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MD4001 > Descending Pathways > Flashcards

Descending Pathways Flashcards

1
Q

What are the classes of movement?

A

• Voluntary:

  • complex actions e.g. reading and writing
  • purposeful, goal directed
  • learned
  • Reflexes
  • Rhythmic motor patterns
  • combines voluntary and reflexive acts
  • initiation and termination is voluntary
  • once initiated, repetitive and reflexive
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2
Q

What are the functions of motor control systems?

A
  • Posture and balance
  • Goal directed movements
  • Communication
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3
Q

What areas of the brain give rise to descending tracts?

A 
• Corticospinal tract from cerebral cortex
From brainstem and medulla:
• Reticulospinal 
• Vestibulospinal 
• Rubrospinal 
• Tectospinal
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4
Q

Where does the corticospinal tract originate?

A

2/3 originate in the motor cortex

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5
Q

Where do the fibres of the corticospinal tract cross?

A
  • Lateral corticospinal crosses at the medulla (pyramidal decussation)
  • Anterior corticospinal remains ipsilaterally to cervical and upper thoracic segments
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6
Q

What is the function of the lateral corticospinal tract

A
  • Runs the length of the spinal cord

* Control voluntary fine movements of distal muscles, particularly flexors

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7
Q

What is the function of the anterior corticospinal tract?

A

Control axial muscles

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8
Q

What does Jacksonian epilepsy highlight?

A
  • Twitching begins at the extremities then movement of the hand and then of the arm
  • Reflects the spread of excitation over the cortex from epileptic focus
  • Shows the somatotropic arrangement
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9
Q

What is the difference in which muscles can be controlled by the primary and secondary motor cortices?

A
  • Primary controls muscles of opposite side of the body

* Secondary controls muscles on both sides

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10
Q

Where does the rubrospinal tract originate?

A

In the red nucleus in the midbrain

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11
Q

Where do the fibres of the rubrospinal tract cross?

A

Midbrain - ventral tegmental decussation

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12
Q

Where do the fibres of the rubrospinal tract terminate?

A

On interneurones of ventral (motor) horn in the contralateral spinal cord

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13
Q

What is the function of the rubrospinal tract?

A

Facilitates flexor motor neurones and inhibits extensor motor muscles

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14
Q

Where does the tectospinal tract originate?

A

In the superior colliculus

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15
Q

Where do the fibres in the tectospinal tract terminate?

A

In interneurones in the contralateral cervical region of the spinal cord

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16
Q

What is the function of the tectospinal tract?

A

Controls head movements in response to visual and auditory input

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17
Q

Where does the vestibulospinal tract originate?

A

In vestibular nuclei

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18
Q

What inputs does the vestibulospinal tract receive?

A
  • Inhibitory input from the cerebellum

* Excitatory from the vestibular apparatus

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19
Q

Lateral vestibulospinal tract

A
  • Fibres don’t cross, terminate on interneurones in ipsilateral spinal cord
  • Control extensor muscle motor tone of the proximal limbs
  • Maintenance of erect posture
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20
Q

Medial vestibulospinal tract

A
  • Bilateral
  • Terminate on interneurones in the cervical region
  • control the neck muscles
  • Keep head upright when body moves
21
Q

Where does the reticulospinal tract originate?

A

Pontine reticular formation

22
Q

Where do the fibres of the reticulospinal tract terminate?

A

Largely uncrossed, terminate on interneurons within the spinal cord

23
Q

What is the function of the reticulospinal tract?

A

Control muscles of the trunk and proximal limbs
• Medullary (lateral) tracts inhibit extensor spinal reflex activity and facilitates flexor activity
• Medial (pontine) tracts facilitate
• Maintenance of posture and startle reactions

24
Q

What may be caused by damage to the reticulospinal tract?

