Motor Control - Reflexes Flashcards Preview

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Flashcards in Motor Control - Reflexes Deck (65):
1

Placing reaction and hopping reaction are examples of

cortical reflexes

2

Stretch (myotactic), golgi tendon, and crossed extensor ar examples of

spinal reflexes

3

vestibular, righting, suckle, yawn, eye/head movements are examples of

Brainstem/midbrain reflexes

4

Reflexes in oder to be effective must be very precise. This "precision" can

make reflexes look like volitional movement

5

difference between reflex and volitional movement

a reflex movement occurs faster than the fastest voluntary motion

6

reflex activity characteristics

precis motions in response to afferent stimuli
mediated at all levels of the CNS
rapid initiation
many elicited even during unconsciousneess

7

volitional activity characteristics

originates in cortical areas associated with judgement, initiative, and motor control
longer onset, latency due to processing
require conscious awareness

8

myotactic reflex (stretch) - appearance

shortening/contraction of a stretched muscle

9

myotactic reflex - purpose

protect mm from tearing due to strain

10

myotactic reflex - characteristics

initiated by muscle spindle
monosynaptic, segmental reflex

11

the muscle spindle is ____ to extra fusel fibers

parallel

12

There are ______ types of fibers with in the muscle____

several
spindle

13

muscle contains _____ and _____ parts

afferent (sensory)
efferent (muscle)

14

intrafual fibers of the muscle spindle have _______ components

both motor and sensory

15

Characeristics of the sensory fiber of a muscle spindle

not contractile
it's the portion sensitive to length
two sensors with different afferents
1. nuclear bag fiber
2. nuclear chain fiber

16

Primary afferent of myotactic reflex

1a fiber

17

characteristics of 1a fiber

large, myelinated
sensitive to both length of mm and how fast that length is changing

18

1a fiber innervates

nuclear bag and nuclear change

19

at resting lenth, the 1a fiber fires

less frequently

20

with stretch, the 1a fiber fires

more frequently

21

with fast stretch, the 1a fiber fires

most frequently

22

The secondary afferent is a ____ fiber

Group II fiber

23

secondary afferent characteristics

smaller, myelinated,
sensitive only to the length of the muscle

24

the secondary afferent innervates

only the nuclear chain

25

Primary Afferent associated with the muscle spindle - summary

large 1a fiber (heavily myelinated, fast velocity, low threshold)
innervates both nuclear bag and nuclear chain fiber
detects length and speed of change of length

26

Secondary Afferent associated with the muscle spindle - summary

group II fiber (smaller, less myelin, still pretty fast)
innervates nuclear chain only
detects only lenth

27

Motor portion of the muscle spindle consists of

intrafusal contractile elements

28

characteristics of motor portion of muscle spindle

same as skeletal muscle
control length of the sensory portion

29

motor portion of the muscle spindle innervated by

gamma motor neuron

30

By contracting intrafual muscles, we

stretch the sensory portion
this renders the sensory portion more sensitive to a superimposed stretch

31

gamma motor neurons are important in

controlling sensitivity

32

alpa motor neurons - summary

large, heavily myelinated fiber
innervates via NMJ the skeletal muscle
responsible for activating muscle
activity directly leads to motion

33

Gamma motor neuron - summary

slightly smaller, slower than alpha, still fast overall
innervates the contractile component of the muscle spindle via nmj
activity causes contraction - controls sensitivity of muscle spindle , does NOT directly lead to motion

34

path of myotactic reflex at spinal level

motor neuron is excited by activation of Ia afferent ==> contraction releives the stretch, returning the Ia discharge rate back to normal

35

stretch reflex - we contract the agonist muscle, what happens to the antagonist muscle? why

it gets stretched
there;s more than just a single synapse, the Ia afferent can also act on interneurons

36

with the stretch reflex, there is a ______ in the activity of the _____ innervating the antagonist allowing____

decrease
alpha motorneuron
relax and lenthen

37

Golgi tendon reflex - aka

invers myotactic, autogenic inhibition

38

Golgi tendon reflex - appearance

sudden relaxation of a contracted muscle

39

Golgi tendon reflex - purpose

to protect muscle from damage due to excessive force

40

Golgi tendon reflex - characteristics

initiated by golgi tendon organ
polysynaptic, segmental reflez

41

Golgi tendon organs

innervate tendon
bare nerve ending with lots of branches
action potentials increase with tension

42

golgi tendon organs use ___ fibers

Ib

43

Golgi tendon reflex - mechanism

Ib afferent is + on the interneurin, which inhibits the motor neuron
result = abrupt relaxation of the muscle occurs, returning golgi tendon organ discharge rate back to normal

44

Myotatic reflex - summary

initiated by muscle spindle
passive stretch of muscle
monosynaptic reflex
contraction of stretched muscle back to normal leng

45

Golgi tendon reflex - summary

reverse myotactic
active contraction of muscle
polysynaptic refles
abrupt relaxation of contracted muscle to prevent damage

46

Motor control - modification of reflexes (general types)

spinal shock
decerebrate posturing
spasticity

47

Spinal shock

even though neurons producing the reflex are below the level of transection, (therefore intact) the reflex fails to occur

48

spinal shock - recovery

results from axonal sprouting below the level of transection
expression of receptor phenotypes that are self activating (5HT-C)

49

Decerebrate posturing results from

loss of all structures rostral to the pons

50

Rigidity

resists motion in all directions
results from maintained mm contraction
continual activation of alpha motor neurons - not due to reflexes, brainstem is activating alpha motor neurons, but why is not clear

51

Spasticity

resists motion in a given direction
myotatic reflex hyperactive
continual activation of gamma motor neurons - contracts nitrafual muscle, lenthens nuclear bag/chain fibers,
brainstem

52

spasticity - brainstem facilitory region

by actuating the gamma motror neurons, makes muscle spindle more sensitive,
this region is spontaneously active

53

Spasticity - brainstem inhibitory region

inhibits gamma motor neurons, making muscle spindle les sensitive
this region requires activation from cortical regions.

54

Spasticity- why the loss the the cortex, the _____ region is not activated, leaving the _____ region to dominate

brainstem inhibitory
brainstem facilitory
the end result of the uncontrolled brainstem facility region is stretch reflexes that fight any passive motion - spasticity

55

patient resists a passive stretch of their muscles
the contraction doesn't start until the stretch occurs
hyperactie myotactic reflex due to increased gamma motor neuron firing

spasticity

56

cause of spasticity

damage to cortex that abolishes activation of the brainstem inhibitory region (brain arousal systems0

57

contraction of muscle in the absence of other stimuli
alpha motor neurons continually active

rigidity

58

cause of rigidity

loss of cortical influence that inhibits a medullary input to the alpha motor neurons.

59

decorticate posturing =

rigidity

60

decorticate posturing - pt position

flexion of upper limb joints
extension of lower limbs
dependant on head position

61

unlike the decerebrate posturing, decorticate posturing is dependent on

head position and while change as the head is moved passively

62

you are extremely likely to see its with unilateral ____ posturing, which commonly results from

decorticate
strokes in the vicinity of the internal capsule

63

Transection of the spinal cord
all reflexes abolished, even if circuit is intact.

Cause>

spinal shock

hyper polarization of spinal neurons due to loss of excitatory input from cortex

64

internal rotation of legs in extended position, flexion of arms, dependent on head position
may be unilateral or bilateral
cause?

Decorticate posturing

loss of cortical inputs - most commonly caused by lesion of internal capsule

65

contraction of all antigravity mm (arms in extension)
usually bilateral and indicative of severe brain injury
cause?

Decerebrate Posture

loss of input from all structures rostral to the pons.