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Flashcards in Somatosensory II Deck (19)
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How many layers are there in neocortex?



What are the major input and output cells of the cortex, and which layers are they in?

Input: Stellate cells, layer IV
Output: Pyramidal cells, layer V


What are Brodmann's areas?

Histologically distinct regions of cortex roughly matching up to functionally-derived brain maps.


What does fMRI measure?

Brain activity.
Active areas undergo local vasodilation. fMRI identifies proton movements to distinguish oxyenated vs deoxygenated blood.


Describe the general organization of the thalamus. Which areas are associated with the somatosensory cortices?

Dor-soposterior: Association cortex
Dorso-anterior: Limbic system
Ventro-posterior: Somatosensory cortex (VPM & VPL)
Ventro-anterior: Motor cortex


Where and what is the primary somatosensory cortex?

Postcentral gyrus
(secondary cortex is deeper into the lateral sulcus)
Elaborate and contextualize sensory information into meaningful experiences.


What are cortical columns?

Neurons with similar sensory modality and receptive fields clustered together. Clearly visible in functional studies.


What is somatotopy?

Describes the CNS feature in which sensory representation of body areas are mapped contiguously and in a relation that mimics the physical body, with larger area given to areas with higher sensory density.


What is meant by cortical plasticity?

Cortical sensory representation changes with experience and learning.
Columns respond primarily to one area of the body, but there are also latent inputs from neighboring areas. If the primary area stops sending inputs or if the neighboring areas are more active, the column may be co-opted to be most responsive to the formerly latent neurons.


Lateral inhibition

A second-order neuron is activated by a sensory neuron from the center of a receptive field, but inhibited by the surround of the receptive field. This enhances the difference between somatosensory fields and is crucial for localization of stimulus.


How do the sensory and motor cortices affect lateral inhibition and information processing in the ascending somatosensory system?

They provide feedback into the sensory pathways for focusing. Descending pathways modulate afferent input in order to select certain sensory inputs relevant to movements and assure sufficient frequency and duration of tactile exploration for information gathering.


What is two-point discrimination and what part of the somatosensory system is responsible for it?

The ability to discriminate between separate but simulatenous pinpricks to the skin.
Dorsal column lemniscal system.


What are the somatosensory “dorsal and ventral streams”?

Ventral stream: SI projects bilaterally to SII in the lateral sulcus for form processing, object recognition. Develops internal 3D model. Also projects to amygdala. (What is it? How do I feel about it?)
Dorsal stream: SI projects posteriorly to posterior parietal cortex for multisensory integration and working with the motor cortex. Creates coherent egocentric representation of space (Where is it in relation to me and how do I touch it?)


How are afferents from different modalities integrated in the cortex?

Slow- and rapid-adapting neurons map to separate cortical columns. Touch, pain, and proprioception project to different Brodmann's areas.
Tactile information converges to areas where it is understood more abstractly, then on to be associated with other senses to generate a body-centered space.
RFs enlarge with each step up the cortical hierarchy.


What aspects of somatosensory information are associated with the PPC and SII?

SII: Tactile and proprioceptive projections, contact with objects

PPC: Touch, proprioception, vision, auditory, etc.



Can't identify objects by touch


Neglect syndrome

Lesion of right inferior parietal lobe
Loss of awareness of one side of space. Left side of perception ceases to exist.


Illusion vs. delusion

Illusion: you're aware it isn't real
Delusion: believe it to be real--problem with PFC


What are the characteristics and cortical issues associated with phantom limb phenomena?

Pt knows abstractly that the limb is gone, yet still feels it to be present.
Reorganization of SI cortex. With loss of afferents from limb, latent neurons in "hand area" from other body parts become more active. Normally the cortical area is reassigned based on use, but in some activation of remaining neurons is misidentified as from lost limb.