CDP Flashcards
How is composed the cord dorsum potential?
Definition: represents a spinal cord field potential arising from the region of spinal cord receiving input from nerve
1) Triphasic spike: extracellular events associated with propagation of sensory action potentials into the SC
Positive: axonal, electrotonically conducted, positive capacitance current, generated at the node of Ranvier.
Negative: depolarization of the cell membrane at the next node induces an influx of Na+ into the axon therefore the extracellular space become negatively charged
Positive: efflux of K+ from the axon into the extracellular space
2) Large negative peak: actual cord dorsum potential: change in the extracellular environment produced by dorsal horn interneuron activity (Na+ enters in the cell bodies and exits into the extracellular space along their ventrally projecting axons)
3) Intramedullary spike: sometimes seen in the large negative peak = propagation of action potentials from primary afferent fibers to the afferent termini
4) Final prolonged positive wave: extracellular representation of primary afferent depolarization, positive current exits extracellular space at the excited axo-axonal synapses and renters along the primary dorsal nerve root afferents.
What is the normal predictive values for canine CDP onset latency following stimulation of the distal tibial nerve in dogs? Radial nerve?
Tibial:
Formula: expected L4-L5 CDP onset latency = -1.194 + 0.014 x pelvic limb length (mm)
Values: 3.1 ± 0.3 ms
Ulnar:
Formula: expected C7-T1 CDP onset latency = -0.9 + 0.014 x thoracic limb length (mm)
Values: 3.0 ± 0.4 ms
Which is not true of cord dorsum potentials? :
a. They can be recorded in the lumbar and caudal cervical/cranial thoracic regions
b. They are purely motor events
c. They are mixed potentials, consisting of a conductive volley and a field potential
d. They may be absent in patients with brachial plexus avulsions
b
What is the significance of increased onset-peak latency in CDP?
Slowing along centrally myelinated sensory fibres or abnormalities affecting dorsal grey horn
What is the difference in CDP between feline diabetic neuropathy and canine shaking pup syndrome?
Feline diabetic neuropathy: demyelinating disorders affecting PNS. Associated findings are:
Loss of triphasic A-wave (volley component).
Increased onset latency.
Increased onset – peak latency difference.
Shaking pup syndrome: hypomyelinating disease related to oligodendrocyte function. Associated findings are:
Normal onset latency.
Increased onset – peak latency difference
What parameters are evaluated during the blink reflex testing?
Preston/kimura:
R1: usually present ipsilaterally to the side being stimulated. It is thought to represent the disynaptic reflex pathway between the main sensory pontine nucleus of V and the ipsilateral facial nucleus.
R1 fibers: tactile sensation
R2: typically present bilaterally. It is mediated by a multisynaptic pathway between the nucleus of the spinal tract of V in the ipsilateral pons and medulla and interneurons forming connections to the ipsilateral and contralateral facial nuclei.
R2 fibers: pain and temperature sensation
Rc: corresponds to the contralateral R2 response.
Cuddon:
latency is the conduction time along the trigeminal and facial nerves, pontine synaptic relay, neuromuscular delay and conduction along orbicularis oculi muscle fibers.
R2: much more variable latency because it is transmitted through polysynaptic reflex pathways involving the trigeminal spinal and sensory nuclei, contralateral ventral thalamic nucleus and bilateral facial nuclei. The latency decrease with increasing stimulation.
Rc: only with sedation, longer latency than R2
R3: inconsistently, nociceptive fibers?
(the thalamic relay is described only in a 1978 paper…)
Habituation: gradual quantitative decrease in amplitude with repeated uniform stimuli (R2 and Rc)
What is the pathway of the direct facial stimulation?
Stimulation of the palpebral nerve (VII) produces both direct (variable amplitude, stable latency < R1) and reflex faciofacial evoked muscle potential in ipsilateral orbicularis oculi muscle.
What is the pathway of the trigemino-trigeminal reflex testing?
Stimulation of the middle mental nerve or infraorbital nerve induces polyphasic reflex evoked muscle potential in the rostral belly of the digastricus muscle.
What is the definition of spinal somatosensory evoked potentials (SSEP)? Which tracts are implied?
Definition: electrical events elicited from neurons, synapses, or axons when sensory axons in peripheral nerves are stimulated.
Tracts: both ipsilateral (major) and contralateral (minor) in the dorsal quadrant but a relatively small area of the most **dorsolateral **regions of the ipsilateral dorsolateral funiculus are very important in the propagation of the early, high amplitude negative peaks = dorsal spinocerebellar tract, **spinocervicothalamic tract **and spinomedullothalamic tract. Dorsal column is less important because of differences in axonal conduction velocities.
What are the 3 kinds of potentials during SSEP?
Compound action potentials: axons in peripheral nerve, cauda equina and spinal cord white matter
Field potentials: de/repolarization of synapse = gray matter, stationary
Injury potential: sharp downward displacement of the entire SSEP
What is the effect of temperature on SSEP velocity?
1 °C decreased => -3 m/s
True or false: during cortical SSEP, a rate of stimulation > 2 Hz increase the amplitude.
False: it reduces the amplitude.
True or false: at each more cranial recording site, first negative peak increases and second negative peak decreases during SSEP.
False: at each more cranial recording site, first negative peak decreases and second negative peak increases.
At what age do conduction velocities reach adult values during SSEP?
9 months
What is the normal cortical SSEP latency for tibial nerve in dogs? Ulnar? Median? Radial?
Tibial: 7.5 + 0.017 x body length
First positive peak: 18.3 ± 1.8 ms
First negative peak: 30.6 ± 2.4 ms
Ulnar:
First positive peak: 14.8 ± 1.6 ms
Median:
First positive peak: 15.2 ± 1.3 ms
Radial:
First positive peak: 15.3 ± 1.4 ms
