Motor Control Reflexes Lecture (Dr. Karius) TEST 3 Flashcards
Motor Control Reflexes
CORTICAL:
- Placing Reaction
- Hopping Reaction
BRAINSTEM/MIDBRAIN:
- Vestibular
- Righting Reflex
- SUCKLE
- YAWM
- Eye/ Head Movements
SPINAL REFLEXES:
- Stretch (Myotatic)
- Golgi Tendon Reflex
- Crossed Extensor
- **IMPORTANT NOTE:
- Reflexes, in order to be effective, must be very “PRECISE”. This “Precision” can make Reflexes look like VOLITIONAL MOVEMENT
A REFLEX Movement occurs FASTER than the Fastest Voluntary Motion*****
Distinguish between Reflex Activity and Volitional Movement
REFLEX ACTIVITY:
- Precise Motions in response to AFFERENT Stimuli
- Mediated at all levels of the CNS
- Rapid Initiation
- Many elicited even during UNCONSCIOUSNESS
VOLITIONAL ACTIVITY:
- Originates in CORTICAL AREAS associated with Judgement, Initiative, and Motor Control
- Longer ONSET LATENCY due to Processing
- Require CONSCIOUS AWARENESS!!!!!
Motor Control: Myotatic Reflex
Myotatic (Stretch) Reflex
APPEARANCE:
- Contraction (Shortening) of a Stretched Muscle
PURPOSE:
- PROTECT Muscle from tearing due to STRETCH
CHARACTERISTICS:
- Initiated by MUSCLE SPINDLE
- MONOSYNAPTIC, SEGMENTAL Reflex
Muscle Spindle
Embedded INTO the Muscle
1) Extrafusal Fibers:
- What you see when you look at a Muscle. Doing the Work
2) INTRAFUSAL FIBERS:
- Parallel to Extrafusal Fibers
- Several different types of Fibers WITHIN Muscle Spindle
- AFFERENT (Sensory) and EFFERENT (Muscle)
Intrafusal Fibers f the Muscle Spindle have BOTH MOTOR (Peripheral) and SENSORY (Center) Components!!!!!!*
Sensory Portion of Muscle Spindle
CHARACTERISTICS:
- NOT Contractile
- Is the portion SENSITIVE to LENGTH
- Is actually TWO SENSORS, with different Afferents
a) NUCLEAR BAD Fiber
b) NUCLEAR CHAIN Fiber
Primary Afferent
CHARACTERISTICS:
- Innervates BOTH the NUCLEAR BAG Fiber and NUCLEAR CHAIN Fiber
- Large, MYELINATED 1A FIBER
- Sensitive to Both:
a) Length of Muscle!!!
b) How fast the Length is Changing!!!
Get more Action Potentials with MORE STRETCH and FASTER Stretch!!!!!
Secondary Afferent
CHARACTERISTICS:
- Smaller, MYELINATED Group II Fiber
- Innervates only the NUCLEAR CHAIN Fiber
- Sensitive only to LENGTH of the MUSCLE!!!!!!!
Primary Vs Secondary Afferent
PRIMARY:
- Large 1A fiber (heavily Myelinated, Fast Velocity, low threshold)
- Innervates both NUCLEAR BAD and NUCLEAR CHAIN fiber
- Detects LENGTH and CHANGE in LENGTH
SECONDARY:
- Group II fiber (smaller diameter, less myelin, still pretty fast)
- Innervates only NUCLEAR CHAIN fiber
- Detects only LENGTH.
Motor Portion consists of the Intrafusal Contractile Elements
CHARACTERISTCS:
- Same as SKELETAL MUSCLE
- Innervaed by a GAMMA MOTONEURON
- CONTROL THE LENGTH OF THE SENSORY PORTION!!!!!!!
