Motor Systems

Question 1

primary motor cortex

Answer 1

• precentral gyrus
• somatotopic organization
• stimulation in animals: brief stim produced twitches, prolonged stim produced more complex movements
• Receives direct input from primary somatosensory cortex; corresponding body areas

Question 2

2 types of descending motor pathways

Answer 2

• Lateral tracts: control independent limb movement, more precise movement, i.e. R and L sides make different movements or one side moves while other does not
• Ventromedial tracts: control more automatic, gross movements of trunk and limbs involved in posture and walking, more automatic movements, i.e. R and L sides are moving reciprocally or in a coordinated fashion

Question 3

3 lateral tracts of descending motor pathways

Answer 3

All cross, all contralaterally mediated

• corticospinal tract
• corticobulbar tract
• rubrospinal tract

Question 4

lateral

corticospinal tract

Answer 4

• primarily from primary and supplementary motor cortex
• crosses over at pyramids in medulla
• terminate in gray matter of spinal cord
• primarily control fine movements of the fingers, hands, arms, lower legs, feet and toes
• when both pyramidal tracts are cut in monkeys
  i. they recover ability to walk and climb
  ii. fine motor control of hands is impaired

Question 5

lateral

corticobulbar tract

Answer 5

bulbar = brainstem

• primarily from primary and supplementary motor cortex
• cross in medulla
• to cranial nerve nuclei that control face, neck, tongue and some eye movements

Question 6

lateral

rubrospinal tract

Answer 6

• from red nucleus which receives its input from the cortex and cerebellum
• crosses over, contralateral
• controls movements of forearms and hands, but not finger movements

Question 7

4 ventromedial tracts of descending motor pathways

Answer 7

• all bilateral innervation
• All except corticospinal originate in brain stem
• receive input from parts of primary motor cortex that control trunk and proximal muscles
• corticospinal tract
• tectospinal tract
• vestibulospinal tract control
• reticulospinal tract

Question 8

ventromedial

corticospinal tract

Answer 8

• primarily from primary and supplementary motor cortex
• uncrossed, descends bilaterally, exits spinal cord on both sides
• control trunk and upper leg movements

Question 9

ventromedial

tectospinal tract

Answer 9

• from superior colliculus
• uncrossed, descends bilaterally, exits spinal cord on both sides
• coordinate head and trunk with eye movements

Question 10

ventromedial

vestibulospinal tract

Answer 10

• from vestibular nuclei
• uncrossed, descends bilaterally, exits spinal cord on both sides
• controls posture through trunk and leg muscles

Question 11

ventromedial

reticulospinal tract

Answer 11

• from reticular formation throughout brain stem
• also from premotor cortex, amygdala, hypothalamus and basal ganglia
• control autonomic functions, i.e. muscle tone, coughing, sneezing and respiration as well as volitional movements such as walking

Question 12

Motor Association Cortex:

premotor and supplementary motor area, input

Answer 12

• Receives highest level of integrated / synthesized sensory info from the parietal and temporal tertiary / multimodal sensory association areas
• This sensory info provides the motor association areas info it needs regarding what is going on in the environment

Question 13

Motor Association Cortex:

supplementary motor area

Answer 13

• involved in learning and performing sequenced movements, when one movement cues the next (but not when cued externally/abstractly)
  b. inactivation of SMA with TMS interferes with animals’ and humans’ ability to execute a sequence of movements they have learned

Question 14

Motor Association Cortex:

pre-supplementary motor area

Answer 14

• *involved in intending to move**

- electrical stimulation produces urge to move; 2-3 seconds before s’s reported decision to move

Question 15

Motor Association Cortex:

premotor cortex

Answer 15

• Involved in learning and executing complex movements that are guided by sensory input (arbitrary external cues, i.e. reaching for an object when its name is spoken, or stopping / accelerating at a traffic signal)
• Patients with damage to premotor association can learn to make movements in response to spatial location but cannot learn to make movements in response to visual, auditory or tactile cues

Question 16

mirror neurons

Answer 16

• Ventral inferior premotor and inferior parietal lobule
• Watching and imitating other’s movements activates neurons in this system
• The greater the level of the observer’s skill in the movement, the greater the activation in the MN system
• MN also activated by familiar sounds that are associated with actions – audiovisual neurons
• When I observe someone execute an action, the motor circuits representing that action are activated in my brain
• Apparently, that motor representation of the action is what allows me to understand others’ actions AND intentions

Question 17

apraxia

Answer 17

“inability to properly execute a learned skilled movement”
- not due to motor weakness or paralysis, not due to info processing deficits
- can be
a. movement of wrong part of limb
b. incorrect movement of correct part of limb
c. correct movements in incorrect sequence
- most often associated with L hemis damage
a. L parietal
b. L frontal: plans and initiates execution of movements based on this information; L frontal damage also impairs ability to comprehend the gestures of others
Story of fish cleaner not being able to do her job after small eschemic stroke in L hemisphere

Question 18

basal ganglia, motor input

Answer 18

Caudate and putamen (neostriatum) receive input mainly from primary motor and somatosensory cortex

• cortical input provides sensory info and info about movements planned and executed
• input to putamen is from motor areas of brain; pathways are somatotopic throughout loop back to motor cortex
• input to caudate is primarily from cognitive and emotional areas of brain
• neostriatum also receives dopamine input from substantia nigra

Question 19

basal ganglia, motor output

Answer 19

Primary output is through thalamus to primary, pre, and supplementary motor areas, forming a loop

• this allows influence of movements controlled by motor cortex based on the integration of sensory and motor input
• Output also to brain stem nuclei that control ventrolateral motor pathways

Question 20

2 primary motor pathways in cortex

Answer 20

→ basal ganglia → thalamus → cortex loop
1. Direct pathway is excitatory
2. Indirect pathway is inhibitory
OCD thought to be a breakdown in the inhibitory process

Question 21

cerebellum, motor input and output

Answer 21

receives input from every brain area involved in motor control;
outputs to most areas that control motor movements

Question 22

basal ganglia and cerebellum

Answer 22

other brain structures/systems heavily involved in motor regulation
they do not initiate movements but refine them and make them precise

Question 23

cerebellum, influences on motor fx

Answer 23

Influences:

• postural reflexes
• rapid, skilled, independent multi-muscle movements, like catching yourself from tripping
• regulate and modify movements initiated in the cortex
• important in timing and sequencing movements that occur too rapidly to be adjusted based on sensory feedback

Question 24

cerebellum, effects of damage on motor fx

Answer 24

Lesions to different areas of the cerebellum produce different symptoms

• Rigidity
• Fragmented, non-smooth movement
• Impaired timing / ballistic movements
• Ataxia (tremor)