Lecture 6. General Sensory Flashcards
What is the minimum distance that can be discriminated as two separate points of contact?
2 mm
What is lateral inhibition important for?
blocking the lateral spread of excitatory signals
Where does lateral inhibition occur?
- each level of major synapse
- dorsal column nuclei
- ventrobasal nuclei of thalamus
- somatosensory cortex
What would happen if our brains did not have lateral inhibition present?
We would not be able to distinguish between two adjacent points of stimulus. would be perceived as one point
What is the fasciculus gracilis?
area in the dorsal medial column of the spinal cord carrying axons from lower limbs
What is the fasciculus cuneatus?
The dorsal lateral portion of the spinal cord that carries axons from upper limbs
Where do axons of the fasciculus gracilis and fasciculus cuneatus synapse?
lower medulla
What are the secondary neurons of he lemniscal tract called and where do they run?
- paired tracts called the medial lemniscus
- from medulla to the basolateral nucleus in thalamus
- these decussate
Where do the tertiary neurons run, in the medial lemniscal pathway?
from thalamus, through the internal capsule to the somatosensory cortex
What type of pain is felt after 0.1 seconds of stimuli, and is mostly superficial?
fast pain
Which stimuli does fast pain respond to?
mechanical and thermal stimuli
What fibers are fast pain carried on?
A-delta fibers
Where do fast pain fibers terminate?
A-delta fibers terminate in lamina marginalis (I) in dorsal horn of spinal cord
Which pain begins after 1 second of stimuli application?
slow pain, if persistent with the stimulus, the response will continue
What can elicit a slow pain response?
mechanical, thermal, chemical stimuli
What type of pain is carried by type C fibers?
slow pain
Where do type C fibers terminate?
slow pain fibers terminate in layers II and III (substantia gelatinosa) of dorsal horns of spinal cord
Which of the nerve fiber types are unmyelinated?
Type C (IV) fibers All others are myelinated
Where do pain fibers decussate?
At the synapse of the primary and secondary neurons, in the dorsal horn of spinal cord
What forms the neospinothalamic tract, and where does it terminate?
- fast pain fibers that terminate in the ventrobasal nuclei of thalamus
What forms the paleospinothalamic pathway, and where doe they terminate?
- consists of slow pain fibers.
2. terminate in the brainstem
What NT is used by A-delta fibers?
glutamate
What NT is used by Type C fibers?
glutamate, substance P
In brown-sequard syndrome what functions will be ipsilaterally lost?
kinesthetics, position sensation, vibration sensation, discrete localization, two-point discrimination below the transection
