Neurologic basis of locomotion in humans Flashcards
main takeaway of human locomotion/ what is it?
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
Evidence for CPG in humans spinal cord
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
scheme for CPG
the motor infrastructure and the vertebra control scheme for locomotion
the motor infrastructure for CPG
- 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
CPG basics
in vertebrates, the rythmic timing and coordination of the muscles generated by the CPG are located in the spinal cord
at rest the CPG is
inactive
to initiate gait
a locomotor command is generated at supra-spinal (brain) levels
what is the grand initiator of gait
BG: choice ( of action and decision making) and emotion
what does the BG relay on input information from
the superior colliculus, cortex, thalamus and dopamine
purpose of the superior colliculus
visuospatial and steering us. We tend to move toward things that attract us
where does the mesencephalic locomotor region modulate information to
the spinal cord/brainstem.
receives info from the BG and limbic system
what is the purpose of the BG in gait
helps select pattern
what does gait require the interactions between
the motor cortex, thalamus and BG
the spinal locomotor network
- associated with the lumbar area of the SC
- burst generators to motor output
- relays of sensory info from MS, GTO and joint receptors
what is continuously being sent back to the motor systems
sensory informations from proprioceptors including GTO, MS and joint receptors
Cognitive Motor interaction
cortex, BG (selects limb pattern), cerebellum - Mesencephalic locomotor region (initiator of neurons) - Reticulospinal Neurons (collect relavent sensory info) - burst generator - CPG in spine
Reticulospinal Neurons
- input: direct somatic, vestibular, tectal, deep cerebellar, and motor excitatory
- integrated whole body movement
- innervate gamma and alpha motor neurons
CPG mechanism
- 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
function fo the pattern formation network in CPG
rhythm maintaining
function fo the rhythm generator network in CPG
rhythm resetting
what levels does afferent feedback affect in CPG
all 3 levels
what are 2 inhibitory interneurons that project to motor neurons
Renshaw cells and reciprocal 1a interneurons.
Renshaw cells can inhibit both the flexor and the extensors
how much does 1a and 1b increase extensor activity
50%
importance of 1a MS in gait
establish monosynaptic connections with synergistic alpha motor neurons. Plays a role in tonus and postural control
importance of 1b GTO in gait
enhance muscular contraction of extensors during the stance phases and to reset stepping to extension when activated during the swing phase
what joint is the most important in gait
THE HIP
why is the hip so important in gait?
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)
Key component loading in mid stance: sensory input
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
trailing limb
- 20-30 degrees of hip extension
- quick stretch (MS) to activate
- aides in the propulsion of the limb in space
Sensory info to the spinal cord from the limb
1) sensory info from the muscle (1a muscle proprioception, 1b muscle force, and 2 muscle length)
2) joint proprioception
3) load receptors
what to focus on with gait training
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
how does correct biomechanical loading at stance phase help gait trailing
- achieve the 1st ankle rocker (to absorb energy)
- propel ground reaction forces over the stance limb
how does tibial advancement over a loaded foot help with gait training
- achieve second ankle rocker
- achievement of trailing limb
how does the metatarsal heads being loaded help with gait training
- achieve the 3rd ankle rocker
- incurring limb propulsion (power)
how does the inverted pendulum theory work
heel strike: absorbs energy
midstance: stores energy
toe off: generates energy
CVA neurologic gait dysfunction
- lack of selective control of synergistic movement
- generalized weakness
- spasticity
- lack of a heel strike
- knee hyperextension in midstance
- absent trailing limb
PD gait pattern
- 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
ataxia gait pattern (cerebellar)
- tremors during walking
- weaving gait pattern
- swing phase dominated by uncoordinated limb movements
- slow movements
