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
