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Physiology II Exam II material > Lecture 11: Spinal Cord and Brainstem Control of Motor Function II > Flashcards

Lecture 11: Spinal Cord and Brainstem Control of Motor Function II Flashcards

1
Q

Which reflex is responsible for polysynaptic excitation of contralateral extensors?

  • A.) stretch reflex (myotactic)
  • B.) Golgi tendon reflex (inverse myotactic)
  • C.) Flexor withdrawal reflex
  • D.) Subliminal occlusion reflex
A

C.) Flexor withdrawal reflex

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2
Q

Definition of pyramidal system

A

These are tracts that pass through the medullary pyramidals. (other motor pathways are extrapyramidal)

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3
Q

Components of pyramidal system

A
  • Corticospinal tract
  • Corticobulbar tract
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4
Q

upper motor neurons of the pyramidal system orginate in the _____. ______% decussate in pyramids and form the lateral corticospinal tracts

A
  • motor cortices
  • 75-85%
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5
Q

75-85% of upper motor neurons decussate in the pyramids and form the lateral corticospinal tracts. The remainder decussate

A

near synapse with lower motor neurons. And form anterior corticospinal tracts

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6
Q

Most upper motor neurons synapse with association neurons in _____

A

spinal cord central gray

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7
Q

Upper motor neurons are classified according to where they synapse in the ventral horn

A
  • medial activation system
    • Innervate postural and girdle muscles
  • Lateral activation system
    • Associated with distally located muscles used for fine movements
  • Nonspecific activating system
    • Facilitate local reflex arcs
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8
Q

Lateral corticospinal tract

A
  • made up of corticospinal fibers that have crossed in medulla
  • supply all levels of spinal cord
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9
Q

Anterior corticospinal tract

A
  • made up of uncrosssed corticospinal fibers that cross near level of synapse with LMNs
  • Supply neck and upper limbs
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10
Q

origin of the corticospinal tract

A
  • Primary motor cortex
  • Premotor cortex
  • Somatosensory area
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11
Q

The corticospinal tract is referred to as the

A

pyramidal tract

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12
Q

What is the pathway of the Corticospinal tract

A
  • site of origin –> internal capsule –> medullary pyramids –> X in lower medulla (most fibers) –> lateral columns of spinal cord (lateral corticospinal tract)
  • some fibers do not cross but continue down ipsilaterally in ventral corticospinal tract
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13
Q

Giant pyramidal (Betz) cells are located in

A

motor cortex

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14
Q

Giant pyramidal (Betz) cells transmit at ___ m/sec

A

70 m/sec

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15
Q

Giant pyramidal (Betz) cells make up about __% (_____) of fibers in the corticospinal tract

A

3% (34,000)

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16
Q

Giant pyramidal (Betz) cells sends ___ back to cortex

A

collaterals

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17
Q

other fibers (not giant pyramidal (Betz) cells) from the cortex in Corticospinal tract pass into _____ and ____. Pass to ____, Pass to ____ and ______. And a large number of fibers pass to ____

A
  • caudate and putamen red nucleus
  • Reticular substance and vestibular nuclei
  • pontine nuclei
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18
Q

Functions of Corticospinal Tract

A
  • Adds speed and agility to conscious movements
    • Especially movements of hand
  • Provides a high degree of motor control: (i.e. movement of individual fingers)
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19
Q

Symptoms of Corticospinal Tract Lesions

A
  • Reduced Muscle Tone
  • Clumsiness
  • Weakness
  • Not complete paralysis
  • (note: complete paralysis results if both pyramidal and extrapyramidal systems are involved )
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20
Q

Complete paralysis results if

A

both pyramidal and extrapyramidal systems are involved

21
Q

The Corticobulbar Tract innervates the

A

head

22
Q

most fibers of the corticobulbar tract terminate in

A

reticular formation near cranial nerve nuclei

23
Q

association neurons of corticobulbar tract leave reticular formation and synapse in _____ and with

A

cranial nerve nuclei, lower motor neurons

24
Q

Fibers from primary motor cortex (corticorubral pathway) and branches from corticospinal tract synapse in ______ of red nucleus

A

magnocellular portion

25
Q

Large neurons from magnocellular region red nuclues give rise to ____ which decussates in lower brain stem

A

Rubrospinal tract

26
Q

Magnocellular region has a ______ representation of all the muscles of the body

A

somatotopic

27
Q

Stimulation of Red nucleus results in

A

Stimulation of flexors Inhibition of extensors (antigravitiy muscles)

28
Q

The extrapyramidal system includes pathways that

A

contribute to motor control but that are not part of the corticospinal system

29
Q

extrapyramidal system includes descending motor tracts that do not pass through ______ or _____

A

medullary pyramids or corticobulbar tracts

30
Q

Extrapyramidal system includes

A
  • Rubrospinal tracts
  • Vestibulospinal tracts
  • Reticulospinal tracts
31
Q

Rubrospinal tract originates in ______

A

red nucleus

32
Q

Rubrospinal tract decussates in ___

A

midbrain

33
Q

Rubrospinal tract descends in ______

A

lateral funiculus (column)

34
Q

Rubrospinal tract function is closely related to

A

cerebral function

35
Q

Lesions of Rubrospinal tract result in

A

Impairment of distal arm and hand movement Intention tremors (similar to cerebellar lesions)

36
Q

Vestibulospinal Tract originates in

A

Vestibular nuclei

37
Q

The vestibulospinal tract receives major input form

A

vestibular nerve (CN VIII)

38
Q

The Vestibular Nuclei descends in _____

A

Anterior funiculus (column)

39
Q

Vestibulospinal tract synapses with ____ to _____

A

LMNs to extensor muscles

40
Q

The Vestibulospinal tract is primarily involved in

A

maintenance of upright posture

41
Q

The Reticulospinal tract originates in various regions of

A

reticular formation

42
Q

The Reticulospinal Tract descends in

A

anterior portion of lateral funiculus (column)

43
Q

What is the function of Reticulospinal tract

A

Thought to mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs

44
Q

Describe the maculae of the utricle and saccule and indicate their planes of orientation and their associated functions

A
  • Urticle
    • Macula
      • Located on a horizontal plane
      • Plays a role in determining orientation of head when head is upright
  • Saccule
    • Macula
      • Located in a verticle plane
      • signals head orientation when person is lying down
45
Q

Describe the structure of a macula and the function of the statoconia in relation to the hair cells

A
  • The macula is covered by a gelatinous layer
    • Contains large number of embedded small calcium carbonate crystals (statoconia)
    • Contains thousands of hair cells which project cilia into the gelatnous layer
    • The weight of the statoconia bends cilia in the direction of gravitional pull
46
Q

Explain how hair cells in the macula become depolarized and hyperpolarized

A
  • Bending of stereocilia towards kinocilium opens hundreds of cation channels causing receptor membrane depolarization and excitation
  • Bending of cilia in opposite direction closes channels and hyperpolarizes receptor membrane
  • Hair cells are oriented such that bending the head in differents cause different groups of hair cells to depolarize
47
Q

Explain how semicircular canals are able to detect motion of the head in three dimensional space

A
  • When head begins to rotate in any direction, intertia of the fluid in one or more of the semicircular canals remains stationary while semicircular canal rotates with the head
  • When head is bent forward 30°
    • Lateral ducts are horizontal
    • anterior ducts are in vertical planes projecting forward and 45° outward
    • Posterior ducts are in vertical planes projecting backward and 45° outward
48
Q

Trace the connections of the vestibular nerves to the vestibular nuclei, fastigial nuclei, red nuclei, and spinal cord

A

*

Physiology II Exam II material (8 decks)

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