Control of Posture & Locomotion

what systems are the key players in postural & locomotor control?

the nervous system and musculoskeletal

posture and locomotion have

key components and must be adaptable

components of posture

orientation:

- segments

stability:

- center of mass

- base of support

components of locomotion

progression

stability

how is static balance maintained?

by keeping the center of mass over the base of support

how is dynamic balance maintained?

requires controlling the COM even as it moves outside the base of support

control of COM relative to BOS but COM can move outside BOS

locomotion

BOS is bounded by

all point of contact

stability limits

area in which COM can be safely moved without changing BOS

cone

sway forward, backward, and side to side

is the stability cone greater forward or backward?

forward because the BOS is larger forward (feet)

postural and locomotor control research utilizes

movable platforms, instrumented treadmills, electromyography and movement analysis

what is the reactive postural control strategy

classic ankle strategy

classic ankle strategy

majority of movement takes place at the ankle

sequential from distal to proximal

sway posture to activate anterior musculature

postural strategies are a

continuum of responses

use to be separate but now they are known to be blended

postural responses are subject to

adaptation as a result of prior experience

get better with practice (more appropriate response)

what precedes voluntary movement

anticipatory postural adjustments

sway/shift body weight (opposite direction) prior to lifting leg

anticipatory postural control relies on

the ability to predict

postural responses differ based upon

the circumstance

how does light touch of an object impact postural sway?

reduce postural sway significantly

sensory inputs for postural control come from

three main sources

- vestibular

- vision

- somatosensory

(am i moving or is the word moving around me)

vestibular sensory inputs

self-to-earth

gravity and head movement

vision sensory input

object-to-object

movement of objects across retina

somatosensory sensory input

proprioceptors:

self-to-self

pressure under feet and muscle length and force

examples of how the three senses contribute to postural control

visual = illusions of motion

vestibular = dizzy relay

somatosensory = muscle vibration

how much importance to we place on each source of sensory information?

we are constantly adjusting how much importance we give to each source of sensory information through a process of sensory reweighing

sensory reweighting

adjusting how much importance we place on each source of sensory information

we do not use each source equally in every situation

sensory reweighting: firm surface

70% somatosensory

20% vestibular

10% vision

sensory reweighting: unstable surface

60% vestibular

30% vision

10% somatosensory (inaccurate bc the surface ismoving)

CTSIB

the clinical test of sensory integration and balance

evaluates ability to use different senses and ingrate information appropriately

what is the relationship between postural sway and the condition

postural sway increases as difficulty of the condition increases

people with bilateral vestibular loss have difficulty in conditions where

one must rely soly on the vestibular system

BESTest

the balance evaluation systems test

assesses each of the six systems underlying postural

six postural control systems

biomechanical constraints stability limits/verticality

anticipatory postural adjustments

postural responses

sensory orientation

stability in gait

the basic gait cycle is described by

standard definitions

we have "norms" that define the kinematic profiles of

each joint during typical gait

muscle activity is

patterned and predictable,, and complex - not just simple flexor/extensor alternation

locomotion is

high adaptable

locomotion can adapt to

obstacles

changing speeds

changing directions

variations in locomotor form

altered walking surfaces

there are many parallels between

locomotor control and postural control

the _______ and ____ have important roles in postural control

spinal cord and brainstem

is the spinal cord sufficient for posture/balance?

no

the spinal cord alone is not sufficient for posture/balance

decerebrate cat can

stand but cannot correct for postural disturbances

red nucleus stimulation in cat

flexion of limb and corresponding adjustments of other 3 limbs

vestibular nuclei

integrate sensory information via vestibulopsinal pathway

vestibulospinal tract

medial and lateral

medial vestibulospinal tract

VPM

bilateral

controls face

lift head so it does not hit the ground when you fall

lateral vestibulospinal tract

VPL

unilateral uncrossed

controls body

put your hands out to catch yourself when you fall

the basal ganglia play

a key role in postural control

basal ganglia role in postural control

regulation of tonic muscle activity

generation of adequate forces

postural set/adaptation to context

selecting desired motor program and inhibiting undesired motor programs

reactive postural responses in PD are characterized by

co-contraction of agonist and antagonist muscles

(lack of adaptation)

what is the role of the cerebellum in posture

the cerebellum is ey for regulating amplitude of postural responses

vestibulocerebellum

lesions impair vertical orientation

anterior lobe of the cerebellum

receives inputs from throughout body and projects to spinal cord via reticular formation, lesions produce ataxia of stance and gait

with cerebellar lesions

normal latencies and sequences but longer duration and larger amplitude postural responses

the cerebellum is also critical for

postural adaptation

cerebral cortex role in posture

key for anticipatory postural adjustments

may not be critical for externally triggered responses

may be more important for anticipitory adjustments

evidence that non-primary motor cortices play a role in quiet stance maintenance and anticipatory adjustment prior to arm lift

