Module 3 Discussion 2 Flashcards
Innervate the ends of intrafusal fibers
Gamma Motor neuron
where does the gamma motor neuron receive information from
Receives info from cerebellum
Function of gamma motor neuron
keep muscle spindle from reaching slack state
Keeps 1A sensory axons active to maintain stretch reflex
_____________ is when the gamma neurons do not communicate with cerebellum → muscle goes slack
Hypotonia:
Gamma Loop first step:
Muscle is stretched → 1A sensory axons send info to alpha motor neurons → extrafusal fibers contract
Gamma loop second step:
Gamma motor neurons fire on intrafusal muscle fibers to cause them to contract
Gamma loop third step:
Gamma motor neurons and alpha motor neurons fire simultaneously
What does the third step avoid
Avoids hypotonia
Gamma look step 4
Intrafusal muscle fibers will not be slack → 1A sensory neurons can fire due to another stimulus
Located in tendon of extrafusal muscle intertwined with 1B sensory neurons
Golgi tendon organ
Function of Golgi tendon organ
ensure muscle is not over contracting
1B sensory axon detects when
muscle contracts
1B synapses on
inhibitory interneuron in spinal cord
Inhibitory interneuron synapses on alpha motor neuron
(using GABA)
Alpha motor neuron stops firing when stimulated by Golgi tendon
Protects tendon and muscle from over contracting
Muscle is stretched (extra/intrafusal muscle) by
extra weight
1A afferent axons detect stretch and synapse with __________
alpha motor neurons
Detect stretch via
mechanically gated channels
Alpha motor neurons stimulate
extrafusal muscle fibers to contract
Gamma motor neurons fire on
intrafusal muscle ends to contract intrafusal muscle fibers
Keeps 1A sensory axons active
1B afferent axons in GTO detect extrafusal muscle contraction and synapse with inhibitory interneurons in spinal cord and then _____________
Inhibitory interneurons synapse on alpha motor neuron to prevent over contraction
Uses inhibitory interneurons
reciprocal inhibition
Excite a muscle and reciprocally inhibit its _____________ to allow for designated contraction
antagonist
Add a weight in hand → muscle is lengthened
1A sensory axon detects stretch in biceps and fires on alpha motor neuron
Alpha motor neuron will fire to contract bicep
1A sensory axon also fires on inhibitory interneuron
Inhibitory interneuron synapses on alpha motor neuron in triceps (antagonist muscle) to prevent contraction
This overcomes the stretch reflex in the triceps
Uses excitatory interneurons and means move leg away from pain
Flexor withdrawal reflex
In flexor withdrawal reflex:
__________ nociceptive axons detect pain
Aδ
In flexor withdrawal reflex:
Synapse on excitatory interneurons that synapse on alpha motor neurons to
contract flexor muscles
In flexor withdrawal reflex:
Synapse on inhibitory interneurons that synapse on
alpha motor neurons of extensor muscles
Cross extensor reflex: allow us
to be supported by other leg
During the cross extension reflex:
Extensor muscles are activated
Flexor muscles are inhibited
Aδ nociceptive axons that detected pain synapse _____________
on interneurons in opposite leg
Flexor withdrawal reflex + cross extensor reflex work together
So we can flex one limb to withdraw it from pain and extend other to stay standing on it
Cross extensor reflex is building block for
locomotion
Movement of single limb is a cycle of 2 phases in bipeds:
Phase 1: stance phase → both feet on ground
Phase 2: gait phase → one foot is off ground
___________ stance phase → both feet on ground
Phase 1:
Locomotion depends on
spinal cord neurons that exhibit a central pattern generator rhythm
____________gait phase → one foot is off ground
Phase 2:
___________ neurons that create action potentials on their ownNot dependent on sensory input or entirely on higher centers in brain
Central Pattern Generators (GPGs):
What experiment shows the central pattern generator
Cat lesion experiments
_____________: planning movement
Highly dependent on sensory input (like knowing where you are)
Sensory info reaches cerebral neocortex
Strategizes with basal ganglia
Strategy
___________: issue instructions of movement
Sends info to neurons in spinal cord on how to execute movement
Primary motor cortex choose final movement
Cerebellum (to contribute to past movements)
Tactics
_________ moving
Coordinates muscles to actually move
Brainstem and spinal cord (alpha motor neurons) send info to body
Execution:
Strategy stage:
Sensory info reaches
cerebral neocortex
Strategy stage:
Cerebral cortex Strategizes with
basal ganglia
Tactics stage:
Sends info to neurons in _______on how to execute movement
movements)
spinal cord
Tactics Stage:
____________choose final movement
Primary motor cortex
Tactics Stage:
___________ (to contribute to past movements)
Cerebellum
Control movement of distal muscles
EX: corticospinal tract, rubrospinal tract
Lateral pathways
Control postural muscles
EX: vestibulospinal tract, tectospinal tract, pontine reticulospinal tract, medullary reticulospinal tract
Ventromedial pathways
Originates in the primary motor cortex Travels through… internal capsule and cerebral peduncles (midbrain) decussates in pyramids of medulla Terminates in the spinal cord
cortico spinal tract
