Tone Flashcards
Ia
Innervate bag and chain
respond to length of muscle –> dynamic (velocity)
II
innervate chain
not velocity dependent
sensitive to absolute length
gamma motor neurons
dynamic and static
IIb: GTO
located in musculotendinous junction
in series with extrafusal fibers
can inhibit alpha motor neurons in response to tension
Phasic Reflexes (Twitchy)
- response to a change in the level of sensation to a specific receptor
- brief depression of muscle activity gives appearance of twitch
- all monosynaptic reflexes are phasic
Tonic Reflex
- emerge in response to change in level of stimulus
- sustained contraction and relatively smooth movement
- all are polysynaptic
Is stretch reflex modifiable?
- yes
- performance outcome is dependent on context
Acute damage to cerebellum results in:
- transient hypotonia
- improves gradually in parallel to recovery of muscle spindle sensitivity
anterior lobe damage
disruption in regulation of muscle spindle sensitivity, reactions to cutaneous stimuli, proprioceptive supporting reactions
Cerebellar sign
many more swings in pendular reflex
What causes clasp knife phenomena?
lesion to descending pyramidal motor system
what is clasp knife phenomena attributed to?
change in balance of reflex effects coming from muscle spindles (resist motion) and GTOs (suppress resistance)
what is spasticity manifested as?
velocity and muscle length dependent increase in resistance to externally imposed muscle stretch
What does spasticity result from?
hyper excitable descending excitatory brainstem pathways and from the resultant exaggerated stretch reflex response
reduced threshold of spinal stretch reflex
motor impairments related to but distinct from spasticity
abnormal synergies
inappropriate muscle activation and co-activation
all share similar pathophysiological signs
is spasticity manifested in active muscles?
no
only resting muscles
What can cause medial reticulospinal pathways to become hyper-excitable?
- disinhibition/ unmasking mechanisms
- unopposed excitatory descending inputs to spinal stretch reflex circuit (elevated activity of spinal motor neurons and reflex circuit OR velocity and length dependent increase)
median time to detect spasticity post-stroke
34 days
does spasticity spontaneously resolve?
rarely
what is acute spasticity ( <4 weeks) an important predictor for?
severe spasticity at 6 and 12 months
proportional recovery of spasticity
severity predicts the amount of recovery expected after stroke
what happens if spasticity is suppressed or treated aggressively during early stages of recovery ?
there is no correlated functional improvement in a later stage
spasticity is “blank” and tone is “blank”
spasticity is neural
tone is multifactorial
Neural factors of tone
- balance of descending facilitory and inhibitory influences of segmental spinal processes
- peripheral afferent processes
- predictive abilities to set gain and threshold for larger loop stretch reflexes
- orientation in space –> righting reflex
Biomechanical factors of tone
- length of muscle, length tension relationship (torque/angle = stiffness)
- visco-elastic properties of muscle and connective tissue (intrinsic muscle/ ct properties)
- speed of lengthening
- physical inertia of extremity
behavioral factors of tone
arousal, fear, pain
Negative signs
- address first
- weakness, lack of dexterity, fatiguability
positive signs
- address second
- flexor and extensor spasm
- conus
- babinski
- exaggerated cutaneous reflex
- clasp knife
- autonomic hyper reflexia
- elements of dystonia
what is the primary basis for disorders following CNS lesions?
inadequate recruitment of agonist motor neurons (negative sign)
What affects “ true” motor recovery in early stages of post cortical lesion
- spasticity and related neuromusculature impairments emerge and evolve from the same pathophysiological process of abnormal neuroplasticity
- no effective treatment to correct abnormal neuroplasticity
when is spastic functional recovery achievable?
when motor impairments are managed
- strengthen weak muscles throughout entire course of recovery
- manage spasticity in chronic stage when it impedes function
