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Ana/Phys/Patho I > Unit 8: neuro reflex & NMJ > Flashcards

Unit 8: neuro reflex & NMJ Flashcards

1
Q

what are the (4) reflex pathways?

A
  1. stretch reflex
  2. tendon reflex
  3. withdrawal reflex
  4. crossed extensor reflex
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2
Q

what comprises a generalized reflex circuit?

A
  1. afferent input
  2. efferent output
  3. interneuron releasing inhibitory transmitter (not always used)
  4. alpha motor neuron
  5. muscle spindle
  6. motor end-plate on extrafusal fiber
  7. 1a fiber from muscle spindle
  8. 1b fiber from tendon organ
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3
Q

how do reflex arcs achieve motor output in both sides of the body?

A

through interneurons

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4
Q

what is the process for the stretch reflex to engage?

A
  1. muscle stretches
  2. stretch sensor activated in the muscle spindles of the muscle being stretched
  3. SENSORY neuron gets excited and input travels to the brain AND to the motor cell body in the ventral horn
  4. MOTOR output gets excited and contracts and relieves the stretching of the SAME MUSCLE
  5. (inhibitory neuron could engage to elicit reflex relaxation to lose muscular tone in the ANTAGONISTIC muscles – to help straighten out limb)

ex) if someone pushes on your foreheard, the reflex that allows you to keep your posture would contract your quadricep muscles
ex) if someone pushes you from the back, the stretch reflex would allow you to keep your posture and your hamstrings would contract

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5
Q

give an example of the stretch reflex in the lower limbs

A
  1. reflex hammer hits the ligaments underneath the patella (quadricep tendons) while legs are hanging and suspended over a seat
  2. stretch of quadriceps engages muscle spindles (foot “jerks” or involuntarily extends foward) to stimulate sensory input
  3. sensory input ascends to brain and to the motor neuron in the ventral horn
  4. motor output travels out of rootlets to the same quadriceps muscle to contract and relieve the stretching of the muscle

an inhibitory neuron may engage the hamstring muscles to relax

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6
Q

describe the tendon reflex arc

A

protective in nature

  1. tendon reflex activated when massive weight on skeletal muscle engages muscles to stretch/contract
  2. the measured tension of the tendons happens via golgi tendon sensors
  3. sensory neurons excited and relay input into spinal cord and to brain
  4. in the spinal cord, inhibitory interneurons cease the actvity in motor neurons that are attached to the muscle group
  5. the effector muscle (same muscles attached to the tendons) will relax and relieve excess tension
    5a. excitatory interneurons in SC will engage the antagonistic muscle motor neurons
    5b. motor neurons to antagonistic muscles are excited and antagonistic muscles CONTRACT to speed the retraction from heavy load source
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7
Q

give an example of how the tendon reflex works in the arm

A
  1. inhibitory interneuron inhibits the biceps
  2. excitatory interneuron excites the triceps
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8
Q

describe the flexor reflex

AKA withdrawal reflex

A

pulls away from pain

  1. painful stimuli relays sensory/afferent input to spinal cord
  2. interneurons in SC are engaged
    * 2a. ascending interneuron engages motor neurons to contract and WITHDRAW from painful stimuli
    * 2b. interneuron (on same level of initial sensory input) will also engage effect muscle to contract and WITHRDRAW from painful stimuli
    * 2c. descending interneurons engages motor neurons to also contract and WITHDRAW from painful stimuli

(sometimes antagonistic muscles are also engaged)

pain AND pressure sensors engaged; typically UNILATERAL

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9
Q

why does the flexor reflex arc contain multiple levels of interneuron engagement?

A

since it is a withdrawal reflex away from pain, it engages multiple muscle groups within the area to act very quickly

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10
Q

where do the ascending and descending interneurons project in the spinal cord?

