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Postural Control > Descending Pathways And Postural Control > Flashcards

Descending Pathways And Postural Control Flashcards

1
Q

Name all the descending pathways

A
  • Lateral corticospinal tract
  • Anterior cortiscospinal tract
  • Corticobulbar tract
  • Rubrospinal tract
  • Medial vestibulospinal tract
  • Lateral vestibulospinal tract
  • Reticulospinal tract
  • Tectospinal tract
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2
Q

Name the pyramidal tracts

A
  • Corticospinal tracts
  • Corticobulbar tract
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3
Q

Name the extra pyramidal tracts

A
  • Rubrospinal tract
  • Reticulospinal tract
  • Tectospinal tract
  • Lateral vestibulospinal tract
  • Medial vestibulospinal tract
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4
Q

Describe briefly the lateral corticospinal tract

A

Cortex (M1, S1, PMC, SMA) -> corona radiata -> Internal capsule -> cerebral pedoncle -> pons -> medulla -> Decussation (90% of fibers) -> anterior horn of spinal cord -> anterior CST is involved with movement of the muscles of the trunk, neck and shoulders/ lateral CST is involved with the movement of muscles of the limbs.

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5
Q

Describe the Rubrospinal tract

A

Red nucleus -> Decussation -> pons -> medulla -> lateral funiculus -> anterior grey horn laminae V to VIII

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6
Q

Describe the medial vestibulospinal tract

A

Medial and inferior vestibular nuclei -> laminae V to IX of the cervical region -> neck muscle extensors and flexors neurons.

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7
Q

Which tracts are responsible for the control of postural muscles ?

A

Extra pyramidal tracts :
- Rubrospinal
- Vestibulospinal
- Reticulospinal
- Tectospinal

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8
Q

What is the role of the Rubrospinal tract ?

A

Mediation of involuntary movement. May play a role in decorticate posturing of upper limb.

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9
Q

What is the role of vestibulospinal tracts ?

A
  • Reflex actions of the body in order to retain its axial position relative to gravity.
  • Antigravity muscle tone response to head tilt.
  • Stabilize the body’s center of gravity and preserve upright posture.
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10
Q

What is the function of the Reticulospinal tract ?

A
  • Together with vestibulospinal tracts they maintain body’s balance and make postural adjustments
  • Plays an important role in coordination of voluntary movement
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11
Q

What composes the corticoreticulospinal system ?

A
  • corticoreticular fibers
  • pontine Reticulospinal tract
  • medullar Reticulospinal tract
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12
Q

What are the roles of the corticoreticulospinal system?

A
  • control muscle tone
  • control reflex activity
  • balance maintenance
  • postural adaptation
  • behavioral arousal
  • somatic motor control
  • cardiovascular control
  • pain modulation
  • sleep
  • consciousness
  • habituation
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13
Q

Define postural control

A

It is a complex sensorimotor behavior mediated by multi-system integration. It is the coordinated, sequenced organization of stability and mobility of the multi-kinetic chain in order to maintain, achieve or restore balance for efficient performance of a motor task. It’s the control of body orientation in space with respect to postural orientation and equilibrium, requiring convergent information from the somatosensory, vestibular and visual systems such as gravity, the support surface, environment, and internal reference.

Clinical relevance: before performing a task one must achieve postural stability first.

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14
Q

What is the center of mass

A

It is the point that is at the center of total body mass. Can be named center of gravity.

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15
Q

Define the concept of stability limits

A

The area over which an individual can move their center of mass and maintain equilibrium without changing their base of support.

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16
Q

What determines the stability limits ?

A
  • The size and nature of support base
  • limitation of joints ROM
  • muscle strength
  • muscle length
  • sensory information available to detect the limits
  • perception of limits
  • fear of falling
  • Experience, learning of limits
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17
Q

What is core stability ?

A

The coordinated and sequenced activation of musculoskeletal structures of the head, neck, scapula trunk pelvis and legs. A multi kinetic chain for efficient functional movement anticipating a destabilization.

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18
Q

What is core stability ?

A

The coordinated and sequenced activation of musculoskeletal structures of the head, neck, scapula trunk pelvis and legs. A multi kinetic chain for efficient functional movement anticipating a destabilization.

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19
Q

What is the role of the fasciculus gracilis ?

