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Term 3 > CNS Unit 7 Descending Systems > Flashcards

CNS Unit 7 Descending Systems Flashcards

1
Q

In the spinal cord, what contents are in the ventral horn?

A
  • This contains motor nuclei that sends axons out
  • Rexed Laminae XI (9), these are motor nuclei for innervation of skeletal muscle - aka Alpha Motor Neurons (LMNs)
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2
Q

The Descending motor pathways are divided into what?

A

Into Medial and Lateral Systems based on their location in the Spinal Cord (SC)

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3
Q

Where does the Lateral Motor System travel, and where does it synapse?
What is this for?

A

(In red)
The Lateral Motor Systems travel in the lateral portion of the spinal cord to synapse on lateral motor nuclei: for Distal limb movements and favoring flexors
Skilled movement

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4
Q

Where does the Medial Motor System travel, and where does it synapse?
What is this for?

A

(In blue)
The Medial motor systems travel in anteromedial portions of spinal cord to synapse on medial motor nuclei for Proximal limb/trunk movements and favoring extensors
Deal with posture and postural balance

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5
Q

What are the tracts in the Lateral Motor System?

A
  • Lateral Corticospinal Tract
  • Rubrospinal Tract
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6
Q

What are the tracts in the Medial Motor System?

A
  • Anterior Corticospinal Tract
  • (Medial/Lateral) Vestibulospinal Tract
  • (Pontine/Medullary)
    Reticulospinal Tract
  • Tectospinal Tract

6 total

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7
Q

What is the function of the Lateral Corticospinal Tract?

A

Most clinically important descending motor pathway
- Controls voluntary, fine, skilled movement of extremities (distal movements)
- Unique contribution is to activate muscles independently of other muscles

Has 2 pathways
- 1st order neuron- UMN
- 2nd order neuron- LMN

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8
Q

Describe the Pathway of the Lateral Corticospinal Tract?

A
  • Originates at the Pre-central Gyrus (B.A 4)
  • It then descends through the Posterior Limb of the Internal Capsule
  • It then travels to the Basis Pedunculi of the Midbrain
  • It then travels to the Basis Pontis of the Pons
  • It then Decussates at the Pyramidal Decussation of the Caudal Medulla (~85-90% of fibers, others go to Anterior Corticospinal tract)
  • It then goes to the Lateral Corticospinal tract, where it then goes to synapse at the Anterior Horn to then go to the muscle
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9
Q

With the Corticospinal Tract, what happens if there is a lesion above the Pyramidal Decussation?

A

This will cause Contralateral weakness

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10
Q

With the Corticospinal Tract, what happens if there is a lesion below the Pyramidal Decussation?

A

This will cause Ipsilateral weakness

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11
Q

The Lateral Corticospinal Tract also contains Corticobulbar Fibers, what do these fibers do?

A

They have direct control of the Cranial Nerves (in “bulb” aka brainstem) to move the face, tongue, jaw, eyelids, and eyes

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12
Q

What is the pathway of the Rubrospinal Tract?

A
  • This originates at Red Nucleus of Midbrain (Mesencephalon)
  • It decussates immediately and crosses to opposite side ventral tegmental decussation
  • It then descends through pons and medulla, then into lateral spinal cord to enter anterior horn and synapse with lateral LMN
    Its thought to be involved in movement of contralateral limbs
  • This tract ends in Cervical Spine
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13
Q

With the Rubrospinal tract, if there is a lesion to one entire half of the midbrain what would happen?

A

It would result in bilateral deficits

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14
Q

What is important to know for the Anterior Corticospinal Tract?

A

remember from the LCST, ~85-90% cross at the pyramidal decussation

  • The Remaining 10-15% of the fibers that did not cross form the Anterior Corticospinal Tract
  • Controls voluntary movement of Bilateral axial and Girdle Musculature (Proximal muscles, i.e. neck, trunk)
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15
Q

What is the Pathway for the Anterior Corticospinal Tract?

