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Neuroendocrine Exam 2 > Motor Control: Reflexes > Flashcards

Motor Control: Reflexes Flashcards

1
Q

Cortical Reflexes

A
  • require cerebrum, but not usual parts involved in voluntary motion
  • placing rxn = hold baby in air, contact with surface will cause them to make weight bearing motion with surface
  • hopping rxn = unexpected shove > hop on side to keep from falling over
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2
Q

Spinal Reflexes

A
  • stretch/myotatic = muscle contraction in response to stretching; keeps muscle at a constant length
  • Golgi tendon = inhibitory effect on muscle resulting from muscle tension stimulating Golgi tendon organs to prevent damage
  • crossed extensor = contralateral limb compensates for loss of support when the ipsilateral limb withdraws from painful stimulus in a withdrawal reflex
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3
Q

Brainstem/Medulla Reflexes

A

vestibular, righting reflex

suckle, yawn, eye/head movements (still seen in anencephalic babies)

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4
Q

Reflexes

A

Function: protection, correct actions without conscious thought, quick response needed, needed for infants
Characteristics: involuntary, fast, short, precise, direct
Level of organization: any CNS level; don’t need cortex most of the time
Initiation: sensory input
Circuitry: fixed
Speed: fast
Specificity: high

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5
Q

Volitional Motion

A

Level of organization: needs cortical and subcortical involvement
Purpose: response to stimuli, need, desire
Initiation: higher cognition, sensory input
Circuitry: variable depending on motion
Speed: variable depending on need
Specificity: high

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6
Q

Myotatic Reflex

A
  • stretch reflex
  • contraction/shortening of stretched muscle
  • protects muscle from tearing due to stretch
  • initiated by muscle spindle
  • monosynaptic and segmental
  • passive stretch of muscle
  • contraction of stretched muscle back to normal length
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7
Q

Muscle Spindle

A
  • detects muscle stretch
  • within skeletal muscle in fusiform capsule
  • parallel to muscle fibers
  • contains afferent and efferent parts
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8
Q

Intrafusal Fibers

A
  • fibers within capsule

- motor and sensory parts

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9
Q

Extrafusal Fibers

A
  • muscle fibers making up remainder of muscle

- working part of muscle

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10
Q

Sensory Part of Muscle Spindle/Intrafusal Fiber

A
  • not contractile
  • sensitive to length
  • two sensors with different afferents: nuclear bag fiber and nuclear chain fiber
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11
Q

1A Fibers

A
  • primary afferents
  • dynamic fiber
  • innervates both nuclear bag and chain fibers
  • large, myelinated to increase conduction velocity and reduce threshold
  • sensitive to length of muscle and how quickly muscle length is changing (changes # of APs fired)
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12
Q

1B Fibers

A
  • secondary afferent
  • slightly smaller and myelinated
  • lesser conduction velocity and sensitivity so increased threshold
  • innervates only nuclear chain fiber
  • sensitive to length of muscle only
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13
Q

Motor Part of Intrafusal Fibers - Myotatic Reflex

A
  • striated like skeletal muscles
  • innervated by gamma motor neuron
  • control the length of the sensory portion of the intrafusal fiber (controls sensitivity to additional length changes)
  • smaller diameter, less myelin, lower conduction velocity, increased threshold
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14
Q

Contraction of Intrafusal Fibers

A

stretches sensory portion and makes it more sensitive to superimposed stretch

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15
Q

Gamma Motoneuron Control of Sensitivity

A
  • contraction of intrafusal contractile fibers stretches sensory portion
  • increases sensitivity of 1a and II fibers to stretch
  • overall length of muscle spindle stays same
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16
Q

Alpha Motoneurons

A
  • large, heavy myelination
  • innervates skeletal muscle extrafusal fibers via NMJ
  • activates muscle
  • activity leads directly to motion
17
Q