connections form the _______ to the _______ are importance for postural control

cerebral cortex to the reticulospinal pathways

postural control is governed by

a complex network of neural structures distributed throughout the nervous system

locomotor control is distributed throughout

the central nervous system from cerebral cortex to spinal cord

how do we determine contributions of different regions of the CNS

experimental lesions are created at different levels

the spinal cord has a foundational role in

locomotor control

spinal cords role in locomotor control

basic circuitry for locomotion

motor neurons, interneurons, afferents

central pattern generators

circuitry shared among different behaviors

central patter generator

a neural network within the spinal cord that can produce rhythmic motor output in absence of descending inputs and movement-related sensory feedback

though CPGs can function without sensory feedback,

normally feedback is present and serves important functions

CPG functions

phase transitions

unloading

hip extension

feedback reinforces ongoing MN activity, Ia and Ib have roles

adaptation depends upon feedback

phase-dependent reflex reversal

same stimulus elicits opposite responses when presented at different times in gait cycle of cats

brainstem functions in locomotion

reticulospinal pathway

brainstem: reticulospinal pathway =

descending influence to spinal interneurons in basic rhythm-generating circuits

what is the primary path for conveying signals from higher motor centers to spinal cord

brainstem

reticulospinal connections could account for

left-right coordination

mesencephalic locomotor region =

stimulation elicits locomotion in animals

reticulospinal neurons provide a means of

intersegmental control and left-right coordination

the basal ganglia role in locomotor control

important for selecting desired motor programs and inhibiting competing, undesired motor programs

interacts with. cerebral cortex in cortico-basal ganglia loops

integration of volitional and automatic control of movement?

the basal ganglia play a role in integrating

volitional and automatic movement

gait in parkinson disease has several hallmark features related to basal ganglia disruption such as

flexed, stooped posture

short, shuffling steps

festination

akinesia: freezinf gait

stride length regulation impaired

difficulty turning

excessive coactivation of muscles

the cerebellum contributes to locomotor control,

different cerebellar lesions result in distinct gait deficits

cerebellar locomotor region =

stim elicits loc in snimals

vestibulocerebellum lesion

fall toward side of lesion, head tilt to side of lesion, circling away from lesion

posterior vermis lesion

gait ataxia without limn ataxia, tandem gait difficult

anterior lobe lesion

ataxic gait, heel-shin ataxia, hop on one leg difficult, leg area so no UE deficits

from chronic alcohol use

typical cerebellar ataxic gait features

staggering

wide BOS

high stepping

drunken appearance

among people with cerebellar damage,

those with balance problems has worse gait than those with leg placement problems

the cerebellum is critical for

gait adaptation

the cerebral cortex allows for

flexible control of locomotion

- corticospinal pathway

- corticoreticular neurons project widely and diffusely

- allows for combination and integration of multiple reticulospinal neurons

- important for flexible control of locomotion and adaptation

- decerebrate = automatic patterns only, not adaptable

cerebral cortex influences gait through

direction projection to spinal cord and via projections to the reticulospinal tract

kids ages 4-6 sway in

all conditions and are more visually dependent than adults

by age 7 responses are adult-like

development of walking over first years of life is related to

timing of myelination

terminal sprouting to contact multiple spinal INs and MNs

process is not complete until 2 years of age

upright walking corresponding with timing of coricospinal tract myelination extending to lover levels of SC

different models of aging

inevitable gradual decline

no decline but specific events that lead to loss of function

regardless, postural control decline with age

with agin, postural latency becomes

longer, with greater delays in impaired vs. non-impaired elderly

the prolonged latency seen with aging is similar to

prolonged latency seen with peripheral neuropathy

older adults have particularly difficulty in conditions where

only vestibular information is accurate

elderly fallers may have

sensory organization problems

dual task conditions cause

decrements in performance that increase with age and balance impairment

gait also changes in predictable ways with typical aging such as

longer double-support periods

decreased push off power

flat footed landing

shorter steps

decreased cadence

decreased hip, knee, ankle flexion

increased muscle coactivation

wide BOS

older adults who fall have more

variable gait than older non-fallers

(increased fall risk)

why do we see age-related changes?

cognitive factors, dual-tasking

sensory impairments - vision, vestibular, somatosensory

muscle weakness

adaptive changes to a safer, more stable gait pattern

balance difficulties underline gait changes, elderly and new walkers share common features

portable means of measuring posture and locomotion

wearable sensors

what is the relationship between posture and locomotion

go hand in hand

cant have gait without postural control

many of the same CNS structures and pathways are involved in

control of both posture and locomotion

rehabilitaiton approaches should address

underlying constraints and challenging use and effective integration of sensory inputs

even though intimately related, treatments should focus on

specific deficits and not assume that practicing gait will improve balance and vice versa