Motor Reflexes Flashcards
Cortical motor reflexes (2)
Placing reaction
Hopping reaction
Brainstem/Midbrain reflexes (5)
Vestibular Righting reflex Suckling Yawning Eye/head movements
Spinal reflexes (3)
Myotatic
Golgi tendon
Crossed extensor
How many synapses in a myotatic reflex?
Monosynaptic
What are the intrafusal fibers vs. extrafusal fibers?
Intrafusal fibers are within a capsule and extrafusal fibers are the noticable fibers.
Intrafusal fibers have both:
Motor and sensory components
Components of sensory portion of muscle spindle:
Nuclear bag
Nuclear chain
What is the sensory portion sensitive to?
Sensitive to length of fibers
What kind of nerves innervate the nuclear bag and chain? What are they sensitive to?
Ia fibers.
Length of muscle and how fast it is changing.
When the sensory component senses changes in length, what happens?
An increase in APs
Secondary afferent is what kind of fiber?
Innervates what?
Sensitive to?
Fiber: group II fiber
Innervates: nuclear chain fiber
Sensitive to: only length of muscle.
What innervate the motor portion of the intrafusal part of the muscle spindle?
What is the motor neuron’s job?
Gamma motorneuron.
Controls the length of the sensory portion.
When the intrafusal muscle contracts, what happens to the sensory portion?
The sensory portion stretches and is now more sensitive to a superimposed stretch
What happens in the antagonist with the synapsing?
Ia afferent synapses on both the motoneuron of the strecthed muscle and the alphamotoneuron of the antagonist
Appearance of golgi tendon reflex:
Purpose:
Sudden relxation of a contracted muscle.
Protect the muscle from damage from excessive force.
How many synapses in the golgi tendon reflex?
Polysynaptic
What does the GTO innervate?
What kind of fiber do they use?
The tendon.
Ib to the SC.
Synaptic setup of the GTO
Ib from GTO activates the interneuron which inhibits the motoneuron.
How do the higher centers of the brain effect reflexes?
They generally inhibit them
Spinal shock
Temporary loss of reflexes after an injury to the SC.
How does one overcome spinal shock?
Axons sprout below the level of the lesion.
Express self-activating receptors (serotonin).
Decerebrate posturing looks like:
What causes it?
Extermities extended with wrists flexed at sides.
From loss of structures rostral to pons.
What causes rigidity?
Continual activation of alpha-motoneurons
What causes spasticity
Continual activation of gamma-motoneurons.
Brainstem facilitory region
Activates gamma-motoneurons by making muscle spindle more sensitive.
Brainstem inhibitory region
Inhibits gamma-motoneurons making muscle spindles less sensitive.
Requires activation from cortical regions.
End result of cortical damage on positioning:
Brainstem inhibitory region is NOT activated and facilitory region dominates. This leaves brainstem to dominate and causes spasticity.
Decorticate posturing
Flexion of UE
Extension of LE
Depending on head position
When will I see decorticate positioning?
Strokes in the internal capsule
