SPINAL PATHWAYS

SOMATOSENSATION

Sensations of touch, pressure, stretch, vibration, temperature, body position, pain recognised through neural receptors in the skin and certain internal organs.

LOCATION OF SOMATOSENSORY CORTEX It is located in the post central gyrus (primary somatosensory cortex), in a tactile representation which is orderly arranged (in an inverted fashion) from the toe (at the top of the cerebral hemisphere) to the mouth (at the bottom). Each cerebral hemisphere of the primary somatosensory cortex contains tactile representations of the OPPOSITE side of the body. Each part being proportional in size to the relative density of cutaneous tactile receptors in that part.

ASCENDING PATHWAYS

1. Spinothalamic

2. Dorsal column-medial lemniscus

3. Spinoreticular

4. Trigeminal sensory

5. Spinocerebellar

SPINOTHALAMIC - PAIN, TEMPERATURE AND CRUDE TOUCH - SLOW CONDUCTION

1. Peripheral sensory neuron, cell body in DORSAL ROOT GANGLION

2. Second order neuron cell body in DORSAL HORN OF SPINAL CHORD

FIRST SYNAPSE IN THE SPINAL CHORD (2-3 spinal levels above entry)

DECUSSATES IN THE VENTRAL SPINAL CHORD

1. Third order neuron cell body in the THALAMUS

SECOND SYNAPSE IN THE THALAMUS (lateral ventro-posterior nucleus)

4. Fourth order neuron in the SOMATOSENSORY CORTEX

THIRD SYNAPSE IN THE SOMATOSENSORY CORTEX

DORSAL COLUMN MEDIAL LEMNISCUS PATHWAY - DISCRIMINATIVE TOUCH, CONSCIOUS PROPRIOCEPTION, VIBRATION - FAST CONDUCTION

1. Peripheral sensory neuron, cell body in DORSAL ROOT GANGLION, carry the information through the DORSAL COLUMN TRACTS

2. Second order neuron cell body in the GRACILE AND CUNEATE NUCLEI OF DORSAL MEDULLA

FIRST SYNAPSE IN THE MEDULLA

DECUSSATES INTHE MEDULLA

1. Third neuron cell body in the THALAMUS, carries information to the PARIETAL LOBE SOMATOSENSORY CORTEX

SECOND SYNAPSE IN THE THALAMUS

DESCENDING PATHWAYS

1. Corticospinal

2. Corticobulbar (cortico-nuclear)

3. Corticospinal and corticobulbar

CORTICOSPINAL - DESCENDING MOTOR PATHWAY - VOLUNTARY MOTOR MOVEMENT, SPINAL REFLEXES

1. First order neuron in the MOTOR CORTEX = UPPER MOTOR NEURON

Decussate in the VENTRAL MEDULLA (DECUSSATION OF THE PYRAMIDS) = LATERAL CORTICOSPINAL TRACT 85%

Do not decussate in the medulla, but AT THE SPINAL CHORD NEAR THE TERMINATION + ANTERIOR/VENTRAL CORTICOSPINAL TRACT 15%

1. Second order neuron in the SPINAL CHORD, NEAR ITS TARGET = LOWER MOTOR NEURON

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