Neuro weeks 14-15 (15-19) Flashcards
1
Q
Position of the center of total body mass
A
Center of Mass (COM)
2
Q
Vertical projection of COM
A
Center of Gravity (COG) -
3
Q
Area of the body in contact with the ground
A
Base of Support (BOS)
4
Q
Postural stability achieved through control of
A
COG or COM within the BOS -a combination (intersection) of task, individual and environment- three components
5
Q
Three important components of Postural stability- TIE
A
- Task
- Individual
- Environment
6
Q
Why is a traffic cone stable?
A
Because it has a Low COM & broad BOS. However if inverted it becomes very unstable - narrow base of support and high COM
7
Q
Humans are like an inverted traffic cone - an inverted pyramid with narrow BOS with a relatively high COM. Cone of stability varies in size depending upon a number of factors
A
True
8
Q
Posturally stability occurs as long as
A
COM stays within the cone of stability
9
Q
Postural instability occurs when
A
COM falls outside cone of stability
10
Q
Postural stability and the relationship between COM and the BOS relationship varies by Individual differences in height Distribution of weight- but varies by the
A
Task Environment Challenge of task depends upon the context in which it is performed (environment)
11
Q
Postural stability is very dependent upon
A
The task and the context in which it is taking place. For instance sitting and using iPad give the person a larger BOS and low COG to that BOS. This is a very stable and safe situation.
12
Q
When standing & using an iPad BOS will be
A
Narrow so easier for COG to be out of BOS but wide stance will improve BOS. This is intrinsically less safe but safety improved by the wider base of support.
13
Q
Walking while using iPad, COG is now regularly moving out of the base of support so this position is
A
Least safe combination of task and environment for postural stability
14
Q
Factors & limitations that define stability WaRM2
A
- Weakness & lack of ROM seen in ageing
- Ability to constrain ROM available to skeletal system
- Ability to coordinate muscle action
- Muscle strength
- All seen in neural diseases & disorders
15
Q
Postural sway is a way to assess factors that create
A
Limits to the cone of stability.
16
Q
T/F- There is always a slight postural sway in a rest in standing
A
True
17
Q
Factors that contribute to the magnitude of postural sway include: PtIBt PMt
A
- Postural tone of extensors of LE & trunk (antigravity muscles)
- Intrinsic stiffness of muscles
- Normal background tone
- Postural alignment
- Muscle tone - resistance of muscles to movement
18
Q
How is normal postural alignment measured?
A
With a plumb line which should hang:
- Through the mastoid process
- Anterior to acromion
- Through the hip joint
- Anterior of center of knee
- Anterior to ankle joint
19
Q
Intrinsic muscle tone due to tissue heating.
A
Thixotropic properties of muscle
20
Q
A characteristic of long proteins or other long chain molecules that produces a stiffness or cohesion simply from the nature of the interaction of the proteins.
A
What is Thixotropy
21
Q
Example of Thixotropy
A
Tip up a bottle of ketchup and nothing comes out. Now Shake it and it will flow at least better if not freely. If it is cold it will not flow but if warm it is more likely to flow. So the shaking and the heating has lessened the molecular cohesion and made it less stiff. This is also one of the explanations for decreased muscle stiffness and increase ROM following message
22
Q
Thixotropic properties of muscle lead to the following characteristics of muscle:
A
- More pliable when stretched or with repetitive movement than when held rigid
- More pliable when warmed up than when cold may be related to density of ground substance of connective tissues in muscle or density of cytoplasm of muscle cells
- Thixotropic properties of muscle also explains the decreased muscle stiffness and increase ROM following message or tissue heating.
