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Exam 3 Systems Study Guide

by: Emma Notetaker

Exam 3 Systems Study Guide NSCI 3320

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Emma Notetaker
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Comprehensive study guide including powerpoint notes and lecture materials.
Systems Neuroscience
Laura Schrader
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This 19 page Bundle was uploaded by Emma Notetaker on Thursday April 7, 2016. The Bundle belongs to NSCI 3320 at Tulane University taught by Laura Schrader in Spring 2016. Since its upload, it has received 72 views. For similar materials see Systems Neuroscience in Neuroscience at Tulane University.

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Date Created: 04/07/16
Thursday, April 7, 2016 Exam 3 Study Guide Limbic System: mainly affects emotion • Broca’s limbic lobe: cortex forming ring around corpus callosum, many brain areas • cingulate gyrus: just above corpus callosum • processes emotion anterior cingulate gyrus: recalling experiences • • medial surface of temporal lobe • subcallosal structures (brainstem areas) • uncus • pyriform gyrus: olfactory information • hippocampus: memory formation entorhinal cortex: spatial memory and spatial localization • • hypothalamus: releases hormones in response to sensory input • controls ANS • paraolfactory areas - direct connection with limbic areas • other associated areas: reward and motivation pathways • septal nuclei habenula • • nucleus accumbens • mammillary hypothalamus • amygdala: centrally located • VTA • anterior/dorsomedial nucleus of thalamus history: • • Broca proposed existence of grande lobe limbic for olfaction in 1878 • Buchannan in the 1930s: hypothalamus involved in emotion • Papez defined limbic system in 1937 • sensory input into PFC —> cingulate gyrus • —> entorhinal cortex —> hippocampus (via perforant path) • • —> hypothalamus (via fornix) • —> thalamus (anterior and mediodorsal) - via mamillothalamic tract • circuit between amygdala, hypothalamus and hippocampus • Kluver Bucy Syndrome • temporal lobectomy in rhesus monkeys (mainly lesioned amygdala) decreased fear and aggression • • decreased vocalization/facial expression in response to stimuli (mainly fearful stimuli) • good visual perception BUT poor recognition of objects • due to lesion of ventral stream • increased interest in sex - less hypothalamic inhibition • explored items by putting them in mouth - due to decreased visual perception temporal lobectomy in humans: relatively few accounts • • exhibit some Kluver Bucy symptoms • flattened emotions (main symptom) • unable to recognize fearful faces 1 Thursday, April 7, 2016 • probably related to destruction of medial temporal lobe/amygdala, which processes emotion amygdala • • tip of hippocampus, lies internal to temporal lobe • associated with emotional memory, emotional cues, anxiety, emotional responses to fearful stimuli • major outputs: • stria terminalis amydalofugal pathways (projections away from amygdala) • • nuclei groups: 3 • basolateral • sensory systems/information • corticomedial: more primitive inputs • olfactory inputs hypothalamus inputs • • central: main output of amygdala • inputs from corticomedial and basolateral system • sends outputs to various brain areas • amydalofugal: to brainstem nuclei • stria terminalis: to hypothalamus and subcortical structures (thalamus and striatum) • general afferents (inputs): basically from every brain area • hippocampus • cortex • cingulate gyrus • dorsal thalamus • hypothalamus • brainstem • norepinephrine enhances emotional stimuli • sensory stimuli sent to hypothalamus, which activates ANS and stress response • release of norepinephrine in amygdala • block norepinephrine in amygdala, emotional stimuli no longer enhanced • fear memory, fear response, fear recognition and fear learning: • higher activation in PTSD patients • bilateral amygdalectomy reduces fear and aggression in all animals tested • anger, sadness, and disgust may also be affected • S.M. case study: Inability to recognize fear in facial expressions - few cases reported • electrical stimulation of amygdala -> Increased vigilance or attention • fearful faces produce greater amygdala activity than happy/neutral faces • learned fear: fear conditioning • amygdala involved in forming memories of emotional events • auditory cortex info goes to basolateral nucleus • this then goes to central nucleus • —> hypothalamus: ANS response • —> PAG: behavioral reaction • —> central cortex: emotional response, emotional memory • confirmed by fMRI images and PET imaging • rabbits respond to pain/fear with an increase in heart rate • animal hears 2 different tones – one tone – mild foot shock the other benign 2 Thursday, April 7, 2016 • heart rate would increase to the tone associated with the footshock and