L21: Cortical control of movement Flashcards Preview

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Flashcards in L21: Cortical control of movement Deck (23):
1

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

2

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

3

Explain why it's normal to see babinski reflex in newborns.

b/c interneurons aren't grown in yet

4

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

5

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.

6

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

7

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

8

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

9

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

10

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

11

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

12

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)

13

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.

14

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.

15

What are 3 things cortical motor cells code for?

-muscle activity
-force
-direction (individual neurons increase discharge rate for certain directions more than others)

16

Are cortical motor neurons more concerned with muscle or movement?

32% -muscle (stiffness, inertia)
50% -movement (direction)

17

There is functional specialization among the neurons in the different motor areas. List the 5 motor areas and describe their functions.

1) primary motor (M1) neurons -execution of "simple" movements

2) lateral premotor neurons (PMd, PMv) -selection of motor responses based on externally-cued (sensory) inputs

3) Medial premotor (supplementary motor cortex (SMA), cingulate motor areas (CMA)) -executing learned sequences; internally-cued movements

4) pre-SMA -learning of sequences

5) pre-frontal -decision for action & working memory; monitoring outcomes

18

Info is conveyed directly to motor areas from sensory areas. How well do we function w/o the signals provided?

We will go off-target.

19

How important is positional/stretch info in directing motor areas?

it can fool the motor system into thinking it is moving (also many muscle afferent fibers sensitive to vibration)

20

Despite our maps of motor cortex somatoptopic organization and results from clinical
observations of patients having seizures, micro-stimulation of non-adjacent regions of
motor cortex can lead to movements in the same body segment. What property of the
motor cortex/spinal cord system can explain this?

A) Functionally similar and non-adjacent columns are interconnected by interneurons
within the motor cortex.

B) Functionally similar and non-adjacent columns are interconnected by interneurons
within the spinal cord.

C) The ventral (uncrossed) corticospinal tract integrates motor cortical output to
'smooth' stimulus-evoked movements.
D) Micro-stimulation activates redundant task-groups in the spinal cord.
E) None of the above.

A

21

Cortical areas that plan and initiate motor sequences:
A) all fall within the primary motor cortex.
B) comprise five functionally distinct and anatomically isolated regions.
C) comprise several functionally distinct but highly interconnected regions.
D) all receive direct inputs from the basal ganglia.
E) all show a high threshold for the elicitation of motor behaviors.

C

22

Which of the following does NOT help explain the high dexterity with which
neurologically-normal humans can manipulate objects with their fingers?

A) A disproportionate area of the motor cortex is devoted to control of the hand and
fingers.

B) A relatively high percentage of upper motor neurons make direct synaptic contact
onto lower motor neurons innervating muscles of the hand and forearm.
C) Muscles of the hand and forearm have relatively low mass.

D) Conduction velocities of the lower motor neurons to muscles of the hand and
forearm are higher than those to other muscles of the body.
E) Both A and B.

D

23

The "indirect pathway" from cortex to spinal cord does all of the following EXCEPT:
A) enable feed-forward postural adjustments.
B) play an important role in weight shifts, as when a cat lifts one paw.

C) enable certain motor functions that are spared after damage to the direct
corticospinal pathway.

D) enable post-injury recovery of fine motor functions such as using two fingers to
pick up food.
E) relay information from cortex to spinal cord via the reticulospinal neurons.

D