BB Lecture 16: Motor System I

Question 1

What are the three types of movements?

Answer 1

i. reflexes
ii. rhythmic
iii. voluntary

Question 2

What are reflexes?

Answer 2

involuntary coordinated patterns of muscle contraction and relaxation elicited by peripheral stimulation

- stereotyped, performance not changed by practice
- but is modulated by descending inputs

Question 3

What are rhythmic movements?

Answer 3

• chewing, swallowing, scratching, locomotion
  
  • circuits in spinal cord and brainstem: CPGs (central pattern generators), beautiful circuits that have evolved to take on repetitive tasks

Question 4

What are CPGs?

Answer 4

Central Pattern Generators
Evolved to take on a repetitive task
-allows you to engage in rhythmic movements

Question 5

What are voluntary movements?

Answer 5

goal directed, purposeful, generated internally  topic of this lecture

- improve with practice
- correction for external perturbations: feedback and feedforward control of movement

Question 6

What is the role of Feedback movement generation?

Answer 6

• signals sent to the motor system once the movement is happening
  
  • error signal  compensatory change
  • necessary to maintain position, hold an object steadily, etc.

Question 7

What is the role of Feedforward movement?:

Answer 7

-ANTICIPATORY control (for example for balance when moving limbs)
3 principles of feed-forward systems
-essential for rapid action
-depends on ability to make predictions
-can modify the operation of feedback mechanisms

Question 8

How is the motor system organized?

Answer 8

Into lateral motor systems and medial motor systems

Question 9

What is the lateral motor system comprised of? What is the overall function of lateral descending pathways? Contralateral or ipsilateral?

Answer 9

Comprised of
	i. Lateral corticospinal tract
	ii. Rubrospinal tract
Function: contributes to goal directed movements of arm and hand. Related with reaching and manipulating
Contralateral

Question 10

Where does rubrospinal tract originate? Function? Course?

Answer 10

Site of origin: red nucleus at level of the MIDBRAIN
-crosses at midbrain at ventral tegmental decussation
Function: allows you to shrug your shoulders
Runs contralateral and terminates at level of shoulders

Question 11

Tectum

Answer 11

general term for “roof” or most posterior part of the brainstem
-obvious only in the midbrain and is composed of inferior/superior colliculus

Question 12

Tegmentum

Answer 12

general term for intermediate region in brainstem. Lies ventral to ventricles and dorsal to the “basis” part of the brainstem

Question 13

Basis

Answer 13

general term for most ventral region in brainstem

-this is where the corticospinal and corticobulbar tracts lie

Question 14

What is the medial motor system comprised of? What is its function? Contralateral or ipsilateral

Answer 14

Comprised of:
i. Anterior corticocpinal tract
ii. recticulospinal tract:
iii. vestibulospinal tract
iv. tectospinal tract
Critical for POSTURAL control by integrating visual, vestibular and somatosensory information
Ipsilateral (except for tectospinal) and terminate on interneurons and propriospinal neurons

Question 15

Comprised of:
i. Anterior corticocpinal tract
ii. recticulospinal tract:
iii. vestibulospinal tract
iv. tectospinal tract
Critical for POSTURAL control by integrating visual, vestibular and somatosensory information
Ipsilateral (except for tectospinal) and terminate on interneurons and propriospinal neurons
What is the origin of the reticulospinal tract? Function? Course?

Answer 15

Site of origin: pontine AND medullary reticular formation (pons and medulla)
Function: automatic posture and gait-related movements
Runs ipsilateral throughout entire cord

Question 16

Site of origin of vestibulospinal tract? Function? Course?

Answer 16

Site of origin: vestibular nuclei (located in pons and medulla)
Function: positioning of head and neck as well as balance (medial and lateral VST respectively
Course: ipsilateral through cervical/thoracic cord (medial VST) and entire cord (lateral VST)

Question 17

Site of origin of tectospinal tract? Function? Course?

