Brainscape's Knowledge GenomeTM

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


See full index

Anatomy 6512 > Descending Motor Systems > Flashcards

Descending Motor Systems Flashcards

1
Q

What does the Lower Motor Neuron innervate?

A

striated muscles, it directly signals the muscle to contract which is the only way movement can be initiated

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

True or false: The Lower Motor Neuron is the first in a chain of neurons.

A

False, it is the last.

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

What two parts are included in the Lower Motor Neuron?

A

1) Alpha motor neuron - extrafusal muscle fibers

2) Gamma motor neuron - intrafusal muscle fibers

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

What are the symptoms of a Lower Motor Neuron lesion?

A

1) Atonia - loss of muscle tone
2) Areflexia - loss of myotatic (knee jerk) reflex
3) Flaccid paralysis
4) Fasciculations - spontaneous muscle contractions
5) Atrophy - loss of muscle tissue

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

What is an Upper Motor Neuron?

A

Axons that descend from the cortex, and end on or near LMN

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

What are the symptoms of an Upper Motor Neuron lesion?

A

1) Spastic paralysis (paresis)
2) Hypertonia (increased resting tension) - Arm flexors, leg extensors
3) Hyperreflexia
4) Pathologic reflexes, e.g. negative plantar reflex or Babinski sign
5) Big toe dorsoflexion with fanning of other toes when side of heal is stroked

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

What are fascinations?

A

spontaneous contractions of small groups of muscle fibers that can be visible at the skin surface.

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

What are fibrillations?

A

are contractions of individual muscle fibers that can not be seen visually but are detected using electrical monitoring.

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

What are clonus?

A

a rapid series of alternating muscle contractions that occur in response to the sudden stretch of a muscle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q 
During a routine exam you note that the patient has tongue fasciculations. This raises concern for:
A) Corticospinal tract injury
B) Primary myopathy
C) Lower motor neuron injury
D) Neuromuscular junction disorder
E) Hypoglossal nuclear injury
A

C) Lower motor neuron injury, decreased muscles tone and stretch reflexes or severe atrophy would also indicate this.

UMN injury would have increased muscle tone, stretch reflexes and mild atrophy, and clonus/pathologic reflexes like Babinski sign etc.

*Both show decreased muscle strength

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

Where are lower motor neuron cell bodies?

A

in anterior horn

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

LMN axons in ventral root divide into …

A

terminal branches widely distributed in target muscle, each branch ends at one neuromuscular junction

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

What is the systematic arrangement of motor neurons?

A

1) Neurons controlling axial muscles are medial to those controlling distal muscles
2) Neurons controlling flexors are located posterior to the extensor groups

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

What is a motor unit?

A

1 motor neuron + all myofibers it innervates = motor unit

They vary in size, related to control we have over the muscle

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

How many muscle fibers are in an extraocular muscle motor unit?

A

10 myofibers/motor unit

*Large antigravity muscle like gastrocneumius 100s up to 1000myofibers/ motor unit

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

What are the three kinds of muscle fibers?

A

1) Standing: contract weakly for long periods
2) Running: contract strongly for short/long periods
3) Jump: contract very strongly for very short periods

*Each muscle fiber type populates one motor unit, no mixing

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

What is the difference between Type 1 and Type 2 muscle fibers?

A

1) “one (type 1) slow (twitch) fat (lipid-rich) red (appearance) ox (oxidative, mitochondria-rich), (duck breast muscle)
2) Type 2 - fast twitch, scant lipids, abundant glycogen, few mitochondria, (turkey breast muscle)

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

How does motor control work?

A

1) Basal ganglia and cerebellum influence cerebral cortical output to cord and brainstem
2) Basal ganglia, cerebellum and association cortex are vital in design, choice and monitoring of movement, but note they have no direct effect on LMN
3) Damage to these areas does not cause weakness, may have involuntary movements, incoordination, difficulty initiating movement

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

Hows does motor control work in higher centers?