23
Q
Intrinsic muscle tone also due to:
A
Spontaneous Ca++ release so constant actin-myosin activity in muscle Postural reflexes and activity of muscle spindles & Golgi tendon organs & various cutaneous afferents ending on lower motor neurons
24
Q
Postural tone is dependent upon- RAD
A
- Reflexes
- Afferent sensory activity,
- Descending postural activity
- Effect of somatosensory/proprioceptive afferents is seen by decrease postural tone following the cutting of dorsal roots
25
Postural tone - Effect of somatosensory/proprioceptive afferents - cutting dorsal roots
* Decrease postural tone Head position either due to vestibular inputs to brainstem or neck proprioceptors (vestibulospinal or interspinal) Descending influences from brainstem which excite postural muscles (particularly the extra-pyramidal pathways)
26
Postural stability is promoted by
Muscle activity.
27
EMG activity during static postures include:TTIEGG
* Tibialis posterior when gravity line anterior to ankle
* Tensor fascia lata
* Iliopoas
* Erector spinae muscles BUT NOT hamstrings & quadriceps femoris muscles
* Gastrocnemius- soleus
* Gluteus medius BUT NOT gluteus maximus
28
Postural stability related to COM position & velocity of the COM movement. As velocity of the COM movement increases the amount of the deviation of COM that it takes to reach the stability limit
decreases
29
As velocity of COM movement increases the base of support
Also increase to maintain stability
30
T / F - When COM falls outside the BOS as a result of a sudden perturbation, postural compensatory strategies are needed to compensate for this imbalance or a fall will occur
True
31
Compensatory strategies include: **CFF**
* Controlling postural sway
* Feedback control
* Feedforward Anticipatory Control
32
Responses to increasing magnitude of anteroposterior instability due to increasing amounts of perturbation: HAS
* Hip strategy
* Ankle strategy
* Stepping strategy
33
When small or low velocity perturbations produce small or slow deviations of the COM out of the BOS the situation can be easily corrected for with the use of
Ankle Strategy pattern
34
Ankle Strategy,
When body sways forward the ankle goes into dorsiflexion. Muscle action must pull the body back posteriorly.
35
Ankle strategy is accomplished by
A series of muscle activations with the sequence of muscle activation beginning with gastrocnemius. This produces plantar flexion at the ankle and occurs within 80 msec after perturbation
36
The Sequence of muscle activation continues with hamstring activation Occurring at about
100 msec after the perturbation
37
Activation of paraspinals occur at about
120 msec following perturbation
38
If the body sways backward the ankles go into
Plantar flexion and Muscle action needs to pull the body forward
39
Distal to proximal sequence of muscle activation begins with
Tibialis anterior producing a dorsiflexion at the ankle at about 80 msec after perturbation
40
Sequence of muscle activation continues with quadriceps femoris contraction at about
100 msec following perturbation
41
Sequence of muscle activation ends with contraction of the
Abdominal muscles at about 120 msec following the perturbation
42
When is ankle strategy initiated?
Whenever there is a small magnitude or slow velocity perturbation .
43
Leaning backward produces a
Backward shift of the COM, which is corrected by bringing the COM back forward over the BOS. This is done by sequential contraction of the tibialis anterior, quadriceps femoris and finally the abdomnals
44
Leaning forward produces a forward shift of the COM, which is corrected by
Bringing the COM back over the BOS- done by sequential contraction of the gastrocnemius/soleus, hamstring and then paraspinals in sequence.
45
Greater magnitude or higher velocity perturbations producing large or fast deviations of the COM out of the BOS and that are greater than can be handled by the ankle strategy are corrected by:
Use of the Hip Strategy pattern
46
In the Hip Strategy If the body sways forward & the COM goes forward, muscle action must
pull the COM back over the BOS
47
A Sequence of muscle activation beginning with quadriceps femoris producing
knee extension within 80-90 msec following the perturbation
48
Greater magnitude or higher velocity perturbations producing large or fast deviations of the COM out of the BOS and that are greater than can be handled by the ankle strategy are corrected by:
Use of the Hip Strategy pattern
49
RTP: Hip Strategy In the Hip Strategy If the body sways forward & the COM goes forward, muscle action must
pull the COM back over the BOS
50
RTP: Hip Strategy A Sequence of muscle activation beginning with quadriceps femoris producing
knee extension within 80-90 msec following perturbation
51
RTP: Hip Strategy Sequence of muscle activation continues almost immediately by the contraction of the
Abdominals Producing a hip flexion pulling the COM back over the feet (BOS)
52
RTP: Hip Strategy What happens If the body sways backward & the COM moves backwards,
Muscle action is needed to pull the COM forward
53
RTP: Hip Strategy Sequence of muscle activation beginning with hamstrings produce knee flexion within
about 80-90 msec after perturbation, followed almost immediately by paraspinal activation which extends trunk pulling the COM back over the feet (BOS)
54
RTP: Hip Strategy summary In HS If the body sways forward & the COM goes forward the Muscle action must pull the COM back over the BOS using what compensatory response
contraction of the quadriceps femoris producing a knee extension and contraction of the abdominals to push the COM backward.
55
In HS If the body sways backward & the COM goes backward the Muscle action must pull the COM forward over the BOS using what compensatory response
Contraction of the hamstrings producing a knee flexion and contraction of the paraspinals to push the COM forward.
56
RTP- Stepping Strategy In a Stepping Strategy.
When greater or higher velocity perturbation produces an even larger or faster deviation of the COM out of the BOS occur, the deviation may be so great that it cannot be compensated for by either the ankle or hip strategies. So the person steps forward or backward to widen the base of support
57
RTP- Stepping Strategy Strategy selected for stepping gate depends upon
Environmental factors.
58
Postural strategies are adaptive to
Different environmental conditions. For instance ankle strategy can be used for moderate perturbations on flat ground but on irregular or compliant surfaces, the person will have to move to higher level strategy sooner
59
Adaptation to mediolateral perturbations occurs at
Hip & trunk because of little movement in those directions at knee & ankle.
60
Pattern of response of mediolateral perturbations begins with . Monoarticular muscle response occur before biarticular muscles are activated
Head/trunk followed by hip with head movement opposite to hip movement
61
When does monoarticular muscle response occur
Before biarticular muscles are activated
62
T / F- A person must maintain Multidirectional Stability with a continuum of response patterns that control stability in the 360-degree continuum of possible perturbation directions. Each muscle can belong to more than one synergy or strategies.
True
63
Within a synergy an individual muscle has a unique or fixed level of
Muscle activation for the different synergies
64
How does humans adapt to perturbations?
by applying different motor strategies- People without neural pathology can shift relatively quickly from one postural movement strategy to another
65
Repeated exposure to a given postural task causes people to
Refine their response characteristics to optimize response efficiency.e.g. by the end of a bus ride strategies and shift in strategies are well worked out so are initiated in a quicker and smoother way than at the beginning of the bus ride
66
Response to perturbation requires the use of multiple sensory systems which include- VSV
Vestibular, Somatosensory System - Proprioception, Vision input
67
Which is the most valuable sensation in maintaining balance.
Peripheral (ambient) vision
68
Provides a principle vertical frame of reference and can easily determine the magnitude of deviation of the head and body from that position. It also provides a horizontal frame of reference about how fast the person is approaching the horizontal frame of reference.
Ambient vision
69
Ambient Vision integrates information about
Horizontals and verticals in the context of gravitational forces which is the integration that is important in maintaining balance
70
In the context of balance
The visual system determines the amount of total motion, but the brain interprets all motion perceived through vision as self motion- the visual system is not good at differentiating exocentric motion from egocentric (self motion). evident when you are stopped at a traffic light next to a large bus or truck. If it moves forward you sense that you are moving backward before you realize that you are not.
71
exocentric motion
object motion
72
Ambient (peripheral) vision gives information needed in
Balance- as a person moves, the optical flow field radiates outward from a distant point central point
73
Optic flow is spatially coincident with
Direction of motion.
74
Optic flow arises from a point projected to the center of the
Retina where the distant point is perceived
75
At the peripheral edges of the field of view, the optical flow field is
Nearly parallel to the line of motion and has been termed "lamellar flow” as opposed to “radial flow”
76
T / f- People are NOT sensitive to moving environment.
