Somatosensory & Visual Pathways

Question 1

where are sensory cell bodies located? what kind of cells are they?

Answer 1

in the dorsal root ganglion or trigeminal ganglion
pseudounipolar

Question 2

what size are axons for fine touch?

Answer 2

thick axons

Question 3

what size are axons for pain and temp?

Answer 3

thin axons

Question 4

what are proprioceptors?

Answer 4

muscle spindle organ - supports contraction
Golgi tendon organs - allows for stretching of muscle

Question 5

what are proprioceptor axons like? what kinds of fibers are they?

Answer 5

large diameter & myelinated
A-alpha fibers travel ~80-120 m/s

Question 6

what are mechanoreceptors?

Answer 6

meissner’s corpuscles and Merkel’s cells - texture and superficial sensation
Ruffini’s corpuscles - deep pressure
pacinian corpuscles - vibration

Question 7

what are mechanoreceptor axons like? what kinds of fibers are they?

Answer 7

medium diameter & myelinated
A-beta fibers travel ~35-90 m/s

Question 8

what are pain and temp receptors?

Answer 8

bare nerve endings (cold/heat/nociceptive)

Question 9

what are bare nerve ending axons like? what kinds of fibers are they?

Answer 9

small diameter
A-delta fibers (myelinated) ~5-40 m/s
C fibers (unmyelinated) ~0.5-2 m/s

Question 10

what is somatotopic organization like in the spinal cord?

Answer 10

more proximal parts of the body will be closer to the grey matter
continues into the posterior limb of internal capsule

Question 11

what is the somatosensory cortex layout like?

Answer 11

similar to motor cortex

Question 12

what is the ventral posterior medial thalamic nuclei important for?

Answer 12

sensation related to the face

Question 13

what is the ventral posterior lateral thalamic nuclei important for?

Answer 13

sensation related to the body

Question 14

what is the medial dorsal thalamic nuclei important for?

Answer 14

emotional processing of pain

Question 15

what does the dorsal column/medial lemniscus pathway carry

Answer 15

fine touch, vibration, conscious proprioception of body

Question 16

dorsal column/medial lemniscus pathway

Answer 16

1st neuron travel through fasciculus gracilis/cuneatus
synapses on 2nd neuron in nucleus gracilis/cuneatus
crosses midline in internal arcuate fibers in medulla
travel through medial lemniscus to synapse on 3rd neuron in ventral posterior lateral nucleus
travels through posterior limb of internal capsule to post central gyrus

Question 17

what does the trigeminal lemniscus pathway carry

Answer 17

fine touch and vibration of face

Question 18

trigeminal lemniscus pathway

Answer 18

1st neuron comes through CN V to synapse on main trigeminal sensory nucleus
2nd neuron crosses midline in pons, travels through trigeminal lemniscus to ventral posterior medial nucleus to synapse on 3rd neuron
travels through posterior limb of internal capsule to post central gyrus

Question 19

what does the mesencephalic trigeminal nucleus contribute to? where are its cell bodies?

Answer 19

conscious proprioception of the face
cell bodies are in midbrain

Question 20

face proprioception pathway
reflexes

Answer 20

first neuron cell bodies are in mesencephalic trigeminal nucleus
synapses on principle sensory nucleus with second neuron
follows trigeminal lemniscus pathway
reflexes are transmitted through trigeminal motor nucleus

Question 21

what does the anterolateral system carry? what are the fibers like?

Answer 21

crude touch, pain, temperature of body
small diameter fibers

Question 22

anterolateral system pathway

Answer 22

neurons travel in dorsolateral fasciculus and ascend/descend 1 or 2 levels before synapsing on dorsal horn
neuron crosses midline in the anterior white commissure to travel in the anterolateral system to synapse on ventral posterior lateral nucleus
neuron travels to the post central gyrus (general) or cingulate gyrus/insula (emotional)

Question 23

what is the emotional pain response?

Answer 23

pain from the body or head can create an emotional response

Question 24

emotional pain response pathway

Answer 24

follows the anterolateral system
gives branches to the reticular formation
synapses in medial dorsal and ventral medial posterior nucleus
terminates in the limbic system (amygdala, insular cortex, cingulate cortex)

Question 25

what does the trigeminothalamic tract carry?

Answer 25

crude touch, pain, and temp of head

Question 26

trigeminothalamic tract pathway

Answer 26

1st neuron descends through the spinal trigeminal tract, synapses on the spinal trigeminal nucleus 2nd neuron crosses and travels through the trigeminothalamic tract to the ventral posterior medial nucleus

Question 27

spinal trigeminal nucleus and tract location anterolateral system location in medulla what would a lesion here cause?

Answer 27

Question 28

trigeminal and medial lemniscus location anterolateral location in caudal pons

Answer 28

Question 29

trigeminal and medial lemniscus location anterolateral location in rostral pons

Answer 29

Question 30

trigeminal and medial lemniscus location anterolateral location in midbrain

Answer 30

Question 31

what is the retina?

Answer 31

layer of the eye containing neurons of the visual system part of the diencephalon

Question 32

what are the layers of the retina?

Answer 32

nerve fiber layer ganglion cell layer inner plexiform layer inner nuclear layer outer plexiform layer outer nuclear layer photoreceptor layer pigmented layer

Question 33

what does the pigmented layer do?

Answer 33

helps protect the photoreceptors from excess exposure to light

Question 34

what does the nerve fiber layer do?

Answer 34

forms the optic nerve at the optic disc

Question 35

what is contained in the outer nuclear layer?

Answer 35

cell bodies

Question 36

what does the outer plexiform layer do?

Answer 36

axon communication with inner nuclear layer

Question 37

rods vs cones

Answer 37

low light, periphery color, high light, central retina

Question 38

what is special about the optic disc

Answer 38

blind spot, central retinal artery passed through here nerve fiber layer axons pass here to become the optic nerve

Question 39

what is the fovea

Answer 39

where there is the highest acuity, central vision only cones here inner layers are gathered around the edge of the foveal pit

Question 40

how many layers of the lateral geniculate nucleus are there?

Answer 40

6, grouped in bilateral pairs switch between ipsilateral and contralateral

Question 41

first two layers of lateral geniculate nucleus

Answer 41

magnocellular layers that deal with motion and spatial analysis

Question 42

layers 3-6 of the lateral geniculate nucleus

Answer 42

parvocellular layers that deal with color and shape

Question 43

input and output of the magnocellular layers

Answer 43

input: retinal ganglion parasol cells output: primary visual cortex, layer 4

Question 44

input and output of the parvocellular layers

Answer 44

input: retinal ganglion midget cells output: primary visual cortex, layer 4

Question 45

where is the primary visual cortex? how is it organized?

Answer 45

surrounds the calcarine sulcus retinotopic organization, central vision located most posteriorly

Question 46

where is the secondary visual cortex?

Answer 46

surrounds the primary cortex

Question 47

circadian rhythm regulation

Answer 47

suprachiasmatic nucleus (SCN) regulates, based on light input from the retina projections from the optic chiasm synapse in the SCN