Neural Control of Walking Flashcards
What are the three general areas of interest for how walking is controlled?
Central Pattern Generators (CPGs), Afferent Input, and Descending Control
What are central pattern generators?
Discovered in 1900s by Graham Brown in cats with full spinal transection
Proposed idea of “half-centre” where excitatory neurons were mutually inhibitory to one another through interneurons
Oscillatory pattern of activity between the two half-centers
What are the key points of half-center (HC) CPG organization? (6)
- Each limb is controlled by a separate CPG
- Each CPG contains two groups of excitatory that directly project to and control flexor and extensor motoneurons
- Mutual inhibitory interconnects ensure only one center active at a time
- “Fatique” process gradually reduces excitation in the active HC
- Phase switching occurs when the reduction in the excitability of one HC falls below a critical value
- Inhibition of antagonist motoneurons is tightly coupled to the excitation of agonists
Unit Burst Generator (3)
The Unit Burst Generator “is unilateral, multipartite, shared and modular” and can do three things:
1. Controls an agonist at a single joint of a hindlimb.
2. Can produce rhythmic bursts of output even when the generator of its antagonist is quiescient.
3. Is “shared” – each UBG can be used in a number of different behaviors
Why do CPGs have two or more level models?
Allow for the independence between the changes in burst duration and timing of the step cycles, also allows for how sensory information can alter step cycle timing while other stimulation can alter amount of motorneuron activity
Describe afferent control of locomotion for the leg moving from Stance phase into swing.
Muscle spindle (stretch) info from the flexors of the hip
OR
Golgi tendon organ (force) info form the extensors of the ankle
What is the Stumbling Corrective Response
In response to hitting an object with your foot during swing phase, cutaneous receptors on the dorsum of the foot activate and cause unexpected extension in parts of the leg. In response, the entire leg will go into flexion to lift the foot over the obstacle
What area of the brain stem is active?
Activation of an area of the brain stem known as the Mescencephalic Locomotor Region (MLR)
- Tonic stimulation of MLR in decerbrate cats generatd a phasic activation of flexors and externsors
- Timing of the locomotor rhythm was not governed by the stimulation pattern
- Greater intensity of stimulus led to faster walking speed
What other areas in the brain stem can affect locomotor generation?
- Locomotion can be induced through stimulation of cochlear nucleus, cuneate nucleus, substantia grisea centralis and spinocerebellar tracts
- Subthalmic locomotor region causes initiation of walking in a goal-directed manner
- Dorsal tegmental field caused suppression of hindlimbs; ventral was opposite
- Lateral hypothalamic area caused cats to walk slowly
What does damage to the cerebellum result in?
Ataxic Gait (drunken sailor walking)
Problem with co-ordination of the walk is due to a lack of modulation of the firing of reticulospinal neurons in the brainstem
Role of the basal ganglia?
No direct anatomical connection to spinal cord, but connection to the MLR
- Does seem to play important role in the initiation of locomotor activity and a role in getting proper force generation in extensor muscles for postural adjustments before pushing foot off floor
Role of the cerebellum?
Visual input to the cortex allow for locomotor adjustments to go around or over obstacles
Stimulation of motor cortex showed that small trains of stimulation caused short latency changes in locomotor pattern
What is gait is seen in children with Cerebral Palsy? (3)
- Scissor gait
- Crouch gait
- Toe walking
