Lec 7: Neurologic Basis of Locomotion in Humans

Question 1

Human Locomotion

Answer 1

“Walking”
-initiated action by brain
-maintained/constrained in steady state execution by spinal mechanisms AKA CPGs
-peripheral afferent contributions interact with CPGs

Question 2

Evidence for CPGs in humans

Answer 2

-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

Question 3

Scheme for CPG

Answer 3

SC (lower): protective reflexes, locomotion
Brainstem: respiration, chewing, swallowing, eye movements
Cerebral cortex: fine motor control
Hypothalamus: feeding, drinking, Locomotion

Question 4

CPG Basics

Answer 4

-CPG located in SC
-CPG generates rhythmic timing and coordination of muscles
-CPGs inactive at rest
-Supraspinal (cortex) initiates locomotor command to start gait

Question 5

Grand Initiators of Gait

Answer 5

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)

Question 6

Gait requires complex interactions between what systems???

Answer 6

Cortex&raquo_space;> Basal Ganglia

Basal Ganglia&raquo_space;> Thalamus, Limbic System, MLR

Thalamus&raquo_space;> Cortex

Question 7

Role of MLR

Answer 7

-received from BG
-initiates information to brainstem

Question 8

Role of Spinal Locomotor Networks

Answer 8

-spinal circuits located in lumbar spine
-consists of flexible burst generators to motor output

Question 9

How is motor output adapted?

Answer 9

-sensory feedback (from proprioceptors: MS, GTO, & Joint Receptors)
-continuously integrated to adapt motor output to external conditions

Question 10

Role of Reticulospinal Neurons

Answer 10

-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

Question 11

CPG Mechanism

Answer 11

BG&raquo_space; MLR&raquo_space; RS Neurons&raquo_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)

Question 12

How do limbs alternate?

Answer 12

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

Question 13

Importance of Ia and Ib to gait

Answer 13

-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

Question 14

Role of Hip Position

Answer 14

-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

Question 15

Key Component in Midstance (Loading)

Answer 15

-longer time spent loading&raquo_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)

Question 16

Key Component in Pre Swing

Answer 16

-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

Question 17

Trailing Limb Phenomenon

Answer 17

-when hip reaches posterior position, sensory input provides transition into lift up phase from support phase

Question 18

Loading Limb

Answer 18

-Support phase activates load receptors (preventing transition to lift up phase)

Question 18

Locomotion sensory input via spinal cord

Answer 18

1. Sensory Information about Muscle
   Ia=Muscle proprioception
   II=Muscle length
   Ib=Muscle force
2. Joint proprioception
3. Load receptors

Question 19

How does sensory input help gait training?

Answer 19

1. Information about muscle: Increase loading during midstance to improve swing phase
2. Information about joint proprioception: Increase hip extension to achieve trailing limb
3. Information from load receptors: erect posture

Question 20

How does sensory input help ankle rockers?

Answer 20

-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

Question 21

Inverted pendulum Theory

Answer 21

-absorbing energy and later generating energy
-Heel strike: GRF absorb energy
-Midstance: Store energy
-Toe off: Generates Energy

Question 22

CVA Gait Dysfunction

Answer 22

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

Question 23

Parkinson’s Gait Dysfunction

Answer 23

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

Question 24

Ataxic Gait Pattern

Answer 24

tremors during walking (limbs, trunk, or both), weaving gait pattern, swing phase dominates by uncoordinated limb movements, slow movements