Lecture 5: Motor Control Part II Flashcards
where is the corticospinal tracts in humans vs in vertebrate animals
humans = mainly in ventral horn and slightly in intermediate zone; S1 doesn’t contribute much
vertebrates = ventral and dorsal horns; takes up almost the whole gray matter in some animals
where are the rubrospinal and reticulospinal tracts located in the spinal cord
rubrospinal = intermediate zone
reticulospinal = ventral horn
LMN somatotopy distribution from medial to lateral in SC
trunk to distal extremity
LMN somatotopy distribution from anterior to posterior in SC
extensors to flexors
where does the medial vestibulospinal tract end and what does it control
ends in neck and upper thoracic region
controls B neck extensors
what does the medial corticospinal tract control
B postural flexor mm control
what does the pontine reticulospinal tract control
B proximal extremity extensors
what does the lateral vestibulospinal tract control
ipsilateral proximal extremity extensors
what does the medullary reticulospinal tract control
B distal extremity flexors
what does the rubrospinal tract control and where does it end in the SC
controls distal UE flexors
ends in neck and upper thoracic
what does the lateral corticospinal tract control
distal extremity flexors
fine motor
what is a motor neuron pool
LMNs for one mm all aligned in a column
more cranial portion of the column = proximal mm
more distal portion of column = distal mm
what is a motor unit; describe its integration
all mm fibers innervated by one LMN
fibers are intermingled, not homogenous
describe type I mm fibers
mainly found in red mm
slow twitch (S)
fatigue resistant
high concentration mitochondria
less glycogen
where are type II mm fibers mainly found
mainly in white mm
describe type IIa mm fibers
fast twitch
fatigue resistant (FR)
medium concentration of mitochondria and glycogen
describe type IIb mm fibers
fast twitch
fatiguable (FF)
low concentration of mitochondria
more glycogen
how can mm fibers be transformed
they can go between any form to another with strenuous work
type II can become type I
what type of mm contain what fiber types
all mm contain all 3 fiber types just with different ratios depending on the use of the mm
each type of mm fibers mingle together but they form individual motor units
describe small LMNs and their function
innervate type I fibers
less powerful but they can last for hours
used with fine motor and postural control
describe medium LMNs and their function
innervate type IIa fibers
more powerful and last about 1 hour
used for gross motor tasks (in between small and large LMNs)
describe large LMNs and their function
innervate type IIb fibers
most powerful but only last about 1 min
used for gross motor and power
describe the motor unit used for gross motor function, the types of fibers that make up that unit, and the purpose of this set up
gross motor = large motor unit (1 LMN innervates hundreds/thousands of mm fibers)
type IIa/IIb fibers controlled by medium and large LMNs
mm example: gastroc (FR/FF)
describe the motor unit used for fine motor function, the types of fibers that make up that unit, and the purpose of this set up
fine motor = small motor unit (1 LMN innervates several mm fibers)
less fibers to control per LMN = more accurate
type I mm fibers controlled by small LMN
mm example: extraoccular mm - 1:3 ratio of LMN to mm fibers; slow twitch
how are saccades still fast with extraoccular mm even though they are slow twitch mm
due to the ratio of LMN to mm fibers (1:3)
still fast movement
generally, 1 LMN controls one motor unit only; what is the exception to this
facial expression mm
multiple LMNs overlap different facial mm
intensity of a stimuli is encoded by what
action potential
what are the steps for LMN activation/force production
- presynaptic membrane AP travels to LMN axon terminal
- postsynaptic membrane AP frequency travels along mm fibers
- force is then produced by mm fiber contraction; force production directly related to AP frequency
**there is a lag at each step due to the process of signal conduction
what is tetanus
AP over 80 Hz
sustained mm contraction
what is spatiotemporal summation
different motor units at different locations
describe the size principle of motor unit recruitment
UMNs are all the same size; LMNs have 3 sizes
small size LMNs (type I) activated first
Ohms law - Voltage = current x resistance
UMN activation signals (ACh release) induce the same current (I), but smaller LMNs have higher resistance (R) compared to Larger LMNs
thus smaller LMNs create a larger voltage
works like voltage gated ion channels to form action potential
type IIa and IIb follow type I when more force is needed; this is regulated by GTOs
3 types mm contraction
concentric = shortening fibers
isometric = stay same length
eccentric = elongating mm fibers
active vs passive insufficiency
active = mm too short to create optimal force
passive = mm too long to create optimal force
these insufficiencies are found in multiple joint mm
2 structural types of muscle spindles
nuclear chain = nuclei aligned in chain/line
nuclear bag = nuclei concentrated as in a bag
3 functional types of mm spindles
nuclear bag
1. static - detect length
2. dynamic - detect velocity
nuclear chain
3. only static type - for length
every spindle has at least 2 nuclear bag cells (1 static and 1 dynamic)
relationship between mirror neurons and mm spindles
mirror neurons transform sensory info to motor
mm spindles transform motor info to sensory
extrafusal mm innervation
alpha motor neuron and free n endings
intrafusal mm innervation
gamma motor neurons
primary type Ia n innervate what type of intrafusal mm
central nuclear bag and chain cells
both static and dynamic
secondary type II nn innervate what type of intrfusal mm
static nuclear bag and chain cells
does NOT innervate dynamic bag cells; dynamic bag cells only innervated by type Ia and gamma motor neurons
what happens at the mm spindle with an isometric contraction
increase in Ia/II fibers from static nuclear bag and nuclear chain cells
