EXSS 380- Locomotion (pt. 1)

define locomotion

motor activity which results in translation of the total body COM

what is locomotion defined by?

rhythmicity

what is the basic definition of locomotion?

how we get our body from point a to point b

what are the three essential requirements for locomotion?

• progression

• postural control

  • adaptation

what is progression?

basic pattern that produces and coordinates rhythmic patterns of muscle activation of the legs and trunk

what is progression in simple terms?

• our stepping pattern

• coordination

• how/when we fire quads? hamstrings? core?

what is postural control?

establishing and maintaining appropriate posture by counteracting various forces

what do we have to maintain as we move from point a to point b?

postural control or upright stance

what is adaptation?

the ability to adjust to obstacles and things being in our way when trying to get from point a to point b

what are the two major phases of gait?

• stance

• swing

what is the stance stage of gait?

generating horizontal and vertical forces using flexible strategies

in terms of the leg, what is stance?

leg in contact with the ground

what is the swing stage?

advancement and repositioning of the swing limb

in terms of the leg, what is the swing phase?

leg swinging in the air

what do we say about gait kinematically between subjects?

gaits are very similar across subjects

what is extremely variable across individual?

muscle activation and force generation

why is muscle activation and force generation different across individuals?

we all have different leg lengths, body weights, heights, etc.; physical components that cause us to change how we produce our gait

what is the technical term for 0% of the gait cycle?

heel strike

describe the heel strike (0%) point of the gait cycle

when the right foot first makes contact with the ground

when is the 50% mark of the gait cycle?

when the left goes through swing phase and makes contact with the ground

what is there a short period of during the gait cycle?

double limb support

when is 100% of the gait cylce?

when the right foot lands again; occurs after right foot swing phase

what does stride reresent?

100% of gait cycle

when do the hamstrings fire?

at the end of swing going into stance

why do the hamstrings fire when they do?

to slow the leg down before it makes contact with the ground

when does the vastus lateralis (quad muscle) fire?

beginning of stance phase

why does the vastus lateralis fire?

quads need to fire a vertical force to accept our body weight as we step down

describe the rectus femoris

a biarticulate muscle crossing at hip and knee joint that helps with hip flexion and knee extension

when does the rectus femoris fire?

• fires twice

• first burst same goal as vastus lateralis

• second burst- beginning of each stance phase to generate momentum

why does the rectus femoris fire?

• 1st burst is to accept our bodies weight

• 2nd burst is to generate momentum for forward stepping

when does the calf fire?

predominantly through stance phase

why does the calf fire?

it pushes our body forward when walking

when does the pretibial fire?

beginning of stance

why does the pretibial fire?

it helps to slowly lower the foot in a controlled manner at the beginning of stance

why does the pretibial slightly fire during swing phase?

to pick toes up to avoid tripping

what is as central pattern generator or CPG important for?

progression

what is a CPG?

neuronal network capable of rhythmic motor activity in the absence of sensory information

what are CPGs NOT driven by?

feedback neuromuscular control

what rhythmic motor systems are CPGs identified for?

• walking

• running

• swimming

• respiration

where is the CPG for gait/locomotion located?

spinal level/spinal cord

describe the cat experiment that provided evidence for CPGs

• cats had their spinal cords transected from their brain making them quadriplegic and then they were supported on a treadmill

• the cats were given electrical stimulation in the spinal cord, which produced coordinated stepping movements

• the electrical stimulation cause reciprocal flexor/extensor activity, and occurred with dorsal roots transected

what was the only thing that could have been stimulated electrically in the cat experiement?

spinal cord and alpha motor neurons; evidence for CPG because brain was disconnected and sensory input was disconnected

what is the evidence of gait CPG in humans?

• electrical stimulation produces stepping movements in spinal cord injured patients

• infants produce rhythmic stepping movements if held erect and moved over horizontal surface

• stepping patterns transferred to walking via 2 mechanisms

why is the electrical stimulation in spinal cord patients not enough to produce locomotion?

• they need environment cues for meaningful locomotion

• they cannot adapt to perturbations

• electricity doesn’t aid postural control

• simply, they cannot maintain postural control or adapt to the environment; only repeated movement

why are infants evidence for CPGs?

they produce steps that are rhythmic in nature, but they can’t maintain balance or adapt

what two mechanisms transfer stepping patterns to walking?

• development of voluntary control of locomotion

• patter is no longer simple flexion/extension, but a more complex gait pattern

how do the two mechanisms involved in walking development come to be?

• maturation of central control (motor cortex and brain stem nuclei)

  • modulated by cerebellum

what is central control of locomotion needed for?

• initiation

• speed

• adaptive control of CPG

centrally, what is movement refined by?

proprioceptive and visual inputs

what is in charge of central control of locomotion?

primary cortex

what form of control is central control of locomotion?

adaptive

describe the relationship between CPG and refinement

CPG does the basic behavior, refinement comes from proprioceptive and visual cues

describe the evidence for speed being controlled centrally

• stimulation of brain stem/spinal cord produces stepping movements

• movements persist when dorsal roots are cut

• still can control speed without sensory input

what is the role of the motor cortex in locomotion?

initiation and adaptation

what does the motor cortex do?

generates plan and assists with adaptation

what is the evidence for the motor cortex being involved with planning and adapting?

when lesions were present, walking on a smooth surface remain unaltered; however, movements requiring visuomotor coordination was severely impaired

what is the role of the cerebellum?

fine tuning movement

what is the evidence for the cerebellum fie tuning movement?

experimental lesions caused ataxia

what is ataxia?

abnormal coupling of contralateral limbs