Sensory Physiology Flashcards
What do Aalpha afferent neurons do?
large and fast
supply primary muscle spindles, golgi tendon organs
What do Abeta afferent fibers do?
secondary muscle spindles
skin mechanoreceptors
What do Aa motor fibers supply?
extrafusal sk m fibers
What do Agamma fibers supply?
intrafusal fibers
What do B motor fibers supply?
preganglionic autonomic fibers
What do c motor fibers supply?
postganglionic autonomic fibers
What is a generator potential and how does it vary?
somatosensory’s response to a stimulus
small with weak stim
strong stim –> large generator potential –> action potential
What is the significance of the thalamus in sensory systems?
info from all sensory systems except olfactory are relayed through the thalamus on way to cerebral cortex
What is convergence?
branches of 2 different primary afferents synapse on one secondary
What is divergence?
one primary neuron has 2 branches that synapse on 2 different secondaries
What are the 2 ways to get a strong stimulus?
all branches of one afferent or branches from multiple afferents converging
How do the number of active receptors change with intensity of stimulus?
increase in number w/ intensity
What is receptor adaptation?
when a stimulus persists unchanged for several min w/out change in position or amplitude –> neural response diminishes and sensation is lost
What are slow adapting and rapidly adapting receptors?
slow adapting: responde to prolonged and constant stim
rapidly adapting: only active at beginning or end of stimulus - when intensity increases or decreases
What are the rapidly adapting receptors and what they sense?
meissner corpuslce - tap, flutter
hair follicle receptor (can also be SA) - motion, direction
pacinian corpuscle - vibration
What are the slowly adapting receptors and what they sense?
hair follicle (can also be RA) - motion, direction
merkel disk - touch, pressure
ruffini corpuscle - skin stretch
What is the relationship btw tactile and acuity and receptive fields
acuity highest in smallest fields (lips)
acuity lowest in largest fields (back)
What is the relationship btw convergence and tactile acuity?
more convergence –> less acuity
What is pre-synaptic inhibition?
powerful form of inhibitory control
diminished excitatory signal: GABA –> Cl influx –> hyperpolarization –> less NT release
How does presynaptic inhibition help you?
helps the brain not get overwhelmed –> can localize signal betters
Are somatotopic maps fixed?
no
continual imput can magnify its map
restricted input decreases part of cortex devoted to that region
What layers of the cortex are enlarged in sensory cortexes?
3 and 4 –> main site of axons from the thalamus
How are neurons arranged in regard to depth?
neurons stacked above and below are very similar
columns side by side are different (explains homunculus) - usually same part of body, but different sensory modality
Where is the primary somatosensory cortex
post-central gyrus
first stop for most cutaneous senses
Where is the secondary somatosensory cortex?
in wal of sylvian fissure
receives input from S1 –> compares btw objects, diff tactile sensations and det whether something becomes a memory
What is the PTO?
parieto-temporal-occipital association cortex
input from multiple places –> high level interpretation of sensory inputs
What does S1 send projections to?
back to subcortical structures
usually thalamus
descending axons > ascending
permits focusing activities
What do cortico-cortico projections do?
est parallel paths of sensation
allows for simultaneous processing
can be ipsi or contra
What are corticofugal signals?
cortex –> lower relay
controls intensity of sensory sensitivity
typically inhibitory
What is the doctrine of specific nerve energies?
no matter where along the afferent path is stim, sensation will occur and will arise from origin of sensation
What type of pain does Adelta encode?
quick pain
What type of pain do C fibers encode?
slow pain
What are the different modes of nociception?
thermal
mechanical
chemical
receptors can be polymodal
can be silent and then turned on
What are the 2 types of free nerve endings?
peptidergic: express substance P, CGRP, responsive to NGF most visceral afferents, 1/2 of cutaneous afferents
non-peptidergic: no neuropeptides, responsive to GDNF, 1/2 of cutaneous afferents
What are TRP receptors?
sense noxious stimuli
ligand-gated non-selective cation channels
activated in response to temp (menthol, capsaicin)
What do C and Adelta use as NTs?
C = EAA and SP/CGRP
Adelta = EAA
What is descending inhibition?
signals from higher brain that dampens pain input
PAG stim by opiates, EAA, and cannabinoids –> locus coeruleus and raphe nucleus –> 5HT and NE –> dorsal horn –> activate inh interneurons –> opiates –> reduction of SP from C fiber –> reduces nociception
What is the gate control theory of pain?
C fiber to 2ndary neuron and also to interneuron that inhibits 2ndary neuron to reduce pain signals
w/ strong pain - C fiber releases glycine –> inhibits interneuron –> EAA to secondary nerve –> pain
Abeta fiber can also stimulate the interneuron at the same time –> inhibits secondary neuron
(like when you rub your finger when you smash it)
What is sub-threshold inflammation?
not apparent on histology but still causes pain
bradykinin involved
What parts of the cortex are important in processing pain?
S1 and S2 - localization
insular cortex - integrates all signals, damage causes asymbolia
What does the amygdala do in pain?
emotional component
What do the hypothalamus and medulla do in pain?
visceral input w/ autonomic nerves –> hypothalamus and medulla –> physio changes
