Upper MN and Basal Ganglia
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Low threshold electrical stimulation will elicit _____ in the motor cortex?
• patterns of movements
What are betz?
• 5% of neurons • important to elicit movement in distal extremities (fingers) • synapse directly onto alpha motor neurons • layer 5 • large
What is the corticospinal tract?
• body muscle control
What is the corticobulbar tract?
• facial muscle control
Where does 90% of the corticospinal axons cross-over to form the lateral corticospinal tract? What tract do the other 10% follow?
• caudal medulla - ventral corticospinal tract
The corticospinal tract also contains some axons from which area and why?
• layer 5 neurons of somatosensory cortex - these mediate proprioceptive modulation of motor circuits
What kind of face paralysis does an upper motor neuron lesion result in? Why?
• weakness of inferior facial muscles contralateral to lesion • below eyebrows • severs output from face representation in primary cortex • cingulate motor area spared because of bilateral projections
What kind of face paralysis does a lower motor neuron lesion result in? Why?
• weakness of superior and inferior facial muscles - severs output from face representation in primary cortex and from cingulate motor area
What type of stroke often results in upper motor neuron lesion?
• strokes that involve the middle cerebral artery - damage to motor areas in the lateral frontal lobe
What does the topographic map in the primary motor cortex represent?
• map of movement - movements rather than muscles are probably encoded
On average, how many contacts does one upper motor neuron make in the wrist?
• one upper motor neuron contacts neurons in 2-3 motor pools in the wrist
What type of stimuli did they apply to monkeys to study the motor cortex topographic map?
• extended the duration of cortical microstimulation to a timescale that more closely corresponds to the duration of volitional movements • applied to the precentral gyrus resulted in purposeful movements
What study was conducted to look at directional properties of upper motor neurons?
• train monkey to move a joy stick in direction of light - record the activity of a single neuron at a time
What was found from experiments studying the directional properties of upper motor neurons?
• single neuron activity increases before action in specific direction • neurons “preferred direction” • population vector
What is the motor function of the basal ganglia?
• gating proper initiation of movement - suppresses unwanted movements, prepares upper MN circuits for movement initiation
Which part of the midbrain is dopaminergic and which is not?
• dopaminergic: substantia nigra pars compacta - not dopaminergic: substantia nigra pars reticulata
What parts of the brain are included in the basal ganglia?
• caudate nucleus • putamen • globus pallidus (external and internal) • substantia nigra pars reticulata
Where do the caudate and putamen receive inputs from?
• motor cortex
What is the main input to the motor cortex?
• from ventroanterior and ventrolateral thalamus
What provides input to the medium spiny neurons of the caudate and putamen?
• from cortex, substantia nigra pars compacta, and local circuits within the corpus striatum
What do the areas of input to the medium spiny neurons of the caudate and putamen indicate?
• the response of the medium spiny neurons to their principle input, derived from the cerebral cortex, can be modulated by dopamine and the inputs of local circuit neurons
What is the primary output of the medium spiny neurons?
• to neurons in the globus pallidus and substantia nigra pars reticulata
Are the medium spiny neurons excitatory or inhibitory?
• inhibitory
Are the globus pallidus and substantia nigra pars reticulata neurons excitatory or inhibitory?
• inhibitory