(9) Ascending Sensory Tracts

Question 1

difference between exteroreceptors, proprioceptors, enteroreceptors

Answer 1

▪︎ exteroreceptors: relay info about external events (pain, temp, touch, pressure)
▪︎ proprioceptors: position in space
▪︎ enteroreceptors: state of internal organs

Question 2

sensory receptos transduce signals via

Answer 2

graded electrical signas (action potentials)

Question 3

What is a pacinian corpuscle?

Answer 3

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

Question 4

What is a meissner corpuscle?

Answer 4

rapidly adapting mechanoreceptor in glaborus skin that is sensitive to light touch and vibration (<50 Hz)

Question 5

What are Merkel’s disks?

Answer 5

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)

Question 6

What are ruffini organs?

Answer 6

slowly adapting mechanoreceptor found only in deep layer of glaborus skin; respond to sustained pressure and skin stretch; contributes to positional sense

Question 7

free nerve endings are responsive to

Answer 7

temp and pain

Question 8

CNS structure that plans and fine tunes movement in response to a sensory stimulus

Answer 8

cerebellum

Question 9

mediated conscious awareness of stimuli

Answer 9

cortex

Question 10

pathways that detects fine discrimination of touch, pressure, vibration, and proprioception

Answer 10

posterior column-medial lemniscus

Question 11

pathway that detects pain, temp, and crude touch

Answer 11

spinothalamic tract

Question 12

spans the entire brainstem to handle both ascending and descending information

Answer 12

medial longitudinal fasciculus

Question 13

Describe the organization of the posterior column-medial lemniscus pathway

Answer 13

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

Question 14

Describe the organization of the spinothalamic pathway

Answer 14

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

Question 15

type of fiber nerve in PC-ML Pathway

Answer 15

fast Abeta (type II)

Question 16

type of fiber nerve in spinothalamic pathway

Answer 16

slower Adelta or C fibers (type III or IV)

Question 17

in the PC-ML pathway the decessating fibers are called

Answer 17

internal arcuate fibers

Question 18

in the PC-ML pathway as the fibers travel in the medial lemniscus, they travel through … on their way to the VPL

Answer 18

pons and midbrain

Question 19

in the PC-ML pathway, projections from VPL travel through …. on their way to the cortex

Answer 19

posterior limb of the internal capsule

Question 20

collaterals of the DC-ML pathway synapse…

Answer 20

dorsal and ventral horns

*collaterals are proprioceptive inputs from muscle spindle organs (basis of monosynpatic stretch reflexes)

Question 21

In what # layer of Rexed laminae do primary protopathic (temp and pain) inputs synapse with second order neurons

Answer 21

1 and 5

Question 22

a lesion at T3 spinal cord level will result in a loss of pain and temp sensations from what levels?

Answer 22

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)

Question 23

what info does the spinocerebellar tract carry?

Answer 23

proprioceptive and tactile info about limb an joints

Question 24

difference in info carried by dorsal and ventral and rostral spinocerebellar tract

Answer 24

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

Question 25

info carried on cuneocerebellar tract

Answer 25

spindle and GTO inputs from ipsilateral arm

Question 26

describe the organization of the dorsal spinocerebellar tracts

Answer 26

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

Question 27

where is Clarke’s nucleus found?

Answer 27

T2-L2 in lamina VII medial grey matter of spinal cord

Question 28

What is the Substantia gelatinosa and where is it found?

Answer 28

site of 1st modulation of pain and temp info

lamina I and II of spinal cord gray matter

Question 29

What is the lissauer tract?

Answer 29

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

Question 30

the somatosensory afferents for the head/face have their cell bodies… except for…

Answer 30

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

Question 31

the trigeminal ganglion is analogous to the

Answer 31

DRG

Question 32

trigeminal projections are to the ….

Answer 32

ventral posteromedial nucleus (VPM)