A

Basically the same was LCST, except it DOES NOT Decussate
- Originates at the Pre-central Gyrus (B.A 4)
- It then descends through the Posterior Limb of the Internal Capsule
- It then travels to the Basis Pedunculi of the Midbrain
- It then travels to the Basis Pontis of the Pons
- It goes to the Pyramid (in the medulla) and continues down to the Ventral horn (Somewhere in C-Spine)

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16
Q

Where does the Lateral Vestibulospinal Tract originate, whats its pathway and what does it do?

A

Originates at the Lateral Vestibular Nucleus in the Pons; It the descends ipsilaterally
- Goes through entire spinal cord
- In charge of balance for the whole body

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17
Q

Where does the Medial Vestibulospinal Tract originate, what its pathway and what does it do?

A

Originates at the medial (and inferior) Vestibular Nuclei in the Rostral Medulla
- This then splits (one contralaterally and one ipsilaterally) and descends bilaterally
- Terminates in cervical and thoracic cord
- In charge in maintenance of head/neck tone

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18
Q

Where does the Pontine Reticulospinal Tract originate, whats it pathway and what does it do?

A
  • Originates in the Reticular Formation in the Pons (Metencephalon)
    Same as Medullary RST
  • It descends ipsilateral through entire spinal cord to anterior horn to synapse on Medial LMNs
  • Involved with Posture and Gait-related movements
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19
Q

Where does the Medullary Reticulospinal Tract originate, whats it pathway and what does it do?

A
  • Originates in the Reticular Formation in the Medulla (Mylencephalon)
    Same as Pontine RST
  • It descends ipsilateral through entire spinal cord to anterior horn to synapse on Medial LMNs
  • Involved with Posture and Gait-related movements
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20
Q

Where does the Tectospinal Tract originate, what is the pathway, whats its function?

A
  • Originates in the Superior Colliculus (tectum of midbrain) and crosses immediately at Dorsal Tegmental Decussation
  • It then descends contralateral, then enters the Anterior Horn to end in the Cervical Spine
  • Involved in coordination of head and eye movement (e.g. movement in response to visual and auditory stimuli), but function is uncertain
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21
Q

Which division of the ANS is responsible for the fight or flight response?

A

Sympathetic

22
Q

Which division of the ANS is located in the Cranial Sacral regions of the spinal cord?

A

Parasympathetic

23
Q

Which division of the ANS has norepinephrine as the main neurotransmitter?

A

Sympathetic

24
Q

Preganglionic neurons in both the sympathetic and parasympathetic systems release what?

A

Release acetylcholine to activate nicotinic cholinergic receptors

25
Q

Postganglionic neurons in the sympathetic system release mostly what?

A

Norepinephrine onto target end organ noradrenergic receptors

26
Q

Postganglionic neurons in the parasympathetic system release mostly what?

A

Acetylcholine onto muscarinic receptors of end organs

27
Q

With Fight or Flight, Short Preganglionic fibers originate and terminate where?

A

Originate at Rexed Laminae VII of ~T1-L2 and terminate outside of the chord onto either long distance fibers:

  • Paravertebral ganglia on each side of the cord (outside vertebrae) which runs from C4-S4 aka the sympathetic trunk/chain
    or
  • Prevertebral ganglia of the Celiac ganglia (Liver, stomach, pancreas) or at the inferior mesenteric ganglia (intestines, bladder, penis/uterus)
28
Q

With Rest or Digest, Long Preganglionic fibers originate and terminate where?

A

Originate in the parasympathetic divisions of CN III, V, IX, X (brainstem) and at Rexed Laminae VII of spinal cord levels S2-S4
Terminate onto short postganglionic fibers at or near the target end organ

29
Q

With an UMN lesion, will the patient have weakness?

A

Yes

30
Q

With an LMN lesion, will the patient has weakness?

A

Yes

31
Q

With an UMN lesion, will the patient have atrophy?

A

No

32
Q

With an LMN lesion, will the patient have atrophy?

A

Yes

33
Q

With an UMN lesion, will the patient have fasciculations?

A

No

34
Q

With an LMN lesion, will the patient have fasciculations?

A

Yes

35
Q

With an UMN lesion, would a patient have increased or decreased reflexes?

A

Increased

36
Q

With an LMN lesion, would a patient have increased or decreased reflexes?

A

Decreased

37
Q

With an UMN lesion, would a patient have increased or decreased tone?

