Lec 7: Neurologic Basis of Locomotion in Humans Flashcards
Human Locomotion
“Walking”
-initiated action by brain
-maintained/constrained in steady state execution by spinal mechanisms AKA CPGs
-peripheral afferent contributions interact with CPGs
Evidence for CPGs in humans
-in SCI
-involuntary LE stepping-like movements in pt with incomplete C/s SCI
-rhythmic movements in pt with complete SCI
-rhythmic patterns of activity resembling bipedal stepping in complete SCI
Scheme for CPG
SC (lower): protective reflexes, locomotion
Brainstem: respiration, chewing, swallowing, eye movements
Cerebral cortex: fine motor control
Hypothalamus: feeding, drinking, Locomotion
CPG Basics
-CPG located in SC
-CPG generates rhythmic timing and coordination of muscles
-CPGs inactive at rest
-Supraspinal (cortex) initiates locomotor command to start gait
Grand Initiators of Gait
Cortex (will to move)
-Choice of action(cognition/volitional process)
-Response (emotion)
BG
-selects pattern
-depends on input from superior colliculus (visuospatial/steering), cortex, thalamus, and dopamine
-modulates SC (via MLR)
Gait requires complex interactions between what systems???
Cortex»_space;> Basal Ganglia
Basal Ganglia»_space;> Thalamus, Limbic System, MLR
Thalamus»_space;> Cortex
Role of MLR
-received from BG
-initiates information to brainstem
Role of Spinal Locomotor Networks
-spinal circuits located in lumbar spine
-consists of flexible burst generators to motor output
How is motor output adapted?
-sensory feedback (from proprioceptors: MS, GTO, & Joint Receptors)
-continuously integrated to adapt motor output to external conditions
Role of Reticulospinal Neurons
-in brain stem, go to CPGs in spine
-receive direct somatic, vestibular, tectal, deep cerebellar, and motor excitatory input to integrate whole body movement
-Output to gamma and alpha motor neurons
CPG Mechanism
BG»_space; MLR»_space; RS Neurons»_space; CPGs in Spine
-BG releases dopamine to MLR
-MLR to initiate gait process
-CPGs (rhythm generating and pattern forming networks)
-Burst generators for synergist muscles at each limb joint appropriately times (Generate Rhythm)
-Locomotor networks of burst generators recruited to produce specific patterns (Pattern forming)
How do limbs alternate?
During locomotion, flexor and extensor motor neurons receive inhibitory and excitatory inputs
-Interneurons play important role in inhibition
-Renshaw cells and Ia (reciprocal inhibition) interneurons project to motor neurons
Importance of Ia and Ib to gait
-Ia and Ib increase extensor activity, modulate and adapt gait
-Ib: activated during swing to reset stepping into extension, enhance extensor contraction during stance phase
Role of Hip Position
-hip position signals which part of a cycle the limb will be in
-hip position signals afferent to regulate step cycle @ SC level
-hip position and length of entire limb transmitted via dorsal spinocerebellar tract to cerebellum
Key Component in Midstance (Loading)
-longer time spent loading»_space;> increase in sensory input (via load receptors) & motor unit activation
-improvements in loading can improve pre swing/trailing limb (leading to greater stride length)
Key Component in Pre Swing
-hip position regulates transition from stance to swing (via termination of extensors and onset of flexors)
-quick stretch (MS) activates trailing limb to mediate swing phase
-aid in propulsion of limb in space
Trailing Limb Phenomenon
-when hip reaches posterior position, sensory input provides transition into lift up phase from support phase
Loading Limb
-Support phase activates load receptors (preventing transition to lift up phase)
Locomotion sensory input via spinal cord
- Sensory Information about Muscle
Ia=Muscle proprioception
II=Muscle length
Ib=Muscle force - Joint proprioception
- Load receptors
How does sensory input help gait training?
- Information about muscle: Increase loading during midstance to improve swing phase
- Information about joint proprioception: Increase hip extension to achieve trailing limb
- Information from load receptors: erect posture
How does sensory input help ankle rockers?
-Stance phase: correcting loading will have to achieve first ankle rocker and propel GRF over stance limb
-Loading Response: improving tibial advancement to achieve second ankle rocker and achieve trailing limb
-Pre Swing: achieve third ankle rocker and limb propulsion
Inverted pendulum Theory
-absorbing energy and later generating energy
-Heel strike: GRF absorb energy
-Midstance: Store energy
-Toe off: Generates Energy
CVA Gait Dysfunction
Presentation: synergistic movement (lack of selective control), generalized weakness, and spasticity
Dysfunction: lack heel strike (forefoot, foot flat, or PF), knee hyperextension in MSt, knee buckling in Mst, absent trailing limb
Parkinson’s Gait Dysfunction
Posture: cervical flexion and thoracic kyphosis, center of mass out of BOS, lack of T/s rotation and arm swing
Gait dysfunction: bradykinesia, freezing of gait, small steps, difficulty initiation gait, narrow foot width, festination
Ataxic Gait Pattern
tremors during walking (limbs, trunk, or both), weaving gait pattern, swing phase dominates by uncoordinated limb movements, slow movements
