Module 14 - Lecture 10 - Motor, Premotor and Descending

Question 1

What is the main concept behind “reflex modulation”? What does it mean in regards to the motor hierarchy and competition amongst the 3 inputs to the LMN (lower motor neurons)?

Answer 1

The three inputs to the LMN are : 1. Local interneuron circuits 2. Sensory inputs 3. UMN system Reflexes are usually stereotyped/consistent in their reactions to a stimulus. You can however suppress a reflex through the use of the descending control from the UMN systems.

Question 2

What is the general outline of the “extrapyramidal system”. Where is it? What does it contain?

Answer 2

Where is it? Brainstem What does it have? - Vestibular Nuclei (x2) - Reticular Formation (2 regions) - Posture respiration and cardiovascular control - Mesocephalic Locomotor region (CPG) - Superior Colliculus (1)

Question 3

What are the names and tracts of the 3 UMN of the extra-pyramidal system? Know the general rules with the UMN of the extrapyramidal system (laterality, output, level of conscious control)

Answer 3

1. Vestibulospincal tract (Vestibular Nuclei). Laterality= on one side and then splits bilaterally, output= recruit LMS for reflexes, level of conscious control= autonomic Lesions primarily effects the same side 2. Recticulospinal tracts (Reticular formation) Laterality= on one side and then splits bilaterally, output= recruit LMS for reflexes, level of conscious control= autonomic 3. Tectospinal tract (Superior Colliculus) laterality= bilateral , output= recruit LMS for reflexes, level of conscious control= autonomic *** Different type of tract for each type of nuclei. When you follow 1& 2 they mainly stay on the SAME side where their nuclei are. #3 is the exception where it crosses sides. #1 covers the ventral side of the spinal cord. ***

Question 4

What is the general idea of the pyramidal system? Where do the neuron cell bodies reside (in what area of what cortex)? How are they organized?

Answer 4

The pyramidal system is primarily the neurons that are contained in the cerebral cortex, and in particular we are talking about what is defined as the primary motor cortex = M1. The neuron cell bodies are organised in a way that they map to general movement of body parts. This mapping, just like the mapping in our spinal cord represents this somatotropic organization!!! Somatotropic organization = the different regions would synapse upon LMN of unique pools. The primary motor cortex (M1) = it is right in front of the precentral gyrus –> recall that the central gyrus separates our frontal lobe to our parietal lobe.

Question 5

What are the different names of the primary motor cortex?

Answer 5

• Brodmann’s Area 4 - M1

Question 6

What are the main white matter tracts the pyramidal system uses to exert controls on local circuits or the LMN cell bodies? Note : Which 3 pathways = just start by naming them

Answer 6

1. Corticobulbar 2. Corticospinal = lateral and anterior branches 3. Cortico-reticulospinal

Question 7

Know the main white matter tracts the pyramidal system uses to exert controls on local circuits or the LMN cell bodies. (Do they cross/ where? What is their target (Cranial LMN? Medial or Lateral SC LMN?)

1. Corticobulbar

Answer 7

Cortiocobulbar § Direct Pathway § Originates from primary motor cortex to internal capsule § Targets the LMN nuclei of cranial nerves with bilateral branches (muscles of face are contralateral instead). § Efferent activation of the cranial nerves (face tongue and throat). Also regulates the indirect pathway mentioned in point 3.

Question 8

Know the main white matter tracts the pyramidal system uses to exert controls on local circuits or the LMN cell bodies. (Do they cross/ where? What is their target (Cranial LMN? Medial or Lateral SC LMN?)

1. Corticospinal –> lateral branches
2. Corticospinal –> anterior branches

Answer 8

Corticospinal Direct Pathway
§ Has lateral and anterior branches

a) Lateral (LCST)
§ Originates from primary motor cotrex to internal capsule
§ Cross over at the Pyramidal decussation
§ Targets the lateral LMN of the spinal cord and short distal circuit
§ Controls contralateral side (due to cross over) with skilled control of the distal muscles.

b) Anterior Branches
§ Originates from primary motor cotrex to internal capsule
§ No crossing until at the target
§ Target is medial LMN and long local circuits.
§ Controls gross control of proximal postural muscles and bilateral collaterals

Question 9

Know the main white matter tracts the pyramidal system uses to exert controls on local circuits or the LMN cell bodies. (Do they cross/ where? What is their target (Cranial LMN? Medial or Lateral SC LMN?)

