Ebner --Motor Cortical Areas

Question 1

criteria to be a motor cortical area

Answer 1

1. cytoarchitectural criteria – agranular (sensory = granular) with pyramidal cells (poor or well developed)
2. stimulation criteria – evoke movements at low stimulus intensities

Question 2

primary motor cortex

Answer 2

Area 4

1. controles individual muscles– very discrete movements about a joint
2. controls global features of movement –direction and amplitude

Question 3

stimulation of the primary motor cortex reveals two features

Answer 3

1. **motor homunculus **
2. columnar orgianization (as you go down a column… same movement) –between columns (get abduction/adduction)

Question 4

Afferent imput to the primary motor cortex comes from where?

Answer 4

dorsal column nuclei (DCN) and thalamus (VPL)

contralateral

via joint afferents, muscle spindle receptors, cutaneous imput

Question 5

What are the four cortical areas of imput to the primary motor cortex?

Answer 5

1. somatosensory (S1)
2. premotor cortex
3. supplementary motor area (SMA)
4. posterior parietal cortex (area 5 and 7) – visual information

Question 6

One of the biggest and most important projections from the brain comes from the premotor cortex and is called the ____.

Answer 6

pyramidal tract

crosses to the contralateral side at the pryramidal decussation

Question 7

corticobulbar target of the primary motor cortex (area 4)

Answer 7

1. Motor trigeminal (Vm) nucleus (locatd in midpons) –> chewing; bilateral!!! no problem in stroke
2. Facial nucleus (VII) –bilateral
3. nucleus ambiguous (NA) –> laryngeal and upper airway; bilateral
4. spinal accessory (XI) –> shrugging shoulders and turning head; ipsilateral
5. hypoglossal (XII) tongue muscles; contralateral

Question 8

If you had a stroke of the right Facial nucleus (VII) side could you wrinkle your forehead?

Answer 8

YES!

upper face controlled by both ipsilateral and contralateral motor cortex (cingulate)

You will have problems with the face (one side)

Question 9

If you have a stroke on the right precentral gyrus affecting the face, what side of the face would you see loss of muscle movement?

Answer 9

contralateral lower face!! So the left side lower face.

The tongue would stick out the the right

Question 10

corticospinal tract terminates where?

Answer 10

dorsal horn (controlling sensory information input), intermediate grey, and ventral horn (alpha-MN)

Also… a single corticospinal axon diverges to alpha- MNs of many differnent muscles.

Question 11

Population coding of the motor cortex

Answer 11

• cells fire as a population and each contributes to the movement.
• can be used to control external devices

Question 12

Lesion studies of the pyramidal (corticospinal) tract show us what?

Answer 12

Deficits in fine motor control of hand – used more like a cup

reaching, locomotion, and other movements intact. Why? Other systems bring motor to the muscles of the arm.

Question 13

If you have a stroke in your left primary motor cortex what happens?

Answer 13

weak on contralateral side (right) (paresis)

increased extensor tone and stretch reflexes (reticulospinal tract)

and babinske reflex (right)

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Question 14

If you have a stroke on the right side of the primary motor cortex, what corticobulbar deficits would you notice?

Answer 14

1. Lower facial muscle loss on left
2. smile impairment on left side
3. inability to puff out cheek on left
4. weakness of ipsilateral trapezius and SCM (weakness turning head to left)
5. weakness of contralateral tongue (tongue to left)

Question 15

What happens when you stimulate the premotor cortex?

Answer 15

• coordinated turning of eyes and head (contralateral)
• synergistic movements –fully constructed movemetns (i.e. contralateral hand seems to lead and head turns to “watch”
• …so higher level of movement than the primary motor cortex
• planning and learning movements
• No homounculus

Question 16

Lesions of the premotor cortex manifest how?

Answer 16

loss of ability to execute complex plans (i.e. reach around an object to grab food).

Interal work

external fails

can’t learn new sensory-motor associations

Question 17

Ventral premotor cortex (PMv)

Answer 17

involved with control of grasping

contains mirror neurons – neurons that discharge when monkey grasps an object or watche another monkey or human grasp the same object.

intention, imitation, and action understanding

Question 18

stimulation of the supplementary motor area results in what?

Answer 18

Evokes contralateral limb movements involving multiple joints and postural changes

important for internal generation of movements and sequences of learned movements

Remember synergies: premotor > SMA > primary motor

homunculus

Question 19

supplementary motor area lesions manifest themselves as…

Answer 19

patients become stimulus bound: utilization behaviors

(patient makes semi-purposeful movements apparently outside of their control)

Question 20

As tasks become highly proficient, the SMA reduces its activity and ____ assumes control

Answer 20

primary motor cortex