Somatosensory tracts Flashcards
(26 cards)
postecentral gyrus
aka somatosensory cortex or Broadmann’s areas 3,1,2
the final destination for somatosensory information from thalamic relay neurons
thalmaic relay neurons
NEVER decussate, receive info from the prethalamic relay neurons (which do decussate
final synapse onto the primary somatosensory cortex
Labeled line code
MODALITY
any stimulus, at any point along a SPECIFIC TRACT, there is the same modality
i.e. stimulate the visual tracts at any point, it will synapse onto the visual cx and transmit a visual stimuli
population code
as intensity of stimulus the number of receptors activated increases—->increased Intensity
frequency code
increased intensity of stimulus increases the rate of AP generation —–> increased intensity
receptive field
the area of which a particular neuron can respond to a particular stimuli
- large receptive field=low density=low resolution=dec localizing ability=decreased cortical neurons
- small RF=high density=high resolution=localizing ability=large number of associated cortical neurons
PCML
posterior column medial lemniscus
- ascending tract GSA from THE BODY Only (C1-S5)
- Conscious
- Modalities: somatosensation: proprioception, discriminative (fine) touch, vibratory sense
- very rapid conduction (A alpha)
Discriminative touch
ability to have fine, two point discrimination with high degree accuracy in location
graphesthesia, stereognosis
sensory ataxia
lack on conscious proprioception
causes dymetria: incorrect metering of limb in space. Base wide stance, stumbling, difficulty turning, truncal sway, inaccurate voluntary movement
results from a lesion of the dorsal columns
anterolateral system
GSA somatosensation
Pain, temp, CRUDE touch
Tested clinically
small, unmyelinated Abeta (touch temp) and Adela and C=pain
**spinothalamic is contralateral projections
all other tracts are bilateral
spinothalamic tract
most axons in ALSO, projects to primary SS cx via thalamus
Conscious perception
Spinoreticular tract
projects to reticular formation, important for alerting the cx of stimulus focusing attention and some autonomic fxns
spinomesensephalic tract
to midbrain
some fibers project to the PAG for pain modulation
also sends fibers to the spinotectal system (visual-grasp reflex)
spinohypothalamic tract
projects to the hypothalamus
controls autonomic responses to stimuli (think tearing up, or become nauseated after a painful stimuli)
provides fibers into the limbic systems—>emotional response to pain
Adelta fibers
part of the anterolateral system
small unmyelinated neurons
control fast pain (short lived and well localized
A C fibers
part of the anterolateral system
small unmyelinated
control slow, long lasting pain that is not well localized (think GVA)
GVA
Sensory info to the gut
some conscioius, but mostly unconcious that drive local reflexes
small C fibers with nociceptive or stretch receptors
info goes into tracts other than STT (i.e. spinoreticular, spinohypothalamic-anything that is NOT headed into the cortex)
opthalmic n.
V1
sensory from nose, around eyes and forehead
maxillary n.
V2
sensory from lat nose, masilla
mandibular
V3
sensory and motor
sense from chin, cheek and lateral head
trigeminal GSA
brought in from primary afferents in all three 3brs
most cell bodes in the trigeminal ganglion
mesencephalic nuc (within CNS) is also a location for cell bodies- EXCEPTION TO THE RULES
spinal nuclei of V
prethalamic relay nuclei
analagous to the dorsal horn neurons in the ALS
relay info form V1-3 about pain, temp and crude touch
Pontine nuclei
aka sensory nuc.
prethalamic relay nuclei for proprioception for fine touch, somatosensation, vibration
aka gracillis and cuneatus
off to the thalamus (Ventroposteriormedial nuc. of the thalamus)
somatotopy of the Spinal V nuc.
V3=posterior
V1=anterior
ear= inferior
face=superior