A

Increased

38
Q

With an LMN lesion, would a patient have increased or decreased tone?

A

Decreased

39
Q

T/F Fasciculations present like spasticity?

A

False

40
Q

T/F Weakness can result from lesions anywhere in the motor bureaucracy?

A

True

41
Q

If a patient has Unilateral face (droop) right arm and right leg weakness or paralysis (hemiparesis) with sensory deficit, which Motor Tract is likely affected? What is a common cause of this?

A
  • This is not likely not medulla/spinal cord. Since they have face weakness this is likely a CN or the corticobulbar fibers that come from the brain.
  • We know that the CN VII comes from the pons so the lesion has to be above the pons, so we know that since its above the Medulla the lesion happened before the pyramidal decussation so we know that the weakness will be contralateral (left side)
  • This is most likely a lesion to BA 4 because there are also sensory deficits, however it may also be internal capsule, basis pontis or cerebral peduncles (LCST and Corticobulbar to face)
  • Can be caused by CVA, hemorrhage, or a tumor may cause this
42
Q

If a patient has unilateral, Right arm and leg weakness or paralysis without sensory deficit, which motor tract is most likely affected? What may cause this?

A

*This is a “pure motor” hemiparesis
- Here we can rule out BA 4 because there are no sensory deficits
- Since they have face weakness this is likely a CN or the corticobulbar fibers that come from the brain, and we know that CN VII comes from above the Pons. So the lesion is above it.
- So the lesion is below the cortex and above the medulla, we are left with Internal capsule, cerebral peduncle or basis pontis, and these are all Lateral corticospinal tract locations
Deficits will be contralateral since lesions was above pyramidal decussation
- Can be caused by lacunar infarct of branches of MCA that feed the insular cortex and Internal capsule

43
Q

What are Motor Neuron Disease (MND)?

A

Diseases that affect UMNs, LMNs, or both without sensory deficits and are most degenerative

44
Q

With Motor Neuron Disease, what is a disease that the UMN is only affect?

A

Primary Lateral Sclerosis

45
Q

With Motor Neuron Disease, what is a disease that both UMN and LMN are affected?

A

Amyotrophic Lateral Sclerosis (ALS)

*Degeneration of both UMN/LMN can lead to respiratory failure and death, onset 50-60 years of age, death within 5 years of diagnosis of norm.

46
Q

With Motor Neuron Disease, what is a disease that the LMN is only affect?

A

Spinal Muscular Atrophy

47
Q

If a patient has a T10 Hemi-cord Lesion (can be caused by stabbing/ bullet), what would be the result of this?

A

Hemicord Lesions: Brown-Sequard Syndrome
- Damage to the lateral corticospinal tract causes ipsilateral weakness
- Damage to posterior columns causes ipsilateral loss of vibration and joint position sense
- Damage to ALS causes causes loss of contralateral pain and temp.

48
Q

If a patient has a T10 Hemi-cord Lesion (can be caused by stabbing/ bullet), where does this often begin?

A

This often begins slightly below the lesion because the anterolateral fibers ascend 2-3 segments as they cross in the anterior commissure (Tract of Lissauer). There may also be a strip of one or two segments of sensory loss to pain and temp ipsilateral to the lesion caused by damage to posterior horn cells at the spinal core entry level before they decussated.

49
Q

With Small lesions-Cervical Cord Syndrome, what will be the result of this?

A

This is damage to spinothalamic fibers crossing in the Anterior Commissure causing bilateral regions of suspended sensory loss to pain and temp.
- Lesions of the cervical cord produce the classic cape distribution; however suspended dermatomes of pain and temp. sensory loss can occur with other levels

50
Q

What is the result of Posterior Cord Syndrome?

A

Lesions of the posterior columns cause loss of vibration and position sense below the level of lesion.
- With larger lesions, there may also be encroachment on the lateral corticospinal tracts causing UMN type weakness

51
Q

What is the result of Anterior Cord Syndrome?

A

This will damage the anterolateral pathways, which causes loss of pain and temperature sensation below the level of the lesion, and damage to to the anterior horn produces LMN weakness at the level of the lesion
- With larger lesions, the lateral corticospinal tracts may be involved causes UMN signs

Term 3 (51 decks)

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