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Neuroendocrine Exam 2 > 13. Motor Reflexes (Karius) > Flashcards

13. Motor Reflexes (Karius) Flashcards

1
Q

Cortical reflexes include

A

placing reaction

hopping reaction

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2
Q

Spinal reflexes include

A

stretch

golgi tendon reflex

crossed extensor

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3
Q

Brainstem/Midbrain reflexes

A

vestibular

righting reflex

sucj=kle

yawn

eye/head movements

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4
Q

What are the purposes of a reflex?

What are the characteristics of reflexes?

A

protective

no voluntary motor control needed

FAST

specific and fast

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5
Q

What must reflexes have in order to be effective that also makes them look like volitional movement?

how would you tell the difference between volitional movement and reflexes?

A

PRECISION!

Reflexes are faster

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6
Q

How do you tell the difference between reflex and volitional motion besides speed?

A

Reflexes:

happen at any CNS level, doesn’t need cortical involvement

direct responses to stimuli, protective

fixed circuitry

high specificity

Volitional:

cortical and subcortical involvement

response to need/desire

variable circuitry

high specificty

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7
Q

Describe the myotactic reflex:

appearance:

purpose:

characteristics:

A

contraction of muscle

protect from tearing due to stretch

initiated by muscle spindle, causes monosynaptic, segmental refex

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8
Q

Describe the muscle spindle

A

found with skeletal muscle, embedded in fusiform capsule

parallel to muscle fibers

both afferent and efferent

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9
Q

Describe Intrafusal fibers

A

capsule is fusiform, so fibers are called intrafusal

muscles around it are called the extrafusal fibers

contain both motor and sensory components

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10
Q

What are the characteristics for the sensory part of the muscle spindle

A

not contractile

sensitive to length

contains nuclear bag and nuclear chain fibers

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11
Q

Describe the Ia fibers (primary afferent)

A

innervates nuclear bag and chain

myelinated, large

sensitive to length of muscle and rate of change

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12
Q

Describe the characteristics of the secondary afferent

A

smaller, mylinated

Group II fiber

innervates only nuclear chain

sensitive only to length of muscle

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13
Q

Describe the motor portion of the intrafusal fibers

A

histologically same as skeletal muscle

innervated by gamma motor neuron

controls length of sensory portion (intrafusal fibers)

causes sensory protion to become more sensitive to stretch

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14
Q

Controlling the sensitivity of the myotactic reflexes

A

even though the overall length of the msucle spindle remains the same, contraction of the intrafusal contractile fibers stretches the sensory portion and increases the sensitivity of the Ia and II fibers to stretch

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15
Q

What are the main features of alpha motor neurons?

A

large, very myelinated

innervates skeletal muscles (extrafusal)

activate muscle

lead to motion

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16
Q

What are the main features of gamma motor neurons?

A

smaller, slower, still fast tho

innnervates the intrafusal muscle spindle

causes contraction

controls sensitivty of muscle spindle

does not DIRECTLY lead to motion

17
Q

Describe the pathway of the reflex

A
  • within the spinal cord, the Ia afferent from the muscle spindle synapses onto the alpha motor neuron innervating the stretched muscle
  • the motor neuron is excited by the activation and contraction relieves the stretch, returning the Ia discharge rate back to normal
  • simultaneously, the antagonist gets stretched
  • another Ia afferent sunapses onto the muscle and activates another a-motor neuron innervating the stretched muscle but EAA causes a release of GABA onto that a-motor neuron causing fewer action potentials (relaxation) of the antagonist
  • thus there is a decrease in the activity of the a motor nueron of the antagonist allowing it to relax and lengthen
18
Q

Describe the golgi tendon reflex

appearance

purpose

characteristics

A

sudden relaxation of a contracted muscle

protect due to excessive force

initiated by golgi tendon organ

polysynaptic, segmental reflex

19
Q

What does the golgi tendon organ innervate?

what kind fiber?

A

the tendon via bare nerve endings with lots of branches

AP increases with tension

Ib fiber to spinal cord

20
Q

path of golgi tendon reflex

A

Ib afferent from golgi tendon to alpha motor neuron of contracting muscle

fewer AP, less tension in muscle

21
Q

The golgi tendon reflex inhibits the motor neuron by activating the spinal interneuron thus causing

A

abrupt relacation of the muscle, returning the golgi tendon organ discharge rate back to normal

22
Q

Normal Reflex Arc

A

muscle stretches

AP increases on the 1a fiber

EAA released and synapse occirs on the a-motor neuron with more EAA release

AMN synapses on NMJ

releases Ach

shortens muscle, does reflex

23
Q

How does a myotactic hyperreflexia arc happen?

A

cortex can modulate reflex activity

if the cortex is damaged: there is decreased inibition and unoppsed excitation in the brain stem so hyperreflexia and clonus can occur

this input goes to yMN

the antagonist stretches and the ymn are effected and trigger the reflex there, so you have opposing reflexes causing that alternating occilation seen in clonus

24
Q

What is the mechanism by which rigidity occurs (like in decerebrate posturing)?

A

results from maintained muscle contraction due to continual activation of a-MN

brainstem is activaing a-MN but not clear on why

Occurs in the extensor muscles

25
Q

What is the mechanism by which spatisicty occurs (like in decorticate posturing)?

A

myotactic reflex is hyperactive due to continual activation of g-MN contracting intrafusal muscles

leads to lengthening of nuclear bag/chain fibers by signals from brainstem

26
Q

How does the cortex modulate reflexes?

A

there is the brainstem faciliatory region that makes teh muscle spindles more sensitive and it becomes spontaneously active (does not rely on input from other parts of the brain)

the brainstem inhibitory region inhibits g-MN, making the muscle spindle less sensitive

this region requires activation from cortical regions

damage to cortex inhibits the inhibitory action thus causing spacitiy from uncontrolled brainstem facillitatory regions

27
Q

identify occurrence and presentation of spasicity

A

pt resists passive stretch of muscles

contraction doesn’t start until the stretch occurs

hyperactive myotactic reflex due to increased gamma motor neuron firing

cause: damage to cortex that abolishes activation of the brainstem inhibitory region (brain arousal systems)

28
Q

identify the pt presentation and occurence of rigidity

A

contraction of muscle in absence of other stimuli

a-motor neurons continually active

cause: loss of cortical influence that inhibits a medullary input to the alpha motor neurons

29
Q

Describe decorticate posturing

A

flexion of upper limbs due to disinhibition of red nucleus and its control of UE flexors

extensino of lower limbs due to disinhibition of reticulospinal and vestibulospinal pathways

Dependent on head position (releases postural reflexes)

likely from stroke in near internal capsule, common site of stroke

bilateral or unilateral

loss of cortical inputs

30
Q

Describe decerebrate posture

A

contarction of all antigravity muscles (arms in extension)

loss of input from all structures rostral to the pons (caudal to red nucleus)

usually indicative of severe brain injury

31
Q

Describe spinal shock

A

caused by transection of spinal cord

all reflexes gon, even if circuit is intact

caused by hyperpolarization of spinal neurions due to loss of excitatory input from cortex

32
Q

Remember that Ia fbers are faster than Ib fibers because

A

1a fibers are larger and more myelinated

Neuroendocrine Exam 2 (25 decks)

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