Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Neuroanatomy > Unit 3: Intro to motor systems & spinal cord reflexes pg 85 - 92 > Flashcards

Unit 3: Intro to motor systems & spinal cord reflexes pg 85 - 92 Flashcards

1
Q

What is the function of the lower motor neurons (LMNS)?

A

Innervate contractile elements in the skeletal muscle

Serve as final common pathway neurons: final link between CNS and skeletal muscle cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where are lower motor neurons located?

A
  • spinal cord ventral horn (lamina IX)

- brainstem motor nuclei of cranial nerves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where do lower motor neurons project their axons?

A

• via ventral rootlets of all spinal nerves
• via (most) cranial nerves: III, IV, V, VI, VII, IX, X, XI, XII
(all except I, II, VIII)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where are upper motor neurons located?

A

Supranuclear motor control areas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

The axons that project from upper motor neurons form what pathway and synapse where?

A

axons form descending motor control

pathways and synapse on lower motor neurons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What kind of control of lower motor neurons do upper motor neurons provide?

A

Voluntary and involuntary control

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Lower motor neurons are also affected by direct sensory input at segmental level in _____ and _____.

A
  • Spinal cord

- Brain regions receiving input from cranial nerves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Direct sensory input from lower motor neurons in the spinal cord mediate what?

A

Spinal cord reflexes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Direct sensory input form lower motor neurons in the brain regions receiving input from cranial
nerves mediate what?

A

reflex responses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

There are two types of lower motor neurons. Where are they both located?

A

lamina IX of

spinal cord or cranial nerve nuclei within brainstem

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

There are two lower motor neuron cell types. What are they?

A

Alpha motor neurons

Gamma motor neurons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Axons of alpha motor neurons are comprised of what group type of fibers?

A

A alpha

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Axons of gamma motor neurons are comprised of what group type of fibers?

A

A gamma

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Both alpha and gamma motor neurons are multipolar neurons. Which are larger?

A

Alpha motor neurons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Both alpha and gamma motor neurons exit the CNS with ______ and _______ nerves.

A
  • Spinal

- Cranial

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What kind of skeletal muscle fibers do alpha motor neurons (a type of LMNS) innervate?

A

Extrafusal muscle fibers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What makes up a motor unit?

A

a single α motor neuron and all extrafusal muscle fibers it innervates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

In a small motor unit, 1 α motor neuron may innervate how many
fibers?

A

Tens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

In a large motor unit, 1 α motor neuron may innervate how many
fibers?

A

Hundreds to thousands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Large muscles that carry out strong but crude actions, such as those in the leg, have what kind of motor units?

A

Large

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Muscles that carry out fine motor movements, such as fingers or eyes, have what kind of motor units?

A

Small

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What kind of skeletal muscle fibers do gamma motor neurons (a type of LMNs) innervate?

A

intrafusal muscle fibers of skeletal muscle

• part of the neuromuscular spindle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How are α and γ motor neurons arranged within lamina IX of ventral horn of the spinal cord?

A

somatotopically
• LMNs that innervate extremity muscles are located
more laterally
• LMNs that innervate trunk muscles are located
medially

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Lower motor neurons that innervate extremity muscles are located where in lamina IX of the ventral horn of the spinal cord?

A

More laterally

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Lower motor neurons that innervate trunk muscles are located where in lamina IX of the ventral horn of the spinal cord?

A

More medially

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Neuromuscular spindles (NM spindles) are what kind of receptors?

A

encapsulated mechanoreceptor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Where are NM spindles found?

A

In skeletal muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the function of NM spindles?

A

Monitor amount or velocity of stretch

29
Q

What is the distribution of NM spindles in skeletal muscles?

A

uneven; clustered near tendon
‐ more NM spindles in muscles involved in
skilled movement

30
Q

What is the morphology of NM spindles?

A

fusiform surrounded by CT capsule attached to CT that encloses extrafusal muscle fibers (endomysium)

31
Q

Spinal cord reflexes require:

A
  • afferent limb
  • efferent limb
  • specialized sensory receptors
  • contractile elements
32
Q

What is the afferent limb of spinal cord reflexes?

A

Sensory input provided by 1˚ sensory

neurons → fibers enter spinal cord via dorsal roots of spinal nerves

33
Q

What is the efferent limb of spinal cord reflexes?

A

Motor output provided by lower motor neurons → motor neuron cell bodies located in ventral horn
(lamina IX)

34
Q

The CT capsule of NM spindles encloses what kind of muscle fibers?

A

Intrafusal muscle fibers

35
Q

What are the “main” muscle fibers of skeletal muscle and comprise the mass of the muscle?

A

Extrafusal muscle fibers

36
Q

How are extrafusal muscle fibers arranged in relation to neuromuscular spindles?

A

They are arranged in parallel to the

neuromuscular spindles

37
Q

What happens when extrafusal muscle fibers are stretched?

A

Increased tension in NM spindle and increased tension of intrafusal fibers

38
Q

What happens when extrafusal muscle fibers are contracted?

A

Decreased tension in NM spindle and decreased tension of intrafusal muscle fibers

39
Q

NM spindles receive both sensory and motor innervation. Sensory innervation is via?

A
  • Group A α (type Ia) fibers -> form annulospiral endings

* Group A β (type II) fibers -> form flower spray endings

40
Q

How are fibers and endings of NM spindles activated?