Cortico-reticulospinal

Answer 9

Cortico-reticulospinal .
§ Indirect Pathway
§ This part allows the control on the extrapyramidal system through collaterals to the reticular formation previously mentioned.
§ Origin: internal capsule
§ Target reticular formation
§ Control extrapyramidal system, posture control, voluntary Control of brain stem functions, pattern generator regulation

Question 10

Considering the function what cortical (spinal or bulbar) tract does the indirect pathways from the cortex best represent?

Answer 10

Corticospinal . No crossing and function is similar to the Anterior Branch. Follows the path of the reticular formation.

Question 11

Contrast the generalized UMN systems in general do they function automatically or with conscious (voluntary) control? Are they used for fine or gross (postural) motor tasks?

Answer 11

The UMN systems function by communicating with the LMN .
The Extra pyramidal system is generally automatically controlled and are used for postural control.
The pyramidal system is generally voluntary controlled and used for Fine motor control

Question 12

Regarding the primary motor cortex know “anatomically” how the neuron cell bodies are linked to their respective “muscle fields” or movements.

Answer 12

Question 13

What does a larger region of primary motor cortex (M1) represent?

Answer 13

These areas have CST projections that may synapse directly on the lower motor neurons. These areas require fine motor control. These are represented by larger regions.
These larger regions tend to:
o Communicate with large number of LMN
o Gives more ability to grade the function of the body part for fine motor control through processes such as changes in the recruitment of the motor units.

Question 14

Compare and contrast the motor map for the fingers and the trunk. Which one is larger? Why do you think it is larger?

What do you feel this conveys about the
a) size of the motor pool = _____________

b) likelihood of directly innervating a LMN or a local interneuron (IN) circuit? _______________________________________________________________

Answer 14

The fingers because they do more fine movements.

What do you feel this conveys about the
a) size of the motor pool = Larger

b) Higher due to need to regulate the fine movements.

Question 16

Functionally what happens if you excite a UMN in the primary motor cortex. Does it excite a single muscle or something else?

Answer 16

Usually produces movement in contralateral body parts by stimulating multiple muscles.

Question 17

Reflect on the somatotopic organization of the motor cortex and what it conveys for “functional movements”…

Answer 17

Stimulating a specific region of the motor cortex can result in a specific functional movement by activating multiple areas at once that are near the area stimulated on the motor map.

Question 18

What is the general “foot to face” organization? If I had a lesion more “medial, middle, or most lateral” from the interhemispheric fissure what body part may be impaired?

Answer 18

Medial: functional movements such as climbing and reaching
Middle: functional movements such as hand to mouth for feeding
Lateral: functional movements such as moving the hand centrally to manipulate a object??

Question 19

Define a Muscle Field.

Answer 19

The muscles that a specific neuron contributes to the contraction of is its muscle field.

Question 20

What is the general concept of what is involved with “motor planning”

Answer 20

Pre motor (secondary motor) cortex.
Broca’s Area
Posterior and anterior cingulate cortex.
From text:
Medial: the cingulate motor areas involved in the expression of emotional somatic behavior.
Lateral premotor area: along with supplementary motor areas are involved in selecting and organizing purposeful movements of the limbs and face; the frontal eye fields organize voluntary gaze shifts

Question 21

Compare and contrast the difference in how one plans for movement using the lateral and medial component of the secondary (premotor) cortex.

Answer 21

Lateral: plan and prepare movement to external cue.
o Plan = visual cue directs movement, starts movement activation through discharge of neurons before the physical movement occurs (readiness potential), followed by physical movement

Medial: postural muscles. Used for spontaneous, self-initiated motions in open loop conditions.

Question 22

What types of movements are planned? Are the internally (self-initiated) or externally cued?

Answer 22

Externally cued movements are planned with the lateral part of the premotor cortex.
Self initiated spontaneous movements are planned with the medial part of the premotor cortex.