activity of central nucleus amygdala neurons increased amydalectomy/lesion can prevent the visceral response • • similar test done in humans with visual stimulus coupled to mild shock • PET studies – 3 sets of visual stimuli – pleasant, frightening or aversive and neutral • frightening or aversive increased amygdala activity and heart rate • recall of frightneing images better than others. • rodent amygdala: triangular amygdala • • Nissl stain stains cell bodies • processes ACh • silver stain stains the axons • basolateral: receives sensory inputs • central: outputs intercalated cells: between basolateral and central nuclei • • fear conditioning and dissection of amygdala circuitry • training: animal placed in novel context, hears tone, gets foot shock • measure freezing behavior of animal • aversive sound processed in basolateral nucleus • LTP occurs (long term potentiation): strengthening of synapses, cellular correlate for memory formation • LTP dependent on glutamate insertion • LTP occurs in amygdala in response to fear conditioning • contextual: animal returned to same context (tests for freezing behavior), NOT given the sound • dependent on hippocampus and amygdala • cued test: placed in novel context, hears TONE, tests for freezing • depends on amygdala • more robust • evidence of activation of basolateral nucleus using optogenetics • channel 2 rhodopsin in amygdala - activated by light • causes depolarization in amygdala • animal exhibits increased freezing due to light stimulation • co-activation of sensory input and lateral amygdala neurons • intercalated cells • excited by infra limbic cortex inputs • PFC inputs to intercalated cells - modulate memory • outputs to central nucleus • influence extinction of conditioned fear memory • experiment: habituated to context and fear conditioned (increased freezing in response to foot shock) • day 3, animals put back into different context BUT exposed to tone • initially, animals freeze, but amount decreases over time due to the fact that the sound is no longer paired with a shock • lesioning of intercalated cells caused fearful response to reactivate • extinction no longer occurred • amygdala also important in anxiety behavior (activation of amygdala causes anxiety) • elevated plus maze experiment: • 4 arms, 2 enclosed and 2 open 3 Thursday, April 7, 2016 • mice want to stay in enclosed arms • when cue for light stimulus (activates/depolarizes channel 2 rhodopsin in basolateral amygdala) occurs, animal becomes LESS anxious and goes into more open arms • circuitry: complicated • summary: • amygdala: 3 areas • basolateral: receives sensory input (from cortex and thalamus) • stimuli will be processed and modulate emotional responses outputs to striatum: motor responses and response memory • • intercalated cells: send GABAergic projections into central nucleus • funtion of these cells works in inhibition of fear response • central nucleus: main output of amygdala • to hypothalamus and brainstem • mediates autonomic responses outputs to nuclei in brainstem to release neurotransmitters • • mediates arousal Prefrontal Cortex • controls executive function • polymodal inputs (various sensory systems) • outputs: • motor • other sensory areas plasticity • • IL of rodents corresponds to the ventromedial PFC (vmPFC) in humans • PrL to the dorsomedial PFC (dmPFC) or dorsal anterior cingulate cortex (dACC) in humans • cognitive function • has access to sensory and motor systems • plastic - changes in conjunction with tules goals and means (goal-directed motor output in response to sensory input) • • bestow “intelligence” • top down signal (controls the flow of processing) • learned - rather than pure sensory function • controlled vs. automatic • gradation of function as we get farther from motor and/or sensory cortex increase in complexity of function • • primary motor causes motor output, but premotor more complex and function to establish how output determined, strategies etc. • farthest areas involved in planning, concepts and goal directed • similar for sensory • 3 main divisions of PFC (organized in hierarchy of complexity of function) 1. orbitofrontal (OFC) and medial (BA 8, 9, 46) • • social interactions (rules), emotion motivation/reward, decision making • involved in more primitive functions • medial division: internal mood control • lateral division: social interactions and behavior • functionally homologous to rodent OFC and medial 4 Thursday, April 7, 2016 • areas: • anterior Cingulate rodent mPFC • • infralimbic, prelimbic • inputs: • chemosensory and visceral info • outputs: • limbic system (emotional - primitive function) behavioral inhibition over choices on objects or rewards • • 2. ventrolateral areas (BA 12 and 45) • interconnects with regions involved in memory and attention • ex: areas of parietal lobe • visual recognition • emotional control inputs: mainly