Motor Systems Flashcards
what is the descending system?
upper motor neurons
what does the descending system consist of?
motor cortex, and BS centers
what are the SC and BS circuits?
local circuit neurons and motor neuron pools (lower motor neurons)
where does the LMN get commands from?
UMNs and local circuitry
what are the LMNs?
alpha motor neurons and gamma motor neurons
convey signals to the intrafusal and extrafusal muscle fibers
what are alpha motor neurons?
large myelinated
extrafusal (typical muscles fibers that are contractible)
somatotopic organization
bodies in the ventral horn
what is the motor neuron pool?
group of alpha motor neurons innervating one muscle
what is the somatotopic organization of the motor pool?
medial ventral horn-proximal muscles
lateral ventral horn-distal muscles
ventral ventral horn-extensors
dorsal ventral horn-flexors
what is the spatial distribution of the motor pool?
extends several SC segments
longitudinal distribution
what are gamma motor neurons?
medium myelinated
intrafusal (in the middle of the muscle spindle)
bodies in the ventral horn
3 parts: muscle spindles, efferent connections, and afferent connection
axons terminate at contractile portion of spindle
all 3 fibers (bag static and dynamic and chain)
what are muscle spindles
sensory receptor in muscle
in belly of muscles (thickest part)
group 1a and 2 afferents and gamma motor neuron
what are the roles of muscles spindles?
detect absolute muscle length and changes in muscle length
fine regulation of muscles length during movement
active lengthening and shortening and passive lengthening
high spindle density= ___ motor control
fine
intrafusal fibers
nuclear bag fibers and nuclear chain fibers within the muscle
nuclear bag fibers
static: detects changes in muscle length
dynamic: detects rate of change in muscle length
spherical nuclei
elastic
stretches quickly
nuclear chain fibers
static: only detects change in muscle length, not rate for change
single row of nuclei
less elastic
stretches slowly
long/sustained stretch
group 1a afferents
large diameter
faster
myelinated
wrap around equatorial region of bag and chain fibers (non contractile region)
rate of change (dynamic/phasic)
fire with acute change in muscle length but not when there’s a sustained change
stops firing when there’s no longer an ongoing change
group 2 afferents
medium diameter
slower
myelinated
next to equator in polar region (contractile region)
steady state-tonic
static lengthened/shortened=constant firing
which causes more afferent activity: a passive stretch or active shortening?
passive stretch causes more afferent activity
what are gamma dynamic fibers?
activate only nuclear bag fibers ]
enhance response of group 1a neurons by adjusting sensitivity of dynamic bag
what are gamma static fibers?
activate nuclear chain and bag fibers
enhances response of group 1a and 2 neurons
what is alpha-gamma co-contraction?
intra and extrafusal fibers contracting together
just alpha activated-fiber on slack w/o gamma activation
when both neuron are activated, muscle spindle can operate entirely at an muscle length
golgi tendon organ (GTO)
sensory receptors
located at MTJ
1b afferent fibers
rod woven into collagen fibers
- contraction-tight-squeezes GTO
- stretch-distortion of GTO
large myelinated axon
no efferent connection
what is the role of the GTO?
sensitive to tension changes from stretch, contraction, or loading (tonic)
responds to muscles output in response to fatigue
- fatigued muscle=reduced GTO firing, but can still fire some
what is the firing pattern of the GTO?
muscle passively stretched-less GTO activity
muscle actively contracted-more GTO activity
response of GTO and 1b afferents are more sensitive to active changes in muscle length
motor function of the SC
integrate somatosensory info
controls of voluntary movement
refine movement plan
what is reciprocal inhibition?
involves inhibitory interneurons
activation of 1a afferents synapsing onto inhibitory interneurons results in inhibition of the alpha MN innervating the antagonist
when muscle is contracting, antagonist is inhibited
what is muscle synergy?
group of muscles controlled as a unit
what is the body schema?
proprioceptive model created by the SC
developed over time
neural rep of body to plan and adapt movement in the SC
nonconscious process
GTO during gait
stretch of GS tendon activates GTO
stance phase-loaded-GTO activation-autogenic activation of own muscles
unloaded-GTO activated-autogenic inhibition of on muscle
locomotor central pattern generator
network of spinal interneurons to generate rhythmic, alternating activities of flexion and extension at hips and knees
flexor activated-extensor inhibited
tonic input
ankle needs more proprioceptive input
loaded GTO activated=prolonged stance phase
what is autogenic excitation?
monosynaptic: only one synapse to cross
faster
less room for other inputs
less modifiability
what is reciprocal inhibition
disynaptic: has to cross 2 synapses
slower
more room for other circuits to modify the output
what is the clinical importance of the stretch reflex?
determine integrity of reflex, state of activity of alpha MN pool, and DTR to see if it’s hyperreflexive/hyporeflexive
GTO reflexes
disynaptic
autogenic inhibition: inhibits own muscle when fully contracted to prevent further contraction
- facilitate antagonist
reciprocal excitation: exciting the antagonist
- protective mechanism
what is the withdrawal reflex?
touch noxious stimuli, withdrawal limb
excite flexors, inhibit extensors
what is the crossed-extension reflex?
supporting limb compensates for loss of support when the ipsilateral limb withdraws from a painful stimulus
extensors excited and flexors inhibited on contralateral limb for weight bearing
what are the cutaneous reflexes?
withdrawal reflex and crossed-extension reflex
descending systems
reflexive and voluntary movements
increased arousal leads to ___ reflex responses
heightened
relaxation/decreased arousal leads to___ reflex responses
decreased
what is muscle tone?
resistance to muscle stretch
what factors contribute to muscles tone?
descending motor commands, proprioceptive info, weak cross bridge binding, and titan
what is co-contraction?
simultaneous contraction of agonist and antagonist muscle to stabilize joints
proximal stabilization
increases stiffness
what is the function of the primary motor cortex?
voluntary controlled movements
what is the function of the premotor area?
controls of trunk and girdle muscles, anticipatory postural adjustments
what is the function of the supplementary motor area?
initiation of movement, orientation planning, bimanual and sequential movements
what is the function of Broca’s area?
motor programming of speech (usually in L hemisphere)
speech production
fine motor function
cerebral cortex
lateral corticospinal and rubrospinal tracts
postural and gross motor functions
BS
medial and lateral vestibulospinal, reticulospinal, and medial corticospinal tracts
ambulatory function
BS and SC
BS can turn on/off
details by CPG
