Somatosensory Part 2 Flashcards
How many cell layers are in the cerebral cortex?
6
What kind of cells are in layer 4 and where do they receive input from?
stellate cells in layer 4 receive input from the thalamus
What kind of cells are in layer 5 and what do they do?
pyramidal cells in layer 5 project information to other areas of the cortex
What are Brodmans areas?
areas of cortex that are histologically distinguishable and identified by numbers
What is fMRI? What does it detect?
functional magnetic resonance imaging, detects changes in spin of hydrogen ions in the brain. detect BOLD (blood oxygen level detection)
Where is the thalamus?
in the diencephalon, on each side of the third ventricle
What is thought to be the basis of consciousness?
thalamo-cortical connections
Where do the VPL/VPM project to?
primary somatosensory cortex
What thalamic nuclei project to the somatosensory cortex?
the VPL/VPM
Where is the primary somatosensory cortex?
postcentral gyrus
the VPL receives information from______ and sends it to _______
dorsal column-lemniscal and anterolateral pathways and sends it to the primary SS cortex
the VPM receives information from _____ and sends it to ______
receives info from the head via the trigeminal nerve, sends it to the primary SS cortex
What are cortical columns?
columns of neurons with similar sensory receptive properties (modalities, RFs, etc), usually 300-600microm wide, perpendicular to the cortical surface
what areas of the body are high in sensory neuron density and have large representations in the homunculus?
mouth and hand
what areas of the body are low in sensory neuron density and have small representations in the homunculus?
the back
what evolutionary trends are seen in the homunculus?
animals have large focus on the face, whereas human homunculi also have large representations in limbs/hands/etc
Are there single or multiple somatotopic representations of areas of the body ?
multiple
How does cortical activity respond to movements of single body parts?
cortical activity starts out in a local homuncular spot, then spreads out into neighboring columns
What structures help spread cortical activity to neighboring areas?
arcuate fibers
What does it mean that some connections are “latent”?
inputs from neighboring areas might project to the same columns but may not elicit activity, allowing learning/cortical plasticity to occur
describe localization in peripheral structures
localization is more specific in peripheral structures. smaller RFs innervate smaller areas
describe localization in the CNS
neural interactions between pathways from different RFS occur, requiring lateral inhibition
How does lateral inhibition work?
stimulus of central RF neurons stimulate DCN neurons, but peripheral RF neurons suppress DCN activity via inhibitory interneurons
What is the purpose of lateral inhibition?
to increase the contrast between RF stimulus, thereby increasing acuity of spatial distribution of sensation
the two-point discrimination test measures the integrity of what system? What does it depend on?
the dorsal column-lemniscal system. depends on density of sensory receptors in the skin and lateral inhibition
What is the function of feedback control? What is it?
feedback from the primary SS and motor cortices can regulate peripheral afferent signals. this is in order to provide focus, adequate frequency and duration of discrimination, etc
elimination of movement does what to tactile discrimination?
loss of discrimination, but not of absolute touch
how does the motor cortex facilitate sensory input from a second RF?
suppresses RF1 by enhancing lateral inhibition
facilitates RF2 by inhibiting lateral inhibition in DCN neurons (focus on stimuli from selective fields)
Meissners Rapid Adapting and Merkels slow adapting inputs project to which of Brodmans areas?
they project to separate columns in area 3b
Information from areas 3a and 3b converge onto areas 1 and 2 where neurons generate:
abstract somatosensory perceptions such as orientation, motion, spatial arrangement
Association of somatosensory and visual inputs into area 5 leads to:
a body centered space
how are global properties of objects determined?
multiple points of contact compared to previously stored visual representations
What happens to RFs with each step in cortical hierarchy?
RFs enlarge, and those large areas get incorporated into a meaningful whole (eg. Finger tips –> finger–> hand, etc)
What information is relayed from the primary somatosensory cortex (S1) to the secondary somatosensory cortex? What stream is this?
Ventral stream: tactile object identification, size, shape
What kind of information is relayed from the primary somatosensory cortex (S1) to the posterior parietal cortex? What stream is this?
Dorsal stream: directing attention, motor- how do I grasp it? Where is it in space? Etc
The secondary somatosensory cortex relays information about an object to the hippocampus, amygdala and other limbic centers. What does this do?
Forms memories based on behavioral significance
What is responsible for generating conscious body image?
The posterior parietal association cortex (dorsal stream)
What does the posterior parietal association cortex do?
Ego-centric space, conscious body image, body awareness, embodiment of sensory experience, peripersonal space
Visual, auditory and somatosensory inout converge at the posterior parietal association cortex. Where does that information go next for behavior and generation of memory and emotions?
Prefrontal cortex and limbic regions
What is astereognosis? What causes it?
Inability to identify things by touch. Caused by damage to the posterior parietal association cortex?
Damage to which side of the ppac causes neglect syndrome? Why is this thought to be?
Damage to the right side of the ppac (causing neglect of the left visual field) is most common. This is thought to be because the right side is most often dominant, so damage to the left side could be compensated for.
What is the remembered present?
The event caused by feedback (both bottom up and top down) into the S1 neurons. This causes S1 activity for a fraction of a second, even if the original stimulus is no longer present. This is a cross-modal sort term memory
Consciousness of tactile stimulus depends on:
Peri personal spatial location
What is somatoperception?
What the body is felt to be like
What is somatorepresentation?
Abstract knowledge, beliefs about ones own and others bodies
What causes phantom limb sensations?
The dissociation of somatoperception (the limb is felt to be there) and somatorepresentation (the limb is not there). Caused by reorganization of the somatosensory cortex after removal of the peripheral nerve stimuli, latent nerves function
Do proximal or distal structures take longer reorganize cortical structures after amputation? Why?
Distal structures, since they had more RFs, more nerves and more cortical space in the homunculus
Why is phantom limb pain insensitive to opiates?
S1 has no opiate system, and the phantom pain is associated with S1 plasticity and remodeling
What does the rubber hand illusion tell us about body representation?
That our sense of body ownership is determined by top- down cortical pathways regulation of sensory input
What is delusional parasitosis and what is it caused by?
Delusion of being infested by bugs or parasites, possibly caused by disrupted prefrontal control of somatosensory representations