A

Spasticity

25
Q

Muscle motor pathway lesion

A
  • Myositis, muscular dystrophy
  • Normal reflexes
  • Weakness/ wasting
26
Q

Neuomuscular junciton motor pathway lesion

A
  • Myasthenia gravis
  • Fatigueable weakness
  • Normal reflexes
  • Normal muscle bulk
27
Q

Motor neurone motor pathway lesion

A
  • UMN: CVA, spinal cord trauma

* LMN: motor neurone disease, neuropathy

28
Q

Cerebellum motor pathway lesion

A
  • Incoordinaiton, multiple sclerosis
  • Normal reflexes and strength
  • Slight change in tone
29
Q

Basal ganglia motor pathway leison

A
  • Parkinsons, Huntington’s

* Movement changes

30
Q

Describe upper motor neurones

A
  • Cell bodies are in the brain or brainstem and do not project outside of the CNS
  • orchestrate complex directed movements
31
Q

Describe lower motor neurones

A
  • Cell bodies are in the brainstem or spinal cord and project outside the CNS to muscle
  • Single muscle innervation, cell bodies in the ventral horn of the spinal cord or motor nuclei of the brainstem
32
Q

Muscle bulk in UMN vs LMN lesion

A
  • UMN - normal

* LMN - decreased

33
Q

Reflexes in UMN lesion vs LMN lesion

A
  • UMN - increased

* LMN- absent

34
Q

Tone in UMN lesion vs LMN lesion

A
  • UMN - increased

* LMN - decreased

35
Q

Power in UMN lesion vs LMN lesion

A
  • UMN - Reduced extensors in arm, flexors in leg

* LMN - decreased

36
Q

Co-ordination in UMN vs LMN lesion

A
  • UMN - normal

* LMN - normal

37
Q

Plantar response in UMN lesion vs LMN lesion

A
  • UMN - extensor (normal is a flexed response)

* LMN - absent if leg/foot involved in lesion

38
Q

What is a normal plantar response - Babinski

A

Toes go down (flexion)

39
Q

Lamina I-VI

A

Terminations for primary afferent sensory neurones and neurones of reflex circuits

40
Q

Lamina VI

A

Sensory input from joints and muscles

41
Q

Lamina VII and IX

A

Cell bodies of motor neurones

42
Q

Describe the location of motor neurones supplying the trunk vs those supplying distal muscles

A
  • Those supplying the trunk are situated medially

* Those supplying the distal muscles are situated laterally

43
Q

Describe the location of motor neurones that flex the limbs vs those that extend the limbs

A

Motor neurones that flex the limbs lie dorsal to those that extend the limbs

44
Q

What are Renshaw cells and what do they do?

A
  • Interneurones

* Suppresses weakly firing motor neurones and dampens strongly firing ones to produce economical movement

45
Q

What reflects the importance of Renshaw cells?

A
  • Strychnine poisoning
  • Disables Renshaw cells
  • Leads to convulsions
46
Q

Describe the Myotatic reflex (knee jerk)

A
  • Monosynaptic stretch reflex
  • Tap of the patellar tenon stretches the quadriceps muscle
  • Stimualtes nuclear bag receptors of the muscle spindle
  • Increases the rate of firing of group IA afferent fibres leading to the contraction of the quadriceps muscle
  • The IA fibres also stimulate inhibitory interneurones which inhibit antagonistic (flexor) muscles of the knee joint
47
Q

When is the knee jerk reflex lost?

A

If there is damage to the lower lumbar dorsal roots of the spinal cord

48
Q

What is the step cycle

A

• Stance phase:
- foot touching the ground, flexion of the knee and ankle
- finishes with extension about all joints for forward movement
• Swing phase:
- bending (flexion) of hip, knee and ankle followed by knee and ankle straightening (extension)
• Alternates between the swing and stance phase

49
Q

What is the central pattern generator

A
  • Located in the spinal cord
  • Capable of autonomous signals
  • Modulated by proprioception input
  • Thought to be initiated by mesencephalic locomotor region - output thought to be through reticular nuclei and reticulospinal tracts

MD4001 (28 decks)

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