Quiz 1- Lectures 1 and 2 Flashcards
Somatosensory afferents carry infro from _______ to _________ via the _________________
skin surface, central circuits, dorsal root ganglia
Describe the pathway from sensation to the cortex
skin, afferent neuron, dorsal root ganglia/trigeminal ganglia, brainstem, thalamus, cortex
Touch in the center of the receptive field _____ firing
increases
Actions requiring lots of cortical circuitry
facial expression, speaking, and hands
Can cortical circuits rearrange?
Yes
On-center ganglion cells
increase firing (more APs) when luminance increases in receptive field center
Off-center ganglion cells
increase firing when luminance decreases in center
signal flow in eye
photoreceptors, bipolar cells, ganglion cells (crossover in chiasm), LGN, V1 cortex
How do LGN neurons work?
They have center-surround receptive fields that respond selectively for changes in luminance
Cells in primary visual cortex
respond to ‘bars’ or edges, and neurons fire most when bar is in a certain orientation
Auditory pathway
Cochlea, spiral ganglion, cochlear nucleus, superior olive, inferior colliculus, thalamus, auditory cortex 1
Cerebellum
coordination of ongoing movement
basal ganglia
initiation of intended movement and suppression of unwanted movement
motor cortex
planning, initiating, directing voluntary movements
brainstem centers
rhythmic, stereotyped movements and postural control
ICM
intracortical microstimulation– small current initiates excitation of several muscles
T or F: motor map is more precise than the somatotopic map
False
motor map location
precentral gyrus
somatotopic map location
postcentral gyrus
stimulation of arm regions in primary motor cortex
movements of arm towards central space
stimulation of lateral motor areas
lead to hand to mouth movements and mouth opening
stimulation of medial areas
climbing or leaping
anterior sites in premotor cortex
defensive and reaching motions
visual cortical neurons are divided into how many groups and based on what?
7; based on how much they respond to either the contralateral or ipsilateral eye
BUT if one eye is sewn shut few cortical cells could be driven and retinal and LGN cells were normal; the eye DISCONNECTS from the visual cortex– this is permanent amblyopia or cortical blindness (no effect if done in adults)
Patient S.M– calcification and atrophy of anterior-medial temporal lopes and amygdala
cannot recognize fear and no self reports of fear
somatosensory system
cutaneous mechanoreceptors– fine touch, vibration, pressure
specialized receptors with muscles, tendons, joints for proprioception
free nerve endings– pain, temp, coarse touch
somatosensation includes
touch, pressure, vibration, limb position, heat, cold, itching, pain (circuits for each modality)– transduced from skin to CNS
Dermatome
territory innervated by each spinal nerve– defined in shingles because shingles associated with dorsal root ganglia – some overlap
1a, 1b, II afferents
large and fast, supply receptors to muscles for proprioception
largest in diameter and most myelinated, found in muscle spindle
ab afferents
merkel, meissner, pacinian, ruffini cells– detection of touch
slightly smaller than 1a,1b,2 but second largest in diameter and conduction velocity/myelination
a-delta and c
smallest, slowest, pain, temp, itch
c are UNMYELINATED and the smallest
does area of skin surface change rate of action potential?