b/c mm is remaining static
what happens at the mm spindle with eccentric contraction
increase Ia on dynamic nuclear bag cells
what happens at the mm spindle with concentric mm contraction
decrease in dynamic stretch on mm spindle and this a decrease in Ia activity from nuclear bag cells
what motor neuron type will be activated with concentric contraction of intrafusal fibers
gamma motor neuron
what mm fibers give feedback to motor actions in regard to position sense and kinesthesia
position sense (stretch) = Ia and II from static nuclear bag and nuclear chain; info sent to cerebellum via posterior spinocerebellar tract
kinesthesia (velocity) = Ia from dynamic nuclear bag cell
Number of CNs with motor function
9
what cranial nn are NOT controlled by corticospinal tract
III, IV, and VI
which CNs do not have B control but rather contralateral control bias
CNs V and XII
vagus and hypoglossal
how is CN VII unique in its motor control
facial expression mm motor unit can be innervated by 2 or 3 LMNs
facial expression is essential for social congnition
all head mm spindle Ia and II innervations are from what CN
CN V
what are the 3 ways UMNs can separately control LMNs for facial mm
cingulate motor cortex:
- level IV
- controls B scalp
- from dorsal motor nucleus CN VII
motor cortex and posterior parietal cortex:
- level IV and III
- controls contralateral face
- from ventral motor nucleus
deep brain structures:
- level II
- controls face and scalp
- from amygdala, basal nuclei, and brainstem nuclei
LMNS for facial mm control what portion of the face
ipsilateral face and scalp
why does a regional injury to the CN VII anastomosis not affect facial expression
CN VII LMN can innervate different motor units
inter CN V and CN VII anastomosis controls what
proprioception of facial mm
what are the components of the spinal/brainstem reflex
receptor
afferent = somatic or visceral sensory input
may/may not have interneurons for integration
efferent = somatic or visceral motor output
effectors = muscles and glands
intrasegmental reflex
afferent and efferent signals at the SAME SPINAL LEVEL
intervsegmental reflex
afferent and efferent at MULIPLE SPINAL LEVELS
what type of loop is used in the spinal/brainstem reflex
bottom up/closed loop
no higher level motor control
what is the flexor reflex
via cutaneous receptors
aka withdrawal reflex/nociceptive reflex
how does the flexor reflex work
noxious stimuli is sent to SC via nociceptive axons (a delta fibers)
interneuons in higher and lower segments elicit an intersegmental reflex
axon terminals ascend/descend through lissauer’s tract
efferent outcome:
flexors are excited and extensors are inhibited (limb is pulled away from noxious stimuli)
- this only happens in UE flexor reflex
describe how the crossed extension reflex works
built upon flexor reflex
noxious stimuli is recieved and travels to SC via nociceptive axons
interneurons alternate excitatory vs inhibitory
efferent result:
- ipsilateral side = flexors are excited and extensors are inhibited (flexor reflex)
- contralateral side = extensors are excited and flexors are inhibited
this combo of effects allows the affected limb to withdrawal while allowing the unaffected limb to extend to maintain balance
describe how the mm stretch reflex works (aka DTR or myotatic reflex)
example = patellar tendon reflex
afferent = mm spindle in quads
alpha motor neurons in quads are activated
- myotatic reflex- monosynaptic
- intrasegmental reflex - afferent/efferent at same lvl
alpha motor neurons in HS are inhibited
- via interneurons
- intersegmental reflex - afferent/efferent at diff. lvl
total effect = knee ext/knee jerk reflex
biceps reflex spinal level and nerve
C5
musculocutaneous
brachioradialis reflex spinal level and nerve
C6
radial n
triceps reflex spinal level and nerve
C7
radial n
patellar (quads) reflex spinal level and nerve
L4
femoral n
achilles (gastroc/soleus) reflex spinal level and nerve
S1
tibial n
true deep tendon reflex is controlled by what? how does this work?
controlled by GTO
excitatory AND inhibitory neurons
total effect depends on which interneurons are activated
has temporal/serial and spatial/parallel patterns
motor units exerting heavily will be inhibited (protective)
involved in size principle during motor recruitment; helps the right size mm fibers be recruited
importance of GTO reflex
allows fine adjustments of force production during ordinary motor activities
initiates additional forms of autogenic inhibition at higher tension levels
what causes the clinical presentation of “clasp knife effects”
constant resistance results to autogenic inhibition through GTO reflex
like PNF?
describe how reflexes can be modulated by the UMN system
mm spindle- Ia fiber conducts signal to SC
various segments = spinal reflex
higher levels = conscious perception and unconscious information of mm contraction
can be overwritten by higher level cortical motor systems
i.e. some people have to be distracted to test DTR
how are CPGS foundational for locomotion
can control rhythmic alternating mobility pattern
no supraspinal control - cat can still walk on treadmill with SC cut
no sensory feedback needed
i.e. stepping reflex in babies
CPG neurons
propriospinal neurons (specialized interneurons)
CPG neurons form what tract and what does it control
fasciculus proprius
tracts coordinate 4 limb locomotion
at what points with walking do you need control from UMN regions
gait patterns, reach, grasp, etc
at start and stop of movement
i.e. if you are walking and suddenly trip on something and need to catch yourself
CPGs relation to locomotion provides a new hope for what
locomoting pathologies
i.e. stroke, TBI, PD, SCI, etc
voluntary locomotor regions are continuous components of what
reticular formation
what are the 2 voluntary locomotor regions
- diencephalic locomotor region (DLR) - in thalamus
- mesencephalic locomotor region (MLR) - boundary of midbrain and pons/pedunculopontine junction
function/regulation of voluntary locomotor regions
still regulated by hierarchical control system
functions to coordinate CPGs
