Study Quiz 3

Question 1

Perception to Action: Primary Motor Cortex (M1)

What is somatotopy

Answer 1

Perserved info about body location

Question 2

Perception to Action: Primary Motor Cortex (M1)

What is the motor homunculus

Answer 2

Disproportional representations of the body parts in the motor cortex

Question 3

Perception to Action: Primary Motor Cortex (M1)

What is the type of centrifugal neurons in the motor cortex and where do they project

Answer 3

Pyramidal neurons (look like pyramids). The send output projections to brainstem and spinal cord

Question 4

Perception to Action: Primary Motor Cortex (M1)

Which descending tracts directly facilitate voluntary movement?

Answer 4

1. Corticobulbar (cortex to brain stem)
2. Corticospinal (cortex to spinal grey)

Question 5

Perception to Action: Primary Motor Cortex (M1)

What descending tracts modulate activity of other descending motor tracts or afferent tracts projecting to the cortex

Answer 5

1. Corticorubral
2. Corticoreticular
3. Corticopontine
4. Corticostriate

Question 6

Perception to Action: Primary Motor Cortex (M1)

Describe the Corticobulbar tract

Answer 6

• Projects from motor coritical pyramidal neurons to motor neurons in brain stem
• These MN innervate muscles of face head, eyes, neck, tongue and larynx
• Cranial nerves relay signals from MN to muscle motor units (many cranial nerves are mix of efferent and afferent axons)
• only ~50% of corticobulbar tract decussates

Question 7

Perception to Action: Primary Motor Cortex (M1)

Describe the Corticospinal tract

project to/from

Answer 7

• Projects from cortical upper MN to contralateral lower MN and spinal internurons [lower MN in ventral horn, IN in intermediate & ventral areas of spinal cord]
• Projections originate from primary motor cortex (30%), premotor corticies (30%) and parietal/cingulate gyri (40%)
• Fibers decussate in medulla
• ~75-90% decussate

Upper MN: pyramidal cell in cortex
Lower MN: motor neuron in brain stem/ spinal cord

Question 8

Perception to Action: Primary Motor Cortex (M1)

Describe the Corticorubral tract

Answer 8

Modulates activity of output to rubrospinal tract (regulation of flexor/extensor muscle tone)

Question 9

Perception to Action: Primary Motor Cortex (M1)

Describe the corticoreticular tract

Answer 9

Modulate activity of the reticulospinal tract neurons (anticipatory postural adjustment during walking)

Question 10

Perception to Action: Primary Motor Cortex (M1)

Describe the corticopontine tract

Answer 10

Modulate projections from the pons to the cerebellum (coordinates voluntary movement functions)

Question 11

Perception to Action: Primary Motor Cortex (M1)

Describe the corticostriate tract

Answer 11

provide input to basal ganglia (movement coordination and cognitive motor integration)

Question 12

Premotor areas

What are premotor areas in general and what are the 2 critical areas

Answer 12

refers to areas of the cortex directly linked to motor planning, action selection and motor execution.
1. Premotor cortex
2. Supplementary motor areas

Both involved in voluntary movement to a degree

Question 13

Premotor areas

Describe Supplementary motor areas

Answer 13

• Projections to primary motor cortex
• Convert abstract idea of intention to act into a defined sequence of action
• Activity is greatest when generating movements from memory

Question 14

Premotor areas

Describe the premotor cortex

Answer 14

• Corticospinal projections coordinate control of proximal muscles in anticipation of movements
• Projections to primary motor cortex associate a visual stimulus with the correct action & determine required kinematics to move limb to point in space
• Activity is greated during movements guided by an external cue (ex. visually guided)

Question 15

Frontal cortex to supplementary motor areas

What is the role of the frontal cortex in action selection

Answer 15

Frontal cortec determines if it is possible to act and if it is appropriate to act

Question 16

Frontal cortex to supplementary motor areas

What are the 3 types of neurons in the supplementary motor areas

Answer 16

1. Sequence selective
2. Movement selective
3. Rank-order selective

SMA originally thought to only include sequence selective

Question 17

Frontal cortex to supplementary motor areas

Describe sequence selective neurons

Answer 17

Code for a specific sequence of movements that must be put together in a specified order to achieve desired outcome
(ex, code for specific sequence Pull-Turn-Push)

