BB Lecture 17: Motor System II: Locomotion Flashcards
What is Posture?
muscle tone sufficient to maintain a desired body position despite the pull of gravity
What is purpose of feedforward mechanisms in context of posture?
ANTICIPATORY
For anticipated postural instability
predict disturbances and produce preprogrammed responses, before a movement commences, using spinal circuits to maintain posture/balance
-modifiable with experience
What tracts are involved in feedforward mechanisms?
i. reticulospinal tract
ii. vestibulospinal tract
iii. uncrossed cortico spinal tract (anterior corticospinal tract)
What is the purpose of feedback mechanism in context of posture?
COMPENSATORY
-for unanticipated postural instability
relatively rapid adjustments (slower than feedforward), commonly involving spinal reflex circuits, evoked by loss of posture and/or balance during movement
-modifiable with experience
What are pathways involved in feedback mechanisms?
- propriocepters such as muscle spindles (stretch) and golgi tendon organs (muscle tension)
- dorsal column
What is an example of anticipatory vs. compensatory mechanisms for posture?
A woman is holding onto a rope, and when she is anticipating the rope to be pulled, she has gastrocnemius tensed
-however, when she is held in place so that the rope pull does not fuck with her postural instability, when the rope is pulled, she tenses her biceps muscle…calf is not tensed because she is not anticipating a movement
What is the step cycle?
- extensors and flexors are contracted and relaxed at opposite times
- when in stance phase, extensor muscle is flexed
- when in swing (foot lifted) phase), flexor muscles are contracted
- won’t have overlap of the swing cycles because that means you are in the air
- for stability during walking, the opposite limbs show an overlapping pattern during stance phase
What is the function of the central pattern generator (CPG)
- rhythmic motor network; rhythmic motor movement
- generates locomotion and is in the same spinal segments that contain the motor neurons that innervate limb muscles
- regulated by descending projections, which consists of reticulospinal projections
- each CPG is the ultimate source of the motor rhythm that it underlies (in that it will continue to function if you lesion UMN control)
- each CPG generates a rhythmic, repeating motor pattern in response to non-rhythmic input
What is fictive locomotion/fictive behaviors?
The idea that the motor pattern is similar to that occurring in the behaving animal but ONLY the CNS is present
-tests done with isolated spinal cord
What is one common feature of CPG organization?
Reciprocal inhibition between functional antagonists (i.e. between extensor and flexor)
What is a locomotor CPG composed of?
i. flexor CPG module
ii. extensor CPG module
At each joint
Do we know what neurons are specific for CPG?
No, CPG neurons have yet to be identified in mammals
Where are locomotor CPGs hypothesized to reside?
Locomotor is located in the intermediate zone
What is the mesenphalic locomotor region (MLR)?
-when activated, it activates walking reflex
-just below inferior colliculus and anterior to the cerebellum
-stimulating an MLR in an intact cat is sufficient to generate episode of walking
MLR sends signals to MRF (medial reticular formation)
What is the locomotor information flow?
Trigger (cortex, could be triggered by occipital visual cortex) mesenphalic locomotor region medial reticular formation reticulospinal neurons CPG neurons MNs (spinal cord) effectors (muscles) sensory (1a, 1b)
