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MD4001 Physiology > Descending Pathways > Flashcards

Descending Pathways Flashcards

1
Q

What are the different classes of movement?

A
  • Voluntary
  • Reflexes
  • Rhythmic motor patterns
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2
Q

What are the 3 phases of movement/motor control?

A
  • Plan/strategy
  • Programme/tactics
  • Execution
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3
Q

What are the 5 areas of the brain which give rise to descending tracts?

A
  • Corticospinal tract (pyramidal) (cerebral cortex)
  • Reticular formation (brain stem + medulla)
  • Vestibular nuclei (brainstem + medulla)
  • Red nucleus (brainstem + medulla)
  • Tectum (brainstem + medulla)
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4
Q

What are the extrapyramidal tracts?

A
  • Reticulospinal (reticular formation)
  • Vestibulospinal (vestibular nuclei)
  • Rubrospinal (red nucleus)
  • Tectospinal (tectum)
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5
Q

What percentage of corticospinal tract fibres originate in the motor cortex?

A

66%

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6
Q

What percentage of corticospinal tract fibres cross at the medulla (pyramidal decussation)?

A

80-90%

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7
Q

In what area are the arm fibres in comparison to the leg fibres located in the spinal tract?

A

The right (more lateral in spinal cord) (more medial in brainstem)

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8
Q

What do the corticospinal fibres which do not cross (remain ipsilateral) control?

A

Cervical and upper thoracic segments (control axial muscles)

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9
Q

In what lobe is the primary auditory complex found?

A

Temporal

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10
Q

What are the 3 areas recognised within the cerebral motor cortex?

A
  • Primary motor cortex (M1 or Brodmann’s area 4)
  • Premotor cortex (Brodmann’s area 6)
  • Secondary motor cortex (supplementary motor cortex, M2 or Brodmann’s area 6 and 8)
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11
Q

What does Jacksonian epilepsy illustrate?

A

Primary and secondary motor cortices are somatotropically arranged
- Twitching begins at extremities then moves to hand then arm etc.

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12
Q

Does the secondary motor cortex control the muscles of the opposite side?

A

Can control muscles of both sides

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13
Q

Where do the rubrospinal tracts originate?

A

Red nucleus

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14
Q

Where do the fibres of the rubrosoinal tracts terminate?

A

Interneurons of ventral (motor) horn in contralateral spinal cord

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15
Q

Where do the rubrospinal tracts receive there input from?

A

Motor cortex area somatotropically

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16
Q

Where do tectospinal tracts originate?

A

Superior colliculus

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17
Q

Where do fibres of the tectospinal tract terminate?

A

Interneurons in the contralateral cervical region of the spinal cord

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18
Q

What is the tectospinal tract thought to control?

A

Head movements in response to visual and auditory input

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19
Q

Where do the vestibulospinal tracts originate?

A

Vestibular nuclei

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20
Q

Where do the vestibulospinal tract fibres receive inibitory and excitatory input from?

A
  • Inhibitory - Cerebellum

- Excitatory - vestibular apparatus

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21
Q

Where do the vestibulospinal tract fibres terminate?

A

Lateral uncrossed, terminate on interneurons on ipsilateral spinal cord

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22
Q

Where do reticulospinal tracts originate?

A

Reticular formation

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23
Q

Where do reticulospinal tracts terminate?

A

Largely uncrossed, terminate on interneurons within spinal cord

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24
Q

WHat do reticulospinal tracts control?

A
  • Muscles of trunk and proximal limbs
  • Maintain posture and startle reactions
  • Damage may lead to spasticity
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25
Q

What do the medullary lateral reticulospinal tracts inhibit?

A

Extensor spinal reflex activity and facilitates flexor activity

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26
Q

What do the Pontine (medial) reticulospinal tracts facilitate?

A

Extensor spinal reflex activity

27
Q

What is the function of the medial motor pathways?

A

Maintenance of posture and startle reactions

28
Q

What can damage to the medial motor pathways lead to?

A

Spasticity

29
Q

What is the usual clinical presentation of a motor pathway lesion in the muscle itself (e.g myositis/muscular dystrophy)?

A
  • Normal reflexes

- Weakness/wasting

30
Q

What is the usual clinical presentation of a motor pathway lesion at the neuromuscular junction (e.g myasthenia gravis)?

A
  • Fatigable weakness
  • Normal reflexes
  • Normal muscle bulk
31
Q

Where can motor pathway lesions take place?

