Term
| what does a golgi tendon organ sense? |
|
Definition
| senses force from muscle firing. ues Ib afferent neurons |
|
|
Term
The Ib axon (afferent) from
the golgi tendon organ
contacts an interneuron in
the spinal cord; the
interneuron is known as the
Ib inhibitory interneuron. Why? |
|
Definition
| to prevent the muscle from ripping off the bone (sort of-it can be modulated) |
|
|
Term
| what same input to your foot at rest can cause two different responses from the Ib golgi afferent neuron. what is this and why does this happen? |
|
Definition
| at rest, you get an inhibitory hyperpolarization, but during walking, that same input causes a depolarization. you can switch from inhibitory to excitatory. may not be hard wired |
|
|
Term
| what are some mechanical proprioceptive pathways? what type of fibers do they use? |
|
Definition
(group II, III)
Plantar skin during stance
phase of walking
Tactile inputs on fingertips
during grasp - if anesthetized, you |
|
|
Term
| what are some noxious proprioceptive pathways, and what type of fibers do they use? |
|
Definition
(group III-IV)
flexion withdrawal reflex - stimulates flexion of one hip, but extension of the other to keep you upright (stepping on a tac)
local sign - pulls away from the noxious stimulus (anywhere else) |
|
|
Term
| stumbling corrective response |
|
Definition
in cats: A mild mechanical stimulus
applied to the dorsal part of the paw during the swing phase produces excitation of flexor motor neurons and inhibition of extensor motor neurons, leading to rapid
flexion of the paw away from the stimulus and elevation of the leg in an attempt to step over the object. Because this corrective response is readily observed in
spinal cats, it must be produced to a large extent by circuits entirely contained within the spinal cord. |
|
|
Term
| which ones are hard wired, and which aren't? |
|
Definition
| flexor withdrawal appears to be hard wired, but local sign and stumbling corrective response appear to be learned. |
|
|
Term
Reflexes modulate and even reverse action in different
conditions
Can not be explained by simple
habituation
Network of cells |
|
Definition
|
|
Term
Decerebrate
transection at the brainstem (midbrain) (a-a’) |
|
Definition
| all you have is brain stem and spinal cord |
|
|
Term
pinal
transection at lower thoracic level (b-b’) |
|
Definition
| just lumbo sacral reflexes (no higher spinal cord, brain, or brainstem |
|
|
Term
deafferented
transection of the dorsal roots |
|
Definition
| no afferent inputs, no reflexes |
|
|
Term
Immobilized
removes movement related feedback by paralyzing the muscles
(fictive locomotion) |
|
Definition
| you can record from the nerves, but no muscle contraction. removes muscle feedback. |
|
|
Term
| Neonatal (and/or) in vitro preparation. |
|
Definition
| good way to compare eNg to eMg. |
|
|
Term
| what is the definition of a central pattern generator? |
|
Definition
circuit with intrinsic
ability to generate rhythmic,
coordinated motor behaviors |
|
|
Term
| describe Graham Brown’s half-center model (1911) |
|
Definition
comprises one set of
neurons that project to motor neurons innervating extensor
muscles and another set that projects to motor neurons
innervating flexor muscles.