Answer 17

Site of origin: superior colliculus
Function: Coordination of head and eye movement (uncertain in humans?)
Course: Contralateral, decussate at midbrain, terminates at cerbical cord

Question 18

What are the three levels of control of the motor system?

Answer 18

1. motor nuclei of the spinal cord spinal cord
2. The brain stem
3. the forebrain (motor cortex, premotor cortex)

Question 19

What modulates the motor system? How do they interact with cerebral cortex?

Answer 19

What modulates the motor system? How do they interact with cerebral cortex?

Question 20

Propriospinal neurons

Answer 20

neurons that assure coordination between motor nuclei

Question 21

What cortical regions do the corticospinal tract originate from?

Answer 21

1/3: area 4 (prefrontal)
1/3: area 6 (M1)
1/3: areas 3,2,1…this is the somatosensory area!!!

Question 22

What are the two pathways of the corticospinal tract?

Answer 22

a. most will cross the midline at the pyramidal decussation
Significance: the axons that cross innervates the nuclei at the lateral (distal muscles) part of the spinal cord
b. ¼ of axons will not cross midline and run ipsilaterally
Significance: the axons that do NOT cross innervates the nuclei at the medial (proximal/posture muscles) part of the spinal cord
-descending fibers provide innervation to the brainstem medial nuclei
-ANTERIOR CORTICOSPINAL TRACT

Question 23

What is the motor cortex divided into?

Answer 23

a. primary motor cortex (M1)
b. supplementary motor cortex (subset of premotor cortex?)
c. premotor cortex

Question 24

What are the cortical inputs to the motor cortex?

Answer 24

i. ventral premotor area (PMv)
ii. dorsal premotor area (PMd)
iii. supplementary motorea (SMA)
iv. primary somatosensory area (S1)

Question 25

What are the SUBcortical inputs to the motor cortex?

Answer 25

i. basal ganglia
ii. cerebellum
via VA and VL of thalamus
significance: motor cortex projects to basal ganglia and to the cerebellum (via pontine nuclei)

Question 26

Why is the homunculus model of the motor cortex incorrect?

Answer 26

Because the motor cortex is NOT a massive switchboard

Muscles are almost never activated individually

Question 27

If the motor cortex is not a massive switchboard, how then are muscles activated?

Answer 27

Via population encoding

Question 28

What is Population encoding?

Answer 28

the activation of any given muscle or set of muscles is carried out by a distributed POPULATION of neurons

- so many neurons are the only ones capable of encoding the amount of activity to do coordinate activity
- it’s almost like all the neurons are voting on how much to stimulate the muscle

Question 29

Is the motor cortex plastic or immutable? What’s the significance?

Answer 29

Motor cortex is plastic
Example: the more movement becomes practiced, the more extensively it is represented in M1
Both size and position of activation in brain can change over time

Question 30

Does the activity of individual neurons depend on muscle force or movement displacement?

Answer 30

Depends on muscle force
Example: monkey makes same motion, but upon different resistances. Action potentials change based on varied resistance…demonstrating that neurons fire in accordance to force

Question 31

What is purpose of M1?

Answer 31

Represents the specific parameters of movement

Question 32

What is the purpose of Supplementary motor area (SMA)

Answer 32

• initiates COMPLEX movement
• determines specific order of responses
• internally generated plan
• based on memory

Question 33

What is the purpose of the lateral premotor cortex?

Answer 33

• movements triggered by external stimuli
• responsible for sensory motor integration
• orchestrates how sensory stimulation is used for direct movement

Question 34

What are Mirror neurons? Where are they located?

Answer 34

: neurons that get activated when one sees another person do the same movements

- so what’s activated by watching someone do something is the same shit that is activated when you are doing it?
- located in ventral premotor area

Question 35

When is premotor cortex activity most involved? When is premotor cortex activity unnecessary?

Answer 35

• premotor cortex is involved in planning and mentally rehearsing voluntary movement
  
  • premotor cortex is mainly involved in sensory motor transformations and therefore in the surveillance of movement execution.
  • When a task is learned and becomes automatic, premotor activity is reduced