Study Quiz 3 Flashcards
Perception to Action: Primary Motor Cortex (M1)
What is somatotopy
Perserved info about body location
Perception to Action: Primary Motor Cortex (M1)
What is the motor homunculus
Disproportional representations of the body parts in the motor cortex
Perception to Action: Primary Motor Cortex (M1)
What is the type of centrifugal neurons in the motor cortex and where do they project
Pyramidal neurons (look like pyramids). The send output projections to brainstem and spinal cord
Perception to Action: Primary Motor Cortex (M1)
Which descending tracts directly facilitate voluntary movement?
- Corticobulbar (cortex to brain stem)
- Corticospinal (cortex to spinal grey)
Perception to Action: Primary Motor Cortex (M1)
What descending tracts modulate activity of other descending motor tracts or afferent tracts projecting to the cortex
- Corticorubral
- Corticoreticular
- Corticopontine
- Corticostriate
Perception to Action: Primary Motor Cortex (M1)
Describe the Corticobulbar tract
- 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
Perception to Action: Primary Motor Cortex (M1)
Describe the Corticospinal tract
project to/from
- 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
Perception to Action: Primary Motor Cortex (M1)
Describe the Corticorubral tract
Modulates activity of output to rubrospinal tract (regulation of flexor/extensor muscle tone)
Perception to Action: Primary Motor Cortex (M1)
Describe the corticoreticular tract
Modulate activity of the reticulospinal tract neurons (anticipatory postural adjustment during walking)
Perception to Action: Primary Motor Cortex (M1)
Describe the corticopontine tract
Modulate projections from the pons to the cerebellum (coordinates voluntary movement functions)
Perception to Action: Primary Motor Cortex (M1)
Describe the corticostriate tract
provide input to basal ganglia (movement coordination and cognitive motor integration)
Premotor areas
What are premotor areas in general and what are the 2 critical areas
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
Premotor areas
Describe Supplementary motor areas
- 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
Premotor areas
Describe the premotor cortex
- 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)
Frontal cortex to supplementary motor areas
What is the role of the frontal cortex in action selection
Frontal cortec determines if it is possible to act and if it is appropriate to act
Frontal cortex to supplementary motor areas
What are the 3 types of neurons in the supplementary motor areas
- Sequence selective
- Movement selective
- Rank-order selective
SMA originally thought to only include sequence selective
Frontal cortex to supplementary motor areas
Describe sequence selective neurons
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)
Frontal cortex to supplementary motor areas
Describe Rank-order neurons
Define overall timing of each element in the action, rather than position. (ex, code for 3rd action in any sequence, regardless of action)
Frontal cortex to supplementary motor areas
Describe movement selective neurons
Define specific position of an element within the action sequence
(ex, code for Pull action regardless of when Pull occurs within the sequence)
Premotor cortex
What are the subdivisions of the premotor cortex
- Dorsal premotor cortex
- Ventral premotor cortex
Premotor cortex
What do the dorsal Premotor cortex neurons code
Movement vectors in space
activity will be different when reaching left vs right for ex
Premotor cortex
What do the ventral Premotor cortex code
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
Parietal cortex
Explain the parietal cortex in comparison/relation to the premotor cortex
visualmotor stuff
- 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
Parietal cortex
Describe the 4 critical areas of the intraparietal sulcus used for action/movement
- 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)
Premotor cortex
Explain the Dorsal premotor cortex and how it can be divided
- 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
Premotor cortex
Describe the Ventral premotor cortex
-
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)
Balance control
What is Postural Orientation
The relative positionaing of the body segments wrt each other and to the env.
Balance control
What is postural stability/equilibrium
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
Balance control
What is Balance (equilibrium) control
a term used to describe the NS control of postural stability
Balance control
Describe equilibrium
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)
Balance control
What 2 things does balance require
- Equal opposing forces (muscle tone)
- Alignment of opposing forces (COM & BOS)
When there is a misalignment, torque will cause instability/potential fall
Balance control
What is Centre of mass (COM)
The mean location of a distribution of mass of the body
sometimes COG (centre of gravity)
Balance control
What is Base of Support (BOS)
the area defined by the parts of the body that are in contact w supporting surfaces
Balance control
What is centre of pressure (COP)
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)
Balance control
What is static stability
what balance control does it rely on?