Two centers inhibit each other reciprocally so that when one
half-center is active, the other is inhibited. |
|
|
Term
What is the most studied/detailed Central Pattern
Generator? |
|
Definition
lobster stomatogastric network.Total of 33 neurons control all feeding behaviors
Approximately 50% of
all possible connections
are present
Anatomy ≠Physiology
Modulated by
sensory information
(food in gut)
descending modulation
(hunger/satiety of
animal) |
|
|
Term
| how was physical therapy influenced by early study of central pattern generators ? |
|
Definition
| it was heavily influenced by reflexes, so we used to do a LOT of reflex testing. |
|
|
Term
| decerebrate animal experiment. what did this show? |
|
Definition
| no cerebrum, limbs are straight out and has lots of tone. when you then knock out the dorsal roots, the animal falls flat, so reflexes were thought to be extremely important. |
|
|
Term
| we moved from this half center model to a modular network model. how does this model work? |
|
Definition
| the modular network model says that each muscle group has its motorneurons, inhibitory interneurons, and excitatory interneurons, all of which are highly interconnected to other muscle groups. |
|
|
Term
|
Definition
| it is a norepinephrine reuptake inhibitor. |
|
|
Term
|
Definition
| cuts down K+ leak channels (increases excitability.) |
|
|
Term
by
electrical stimulation of high
threshold cutaneous & muscle
afferents (FRAs) in spinalized
cats treated with L-Dopa and
nialamide |
|
Definition
| with just one input, you get a rhythmic pattern of output (first flexor fires, then extensor, and back again!) reciprocal |
|
|
Term
| what are some neurotransmitters that are used to initiate or inhibit locomotion? |
|
Definition
Excitatory (primarily glutamate)
Specific agonists elicit rhythmic activity in virtually
all systems –inconsistent with locomotion
Inhibitory (antagonists)
Strychnine (glycine) and biccuculine (GABAA) |
|
|
Term
Both NE and 5HT
increase the
excitability of the motor neurons and can lead to what? |
|
Definition
| spontaneous generation of locomotion (walking half rat) |
|
|
Term
| 5HT and NMDA trigger locomotor patterns similar to regular real locomotion. what does this mean? |
|
Definition
| this means you do not NEED sensory input to get locomotion |
|
|
Term
| has this rhythmic generator been activated in humans with a complete spinal injury? |
|
Definition
epidural electrodes at
T11-L1 (Dimitrijevic et al.
1998)
Variable “pattern”
generation with variable
intensity stimulation |
|
|
Term
| why can’t really identify CPGs in humans? |
|
Definition
Unable to isolate spinal cord networks from both descending and
afferent sources
Does it really matter – do humans demonstrate automaticity
related to stepping behaviors?? YES |
|
|
Term
| what is the Mesencephalic Locomotor Region (MLR)? |
|
Definition
its in the midbrain (brainstem) closely related to the reticular system. it has Direct projections from cortex, basal ganglia,
thalamus. |
|
|
Term
| how are actions exerted through the Mesencephalic Locomotor Region? |
|
Definition
medial reticular formation (reticulospinal
pathway)
– chemical and electrical activation
– modulates with ipsilateral swing phase
– posture/muscle tone (thermostat-like behavior)
ventrolateral/ventromedial spinal pathways
– reduction in postural tone/locomotor ability with
ventral spinal hemisection (Brustein and Rossignol
1998)
– Some recovery can still occur |
|
|
Term
what is the significance of the experiment where EMG activity was recorded from a walking decerebratecat with
hindlimb muscles that were de-afferented. (LG = lateral
gastrocnemius, EDB = extensor digitorum brevis, IP = iliopsoas, ST
= semitendinosus |
|
Definition
| descending pathways can modulate this. you do NOT need afferent pathways |
|
|
Term
| how can you walk without afferent input or descending commands? |
|
Definition
| from CPG's. we saw emg activity in decerebrated + deafferented cats. no descending commands and no sensory, but the motor units were still firing. |
|
|
Term
what does this experiment show? hronic spinal cats
transected after birth
(Forssberg et al. 1980)
Treadmill walking
(motorized)
EMG recorded from
hindlimb muscles |
|
Definition
| you don't need the brain, you can just have sensory input and get learning. |
|
|
Term
| how is Load through stance-phase limb afferent input important? |
|
Definition
Too little – reduced Ia, Ib,
cutaneous input
Too much – 1) can’t bear weight
and 2) Doesn’t allow swing
initiation in late stance
sensory information reinforces the stance phase. |
|
|
Term
| how is Hip extension in late stance important? |
|
Definition
Stretch of sartorius muscle
activates whole limb flexion
Moving limb back increases
stretch earlier . .
Moving limb forward reduces
swing initiation (Lam and Pearson
2001) Ia and group II inputs. this is spinally mediated! |
|
|
Term
| Hip flexion in swing triggers ?? |
|
Definition
|
|
Term
Behavior of limb dependent on
multiple afferent inputs. what are some examples? |
|
Definition
IF hip flexed and extensor
muscle force high . .
