Motor Control: Reflexes Flashcards
Motor Control:
Cortical
- Placing reaction
* hopping reaction
Motor Control:
Spinal Reflexes
- stretch (myotatic)
- golgi tendon reflex
- crossed extensor
Motor Control:
Brainstem/Midbrain
- vestibular
- righting reflex
- suckle*
- yawn*
- eye/head movements*
- contraction (shortening) of a stretched muscle
- Protect muscle from tearing due to stretch.
- initiated by MUSCLE SPINDLE.
- MONOSYNAPTIC, segmental reflex.
myotatic reflex
myotatic reflex:
-Contains both afferent (sensory) and efferent (contractile) components
MUSCLE SPINDLE
myotatic reflex:
- Because the capsule is “fusiform”, the fibers within the capsule are called?
intrafusal fibers
myotatic reflex:
- The muscle fibers that make up the bulk of the muscle are called the?
extrafusal fibers
myotatic reflex:
- The intrafusal fibers of the muscle spindle have both ? and ? components
motor and sensory
myotatic reflex: ? •is not contractile. •Is the portion sensitive to length. •Is actually TWO sensors - with different afferents - ? - ?
- The sensory portion of a muscle spindle
- nuclear bag fiber
- nuclear chain fiber
myotatic reflex:
Nuclear chain and bag are innervated by?
1a fiber (primary afferent)
large and myelinated
myotatic reflex:
Primary afferent is sensitive to both:
- ?
- ?
- length of muscle
* how fast the length is changing.
myotatic reflex:
Secondary Afferent Characteristics:
- smaller, myelinated ? fiber
- innervates only the ?.
- sensitive only to the ? of the muscle.
- Group II
- nuclear chain fiber
- length
myotatic reflex:
The motor portion consists of the?
intrafusal contractile elements
myotatic reflex:
intrafusal contractile elements characteristics:
- same histology as ?
- innervated by a ?.
- Control the ? of the sensory portion **
- skeletal muscle
- gamma motoneuron
- length
myotatic reflex:
- Within the spinal cord, the Ia afferent from the muscle spindle synapses directly onto the ? innervating the stretched muscle.
alpha- motoneuron
- 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 reflex
(aka inverse myotatic)
(aka autogenic inhibition)
- innervate tendon
- bare nerve ending with lots of branches.
- Action potentials increase w/ tension.
- Ib fiber to spinal cord. **
Golgi Tendon Organs
Golgi Tendon reflex:
- The motoneuron is inhibited by the activation of the spinal ? (via release of ?)
- Abrupt relaxation of the muscle occurs, returning the Golgi Tendon organ discharge rate back to normal
- interneuron
- GABA
The ? centers of the brain are often seen to be inhibitory to the reflexes, but certain regions do provide an excitatory input. This is called ?
- higher
- Central Modification
Even though the neurons producing the reflex are below the level of the transection (and are therefore intact), the reflex fails to occur.
Spinal Shock
Recovery of reflexes from Spinal Shock is believed to result from:
- ?
- ?
- Axonal sprouting below the level of the transection.
* Expression of receptor phenotypes that are self- activating (5HTC receptor).
Results from loss of all structures rostral to the pons (caudal to the red nucleus).
Decerebrate Posturing
Decerebrate Posturing:
•resists motion in all
directions.
•Results from maintained
muscle contraction.
•Continual activation of
ALPHA-MOTONEURONS
- Brainstem is activating alpha – motoneurons
Rigidity
Decerebrate Posturing:
•resists motion in a given
direction.
•Myotatic reflex
hyperactive.
•Continual activation of GAMMA-MOTONEURONS - contracts intrafusal muscle. - Lengthens nuclear bag/chain fibers. - brainstem
Spasticity
Spasticity:
- by activating the gamma-motoneurons, makes muscle spindle more sensitive.
- This region is spontaneously active.
Brainstem facilitatory region
Spasticity:
- inhibits gamma motoneurons, making muscle spindle less sensitive.
- This region requires activation from cortical regions.
Brainstem inhibitory region
Spasticity:
- With the loss of the cortex, the ? region is not activated, leaving the ? to dominate.
- brainstem (-)
- (+) region
•Flexion of the upper limb joints (disinhibition of red nucleus & its
control of UE flexors).
•Extension of the lower limbs (disinhibition of reticulospinal and
vestibulospinal pathways)
•Dependent on head position (release of postural reflexes)
Decorticate posturing (rigidity)
(likely unilateral)
(results from strokes in the vicinity of the internal capsule
• a relatively common site for a stroke.
Decorticate posturing (rigidity)
-likely unilateral
- results from strokes in the vicinity of the ?
- a relatively common site for a ?.
- internal capsule
- stroke
