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Neuroscience > Lecture 8: Reflexes > Flashcards

Lecture 8: Reflexes Flashcards

1
Q

what is the main role of upper motor neurons

A

Integrates excitatory and inhibitory signals from the cortex and translates them into a signal to modulate LMN activity

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2
Q

what is the main role of lower motor neurons

A

Receives the signal from UMN and transmits it to effector muscle to perform a movement

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3
Q

how does sensory information help guide movement? (2 ways)

A

Receives the signal from UMN and transmits it to effector muscle to perform a movement

Sensory information is integrated to modulate the activity of LMN and UMN

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4
Q

where are the cell bodies of sensory neurons located

A

posterior (dorsal) root ganglia

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5
Q

how do sensory neurons sneed their messages to the spinal cord

A

via the posterior (dorsal) roots

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6
Q

are peripheral nerves typically mixed?

A

(sensory and motor)

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7
Q

the somatosensory systems convert which types of information

A

touch, proprioceptive, pain, and temperature

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8
Q

what transmits reflexes to the CNS

A

Peripheral afferents

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9
Q

what do muscle spindles do

A

Detects muscle length and velocity

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10
Q

what are the 2 types of sensory axons in muscle spindles

A

group 1a axons

group 2 axons

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11
Q

what are group 1a axons

A

Changes in length and velocity

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12
Q

what are group 2 axons

A

measures length

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13
Q

when is there a decrease in muscle spindle activity?

A

when there’s stimulation of the alpha motor neurone only, not actively contracting the muscle voluntarily

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14
Q

do gamma motor neurons directly cause muscle contraction

A

no

they Innervate muscle spindles and dictate their sensitivity

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15
Q

do alpha motor neurons or gamma motor neurons have a lower threshold for activation

A

gamma motor neurons

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16
Q

how can gamma motor neurons be modulated

A

ascending pathways

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17
Q

what is muscle spindle alpha-gamma co-activation

A

during active muscle contraction, gamma motor neurons cause intrafusal fibres to contract at the same time as extrafusal fibres

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18
Q

why is Alpha-Gamma Co-activation important

A

Maintains sensitivity of the muscle spindles during different muscle lengths

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19
Q

does Alpha-Gamma Co-activation occur during reflexes

A

no.

alpha-gamma co-activation only occurs in movements initiated by the CNS

only alpha motor neurons are activated during reflex

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20
Q

what are Golgi tendon organs

A

Group 1b afferent

Designed to measure muscle tension/force

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21
Q

does muscle stretch affect afferent activity in Golgi tendon organs

A

no

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22
Q

does active muscle contraction affect afferent activity in Golgi tendon organs

A

yes activity increases

23
Q

what is the simplest level of movement

A

reflexes

24
Q

what are reflexes largely controlled by

A

local circuitry in the spinal cord

25
Q

how are reflexes stereotyped

A

stimulus input = set motor output every time

26
Q

how are reflexes modulated

A

Amplitude is larger with increasing stimulus input

Reflexes can be excited or inhibited via descending control

27
Q

how can reflexes be excited

A

someone jump scares you when its dark outside and you’re already scared = greater reaction

28
Q

how can reflexes be inhibited

A

we need to touch a hot pan we know its hot but our body doesn’t drop it

29
Q

what is the stretch reflex

A

Stretch reflex is homonymous - same muscle that is stretched is excited and contracts

Spindle sensitivity modulated
by UMNs

30
Q

what is the purpose of the stretch reflex

A

Maintain muscle length

compensate for limb
during movement

31
Q

what is reciprocal inhibition of the stretch reflex

A

Automatic inhibition of the antagonist alpha motor neuron (biceps) caused by contraction of the agonist muscle (triceps)

  • Occurs in conjunction with stretch reflex
32
Q

what is the purpose of reciprocal inhibition

A

to allow agonist to contract

33
Q

what is the Golgi Tendon Organ (GTO) Reflex

A

Excitation of the inhibitory interneuron
* Inhibit “agonist” homonymous muscle LMN pool (biceps)

  • Excitation of the excitatory interneuron
  • Excites “antagonist” muscles LMN pool
    (triceps)
34
Q

what is the function of the Golgi Tendon Organ (GTO) Reflex

A

Release load to prevent muscle tearing and
maintains muscle tone during muscle fatigue

35
Q

what is the flexor withdrawal reflex?

