L21: Cortical control of movement Flashcards
List in order the main motor structures in CNS from highest (complex planning & selection) to lowest (most automatic behaviors).
- Association cortex
- cortical motor areas
- basal ganglia
- cerebellum
- spinal cord
Corticospinal pathway can terminate directly on spinal cord motor neurons in ventral horn or indirectly to intermediate gray neurons (interneurons). Describe the interneurons.
*interneurons aka local circuit neurons supply the medial & lateral regions of ventral horn
2 types:
1) long-distance local circuit neurons that connect muscles concerning axial movement
2) short-distance local circuit neurons that interconnect motorneurons concerning distal limbs
Explain why it’s normal to see babinski reflex in newborns.
b/c interneurons aren’t grown in yet
List the 4 indirect pyramidal tracts and briefly describe their functions
1) vestibulospinal tract –> regulate axial muscles & proximal limbs, facilitate anti-gravity muscles = balance
2) reticulospinal tract –> changes in axial & proximal limbs; central pattern regulator
3) tectospinal tract –> axial & midline body orientation
4) rubrospinal tract –> support the lateral corticospinal in distal limb control; mainly arm flexion
What are betz cells?
betz cells are enormous cells that are absolutely found in motor areas so as you move away from motor areas, the # of betz cells will decrease.
What are the 3 main groups of cortical control of skeletomotor function and list subsets within each if applicable?
1) primary motor cortex **this is the one that has the most direct control on motoneurons
2) Premotor areas
- lateral premotor areas: ventral and dorsal premotor areas involved in responding to external cues
- medial premotor areas: SMA & CMA
3) Association areas
- pre-SMA
- temporal and parietal cortex: ventral and dorsal pathways
- pre-frontal cortex
What is needed for an area to be defined as a motor area?
1) projections directly to spinal cord via motoneurons or indirectly via interneurons (local circuits)
2) projections to primary motor cortex
3) contains Betz cells or equivalently large layer V projection neurons
4) can be stimulated to produce motion
5) displays changes in activity related to parameters of movement
Are association areas (prefrontal & posterior parietal) that can participate in regulation of motor function be considered cortical motor areas?
No, because they do not meet the following requirements:
1) projections directly to spinal cord via motoneurons or indirectly via interneurons (local circuits)
2) projections to primary motor cortex
3) contains Betz cells or equivalently large layer V projection neurons
4) can be stimulated to produce motion
5) displays changes in activity related to parameters of movement
The premotor cortex can be divided into the lateral premotor cortex & the medial premotor cortex. What are within those regions?
Lateral premotor cortex:
dorsal premotor cortex
ventral premotor cortex
Medial premotor cortex:
supplementary motor cortex
cingulate motor areas
If there’s a lesion at the lateral corticospinal tract, what are some of the symptoms? How does recovery progress?
- will lose fine motor control of distal limbs
- recovery is aided by local circuit neurons (interneurons) above lesion
There are many different methods to study motor cortex, such as anatomical staining & tracing, microelectrode stimulation, micro & macroelectrode recordings, lesions and non-invasive imaging. What are 2 important findings that help us understand the role of cortical motor areas in motor control.
1) individual muscles are represented in multiple locations
- motor map reveals re-representations of individual muscles
- outputs from disparate parts of motor areas converge on a common set of motorneurons
2) individual corticospinal neurons diverge to influence multiple motor neuron pools & hence multiple muscles
- these muscles often have similar activities
What were some of the results of the microstimulation studies on motor cortex?
- outputs are arranged in columns
- multiple representations of each body part even within a single motor area
- cells w/ similar targets ARE NOT located adjacent to one another, but they are still connected by horizontal connections (fractured somatotopy)
What is fractured somatopy?
Fractured somatotopy is the phenomenon in which cells with similar targets are not located adjacent to one another. Columns of functionally-related neurons are connected by horizontal connections. Impt in surgical management of epilepsy b/c can cut horizontal connections to preserve motor function.
What can spike-triggered averaging recorded by EMG study?
They can study connections btw 1 cortical neuron & multiple muscles that it might innervate.
- individual corticospinal neurons diverge to influence multiple motor neuron pools
- UMNs likely to contact lower motoneurons of 2-3 pools. A given UMN probably synapses w/ all the lower motorneurons within a given pool.
What are 3 things cortical motor cells code for?
- muscle activity
- force
- direction (individual neurons increase discharge rate for certain directions more than others)
