Lecture 3: Voluntary Motion Flashcards
What are Central pattern generators (CPGs)?
- Set of cyclic, coordinated timing signals that are generated by a clustr of interconnected neurons
- CPG neurons act like pacemaker cells that when combine with local interconnected circuits generates rhythms
What does the dorsal pathway leaving the occipital cortex and going to the parietal/frontal cortex enable us to do?
- Enables us to complete motor acts based on visual input.
- This path allows you to play catch with your friends
The act of reaching for an object begins with information arising from V1 to the parietal cortex, which specific areas and what is the end result?
- From visual cortex to parietal cortex, specifically V6A, the PEc, the MIP (medial intraparietal area), and the VIP (ventral intraparietal area)
- The end result: the VIP creates a rough map of the space around you
After the VIP (ventral intraparietal area) creates a rough map of the space around you, where is the information sent and what is the end result?
- From the VIP, the info is sent to F4 within the premotor cortex
- The end result: F4 creates a detailed map of the space around you. Neurons here are particularly excited by proximity!
In the act of reaching for an object your brain will create a detailed map of the space around you, but also requires mapping of your arms in location to the object, what is involved and the end result?
- Visual info sent to Superior Parietal cortex and moves from V6A to PEc, AIP then to F2 (part of premotor cortex)
- F2 constructs the map containing info about where your arm is in relationship to your body and the things around you.
In motor control for grasping an object the anterior intraparietal and PFG contain neurons that respond to what 3 conditions (i.e., what are the neurons)?
- Visual dominant neurons - seeing an object you want to grasp
- Motor dominant neurons - actually grasping what you want
- Visumotor neurons - either condition
The anterior intraparietal area and PFG involved in grasping an object relay their information to _____, these neurons fire and code based on what part of the action?
- The anterior intraparietal area and PFG involved in grasping an object relay their information to F5 neurons
- Interestingly, the F5 neurons fire with the GOAL, not the motor act
If you are grasping an object in different ways, but the end goal is the same how does this affect the F5 neurons?
- Means the same F5 neurons will be active in 2 completely different settings IF the end goal is the same
- Even if the grip is also very different
Where does the sensory information to the Premotor Cortex in regards to voluntary motion arise from and via what pathway; what is the function of the premotor cortex after receiving this information?
- Receives info particularly from F4 and F5 - the ventral parts
- Dorsal applies the ‘rules’ that determine whether it is appropriate to move
- Identifies the intent of the motion and decides what motion to produce
What portion of the premotor cortex applies the ‘rules’ that determine whether its appropriate to move at a particular time?
Dorsal portion
What are the 2 divisions of the supplementary motor cortex and the function of each?
1) Supplementary motor area (SMA): postural control
2) Pre-supplementary area (pre-SMA): plans the motor program required to make the action occur
What are the main functions of the Supplementary Motor Cortex?
- Organize motor sequences
- Acquire motor skills
- Executive control (particularly the decision to switch actions/strategies)
- Mentally practicing a complex movement
Only after the premotor cortex and supplementary motor cortex have created the map and plan for your voluntary motion, what is the last piece of actually making the movement happen?
Primary Motor Cortex
What does the primary motor cortex control and how is it arranged?
- Controls specific movements
- Arranged in columns
How are regions of the body involved in fine movements represented in the primary motor cortex?
Proportionally high representation
Layer IV within a column of the primary motor cortex receives what information?
Sensory input (muscle and joint proprioceptors, among others)
Layer V within a column of the primary motor cortex has what function; contains what cells?
- Becomes the output for the corticospinal (pyramidal) pathway
- Contains Betz cells which are the UMN’s
There appears to be 2 sets of neurons in each column of the primary motor cortex with what functions?
1) One to start the motion
2) One to maintain as long as necessary
Neighboring columns of the primary motor cortex control what motions and not what?
Control related motions, but NOT neighboring muscles
What are the 2 types of columns found within the primary motor cortex?
1) On/off for the agonist muscle
2) On/off for the antagonist muscle
The Vermis portion of the Spinocerebellum recieves what inputs and produces what outputs?
Inputs: from vestibular, visual and auditory, and an efferent copy (a branch off UMN which is a copy of the planned movement)
Outputs: to the interpositus and fastigial nuclei and the rubrospinal tract
The main function of the Vermis portion of the Spinocerebellum is control of what?
- Postural control
- Modulates the descending motor systems
What is the main function of the Cerebrocerebellum?
- Sequencing of rapid movements
- Planning complex motions
The Vestibulocerebellum receives inputs from where and what are its outputs?
Inputs: from vestibular apparatus (direct or indirect)
Outputs: to fastigal nucleus to vestibular nuclei (ascend or descend)
What are the main functions of the Vestibulocerebellum?
- Balance and eye movements
- Future movements
- Planning balance
The lateral portion of the Spinocerebellar tract is receiving what inputs and ouputs to where; primarily concerned with what function?
Inputs: muscle afferents via the spinocerebellar tract and the efferent copy (from UMN’s)
Outputs: to the interpositis nucleus and to rubrospinal tract
- Controls ballistic motions
Together the putamen and the caudate nucleus are called the ______
Striatum
The Basal ganglia is especially important in what aspcects of movement?