A

Tract of Lissaur

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11
Q

describe the crossed extensor reflex arc

A

this reflex uses the most interneurons; a pain-mediated reflex arc
this reflex arc engages while body is IN MOTION

ex)
1. LEFT foot steps on a tack while mid-stride
2. sensor input relayed to spinal cord
3. ascending/descending interneruons engages flexor muscles (LEFT hamstrings) to CONTRACT and **WITHDRAW ** the LEFT leg
* 3a. interneuron communication occurs at crossover point
* 3b. ascending/descending interneurons on RIGHT side will engage the RIGHT leg extensor muscles (quadriceps) to CONTRACT and extend right leg
4. (antagonistic muscle groups may also engage)

overall, this reflex stabilizes the body to have a balanced base

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12
Q

differentiate the (3) different types of n-ACh-Rs

A
  1. low-conductance channel (immature)
    * WHEN OPEN: slow, long activation period
  2. high-conductance channel (mature)
    * WHEN OPEN: high-speed, short activation period
  3. alpha-7 ACh-R
    * depolarization (neuronal in muscle)
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13
Q

what 5 subunits do low-conductance (immature) channels have?

A
  1. alpha
  2. alpha-1
  3. beta-1
  4. delta
  5. gamma
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14
Q

what 5 subunits are found on high-conductance (mature) channels?

A
  1. alpha
  2. alpha-1
  3. beta-1
  4. delta
  5. epsilon
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15
Q

differentiate immature vs mature n-ACh-Rs vs alpha-7 n-ACh-Rs

A

immature
* slower conductance
* open for longer periods
* expressed in NMJ & muscles outside the NMJ

mature
* fast conductance
* open for a shorter period of time
* only found in NMJ

alpha-7
* found in CNS

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16
Q

explain how succinylcholine would affect immature n-ACh-Rs differently than mature n-ACh-Rs

A

immature n-ACh-Rs would be open much longer than mature n-ACh-Rs because, at baseline, immature n-ACh-Rs are already open for a longer period of time when receptors are open; therefore, sux will prolong the time it’s open

also, immature n-ACh-Rs will collect outside of the CNS and can cause a potassium leak

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17
Q

if the muscle spindles sense a change in tension in the muscle, but does not relay that information to the brain, what will be the body’s response?

A
  1. CNS wil identify the problem
  2. body will try to fix by increasing ACh-Rs on skeletal muscles
  3. often expresses IMMATURE n-ACh-Rs over mature n-ACh-Rs

most often seen in CVA patients

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18
Q

differentiate: junctional area, peri-junctional area, and post-junctional

A

junctional: normally, ACh-Rs should be limited to this area
peri-junctional area: in-between junctional area and post-junctional area
post-junctional: normally does NOT contain n-ACh-Rs here; this area may contain immature (fetal) type n-ACh-Rs depending on the health of the patient

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19
Q

when conducting peripheral nerve stimulation (PNS), what muscle does the ulnar nerve innervate?

A

Adductor pollicis

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20
Q

how does peripheral nerve stimulation work in terms of creating an AP in a nerve?

A
  • electrodes are paced along a nerve on the skin
  • current is sent through the electrodes to remove polarity in the nerve
  • since the inside of a nerve is negatively charged and the outside is positively charged, the induced current will send electrons across the electrodes to create an overall negative charge outside the nerve
  • if there is NO charge difference, there is no polarity (depolarized), therefore an AP will occur
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21
Q

explain what a supramaximal stimulus is

A

supra = above
maximal = maximum

so, above the maximum – this is in reference to the dialed in voltage to elicit a depolarization to recruit ALL of the motor neurons in the underlying nerve

this level of voltage is also used to create a baseline prior to paralyzing a patient

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22
Q

what is TOF?

A

a repetitive stimulation occuring at 2 hz/2 seconds

a Hertz (Hz) is a single event occuring over one second

so, TOF = 2 Hz/2 seconds = 2 impulses over 2 seconds = 4 impulses of 4 seconds

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23
Q

what is a tetanic PNS?

A

a high frequency stimulation over a short period of time (repetitive, high speed contraction)

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24
Q

what is the post-tetanic count (PTC)?

