Motor Control Reflexes - 4/20 Karius Flashcards
Appearance of myotatic reflex?
Purpose?
Characteristics?
Contraction of a stretched muscle
Protect muscle from tearing due to stretch
Initiated by muscle spindle
Monosynaptic, segmental reflex
The sensory component of intrafusal fibers are located where?
Motor component?
Center
Periphery
What are the characteristics of the sensory part of a muscle spindle?
Not contractile
Portion sensitive to length
Nuclear bag and chain fibers
The primary Afferent fiber of the intrafusal muscle fiber innervates what?
What kind of fiber?
Sensitive to what?
Nuclear bag and chain
Large, myelinated Ia fiber
Length of muscle
How fast the length is changing
Secondary afferent associated with the muscle spindle are what type of fiber?
Innervates what?
Detects what?
Group II (smaller diameter, less myelin)
Only nuclear chain
Only length
The motor portion of the muscle spindle is innervated by what?
Controls what?
Renders the sensory component what?
Gamma motor neuron
Length of sensory component
More sensitive to superimposed stretch
Does activity of the gamma motor neuron directly lead to motion?
Alpha?
NO
YES
How is the motor neuron excited?
Causes what?
Activation of Ia afferent
Contraction relieves the stretch, returning Ia discharge rate back to normal
Reciprocal inhibition allows for what between the agonist and antagonist?
Decrease activity of the alpha motor neurons innervating the antagonist muscle, allow it to relax and lengthen
Appearance of Golgi tendon reflex?
Purpose?
Characteristics?
Sudden abrupt relaxation of a contracted muscle
Protect muscle from damage due to excessive force
Initiated by Golgi tendon organ
Polysynaptic, segmental reflex
Golgi tendon organs innervated by what type of fiber?
APs?
Ib fiber
INC w/tension
In spinal shock are the neurons producing the reflex below the level of the transection intact? What happens?
YES
Reflex fails to occur anyway
Recovery of spinal shock results from?
Expression of what self-activating receptor?
Axonal sprouting below the level of the transection
5HTC receptor
Decerebrate posturing results from what?
Loss of all structures rostral to pons
What happens when the brainstem facilitatory region is active?
When is it active?
Activates the gamma-motor neurons, making the muscle spindle more sensitive
Spontaneously
What does the brainstem inhibitory region inhibit?
When is it active?
Gamma motor neurons, making muscle spindle less sensitive
Requires activation from cortical regions
Describe spasticity
When does contraction start?
Patient resists a passive stretch of their muscles
Contraction doesn’t start until the stretch occurs
What kind of reflex? Involves what motor neurons?
Cause?
Hyperactive myotatic reflex due to INC gamma motor neuron firing
Damage to cortex abolishes activation of brainstem inhibitory region
Describe rigidity
What neurons are involved?
Cause?
Contraction of muscles in absence of others
Alpha-motor neurons continually active
Loss of cortical influence that inhibits alpha-motor neurons
Describe decorticate posturing (rigidity) characteristics
Flexion of upper limb joints
Extension of lower limbs
Dependent on head position
In decorticate posturing, if the head is turned to the right, describe the motions of the right and left arms
Left arm flexes
Right arm extends
How can unilateral decorticate posturing occur?
Strokes near internal capsule (common)
Spinal shock is what?
Reflexes?
Cause?
Transection of spinal cord
All reflexes abolished
Hyperpolarization of spinal neurons due to loss excitatory input from cortex
Which motions require cortical input?
Placing reaction
Hopping reaction
What reflexes require brainstem/midbrain?
Vestibular Righting reflex Suckle Yawn Eye/head movements
Where does volitional activity originate?
Cortical areas associated with judgement, initiative, and motor control
