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16. Neuroscience Exam 2 > 14. Motor Control Reflexes > Flashcards

14. Motor Control Reflexes Flashcards

1
Q

What are two cortical reflexes?

A

placing reaction

hopping reaction

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2
Q

What are 3 spinal reflexes?

A

stretch (myotatic)
golgi tendon reflex
crossed extensor

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3
Q

What are 4 brainstem/midbrain reflexes?

A

vestibular
righting reflex (keeps from falling over)
suckle
yawn

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4
Q

What are the main purposes of a reflex? 3

A

protection
corrective actions
quick response

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5
Q

What are 4 characterisitcs of a motor controlled reflex?

A

involuntary
fast
short-acting
precise

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6
Q

What is needed for reflexes to be effective?

A

precision and SPEED

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7
Q

What is the main difference of vilitional motion compared to reflexes?

A

Volitional requires cortical and subcortical involvement and is at a slower speed

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8
Q

Myotatic/stretch reflex is shortening of a stretched muscle to protect muscles from tearing. What are two characteristics?

A

initiated by muscle spindle

monosynaptic (aff synapses on efferent)

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9
Q

Muscle spindle is within and parallel skeletal muscle in a fusiform capsule, and has what 2 components?

A

afferent (sensory) and efferent (contractile) components

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10
Q

The fibers outside the fusiform capsule are called extrafusal fibers (actin/myosin) and inside are called?

A

intrafusal fibers

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11
Q

The intrafusal fibers have motor (lateral) and sensory (medial) fibers. The sensory portion of intrafusal fibers/muscle spindle is not contractile and has what twoparts?

A

nuclear bag fiber
Nuclear chain fiber

both have different afferents, sensitive to length

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12
Q

The primary afferent that innervates both bag and chain, sensitive to static/dynamic or length and how fast its changing is?

A

1a fiber large and myelinated

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13
Q

The 1a fiber has a slow basal firing rate to manage stretch. What occurs during stretch?

A

firing rate increases in the 1a fiber, and even fasting during a FAST stretch

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14
Q

The secondary afferent is smaller and myelinated. What does it innervated and what is it sensitve to?

A

Group 2/II fiber innervates nuclear chain fiber

sensitive to length only

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15
Q

What is the difference between primary and secondary afferents?

A

primary are 1a fibers, innervates both, and detects length and change in length
secondary are 2 fibers, innervates chain only and detects length (static) only

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16
Q

The intrafusal contractile elements are innervated by ____ which controls what?

A 
gamma motoneuron (not alpha)
control length of sensory portion
17
Q

By contracting the intrafusal muscles, we stretch the sensory portion which leads to what?

A

increases the sensitivity of the Ia and II fibers to stretch

18
Q

What is the main difference between alpha and gamma motoneurons?

A

Alpha is innervation to extrafusal leading to motion

Gamma is innervation to intrafusal, causing contraction

19
Q

The 1a (and 2) afferent fibers goes to SC via dorsal root and synapse directly onto alpha motoneuron, using what NT and causing what?

A

using EAA, causing contraction of the extrafusal muscles via Alpha motoneuron, allowing discharge firing rate to go back to normal

20
Q

When the stretch reflex is elicited, what happens to the antagonist muscle?

A

it gets stretched

21
Q

To allow the antagonistic muscle to relax/stretch during myotatic reflex, the 1a afferent fiber also synapses on an interneuron of the antagonist M which does what?

A

releases GABA, decreasing APs, inhibiting the Alpha motoneuron of the antagonist M

22
Q

Golgi tendon reflex AKA inverse myotatic, appears during sudden relaxation of a contracted muscle to protect?

A

muscle from damage due to excessive force

23
Q

What is characteristic of the golgi tendon reflex? (2)

A

initiated by golgi tendon organ GTO

polysynaptic - many synapses

24
Q

GTOs innervate tendons via bare nerve endings. APs increase with tension, which is relayed via what to the SC?

A

1b fiber (slightly smaller and slower)

25
Q

What is the pathway for the GTO reflex?

A
  1. 1b afferent fiber from GTO in tendon goes to SC
  2. synapses on interneuron of contraction muscle
  3. Interneuron releases GABA, causing fewer APs and less tension in the muscle
26
Q

What is the main difference between myotatic and golgi tendon reflexes?

A

myotatic prevents stretch of muscle

GTO prevents damage from over contraction

27
Q

Most of input from the brain is inhibitory to reflexes, but certain regions provide ?

A

excitatory input

28
Q

How do we know that the brain has some things to do with lower reflexes?

A

if there is a transection at C1, the reflex at L4/5 no longer works

29
Q

Spinal shock (after complete transection) may take months to years until reflexes come back. What are the two reasons they may come back?

A
  1. axonal sprouting below level transection

2. expression of receptor phenotypes that are self-activating (such as 5HTC receptor)

30
Q

Decerebrate posturing results from loss of all structures that are ?

A

rostral to the pons and CAUDAL to the red nucleus

31
Q

Rigidity is resisting motion in all directions due to maintained contraction/activation of alpha motoneurons. What is activating these motoneurons?

A

the brainstem-we dont know why

32
Q

Spasticityis resistin motion in a given direction due to hyperactive myotatic reflex/continual activation of gamma-motoneurons. Why?

A

brainstem contracting intrafusal M, lengthening nuclear bag/chain fibers (become extremely sensitive)

33
Q

What is the region of the brain that is spontaneously active and activates gamma-motoneurons making muscle spindles more sensitive?

A

brainstem facilitatiry region

34
Q

What is the region of the brain that inhibits gamma motorneurons making the muscle spindle fibers less sensitive. The region requires activation from cortical regions….

A

Brainstem inhibitory region

35
Q

So when there is brain damage that knocks out the brainstem inhibitory region, this leads to what and why?

A

leads to spasticity because the brainstem facilitory region is activating gamma motoneruons = stretch reflexes that fight ANY passive motion

36
Q

Main difference between rigidity and spasticity?

A

rigid: contraction muscles
spas: excessive stretch d/t hyper myotatic

37
Q

What can be seen with decorticate posturing?

A

flexion of upper limbs (disinhibition red nucleus)
extension of lower limbs w internal rotation (disinhibition of reticulospinal and vestibulospinal)
dependent on head postioin

38
Q

What is the most common site for a stroke at which there is unilateral decorticate posture afterwards?

A

internal capsule stroke (loss cortical input)

39
Q

What is contraction of all anti-gravity muscles (arms in extension), loss of input from all structures rostral to the pons (caudal to red nucleus), severe brain injury?

A

decerebrate posturing

16. Neuroscience Exam 2 (17 decks)

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