A

this measures what happens after immediately after the tetanic stimulation

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25
Q

what is a double-burst stimulation?

A

two tetanic stimulations in succession

26
Q

what is expected to be seen when the ulnar nerve stimulates the Adductor pollicis muscle

A
  1. the thumb twitch forward
  2. the pinky may also twitch
27
Q

name 3 other places to measure PNS

A

facial nerve: obicularis oculi muscle
peroneal nerve
post-tibial nerve

28
Q

differentiate how a NDMR block would look versus a depolarized block with a SINGLE TWITCH PNS

A

NDMR would show a gradual decline in twitch strength and around 3 seconds it would dissipate over a long period of time (>25 mins)

a depolarized bock would show an immediate loss of twitch and a quick, gradual return of twitches around the 3 minute mark

29
Q

NMDRs: TOF B/A ratio

A

A will always be stronger than B

“B: something small over A: something large”

30
Q

Depolarizing NMBAs: TOF B/A ratio

A

should always be “1”, because the first twitch will have the same measured strength throughout all

31
Q

what does the alpha-3-beta-2 n-ACh-R do?

A

the majority of ACh is bound to the ACh-Rs in the NMJ on the motor end-plate; a small amount of ACh gets bound to the neuronal alpha-3-beta-2 ACh-Rs

named alpha-3-beta-2 d/t the fact that there may be 3-AChs needed to bind to the 3 alpha subunits

AKA AUTO RECEPTORS

these n-ACh-Rs help facilitate VP-1 vesicles transition into the VP-2 pool

32
Q

relate the function of autoreceptors on the neuron to neuromuscular blocking agents

A

if a NON-DEPOLARIZING NMBA is used, it will bind primarily to:

  1. the n-ACh-Rs on the motor end plate
  2. the autoreceptors on the pre-synaptic neuron to inhibit VP-1 transitioning to VP-2

because there isn’t enough ACh being released with each subsequent contraction d/t the VP-1 vesicles being inhibited, there will be a much weaker twitch after the intial twitch in a TOF

33
Q

why wouldn’t a depolarizing agent have a loss of twitch strength with each subsequent twitch during a TOF PNS?

A

since the agent is depolarizing, it would bind to the autoreceptor and PROLONG the channel being open; therefore, VP-1 will still be able to transition into VP-2, and there will be plenty of ACh at the ready-release state in the pre-synaptic neuron

34
Q

succinylcholine is broken down by what enzyme?

A

plasma-cholinesterase
AKA pseudocholinesterase

NOT AChE

35
Q

what are L-type Ca2+ channels role in the motor neuron?

A
  • they are secondary to P-type Ca2+ channels for neuronal AP
  • they are fast Ca2+ channels
  • if L-type Ca2+ channel blockers are given, “calming effect” will occur (less Ca2+ in presynaptic neuron, causing less neuronal activity = calming effect)
36
Q

what type of muscle is the diaphragm?

A

skeletal muscle

37
Q

why does it take more paralytic to paralyze the diaphragm vs the adductor pollicis muscle?

A

higher doses are required for higher/more vital functioning muscle groups

38
Q

what nerve innervates the diaphragm? and at what levels?

A

phrenic nerve originates in C3, C4, and C5

C-3, 4, 5 > keeps you alive

39
Q

if your patient has 4 strong switches in the adductor pollicis muscle in recovery, what can you infer about the ventilation of this patient?

A

the pt will most likely have no issues ventilating due to the fact that it takes MUCH MORE paralytic to paralyze the diaphgram versus the adductor pollicis muscle

the max dose for paralytic to adminster to fully paralyze the adductor pollicis is where we barely start to paralyze the diaphragm

40
Q

differentiate when your 4th, 3rd, 2nd, and all of the twitches dissappear in relation to the quantity of n-ACh-Rs blocked

A
  • 4th twitch dissapears when ~75-80% of n-ACh-Rs blocked
  • 3rd twitch dissapears when ~85% of n-ACh-Rs blocked
  • 2nd twitch dissapears when ~85-90% of n-ACh-Rs blocked
  • all twitches dissapear when ~90-95% of n-ACh-Rs are blocked
41
Q

at what percentage of n-ACh-Rs blocked would “head-lift” be able to occur in a reasonably healthy patient?