THEN prolong stance phase
duration |
|
|
Term
IF hip extended and extensor
muscle force low? |
|
Definition
| then initiate swing phase |
|
|
Term
Complete injury –
NE alpha 2
agonists
in cats triggers
locomotion 8 days
post-SCI
Incomplete injury –
specific NE alpha 1 and
5HT agonist facilitate
weightbearing |
|
Definition
|
|
Term
Different CPGs
for different
tasks or available
neural circuits
used selectively?? |
|
Definition
| we have shared networks and you can select what you need based on inputs and CPGs |
|
|
Term
|
Definition
roup of muscles activated
in a fixed balance
Across single or multiple joints
Synchronous (simultaneous) (walking, standing) vs
Temporal (time-varying) synergies |
|
|
Term
| why do we have synergies? |
|
Definition
Provides variety of movement strategies based on
“task-relevant subspace of control variables”
Simplified control of particular biomechanical
features of the limb (global limb vs single joint
Primitive solution to motor coordination |
|
|
Term
| how do synergies function? |
|
Definition
| Selection of interneuronal subgroups |
|
|
Term
| how does the telencephelon modulate locomotion? |
|
Definition
Motor cortex stimulation initiates locomotion
80% of corticospinal fibers modulate with locomotor
activity (increased to flexors; Drew et al. 2002)
Contribution of corticospinal tracts
bilateral pyramidotomy – temporary alteration in gross
walking pattern (depends on lesion size)
dorsolateral spinal hemisection (Jiang and Drew 1996)
– toe drag; no ladder or beam walking
– inability to modulate stepping responses to first obstacle (this is due to coritcal control of distal flexors)
Humans: Motor Evoked Potential modulation greater to TA than MG
(Schubert et al. 1997; Capaday et al. 1999
extensors are more spinally mediated, flexors are more cortically mediated. |
|
|
Term
| how does the diencephalon modulate locomotion |
|
Definition
Behavioral context for locomotion (Sinnamon
1993)
Exploratory system
– basal ganglia, hippocampus - inhibitory control
Appetite system
– lateral hypothalamus, perifornix
– “brings in contact with incentive and consummative
stimuli”
Defense system
– Medial hypothalamus, periaqueductal gray
– “increase distance between threatening/painful stimuli”
Direct projections from these centers to
brainstem locomotor regions |
|
|
Term
| how does stimulation of the mesencephalic locomotor region initiate CPGs? |
|
Definition
| the signal goes from MLR --> medial reticular formation --> ventrolateral or ventromedial spinal pathways -->CPG's |
|
|
Term
| how does feedback control motor behaviors? |
|
Definition
Utilize afferent
information on moment to
moment basis
sensory signal
compared with desired
state (i.e., internal
representation) –
reference signal
Difference between
actual and intended
behavior–error signal
Negative/proportional
feedback in closed loop
chain(e.g., thermostat)
Gain of feedback (ratio of
input to output) |
|
|
Term
| how does feedforward control motor behaviors?? |
|
Definition
Motor commands in advance to
“expected” perturbations
Open loop control
Feedback signals do not
contribute to second to
second variations in behavior
Generation of an internal
model of desired state
Still dependent on sensory
information, but a
“representation” of this
information
raising a weight while
standing
catching a ball |
|
|
Term
how do we know that Motor actions have similar features regardless of conditions ?
(Donald Hebb 1950s |
|
Definition
trajectory of reaching
handwriting examples
Motor plan
movement is planned by higher centers
abstract form; not series of contractions/consequences
Motor program- signal to specify
the intended movement given the
biomechanical constraints |
|
|
Term
| what are the parts of the sensorimotor cortex? |
|
Definition
Frontal lobe
– Primary motor cortex (M1,Area 4)
– Premotor cortex (PM, Area 6)
– Supplementary motor area (SMA,
Area 6)
Parietal lobe
– Primary sensory cortex (S1, Area
1,2,3)
– Posterior parietal cortex |
|
|
Term
| what do basal ganglia do? |
|
Definition
initiation and
selection of motor programs |
|
|
Term
| what does the cerebellum do? |
|
Definition
| coordination, timing, learning |
|
|
Term
| what is the role of the primary motor cortex? |
|
Definition
articipates in specific
trajectory planning
delivers commands to lower
levels for initiation/
modulation of movement
Motor programs located here
or at lower levels (CPGs,
interneuron networks |
|
|
Term
what is the role of the Primary somatosensory
cortex |
|
Definition
rovides sensory information
required for movement
planning and initiation
modulation of ongoing
movement |
|
|
Term
| how does the cortex control movement? |
|
Definition
primary cells – Layer 5 – pyramidal
cells (include large Betz cells),
distributed in specific cortical
areas
Cortical maps (Penfield 1930-50s)
stimulated the primary
somatosensory cortex - asked the
patient about the sensation
Obtained movements with
stimulation in primary motor
cortex
The results led to a debate
about whether musclesor
movementswere represented in
the cortex. (its both, moreso movements)
individual muscles are
represented in many locations. |
|
|
Term
| pyramidal decussation happens where? |
|
Definition
| at the base of the medulla for cortex control of motor signals |
|
|
Term
| what is the descending pathway of modulation? |
|
Definition
The corticospinal tract(CST) comprises
~ 1 million descending axons.