1) By CONTRACTING the Intrafusal Muscles, we stretch the Sensory Portion:
- This renders the Sensory Portion MORE SENSITIVE to a SUPERIMPOSED STRETCH
Alpha vd Gamma Motoneurons
ALPHA:
•Large, heavily Myelinated fiber
- Innervates (via NMJ) the skeletal muscle
- Responsible for ACTIVATING MUSCLE
- Activity directly leads to MOTION.
GAMMA:
•Slightly smaller, slower than alpha. Still fast overall.
- Innervates the CONTRACTILE component of the muscle spindle via NMJ
- Activity causes CONTRACTION
- Controls SENSITIVITY of Muscle Spindle
- Activity does NOT directly lead to motion.
Motor Contro: Myotatic Reflex
1A Afferent: DORSAL
Alpha Motorneuron: VENTRAL
1) The Motorneruon is EXCITED by the activation of the 1A Afferent!!!
2) Contraction relieves the STRETCH, returning the 1A Discharge Rate back to Normal
Myotatic Reflex:
1) We elicit the Stretch Reflex
2) The ANTAGONIST Muscle gets STRETCHED
* ***RECIPROCAL INHIBITION!!!!!!!
Reciprocal Inhibition
- There is a DECREASE in the activity of the Alpha Motoneuron Innervating the ANTAGONISH Muscle
—->
Allowing it to RELAX and LENGTHEN!!!!
Golgi Tendon Reflex
Introduction
GOLGI TENDON REFLEX:
- INVERSE Myotatic
- Autogenic Inhibition
APPEARANCE:
- Sudden (Abrupt) RELAXATION of a Contracted Muscle
PURPOSE:
- Protect Muscle from DAMAGE due to EXCESSIVE FORCE
CHARACTERISTICS:
- Initiated by GOLGI TENDON ORGAN
- POLYSYNAPTIC, Segmental Reflex
Golgi Tendon Organs
- Innervate Tendon
- Bare Nerve Ending with LOTS OF BRANCHES
- Action Potentials INCREASE WITH TENSION
- 1B Fiber to SPINAL CORD!!!!
- (Shuts off the Alpha Motoneuron Totally)*
Golgi Tendon Reflex Steps
1) The Motoneuron is INHIBITED but e activation of the Spinal INTERNEURON
2) Abrupt Relaxation of the Muscle occurs, returning the GOLGI TENDON Organ Discharge rate BACK TO NORMAL
Muscle Spindle and Golgi Tendon Reflexes
MYOTATIC REFLEX:
•Initiated by Muscle Spindle
- PASSIVE STRETCH of the muscle
- MONOSYNAPTIC reflex
- CONTRACTION of Stretched Muscle BACK to Normal Length.
GOLGI TENDON (Reverse Myotatic) •Initiated by GOLGI TENDON
- Active CONTRACTION of muscle
- POLYSYNAPTIC Reflex
- ABRUPT RELAXATION of contracted muscle to PREVENT DAMAGE.
Modification of Reflexes
** Nociceptors Mechanoreceptors: Influence from Higher Up in the Brain Stem can be INHIBITORY!!!
Spinal Shock
- Even though the Neurons producing the REFELX are BELOW the Level of the TRANSECTION (And are therefore Intact), the Reflex FAILS to OCCUR
RECOVERY is believed to RESULT FROM:
- AXONAL SPROUTING below the Level of the TRANSECTION!!!
- Expression of Receptor Phenotypes that are SELF-ACTIVATING (5HTC Receptor)!!!!!
Decerebrate Posturing
- Results from LOSS of ALL Structured ROSTRAL to the PONS!!!!!!!