A

~70% of n-ACh-Rs blocked

42
Q

some ocular muscles in the eye are controlled by several motor neurons; what would happen if succinylcholine were to be given?

typically: 1 motor neuron per 1 skeletal muscle cell

A

increased IOP

there will be multiple NMJs, which will allow Ca2+ to influx at various places, which will contract the muscles

will be exacerbated in prone position > risk for vision loss

43
Q

what are the two main inhibitory NTs in the spinal cord?

A
  • GABA
  • glycine
44
Q

how does ACh affect LOC?

A

ACh increases awareness through agonizing the m-ACh-Rs

45
Q

how does benadryl decrease awareness/increase drowsiness?

A

benadryl is an anti-histamine but also has cross-reactivity with m-ACh-Rs; by blocking these receptors, benadryl will increase drowsiness

46
Q

can benadryl affect HR?

A

yes, since it has cross-reactivity with central m-ACh-Rs

it is an anti-cholinergic drug and will increase HR

47
Q

how would AChE-i’s increase awareness?

A

it would inhibit the breakdown of ACh, therefore it would increase the amount of ACh

48
Q

how do AChE-i’s affect HR?

A

it would drop the HR
since there are m-ACh-Rs on the heart, if we were to inhibit AChE from breaking down ACh, there would be more ACh binding to m-ACh-Rs

49
Q

how does AChE-i’s affect gland functioning?

A

most glands use the NT AChE to “turn on” gland function

if AChE’s normal function to breakdown ACh is being blocked, there will be more cholinergic activity at sites that (for example) may increase secretions and cause problems with overall gas exchange

50
Q

what does histamine do in the CNS?

A

works similar to ACh in the CNS by increasing awareness

this is why benadryl will cause drowsiness because it is an anti-histamine

51
Q

what is glutamate’s role in the CNS

A

it is a stimulatory NT in the CNS

too much glutamate can be bad

52
Q

what is dopamine’s role in the CNS?

A
  • reward center NTs
  • inhibits motor activity
    +in Parkinson’s, there is an overactive motor system d/t a dyfunction in dopamine production
53
Q

what is NE’s role in the CNS?

A

increases awareness

54
Q

a low pH causes ______ CNS activity

A

reduces

55
Q

a higher pH ______ CNS activity

A

increases

56
Q

carbonic acid (H2CO3) can dissociate into:

A

CO2 + H2O

57
Q

if albumin binds more protons than Ca2+, what happens to CNS activity?

A

there is more unbound, free Ca2+, and therefore, the increased amt of Ca2+ will DECREASE CNS activity

58
Q

if albumin binds more Ca2+ than H+, what happens to CNS activity?

A

there is more bound Ca2+, and therefore, the increased amt of BOUND Ca2+ will INCREASE CNS activity

59
Q

hyperventilation will cause a(n) _____ in CNS activity. why?

A

INCREASE in CNS activity

  1. hyperventilation blows off MORE CO2 (alkalosis)
  2. alkalosis = less H+ hanging around albumin
  3. albumin will more readily bind to Ca2+ than H+
  4. less FREE Ca2+ = increased CNS activity
60
Q

hypOventilation will cause a(n) _____ in CNS activity. why?

A

DECREASE in CNS activity

  1. hypoventilation does not blow off as much CO2 (acidosis)
  2. acidosis = more H+ hanging around albumin
  3. albumin will more readily bind to H+ than Ca2+
  4. more FREE Ca2+ = decreased CNS activity
61
Q

given an example of when the tendon reflex does NOT engage with an enormous amount of tension on the muscle is applied?

A

someone is trying to rescue lift a heavy car off a child
(if the reflex was ACTIVATED, this would not allow this action to happen)

Ana/Phys/Patho I (14 decks)

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