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EP 4703 Unit 2 > Lecture 8 > Flashcards

Lecture 8 Flashcards

1
Q

What is a reflex (simplified)

A

involuntary reaction to some type of stimulus

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2
Q

A reflex is a stereotyped response to specific stimuli that are generated by simple neural circuits in the ________ and _________

A

spinal cord and brain stem

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3
Q

One central synapse

A

monosynaptic

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4
Q

Where are the monosynaptic synapses located

A

in the spinal cord

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5
Q

A few central synapses; usually 2-3, with interneurons involved

A

oligosynaptic

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6
Q

Many central synapses; pathway cannot be traced

A

polysynaptic

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7
Q

Describing a reflex as slow, steady state, maintained

A

tonic

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8
Q

Describing a reflex as fast, transient, in response to a change in the stimulus

A

phasic

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9
Q

How would you describe a monosynaptic reflex

A

phasic

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10
Q

How would you describe a polysynaptic reflex

A

tonic

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11
Q

A muscle contraction induced by an external stimulus that cannot be changed by pure thinking

A

reflex

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12
Q

Reflexes are highly __________ to changes in behavioral goals, mainly b/c several different circuits exist to connect sensory and motor neurons, but they cannot be directly controlled ________.

A

adaptable

voluntarily

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13
Q

Why should we study reflexes

A
  1. can assist in the diagnosis of certain conditions

2. help localize injury or disease in the CNS

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14
Q

Hypoactive reflexes

A

absent or weak, often indicate disorder in one or more of the components of the reflex arc

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15
Q

__________ can cause both hyperactive and hypoactive reflexes

A

lesions in the CNS (spinal cord)

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16
Q

What is the most common form of hyperactive reflexes

A

spasticity

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17
Q

What does spasticity result in

A

hypertonia or increase muscle tone

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18
Q

What is an example of a disease that causes spasticity

A

cerebral palsy

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19
Q

What does a reflex arc consist of

A 
a sensory element (receptor)
an afferent (sensory) nerve
a central processing unit
an efferent (command) nerve
an effector (for example a muscle)
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20
Q

Where is the central processing unit located

A

in the spinal cord

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21
Q

What are the components of the reflex latency

A

afferent conduction delay (get into the spinal cord)
central processing delay (get through the spinal cord)
efferent conduction delay (down motor to muscle)

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22
Q

What would affect each reflex delay (latency)

A

the location of the tendon (achilles vs. patellar)

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23
Q

Where do the monosynaptic reflexes originate from in humans and what do they induce

A
  • Ia spindle afferents

- induce responses in the same muscle or in muscles in the same vicinity (share common functions)

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24
Q

What is the H-reflex

A

technique for examining monosynaptic reflexes

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25
Q

Who came up with the H-reflex and when

A

P. Hoffman in the 1950s

26
Q

How does the H-reflex work

A

electrically stimulate Ia afferents in a peripheral nerve and recording the motor (reflex) response in the same muscle

27
Q

How is the H-reflex commonly assessed

A

by stimulating the tibial nerve and measuring the response of the soleus

28
Q

Where would you place the electrode when trying to stimulate the tibial nerve

A

in the popliteal region of the knee (behind the knee)

29
Q

What two pieces of equipment are needed for the H-reflex test

A

a nerve stimulator

EMG

30
Q

Why is the H-reflex better than the tendon tap method

A

it allows for better control

31
Q

What are the 5 components of the standard reflex arc

A
  1. receptor(s)
  2. sensory (afferent) neuron(s)
  3. central processing unit
  4. motor (efferent) neuron(s)
  5. muscle(s)
32
Q

In a monosynaptic reflex, what type of receptor is activated to begin the reflex group

A

primary spindle endings (Ia)

33
Q

In a monosynaptic reflex, which muscle is activated/contracts to complete the reflex loop

A

same one that was lengthening

34
Q

diminished reflex?

A

hypoactive

35
Q

exaggerated reflex?

A

hyperactive

36
Q

why is electrical stimulation of a peripheral nerve applied to both afferent and efferent fibers

A

a peripheral nerve has both fibers running close together and the electrode cannot be selective between the two

37
Q

what fibers are the first to react to a slowly increasing electrical stimulus

A

afferent

38
Q

what do afferent fibers induce

A

reflexive muscle contraction (H-reflex)

39
Q

what do efferent fibers induce

A

direct muscle contraction (M-response)

40
Q

what is the M-response

A

direct stimulation of the muscle

41
Q

why is the M-response faster than the H-reflex

A

b/c it does not have to travel to the spinal cord first

42
Q

voltage, strength of a current measured in Volts or millivolts

A

intensity

43
Q

strength of the muscular response measured in Volts or millivolts

A

amplitude

44
Q

how often the stimulation is applied measure in Hertz

A

frequency

45
Q

further increase in the strength of the stimulation leads to an increase in the _________ and a suppression in the __________

A

M-response

H-reflex

46
Q

what does the peak-to-peak amplitude of the H-reflex and M-response depend on

A

the strength of the stimulation

47
Q

Why does the H-reflex increase and then decrease, while the M-response gradually continues to increase until in plateaus and remains at that level

A

it has to do with the response of the motor neurons to the stimulation as the intensity increases

48
Q

The stimulation of the afferent fiber results in the _______

A

H-reflex

49
Q

once the afferent fiber is stimulated, the signal travels _______ up the sensory neuron, into the spinal cord where it synapses with an _________

A

antidromically

alpha motoneuron

50
Q

Once the signal synapses with the alpha motoneuron, it travels __________ down the motor neuron to the target muscle, resulting in a ________ muscle contraction

A

orthodromically

reflexive

51
Q

the stimulation of the _________ fiber results in a signal traveling orthodromically down the motor neuron to the muscle, resulting in a _____- ______ contraction (M-response wave)

A

efferent

direct muscle

52
Q

time for M-response

A

8ms

53
Q

time for H-reflex

A

35ms

54
Q

why can’t a motoneuron generate another efferent AP when an afferent fiber delivers a presynaptic AP to an alpha motoneuron whose axon hillock has just responded to and antidromic efferent AP

A

b/c of the refractory period

55
Q

sensory neurons conduct action potentials _________

A

antidromically

56
Q

motor neurons conduct action potentials ___________

A

orthodromically

57
Q

when can motor neurons also start generating APs antidromically

A

at high levels of electrical stimulation

58
Q

how does the H-reflex disappear

A

the antidromic AP from the motor neuron cancels out the antidromic AP from the sensory neuron

59
Q

what does successive stimuli at a high frequency induce

A

similar M-responses but progressively smaller H-reflexes

60
Q

the refractory period for the central synapse is longer than ________

A

the refractory period for the axon of the motor neuron

EP 4703 Unit 2 (3 decks)

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