sensory • • visual • somatosensory • auditory • polymodal (overlapping information) • 3. dorsolateral prefrontal cortex (BA 10, 11, 13, 14) functions: attention, cognition, action, working memory, executive control • • temporal organization of behavior • mediates slightly higher cognitive function than ventrolateral • connections with many motor systems • control over motor output connections to premotor and basal ganglia (NOT directly connected with M1) • connections with posterior cingulate cortex (involved in attention and eye movement) • interactions among prefrontal cortical areas, brainstem, limbic, thalamus • NO direct connections betters PFC and primary motor cortex • motor function goes to basal ganglia and frontal eye field • thalamus highly interconnected with PFC (mediodorsal nucleus) • prefrontal cortical function • executive function: not fully developed until adolescence • disrupted by aging, stress, disease, lesions • dysregulation in drug addiction, schizophrenia, PTSD, OCD • decision-making and goal seeking behavior • direct situations that need mediation • direct attentional processes to situations • suppresses distractions • bring online relevant memories and integrate to execute action • encode motor function • future planning • working memory • can modulate ANS via hypothalamus • inputs from brainstem, diencephalon and limbic system • internal environment, arousal levels, motivation, visceral outputs of emotion • amygdala and hypothalamus: project to medial and ventral PFC • motivational significance of sensory stimuli • all PF areas get inputs from hippocampus (to direct) 5 Thursday, April 7, 2016 • dlPFC; projects to dorsal striatum, nucleus accumbent and VTA (reward/goal directed behavior) damage to PFC • • Phineas Gage • after accident, becomes horrible person • drastic personality change after • dysexecutive syndrome: impaired in goal-directed tasks • cant stay married, hold job, etc. impulsive, can’t plan and organize • • disinhibited: lack behavior control to social norms • OFC: ibhibitory control, hypothalamus, basal ganglia and other PFC areas • say things they shouldn’t say • can’t tell white lies to save someone’s feelings • issues in planning (lateral PFC) anterior cingulate: lack of sustained effort and concentration • • impaired working memory • vlPFC: working memory • dlPFC: activated when information must be manipulated, sensory info functional but performance decreases with distraction • emotional impairment hyperemotional • • indifferent and apathetic • aware of changes!! • orbitofrontal anterior cingulate • OTHER AREAS MAY ALSO BE DAMAGED! (premotor, insular cortex) • tests to diagnose PFC disfunction: • stroop test: word is a different color than the color it spells • uses lateral PFC • Wisconsin card-sorting task • deck of cards with different symbols • people asked to sort cards based on number, color or shape • people with issues keep going back to previous rule (can’t switch from sorting by number to by color, etc.) • uses ventrolateral PFC • tower of London task • start with arrangement of beads on poles, try to get to a specific sequence • dysfunction: can’t plan and organize • uses lateral PFC • gambling task • person given choice between large reward with large punishment or small of both • dysfunctional people can’t evaluate consequences • continue to take money from the larger pile • uses orbitofrontal cortex (reward) • can also be from amygdala and reward areas • prefrontal cortical neurons • polymodal: respond to many sensory modalities • can sustain activity: respond during delay of delayed-response task • ex: press button, 5 minutes later will get reward • PFC active throughout the 5 minutes 6 Thursday, April 7, 2016 • reflects task demands - code “rule” • plastic activity - rapid modification of activity to meet task demands • lots of input from various modulatory neurotransmitters • encode reward: consequences of action • interactions with amygdala • fear memory formation/extinction • amygdala gets sensory input, which is sent out via central amygdala (increase in fear response) • infralimbic (like vmPFC) stimulation evokes activity in lateral neurons • ENHANCES ACTIVITY IN AMYGDALA • prelimbic (like dlPFC) stimulation evokes activity in basolateral nucleus • ITC cells decreases output of ventromedial nucleus, which decreases fear response • this goes to GABAergic neurons —> inhibits output • DECREASES ACTIVITY IN AMYGDALA • hippocampus also modulates what is going on in PFC Motor Systems Spinal Control • hierarchical organization of neural structures involved in the control of movement level function structures high strategy association areas, basal ganglia middle tactics motor cortex, cerebellum low execution brain stem, spinal cord • lower motor neuron: from spinal cord to innervated muscles important for muscle contraction - releases ACh onto nicotinic