lecture 14 Flashcards
(23 cards)
corticospinal and corticobulbar tracts
spinal- body
bulbar- face
output of motor cortex to lower MN of spinal cord/brainstem
caudal medulla cross over
facial weakness
upper motor neuron lesion: (common stroke)
medial cerebral artery - no forehead
lower motor neuron lesion: (cingulate cortex)
anterior cerebral artery - forehead
what do motor maps represent
movements (patterns) rather than muscles
ex. hand to mouth, defensive, reach
1 upper motor neuron
contacts neurons in 2-3 motor pools
ex. motor neuron for multiple muscles
directional tuning of UMN in primary motor cortex
individual cell might fire high in 1 direction but low in another
if you look at entire pop you get a summed response
basal ganglia and corpus striatum
C.S- caudate nucleus + putamen
B.G - putamen + globus pallidus (i/e)
modulation of movement by basal ganglia
motor cortex sends inputs to caudate/putamen
caudate/putamen sends inhibitory input to GP
GP sends inhibitory input to VA/VL thalamus
VA/VL thalamus sends input to cortex
overall: disinhibit the thalamus to allow signals to go through to motor cortex
dopaminergic part of basal ganglia
substantia nigra pars compacta sends dopaminergic input to caudate/putamen
affects ability of caudate to respond, acts as a modulator
medium spiny neurons
receive inputs from cortex/substantia nigra pars compacta and local circuit neurone w/in corpus striatum
project to GP and SNPR
make multiple contacts on neurone of GP/SNPR
inhibitory
functional organization of output from basal ganglia
caudate and putamen inhibit GP/SNPR
SNPR inhibits superior collicullus
GP inhibits VA/VL complex of thalamus
Va/VL complex sends input to motor cortex
chain of neurone arranged in disinhibitory circuit
striatum at rest: GP active, VA/VL inhibited, MC not activated
striatum excited: GP inhibited, VA/VL disinhibited, MC excited
direct motor pathway
caudate and putamen through internal GP activation leads to release of tonic inhibition of thalamic neurons
cortex excites caudate–> inhibits GPi–> inhibits VA/VL–> excites cortex (input from D1 to caudate)
indirect
putamen to external GP to sub thalamic nucleus to internal GP to thalamus and cortex
additionally, excitatory cortical neurons project to sub thalamic nuclei that work synergistically with GP
indirect increase inhibitory effects of GPinternal
indirect/direct summary
indirect through basal ganglia modulates disinhibitory actions of the direct
increases inhibitory effect of some BG neurons to suppress off target movement programs
direct pathway releases thalamic cells from inhibition
balance b/w direct and indirect facilitates expression of intended motor program
selection of motor programs
putamen synapses onto single neurons created directed disinhibition of thalamus
subthalamic nucleus synapse onto GPi diffusely giving an excitatory surround in Gpi and inhibitory surround in thalamus
sharpens the motor commands delivered from thalamus
d1/d2 receptors
d1 increases direct
d2 decreases indirect
parkinsons hypokinetic disorder
degenerated input from SNPC (D1 and D2)
indirect: increased inhibition of GPe, decreased inhibition of SN, increased excitation of GPi
direct: diminished inhibition of GPi
results in more tonic inhibition of thalamus and less excitation of frontal cortex
treatment for parkinsons
increase DOPA and get more dopamine put into vesicles
step below rate limiting step
huntington cause
genetic- repeated CAG sequences in huntington gene
>35 repeats
hemiballismus
rapid jerky motions with no clear purpose
huntingtons hyperkinetic disorder
degenerated caudate to GPe - increased inhibition to subthalamic nucleus and diminished GPi- less tonic inhibition to VA/VL and increased excitation to cortex
overall: reduced excitation from SN and less controlled GPi input
what happens when you inject a GABA agonist
produces involuntary movements resembling hyperkinesia
eyes fire spontaneously in different directions
does DAergic input modulate behavior
move faster to goal when associated with large reward
D1 antagonist eliminates
D2 antagonist enhances