yes, nearer to receptive field’s center causes more neural activity
what body parts have the lowest two point discrimination threshold
(smaller receptive field, more sensitive)– hands including palm and fingers, face
slowly adapting afferents
sustained discharge, provide info about size and shape of stimulus
rapidly adapting afferents
fire rapidly at stimulation and then fall silent; best for changes
layers of skin from top to bottom
epidermis, dermis, subcutaneous
order of receptors in skin from top to bottom
nerve endings (pain), meissners corpuscle (motion detection and grip), merkel cell neurite complex (shape/texture), ruffini corpuscle (force, shape, internal motion), pacinian corpuscle (vibration)
merkel cells
found in epidermal sweat ridges, form and texture, responds to edges, points, corners, curvature, smallest receptive field, slow adapting, 25% of mechanoreceptors in the hand
meissner corpuscle
close to skin surface, near dermal papillae– help with motion detection and grip, responds to skin potion, rapid adaptation, small receptor field, 40%
small and large receptor fields (somatosensory)
small– merkel, meissner
large- pacinian, ruffini
fast and slow adaptation (somatosensory)
slow– merkel, ruffini
fast– meissner, pacinian
pacinian
dermis and deeper tissues, perception of distant events through vibrations, tool use, receptive field is entire finger or hand and it has rapid adaptatio, 10-15% of receptors
ruffini
least understood, dermis, responds to tangential force, hand shape, motion direction, responds to skin stretch,
responses when reading braille, most to least specific
merkel, meissner, ruffini, pacinian
proprioceptors
info about position of limbs and body parts
proprioceptive receptors
muscle spinfles, golgi tendon organs, joint receptors
muscle spindles
signal changes in muscle length; afferents coil around intrafusal muscle fibers
Primary endingd (1a afferents): largest myelinated sensory axons have rapidly adapting responses to changes in muscle length, they transmit info about limb dynamics, velocity and direction of movement
secondary (group 2): sustained responses to constant muscle lengths, static limb position
golgi tendon organs
signal changes in muscle tension;
these 1b afferents are distributed among the collagen fibers forming the tendons
joint receptors
relay finger position for range of motion protection; around and in joints
tactile from body pathway
dorsal column medial lemniscal pathway
tactile from face
trigeminothalamic pathway
proprioception pathway
spinocerebellar tract
Dorsal colunm medial lemniscal pathway first order neurons
info ascends in columns ipsilaterally in spinal cord to medulla- medial-lateral bundles
fasiculus gracilis to gracile mucleus (the fracile tract is lower limbs, more medial)
fasciculus cuneatus to cuneate nucleus: upper limbs, trunk, neck– more lateral
Dorsal colunm medial lemniscal pathway 2nd order
internal arcuate fibers are the axons of second order neurons– they cross over the midline and form one neuron– the medial lemniscus
second order neurons synapse with the incoming first order neurons
they synapse at the ventral posterior lateral nucleus vpl of the thalamus
Dorsal colunm medial lemniscal pathway third order neurons
ventral posterior lateral neurons send axons to synapse in s1 and s2 somatosensory cortex
Tactile from face first order
cell bodies in trigeminal ganglia, enter brainstem at pons to synapse on the trigeminal brainstem complex with different nuclei processing different stimuli submodalities (principal and spinal nuceli)
Tactile from face second order
cross over and ascend as the trigeminal lemniscus (tri because divisions are opthalmic, maxilliary, mandibular), synapse at ventral posterior medial nucleius of thalamus
Tactile from face 3 order
vpm send axons to synapse in somatosensory cortex s1
proprioception first order
travel with axons in dorsal column
bifurcate into ascending and descending branches (dorsal and ventral horns); lower limbs innervate clarkes nucleus in medial dorsal horn
second order proprioception
travel to medulla and into ipsilateral cerebellum via dorsal spinocerebellar tract, synapse in proprioceptive neurons of dorsal column nuclei
third order proprioceptive
decussate and travel in medial lemniscus to vpl
ventral posterior lateral nucleus vs ventral posterior medial nucleus
both in thalamus, but vpl is body and vpm is face
somatotopic maps- foot, leg, trunk, etc are in a _____ arrangement
medial to lateral
somatosensory cortex 1 areas from left to right
3a,3b,1,2
3b and 1 in s1
cutaneous stimuli
3a
proprioceptors
2
tactile and proprioception
where does info from s1 go?
all go to secondary somatosensory cortex, then amygdala and hippocampus for tactile learning and memory
3a (propioeptors) and b(curaneous) also goes to areas 1 and 2
2 goes to parietal areas 5 and 7 which goes to motor and premotor cortical areas and helps with integration of sensory and motor info
can cortical circuits reorganize?
yes- after lesion of digit 3 on cortex, cortical region is unresponsive but after few weeks responds to stimulation of neighboring areas- so region 3 disappears and regions 2 and 4 grow in the cortex
similarly, after stimulating certain cortical areas, they grow in the cortex
