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Neuroscience I > Motor Control Reflexes Lecture (Dr. Karius) TEST 3 > Flashcards

Motor Control Reflexes Lecture (Dr. Karius) TEST 3 Flashcards

1
Q

Motor Control Reflexes

A

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*****

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2
Q

Distinguish between Reflex Activity and Volitional Movement

A

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!!!!!
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3
Q

Motor Control: Myotatic Reflex

A

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
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4
Q

Muscle Spindle

A

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!!!!!!*

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5
Q

Sensory Portion of Muscle Spindle

A

CHARACTERISTICS:
- NOT Contractile

  • Is the portion SENSITIVE to LENGTH
  • Is actually TWO SENSORS, with different Afferents
    a) NUCLEAR BAD Fiber
    b) NUCLEAR CHAIN Fiber
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6
Q

Primary Afferent

A

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!!!!!

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7
Q

Secondary Afferent

A

CHARACTERISTICS:
- Smaller, MYELINATED Group II Fiber

  • Innervates only the NUCLEAR CHAIN Fiber
  • Sensitive only to LENGTH of the MUSCLE!!!!!!!
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8
Q

Primary Vs Secondary Afferent

A

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.
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9
Q

Motor Portion consists of the Intrafusal Contractile Elements

A

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

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10
Q

Alpha vd Gamma Motoneurons

A

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.
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11
Q

Motor Contro: Myotatic Reflex

A

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!!!!!!!

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12
Q

Reciprocal Inhibition

A
  • There is a DECREASE in the activity of the Alpha Motoneuron Innervating the ANTAGONISH Muscle

—->

Allowing it to RELAX and LENGTHEN!!!!

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13
Q

Golgi Tendon Reflex

Introduction

A

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
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14
Q

Golgi Tendon Organs

A
  • 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)*
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15
Q

Golgi Tendon Reflex Steps

A

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

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16
Q

Muscle Spindle and Golgi Tendon Reflexes

A

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.
17
Q

Modification of Reflexes

A

** Nociceptors Mechanoreceptors: Influence from Higher Up in the Brain Stem can be INHIBITORY!!!

18
Q

Spinal Shock

A
  • 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)!!!!!
19
Q

Decerebrate Posturing

A
  • Results from LOSS of ALL Structured ROSTRAL to the PONS!!!!!!!
20
Q

Rigidity

A
  • 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

21
Q

Spasticity

A
  • 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

22
Q

Motor Control- SPASTICITY

A

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!!!!

23
Q

Spasticity vs Rigidity

A

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
24
Q

Decorticate Posturing

A 
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

25
Q

Spinal Shock vs Decorticate Posture vs Decerebrate Posture

A

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.
26
Q

Which of the Following Reflexes Requires CORTICAL Input?

A
  • HOPPING Reaction
27
Q

Which of the Following Innervates the INTRAFUSAL Muscle Fibers (Contractile Elements)?

A
  • GAMMA MOTONEURON
28
Q

Complete Relaxation of the Muscle. What Fiber type is produced in this Response?

A
  • 1B Fiber!!!
29
Q

How Many Synapses in the Spinal Cord are required for this Relaxation Reflex?

A
  • 2 Synapses
30
Q

What receptors is most likely found on the Alpha Motoneuron as part of this Relaxation Reflex?

A
  • GLYCINE!!!

** Found in the Spinal Cord!!!

Glycine Receptor:

1) A Subunit: Glycine Binding
2) B Subunit: Structural
* BLOCKED by STRYCHNINE!!!!!*

Neuroscience I (18 decks)

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