A

when muscle is stretched -> tension in NM spindle increases -> NM spindles are activated -> endings
stimulated -> proprioceptive data produced

41
Q

extrafusal muscle fibers stretched= ________ firing rate of sensory fibers

A

Increased

42
Q

extrafusal muscle fibers contracted= _______ firing rate of sensory fibers

A

Decreased

43
Q

NM spindles receive both sensory and motor innervation. Motor innervation is via?

A

γ motor neurons

44
Q

γ motor neurons control length/tension of ________ within NM spindles and determine sensitivity to stretch of ________.

A
  • intrafusal fibers
  • extrafusal fibers

I.e. increased firing rate of gamma motor neurons = contraction of intrafusal fibers; increased sensitivity to stretch of extrafusal fibers

45
Q

Stretch Reflex (aka deep tendon reflex; DTR) requires 2 neurons:

A
  • ‘afferent limb’: sensory neuron (type Ia, II fibers) - - ‘efferent limb’: alpha motor neuron -> supplies extrafusal fibers
46
Q

What is a monosynaptic reflex?

A

two neurons, one synapse as seen in stretch reflex

47
Q

High velocity muscle stretch initiates _____.

A

Stretch Reflex (aka deep tendon reflex; DTR)

48
Q

Tapping the quadriceps/infrapatellar tendon will cause what chain of events?

A
  • high velocity muscle stretch
  • spindle (sensory endings) activation
  • sensory info relayed to spinal cord via Type Ia and II fibers
  • some collateral processes join ascending pathways
  • some collateral processes synapse on alpha motor neurons
  • alpha motor neurons cause contraction of extrafusal fibers of homonymous muscle
49
Q

During muscle contraction caused by deep tendon reflex, why does the contraction not last indefinitely?

A

Because, during the contraction, the spindle tension decreases which decreases firing of sensory fibers, loss of activation of alpha motor neurons and muscle relaxation.

50
Q

What kind of receptors are Golgi tendon organs (GTOs; neurotendinous spindles)?

A

encapsulated proprioceptors that contain thin capsule of CT that surrounds
some collagenous fibers of the tendon

51
Q

Where are Golgi tendon organs (GTOs; neurotendinous spindles) most numerous?

A

near attachments of tendons to muscle

52
Q

Golgi tendon organs (GTOs; neurotendinous spindles) are supplied by what group of fibers?

A

type Ib fiber type sensory

afferents

53
Q

What do Golgi tendon organs (GTOs; neurotendinous spindles) monitor in muscle-tendon units?

A

Tension

54
Q

What happens to GTO tension during muscle contraction? What does this do to the firing of the type Ib fibers?

A

GTO tension increases = Increased type Ib fiber firing

55
Q

UMNs are able to influence motor activity (muscle tone) by two mechanisms:

A
  • directly synapsing on γ (gamma) motor neurons

- indirectly synapsing on α (alpha) motor neurons

56
Q

What does a poly synaptic reflex involve?

A

More than 2 neurons and more than 1 synapse

57
Q

What is a flexor reflex?

A

protective reflex involving withdrawal of a body part from a noxious stimulus

58
Q

Interneurons of the flexor reflex will synapse on two things:

A
  • α motor neurons of flexor muscles to stimulate them

- α motor neurons of extensor muscles to inhibit them

59
Q

What is reciprocal innervation?

A

activation of flexor muscles, inhibition of antagonist muscles (extensors)

60
Q

In the flexor reflex, how is significant muscle activation achieved?

A

Motor neurons at multiple cord levels must be activated via collaterals traveling to superior and inferior segments

61
Q

What two pathways can the flexor reflex travel to different spinal cord levels in order to involve motor neurons at multiple levels for sufficient muscle activation in the flexor reflex?

A
  • collaterals of Lissauer’s tract

- interneurons within fasciculus proprius (propriospinal tract)

62
Q

Where is fasciculus proprius located?

A

immediately adjacent to spinal cord gray

63
Q

The neurons that travel in fasciculus proprius are termed________.

A

Spinospinalis neurons

64
Q

What is crossed extension/extensor reflex?

A

some dorsal horn neurons (interneurons) have axons that decussate and synapse on neurons in the contralateral ventral horn for activation of contralateral ventral horn neurons to induce muscle contraction of contralateral extensor muscles

65
Q

When GTOs ‘fire’ due to increased tension and send sensory impulses through type Ib fibers along ascending
conscious pathways and onto interneurons in the spinal cord gray to do what?

A

inhibit alpha motor neurons that

supply the homonymous muscle

66
Q

What is the gamma reflex loop?

A

“functional complex’ of structures that play an

important role in controlling muscle tone

67
Q

What are the components of the gamma reflex loop?

A

a. γ motor neurons
b. intrafusal muscle fibers of the NM spindle
c. type Ia, II fibers
d. α motor neurons
e. extrafusal muscle fibers

68
Q

Interruption of the gamma reflex loop results in:

A
  • no paralysis
  • decreased muscle tone
  • loss of associated DTR
  • loss of stretch reflex
  • lack of strength and precision of muscle contraction
69
Q

descending motor control fibers from higher centers that influence LMNs terminate on gamma motor neurons resulting in:

A

increased activity of γ motor neurons → increased type Ia, II fiber firing → info travels to spinal cord → increased facilitation of α motor neurons → increased tone of extrafusal fibers → increased muscle tone

Neuroanatomy (21 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions