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CNS Anatomy > Sheet 6 > Flashcards

Sheet 6 Flashcards

1
Q

What does the brainstem connect?

A

Spinal cord and forebrain

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2
Q

What are the parts of the brainstem?

A

1) Medulla oblongata
2) Pons
3) Midbrain

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3
Q

Where do the anterior and lateral corticospinal tracts start from?

A

The precentral gyrus of cerebral cortex, mainly area 4 (frontal lobe).

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4
Q

Where does the corticospinal tract split into 2 tracts?

A

At the level of medulla oblongata (it decussates there)

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5
Q

What is the path of the corticospinal tract? (Until the midbrain)

A

1) Fibers descend from corona radiata
2) Go to internal capsule (between thalamus + caudate nucleus medially and lentiform nucleus laterally)
3) To the brainstem (midbrain). Fibers will pass through middle 3/5th of the crus cerebri (part of the white matter), named basis pedunculi of the midbrain.

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6
Q

Where is every muscle in our body represented?

A

In the cortex

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7
Q

What does the gray matter of the brainstem contain?

A

1) Sensory nuclei
2) Motor nuclei
3) Parasympathetic nuclei

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8
Q

What is the path of the corticospinal tract? (From the midbrain until the interference)

A

1) the fibers descend from the crus cerebri of the midbrain to reach the pons.
2) Inside the pons, we have pontine nuclei (collection of separate cell bodies). Here the fibers will scatter between the pontine nuclei in the anterior (basilar) part.

3) Here, the corticospinal tract will interfere with another pathway called middle cerebellar
peduncle which goes from the cerebrum to the pons to the cerebellum (the cerebroponto-cerebellar pathway). This pathway goes horizontally at the same time the corticospinal
pathway descends vertically

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9
Q

What is the path of the corticospinal tract? (From the interference until the split)

A

1) Fibers will descend from the pons to the medulla oblongata

2) The fibers will recollect
again and form the anterior and medial aspect of the medulla which is the pyramid.

3) In the lower part of the medulla, the fibers will split up:
a) The majority of the fibers (85% approximately) will cross-over to the opposite side (primary motor decussation). These fibers are called the lateral corticospinal tract.

b) The rest (15%) descend ipsilaterally and are called the anterior corticospinal tract.

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10
Q

What is the path of the lateral corticospinal tract?

A

Descends in the lateral funiculus of the spinal cord

to the lateral part of the anterior horn and then supplies the lateral muscles.

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11
Q

What is the path of the anterior corticospinal tract?

A

Crosses-over at the level of the spinal cord and goes

to the medial part of the anterior horn to supply the axial muscles.

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12
Q

What do the lateral corticospinal tract (LCST) fibers synapse with?

A

Alpha and gamma motor neurons

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13
Q

Lateral corticospinal tracts are responsible for:

A

Skilled movements

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14
Q

What is the Lateral corticospinal tract fiber distribution?

A

1) 55% of the fibers will end up in the Cervical region (hand).
2) 20% in the Thoracic (trunk- the least).
3) 25% in the Lumbar & Sacral (foot-lesser extent than the hand).

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15
Q

LCST synapses mainly by __ in lamina __.

A

Interneurons; 8 (mainly), but also 4, 5, 6, 7 (in

the dorsal horn).

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16
Q

What are the 2 theories regarding lamina 4-7?

A

1) These tracts that supply lamina 4-7 mainly come from cortex area 312 (not 4).

2) These are related to the control of pain (that can be
avoided by certain movements).

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17
Q

What is the exception regarding synapses in the LCST?

A

3% of upper motor neurons directly synapse with lower motor neurons (without interneurons). These originate from giant cells of betz in the fifth layer of
area 4, and they are
responsible for very fine movements (less synapses = more accurate movement).

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18
Q

What is the Corticonuclear Tract (Corticobulbar) for?

A

Cranial nerves and muscles of the head & neck area

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19
Q

Are there anterior and dorsal horns in the brainstem?

A

No, there are motor nuclei

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20
Q

What do the motor nuclei do?

A

The same function as the anterior horn (have cell bodies of the lower motor neuron that supply skeletal muscles in the head and neck area).

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21
Q

Why is it called Cortico-nuclear Tract?

A

Because the fibers descend from the cortex (lower ¼) to a nucleus (motor nucleus),

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22
Q

Which descending fibers terminate in the motor nuclei of the midbrain?

A

1) Oculomotor (3rd cranial)

2) Trochlear (4th cranial)

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23
Q

Which descending fibers terminate in the motor nuclei of the pons?

A

Trigeminal (5th cranial)

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24
Q

Which descending fibers terminate in the motor nuclei of the Ponto-medullary junction (between the pons and
medulla)?

A

1) Abducent (6th cranial)

2) Facial (7th cranial)

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25
Q

Which descending fibers terminate in the motor nuclei of the medulla?

A

9-12th cranial nerves.

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26
Q

In the corticospinal tracts, which part of the cortex controls which part of the body?

A

The right cortex controls the

left side of the body and vice versa (contralateral).

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27
Q

In the corticonuclear tracts, which part of the cortex controls which part of the body?

A

It is bilateral! The corticobulbar fibers from one side of the brain project to the motor nuclei on both sides of the brainstem.

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28
Q

What are the 2 exceptions to the bilateral corticonuclear input?

A

1) Part of facial nerve (7th cranial) which supplies the LOWER facial muscles.
2) Part of the hypoglossal nerve (12th cranial) which supplies the genioglossus muscle.

These exceptions are contralateral not bilateral (same as the spinal).

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29
Q

Are corticonuclear tracts pyramidal or extrapyramidal tracts?

