Movement and Regulation of Movement Flashcards
The central pattern generator
CNS system which produces a rhythmic output for coordinated movement without sensory input
(the sensory caveat is simply a corollary of the fact that sensory input can alter the pattern)
Spinal interneurons and limb movement coordination
In murine models, spinal V0 interneurons seem key for coordinating left-right alternation of movement.
A Cre-based model in which diphtheria toxin was selectively expressed under Dbx1+ cells (V0 interneurons), mice exhibited “hopping” by moving both sides simultaneously rather than alternating sides for movement.
Mesencephalic locomotor region (MLR)
Found to initiate locomotion and control the pace of locomotion by rate of firing.
The MLR synapses on reticulospinal neurons in the brainstem, which in turn synapse on spinal interneurons and motor neurons.
Medullary reticular formation ventral part (MdV)
Medullary region which glutaminergically innervates primarily forelimb and hindlimb motor neurons and associated spinal interneurons.
The MdV also receives input from the deep cerebellar nuclei projections and superior colliculus.
Organization and information flow in the cerebellum
The deep cerebellar nuclei are the primary decision makers which supply information to the thalamus and motor cortex.
The deep cerebellar nuclei are primarily regulated by Purkinje cells (inhibitory), climbing fibers (originating from the inferior olivary nucleus, excitatory), and mossy fibers (originating from the spinal cord, excitatory).
Purkinje cells are regulated by excitatory parallel fibers that emanate from granule cells and also receive input from mossy fibers.
Three cerebellar interneurons exist: basket cell, stellate cell, and Golgi cell. All receive input from parallel fibers. Basket and stellate cells produce feed-forward inhibition on Purkinje cells, while Golgi cells produce feed-back inhibition on granule cells.
Long-term depression
Coincident firing of both the climbing and parallel fibers innervating the same Purkinje cell, which results in a decrease of the synaptic strength between the parallel fiber and Purkinje cell.
“Striatum”
= Caudate + putamen + nucleus accumbens
The input for the basal ganglia circuit. The striatum is one structure in most animals, but in primates is divided into these components.
While most of the striatum regulates movement or cognitive processes, the nucleus accumbens regulates motivational behavior.
Direct and Indirect basal ganglia pathways
Dopamine in the basal ganglia pathways
Dopamine binds to activating D1 receptors in the direct pathway (pro-movement), while it binds to inhibitory D2 receptors in the indirect pathway (anti-movement).
How do the basal ganglia actually regulate movement initiation?
Neurons of the GPi/SNr have a basal level of activity, sending out tonic signals that inhibit movement.
Immediately prior to voluntary movement, cortical excitation activates spiny projection neurons which stimulate the striatum. This inhibits the GPi/SNr tonic signal, subsequently disinhibiting movement control centers in the superior colliculus and brainstem.
Thus, movement initiation is facilitated.
Neuromodulatory system diagram