False people are sensitive- this can be demonstrated by moving visual surround around the individual
77
Postural adjustments occur as a result of
Movement of the surrounding environment -can be simulated by moving room experiments in which the person stands stable but the walls of the room are moved around the subject causing Increased Postural sway
78
What happens when the room is moved forward?
The person perceives a backward motion and contracts muscle to pull themselves forward
79
What happens when the room is moved backward?
The person will perceive a forward motion and contract muscle to pull themselves backward
80
Active movement through the environment is viewed differently than passive movement (sitting with moving field of reference using video). More information is gained when active locomotion is involved
T
81
Other vision factors that play a role in balance and falling.
Visual acuity and Depth perception (stereopsis). increased risk of falling when decreased
82
Contrast Sensitivity Preliminary evidence suggest that the ability to distinguish varying levels of brightness against a constant background perhaps plays the greatest role in balance. Studies show that distant contrast sensitivity and depth perception are independent predictors of increased sway in older people
T
83
Contrast Sensitivity
Poor contrast sensitivity add more risk in ambulation and people with poor contrast detection may have less capacity to detect ground-level hazards
84
Types of balance tests CDP
Wide variety of balance tests- Computerized Dynamic Posturography (CDP)testing system that tests for the specific sensory deficits involved in balance disorders
85
Computerized Dynamic Posturography includes: Isolation and quantification of
Orientation inputs from the visual, vestibular and somatosensory systems Central integrating mechanisms for selecting functionally appropriate orientation sense(s) Functionally appropriate movement strategy(s) in a variety of controlled task conditions Motor output mechanisms for generating timely and effective postural movements
86
In Computerized Dynamic Posturography testing
Patient stands on a movable, dual forceplate support surface within a moveable surround (enclosure) Under control of a computer, the force platform can either move in a horizontal plane (translate), or rotate out of the horizontal plane (yaw) Standardized test protocols have support surface and visual surround motions, during which the patient's postural stability and motor reactions are recorded
87
Standardized test protocols for CDP include: SAM
Sensory Organization Test (SOT) Motor Control Test (MCT) Adaptation Test (ADT)
88
Sensory Organization Test
Objectively identifies problems with postural control by assessing the patient's ability to make effective use of (or suppress inappropriate) visual, vestibular, and proprioceptive information. Patients stand on a support surface that measures postural sway
89
Sensory Organization Test controls the sensory information available to the patient Sensory input from
Feet and ankles is effectively eliminated through calibrated "sway referencing" of the support surface, Visual sensory input is effectively removed by calibrated "sway referencing" of the support surface with the visual surround
90
The device will directly follow the patient's anteroposterior body sway therefore eliminating orientation information through support surface tilt and/or visual surround will
challenge the patient’s ability to maintain their stability
91
Sensory Organization Test utilizes 6 conditions including
With and without ankle tilt With and without vision and With sway referenced vision (distorted vision)
92
Condition 1
Eyes open, fixed surface and visual surround so when platform moves horizontally there is normal vision, vestibular & ankle proprioception feedback
93
Condition 2
Eyes closed, fixed surface So when platform moves horizontally there is no visual feedback but normal vestibular & ankle proprioceptive feedback
94
Condition 3
Eyes open, fixed surface, sway referenced visual surround So when platform moves horizontally there is abnormal visual feedback but normal vestibular & ankle proprioceptive feedback
95
Condition 4
Eyes open, sway referenced surface, fixed visual surround So when platform moves horizontally there is normal vision & vestibular feedback but abnormal ankle proprioceptive feedback
96
Condition 5
Eyes closed, sway referenced surface So when platform moves horizontally there is no vision, abnormal ankle proprioception & normal vestibular input
97
Condition 6
Eyes open, sway referenced surface and visual surround So when platform moves horizontally there is abnormal vision & proprioceptive ankle feedback & normal vestibular feedback