receptors • • exits via ventral horn of spinal cord • alpha motor neurons • inputs: • spinal interneurons • help to generate central patterns • muscle spindles (sensory input) • Aa neurons get proprioceptive info from here, send to spinal cord • upper motor neurons in brain • inputs enter at dorsal root, branch repeatedly and form excitatory synapses on interneurons and alpha motor neurons in ventral horn upper motor neuron: from brain to spinal cord • • input from corticospinal tract • synapses on alpha motor neuron • muscle terminology: • axial muscles: movement of trunk • lie medially • maintenance of posture • proximal muscles: for movement of shoulder, elbow, pelvis and knee (girdle) • distal muscles: movement of hands, feet, digits • lie laterally 7 Thursday, April 7, 2016 • smooth muscle: enteric motor system • innervated by nerve fibers from autonomic nervous system innervated by lower motor neurons • • ex: digestion and blood pressure • striated: cardiac and skeletal • skeletal muscle: mediates movements • bulk of muscle mass • extensors: triceps, quads lie laterally • • flexors: biceps, hamstrings • lie laterally • motor neurons controlling flexors lie dorsal to those controlling extensors • motor neuron pool: muscle and all axons that innervate it • types of motor neurons: alpha: directly trigger generation of force by muscles • • innervate extrafusal fibers (cause muscle contraction) • gamma: innervate intrafusal fibers within muscle spindle • intrafusal fibers contain muscle spindles • muscle spindle: stretch receptor, inside muscle fibers • spindles and associated Aa sensory neurons sense muscle length proprioceptors Aa: largest and fastest conducting axons • • contained in intrafusal fibers • Aa axons contain info about muscle length • synapse in ventral horn • myotactic reflex: • sensory neurons (Aa) synapse on alpha motor neurons: monosynaptic reflex arc • weight added to the muscle, transiently elongated (stretched) • Aa axon sends info about stretch to the lower motor neuron (depolarization of Aa) • leads to discharge of action potential to alpha motor neuron • alpha motor neuron causes muscle contraction • ex: knee-jerk reflex • tap of quadricep tendon to stretch • Aa fiber sends muscle lengthening information to dorsal horn • synapses on alpha motor neuron • causes reflex contraction of quads and extends leg • intrafusal fibers: • Aa wrap around muscle spindles, which contain intrafusal fibers • muscle spindles contain modified skeletal muscle fibers (intrafusal) • innervated by gamma motor neurons • cause contraction of intrafusal fibers to maintain firing of Aa neuron • contraction in response to shortening of extrafusal fibers (when muscle is shortened, the Aa neurons stop firing) • contraction pulls on non-contractile equatorial region and keeps Aa axons active • alpha activation decreases Aa activity, gamma activation increases Ia activity • important for maintaining sensitivity of sensory response to gauge muscle length and contraction • shortened muscle shortened intrafusal fibers • golgi tendon organs: act as strain gauge • lies in series with muscle 8 Thursday, April 7, 2016 • monitor muscle tension or the force of contraction • innervated by group Ab axons in series with muscle (carry muscle tension info) • • group Ib enters spinal cord, branch repeatedly and synapse on interneruons in ventral horn • mediates reverse myotactic reflex: • mediated by inhibitory response in alpha motor neuron • provides feedback about muscle tension protects muscle from being overloaded • • normal function: regulate muscle tension in an optimal range • reciprocal inhibition: contraction of one set of muscle is couple to relaxation of antagonistic muscle (flexors vs. extensors) • mediated by inhibitory interneuron • flexor reflex: reflex arc within spinal cord to flex limb from aversive stimulus sensory pain axons enter spinal cord and branch to activate interneurons at various • segments • excite the alpha motor neurons that control flexor muscle of affected limb —> inhibits antagonistic muscles • crossed extensor reflex: compensates for extra load imposed by limb withdrawal on the antigravity extensor muscle of the opposite leg important so that you maintain standing when flex one leg to withdraw from pain • • excitatory input to flexors of one leg (aversive) • extensors of OTHER leg excited • provides building block for locomotion • circuits that give ride to rhythmic actions • generate central patterns • some children can come out of incomplete spinal cord injury - training • diseases: • amyotrophic lateral sclerosis: Lou Gehrig’s Disease • muscle weakness and atrophy, slow deterioration • degeneration of alpha motor neurons • loss of superoxide disputes: can’t break down free radicals • excitoxicity: glutamate overstimulation • treatment targets release of glutamate • muscular dystrophy: progressive