A

Convey tactile, vibratory and proprioceptive information from the lower limbs.

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20
Q

What is the role of the fasciculus cuneatus ?

A

Convey vibratory, tactile and proprioceptive information from the upper limbs.

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21
Q

What is the role of the posterior column- medial lemniscus pathway ?

A

Sensory pathway conveying info about fine touch, two-point discrimination, proprioception and vibration from skin and joints.

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22
Q

What forms the posterior column of the posterior column-medial lemniscus pathway?

A
  • fasciculus cuneatus
  • fasciculus gracilis
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23
Q

What is core stability ?

A

The coordinated and sequential activation of the muscles of the head, neck, scapula, trunk, pelvis and legs as a multi-kinetic chain for the efficient functional movement and the anticipation of destabilization.

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24
Q

What is the function of muscle spindles ?

A

Monitor change in muscle length and the speed of change in muscle length.
They mediate reciprocal inhibition.
Promote proprioception.

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25
Q

What are the different mechanoreceptors ?

A
  • Merkel cells
  • Meissner corpuscules
  • Pacinian corpuscules
  • Ruffini endings
  • Baroreceptors
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26
Q

What is the function of Merkel cells ?

A

Prolonged light touch

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27
Q

What is the function of Meissner corpuscules ?

A

Precise manipulations with fingertips

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28
Q

What is the function of Pacinian corpuscles ?

A

Discriminating fine surface textures and vibration

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29
Q

What is the function of Ruffini endings ?

A

Skin stretch, joint activity and warmth.

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30
Q

What is the function of barorecptors ?

A

Located in big vessels and viscera, they give the position of blood fluids in relation to gravity and therefore contribute to the perception of postural verticality.

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31
Q

What is the link between graviceptors (baroreceptors) and postural control ?

A

Abdominal pressure is a feed-forward mechanism working for a response of movement. When the intra abdominal pressure increases due to abdominal muscles contraction, more information is received from the gravicetpors. This gives patient a better sense of verticality and a better postural control.

32
Q

How does gravity influence postural orientation ?

A
  • If the center of mass is posterior to base of support, there will be a flexor drive.
  • If the center of mass is anterior to base of support, there will be an extensor drive.
33
Q

What is the proprioceptive base of support ?

A

The surface contact area of the feet

34
Q

What are the different strategies of treatment regarding postural orientation ?

A
  • Use the influence of gravity
  • Use the influence of base of support
  • Use the influence of supporting surface
  • Use core muscles activation
  • Use light touch (ascending pathways)
35
Q

Why is light touch a good strategy to improve postural control ?

A

According to Fransen et al. Axial postural tone can be modified by remote somatosensory input.
Light touch activates postural muscles using sensory integration at the level of the spinal cord.

36
Q

What is the influence of vision on postural control ?

A

Vision is not the primary resource for postural control.
- Somatosensory = 70%
- Vestibular = 20%
- Vision = 10%
But it plays a role in navigation and reach.

37
Q

What is the body schema ?

A

It is an abstract representation of the body parts in external space which is dynamically updated during body movement and used to estimate body configurations.

Representation of our various body parts and of spaces within which they can act are constructed in a multi sensory fashion. Tactile sensation on a particular body part interacts with visual and proprioceptive information.

38
Q

Why do we say that body schema has an online modification ?

A

Because it can be modified by sensory stimulus

39
Q

What are the two components of postural control ?

A
  • Postural orientation, an afferent system utilizing information from somatosensation, graviceptors, vestibular receptors and vision
  • Postural stability, an efferent system.
40
Q

What are the concepts linked to postural orientation ?

A
  • midline
  • alignement of body segments with respect to the environment
  • vertical orientation with respect to gravity
  • light touch/ contractual hand orientation response
  • body schema
    = perception
41
Q

What are the concepts linked to postural stability ?

A
  • stability limits
  • maintenance of the center of mass within the base of support
  • anticipatory postural adjustments
  • reactive postural adjustments
  • length and strength of muscles
    = action
42
Q

Describe the steps of postural adaptation to perform an action.

A

Visual input -> Sensorimotor memory -> Feed forward (predictive mechanisms / corticoreticulospinal medullary and pontine system activation) -> Motor command scaling -> grip force -> cutaneous afferents -> feed back (reactive mechanisms/ cerebellum) -> maintenance or adaptation -> sensorimotor memory.