A
  • Muscle
  • Neuromuscular junction
  • Motor neurons (UMN, LMN)
  • Cerebellum
32
Q

What afre the usual clinical presentations of an individual with a motor pathway lesion in the cerebellum?

A

Normal reflexes, strength, slight decrease in tone

33
Q

What are the usual clinical presentations with an individual with a motor pathway lesion in the basal ganglia (e.g Parkinson’s, Huntington’s)?

A

Movement changes

34
Q

Where are upper motor neuron’s cell bodies located?

A

In brain or brainstem and do not project outside CNS

35
Q

Where are lower motor neuron’s cell bodies located?

A

Brainstem or spinal cord and project outside the CNS to muscle

36
Q

What happens to muscle bulk in an UMN lesion compared to a LMN lesion?

A

UMN - normal

LMN - decreased

37
Q

What ahppens to reflexes in UMN and LMN lesions?

A

UMN - increased

LMN - Absent

38
Q

What is the effect of a UMN on power?

A
  • Reduced extensors in arm

- Reduced flexors in leg

39
Q

What is the effect of a LMN lesion on power?

A

Decreased

40
Q

What happens in the Plantar response / Babinksi test if the patient has a UMN lesion?

A

Extension

41
Q

What happens in the Plantar response / Babinksi test if the patient has a LMN lesion?

A

Absent if leg/foot involved in lesion

42
Q

What does hemiplegia mean?

A

Paralysis of limbs on one side of the body

43
Q

What are the patterns of weakness in an UMN lesion?

A
  • Arm extensors weaker than flexors (flexors are stronger)
  • Leg flexors weaker than extensors (extensors are stronger)
  • Causes bent arm and walking on tip toes
44
Q

More distal muscles’ motor neurons are situated where in the spinal cord?

A

More laterally

45
Q

The neurons of extensors are situated where in comparison with flexors?

A

Extesnors - ventral

Flexors - dorsal

46
Q

Where are alpa-motorneuron’s cell bodies located?

A

Clumps within ventral horn of spinal cord (LMNs)

47
Q

What does each motorneuron activate?

A

A motor unit (6-1500 skeletal muscle fibres)

48
Q

What are the interneurons which cause recurrent or feedback inhibition called?

A

Renshaw cells (suppress weakly firing motor neurons and dampening strongly firing ones, produces economical movement)

49
Q

What is the overall purpose of Renshaw cells?

A

Helps make smooth, sustained movement, removes certain jerkiness

50
Q

What fibres are involved in the myotatic (knee jerk) reflex?

A

Ia fibres - muscle spindles

51
Q

What are muscle spindles?

A

Main proprioceptorsthat provide information about the state of musculature
Sensory muscle fibre

52
Q

What are the muscle spindles motor input called?

A

Gamma input

53
Q

What are the sensory muscle spindle fibres called?

A

Ia and II

54
Q

Where are muscle spindles particularly numerous?

A

Fine motor control muscles

55
Q

How long is a muscle spindle?

A

1cm

56
Q

What is the purpose of the motor input (gamma) on the muscle spindles?

A

Allows muscle spindle to detect changes in length irrespective of what is happening to the muscle itself

57
Q

What is the main role of muscle spindle?

A

Used as comparators for maintenance of muscle length during goal directed voluntary movements

58
Q

What is alpha gamma coactivation?

A

Simultaneous activation of extrafusal fibres (alpha-motorneurons) and intrafusal fibres (gamma-motorneurons) (whenever muscle is contracted, muscle spindle also is)

59
Q

What info does the golgi tendon provide?

A

Force of contraction in a muscle (tension generated in muscle)

60
Q

Where is the golgi tendon situated?

A

Within the tendon

61
Q

What is the purpose if the inverse myotactic (golgi tendon) reflex and how does it work?

A
  • Contributes to maintenance of posture
  • Increase in tension causes increase in firing to dorsal root - inhibits extensor and stimulates flexor
  • Prevents overuse of force in muscle and ripping of muscle
  • When tension is generated nerve fibre is squashed setting of signals
62
Q

What does the withdrawal reflex and crossed extensor reflex allow for?

A
  • Protective reflex of rapidly removing limb from damaging stimuli
  • Simulation of withdrawal reflex, frequently elicits extension of the contralateral limb 250ms later
  • Helps maintain posture and balance
63
Q

What is the Central Pattern Generator (CPG)?

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

MD4001 Physiology (22 decks)

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