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NHB > Descending Motor Pathways > Flashcards

Descending Motor Pathways Flashcards

1
Q

What does the ventromedial pathway do?

A

Controls axial and proximal limb muscles

Whole body movement

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2
Q

What are the three types of ventromedial pathway?

A
  1. Reticulospinal
  2. Vestibulospinal
  3. Tectospinal
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3
Q

What are the dorsolateral systems for?

A

Goal-directed movements of limbs, esp. hands, feet and face

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4
Q

What is the rubrospinal pathway?

A

Arises in red nucleus in midbrain

Type of dorsolateral system

Vestigial in man

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5
Q

What is the corticospinal tract?

A

Arises in motor cortex

Largest descending pathway in mammals

Dominant descending control system in man

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6
Q

Give three systems that contribute to postural stability

A
  1. Somatosensory
  2. Vestibular
  3. Visual
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7
Q

What is the vestibular system?

A

Proprioceptive system located in the inner ear labyrinth

Particular important for postural control

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8
Q

What are the vestibular system receptors?

A

Sensory hair cells

Located in the labyrinth in the semicircular canals and otolith organs (utricle and saccule)

Hair cells have directional sensitivity

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9
Q

What is the structure of the utricle and saccule?

A

Hair cells project into a jelly-like mass on which gravity acts

Different hair cells arranged to have different directional sensitivity

Afferents give head position signal

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10
Q

What is the structure of the semicircular canals?

A

Hair cells embedded in a cupula, which almost closes off the canal

Cupula is neutrally buoyant in the endolymph so is stationary when the head is stationary

Hair cells activated when cupula is deflected

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11
Q

What is the fluid in the semicircular canals?

A

Endolymph

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12
Q

What kind of signal do the utricle and saccule send?

A

Head position

Static signal

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13
Q

What kind of signal do the semicircular canals send?

A

When head movement begins or stops

Dynamic signal

Provide signals for feedforward control

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14
Q

What is the vestibular reflex?

A
  1. Postural instability detected by vestibular receptors
  2. Generates powerful vestibular correcting responses through connections in vestibulospinal pathway
  3. Principally influences extensor anti-gravity muscles
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15
Q

When might the vestibular system be damaged?

A
  1. Labyrinthitis (peripheral damage)
  2. Brainstem stroke (central)
  3. Cerebellar damage (central)

Plasticity reduces symptoms with time

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16
Q

What are neck reflexes?

A

Exactly equal and opposite to vestibular reflexes

Generated by neck proprioceptors

Permits differentiation between vestibular signals generated by body sway or neck movement

17
Q

What mediates adjustment of neck reflexes?

A

The cerebellum

18
Q

Where is the control system for consensual eye movement?

A

Brainstem

19
Q

What is the vestibulo-ocular reflex?

A

Vestibular system detects head movement and drives equal and opposite movement in the eyes

Feedforward control mechanism

Calibration performed by cerebellum

20
Q

What is the pathway of the vestibulo-ocular reflex?

A
  1. Movement detected in semicircular canals
  2. Afferents to vestibular nuclei
  3. Efferents from oculomotor nuclei
    via MLF (medial longitudinal fasciculus) in brainstem
21
Q

What is the optokinetic system?

A

Moves eyes to follow slow smooth movements in visual field

Movements driven by visual cortex

22
Q

What is nystagmus?

A

Rapid resetting of eye in orbit by saccade once it has reached its limit of movement

23
Q

When does nystagmus occur?

A
  1. In response to optokinetic or vestibular stimuli (physiological)
  2. Following cerebellar or vestibular damage (pathological)
24
Q

What are saccades?

A

Rapid movements of the eyes to foveate visual stimuli

Gaze-shifting mechanism

Minimise time of blurring

25
Q

Where are saccades generated?

A

Brainstem

Organised by superior colliculus of midbrain

Controlled by cerebral cortex and basal ganglia

26
Q

What is the saccadic pathway?

A
  1. Retina
  2. Superior colliculus (retinotopic representation)
  3. Brainstem reticular formation
  4. Oculomotor nuclei
27
Q

What is the tectospinal tract?

A

Deep layers of superior colliculus project to cervical spinal cord

Coordinate neck muscle contractions to generate head movements to accompany eye movements

28
Q

What is smooth pursuit?

A

Feedforward predictive movements to slowly ‘follow’ moving objects

Visual signals used to predict future position of moving object

29
Q

What brain regions are involved in smooth pursuit?

A
  1. Visual cortex
  2. Medial temporal cortex
  3. Frontal eye fields
  4. Brainstem
  5. Cerebellum

NHB (17 decks)

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