Dorsal Column

Dorsal Column lesion

Agraphesthesia - can't tell what letter is drawn on hand. Astereognosia - can't identify items by touch.

Upper pathway

Axons will synaps IPSI with cells in Nucleus Gracilis/Cuneatus. Those cells send axons across the midline in the medulla thought internal arcuate to the the medial lemniscus. ML axons synapse in the thalamus (VPL - Ventral posterior later thalamic nucleus) Those send info to somatosensory cortex.

White matter

Axons, white because of myelanation. Divided into faniculi: Dorsal faniculus, lateral faniculus, ventral faniculus. Ventral Medial Fissure is involved in blood supply.

Gray matter

Cell bodies. Consists of Dorsal horn, ventral horn, lateral horn, Commissure (middle connection between left and right) Central canal is continuous with the 4th ventricle and filled with CSF.

Receptive fields

Deeper receptors (pacinian/ruffini) have larger receptive fields. More superficial receptors are fast adapting so they stop (slow) firing with continuous stimulation.

2 point discrimination

Determine how concentrated the receptors are. Concentration is higher in your fingertips, lips.

Lamina of Rexed

Different layers of the gray matter of the spinal cord divided by type of cell.

Fasciculus Gracilus

Dorsal part of the dorsal faniculus.

somatosensory cortex

Homunculus gets inputs from the VPL/VPM. Amputation will result in phantom limb because missing input will be replaced with collaterals from neighboring neurons.

Lhermitte's sign

If patient stretched cord by bending head forward it can create sensation in the lower extremities.

Lesions

If you have a disruption below the internal arcuate, you will lose sensation on the ipsilateral side of the body. If you have the disruption above the internal arcuate, you will have a contralateral deficit.

Alpha beta axons

Large, fast. Transport touch press, vibration, proprioception, 2 pt discrim in the dorsal column. Info comes from Meissner's (light touch/testure), Pacinian corp (deep pressure /stress/vibration) merkel discs (unencapsulated, touch pressure), ruffini endings (deep pressure/stretch), hair folicle receptors (unencapsulated).

Dorsal column system

Runs in dorsal faniculus. These axons are Alpha beta axons. They carry touch, pressure, proprioception, skin vibration. Cell bodies are located into the DRG and the axons head up to the brainstem. As you get closer to the brainstem, the alpha beta axons segrate to the dorsal part of the dorsal faniculus.

Romberg sign

Test of vestibular system. If you close your eyes and you start to sway that is a positive rhomberg. If you sway with your eyes open, it is most likely a cerebellar or vestibular problem.

Ascention of the Alpha Betas

They enter the outside of the dorsal faniculus but as you ascent and more axons enter, they get pushed towards the center. The Fasciculus gracilis is most of the dorsal faniculus caudally but then the faniculus cuneatus pushes in from the outside. Below T7 the axons enter the fasciculus gracilus (grass - feet) but T6 and above they enter the fasciculus cuneatus. Sacral are medial, then lumbar, then thorasic, then cervical are lateral. Body is represented in the fasciculi.

Facial pathway

Trigeminal nerve (CN5) goes into the brainstem and synapses on the chief nucleus. Chief nucleus sends axons to VPM (ventral posterior medial thalamis nucleus) contralaterally.

Joint receptors

Type 1 - golgi like position, movement. Type 2 - Ruffini position, velocity. Type 3 - pressure.