A

Anatomically, no because they don’t pass through the pyramids of the medulla.
Functionally (more important), yes.
So yes, they are considered pyramidal tracts.

30
Q

Extrapyramidal tracts (subconscious control) have 4 types:

A

1) Rubrospinal tracts
2) Reticulospinal tracts
3) Vestibulospinal tracts
4) Tectospinal tracts

31
Q

Extrapyramidal tracts’ general function is:

A

Coordination

32
Q

Extrapyramidal tracts are __ and __ and regulate:

A

Complex; multisynaptic;

1) Axial muscles that maintain balance and posture.
2) Muscles controlling coarse movements of the proximal portions of limbs
3) Head, neck, and eye movement

33
Q

Extrapyramidal tracts arise in the __ but are under the influence of the __.

A

Brainstem; cerebral cortex.

34
Q

What does the rubrospinal tract refer to?

A

The red nucleus located in the midbrain at the level of

superior colliculus.

35
Q

What does the rubrospinal synapse with?

A

Alpha and gamma through

interneurons.

36
Q

Red nucleus receives input from:

A

1) Cerebral cortex

2) Cerebellum

37
Q

What is the cerebellum aware of?

A

Your current position.

38
Q

The cerebellum has 4 deep cerebellar nuclei:

A

1) Dentate nucleus
2) Emboliform nucleus
3) Globose nucleus
4) Fastigial nucleus
(Don’t Eat Greasy Food)

39
Q

Where does the rubrospinal tract decussate?

A

At the level of the nucleus

40
Q

What is found anterior to the red nucleus?

A

A nucleus known as substantia nigra

41
Q

Which nucleus is related to Parkinson’s disease?

A

Substantia nigra

42
Q

The 2nd and 3rd nuclei (Emboliform and Globose) are called:

A

Interposed nuclei

43
Q

Which pathway emerges from the interposed nuclei?

A

The globose-emboliform-rubral pathway (which runs from deep cerebellar to red nucleus).

44
Q

What is the path of the rubrospinal tract?

A

Descends from the red nucleus to the spinal cord through the lateral white column, which is related to the activity of the lateral corticospinal tract (an
exception of the extrapyramidal types).

45
Q

What is the lateral motor system?

A 
The rubrospinal tract (extrapyramidal) +
lateral corticospinal (pyramidal)
46
Q

What is the function of the rubrospinal tract?

A

To facilitate the activity of flexors (excitatory) and inhibit the activity of extensors (inhibitory).

47
Q

What does the rubrospinal tract supply?

A

The distal flexor muscles mainly with little effect on the proximal muscles
(exception to extrapyramidal tracts).

48
Q

What is the reticular formation in the pons called?

A

Pontine reticulospinal tract

49
Q

What is the reticular formation in the medulla called?

A

Medullary reticulospinal tract

50
Q

What is the path of the pontine reticulospinal tract?

A

From the reticular formation in the pons to the anterior white column.

51
Q

Do the fibers cross in the pontine reticulospinal tract?

A

No, they stay uncrossed.

52
Q

The pontine reticulospinal tract is ___, which means that:

A

Tonically active; there is continuous firing, but the
effect of the cortex on it is inhibitory. This is called the mechanism of
disinhibition.

53
Q

What will happen if you u remove the inhibitory effect of the cortex on the pontine reticulospinal tract? What is this called?

A

Overfiring and more activation of the reticulospinal

tract will occur; It is called decorticate

54
Q

What is the function of the pontine reticulospinal tract?

A

Activate the axial and proximal limb extensors (antigravity muscles) so you can stand upright

55
Q

Where does the Vestibulospinal tract start from?

A

From vestibular nuclei in the brainstem, specifically pons and medulla beneath the floor of 4th ventricle, which are sensory nuclei.

56
Q

Where do the sensory neurons synapse?

A

In the dorsal horn

57
Q

The vestibular nuclei receive afferent (sensory) fibers from:

A

1) The inner ear, from the vestibule (semicircular canals) = it’s responsible for the sense of balance.
2) Input from deep cerebellar nucleus (Fastigial nuclei).

58
Q

The data received to the vestibular nucleus is related to:

A

1) Position

2) Gravity

59
Q

Does the Vestibulospinal tract descend crossed or uncrossed? Through what does it descend?

A

Uncrossed; through the

anterior white column.

60
Q

What is the function of the Vestibulospinal tract?

A

Facilitate the activity of extensor muscles and

inhibit the activity of flexor muscles in association with the maintenance of balance

61
Q

Vestibulospinal tracts + Pontine reticulospinal tract =

A

Help you to stand

in the upright position

62
Q

What is the opposite of the Pontine reticulospinal tract?

A

Medullary

reticulospinal tract.

63
Q

What is the tectum?

A

Posterior aspect of the midbrain

64
Q

The tectum is divided into 4 colliculi:

A

1) 2 superiors (related to visual reflexes).

2) 2 inferiors (auditory reflexes).

65
Q

Is the Tectospinal tract crossed or uncrossed?

A

Mainly crossed

66
Q

What does the Tectospinal tract descend through?

A

In the anterior white column close to anterior median fissure.

67
Q

In the spinotectal tract (ascending), its reflex is __.

A

Spinovisual

68
Q

What is the function of the Tectospinal tract?

A

The reflex movement of

the head & neck in response to visual stimulus. (visuospinal reflex)

69
Q

What is the upper head & neck supplied by?

A

Upper cervical segments

70
Q

Where do the majority of the Tectospinal tract fibers terminate?

A

In the anterior gray column
of upper cervical segments of spinal
cord.

CNS Anatomy (19 decks)

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