The planning and programming of movement
What recieves most of the inputs to the basal ganglia?
The striatum
What inputs does the Striatum receive?
- From cortex regions (glutamate)
- From dopaminergic neurons of substantia nigra pars compacta
What is the intrastriatal cholinergic system and the NT released; damage to this system linked with what disease?
- A stimulatory/excitatory loop between nuclei within the striatum
- ACh is the excitatory NT released
- Huntington’s disease
The nigrostriatal dopaminergic system is between where and acts on what receptors?
- From SNPC to nuclei of striatum
- Acts on D1 receptors (+) and D2 receptors (-)
Where are the cells bodies of striatonigral GABAergic pathway, where do the axons travel and the function?
- Cell bodies: striatum
- Axons travel to GPi and SNPR
- Inhibition
What are the Corticostriate tract and Nigrostriatal tract of the basal ganglia; what does each release?
- Corticostriate tract (from cortex to striatum) releases EAA
- Nigrostriatal tract (from SN to striatum) is tonically active and releases dopamine
What is the direct pathway within the basal ganglia and its function?
- Facilitates the flow of information through the thalamus
- Increases consequential excitation of cortex
- Disinhibition (removal of inhibition)
What is the indirect pathway within the basal ganglia and its function?
- Inhibits the flow of information through the thalamus
- Decreases activity of the thalamus and consequently decreases activity of the cortex
- Inhibition
What is the flow of info through the direct pathway of basal ganglia (structures and NT’s) and end result?
- Cortex releases MORE (glutamate) —> Striatum
- SNPC (dopamine) —> D1 receptors (+) of Striatum
- Striatum releases MORE (GABA, Substance P, or dynorphin) —> GPi and SNPR
- Inhibition of SNPR and GPi causes LESS GABA release
- Releases thalamus from tonic inhibition
- Thalamus signal is allowed to go to cortex and facilitate motion
What is the flow of info through the indirect pathway of basal ganglia (structures and NT’s) and end result?
- Striatum release MORE (GABA or encephalin) —> GPe (activity decreased)
- GPe releases LESS (GABA) –> Subthalamic nucleus
- Subthalamic nucleus is normally tonically inhibited by GPe, but GPe now less active so there is less inhibition of subthalamic nucleus (more active)
- Subthalamic nucleus release MORE (glutamate) –> GPi and SNPR
- GPi and SNPR release MORE (GABA) –> Thalamus
- Decreases thalamic signal to corex —> inhibits motion
How does dopamine from the pars compacta of substantia nigra affect the direct and indirect pathways of the basal ganglia?
- Direct pathway (D1 receptors) is excited by dopamine = allows motion
- Indirectpathway (D2receptors) isinhibited by dopamine
- Dopamine acts by activating the direct pathway (D1) and inhibiting the indirect pathway (D2). For the indirect pathway to become activated requires EAA/ACh from Cortical areas
What activates the direct pathway of the basal ganglia?
SNPC sends dopamine to striatum, which binds D1 receptos
In Parkinson Disease what input is abolished and what 2 effects does this have?
- The SNPC input is abolished
1) The direct pathway becomes difficult to activate
2) The indirect pathway becomes overactive (due to loss of inhibition) - Therefore, we see an inability to initiate motion
What is Alpha-gamma coactivation and why is it important?
- Coactivation of both sets of fibers causes the tension on the muscle spindles to be maintained as the muscle shortens
- Thus sensitivity to stretch is maintained
- If the brain activates the alpha-motorneuron, it also activates the gamma-motorneuron for spindles in the CONTRACTING (agonist) muscle
- If the brain inhibits the alpha-motorneuron, it also inhibits the gamma-motorneuron for spindles in the STRETCHING (antagonist) muscle
Without alpha-gamma coactivation and only having the alpha motor neurons firing would cause what?
- Only extrafusal muscle fibers would contract
- The muscle spindle becomes slack and no APs are fired
- It is unable to signal further length changes
What are the 8 steps of initiating movement in the direct pathway after increased activity of SNPC?
1) Depolarization (EPSP) and striatal cells of direct path
2) AP in striatal cells connecting direct pathway
3) Release of GABA in SNPR/GPi
4) IPSP’s in SNPR/GPi
5) Decreased release of GABA in VA/VL of thalamus
6) Increased activity of thalamic neurons
7) Increased release of EAA in motor cortices
8) Increased activity of cortex
What are the 7 steps in the indirect pathway after increased activity of SNPC and leading to initiation of movement?
1) IPSP’s in neurons on indirect pathway
2) Decreased release of GABA in GPe
3) Depolarization of GPe neurons
4) Increased release of GABA in subthalamic neurons
5) IPSP’s in subthalamic neurons
6) Decreased release of EAA in GPi/SNPR
7) Decreased release of GABA in VA/VL of thalamus
Interactions between the frontal, premotor, SMC, and the basal ganglia (dopamine) determine what about motion?
Determine IF the motion will occur