Cortico spinal tract
primary motor cortex -> internal capsule -> cerebral peduncles (midbrain) -> pyramids fo medulla-> spinal cord
Parallel to the corticospinal tract Receives input from frontal cortex Originates and decussates in red nucleus Travels through: Midbrain Medulla Terminates in spinal cord
rubrospinal tract
Path of rubiospinal tract
frontal cortex-> red nucleus -> midbrain-> midbrain -> medulla -> Spinal cord
Lesioning lateral pathways:
____________→ can’t move joints independently
Loss of fractional movement
Lesioning lateral pathways:
Voluntary movement was _________________
fragmented (slower, less accurate)
Lesioning lateral pathways:
Postural muscles were ________
unaffected (b/c from ventromedial pathways)
__________________________
Symptoms similar to lateral pathways, but it recovers due to compensation of rubrospinal tract
Lesions to the corticospinal tract alone
Lesions to the corticospinal tract alone:
Permanent deficit in
distal flexors and fractional movement
Lesions to rubrospinal tract reverse recovery →
permanent damage
Motor control comes from the
motor cortex
__________ aka M1 aka motor cortex
The actual execution of movement
Somatotopy. A certain area of the cortex controls a certain part of the body
Area 4
\_\_\_\_\_\_\_\_\_\_\_\_\_\_ SMA (supplementary motor area) Planning of movement PMA (premotor area) Planning of movement
Area 6
Somatosensory cortex (Parietal lobe (area 3b)) aids
motor control
____________ Is the SMA and the PMA
Area 6
___________________
Located in medial parts of Area 6
Supplementary motor area (SMA)
________________
Located in lateral part of Area 6
Contains mirror neurons: respond when a movement is executed, imagined, and observed
Premotor area (PMA)
Contains ______________respond when a movement is executed, imagined, and observed
Enable us to understand actions and intentions of others
mirror neurons:
Perhaps dysfunction of ___________is related to autism
mirror neurons
___________ Planning of movement + strategy
Active right before execution of movement and when movement is observed
Activity stops shortly after action is initiated
Firing is highly specific to activity observed
SMA + PMA:
Communicates with body via brainstem and spinal cord
Pyramidal neurons in layer V (Betz cells)
Cell bodies are in cortex
Project out and synapse directly on alpha motor neurons or indirectly with interneurons
Active when a movement is executed
Receive inputs from area 6 (SMA/PMA), 3, 1, 2 (parietal lobe) and thalamus
Area 4 aka primary motor cortex
what cells are in area 4 or primary motor cortex
Pyramidal neurons in layer V (Betz cells)
Project out and synapse directly on
alpha motor neurons or indirectly with interneurons
Active when a movement is executed
Receive inputs from area 6 (SMA/PMA), 3, 1, 2 (parietal lobe) and thalamus
area 4
Implant electrode in vivo (primates)
Train monkey to move joystick in a certain direction based on light
Coding of M1 Neuronal Function
Burst of activity occurs immediately before and during movement
Activity correlated with force and direction of movement
All individual neurons have “broad tuning” for direction
All neurons can fire in a wide range of directions with various force
Neurons have a prefered movement
There’s a population of neurons firing per direction =___________
NOT just one direction per neuron
A population of neurons in motor cortex is active for
every movement
Activity of a single neuron represents a “vote” for a direction of movement
Neurons have a preference for specific directions
Resulting movement is an average of _____________
“votes” of the neurons
One neuron has different direction _______
preference than another
___________mportant for planning a movement (proprioception/strategy)
Parietal Lobe
Parietal Lobe: Sends info to______________________
primary somatosensory cortex (area 3b)
Parietal Lobe
Receives input from _____________
Neurons responsive to ________________
ventral posterior nucleus of thalamus
somatosensory stimuli only
Parietal Lobe
Lesions impair __________
somatic sensation
PET studies: ____________
Subject move finger = blood to ________
change in blood flow
areas 5, 6, 7, 4
Subject thinks about moving finger = blood to ______________
Subject move finger = blood to ________________
Subject thinks about moving finger = blood to ___________
area 6PET studies: change in blood flow
areas 5, 6, 7, 4
area 6
Certain areas of the motor cortex are ____________
“malleable”
Cortex can reorganize to innervate a ______________
different target
Whisker experiment: motor neurons innervating whiskers were
lesioned
Motor neurons were remapped and innervated
forelimb and periocular muscles
If you learn an instrument, can reorganize
motor innervation
Regulates motor control
basal ganglia
2 functions, but likes doing 1 at a time of basal ganglia →
grouping/chunking:
Action selection
General circuitry:
Motor cortex sends excitatory info to 1. _________ to process
- _________ send inhibitory info to 2. __________ or 3. ____________
- ___________ sends excitatory info 3. _____________
- ___________ sends excitatory info to 4. ____________
basal ganglia
superior colliculus or thalamus
superior colliculus to thalamus
Thalamus to motor cortex