43
Q

Is feed forward or feed back more affected in event of stroke ?

A

In most stroke survivors feed back is impacted (corticoreticulospinal pontine and medullary system).

44
Q

Give a simplified definition of anticipatory postural adjustments

A

The corticoreticulospinal pontine and medullary system activates before movement initiation to prepare the body to the upcoming perturbation in order to ensure more stability.

45
Q

What are the factors influencing anticipatory postural adjustments ?

A
  • start posture (including orientation, foot cutaneous afferents and base of support)
  • prior experience (including training, expectations, fears and goals)
  • cognitive processing
  • body schema (including light touch)
  • musculoskeletal biomechanics
  • perturbation (direction, magnitude, load)
46
Q

How long before movement initiation do early anticipatory postural adjustments take place ?

A

500ms before task.

47
Q

Define early preparatory adjustments and give an example.

A

Adjust posture in preparation of expected perturbation.
Occurs prior to anticipatory postural adjustments.
In gait initiation: the displacement of the center of pressure backward and to the supporting foot.

48
Q

Define anticipatory synergy adjustments

A

Feed forward control in preparation of fast actions. Taking place from 300ms to 200ms before action. They are independent to the direction of the perturbation (think about the goal keeper ready to intercept the ball).

49
Q

When do anticipatory postural adjustments take place before action ?

A

From 150ms to 100ms before action.

50
Q

Define corrective postural adjustments

A

Initiated by the sensory feedback signals and serve as a mechanism of restoration of the position of the center of mass after perturbation has already occurred. They take place from 70ms to 300ms after action.

51
Q

Define synergy (preferred definition)

A

According to Latash synergies are neural mechanisms ensuring task-specific movement stability. This definition is based on the princple of abundance.

52
Q

Define the principle of abundance

A

As opposed to the principle of redundancy. Because there is no redundancy in human movement but motor abundance. The principle of abundance differs from traditional methods of addressing problems of motor redundancy by conceptualizing the apparent redundant design of the human body not as a source of computational problems for the brain but as a rich apparatus that ensures the proper stability of actions in combination with the possibility of performing several actions with the same set of elements.

53
Q

Explain the old concept of motor redundancy

A

It is an excess of elements that allow numerous solutions for typical problems. It implies that there are more elements (muscles, joints, etc.) than minimally necessary to perform an action.

54
Q

What is the role of the basal ganglia ?

A

Contributes to the planning and execution of voluntary movement and is specialized in reinforcement of learning, guided by the reward signals encoded in dopaminergic input from the substantia nigra pars compacta.

55
Q

What are the major inputs of basal ganglia ?

A
  • Cx
  • Thalamus
  • Limbic system
56
Q

What are the major outputs from basal ganglia ?

A

-Cx
- Thalamus
-Brain stem nuclei

57
Q

What is the corticostriate loop ?

A

= cortico basal ganglia motor loop.
A motor loop which determines and controls which movement will be performed. = Behavior selection.

58
Q

What are the roles of the corticoreticulospinal system ?

A
  • Transmits descending signal that initiate locomotion.
  • Determines the relative level of postural muscle tone in different muscles, particularly in asymmetrical pattern.
  • Production of feedforward responses (APAs).
  • Modulation of vestibulospinal system.
  • Modifies the pattern of activity in multiple limb and trunk muscles.
  • Complex bilateral postural changes during voluntary movement.
  • Provides a balance of descending facilitation and inhibition bilaterally to allow the loss and regaining of midline.
  • Modification of sensory input for tension control through projection to 1b interneuron.
59
Q

What are the two tracts composing the corticoreticulospinal stystem ?

A
  • Reticulospinal medullary (lateral) tract
  • Reticulospinal pontine (medial) tract
60
Q

What are the outputs of the corticoreticulospinal pontine tract ?

A

Ipsilateral
Excitatory to axial muscles and lower limbs extensors to maintain postural support.
Reinforces the vestibulospinal tract action.
Initiate locomotion.

61
Q

What are the outputs of the Reticulospinal medullary tract ?

A

Bilateral.
Excites and inhibits bilateral limbs proximal physiological extensors.
Plays a role in initiation of locomotion.

