Sensory physiology Flashcards
what two schemes are peripheral nerves classified by
contribution to compound AP
fiber diameter, myelin thickness, conduction velocity
what is receptor adaptation
when a stimulus persists without change in position or amplitude, neural response diminishes => sensation is lost
what receptors respond to prolonged and constant stimulation
slowly adapting receptors
what receptors respond only at the beginning/end of a stimulus
rapidly adapting receptors
what are mechanoreceptors responsible for
sense of touch
what does meissner’s corpuscle sense
tap, flutter
are meissner’s corpuscles rapidly or slowly adapting
rapidly adapting
what do hair follicle receptors sense
motion, direction
are hair follicle receptors rapidly or slowly adapting
either slow or rapidly adapting
what do pacinian corpuscles sense
vibration
are pacinian corpuscles rapidly or slowly adapting
rapidly adapting
what do Merkel discs sense
touch, pressure
are merkel discs rapidly or slowly adapting
slowly adapting
What do ruffini corpuscles sense
skin stretch
are ruffini corpuscles rapidly or slowly adapting
slow adapting
where are receptive fields largest
calf, back and thigh
what stimuli initiates pre-synaptic inhibition?
GABA => influx of Cl-
what improves the brain’s ability to localize signals?
reduced NT release secondary to presynaptic inhibition
what are the three steps of cortical processing
initial processing
integration
emotional response
how does an amputation affect the homonculus?
because input to the leg is restricted, the portion of cortex devoted to that region decreases
what are the main output neurons of the cortex
pyramidal cells
what layers of the cortex are enlarged in the primary sensory cortex and why
layer III (medium sized pyramidal cell layer) layer IV (granular layer) because axons from the thalamus terminate in these layers
through what layers of the cortex do the neuronal columns extend
all of them, 1-6
how are neuronal columns organized functionally?
neighboring columns receive sensory information from the same part of the body, but a different modality
what are the three parts of the somatosensory cortex
primary area (SI) secondary area (SII) association area
what brodmann areas make up the primary somatosensory cortex
1,2,3
which part of the somatosensory cortex is responsible for proprioception and size/shape discrimination
SI
which part of the somatosensory cortex is responsible for comparison btwn objects and tactile sensations and determining whether a memory is stored
SII
where is S2
in the wall of the sylvian fissure
which part of the somatosensory cortex names objects and helps w proprioception
parieto-temporal-occipital (PTO) association cortex
what characteristic of SI allows focusing activities
projections sent back to the thalamus and other subcortical structures
how are primary and association areas of the sensory cortex linked?
via cortico-cortical projections
are cortico-cortical projections on the same between the same or opposite hemispheres
either!
what are corticofugal signals
signals transmitted cortex => postcortical structures to inhibit and suppress sensory input
what is the difference between nociception and pain
pain is the SENSATION of tissue damage
nociception is the autonomic or behavioral conseqences of tissue damage
what fibers carry slow pain
C
what fibers carry fast pain
Adelta
are axons of nociceptors typically myelinated?
no, usually unmyelinated or thinly myelinated
what are free nerve endings
nerve endings which lack specialized receptor cells or encapsulations
what kind of free nerve endings express substance P and cGRP
peptidergic
what stimulus do peptidergic nerve endings respond to
NGF (nerve growth factor)
what stimulus do non-peptidergic nerve endings respond to
GDNF (glial-derived neurotrophic factor)
what kind of nerve endings are implicated in diabetic neuropathy
non-peptidergic
what receptors sense noxious stimuli?
TRP receptors
what is the MOA of TRP receptors
ligand-gated non-selective cation channels permeable to Ca, Na and K
describe the gate control theory of pain
in the absence of pain signalling, tonically active inhibitory neurons suppress the pain pathway
what function does the insular cortex have in the pain pathway
it integrates all signals related to pain
what structure is important to the emotional component of pain
amygdala
what is the underlying premise to referred pain
afferents from the injured site and site of referred pain converge in the dorsal horn
what part of the cortex is most important for interpretation of nociception
insular cortex
what ligand do we need to know that propagates neurogenic pain
BRADYKININ (increases nociceptor density in area of inflammation)
what is the path of descending inhibition
periaqueductal grey matter =>
locus coerulus and raphe nucleus release NE/serotonin =>
activate local inhibitory interneurons
what fibers are activated by rubbing an area of pain, and how does it reduce sensation of pain
Abeta fibers activate inhibitory interneurons
do Adelta fibers react to substance P and CGRP?
no, only C fibers do
does EAA bind to NMDA or non-NMDA receptors
non-NMDA
what TRP receptor is activated by physical heat and capsacin
TRPV1
what TRP receptors is activated by menthol and cold
TRM8
what neuropeptides are expressed by peptidergic nerve endings
substance p
CGRP
