Motor Systems I

Question 1

What are the 4 motor cortical areas?

Answer 1

1. Primary motor cortex (Area 4)
2. Premotor cortex (Area 6)
3. Supplementary motor cortex (Area 6)
4. Frontal eye fields (Area 8)

Question 2

What is the function of the motor cortical areas?

Answer 2

1. Access to BRAINSTEM and SPINAL CORD via** **corticobulbar, corticopontine, corticoreticular and corticospinal projections
2. Heavily interconnected with the cerebellum, basal ganglia and descending systems that control muscle tone
3. Responsible for “Motor command–internally/externally generated movements

Question 3

If the motor cortical area is injured, what are its deficits?

Answer 3

Loss of voluntary movement (stroke, epilepsy, tumor)

Paresis

Increased tone/stretch reflexes

Question 4

What are the criteria to be a mortor cortical area?

Answer 4

1. Cytoarchitectural criteria

Motor areas are AGRUANULAR (have many pyramidal cells)

2 and 4–poorly developed

3 and 5–well developed

Sensory areas are GRANULAR (have more little receiving cells)

2. Stimulation criteria

Evoke moments at low stimulus intensities

Question 5

What are the 2 funcitons of the primary motor cortex?

Answer 5

1. Control individual muscles/forces–generate motor command
2. Control more global features of movement: direction and amplitue of reach

Question 6

What are the 2 features that stimulation reveals?

Answer 6

1. Motor homunculus

Outter to inner (leg, trunk, arm, face, mouth)

2. Columnar Arrangement

Stimulation to a specific column leads to specific/rapid contraction in the motor cortex

Stimulation studies support a role for the primary motor cortex in controlling individual muscles/forces

Question 7

What are the forms of afferent input to the primary motor cortex?

Answer 7

1. Input–> Dorsal Column Nuclei (DCN)–> Thalamus (VPL)

Joint afferents, Muscle spindle receptors, Cutaneous input

ALL CONTRALATERAL–sensory input necessary to control movements

2. Cerebellum and basal ganglia

3. Cortical input

Somatosensory cortex (S1)

Premotor cortex

SMA

Posterior parietal coretx (Areas 5 and 7)- visual information/spatial cognition

Question 8

Where do OUTPUT projections from the premotor cortex go?

Answer 8

Primary motor cortex (Area 4)

Premotor and supplementary motor area (Area 6)

Somatosensory areas (Areas 3,1,2) and parietal cortex (Areas 5 and &)

Frontal Eyefields (Area 8)

Question 9

What is the composition of the output projections from the motor cortex?

Answer 9

2,000,000 axons

3% axons from giant Betz cells in Area 4

Question 10

What are the targets of the output projections from the primary motor cortex?

Answer 10

Basal ganglia-corticostriate

Red nucleus- corticorubral- cerebellum

Pontine nuclei- corticopontine-cerebellum

Reticular formation- corticoreticular (tone, reflexes)

Cranial nerve nuclei (corticobulbar)

Spinal cord (corticospinal)

Question 11

What are the targets of the corticobulbar tract?

Answer 11

Motor Trigeminal (Vm chewing) BILATERAL

Facial nucleus (VII facial expression) CONTRALATERAL AND IPSILATERAL

Nucleus Ambiguous (NA laryngeal and upper airway) BILATERAL

Spinal Acessory (shrugging shoulders, turning head) More IPSILATERAL than bilateral

Hypoglossal (tongue muscles) CONTRALATERAL

Question 12

How are the upper and lower face controled?

How would this effect an in dividual who has a stroke that affects the right motor cortex?

Answer 12

Lower face = CONTRALATERAL motor cortex (M1)

Upper face= IPSILATERAL and CONTRALATERAL motor cortex (cingulate)

A person who has had a stroke in the RIGHT cerebral cortex can

Wrinkle their forehead on BOTH sides, but can’t control the LOWER side of their face.

Question 13

In sections, where are the cranial nerve located on the corticobulbar tract?

Answer 13

Midpons: Vm= trigeminal

Caudal pons: VII= facial upper and lower

Rostral medulla= NA and XII

Upper cervical cord= XI

Question 14

How does the primary motor cortex relate to the frontal eye fields?

Answer 14

The PMC projects to BRAINSTEM GAZE CENTERS which surround and in turn project to cranial nerve nuclei 3, 4, and 7.

Question 15

What is the corticospinal tract?

Where does it terminate?

What does it innervate

Answer 15

The CST is the tract from the primary motor cortex that travels through and to the spinal cord.

It terminates in the:

dorsal horn (contral sensory info coming in)

Intermediate gray horn

Ventral horn (alpha motor neurons–control movement)

A single corticospinal axon diverges to alpha motor neurons of many muscles.

Question 16

What are the 3 physiological principles of the motor cortex?

Answer 16

1. Cells can encode FORCE and/or muscle activation

Neurons fire BEFORE a movment and maintian a level of activity afterwards

2. Cells can econde MOVEMENT DIRECTON (force, speed, position)

3. Population code

Cells are broadly tuned to a movment parameter

Cells fires as a population and each contributes to movement

4. Can use to control external devices

Question 17

Which is false concerning the primary motor cortex?

A) It projects via the corticobulbar tract to motor cranial nerve nuclei
B) It receives input directly (mononsyaptic) from primary visual cortex
C) It projects to the spinal cord via the corticospinal tract
D) It modulates muscle tone via projections to the pontine and medullary reticular formation
E) It has a motor homunculus

Answer 17

b