Lecture 19 Flashcards
What can regulate reflexes?
- Descending Input (from brainstem)
Do Motor Neurons have multiple inputs?
Yes
- IPSPs
- EPESs
What do the inputs on MN do? what might they not do?
Do
- Change the membrane potential
Not Do
- make it reach the threshold
Do reflexes themselves reach the threshold?
- No
Where can descending neurons make synaptic connections?
- With neurons in the reflex arc
What does a descending neuron’s synapse with neurons in the reflex arc do?
- Changes the background level of activity
- Shift membrane of the MNP to make it closer to threshold
- Tonic because neurons might be firing like crazy
What does a descending neuron’s synapse with neurons in the reflex arc do?
- Changes the background level of activity
- Shift the membrane of the MNP to make it closer to the threshold
- Tonic because neurons might be firing like crazy
Can Tonic activity bring the membrane to the threshold?
- NO
How can you generate an AP in the MN with just Tonic and Reflex (peripheral input) activity?
- Combined them
What is the timing of a Action Potential from Tonic and Reflex activity determined by?
- The Reflex input
What happens when you change tonic input in response to reflex activity?
- Responses in the MNP driven by reflex activity
- Can also be inhibitory
What does tonic input do?
- Sets the stage for potential movements to happen
What kind of feedback travels via the reflex pathway? what does it do?
Sensory Feedback
- Influences many types of movement
What travels via the longer loop pathways?
- Sensory Feedback
What is the crossed-extensor reflex? what is it an example of?
Do
- Multiple segments coordinated to all do the same thing
Example
- Sensory Feedback traveling via a longer loop pathway
How would you bias reciprocal inhibition from one muscle but not the other?
- Cortex facilitates MNP with an EPSP
- EPSP facilitates the 1a inhibitory interneuron
What happens when you want to flex your elbow?
- Cortical Drive biases the probability that biceps will contract and triceps wont
What happens when you make any arm movement?
- Cortical Command is turning the agonist muscle on
- Cortical Command is controlling reciprocal inhibition to the antagonist muscle so it wont contract
Can pathways connect to both agonist and antagonist MNPs?
- YES
What happens during an isometric contraction?
- You have descending input that comes down and inhibits both MNPs
- No reciprocal inhibition
- You can contract
How does descending input help control movement?
- Controls the level of inhibition
- creates a balance between excitation and inhibition
Where are Central Pattern Generators?
- In the spinal cord
What do the Central Pattern Generators couple up with?
- Muscle to create motion
What does the segmental feedback regulate in mammalian walking? what else contributes to this?
Regulate
- Motor pattern
- Adaptation to immediate environment
Helps
- Somatosensory Feedback: Cutaneous, Joint, GTO, Spindles
How do the Tonic Signals help mammalian walking?
Signals from brainstem
- overlaid on top of CPG
How does Supraspinal control from motor cortex and the brain stem help in mammalian walking?
- Balance and Stability
- Task Selection
- Navigation
- Obstacle Avoidance
How do mammals avoid obstacles when walking?
Supraspinal Control
- Changing locomotor pattern
How does navigation work in mammalian walking?
Supraspinal Control
- Visual Locomotor Control
How does task selection work in mammalian walking?
Supraspinal Control
- Accommodating obstacles
- Change in footing
- Pace change
What is involved in the neuronal organization of mammalian walking?
- Central Pattern Generator: create motion
- Segmental/somatosensory feedback: adaptation to the immediate environment
- Tonic Signals: Overlaid on top of CPG
- Supraspinal Control: environmental navigation and balance/stability
What is faster? Pre-programed responses (M2 and M3), M1, or Volitional Activity?
Fastest: M1 Response
Fast: Pre-programmed
Slowest: Volitional Activity (response to stimuli)
How fast do Pre-programmed responses happen?
- 400ms
Why are M2 and M3 responses called pre-programmed responses?
- They can be tuned in advance of the disturbance
- Either up or down
What drives M2 and M3 responses?
- Afferent system
How do M2 and M3 Responses occur?
- Get the MNP started when need to make corrective responses
- Think about whats going to happen
How do we know there is a Central Pattern Generator in the Spinal Cord?
Severed Spinal Cord
- Hind legs continue to walk with the presence of afferent feedback (without descending input from the brain)
What happens when you deafferent the hind legs?
Oscillation
- Uncoordinated
What does the Spinal Cord contain in regards to walking?
Central Pattern Generator
- Network of interneurons that generate oscillation needed for walking
How does Scaffolding work in the CPG? what makes the CPG work efficiently?
Scaffolding
- Adds to the model of locomotion
Efficiently
- Afferent Feedback
What does afferent feedback do?
- Initiates walking
- Phase Transitions
- Regulate Different types of muscle activity
- Correct for unexpected distrubances
How does afferent feedback initiate walking?
- Jumpstarts the CPG
How does afferent feedback help with phase transitionS?
- Helps decide when its safe to put one leg from stance to swing
What is an example of when afferent feedback can help regulate different types of muscle activity?
Tilt treadmill to a different angle
- Can still walk
How does afferent feedback help correct for unexpected disturbances?
If you Slip/Trip/Stumble
- Balance corrections
- Layers on top of CPG
How does the stimulation of group 1 afferents inhibit flexion in a decerebrate walking cat?
- Nervous system is told the leg was carrying weight/loaded
- It won’t flex
What happens when you stimulate a group of 1 afferents in a decerebrate walking cat?
Stop transition from stance to swing
- inhibits flexion
- stops locomotion
Describe the foot in the hole experiment
- Just as cat hit step, the step drops
- ## the cat shifts amount of force on plate until it stops moving
What happens to the EMG levels during the foot in the hole experiment?
- Anticipatory burst is the same
- EMG levels drop when plate drops instantaneously
- Big burst in EMG when plate stops, corresponds with loading
What can explain the reaction during the foot-in-the-hole experiment?
- Afferent feedback layering on top of the CPG
