Motor Control: Reflexes Flashcards
What are the cortical reflexes
Placing and Hopping Reaction
What are the brainstem/midbrain reflexes
Vestibular righting reflex suckle yawn eye/head movements
What are the spinal reflexes
stretch
golgi tendon
crossed extensor
What requires cortical and subcortical involvement
Volitional motion
What is the appearance of a myotactic reflex
contraction of stretched muscle
What is a myotatic reflex initiated by
muscle spindle
What components are found in a muscle spindle
afferent and efferent components
What forms the bulk of the muscle
extrafusal fibers
What are characteristics of a sensory portion of a muscle spindle
Not contractile, sensitive to length, have two sensors.
What do Ia fibers innervate
nuclear bag and nuclear chain
What is the Ia fiber sensitive to
length of muscle, and how fast the length is changing
What are characteristics of the Secondary Afferent
smaller, myelinated Group II fiber
only nuclear chain
sensitive to length of muscle
What is innervated by a gamma motorneuron
Intrafusal contractile elements
What is the purpose of a gamma motorneuron
control length of sensory portion
Within spinal cord, what does the Ia fiber synapse to
alpha motorneuron innervating stretched muscle
How is the antagonist muscle relaxed during a reflex
Ia afferent interacts with interneuron that inhibits alpha motorneuron of antagonist muscle
What is the appearance of a golgi tendon reflex
abrupt relaxation of contracted muscle to protect it from damage. Is polysynaptic
What type of fiber is the golgi tendon reflex
Ib fiber to spinal cord
What do recovery of reflexes come from
axonal sprouting below level of transection, or expression of phenotypes that are self activating
What causes decerebrate posturing
loss of all structures rostral to pons (caudal to red nucleus)
What causes rigidity
continual activation of alpha-motorneurons, maintains muscle contraction
What causes spasticity
Continual activation of gamma motorneurons, which contracts intrafusal muscle and lengthen nuclear bag/chain
What is the characteristic movement of rigidity
resists motion in all directions
what is the characteristic movement of spasticity
resists movement in a given direction
What is the function of the brainstem facilitatory region
makes muscle spindle more senstitive by activating gamma neurons. Spontaneously active.
What ist he function of the brainstem inhibitory region
makes muscle spindle less sensitive by inhibiting gamma motorneurons, which requires activation from cortical regions
What does decorticate posturing look like
flexion of upper limb joints, extension of lower limbs, dependent on head position
What causes flexion of upper limbs in decorticate posturing
disinhibition of red nucleus and its control of UE flexors
What causes extension of lower limbs in decorticate posturing
disinhibition of reticulospinal and vestibulospinal pathways
What is decorticate posturing commonly associated with
strokes in vicinity of internal capsule