weakness and muscle deterioration • genetic loss of dystrophin • myasthenia gravis: autoimmune disease • nAChRs Central control of movement • when pitcher is throwing, controlled by lateral pathways: initiation of movement, cause muscle contractions (through alpha motor • neurons) • corticospinal tract: command for skilled movements, correction of motor patterns from spinal cord • rubrospinal tract: command for skilled movements, correction of motor patterns from spinal cord 9 Thursday, April 7, 2016 • ventromedial pathways: maintain posture, control balance • reticulospinal: activation of spinal programs for stepping and stereotypic movements vestibulospinal: utonic sctivity in antigravity muscles • • descending motor tracts in spinal cord: (look at diagram slide 4) • lateral voluntary movement control of distal musculature (primarily flexors) • corticopinal: aka pyramidal tract • controls distal muscles • lateral spinal cord particularly controls extensors • • lesions cause inability to move limbs separately • slow and inaccurate voluntary movement • sometimes rubrospinal flexor control may compensate for this • starts in primary motor cortex and goes through internal capsule • goes through base of midbrain and crosses at medullary pyramids (decussation) synapses on alpha motor neurons of contralateral spinal cord • • 10% of fibers remain ipsilateral • rubrospnial: • primarily flexors of upper extremities • central input from cortex • starts in red nucleus of midbrain crosses in pons, travels contralaterally • • next to corticospinal tract (lateral spinal cord) • ventromedial: originiate in brainstem • integrate sensory information about balance and position to maintain balance and posture • tectospinal: head movement • starts in superior colliculus (tectum) • head and neck posture and movement • vestibulospinal: where things are in space • originates in vestibular nuclei, sends bilateral outputs through spinal cord • remains ipsilateral • vestibular labyrinth cranial nerve VIII • projects to lumbar areas to facilitate extensors of legs (hamstrings) • control of neck and back muscles • cerebellar inputs (mainly inhibitory) • ALMOST NO CORTICAL INPUT • medial longitudinal fasciculus: projections from vestibular nuclei to cranial nerves • reticulospinal tracts: primarily innervate gamma motor neurons • influenced by corticoreticular and ascending spinoreticular tract • sensory info from cortex and spinal cord • pontine: starts in pons, travels down spinal cord • enhances antigravity reflexes of spinal cord • facilitates extensors • maintains upright position, movements and tone • medullary: starts in medulla, travels down spinal cord • opposite effects of pontine • relieves antigravity muscles from reflex control • inhibits extensors • function of ventromedial pathways in absence of cortical inputs 10 Thursday, April 7, 2016 • lower motor neuron lesions: weakness and muscle atrophy • upper motor neuron lesions (from cortex or brainstem): still have innervation from alpha and gamma motor neurons • no muscle atrophy • mainly causes extensor rigidity • lesion that extends into brainstem • decerebrate rigidity: • essentially inhibited everything in cerebral area rigidity in all extensors (whole body tenses) • • reticular spinal tract still innervating gamma motor neurons, which still cause muscle contraction • transection of dorsal root can relieve some extensor hypertonus - blocks input to alpha motor neuron so that it stops sending signals (relaxes rigidity) • decorticate rigidity: corticospinal tract NOT intact, but rubrospinal tract is intact abnormal flexion of upper arms (due to issues with corticospinal) • • rigidity and extension of lower limbs • descending motor information: • input originates in motor cortex • area 4: primary motor cortex (M1) • Wilder Penfield: experimented with stimulation of the cortex which led to movement or twitching in arm or limb • actual movement of muscles • area 6: premotor area (PMA) • skilled voluntary movement • planning of movement • integrates sensory input • sensorimotor associations • projections to reticulospinal to innervate proximal muscles • also sends info to primary motor cortex • activity encodes intention and planning • supplementary motor area (SMA): • sequences and bimanual coordination • ex: buttoning shirt • innervation to distal muscles • lesions: apraxia (inability to perform skilled movements) • experiment with monkey: receives stimulus and has to push a button • ready: parietal and frontal lobes (attention) • set: SMA and PMA (PMA active during mental rehearsal/planning) • go: M1 • precentral gyrus organization: homunculus (similar to somatosensory cortex) • face and hands: lateral • trunk and lower limbs: medial • areas requiring higher motor control take up more space on the cortex • activity of M1 neurons • area 4: lower threshold for elicitation of