinocerebellar Tract B) Cuneocerebellar Tract C) Anterior(ventral) Spinocerebellar Tract D) Rostrospinocerebellar Tract

To Cerebellum(2) 2- Indirect Pathways A) Spinocervicocerebellar Tract B) Spinoolivocerebellar Tract

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

Thalamocortical Pathway Origin - VPL Course – Posterior limb of internal capsule Laterality - Uncrossed Topographical Organization - yes Destination – Primary somatosensory cortex, areas 1, 2, 3 Function – DC- ML functions 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

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

Brown-Sequard syndrome