Rigidity
- Resists Motion in ALL DIRECTIONS
- Results from MAINTAINED MUSCLE CONTRACTION
- Continual Activation of ALPHA- MOTONEURONS:
a) NOT Due to REFLEXES
b) Brainstem is Activating ALPHA Motoneurons, but why is NOT CLEAR
Spasticity
- Resits Motion in a GIVEN DIRECTION
- MYOTATIC Reflex HYPERACTIVE
- Continual Activation of GAMMA- MOTONEURONS:
a) Contracts INTRAFUSLA Muscle
b) Lengthens NUCLEAR BAD/ CHAIN Fibers
c) Brainstem
Motor Control- SPASTICITY
1) BRAINSTEM FACILITATORY REGION:
a) By activating the Gamma- Motoneurons, makes Muscle Spindle MORE SENSITIVE
b) This region is SPONTANEOUSLY ACTIVE
2) BRAINSTEM INHIBITORY REGION:
a) INHIBITS Gamma Motoneurons, making Muscle Spindle LESS SENSITIVE
b) This region requires ACTIVATION from CORTICAL REGIONS
3) With the LOSS of the CORTEX, the Brainstem (-) Region is NOT ACTIVATED, leaving the (+) Region to DOMINATE!!!
Result:
- Uncontrolled Banister Facilitatory Region is STRETCH REFLEXES that Fight any PASSIVE MOTION, SPASITICITY!!!!
Spasticity vs Rigidity
SPASTICITY:
• Patient RESISTS a PASSIVE Stretch of their muscles
- The contraction doesn’t start until the stretch occurs
- HYPERACTIVE Myotatic reflex due to INCREASED Gamma motoneuron firing.
- CAUSE: DAMAGE to Cortex that ABOLISHES Activation of the brainstem INHIBITORY region (brain arousal systems)
RIGIDITY:
• CONTRACTION of muscles in the ABSENCE of other stimuli.
- Alpha-motoneurons continually active
- CAUSE: LOSS of CORTICAL INFLUENCE that INHIBITS a medullary input to the Alpha-motoneurons
Decorticate Posturing
DECORTICATE POSTURING (Rigidity) - FLEXION of the UPPER Limb Joints
- EXTENSION of the LOWER Limbs
- Dependent on HEAD POSITION
**Unlike the DECEREBRATE Posturing, Decorticate Posturing is DEPENDENT on Head Position and will CHANGE as the Head is moved PASSIVELY
- **You are Extremely likely to see Patients with UNILATERAL Decorticate Posturing:
a) Results from STROKES in the Vicinity of the INTERNAL CAPSULE
b) A Relatively COMMON SITE for STROKE
Spinal Shock vs Decorticate Posture vs Decerebrate Posture
1) SPINAL SHOCK:
• Transection of the SPINAL CORD
- All reflexes ABOLISHED, even if circuit is intact
- CAUSE: HYPERPOLARIZATION of Spinal Neurons due to loss of excitatory input from cortex?
2) DECORTICATE POSTURE:
• INTERNAL ROTATION of LEGS in EXTENDED position; FLEXION of ARMS; dependent on head position.
- May be BILATERAL or UNILATERAL.
- LOSS OF LOCAL INPUTS – most commonly caused by lesion of internal capsule in humans.
3) DECEREBRATE POSTURE:
• Contraction of all ANTI-GRAVITY Muscles (arms in extension)
- Loss of input from all structures ROSTRAL to the PONS.
- Usually BILATERAL and INDICATIVE of Severe Brain Injury.
Which of the Following Reflexes Requires CORTICAL Input?
- HOPPING Reaction
Which of the Following Innervates the INTRAFUSAL Muscle Fibers (Contractile Elements)?
- GAMMA MOTONEURON
Complete Relaxation of the Muscle. What Fiber type is produced in this Response?
- 1B Fiber!!!
How Many Synapses in the Spinal Cord are required for this Relaxation Reflex?
- 2 Synapses
What receptors is most likely found on the Alpha Motoneuron as part of this Relaxation Reflex?
- GLYCINE!!!
** Found in the Spinal Cord!!!
Glycine Receptor:
1) A Subunit: Glycine Binding
2) B Subunit: Structural
* BLOCKED by STRYCHNINE!!!!!*
