Voluntary Motion (Karius) Flashcards
What cortical areas are responsible for voluntary motion?
Primary, supplementary and pre-motor cortices
Also prefrontal and parietal cortex also contribute
Briefly, how does visual input get processed and how does this help voluntary motion?
Axons on the dorsal visual pathway go from the occipital cortex to parietal/frontal cortex. Visual input from these axons are used by the parietal/frontal cortex to plan and do movements
Explain the mechanism of “reaching” (or knowing where an object is relative to you)
Input from the visual cortex > parietal cortex on the v6a, PEc, MIP and VIP > rough map of space around you is created > F4 in premotor cortex > creates a more detailed map of the space around you
Properties of F4 neurons
Are excited by proximity, the closer the object is the more they fire
How does the superior parietal cortex help?
Receives visual info about where your arm is in space > send to F2 in premotor cortex > F2 constructs related map (relationship of your arm to body and things around you)
Explain the mechanism of grasping:
Anterior intraparietal area and PFG have visual, motor and visuomotor neurons that respond to seeing and grasping object > F5 in premotor cortex > F5 will fire with goal of action, not the motor act itself
F5 neurons
Are active when goal is achieved (grasping and drinking tea) even if the grip is different
Summarize the role of the premotor cortex in control of voluntary motion:
Receives sensory info required for movement (from F4 and F5)
Dorsal portion applies the rules that determine when it is appropriate to move
Identifies the intent of motion and what motion to produce
Summarize the role of the supplementary motor cortex in control of voluntary motion:
Organizing motor sequences, acquiring the motor skills and executive control (e.g. deciding to switch action/strategy to complete action
Divisions of the supplementary motor cortex:
2 divisions. The Supplementary motor area (SMA) = postural control
Pre-supplementary area (pre SMA) = planning the action required to make the action occur
Describe how the primary motor cortex plays a role in the activation of motor neurons
PMC is arranged in columns. Stimulation of a given column will produce a specific movement
General motion vs fine motion in the primary motor cortex
General motion - if this area is stimulated at the PMC, this may produce contraction of a group of muscles
Fine motion - if this area is stimulated at the PMC, this may produce contraction of a single muscle
What do layers 4 and 5 of the PMC column do?
4 - receives sensory input
5 - does the action (serves as the output for the corticospinal pathway)
Properties of the columns:
What is found in each column?What do neighboring columns do?
What types of columns are present?
Two sets of neurons present. 1 to start motion and 1 to maintain the motion as long as necessary
Neighboring columns control related motion not neighboring muscles
On/off for agonist and on/off for antagonist muscle
What is the role of the cerebellum in voluntary motion?
Sequence of complex actions, correct fore/direction, balance/eye movements, learning of complex actions
Spinocerebellum functions
Central: posture
Either side of the vermis: force and direction
Vestibulocerebellum functions
Balance/eye movements and future movements
Where do outputs from the cerebellum originate from?
Dentate, fastigial and interpositus nuclei
Draw the schematic for inputs/outputs through each part of the cerebellum:
Ok
General concepts about the Basal ganglia:
Default action is inhibitory, the entire pathway is loaded with GABA. It has two controls that basically allow or suppress motion (via Dopamine)
Major actions of the basal ganglia:
Planning and programming movement
Initiation of movement
Briefly, describe the direct pathway of basal ganglia:
Striatum receives input > GABA release> SNPR and GPI > GABA release > VL and VA of thalamus > EAA to cortex
When activated the direct pathway does what?
Allows motion
Briefly, describe the indirect pathway of Basal ganglia:
Striatum > release GABA > GPE > release GABA > subthalamic nucleus > release EAA > Subsantia Nigra and GPI > release GABA > VA and VL of thalamus > EAA to cortex
When activated, the indirect pathway does what?
Inhibit motion
Draw the direct and indirect pathways of basal ganglia circuit to allow motion
Ok
Draw what happens at the basal ganglia circuit to inhibit motion
What pathways lead to the activation of the indirect pathway?
Ok
Corticostriate pathway and the Interstriatal cholinergic pathway
Huntington’s chorea is physiologically due to ….
Inability to turn on the indirect pathway. Striatum neurons are not producing desired amounts of GABA
What are the major functions of the prefrontal cortex?
Planning complex motor actions
Carrying out thought processes
How does the prefrontal cortex work to coordinate complex movements?
It interacts with the parieto-temporal-occipital association area, frontal association area, supplementary motor cortex, premotor cortex and cerebrocerebellum (basically everybody)
*if the motion is less complex, need less players
Prefrontal cortex and initiation of motion:
Interacts with frontal, premotor, SMC and basal ganglia will determine if the motion will occur. Basal ganglia has the final say.
Once motion is planned, sequenced and approved, what happens?
Columns associated with the motion are activated in the PMC > Action potentials travels down the axons and activate the alpha motor neurons that innervate the required muscles
What is an obstacle to voluntary motion?
Muscle spindle of the antagonist. It opposes the stretching of the antagonist (because the agonist is contracting) and try to stop it.
How does the brain overcome the opposition by the muscle spindle?
Cortex inhibits the alpha and gamma motor neurons in the antagonist to decrease the sensitivity of the muscle spindle to the stretching. This way, the antagonist is relaxed and the agonist is allowed to contract
When motion is started, what happens?
Spinocerebellum is called upon to make sure the motion is correct
