(9) Ascending Sensory Tracts Flashcards
difference between exteroreceptors, proprioceptors, enteroreceptors
▪︎ exteroreceptors: relay info about external events (pain, temp, touch, pressure)
▪︎ proprioceptors: position in space
▪︎ enteroreceptors: state of internal organs
sensory receptos transduce signals via
graded electrical signas (action potentials)
What is a pacinian corpuscle?
rapidly adapting mechanoreceptor in subcut that senses vibration (~250 Hz) and pressure in skin, joints, muscle, mesentery
- *free nerve endings encapsulated by lamellae (~schwann cells)
- *only signals AP when stim applied and released not during
What is a meissner corpuscle?
rapidly adapting mechanoreceptor in glaborus skin that is sensitive to light touch and vibration (<50 Hz)
What are Merkel’s disks?
slowly adapting mecanoreceptors in glaborus skin (right below ridges in fingertips). they also form touch domes or hair disks (specialized epithelial structures in hairy skin)
What are ruffini organs?
slowly adapting mechanoreceptor found only in deep layer of glaborus skin; respond to sustained pressure and skin stretch; contributes to positional sense
free nerve endings are responsive to
temp and pain
CNS structure that plans and fine tunes movement in response to a sensory stimulus
cerebellum
mediated conscious awareness of stimuli
cortex
pathways that detects fine discrimination of touch, pressure, vibration, and proprioception
posterior column-medial lemniscus
pathway that detects pain, temp, and crude touch
spinothalamic tract
spans the entire brainstem to handle both ascending and descending information
medial longitudinal fasciculus
Describe the organization of the posterior column-medial lemniscus pathway
receptor in periphery → spinal ganglion in dorsal root → ipsilateral dorsal column within fasciculus gracialis (below T6) or fasiciculus cuteatus (above T6) → in caudal medulla they synapse with secondary neuron in nucleus graciis or nucleus cuteantus → axons cross midline and ascends contralateral side and runs in medial lemniscus to the thalamus → synapses in ventral posterolateral nucleus → third order neuron sends axon to ipsilateral (contra to primary neuron in periph) somatosensory cortex
Describe the organization of the spinothalamic pathway
free nerve endings → spinal ganglion in dorsal root → at the level of entry primary neuron synapses with secondary neuron in ipsilateral dorsal horn → axon of secondary neuron decussates at this same level → ascends via contralateral anterolateral funciculus → synapse in VPL of thalamus → third order neuron sends axon to ipsilateral somatosensory cortex
type of fiber nerve in PC-ML Pathway
fast Abeta (type II)
type of fiber nerve in spinothalamic pathway
slower Adelta or C fibers (type III or IV)
in the PC-ML pathway the decessating fibers are called
internal arcuate fibers
in the PC-ML pathway as the fibers travel in the medial lemniscus, they travel through … on their way to the VPL
pons and midbrain
in the PC-ML pathway, projections from VPL travel through …. on their way to the cortex
posterior limb of the internal capsule
collaterals of the DC-ML pathway synapse…
dorsal and ventral horns
*collaterals are proprioceptive inputs from muscle spindle organs (basis of monosynpatic stretch reflexes)
In what # layer of Rexed laminae do primary protopathic (temp and pain) inputs synapse with second order neurons
1 and 5
a lesion at T3 spinal cord level will result in a loss of pain and temp sensations from what levels?
T3 and T4, 5, and maybe 6
(2-3 levels below lesion because it takes 2-3 levels for all afferents entering at a given level to cross to the contralateral side)
what info does the spinocerebellar tract carry?
proprioceptive and tactile info about limb an joints
difference in info carried by dorsal and ventral and rostral spinocerebellar tract
dorsal: muscle spindle and GTO input from ipsilateral leg and body
ventral: GTO input from ipsilateral leg and body
rostral: GTO inputs from ipsilateral arm
info carried on cuneocerebellar tract
spindle and GTO inputs from ipsilateral arm
describe the organization of the dorsal spinocerebellar tracts
afferents enter in the spinal cord and ascend to Clarke’s Nucleus (T2-L2) via fascivulus gracilis → via inferior cerebellar peduncle to ipsilateral anterior lobe of cerebellum → synapse in accessory cuneate nucleus
where is Clarke’s nucleus found?
T2-L2 in lamina VII medial grey matter of spinal cord
What is the Substantia gelatinosa and where is it found?
site of 1st modulation of pain and temp info
lamina I and II of spinal cord gray matter
What is the lissauer tract?
in the spinothalamic tract, after the axons have entered the spinal cord they travel up or down 1-2 segements in the lissauer tract before the synapse in the posterior horn → cross midline
the somatosensory afferents for the head/face have their cell bodies… except for…
in a ganglion OUTSDE THRE BRAIN = Trigeminal Ganglion
except for the muscles of mastication which are found in the mesencephalic nucleus which is in the brainstem
the trigeminal ganglion is analogous to the
DRG
trigeminal projections are to the ….
ventral posteromedial nucleus (VPM)