A
  • Hierarchical in that cortex “decides” what movement should occur - Premotor cortex plans and tells motor cortex and then the LMN what to do
  • Parallel arrangement as premotor cortex can directly “talk to” LMN
  • Basal ganglia and cerebellum involved in planning and monitoring movements, have no (few) outputs to spinal cord instead they effect motor and premotor cortex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Where do descending motor pathways terminate or synapse?

A

Dorsal horn neurons & Interneurons

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

Where does the Corticospinal tract (pyramidal tract) run?

A
  • Cortex to spinal cord, classic upper motor neuron

- Some fibers to hand region of cord terminate on primary motor neurons in anterior horn

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

Where does the Corticobulbar (corticonuclear) tract run?

A
  • Cortex to brainstem
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Where does the Corticopontine tract

run?

A
  • Cortex to basilar pons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are other descending motor pathways?

A

1) Rubrospinal tract
2) Reticulospinal tract
3) Vestibulospinal tract

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

What percentage of the corticospinal tract fibers is from the precentral gyrus?

A

40% from primary motor area (Area 4)

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

What percentage of the corticospinal tract fibers is from the post central gyrus?

A

~ 25% from Somatic sensory area (Areas 3, 1, & 2)

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

What percentage of the corticospinal tract fibers is from the Premotor area?

A

~ 20% Area 6, lateral surface

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

What percentage of the corticospinal tract fibers is from the Supplementary motor area?

A

~ 10%, Area 6, medial surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What percentage of the corticospinal tract fibers is from the Superior parietal lobule?

A

~ 5% (Areas 5 & 7)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Where is the primary motor area?

A

Area 4 on medial and lateral aspect

31
Q

What is the function of the primary motor area?

A

Function:

1) Execution of contralateral voluntary movements
2) Control of fine digital movements

32
Q

Where do projections from the Primary Motor Area go?

A

Projects to brainstem & spinal cord – some monosynaptic terminations on spinal cord motor neurons (hand)

33
Q

What is the result of a lesion on the Primary Motor Area?

A

Paralysis of contralateral musculature

34
Q

Where is the premotor area?

A

Area 6 on lateral aspect

35
Q

What is the function of the premotor area?

A
  • Plans movements in response to external cues (e.g., instructions)
  • Control of proximal and axial musculature (trunk, shoulder, hip)
  • May assemble empathetic facial movements
36
Q

Where do projections from the Premotor Area go?

A

to primary motor area and reticular formation

Some fibers project to all spinal cord levels

37
Q

What is the result of a lesion on the Premotor area?

A

Moderate weakness of contralateral proximal muscles

Loss of ability to associate learned hand movements to verbal or visual cues

38
Q

Where is the supplementary motor area?

A

Area 6 on medial aspect

39
Q

What is the function of the supplementary motor area?

A

Function:

  • Plans movements while thinking (internally paced)
  • Assembles (learns) new sequence (playing new music)
  • Assembles previously learned sequence (music scale)
  • “Imagines” movements
40
Q

Where do projections from the supplementary motor area go?

A

Projects to premotor and primary motor areas

41
Q

What areas does the Parietal Lobe take up?

A

Areas 3, 1, & 2 Somatic sensory areas; Areas 5 & 7 Superior parietal lobule

42
Q

Where do projections from the Parietal Lobe go?

A
  • Project to primary motor area - Direct motor patterns in response to sensory input
  • Project to sensory areas of brainstem and spinal cord
    Modulate sensory signals
43
Q

Where do collateral projections from the Corticospinal tract go?

A

to basal ganglia, thalamus, reticular formation, various sensory nuclei (posterior column nuclei), posterior & intermediate horns of spinal cord

44
Q

True or false: all movements are dependent on CST

A

False, if cut in monkeys, after a period of flaccid paralysis, they move again, fine finger movement lost permanently

45
Q

Where does Corticospinal tract originate?

A

in cerebral cortex, precentral gyrus and nearby areas (Betz cells; layer V)

46
Q

Where does Corticospinal Tract descends and decussate?