At the junction of the medulla and
spinal cord, the CST divides into ventral
and lateral tracts.
VentralCST projects bilaterally to
motor neurons that innervate axial
muscles and to the intermediate
zone.
LateralCST (shown here) projects to
motor neurons of distal muscles and
interneurons in intermediate zone.
Some axons make monosynaptic
connections onto motor neurons,
particularly those that control finger
movements.
Other fibers synapse on interneurons
within the spinal cord |
|
|
Term
| wrist and fingers are the last thing to come back after cortical damage. why? |
|
Definition
| there are many interneurons which can be modulated for a muscle like the bicep or pec major if you lose it. the fingers, however, are probably just controlled by 1 part of the motor cortex with little internuerons? |
|
|
Term
What is transcranial magnetic stimulation
(TMS) – also Transcranial
Electrical Stimulation (TES) |
|
Definition
(magnetic fields induce currents in wireds - faraday's law). Magnetic coil generates field
along cortical surface
Activate smaller cortical
cells which activate
pyramidal cells
(TES may bypass this, though
mechanisms controversial) |
|
|
Term
| how much of the coritcal tracts are from M1 region? |
|
Definition
Cortical tracts
40% from M1 region
S1 and PM areas contribute
significantly
Typically to interneuron
pools – except to distal
motor pools |
|
|
Term
Corticospinal neurons make
direct excitatory connections
with only some motor neurons. which ones?
After a bilateral resection of the
corticospinal tracts, monkeys unable
to grasp small objects with
thumb/index finger |
|
Definition
Direct connections for fine control
of the digits. |
|
|
Term
how is Walking affected after a bilateral resection of corticospinal tracts?
– |
|
Definition
unable to negotiate in feedforward
manner (obstacles, balance beam/ladder)
– Toe/ankle dorsiflexion problems, can’t walk balance beam |
|
|
Term
The discharge of action potentials by neurons in the primary motor
cortex (CM = corticomotoneuronal cell) depends on the motor task. how does this affect precision grip vs power grip? |
|
Definition
Precision vs Power grip involve separate cortical/subcortical
circuits acting on similar IN/MN pools |
|
|
Term
| do cortical cells encode direction-specifically? |
|
Definition
yes. they are Population vectors that encode both direction
and magnitude |
|
|
Term
| do motor cortical cells also encode for force? |
|
Definition
yes. Motor cortical cells alter firing
patterns according to extent of
muscle activity required to complete a
task
Tonic and Phasic cortical cells may
participate |
|
|
Term
| how is Direction-specific information and force specific information encoded in cortical cells |
|
Definition
when you load AGAINST the preferred direction, cortical cells fire very hard.
when you load WITH the preferred direction, the cells don't fire as hard |
|
|
Term
| what does the Premotor area do? |
|
Definition
involved in goal-directed movements
Activity prior to visually-guided movements |
|
|
Term
| what does the Supplementary motor area do? |
|
Definition
ensures correct sequencing of movement (order of
movement)
– biomechanical constraints
– task performed
– external conditions
Activity prior to internally-guided movements |
|
|
Term
| what does the Posterior parietal cortex do? |
|
Definition
encodes complex sensory information
internal sensory representation |
|
|
Term
| what are the four premotor areas? |
|
Definition
Lateral premotor areas
– Dorsal premotor
– Ventral premotor
Medial premotor areas
– Supplementary motor area
–Cingulate area |
|
|
Term
| visually guided inputs go where? |
|
Definition
|
|
Term
what is the difference in activation of the Premotor (dorsal or ventral) and
Supplementary motor area during visually guided vs.
internally guided movements |
|
Definition
for a visually guided movement, you have a normal distribution of activation of the two areas.
