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NPB 101L > Lab 3 Prelab > Flashcards

Lab 3 Prelab Flashcards

1
Q

Define reflex.

A

A patterned, involuntary response to a stimulus

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2
Q

What does it mean for a response to be “graded”?

A

The strength of the response is proportional to the strength of the stimulus

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3
Q

Are most reflexes learned or unlearned? Exceptions?

A
  • Unlearned
  • Exception: acquired reflexes like muscle memory
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4
Q

What is a monosynaptic reflex?

A

A single synapse b/t afferent and efferent neurons

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5
Q

What is a polysynaptic reflex?

A

Multiple synapses b/t afferent and efferent neurons

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6
Q

What are reflex arcs?

A

A pattern of defined segments which describe the components of a reflex

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7
Q

List the components of a reflex arc.

A
  • Recepter
  • Afferent nerve fibers
  • Integrator
  • Efferent nerve ribers
  • Effector
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8
Q

What is the function of the receptor?

A

Converts stimulus to an electrical signal, activating an AP in the afferent neuron

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9
Q

What is the function of the afferent nerve fibers?

A

Propagate AP to integrator

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10
Q

What is the function of the integrator?

A

CNS (spinal cord or brain) areas that determine how a response to afferent should be made

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11
Q

What is the function of the efferent nerve fibers?

A

Propagate AP from integrator to effector

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12
Q

What is the function of the effector?

A

Receives the signal and carries out the response

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13
Q

What causes a monosynaptic reflex?

A

Stretching of the muscle spindle

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14
Q

Describe the mechanism of a stretch reflex.

A
  1. Tap deflects tendon, stretching muscle spindle
  2. Excites 1A afferents
  3. Dorsal root of spinal cord integrates signal
  4. 1A axons make a monosynaptic connection to an alpha motor neuron
  5. Activated alpha motor neuron (efferent) synapses w/ muscle fibers (effector), causing contraction
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15
Q

What is a muscle spindle? Function? Characteristics?

A
  • Special sensory receptors that measure length and rate of stretch of a muscle
  • Modified intrafusal muscle fiber
  • Encircled by 1A afferents
  • Runs parallel to muscle fibers
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16
Q

Typically, are muscle fibers extrafusal or intrafusal?

A

Extrafusal

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17
Q

What is the Hoffman Reflex? What part of the reflex arc does it lack?

A
  • Electrically induced monosynaptic reflex
  • Doesn’t have a receptor component to its reflex arc
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18
Q

In lab, what nerve will we be directly stimulating to produce the Hoffman Reflex? Why?

A

Tibial nerve b/c:

  • bypasses muscle spindle
  • contains both 1A afferent and alpha motor neurons, so we’ll see 2 types of waves
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19
Q

What causes an H-wave?

A

1A afferent activation synonymous w/ normal route of the spindle reflex

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20
Q

What causes the M-wave?

A

Directly activating alpha motor neurons

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21
Q

Typically, do 1A afferents or alpha motor neurons have a lower threshold to direct stimulation? Why?

A
  • 1A afferents have a lower threshold to direct stimulation b/c of their large diameter
  • Alpha motor neurons are smaller in diameter and require strong electrical stimulation to be excited to threshold
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22
Q

Define antridromic.

A

Reverse direction of AP travel toward the cell body of the neuron

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23
Q

Define orthodromic.

A

Forward-direction of AP travel toward the axonal terminal

24
Q

How does increasing voltage magnitude affect the H and M waves?

A

Increase size of both waves at first, then H-wave decreases b/c antidromic APs start to decrease the voltage

25
Q

Define latency.

A

Time period b/t stimulation and response

26
Q

What is a Renshaw cell?

A

An inhibitory interneuron utilizing glycine

27
Q

What is an axon collateral? What does it synapse with?

A

Branch-off of the alpha motor neuron that synapses w the Renshaw cell

28
Q

When is the Renshaw cell stimulated?

A

When its alpha motor neuron is activated at high frequency

29
Q

What is recurrent inhibition?

A

Single interneuronal synaptic self-inhibition used during the Renshaw circuit to prevent overstimulation of its own circuit at high frequencies

30
Q

What happens when the Renshaw cell synapses w its own motor neurons and others nearby?