movement by electrical stimulation • entire cortex may be active for specific movement • direction and force preference • pathways starts in layer V (Betz cells) • gets inputs from other areas and thalamus 11 Thursday, April 7, 2016 • sends info down to somatosensory areas 3, 1, 2 • cortical areas outside M1 use wide variety of sensory cues to select and guide monkey trained to move stimulus to the right • • firing of a large part of the motor cortex - major choice of those cells causes movement • encoding direction in motor cortex: • most of cortex active for every movement (not just the areas specific for certain body parts) • activity of each cell codes a choice for particular movement (force and direction preference) • direction of each movement determined by averaging choices of many cells (“votes”) Basal Ganglia • subcortical inputs to motor cortex: motor loops • basal ganglia: • cortical basal ganglia to thalamus (VLo) • VLo input to area 6 • planned movements cerebellum: • • input to thalamus (VLc) • VLc input to area 4 • projection to layer 5 • Betz cells • coordinated motor function parallel loops through basal ganglia • • motor • sensorimotor cortex —> putamen —> substantia nigra/GP —> thalamus • cognitive • association cortex (PFC) —> caudate nucleus —> substantia nigra/GP —> thalamus • caudate main area limbic —> ventral striatum —> substantia nigra/GP —> thalamus • • striatum most important • function of basal ganglia: planning movements, higher cognitive functions than cerebellum • pathologies include OCD and Tourette’s (inability to suppress unwilled or unwanted movements/thoughts • lots of input from PFC into basal ganglia, which then output through ventrolateral nucleus of the thalamus • which projects back to area 6 • skilled motor and strategy planning • cerebellum receives mostly sensory information from cortical sensory areas and brainstem • outputs back up to area 4 • basal ganglia cortex feedback loop: cortex —> basal ganglia —> thalamus —> cortex • • inputs from neocortex • frontal, prefrontal, parietal • BG projections to thalamic ventral lateral nuelcei (VLo) • VL0 projections to area 6 • lesions to BG cause movement abnormalities (Parkinson’s) 12 Thursday, April 7, 2016 • also in aspects of memory and cognitive function • output generally inhibitory members • • striatum: • putamen: lies lateral to globus pallidus • caudate nucleus: wraps under lateral ventricles (follows corpus calossum) • nucleus accumbens • in rodents, caudate and putamen not divided out (just referred to as striatum) target of cortical inputs • • telencephalon • globus pallidus: • source of output to thalamus • medial (internal) and lateral (external) capsule • telencephalon subthalamic nucleus: from diencephalon • • substantia nigra: midbrain structure reciprocally connected to striatum • pars compacta: mainly affected in Parkinson’s • dopaminergic neurons that project back into striatum • pars reticulata • part of telencephalon basal ganglia motor loop: direct loop to facilitate WILLED movement • • cortex —> putamen (excitatory - glutamatergic synapse) • putamen —> medial (internal) capsule of globus pallidus (inhibitory) • cells of globus pallidus are spontaneously active (tonically release action potentials) • inhibitory input silences these AP • GP —> VLo (inhibitory) • this inhibitory input is silences by the lack of AP from globus pallidus, which releases inhibition in VLo • now thalamus is disinhibited • VLo —> SMA (excitatory) • BG may focus inputs from multiple cortical areas onto SMA to initiate movement • SMA projects to M1 to trigger movement • cortical activation excites putamen and inhibits GP, which releases VLo from inhibitions, which allows activation in SMA • command front from cortex —> putamen —> internal GP (which silences GP neurons) —> disinhibited thalamus —> cortex • other input • substantia nigra also sends excitatory input to putamen • subthalamus sends excitatory input to internal globus pallidus • pathways to thalamus • direct: facilitates flow through thalamus (helps willed movement) • cortex (+)—> neostriatum (putamen) • neostriatum (-) —> medial GP • medial GP (-) —> thalamus • thalamus (+) —> cortex • indirect: • inhibits flow through thalamus (inhibits spontaneous movement) • brings in sub thalamic nucleus • normally, subthalamic nucleus excites thalamus, but now it is inhibited 13 Thursday, April 7, 2016 • projects back to medial GP to inhibit thalamus • pathway: cortex (+)—> striatum (putamen) • • neostriatum (-) —> lateral GP • lateral GP (-)—> subthalamic nucleus • now projects larger excitatory input into medial GP • subthalamic nuelcus (+) —> medial GP • medial GP (-) —> thalamus (inhibits thalamocortical output) suppresses unwilled movements - inhibits spontaneous movement • • lesions to striatum • lesion causes lack of inhibitory input into medial/internal GP • allows cells