Gamma Motoneurons

A
  • slightly smaller, slower than alpha
  • still fast
  • innervates contractile component (intrafusal fibers) of muscle spindle via NMJ
  • activity causes contraction
  • controls sensitivity of muscle spindle
  • activity doesn’t directly lead to motion
18
Q

Golgi Tendon Reflex

A
  • reverse myotatic
  • autogenic inhibition
  • initiated by golgi tendon organ
  • active contraction of muscle
  • polysynaptic reflex (inhibitory)
  • segmental
  • abrupt relaxation of contracted muscle to prevent damage from excess force
19
Q

Synapses of Myotatic Reflex

A
  • within spinal cord, 1A afferents from muscle spindle synapses directly onto alpha-motoneuron innervating the stretched muscle
  • releases EAA > triggers EPSP in alpha motoneuron > more action potentials > contraction in stretched muscle > 1a discharge rate returns back to normal
  • 1A afferent from muscle spindle also synapses on interneuron that releases GABA or glycine
  • causes IPSP in alpha motoneuron of antagonist muscle and thus fewer action potentials (relaxation and lengthening)
20
Q

Golgi Tendon Organs

A
  • innervate tendon
  • bare nerve endings with many branches
  • action potentials increase with tension
  • tension generated by contraction of attached muscles
  • 1B fiber to spinal cord
21
Q

Synapses of Golgi Tendon Reflex

A
  • 1b afferent from golgi tendon releases EAA at interneuron
  • spinal interneuron releases GABA
  • causes IPSP in alpha motoneuron of contracting muscle
  • fewer APs causes less tension in muscles
  • abrupt relaxation of muscle occurs returning golgi tendon organ discharge rate back to normal
  • high threshold needed for reflex to kick in because don’t want it to kick in until tendon is compromised
22
Q

Central Modification of Reflexes

A

higher centers of brain often inhibitory of reflexes

some regions provide excitation

23
Q

Spinal Shock/Transection

A
  • loss of reflexes bc excitatory inputs have been lost although circuitry/neurons is still intact
  • spinal neurons become hyperpolarized
  • reflex recovery comes from axonal sprouting below level of transection (looking for new input) and from expression of receptor phenotypes that are self-activating such as 5HTC receptor
24
Q

Brainstem Facilitatory Region

A
  • associated with reticular activation system
  • activates gamma moto neurons and makes muscle spindles more sensitive
  • spontaneously active
25
Q

Brainstem Inhibitory Region

A
  • inhibit gamma motoneurons, making muscle spindles less sensitive
  • requires activation from cortical regions
26
Q

Spasticity

A

-with loss of cortex, brainstem inhibitory region is not activated
-brainstem facilitatory region dominates = cont. activation of gamma-motoneurons which contracts intrafusal muscle and lengthens the nuclear bag/chain fibers
-uncontrolled facilitatory region causes stretch reflexes that fight any passive motion = spasticity and hyperactive reflexes
-resists motion in given direction
Presentation: pt resists passive stretch of muscles; contraction doesn’t start until stretch occurs

27
Q

Decerebrate Posturing

A
  • all anti-gravity muscles in extension, usually bilat
  • caused by loss of input from all structures rostral to pons / caudal to red nucleus
  • indicative of severe brain injury
28
Q

Rigidity

A

-resists motion in all directions
-results from maintained muscle contraction
-cont. activation of alpha-motoneurons by brainstem
-loss of cortical influence that inhibits medullary input to alpha motoneurons
Presentation: contraction of muscles in absence of other stimuli

29
Q

Decorticate Posture

A
  • rigidity
  • flexion of upper limb joints = disinhibition of red nucleus and its control of UE flexors
  • extension of lower limbs = disinhibition of reticulospinal and vestibulospinal pathways
  • depending on head position left or right will change a
  • internal rotation of legs in extended position; flexion of arms dependent on head position
  • bilat or unilat
  • loss of cortical inputs caused by lesion of internal capsule
30
Q

Stroke

A

unilateral decorticate posturing results from strokes in vicinity of internal capsule

Neuroendocrine Exam 2 (11 decks)

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