Somatosensory & Visual Pathways Flashcards
where are sensory cell bodies located? what kind of cells are they?
in the dorsal root ganglion or trigeminal ganglion
pseudounipolar
what size are axons for fine touch?
thick axons
what size are axons for pain and temp?
thin axons
what are proprioceptors?
muscle spindle organ - supports contraction
Golgi tendon organs - allows for stretching of muscle
what are proprioceptor axons like? what kinds of fibers are they?
large diameter & myelinated
A-alpha fibers travel ~80-120 m/s
what are mechanoreceptors?
meissner’s corpuscles and Merkel’s cells - texture and superficial sensation
Ruffini’s corpuscles - deep pressure
pacinian corpuscles - vibration
what are mechanoreceptor axons like? what kinds of fibers are they?
medium diameter & myelinated
A-beta fibers travel ~35-90 m/s
what are pain and temp receptors?
bare nerve endings (cold/heat/nociceptive)
what are bare nerve ending axons like? what kinds of fibers are they?
small diameter
A-delta fibers (myelinated) ~5-40 m/s
C fibers (unmyelinated) ~0.5-2 m/s
what is somatotopic organization like in the spinal cord?
more proximal parts of the body will be closer to the grey matter
continues into the posterior limb of internal capsule
what is the somatosensory cortex layout like?
similar to motor cortex
what is the ventral posterior medial thalamic nuclei important for?
sensation related to the face
what is the ventral posterior lateral thalamic nuclei important for?
sensation related to the body
what is the medial dorsal thalamic nuclei important for?
emotional processing of pain
what does the dorsal column/medial lemniscus pathway carry
fine touch, vibration, conscious proprioception of body
dorsal column/medial lemniscus pathway
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
what does the trigeminal lemniscus pathway carry
fine touch and vibration of face
trigeminal lemniscus pathway
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
what does the mesencephalic trigeminal nucleus contribute to? where are its cell bodies?
conscious proprioception of the face
cell bodies are in midbrain
face proprioception pathway
reflexes
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
what does the anterolateral system carry? what are the fibers like?
crude touch, pain, temperature of body
small diameter fibers
anterolateral system pathway
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)
what is the emotional pain response?
pain from the body or head can create an emotional response
emotional pain response pathway
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)
what does the trigeminothalamic tract carry?
crude touch, pain, and temp of head
trigeminothalamic tract pathway
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
spinal trigeminal nucleus and tract location
anterolateral system location in medulla
what would a lesion here cause?
trigeminal and medial lemniscus location
anterolateral location in caudal pons
trigeminal and medial lemniscus location
anterolateral location in rostral pons
trigeminal and medial lemniscus location
anterolateral location in midbrain
what is the retina?
layer of the eye containing neurons of the visual system
part of the diencephalon
what are the layers of the retina?
nerve fiber layer
ganglion cell layer
inner plexiform layer
inner nuclear layer
outer plexiform layer
outer nuclear layer
photoreceptor layer
pigmented layer
what does the pigmented layer do?
helps protect the photoreceptors from excess exposure to light
what does the nerve fiber layer do?
forms the optic nerve at the optic disc
what is contained in the outer nuclear layer?
cell bodies
what does the outer plexiform layer do?
axon communication with inner nuclear layer
rods vs cones
low light, periphery
color, high light, central retina
what is special about the optic disc
blind spot, central retinal artery passed through here
nerve fiber layer axons pass here to become the optic nerve
what is the fovea
where there is the highest acuity, central vision
only cones here
inner layers are gathered around the edge of the foveal pit
how many layers of the lateral geniculate nucleus are there?
6, grouped in bilateral pairs
switch between ipsilateral and contralateral
first two layers of lateral geniculate nucleus
magnocellular layers that deal with motion and spatial analysis
layers 3-6 of the lateral geniculate nucleus
parvocellular layers that deal with color and shape
input and output of the magnocellular layers
input: retinal ganglion parasol cells
output: primary visual cortex, layer 4
input and output of the parvocellular layers
input: retinal ganglion midget cells
output: primary visual cortex, layer 4
where is the primary visual cortex? how is it organized?
surrounds the calcarine sulcus
retinotopic organization, central vision located most posteriorly
where is the secondary visual cortex?
surrounds the primary cortex
circadian rhythm regulation
suprachiasmatic nucleus (SCN) regulates, based on light input from the retina
projections from the optic chiasm synapse in the SCN
