Exam 3 Week 14/15 ppt 15 Postural Stability

Question 1

What is COM?

Answer 1

Center of Mass position of the center of total body mass

Question 2

What is COG?

Answer 2

Center of Gravity vertical projection of COM

Question 3

What is BOS?

Answer 3

Base of Support area of the body in contact with the ground

Question 4

What is postural stability?

Answer 4

controlling COG or COM within the BOS

Question 5

Postural stability is a combination of 3 things

Answer 5

1. Individual 2. Task 3. Environment

Question 6

Why is a traffic cone stable?

Answer 6

Low COM and broad BOS If inverted it becomes unstable - narrow base of support and high COM

Question 7

How are humans like an inverted traffic cone?

Answer 7

an inverted pyramid with a narrow base of support with a relatively high COM. We have cone of stability (A in this illustration) which varies in size depending upon a number of factors

Question 8

How does postural instability occur?

Answer 8

when the COM falls outside cone of stability (C)

Question 9

How does postural stability and the relationship between center of mass and the cone of stability vary in the individual?

Answer 9

differences in height and distribution of weight

Question 10

Examples of how postural stability in a task can rely on context in which it is performed (environment)

Answer 10

1. Sitting and using iPad- larger BOS sitting with COG low to that BOS — Stable and safe
2. Standing and using iPad- same position of UE but BOS narrow so easier for COG to be out of BOS–Less safe
3. Walking and using iPad- same position of UE but COG now regularly moving out of the base of support–Least safe

Question 11

Factors and Limitations that define stability

Answer 11

1. Limits of stability defined by:

• Muscle strength
• Ability to coordinate muscle action
• Ability to constrain range of motion (ROM) available to skeletal system

2. Weakness and lack of ROM seen in aging
3. All seen in neural diseases and disorders

Question 12

What information does a postural sway provide? Frequency?

Answer 12

way to assess the factors that create the limits to the cone of stability. A rest in standing there is always a slight postural sway.

Question 13

Factors that contribute to postural sway

Answer 13

• body postural alignment
• muscle tone
• resistance of muscles to movement
• intrinsic stiffness of muscles
• normal background tone
• Postural tone of extensors of LE and trunk (antigravity muscles)

Question 14

Where should a plumb line hang to assess normal posture?

Answer 14

• through the mastoid process
• anterior to acromion
• through the hip joint
• just in anterior of center of knee
• just anterior to ankle joint

Question 15

What is Thixotropy

Answer 15

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.

Question 16

What does thixotropy have to do with intrinsic muscles?

Answer 16

Some of intrinsic muscle tone probably due to thixotropic properties of muscle

Question 17

Three Thixotropic properties of muscle

Answer 17

1. More pliable when stretched or with repetitive movement than when held rigid
2. More pliable when warmed up than when cold
3. May be related to density of ground substance of connective tissues in muscle or density of cytoplasm of muscle cells

Question 18

Two other probable causes of intrinsic muscle tone

Answer 18

1. Spontaneous Ca++ release so constant actin-myosin activity in muscle
2. Postural reflexes and activity of muscle spindles and GTOs and various cutaneous afferents ending on LMNs

Question 19

What is postural tone dependent upon?

Answer 19

afferent sensory activity, reflexes and descending postural activity

Question 20

Connection of afferent sensory activity to postural tone

Answer 20

Effect of somatosensory/proprioceptive afferents is seen by the decrease postural tone following the cutting of dorsal roots

Question 21

Connection of reflexes to postural tone

Answer 21

Head position either due to vestibular inputs to brainstem or neck proprioceptors (vestibulospinal or interspinal) will change tone as we have seen in the various postural reflexes

Question 22

Connection of descending postural activity to postural tone

Answer 22

Descending influences from brainstem which excite postural muscles (particularly the extra-pyramidal pathways – reticulospinal and vestibulospinal pathways

Question 23

Which muscles show EMG activity during static postures?

Answer 23

• Gastrocnemius
• soleus and tibialis posterior when gravity line anterior to ankle
• Gluteus medius and tensor fascia lata but NOT gluteus maximus
• Iliopoas but NOT hamstrings and quadriceps femoris muscles
• Erector spinae muscles

Question 24

How is postural stability related to COM position and velocity of the COM movement? (2)

Answer 24

1. As the velocity of the COM movement increases the amount of the deviation of COM that it takes to reach the stability limit decreases
2. As velocity of COM movement increases the base of support must also increase to maintain stability