A

Induces IPSPs

31
Q

How do low frequencies affect the H wave? High frequencies?

A
  • Low frequencies: alpha motor neuron recovers from the IPSP before the next stimulus –> a peak is seen
  • High frequencies: can’t recover from recurrent inhibition, is less responsive to 1A stimulation –> peak is decreased
32
Q

How does holding at a moderate voltage and increasing frequency affect the M-wave? Why?

A

No affect on M-wave b/c all inhibition occurs upstream of its pathway

33
Q

What is the purpose of having more than one interneuron b/t the afferent and efferent branches for a polysynaptic reflex?

A

Interneurons allow the integrator to collect multiple sources of info together before sending out a final decision to the efferent

34
Q

What is the example of a polysynaptic reflex we will be observing in lab?

A

Vestibular-Ocular Reflex

35
Q

What is the Vestibular-Ocular Reflex involved in?

A

Involved in sensing angular acceleration and deceleration, balance, and centering of visual field

36
Q

What is the primary sensory structure of the VOR?

A

Semicircular canals

37
Q

How many semicircular canals do we have? How are they oriented?

A

3 orthogonally oriented canals in each ear

  • X, Y, Z axis = one in each plane
  • situated at a 30° posterior angle to the head
38
Q

What are hair cells?

A

Mechanoreceptors able to detect angular acceleration, axial movement caused by flow of endolymph

39
Q

What is endolymph? Function? Location?

A

Fluid medium in the semicircular canals that detects and measures motion

40
Q

What branch off of hair cells? Heights?

A
  • Kinocilium (tallest branch)
  • Stereocilia (shorter branch)
41
Q

What fibers do cells synapse w/ in the semicircular canals?

A

Vestibular nerve fibers

42
Q

What are cilia?

A

Bundles of hair cells

43
Q

What is a cupola?

A

Cilia embedded in a gelatinous mass

44
Q

When endolymph moves in the semicircular canals, what does it bend?

A

Hair cells’ kinocilia and stereocilia

45
Q

What are tip links? Location? Function?

A

Mechanoreceptors on stereocilia that open K+ channels in response to bending

46
Q

What is the K+ content of endolymph? Significance?

A

High K+ content compared to inside the cells, so opening mechanoreceptor channels cause K+ influx

47
Q

What happens when stereocilia are bent toward the kinocilium? Away?

A
  • Toward = increased K+ influx –> depolarization
  • Away = decreased K+ influx –> hyperpolarization
48
Q

Describe the bending of cilia and movement of endolymph during acceleration and deceleration.

A
  • Acceleration: endolymph is extremely viscous, so it doesn’t move at first –> cilia bend in opposite direction of spin
  • Constant speed: endolymph catches up w/ hair cells and they move together –> cilia no longer being bent
  • Deceleration: endolymph moves faster while hair cells start to slow down –> cilia bend toward direction of spin
49
Q

Describe the components of the VOR reflex arc.

A
  1. Hair cells (receptor) sense angular momentum (stimulus)
  2. APs propagated along the vestibular nerve (afferent) to the brainstem (integrator)
  3. Motor neurons (efferent) to the lateral and medial eye muscles (effectors) are either activated or inhibited according to the response program
  4. Nystagmus (response)
50
Q

Define nystagmus.

A

Alternating slow and fast pattern of eye movements in response to changing acceleration of the head

51
Q

Define saccades.

A

Fast component which occurs in the direction of acceleration or perceived motion

52
Q

When do slow eye movements occur?

A

Opposite direction of acceleration or perceived motion

53
Q

What is the best-known example of a monosynaptic reflex?

A

Knee jerk or stretch reflex

54
Q

Why is the latency of the M-wave much shorter than the H-wave?

A

Motor neuron is directly stimulated and the signaling pathway is much shorter than that of the H-wave

55
Q

What do defects in the VOR lead to?

A
  • Dizziness
  • Loss of balance
  • Impaired postural control
56
Q

Why is direct stimulation less efficient thatn neuronal stimulation?

A

Neuronal stimulation takes advantage of the structure of motor units

NPB 101L (13 decks)

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