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+--- Thread: q.3___________? - sarim (/showthread.php?tid=772179)
0 - ArchivalUser - 03-22-2014
@abodere3, so what happen if a) there is brainstem lesion b) there is no brainstem lesion
@daman, the mnemonic COWS refers to the fast component or slow component direction?
0 - ArchivalUser - 03-22-2014
@miracoli, neumonic COWS refers to fast component direction...
0 - ArchivalUser - 03-22-2014
@daman, great. Can you explain the neural pathway for a) the fast component b) slow component?
0 - ArchivalUser - 03-22-2014
@miracoli...I am too confused with this question...I donot know the explaination...Can someone make this concept clear for us..
0 - ArchivalUser - 03-22-2014
Jus remember COWS ie wen cold water is put in the ear it causes nystagmus towards opposite side and when warm water is put in the ear, it causes nystagmus on the same side the water put in the ear. So in the question here they are stating when warm water is instilled in the left ear the response is nystagmus to the same side but when it's put in the rt ear there is no nystagmus meaning that there is a lesion on the right side ie the same side..hope this clears your confusion. COWS meaning cold opposite, warm same side
0 - ArchivalUser - 03-22-2014
@atkal..Rt side is not the same side...fast component is towards left side..left side is the same side
0 - ArchivalUser - 03-22-2014
Ok.
Warm H2O in the LEFT ear --> stimulation of the LEFT horizontal semicircular canal of the vestibular labyrinth --> increase frequency of APs in the LEFT CN8 and vestibular nuclei--> Neurons in the LEFT vestibular nuclei send their axons, via MLF, to the nuclei of the left CN3 & right CN6--> contraction of LEFT medial rectus [ adduct the left eye] and right lateral rectus[abduct right eye]--> both eyes look to the RIGHT (slow component of the nystagmus to the RIGHT)
but the cortex realizes the head did not move to the left so the cortex causes both eyes to look to the LEFT (Fast or corrective phase of the nystagmus to the LEFT) (may be the signal originates in the RIGHT frontal eye field and then to the left PPRF-->left CN6&right CN3)
The slow component is also explained this way
Warm H2O in the LEFT ear --> stimulation of the LEFT horizontal semicircular canal of the vestibular labyrinth --> increase frequency of APs in the LEFT CN8 and vestibular nuclei--> Neurons in the LEFT vestibular nuclei send their axons across the midline to the contralateral(RIGHT) PPRF--> Neurons in the Right PPRF project to the RIGHT ABDUCENS nucleus--> firing of Axons of CN VI--> contraction of RIGHT LATERAL RECTUS. Other Neurons in the Right PPRF have axons that CROSS the midline and ASCEND in the contralateral(left) MLF to terminate in the oculomotor nucleus (C.N. III)-- contraction of the left MEDIAL RECTUS muscle.
PPRF= PARAMEDIAN PONTINE RETICULAR FORMATION
MLF=medial longitudinal fasciculus
0 - ArchivalUser - 03-22-2014
Right vestibular apparatus lesion--> no stimulation by warm H20--> no firing of CN8-->NO slow component--> no fast component
0 - ArchivalUser - 03-22-2014
hi all participating guys; very nice miracoli
let us to forget about slow fast cold warm, if the 8 CN (vestibular apperatious on the same side of stimulus ) is injured no of these whole story well occur & the stem of sarim Q tell NO response so take it easy... but the discussion about is so useful 4 me at least >thanks to all & to sarim B4
0 - ArchivalUser - 03-22-2014
@microli..thanks a lot..I got it..