Central Pattern Generator

Question 1

Central Pattern Generator (CPG)
* Reflexes can perform **, but not **
* e.g. stretch reflexes cannot **: ** is required
* Posture and movement are ‘programmed’ by **, or **
* CPGs are located principally in the ** and in ** (see also
hypothalamus)
* Often these CPGs are activated in order **
* Often very important in ** as well
* Particularly important in ** and **

Answer 1

Central Pattern Generator (CPG)
* Reflexes can perform simple elements of movements, but not complex patterns
* e.g. stretch reflexes cannot restore postural stability after a perturbation: a
centrally coordinated response is required
* Posture and movement are ‘programmed’ by CPGs, or functional networks of
neurons
* CPGs are located principally in the spinal cord and in brainstem (see also
hypothalamus)
* Often these CPGs are activated in order of relevance
* Often very important in behavioural responses as well
* Particularly important in locomotion and motor control

Question 2

1. Locomotion: Leg Step Cycle
   The step cycle of each leg during walking is programmed by a **
   within the ** of the **
   * Properties of network:

Answer 2

1. Locomotion: Leg Step Cycle
   The step cycle of each leg during walking is programmed by a network of neurons
   within the intermediate zone of the lumbar cord
   * Properties of network:
2. Pacemaker neurons, diffuse excitation
3. Reciprocal inhibition
4. Phase-dependent reflexes

Question 3

1. ‘Half-Center’ Structure
   * CPG organized **:
2. Flexor burst generator drives **
3. Extensor burst generator drives **
   * ** one another
   * ** when not inhibited**

Answer 3

1. ‘Half-Center’ Structure
   * CPG organized into 2 half-centers:
2. Flexor burst generator drives flexor motor nuclei
3. Extensor burst generator drives extensors
   * Mutually inhibit one another
   * Both spontaneously active when not inhibited

Question 4

1. Flexor Burst Generator
   * Flexor burst generator () connects with the **
   * Activation of flexor burst generator -
   > ** -> ** ->
   **
   * Extensor burst generator connects with the **
   * Activation of extensor burst generator -> ** -> ** -> **
   * Mutually **
   * Flexion phase of swing has a **, regardless of **
   * Flexor burst network has a build-up of ** that eventually ** > end of **
   * Reciprocal inhibition of extensor burst network ceases > **
   * ** feedback

Answer 4

1. Flexor Burst Generator
   * Flexor burst generator (pacemaker) connects with the flexor MN
   * Activation of flexor burst generator -
   > activate flexor MN -> leg flexion ->
   swing
   * Extensor burst generator connects with the extensor MN
   * Activation of extensor burst generator -> activate extensor MN -> leg extension -> stance
   * Mutually inhibitory
   * Flexion phase of swing has a fixed
   duration, regardless of speed of locomotion
   * Flexor burst network has a build-up of inhibition that eventually stops the burst of action potentials > end of activation of flexor motoneurons
   * Reciprocal inhibition of extensor burst network ceases > extensor network active
   * Sensory feedback

Question 5

Stance Phase
* ** duration, depending on **
* Regulated by ** (** will feed sensory information)
* ** reflexes: (can be **)
– ** reflex,
– ** reflex
– ** reflex

Answer 5

Stance Phase
* Variable duration, depending on speed
* Regulated by sensory feedback (mechanoreceptors will feed sensory information)
* Phase-dependent reflexes: (can be modulated)
– Stretch reflex,
– Golgi tendon reflex
– Extensor thrust reflex

Question 6

Need for Sensory Control
* Essential to match muscle contraction to **** these vary
with every **** and are ****
* Reflexes provide **** of **** to ****
* Sensory cues inform CPG when **

Answer 6

Need for Sensory Control
* Essential to match muscle contraction to loading conditions on the leg; these vary
with every step and are unpredictable
* Reflexes provide automatic adjustment of extensor contraction to load experienced
* Sensory cues inform CPG when it is safe to start next swing phase

Question 7

Transition to Leg Swing
* E3 phase stops (and thus disinhibits **) only if:
1. Leg is **
2. Hip is **
3. Opposite leg is **
* Crossed projections provide **

Answer 7

Transition to Leg Swing
* E3 phase stops (and thus disinhibits flexor burst generator) only if:
1. Leg is not bearing weight
2. Hip is extended
3. Opposite leg is in stance (bearing weight)
* Crossed projections provide correct phase-linking of CPGs on each side