For an internally guided movement (eyes closed!) you have less activation of the premotor area, and more activation of the supplementary motor area |
|
|
Term
| when is the supplemetary motor areas active? |
|
Definition
active during
sequential (vs just
simple movements)
Active during mental
rehearsal |
|
|
Term
| when are the ventral and dorsal premotor areas active? |
|
Definition
Different tasks utilize
different pathways w/
external cues
Reaching (visual-parietal-dorsal
PM areas)
Grasping (visual-parietal-ventral
PM areas)
Activity related to association
of stimuli to learned
movements
Oftentimes activity without
movement (mirror neurons) |
|
|
Term
| how do the basal ganglia and cerebellum modulatie descending motor patterns? |
|
Definition
Two systems of brain stem
neurons (medial and lateral
descending systems) receive input
from the cortex & subcortical
nuclei and project to the spinal
cord.
The cerebellumand basal ganglia
provide feedback through the
thalamus(not shown) that regulate
cortical and brain stem motor
areas.
The basal gangliaare involved in
motivation and initiation and
selection of motor programs.
The cerebellumis involved with
the timing and coordination of
movements (error detection) and
with the learning of motor skills |
|
|
Term
| is cerebellum ipsalateral or contralaterally controlling? |
|
Definition
|
|
Term
| descending modulation by the cerebellum. |
|
Definition
receives information about goals,
commands, and feedback signals
associated with the execution of
movement
40X more axons project into it than
exit it (Greater number of neurons
than rest of CNS)
Assists with spatial accuracy and
coordination of movement
Largely motor function, some
cognitive
Lateralization, topography of
organization
Input and output: descending, spinal,
brainstem pathway |
|
|
Term
| what is the vestibulocerebellum? what is its function? |
|
Definition
flocculonodular lobe (most primitive)
Receives vestibular, postural, ocular
information; controls balance and eye
movements |
|
|
Term
| what is the spinocerebellum (vermis)? what is its function? |
|
Definition
intermed hemisphere and Vermis –
interposed and fastigial nuclei
proprioceptive/exteroceptive inputs
Governs “performance of movement |
|
|
Term
| what is the cerebrocerebellum? what is its function? |
|
Definition
Lateral hemisphere –Dentate nuclei
Projections from pontine nuclei
Information of planned movement |
|
|
Term
| what are the layers of the cerebellar cortex? |
|
Definition
molecular layer
Stellate and basket cells
Axons of Granule cells
(parallel fibers)
Terminals of climbing fibers
Dendrites of Purkinje cells
Purkinje cell layer
(projection neurons to nuclei)
Granular layer
Granule cells
Inputs from mossy fibers |
|
|
Term
| mossy fibers synapse with which cerebellar cells? |
|
Definition
|
|
Term
| granule cells go into which cerebellar cells? |
|
Definition
|
|
Term
| parallel fibers synapse with the which cerebellar cells? |
|
Definition
|
|
Term
| where do mossy fibers originate? |
|
Definition
|
|
Term
| where do climbing fibers originate? |
|
Definition
| inferior olivary nucleus. |
|
|
Term
| what is the relay center of the brain? |
|
Definition
|
|
Term
| role of cerebellum - 1st movement vs 2nd movement. |
|
Definition
| we get refinement of the motor signal based on error signal from the cerebellum |
|
|
Term
| role of cerebellum - 1st movement vs 2nd movement. |
|
Definition
| we get refinement of the motor signal based on error signal from the cerebellum |
|
|
Term
|
Definition
immediate change in behavior
driven by prior experience and the ability to predict that
new demands will exceed “current state” (feed-forward
strategies) |
|
|
Term
|
Definition
radual change in behavior that results from experience
(“feedback strategies”)
Driven by demands that exceed “current state" |
|
|
Term
|
Definition
Relatively permanent changes
Resulting from repeated exposure (adaptation may be a
precursor) |
|
|
Term
| prism adaptation research |
|
Definition
Prisms inserted into eyeglasses
Displace visual field
Leads to initial errors in
movement accuracy, but cerebellum comparator functions lead to adaptations and then learning. |
|
|
Term
With extensive training, throwing
with wedge prisms can become a
skill. Adaptations result in Learning–which allow faster Transitions |
|
Definition
|
|
Term
| locomotor adaptations - podokinetic system |
|
Definition
| after walking on a circular treadmill for a while, if you get off and close your eyes and walk, you walk in circles, and you have no idea you are walking in circles |
|
|
Term
| how does podokinetic adaptation occur? |
|
Definition
| there are both vestibular and cerebellar contributions to the adaptation response. |
|
|
