Motor Cortices

Question 1

Principal elements of any voluntary movement

Answer 1

. Location and identification of a target
. Movement programming
. Execution of a movement

Question 2

Location and identification of target

Answer 2

. External cues: Premotor cortex (PMC) and post. Parietal motor area (PMA) areas 5 and 7 and sensorimotor transformations
. Internal cues: function of supplementary motor area (SMA)

Question 3

Movement programming

Answer 3

. Praxic programs: how of movement, function of cortex area

. Intentional programs:when of movements, function of basal ganglia

Question 4

Execution of movement

Answer 4

. Midcourse corrections of movement

. Involve cerebellar circuitry

Question 5

Lower motor neurons

Answer 5

. Directly innervate skeletal mm.

Question 6

Upper motor neurons

Answer 6

. Influence the lower motor neurons

Question 7

Cortical areas that play significant role in motor function

Answer 7

. primary motor cortex (M-1)
. PMC
. SMA
. PMA
. Frontal eye fields

Question 8

Primary motor cortex (M-1)

Answer 8

. Inside precentral gyrus (area 4)
. Typographically similar to S-1 (motor homunculus
. Neurons in layer V give rise to axons that contribute to corticospinal tract and terminate in ventral horn of all levels spinal cord
. Individual corticospinal axons Freuq. Diverge to influence motor neurons that innervate several mm.
. Divergence small for distal mm. So there is h gig degree of control (opp. For prox. Mm.)

Question 9

Functional aspects of M-1

Answer 9

. Activation primarily of fine distal movements
. Ingidivual and simple movements occurring around single joint
. Execution of specific well-defined motor movement
. Electrical threshold for eliciting movement is lower than in any other part of cortex

Question 10

Specific characteristics to M-1

Answer 10

. Direction of movement determined by population of neurons, not just 1
. Kept informed about position of limb and speed of movement through sensory input
. Some input directly from thalamus via thalamic-cortical connections
. Some input rom S-1 via corticocortical connections
. Allow M-1 neurons to adjust their activity based on change in limb position, load, etc

Question 11

Premotor cortex (PMC)

Answer 11

. Most of sup. And middle frontal gyri, lat. aspect of areas 6
. Less precise homunculus
. Extensive receiproal connections w/ M-1, SMA, and PMA
. Small contribution to corticospinal tracts in ventral horn neurons controlling prox. Limb and axis mm.
. Role in planning movement
. Coordinated movement of limbs can be elicited by stimulating PMC but movement is slower and more likely to involve larger mm. Groups than M-1 activation

Question 12

How PMC plans movement

Answer 12

. Prepares motor system for movement and then dec. in activity w/ initiation of that task
. How stimuli for movement is used to direct a movement is function of this
. Important for control in visually guided movements bc you need proper orientation of hand and fingers when they approach object to be grasped
. Planning and execution relies on sensorimotor transformations where sensory representations of external environment are integrated into motor programs (function of PMC and PMA)

Question 13

Supplementary motor area (SMA)

Answer 13

. Med. sand superolat. Portion of frontal lobes, med. aspect area 6
. Contains less precise motor homunculus than M-1
. Gives rise to fibers of corticospinal tracts
. Extensive connections w/ both M-1 and PMC
. Neurons excite M-1 neurons
. Role in coordinating movement and posture
. Function in movements that are internally generated (mental imaging of movement)
. Helps select motor programming for learned motor sequences (presupplemetnary cortex learns new movement and SMA retains it)

Question 14

Stimulation of SMA

Answer 14

. Complex motor movements
. Threshold for movement higher than M-1
. Coordinates movements on both sides of body
. Action of prox. Mm. Occurs directly via corticospinal projections from SMA to ventral horn of spinal cord
. Action of distal mm. Occurs indirectly via connections from SMA to M-1 (which then projects onto ventral horn)

Question 15

Posterior parietal motor area (PMA)

Answer 15

. Parietal lobe, areas 5 and 7
. Inputs primarily from S-1
. Relates sensory info to limb position
. Area 5 receives inputs from vestibular system about head orientation and from PMC about motor plans and from limbic system about motivational state
. Area 7 receives visual and auditory inputs in addition to somatosensory info

Question 16

Functional aspects of PMA

Answer 16

. Role in correlating info about external world w/ info about position of our body and limbs and our motivational state
. Neuron activity modulated by states of attention (driven by sensory stimuli only in context of goal-oriented behavior)
. Play role in initiation of movement by creating context for directing movement
. Functions in sensorimotor transformations

Question 17

Frontal eye fields

Answer 17

. Post. Portion of middle frontal gyrus, area 8, just ant. To face representation in PMC
. Initiation of rapid horizontal eye movements (saccades)

Question 18

Unilateral lesion in frontal eye field

Answer 18

. Result in a game preference to the side of the lesion and rest and an inability to voluntarily look to contralat. Side
. Vertical eye movements not impaired

Question 19

Bilateral lesion of frontal eye fields

Answer 19

. Unable to do saccades at all

Question 20

T/F lesions of S-1 may cause what appear to be motor deficits

Answer 20

T

Question 21

Prefrontal cortex (PFC)

Answer 21

. Part of frontal lobe ant. To PMC, SMA, and FEF
. Role in complex motor activities through connections w/ PMC SMA, and PMA, does not elicit motor movements by itself
. Receives info about all sensory modalities and motivational/emotional state
. Related to capacity of person to weigh consequences of future actions and plan accordingly

Question 22

Lesions of prefrontal cortex

Answer 22

. Result in alterations in attention, motivation, and ability to change a response when a stimulus changes
. Changes in motor behaviors