Neurologic basis of locomotion in humans

Question 1

main takeaway of human locomotion/ what is it?

Answer 1

an action initiated by the brain but yet are maintained in steady state execution by mostly spinal mechanism (CPG) with the interaction of peripheral afferent contributions

Question 2

Evidence for CPG in humans spinal cord

Answer 2

1) involuntary LE stepping like movements were expressed with spontaneously in a subject with incomplete SCI
2) in supine position: rhythmic, alternating and forceful involving muscles of the legs bilaterally
3) subsequently rhythmic movements in a pt with complete SCI
4) complete SCI expressed EMG- recorded movements occurring spontaneously, and characterized by rhythmic patterns resembling bipedal stepping

Question 3

scheme for CPG

Answer 3

the motor infrastructure and the vertebra control scheme for locomotion

Question 4

the motor infrastructure for CPG

Answer 4

• spinal cord: protective reflexes and locomotion
• brainstem: for respiration, chewing, breathing, swallowing and eye movements
• hypothalamus: for feeding drinking and locomotion
• BG
• Cerebral cortex: fine motor control
• Cerebellum

Question 5

CPG basics

Answer 5

in vertebrates, the rythmic timing and coordination of the muscles generated by the CPG are located in the spinal cord

Question 6

at rest the CPG is

Answer 6

inactive

Question 7

to initiate gait

Answer 7

a locomotor command is generated at supra-spinal (brain) levels

Question 8

what is the grand initiator of gait

Answer 8

BG: choice ( of action and decision making) and emotion

Question 9

what does the BG relay on input information from

Answer 9

the superior colliculus, cortex, thalamus and dopamine

Question 10

purpose of the superior colliculus

Answer 10

visuospatial and steering us. We tend to move toward things that attract us

Question 11

where does the mesencephalic locomotor region modulate information to

Answer 11

the spinal cord/brainstem.
receives info from the BG and limbic system

Question 12

what is the purpose of the BG in gait

Answer 12

helps select pattern

Question 13

what does gait require the interactions between

Answer 13

the motor cortex, thalamus and BG

Question 14

the spinal locomotor network

Answer 14

• associated with the lumbar area of the SC
• burst generators to motor output
• relays of sensory info from MS, GTO and joint receptors

Question 15

what is continuously being sent back to the motor systems

Answer 15

sensory informations from proprioceptors including GTO, MS and joint receptors

Question 16

Cognitive Motor interaction

Answer 16

cortex, BG (selects limb pattern), cerebellum - Mesencephalic locomotor region (initiator of neurons) - Reticulospinal Neurons (collect relavent sensory info) - burst generator - CPG in spine

Question 17

Reticulospinal Neurons

Answer 17

• input: direct somatic, vestibular, tectal, deep cerebellar, and motor excitatory
• integrated whole body movement
• innervate gamma and alpha motor neurons

Question 18

CPG mechanism

Answer 18

• BG release Dopamine to the MLR region to initiate the gait process and in turn activate the reticulospinal cells to the SC
• Burst generators activate synergist muscles at each limb joint
• 3 levels: the motor neuron pool level, the pattern formation network, and the rhythm generator network

Question 19

function fo the pattern formation network in CPG

Answer 19

rhythm maintaining

Question 20

function fo the rhythm generator network in CPG

Answer 20

rhythm resetting

Question 21

what levels does afferent feedback affect in CPG

Answer 21

all 3 levels

Question 22

what are 2 inhibitory interneurons that project to motor neurons

Answer 22

Renshaw cells and reciprocal 1a interneurons.
Renshaw cells can inhibit both the flexor and the extensors

Question 23

how much does 1a and 1b increase extensor activity

Answer 23

50%

Question 24

importance of 1a MS in gait

Answer 24

establish monosynaptic connections with synergistic alpha motor neurons. Plays a role in tonus and postural control

Question 25

importance of 1b GTO in gait

Answer 25

enhance muscular contraction of extensors during the stance phases and to reset stepping to extension when activated during the swing phase

Question 26

what joint is the most important in gait

Answer 26

THE HIP

Question 27

why is the hip so important in gait?

Answer 27

1) step cycle signals which part of the step cycle the limb is at in a given moment 2) afferent influences by hip position help regulate the step cycle at the SC level 3) info regarding the length of the limb from hip to toe is transmitted to the cerebellum via the dorsal spinocerebellar tract 4) position of the hip regulates the transition from stance (extensor) to swing (flexor)

Question 28

Key component loading in mid stance: sensory input

Answer 28

1) increased loading through the limb 2) longer the loading the increase in hip extension with increase motor unit activation and sensory input 3) greater opportunity for pre-swing or trailing limb 4) leads to a greater stride length

Question 29

trailing limb

Answer 29

- 20-30 degrees of hip extension - quick stretch (MS) to activate - aides in the propulsion of the limb in space

Question 30

Sensory info to the spinal cord from the limb

Answer 30

1) sensory info from the muscle (1a muscle proprioception, 1b muscle force, and 2 muscle length) 2) joint proprioception 3) load receptors

Question 31

what to focus on with gait training

Answer 31

1) loading: the higher the midstance load the better the swing phase 2) hip position: more hip extension able to achieve trailing limb 3) erect posture

Question 32

how does correct biomechanical loading at stance phase help gait trailing

Answer 32

- achieve the 1st ankle rocker (to absorb energy) - propel ground reaction forces over the stance limb

Question 33

how does tibial advancement over a loaded foot help with gait training

Answer 33

- achieve second ankle rocker - achievement of trailing limb

Question 34

how does the metatarsal heads being loaded help with gait training

Answer 34

- achieve the 3rd ankle rocker - incurring limb propulsion (power)

Question 35

how does the inverted pendulum theory work

Answer 35

heel strike: absorbs energy midstance: stores energy toe off: generates energy

Question 36

CVA neurologic gait dysfunction

Answer 36

- lack of selective control of synergistic movement - generalized weakness - spasticity - lack of a heel strike - knee hyperextension in midstance - absent trailing limb

Question 37

PD gait pattern

Answer 37

- posture: cervical flexion and thoracic kyphosis - center of mass out of base of support - lack of thoracic rotation - bradykinesia - freezing of gait - difficulty to initiate gait - narrow foot width - festination

Question 38

ataxia gait pattern (cerebellar)

Answer 38

- tremors during walking - weaving gait pattern - swing phase dominated by uncoordinated limb movements - slow movements