A

Descends thru cerebral peduncle, basis pontis, medullary pyramid, decussates at spinomedullary junction

47
Q

Lateral CST

A
  • 85% of fibers cross in decussation in medulla descend in lateral funiculus
  • The CST is Somatotopically organized
48
Q

Anterior CST

A
  • 15% of fibers, uncrossed descend in anterior funiculus

* Axial muscle activity, some actually cross in anterior commissure prior to synapsing

49
Q

Select the true response about the corticospinal tract (CST).
A) It has no somatotopic organization
B) It consists of small bundles in the midbrain
C) A left sided spinal cord lesion that involved the CST would cause ipsilateral weakness
D) Lesions are associated with flaccid paralysis
E) Decussates in the pons

A

D) Lesions are associated with flaccid paralysis

50
Q

What does Rubrospinal tract

control?

A

Control of shoulder and proximal arm musculature

51
Q

What does Reticulospinal tract control?

A

Control of axial musculature - walking

52
Q

What does Vestibulospinal tract control?

A

Control of axial musculature - balance

53
Q

What does Tectospinal tract control?

A

believed to be important in head turning reflexes in response to visual stimuli, unclear function in humans

54
Q

Where is the origin of the Vestibulospinal tract?

A

Origin: vestibular nuclei in pons

55
Q

Where does the Vestibulospinal tract receive input from?

A

Vestibular end organ and cerebellum (balance)

56
Q

Lateral vestibulospinal tract

A

Projects via lateral funiculus to:

- Ipsilateral spinal cord, facilitates antigravity muscles

57
Q

Medial vestibulospinal tract

A

Projects via anterior funiculus to:

Spinal cord cervical levels bilaterally, controls head movements in response to gravity

58
Q

What is the function of the vestibulospinal tract?

A

Function:

  • Mediates postural adjustments & head movements
  • Antigravity reflexes
  • Righting reflex (cats); righting reflex to head inversion
59
Q

What is the origin of the Rubrospinal tract?

A

Origin: red nucleus of midbrain (so “rubro”)

60
Q

Where does the Rubrospinal tract receive input from?

A

Receives input from:
Primary and premotor areas – shoulder and arm control
Cerebellum

61
Q

What is the course of the Rubrospinal tract?

A
  • Ventral tegmental decussation

- Lateral funiculus

62
Q

Where do projections from the Rubrospinal tract area go?

A

Projects to contralateral spinal cord

63
Q

What is the function of the rubrospinal tract?

A

Function: like that of vestibulospinal tract;

  • Facilitates upper extremity flexor muscle tone
  • Believed to be small in humans, some question significance
64
Q

What is the origin of the Reticulospinal tract?

A

Origin: brainstem reticular formation (pons and medulla)

65
Q

Where does the Reticulospinal tract receive input from?

A

Receives input from:

Motor and somatic sensory cortex

66
Q

What is the course of the Reticulospinal tract?

A
  • Brainstem - anterior to medial longitudinal fasciculus (MLF)
  • Spinal cord – anterior funiculus
67
Q

Where do projections from the Reticulospinal tract area go?

A

Spinal cord bilaterally (courses in anterior funiculus)

68
Q

What is the function of the rubrospinal tract?

A

Supports rhythmic motor actions including walking

*May support recovery of function via projections to motor neurons controlling arm and hand

69
Q

Where does the Tectospinal tract originate?

A

Originating here from superior colliculus (SC)

70
Q

What is the course of the Corticobulbar pathway?

A

fibers leave the cerebral cortex and descend to the brainstem where they end directly on motor neurons (XII), but most end on interneurons in the reticular formation

71
Q

Do III, IV, VI receive direct input from the Corticobulbar pathway?

A

No

72
Q

What receives bilateral input from the Corticobulbar pathway?

A

V, VII, XII, nucleus ambiguus & XI

73
Q

True or false: no corticobulbar decussation exists

A

True, it descends with CST to level of target nucleus, then splits off

74
Q

Facial motor nucleus

A
  • Exception to typical CBP pattern
  • Motor neurons to lower facial muscles mainly innervated by contralateral cortex, but upper facial muscles innervated bilaterally
  • Unilateral damage to CBP (e.g. in cerebral peduncle) result:
  • Inability to smile or show teeth symmetrically; but ability to wrinkle forehead is unaffected

Anatomy 6512 (26 decks)

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