Question 18

Frontal cortex to supplementary motor areas

Describe Rank-order neurons

Answer 18

Define overall timing of each element in the action, rather than position. (ex, code for 3rd action in any sequence, regardless of action)

Question 19

Frontal cortex to supplementary motor areas

Describe movement selective neurons

Answer 19

Define specific position of an element within the action sequence
(ex, code for Pull action regardless of when Pull occurs within the sequence)

Question 20

Premotor cortex

What are the subdivisions of the premotor cortex

Answer 20

1. Dorsal premotor cortex
2. Ventral premotor cortex

Question 21

Premotor cortex

What do the dorsal Premotor cortex neurons code

Answer 21

Movement vectors in space

activity will be different when reaching left vs right for ex

Question 22

Premotor cortex

What do the ventral Premotor cortex code

Answer 22

Effector orientation relative to an object

ex if activity is greatest for a ring, a sphere will have activity (but weaker) as well but a cube would not

Question 23

Parietal cortex

Explain the parietal cortex in comparison/relation to the premotor cortex

visualmotor stuff

Answer 23

• transforms visual info
• Premotor converts body to environment, parietal converts environtment to body
• Parietal association areas are critical areas of convergence for the different senses
• Posterior parietal cortex plays critical role in use of somatosensory & visual cues to support action
• Intreparietal sulcus critical to converting visual into body-centered coordinates

Question 24

Parietal cortex

Describe the 4 critical areas of the intraparietal sulcus used for action/movement

Answer 24

• Medial intraparietal sulcus (MIP): maps visual env. relative to arm (Reaching)
• Anterior intraparietal sulcus (AIP): maps object shape/orientation to hand (Grasping)
• Lateral intraparietal sulcus (LIP): maps location in visual env. relative to eye (Eye movements)
• Parietal Reach Region (PRR): overlaps MIP, though to contain neurons that relate eye & hand location as eyes move (hand-eye coordination)

Question 25

# Premotor cortex Explain the Dorsal premotor cortex and how it can be divided

Answer 25

* **Rostral dorsal premotor cortex**: maps stimulus response rules * **Caudal dorsal premotor cortex**: takes MIP/PRR input about where things are in relation to body and determines required kinematics to get effector to that point in space

Question 26

# Premotor cortex Describe the Ventral premotor cortex

Answer 26

* **Rostral Ventral Premotor Cortex**: 2 functions 1. determine grip aperature given orientaion/shape of object relative to hand 2. Relate object centered actions of other people to ourselves (mirror neurons)

Question 27

# Balance control What is Postural Orientation

Answer 27

The relative positionaing of the body segments wrt each other and to the env.

Question 28

# Balance control What is postural stability/equilibrium

Answer 28

the coordination of movements to stabalize the centre of body mass wrt the base of support during both self initiated and externally triggered disturbances of stability

Question 29

# Balance control What is Balance (equilibrium) control

Answer 29

a term used to describe the NS control of postural stability

Question 30

# Balance control Describe equilibrium

Answer 30

A state in which opposing forces are equal (in balance it i achieved when force due to gravity is cancelled by the opposing reaction force)

Question 31

# Balance control What 2 things does balance require

Answer 31

1. Equal opposing forces (muscle tone) 2. Alignment of opposing forces (COM & BOS) When there is a misalignment, torque will cause instability/potential fall

Question 32

# Balance control What is Centre of mass (COM)

Answer 32

The mean location of a distribution of mass of the body ## Footnote sometimes COG (centre of gravity)

Question 33

# Balance control What is Base of Support (BOS)

Answer 33

the area defined by the parts of the body that are in contact w supporting surfaces

Question 34

# Balance control What is centre of pressure (COP)

Answer 34

the point of application of the overall ground reaction force which represents the sum of all forces acting b/w the person and the BOS (application/mean point of BOS, is contained within BOS)

Question 35

# Balance control What is static stability | what balance control does it rely on?

Answer 35

* The NS maintains the position of the COM withing a fixed (stationary) BOS. * Motion of COM occurs spontaneously (due to instability) * **Relies on reactive balance control** * Ex: standing still ## Footnote Humans have high COM that is far from BOS and relatively small BOS, they re therefore unstable even when standing 'still'

Question 36

# Balance control What is dynamic stability: | and what balnce control does it rely on

Answer 36

* NS contros movement to maintain relationship b/w COM & BOS when the COM is externally disturbed and/or when COM and/or BOS are changing * **Relies on both reactive and predictive control** * Ex: controlling stability when a bus pulls away from stop, when walking, ect

Question 37

# Balance control What is reactive balance control

Answer 37

**Control of balance in response to a sensed moment of instability** (ex. control of reactions following an unexpected push) ## Footnote aka **feedback/ compensatory control**

Question 38

# Balance control What is predictive balance control

Answer 38

control of movement in anticipation of potential moment of instability (ex. prior to executing a movement that could cause instbility such as a vouluntary step) ## Footnote AKA **feedforward/ anticipatory control**

Question 39

# Establishing the equilibrium What must happen if our COM moves outside our BOS?

Answer 39

We must change our BOS or risk falling

Question 40

# Establishing the equilibrium What direction is the motion of our body's COM during quiet standing? | as bipeds with high COM and non-rigid muscles, we're inherently unstable

Answer 40

Anteroposterior direction

Question 41

# Establishing the equilibrium Explain balance in terms of muscles | acitve or passive

Answer 41

Balance is an active process, passive forces are not sufficient. Therefore, coordinated muscle responses/contractions are necessary to control whole body stability.

Question 42

# Establishing the equilibrium Which planes require stability control

Answer 42

Both the anterior-posterior and medial-lateral require stability control, as they both sway the farther up the body we move from the BOS

Question 43

# Establishing the equilibrium How can dynamic balance control be probed?

Answer 43

Using a destabilizing even caused by an external perturbation [reactive] (push, pull) or asking participant to internally initiate perturbation [predictive] (stepping, reaching)

Question 44

# Establishing the equilibrium What cn you manipulate during 'event related' studies of balance control

Answer 44

1. Perturbation type (will provide infor about mechanism eg. reactive vs predictive) * external * Internal 2. Perturbation predictability (will privide info abt mechanism, what is predictable/unpredictable matters like time, duration, amplitude etc) * Unpredictable * predictable

Question 45

# Predictive (anticipatory) control What is Anticipatory Postural Adjustment (APA)

Answer 45

Activation of postural muscles in a feedforward manner before a voluntary movement or an expected event begins, in anticipation of the destabilizing forces caused by event/movement * **derived from past experience where loss of balance occurred** from a specific event

Question 46

# Predictive control: Voluntary movement Explain the APA that is observed during stepping | Anticipatory Postural Adjustment

Answer 46

APA control observed prior to lifting the swing foot. 2 APA responses occur before swing foot lifts off: 1. **Initial movement of COP towards the foot that will swing forward** (stepping foot) 2. **Subsequent shift of COP towards stance foot** both responses developed through experience as we learn to walk

Question 47

# Predictive control: external perturbation When and how can APAs be initiated for external perturbations

Answer 47

APAs to external perturbations will be initiated **when an external perturbation can be predicted.** They will be **generated based on context** around external perturbation. Ex: bracing when hearing an auditory warning before handle is pulled away (trained)

Question 48

# Reactive (compensatory) control What are Automatic Postural Reactions (APR)

Answer 48

APR are highly stereotypes patterns of EMG activity in various muscles that are triggered in response to sudden perturbations to stability

Question 49

# Reactive control What are fixed support reactions

Answer 49

responses to instability where BOS does not change (ex leaning forward/backward) | Goal to keep COM above COP

Question 50

# Reactive control What are change in support reactions

Answer 50

reactions to instability that involve rapid change in BOS to maintain stability (ex grab a railing) | goal to keep COM above COP

Question 51

# Reactive control Describe some characteristics of fixed support APRs

Answer 51

* rapid onset latence (~100ms) * Complex pattern of coorditation (agonist/antagonist) * Highly adaptable * Scaled by ampitude of perturbation * tuned to direction of perturbtion * Yield no errors in amplitude or direction ( but are adaptible if APR is not appropriate)

Question 52

# Reactive control Describe some characteristics of change in support APRs

Answer 52

* Have rapis onset latency (~100ms) * Have complex pattern of coordination * Highly adaptable * have a direction, pattern and amplitude influenced by both perturbation AND surrounding environment * have additionl challenge of making contact with new support (ie grasp) * Yield no errors in amplitude or direction (but are adaptable if APR is not appropriate)

Question 53

# Balance control What is similar about voluntary vs reflexive reach-to-grasp

Answer 53

both use same generalized motor plans, reflexive is just slightly faster

Question 54

# Reactive control Explain how vision affects APR

Answer 54

**Peripheral vision** is important to *change in support* APRs, reach-to-grasp APRs **DO NOT require shift in gaze**

Question 55

# NS control of balance What does the NS rely on to detect stability/instability and what factors (3) affect the vaule assigned?

Answer 55

NS relies on a multitude of senses * single sense can be ambiguous * converging info provides clearer overall picture NS assigns value to difference sensed depending on: * Past Experience * Body State * Movement Context | Remember: **Reflexes are adaptable**

Question 56

# NS control of balance What determines which senses are given more value in balance control

Answer 56

There is a hierarchy established based on past experience Vision is often given priority as it is reliable and NS favours it (can remove or trick vision to measure visual dependance to balance control)

Question 57

# NS control of balance Why might young children/older adults depend more on vision than young adults

Answer 57

Myelination affects conduction (still developing in children and deteriorating in older adults)

Question 58

# The Postural Set or Central Set What are postural sets influenced by

Answer 58

specific behaviour/tasks/condition and prior experience/expectation

Question 59

# The Postural Set or Central Set What is a postural (or central) set

Answer 59

A body position characterized by increased muscle tone, that is adopted in preparation for a response (such as baseball batters stance before a pitch) * Narrows the likely postural response required to correct for instability during behaviour (NS tries to adopt postures that will minimize instability during behaviour)

Question 60

# NS balance control Where in the CNS is balance control occuring

Answer 60

* Spinal cord * Brain stem * Cerebellum * Basal ganglia * Cortex

Question 61

# NS balance control Explain the Spinal Cords role in balance | and how can we understand its contributions

Answer 61

After removing the influence of higher control centres: 1. Lower-limb geometry during stance is perserved 2. Tonic weight support possible but with no medio-lateral stability 3. animals could not stabilize after large perturbations | Understand by separating SC from 'higher control centres'

Question 62

# NS balance control Explain the Brain stems role in balance | and how can we understand its contributions

Answer 62

After removing the influence of basal ganglia and cortex, 3 descending tracts can be assessed: 1. Vesibulospinal (originate from vesibular nuclei) 2. Reticulospinal (originate from reticular formation) 3. Rubospinal (originale from red nucleus, less critical to balance in primates) | Understand by comparing spinal preparations to decerebate preparations

Question 63

# NS balance control Explain the Vestibulospinal tract | input,terget, output

Answer 63

Connecting orientation of body through vestibular system to motor neuron * **Input:** vestibular nuclei recieve input from *vestibular nerve/system & cerebellum* (descending/centrifugal) * **Target:** Vestibulospinal tract projects to *interneurons in spinal cord* * **Function:** *Modulate spinal reflexes* based on the context of vestibular info

Question 64

# NS balance control Explain the Reticulospinal tract | input,terget, output

Answer 64

Connected to arousal levels * **Input:** *peripheral sensory receptors, cerebellum and cerebral cortex*(descending/centrifugal) * **Target:** reticulospinal tract projects to *interneurons in spinal cord* * **Function:** *Modulate flexor and extensor muscle activity* during stance and locomotion

Question 65

# NS balance control Explain the Cerebellums role in balance | whatwould be the effects of lesions here

Answer 65

* High processing power structure in NS * does not send output/directly influence the spinal cord * Instead, uses its **dense connections with brain stem and cortex to shape theur output** * Plays **critical role in coordination and learning.** Lesions to cerebellum compromise balance control and gait and disrupt learning of postural sets through experience

Question 66

# NS balance control Explain the role of the basal ganglia in balance | andwhat do lesions lead to?

Answer 66

* less understood * We know BG sends projections to cortex to help initiate some behaviours and suppress others * Could **shape coticospinal (voluntary movement) and corticoreticular (anticipatory postural control) outputs from cortex** * lesions to BG **disrupt ability to initiate and scale postural adjustments** during balance

Question 67

# NS balance control Explain the role of the Cortex in balance

Answer 67

* More recent area o investigation * emerging evidence that there is a broad cortical involved in reactive and predictive balance control * parietal cortex may help determine postural adjustments given postural set