- 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
Humans have high COM that is far from BOS and relatively small BOS, they re therefore unstable even when standing ‘still’
Balance control
What is dynamic stability:
and what balnce control does it rely on
- 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
Balance control
What is reactive balance control
Control of balance in response to a sensed moment of instability (ex. control of reactions following an unexpected push)
aka feedback/ compensatory control
Balance control
What is predictive balance control
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)
AKA feedforward/ anticipatory control
Establishing the equilibrium
What must happen if our COM moves outside our BOS?
We must change our BOS or risk falling
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
Anteroposterior direction
Establishing the equilibrium
Explain balance in terms of muscles
acitve or passive
Balance is an active process, passive forces are not sufficient. Therefore, coordinated muscle responses/contractions are necessary to control whole body stability.
Establishing the equilibrium
Which planes require stability control
Both the anterior-posterior and medial-lateral require stability control, as they both sway the farther up the body we move from the BOS
Establishing the equilibrium
How can dynamic balance control be probed?
Using a destabilizing even caused by an external perturbation [reactive] (push, pull) or asking participant to internally initiate perturbation [predictive] (stepping, reaching)
Establishing the equilibrium
What cn you manipulate during ‘event related’ studies of balance control
- Perturbation type (will provide infor about mechanism eg. reactive vs predictive)
* external
* Internal - Perturbation predictability (will privide info abt mechanism, what is predictable/unpredictable matters like time, duration, amplitude etc)
* Unpredictable
* predictable
Predictive (anticipatory) control
What is Anticipatory Postural Adjustment (APA)
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
Predictive control: Voluntary movement
Explain the APA that is observed during stepping
Anticipatory Postural Adjustment
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
Predictive control: external perturbation
When and how can APAs be initiated for external perturbations
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)
Reactive (compensatory) control
What are Automatic Postural Reactions (APR)
APR are highly stereotypes patterns of EMG activity in various muscles that are triggered in response to sudden perturbations to stability
Reactive control
What are fixed support reactions
responses to instability where BOS does not change (ex leaning forward/backward)
Goal to keep COM above COP
Reactive control
What are change in support reactions
reactions to instability that involve rapid change in BOS to maintain stability (ex grab a railing)
goal to keep COM above COP
Reactive control
Describe some characteristics of fixed support APRs
- 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)
Reactive control
Describe some characteristics of change in support APRs
- 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)
Balance control
What is similar about voluntary vs reflexive reach-to-grasp
both use same generalized motor plans, reflexive is just slightly faster
Reactive control
Explain how vision affects APR
Peripheral vision is important to change in support APRs, reach-to-grasp APRs DO NOT require shift in gaze
NS control of balance
What does the NS rely on to detect stability/instability and what factors (3) affect the vaule assigned?
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
NS control of balance
What determines which senses are given more value in balance control
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)
NS control of balance
Why might young children/older adults depend more on vision than young adults
Myelination affects conduction (still developing in children and deteriorating in older adults)
The Postural Set or Central Set
What are postural sets influenced by
specific behaviour/tasks/condition and prior experience/expectation
The Postural Set or Central Set
What is a postural (or central) set
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)
NS balance control
Where in the CNS is balance control occuring
- Spinal cord
- Brain stem
- Cerebellum
- Basal ganglia
- Cortex
NS balance control
Explain the Spinal Cords role in balance
and how can we understand its contributions
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’
NS balance control
Explain the Brain stems role in balance
and how can we understand its contributions
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
NS balance control
Explain the Vestibulospinal tract
input,terget, output
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
NS balance control
Explain the Reticulospinal tract
input,terget, output
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
NS balance control
Explain the Cerebellums role in balance
whatwould be the effects of lesions here
- 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
NS balance control
Explain the role of the basal ganglia in balance
andwhat do lesions lead to?
- 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
NS balance control
Explain the role of the Cortex in balance
- 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
