Unit 3: Corticospinal And Corticobulbar (CN) Pathways Pg 93-101

Question 1

Pyramidal system refers to what pathways

Answer 1

Corticospinal and Cortibobulbar/Corticonuclear pathways

Question 2

There are many descending motor pathways that do not traverse the pyramids and are sometimes collectively called

Answer 2

Extrapyramidal system

Question 3

What is the origin of the coritospinal and corticobulbar (corticonuclear) tracts?

Answer 3

Frontal lobe (several regions) and Parietal lobe

Frontal lobe:

• precentral gyrus and anterior paracentral lobule
• posterior part of the superior frontal and middle frontal gyri
• medial frontal gyrus and anterior portion fo cingulate gyrus

Parietal lobe:

• post central gyrus
• posterior paracentral lobule
• superior parietal lobule

Question 4

What 2 locations of the frontal lobe individually contributes about 30% of pyramidal fibers? (So 60% together)

Answer 4

30% - Precentral gurus and anterior paracentral lobule

30% - premotor and supplementary motor areas of frontal lobe

Note: other 40% is from the parietal lobe

Question 5

Anatomically: Precentral gurus and anterior paracentral lobule

Functionally:

Answer 5

Primary motor cortex (M1)

Question 6

Pyramidal neurons are called

Answer 6

Betz cells

Question 7

The primary motor cortex corresponds to Brodmann map area

Answer 7

4

Question 8

Functionally: Premotor area

Anatomically:

Answer 8

Posterior part of superior frontal and middle frontal gyri; anterior to the primary motor area

Question 9

Functionally: supplementary motor

Anatomically:

Answer 9

Medial frontal gyrus and anterior portion of the cingulate gyrus

Question 10

Premotor and supplementary motor areas of frontal lobe corresponds to Brodmann Map area

Answer 10

6

Question 11

The premotor and supplementary motor area is involved in what function?

Answer 11

Planning the execution of movement and the programming of skilled movements

Question 12

Some of the descending fibers that originate in the parietal lobe are not upper motor neurons

Answer 12

True. They terminate on sensory neurons in the brainstem and spinal cord

Question 13

The corticospinal fibers in the pyramids that do not decussate at the pyramidal decussations do what?

Answer 13

Uncrossed fibers descend in the anterior funiculus of spinal cord to form the ventral/anterior corticospinal tract and decussate at the spinal level

Question 14

Corticospinal and corticobulbar (corticonuclear) tracts help provide voluntary control of motor activity’s that involve distal parts of extremities and face such as:

Answer 14

Eyes
Tongue
Facial expression
Fingers
Toes

Question 15

Corticospinal and corticobulbar (corticonuclear) tracts confers that movements of the distal and extremity body parts (eye, tongue, facial expression, fingers, toes) can be performed with

Answer 15

Speed
Agility
Precision

Question 16

A “pure” lesion of the Corticospinal tract can be performed in a non-human primate by abating (cutting) through a pyramid (above the decussations). The initial result if this is:

Answer 16

Hypotonia of contralateral muscles (esp distal extremities and face)

Initial period of flaccid paralysis contralateral to lesion (esp distal extremities)

NOTE: over a period of several months motor control returns so that

• chronic loss of voluntary motor control is minimal
• permanent difficulty with performing highly skilled activities with distal extremities
• execution of movements requires much attention and there is a permanent loss of speed, agility and precision of movements

Question 17

What are long term deficits resulting from a “pure” lesion of the C-S tract (after return of motor control)

Answer 17

1. Permanent difficulty with performing highly skilled activities with distal extremities
2. Execution of movements requires much attention with permanent loss of speed, agility and precision of movements

Question 18

Corticobulbar (corticonuclear) Tract originates from

Answer 18

UMNs located in inferior 1/3 of precentral gyrus, the premotor area and areas of parietal lobe

Question 19

The motor nuclei of cranial nerves that receive C-B/C-N innervation include

Answer 19

Oculomotor nuclear complex including LMNs of CN III
Trochlear nucleus — CN IV
Trigeminal motor nucleus — CN V
Abducens nucleus — CN VI
Facial motor nucleus — CN VII
Nucleus ambiguus — CN IX, X, (cranial root of) XI
Hypoglossal nucleus — CN XII

Note: the only CNS not mentioned 1, 2, and 8

Question 20

Which 3 nuclei receive C-B/C-N innervation, but not directly?

Answer 20

III
IV
VI

Question 21

Most C-B/C-N fibers innervate nuclei of V, VII, nucleus ambiguus and XII on which side?

Answer 21

Contralateral

Note: there are significant C-B/C-N fibers to these nuclei that end ipsilaterally. Thus most LMNs of CN receive bilateral C-B/C-N innervation and there is no significant paralysis of most muscles innervated by CN following unilateral lesions of C-B/C-N fibers

Question 22

What cranial nerves are included in the nucleus ambiguus?

Answer 22

IX
X
XI (cranial root)

Question 23

What are the two exceptions to the pattern of bilateral C-B/C-N innervation?

Answer 23

1. LMS within the caudal portion of the facial motor nucleus that innervate muscles of facial expression on the lower 1/2 of the face
2. LMNs of the hypoglossal nucleus that innervate muscles of the tongue

Question 24

Vergence movements

Answer 24

Eyes move in opposite directions

Question 25

Divergence

Answer 25

Eyes abduct

Question 26

Convergence

Answer 26

Eyes adduct

Question 27

Activity of the LMNs of motor nuclei III, IV, and VI are coordinated to ensure that:

Answer 27

Both eyes maintain visual fixation on the same object in the visual field

Question 28

Conjugate movements

Answer 28

Eyes move in parallel (‘yoked’ movement)

Question 29

Involuntary conjugate movement include

Answer 29

Visual tracking when watching an object move across the visual field

Ie. Smooth pursuit; automatic tracking

Question 30

What area of the cortex controls smooth pursuit activity?

Answer 30

Visual cortex

Hello, exam 2 content.

Question 31

Voluntary conjugate movement occurs when

Answer 31

Scanning a landscape or a page

Question 32

Voluntary conjugate movement results in what kind of eye movements

Answer 32

Saccadic

Voluntary conjugate

Question 33

What area/location of the cerebral cortex controls saccadic eye movements?

Answer 33

FEF in the posterior part of the middle frontal gyrus (Brodmann’s 8)

Question 34

What is the name of the posterior part of the middle frontal gyrus that results in saccadic eye movements?

Answer 34

Frontal eye field (FEF)

Question 35

Anatomically: posterior part of the middle frontal gyrus

Functionally:

Answer 35

Frontal eye field (FEF)

Question 36

Though it can be considered part of premotor area, frontal eye field (FEF) corresponds to what Brodmann’s map?

Answer 36

8

Note: premotor and supplementary motor area is part of Brodmann map area 6

Question 37

Unilateral stimulation of the FEF results in

Answer 37

Conjugate movements of the eyes to the side opposite of stimulation

Question 38

Conjugate movement of the eyes in the horizontal plane requires participation of special neurons in the brainstem

Answer 38

Paramedian pontine reticular formation (PPRF)

Question 39

What are the neurons that form the center for control of coordinated lateral/horizontal gaze

Answer 39

Paramedian pontine reticular formation (PPRF)

Question 40

Paramedian pontine reticular formation (PPRF) receives input from

Answer 40

Cerebral cortex
Superior colliculus
Vestibular nuclear complex