A

Ipsilateral limb (painful stimulus)
* Interneuron to excite flexors
* Inhibitory interneuron to
inhibit extensors

36
Q

what is the function of the flexor withdrawal reflex

A

Remove limb from noxious stimulus

37
Q

what is the crossed extensor reflex

A

Occurs with flexor withdrawal reflex

Input: Noxious stimulus detected
* Synapse on long distance interneuron networks
* Contralateral limb (cross-extensor)
* Excite Extensors (postural)
* Inhibit Flexors

38
Q

what is the purpose of the crossed extensor reflex?

A

Ground stance limb to allow ipsilateral limb to withdraw from pain

39
Q

which is the only reflex that crosses spinal cord

A

crossed extensor reflex

40
Q

what is the 5 point scale of reflexes

A

0 - No response

1+ - Present but depressed (hyporeflexic; may or may not be normal)

2+ - Normal (average)

3+ - Brisk (increased; possibly abnormal)

4+ - Very brisk, hyperactive, with clonus (abnormal)

5+ - Sustained clonus

41
Q

what do we usually see in terms of the reflex grading scale with upper motor neuron lesions

A

3+ - Brisk (increased; possibly abnormal)

4+ - Very brisk, hyperactive, with clonus (abnormal)

5+ - Sustained clonus

42
Q

where does the Reticulospinal tract originate and terminate

A

originates in reticular formation and terminates bilaterally in spinal cord

43
Q

what is the Dorsal/lateral reticulospinal tract responsible for

A

descending inhibition (hitting the breaks)

44
Q

what is the Medial reticulospinal tract responsible for

A

descending excitation (hitting the gas)

45
Q

what happens with both reticulospinal tracts we have a complete spinal cord injury

A

both are damaged

  • Excessive firing of LMNs BUT
    Inhibitory interneurons unable to inhibit LMNs (driving down a hill with no breaks)
  • Hypertonia is due to a loss of descending control
46
Q

What happens when we have a stroke on the right side of our brain

A

Right lateral corticospinal tract damaged

Reduced cortical drive to dorsal/lateral reticulospinal tract

Medial reticulospinal tract increases descending drive from the contralesional side

  • Results in excessive (medial) reticulospinal drive (all gas no breaks)
47
Q

In UMN lesions, there is excessive neural signaling due to a loss of descending control, which contributes to

A

Hypersensitivity of the muscle spindle

Excitable  motor neuron

48
Q

what happens when we do a tendon tap of the patella

A

muscle stretches causing increase activation of 1a afferent

shortly after, alpha motor neurons are recruited, causing shortening of muscles due to stretch reflex

49
Q

what happens in clonus

A

muscle stretches causing increase activation of 1a afferent

shortly after, alpha motor neurons are recruited, causing shortening of muscles due to stretch reflex

there is repeated activity of 1 a afferents, and the cycle repeats

50
Q

what is the babinski test

A

stroke the lateral side of foot across base of toes, extension of big toes, other toes fan out

normal in infants and not in adults

51
Q

what is Hoffman’s Reflex

A

flick middle finger tip down

Positive if tip flicks back thumb flexes and adducts
More likely to have a false positive than Babinski

52
Q

what do we usually see in terms of the reflex grading scale with lower motor neuron lesions

A

0 - No response (areflexia)

1+ - Present but depressed (hyporeflexic; may or may not be normal)

53
Q

when would we see hyporeflexia

A

Lower motor neuron lesions

Neuroscience (10 decks)

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