to continue to fire, which causes more inhibitory drive into the thalamus • —> inability to initiate movement • lesions to subthalamic nucleus inhibitory drive taken out • • same striatopallidal input to lateral GP • still have inhibitory drive into sub thalamic nucleus, but now no projection back into internal/medial GP • less inhibitory drive into pallidothalamic nucleus —> less inhibition of unwilled movements (manifests as wild flighting of limbs, etc) basal ganglia disorders: • • Parkinsons: • degeneration of substantia nigra neurons (which release dopamine into striatum) • decreased excitatory input into striatum, which reduces inhibitory drive into medial GP • therefore, disinhibition of thalamus reduced • overall increase of tonic thalamic inhibition —> inability to initiate movements • issues in direct pathways • hypokinesia: lack of/reduced movement • increased inhibition of thalamus from basal ganglia • bradykinesia: slowed movements • akinesia: difficulty initiating movement • increased muscle tone and rigidity • tremors of hands and jaw - possibly due to oscillatory activity in thalamus • treatments: • L-Dopa (substitutes for dopamine for short period of time) • go back to Parkinson’s state after body gets used to medicine • deep brain stimulation: high frequency stimulation of sub thalamic nucleus (usually) • decreases activity in indirect pathway, which suppresses pathway and allows more function to come through direct pathway • Huntington’s: essentially the opposite of Parkinson’s • hyperkinesia: excessive movement • decreased BG output • dyskinesias: abnormal, purposeless movements • often repetitive • chorea: spontaneous, uncontrolled movements • hyperkinesia: • ballism: wild flinging of extremities • often caused by lesions and damage to specific areas 14 Thursday, April 7, 2016 • caused by lesion in sub thalamic nucleus • hemiballism: on one side of the body wild flinging of limbs mainly due to damage of sub thalamic nucleus • • loss of excitatory input to GP • facilitation of VLo (disinhibition) • loss of neurons/inputs in caudate putamen and GP • loss of inhibitory input to thalamus • loss of cortical connections into striatum: dementia, personality changes lesions cause issues on contralateral side • Cerebellum • main function: motor coordination, error signaling and correction of motor programs • learning of motor sequences and multi-joint movements • lesions cause ataxia (inaccurate, uncoordinated movement) • contains over 50% of neurons in the brain • inputs: • sensory input from brainstem and spinal cord proprioceptive and touch info • • sensory input from cerebral cortex: coordinates motor outputs • nuclei in pons • main motor loop: • pons —> cerebellar cortex —> VLc thalamus —> primary motor cortex • outputs: spinal cord/vestibular system (main output) • • thalamus (ventrolateral caudalis) • brainstem • deep cerebellar nuclei are the outputs • 3 functional divisions: • vestibulocerebellum (aka archicerebellum): oldest part of cerebellum • • medial • cortical areas: • vermis • flocculonodular lobe • paraflocculus functions: • • position of head and body in space • equilibrium, eye orienting • balance • inputs from vestibular system (inner ear and vestibular nuclei in brainstem) • outputs: superior colliculus vestibulospinal and reticulospinal tracts • • weak projection to VL thalamus • deep nucleus: fastigial nucleus • damage to flocculonodular lobe and/or fastigial nucleus • unsteady gait • drunken appearance - tendency to fall 15 Thursday, April 7, 2016 • spinocerebellum: • more sophisticated control of limbs intermediate area • • cortical areas: • paravermal/ • vermal • functions: • motor coordination, limb movement control of axial muscles through fastigial and verbal cortex • • control of limb muscles through interposed nuclei and paranormal cortex • deep nuclei: • interposed (globose and emboliform) • fastigial • inputs: spinocerebellar tracts (touch and proprioceptive info from periphery) outputs • • to vestibular and reticular nuclei in brainstem (via fastigial nucleus) • to red nucleus and VL thalamus (via interposed nuclei) • pontocerebellum (aka neocerebellum): • area: lateral (hemispheres) • functions: smoothness and coordination of upper limb movement • • deep nucleus: dentate nucleus • inputs: • pons • olivary nuclei (of medulla) • outputs: • VL thalamus (untilately projects to primary motor cortex to modulate limb movements) • red nucleus • main cerebellar system of study • lesions of hemispheres and/or dentate gyrus: • decrease in coordinated movement • hypotonia • ataxia • intention tremor • anatomy: • at base of cerebrum, under occipital lobe, above pons and medulla • folia: folds; increase surface area • main divisions • vermis (middle) • lateral hemispheres • flocculonodulus • cerebellar peduncles: white matter connecting to brainstem • deep cerebellar nuclei are