N36 Flashcards
Local circuitry
LMN and local circuit interneurons that receive proprioceptive information and info from higher centers
Descending systems from motor cortices
UMN–>(interneurons)–>LMN for initiation and planning of voluntary movement
Cerebellum and basal ganglion
no direct access to motor neurons, control movement via regulation of UMN
Interneurons
integrate inputs from higher centers, peripheral receptors, other interneurons (final determination of which neurons are activated)
Central Pattern Generators (CPG)
interconnected interneurons that generate rhythmic outputs (timing sequence of activation and inhibition)
Spinal cord transection can still walk because
CPG of interneurons
Alpha motor neurons innervate
innervate extrafusal fibers that generate force
Alpha motor neurons receive input from
descending motor pathways and reflex circuits
Gamma motor neurons innervate
intrafusal fibers (no force)
Gamma motor neurons receive input from
descending motor pathways and reflex circuits
muscle spindles and stretch receptors monitor
Absolute muscle length and rate of change of muscle length (kinesthesia, locomotion, muscle tone)
Structure of muscle spindles
deep in belly, nuclear chain and nuclear bag fibers
Afferent innervation of muscle spindles
Primar endings: Ia, innervate chain and bag fibers are sensitive to the onset of muscle stretch
Secondary endings: II, innervate chain fibers and are sensitive to absolute length (slow adapting)
Efferent innervation of muscle spindles
GAMMA motor neurons
How can the CNS control the sensitivity of spindles to stretch?
by contracting the intrafusal muscle fibers
Stretching =
stretches the intrafusal fibers and activates the muscle spindle stretch receptors
Contracting =
extrafusal contraction, slows the rate of stretch receptor activation
alpha-gamma coactivation
Too much contraction of extrafusal fibers (alpha) causes intrafusal fibers to contract (gamma) to maintain information on muscle length
Golgi tendon organs monitor
tension (muscle length, load, and degree of fatigue)
Golgi tendon organs location
junction of tendon and muscle
Golgi tendon organs innervation
Ib unmyelinated and intertwined with collagen fibers
Golgi tendon organs tension monitoring system
connected to extrafusal fibers and contraction causes tension and firing, causing inhibition of contracting muscle and activation of antagonistic muscle
Muscle spindle and golgi tendon
muscle spindles fire when the muscle is stretched (muscle length and dynamic change in length) and golgi tendons fire when muscle is contracted (tension)
Unmyelination of Ia, Ib, II
gait impairment, errors in positioning and force
Spinal reflexes are
Fast, automatic, predictable
Mytotatic reflex
stretch receptors activated when extrafusal, intrafusal, and muscle spindles are stretched causing muscle activation
Autogenic excitation
Monosynaptic, Ia muscle spindle afferent –> alpha motor neuron of the homonymous muscle (excitation and contraction)
Synergistic Activation
Ia afferent –> alpha motor neurons of synergistic muscles causing excitation and contraction
Reciprocal Innervation
Ia afferents –> excitatory connection on an inhibitory interneuron of alpha motor neuron to antagonistic muscle (polysynaptic)
Negative Feedback Control Loops
maintain stability of system by returning it to a “set-point” or dampening the oscillations in a perturbed system (muscle spindles and golgi tendons)
Recurrent Inhibition
produced by Renshaw cells which acts to decrease the activity of a motor neuron
Renshaw cells
alpha motor neuron collateral branches innervate them and upon activation, they release inhibitory glycine to decrease the firing rate
Tetanus
inhibits the release of glycine from Renshaw cells, inhibition cannot occur and overexcitation occurs in alpha motor neurons
Strychine
poison that binds glycine receptors and causes tetanic contractions
Reciprocal inhibition
relaxation of antagonistic muscles to enhance speed and efficiency
Co-contraction
prime mover and antagonist muscles both contract to stiffen joint (precision and joint stability)
Tendon reflex
golgi tendon –> Ib afferent –> inhibitory interneurons –> inhibition of alpha motor neurons (relaxation)
another name for tendon reflex
autogenic inhibition (also excites antagonistic muscles)
Flexion reflex
sensory input –> flexion of ipsilateral limb –> inhibition of ipsilateral extensors (and opposite for contralateral limb)
Crossed extension reflex
input causes flexion of ipsilateral limb and extension of contralateral limb via
Flexor withdrawal reflex
protective reflex that results in flexion away from a noxious stimuli
Local sign
modification of the reflex response so that it reflects the area being stimulated