62
Q

What are the functions of the vestibulospinal tract ?

A

No direct cortical control.
- Maintenance of upright posture (antigravity activity).
- Adaptations of postural tone in response to gravity and displacement.
- Head stability.
- Eye tracking.
- Coordination of eye and head movement.
- Disynaptic excitation of physiological extensors neurons and inhibition of flexors neurons.

63
Q

What are the inputs of the vestibulospinal system ?

A
  • Labyrinth
  • Vision (indirect)
  • Somatosensory inputs via Cerebellum
  • Corticoreticulospinal system
64
Q

What is the function of the vestibulospinal system ?

A

Facilitate anti-gravity muscles

65
Q

What is the function of the vestibulospinal system ?

A

Facilitate anti-gravity muscles

66
Q

What is the connectome ?

A

The complete set of structural connections between neurons in the brain.

67
Q

Where is located the body schema ?

A

In the temporo-parietal cortex

68
Q

What are the two main roles of postural control ?

A

-Maintain balance
-Preserve standing posture (orientation)

69
Q

What is postural orientation ?

A

It’s the position of body segments with respect to each others and the environnement. Postural orientation comes before balance.

70
Q

What is exteroception ?

A

It’s the sense of direct interaction with the world as it impacts the body. The principal mode of exteroception is the sense of touche which includes sensation of contact, pressure, stroking, motion and vibration and is used to identify objects. It’s a cortical function in opposition to proprioception which is a cerebellar function mostly unconscious.

71
Q

What is proprioception ?

A

Sense of one’s self. Receptors in skeletal muscles, joint capsules and skin enables us to have conscious awareness of the posture and movement of our own body, particularly the four limbs and head. It’s taking place in the cerebellum and is mostly unconscious.

72
Q

What are the sensory inputs mediating postural orientation ?

A
  • free nerve endings
  • greviceptors
  • vision
  • proprioception
  • vestibular sensory organs
73
Q

What is the role of the tectospinal tract ?

A

Coordinated control of head and eye movements directed towards visual target. Feed-forward, taking place before movement. So head and trunk must be prepared before postural control. Reflex response to visual stimuli. Orientation of head and trunk toward auditory stimulus or visual stimulus.

74
Q

From which cortical areas does the cortico spinal tract originate ?

A
  • 30% M1
  • 30% SMA
  • 40% S1
75
Q

What is the function of the cortico spinal system ?

A

Speed and fractionning of movement, selective movement of the fingers, adjustments of the central pattern generators, modification in quantity and type of sensory inputs, sensory discrimination. = Sensorimotor system.

76
Q

Describe the neuroanatomy of the cortico spinal tract

A

Composed of lateral cortico spinal tract and anterior cortico spinal tract.

1) M1, PMC, SMA, S1
2) fibers from the upper motor neuron converge in the corona radiate
3) move inferiorly to form a white matter structure of the brain: the internal capsule (between basal ganglia and thalamus)
4) cerebral peduncule (midbrain)
5) pons and medulla
6) 80% decussate to form lateral cortico spinal tract and 20% don’t to become anterior corticospinal tract.
7) LCST descend in the lateral funiculus along the entire spinal cord
8) synapse in lower motor neuron min the ventral horn at each level of spinal cord
9) anterior root of spinal nerve, through the peripheral nerve plexuses (cervical, brachial and lumbosacral)
10) individual peripheral nerve to skeletal muscles -> motor endplates of neuromuscular junction

77
Q

Describe the neuroanatomy of the cortico-reticulo spinal tract

A

1) cortico reticular fibers arise from PMC, SMA.
2) brainstem
3) synapse bilaterally with the neurons of the pontine and medullary reticular formation giving rise to reticulospinal tracts.
4) medullary reticulospinal tract assise from medullary nuclei of reticular formation (rostral medulla of brainstem)/ pontine reticulospinal tract pontine nuclei of reticular formation (ventral pons)
5)pontine tract descend uncrossed within anterior column of the spinal cord -> exterior gray horn of spinal cord
6) medullary tract descending in lateral column of sc -> exterior gray horn of sc
7) both synapse with alpha and gamma motor neurons that supply paravertebral and limb extensor musculature.

= muscle tone and reflex activity

Postural Control (4 decks)

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