the output • cell layers: structural divisions • Purkinje: middle layer • huge dendritic trees - arborize in molecular later • only output cells of cerebellum • inhibitory output - release GABA onto deep cerebellar nuclei 16 Thursday, April 7, 2016 • inputs • from climbing fibers (coming from inferior olive) multiple synapses (powerful) • • from parallel fibers (from granule cells) • plasticity from synapses of climbing fibers and parallel fibers • projects to deep cerebellar nuclei and vestibular nuclei • granule: inner layer • send axons to synapse onto Purkinje cells release glutamate onto Purkinje • • send excitatory parallel fibers • Golgi: inhibitory • unipolar brush cells • in the vestibulocerebellum • send excitatory parallel fibers to Purkinje cells sensory excitatory input from mossy fibers (from pons and medulla) • • molecular: outer layer • axons of parallel fibers synapse on dendrites of Purkinje cells • dendritic trees of Purkinje cells • basket and stellate cells • inhibitory types of cerebellar cortex afferents: • • mossy fibers • originate from deep nuclei, medulla and pons • glutamate • output to granule and golgi cells • climbing fibers • to cerebellar cortex • from inferior olive • synapses multiple time on Purkinje cells • releases excitatory aspartate on Purkinje cells • multilayered fibers • inputs from locus coruleus, raphé nuclei and hypothalamus • usually inhibitory • monocircuitry and function of the inferior olive • cerebellar cortex sends info into deep nuclei of cerebellum, which project inhibitory information into inferior olive • this modulates sensory input into the cerebellar cortex • cortex sends motor command to cerebellum (deep nuclei) • this is modulated by sensory input into the inferior olive • goes to cerebellar cortex • cerebellar cortex sends inhibitory information into deep nuclei • OR meso-dencephalic junction (thalamo-brainstem area) - inputs into inferior olive as well • deep cerebellar nuclei: • inputs: • input from cerebellar cortex • inhibitory from Purkinje cells • excitatory (collateral) from mossy and climbing fibers • output to various brain areas (only output of cerebellum) • fastigial nucleus: most medial 17 Thursday, April 7, 2016 • vermis • flocculonodular lobes vestibulocerebellum • • globose and emboliform nuclei (interposed nuclei) • more lateral • paravermal (intermediate) • spinocerebellum • dentate nucleus: lateral hemispheres • • pontocerebellum • motor learning and synaptic plasticity • hypothesized that dendrites of Purkinje cells get 2 sensory inputs (parallel and climbing fibers) • plasticity at this synapse important for motor learning, especially long term depression (weakening of synapse) • decrease of synaptic efficacy decreases output of Purkinje • decreases inhibition of cerebellar nucleus • potentially enhances motor learning • we know that LTD does occur at synapses: • climbing fiber into Purkinje a mossy fiber into granule • • conditioned eye-blink reflex: mainly in rabbits • learn to associate tone with puff of air in the eye • eventually, animal learns to close eyes in response to ton • model used mainly for motor learning • sensory input: air puff into eye • auditory cue: into granule and climbing fibers • come together in Purkinje cell synapse • LTD at this synapse • inferior olive: muscle proprioceptors • climbing fibers • pontine nuclei • mossy fibers synapse onto granule cells • parallel fibers: axons of granule cells • output: • Purkinje cells (GABAergic) - synapse onto deep cerebellar nuclei • stimulation of climbing fiber and parallel fibers results in long term depression at synapse between Purkinje cells and parallel fibers • optogenetics: • circuit mechanisms underlying motor memory formation in the cerebellum • expressed channel rhodopsin (excitatory) or archirhodopsin (inhibitory) onto Purkinje • shines light onto Purkinje cells • light in channel rhodopsin—> depolarized Purkinje cells • increase in firing of Purkinje cells • decrease in firing of deep cerebellar cells while light it on • when light turned off, over-excitation of the deep cells causes robust increase in firing AFTER light leaves • increased movement • light in archirhodopsin —> hyperpolarized Purkinje cells 18 Thursday, April 7, 2016 • decrease in firing of Purkinnje • increase in firing of deep cerebellar nucleus circuit mechanisms underlying motor memory formation in cerebellum • • increased duration of motor stimulus - affects limb movement • not until after laser stimulation that firing/movement happens • channel rhodopsin creates larger/longer movement than Arch • associative learning: • paired stimulation of Purkinje cells with tone when laser is stimulated, large movement • • magnitude increases over time, then extinguished • enhanced motor learning mediated by Purkinje cell depolarization 19


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