25 - NeuroAnatomy - Motor Pathways

Question 1

Which two structures regulate descending cortical and descending brainstem pathways?

Answer 1

Cerebellum

Basal Ganglia

Question 2

Cerebellum - In charge of what?

Answer 2

Controls pining and the patterns of muscles activated with eye movements, head movements, limb movements, body movements

Question 3

Basal Ganglia - In charge of what?

Answer 3

Selection and initiation of specific motor programs

Question 4

Cortical Motor Areas

Answer 4

Project to brainstem and spinal cord.

Important for skilled movement

Question 5

Brainstem

Answer 5

Important for posture, eye movements, eating, breathing, “that kind of thing”

Question 6

What are the clinical consequences of the combined hierarchical and parallel organization of the motor pathways?

Answer 6

Alternate pathways for producing movement.

After a stroke, there are some back-up pathways that can contribute to partial functional recovery.

Question 7

Three Primary Cortical Motor Pathways

Answer 7

Lateral Corticospinal Tract
Ventral Corticospinal Tract
Corticobulbar Tract

Question 8

Lateral Corticospinal Tract

Answer 8

Major component of the lateral pathway

Skilled limb movements

Question 9

Ventral Corticospinal Tract

Answer 9

Major component of the medial pathway

Axial muscle control (the 10% of the fibers in the pyramids that don’t cross)

Question 10

Corticobulbar Tract

Answer 10

Brainstem equivalent of Lateral & Ventral Corticospinal Tracts
Controls primarily cranial nuclei, facial muscles, jaw muscles, and muscles for swallowing & speaking

Question 11

Four Brainstem Motor Pathways

Answer 11

Rubrospinal Tract
Tectospinal Tract
Reticulospinal Tract
Vestibulospinal Tract

Question 12

Rubrospinal Tract

Answer 12

Minor component of the Lateral Descending Pathway

Originates from Red Nucleus, involved in limb control

Question 13

Tectospinal Tract

Answer 13

Medial Descending Pathway
Originates from Superior Colliculus
Head-eye coordination during gaze

Question 14

Reticulospinal Tract

Answer 14

Medial Descending Pathway

Automatic movements and posture

Question 15

Vestibulospinal Tracts

Answer 15

Medial Descending Pathway

For posture and balance

Question 16

Areas in which lobe are the primary source of descending cortical pathways?

Answer 16

Frontal Lobe

Question 17

From which cortical layer (and in which areas) do the three primary cortical motor pathways arise?

Answer 17

Projection Neurons (Layer V + a little bit of IV) in the following areas:
Primary Motor Cortex
Premotor Cortex
Supplementary Motor Cortex/Area (SMA, SMA medial surface)
Cingulate Motor Area (CMA, medial surface)

Question 18

Primary Motor Cortex

Answer 18

Brodmann’s Area 4
Precentral Gyrus
Execution of Movements

Question 19

Lesions in the Primary Motor Cortex produce

Answer 19

Weakness
Paralysis
Incoordination

Question 20

Premotor Region

Answer 20

Brodmann’s Area 6
Contains Supplementary motor Area (SMA)
Planning of complex sequences of movements involving coordination of both limbs, especially the distal extremity

Question 21

Where within Brodmann’s Area 6 (Premotor Region) is the Supplementary Motor Area (SMA) located?

Answer 21

Dorsomedial

Question 22

Where within Brodmann’s Area 6 (Premotor Region) is the Premotor Cortex located?

Answer 22

Lateral

Question 23

Premotor Cortex

Answer 23

The lateral portion of the Premotor Region (Brodmann’s Area 6)
Receives input from the “Where” pathways of both vision and auditory systems
Directs limb movements to targets of interest (reaching for thangs)

Question 24

Cingulate Motor Area (CMA)

Answer 24

Brodmann’s Area 31
Within cingulate sulcus and on cingulate gyrus
Receives input from areas involved in cognitive and emotional functions
May participate in emotionally-driven motor behaviors

Question 25

Where do projections from the Primary Motor Cortex descend?

Answer 25

Through the Genu and Posterior Limb of the Internal Capsule

Question 26

Where do projections from the SMA, CMA and Premotor Cortex descend?

Answer 26

Through the Anterior Limb of the Internal Capsule

Question 27

Which is more important? Projections from the Primary Motor Cortex, or projections from the SMA, CMA and Premotor Cortex?

Answer 27

Primary Motor Cortex! Damage to the Genu and Posterior Limb of the Internal Capsule can produce paralysis. Damage to the Anterior Limb does not!

Question 28

Internal Capsule - From Genu through Posterior Limb, what is the somatotopic organization of descending motor fibers?

Answer 28

Face (Genu) Arm Trunk Leg

Question 29

After the decussation of the pyramids, where are 90% of the descending motor fibers? This refers to the 90% that crossed over.

Answer 29

In the Lateral Pathways (the lateral column of the white matter in the spinal cord)

Question 30

What's contained in the lateral column of the white matter of the spinal cord?

Answer 30

Lateral Corticospinal Tract | Rubrospinal Tract

Question 31

Which lateral descending systems go to the limbs, especially the hands and the feet?

Answer 31

Lateral Corticospinal Tract | Rubrospinal Tract

Question 32

Where do the Lateral Corticospinal Tract and the Rubrospinal tract project within the spinal cord?

Answer 32

Lateral Column on the ventral horn | Lateral aspects of the intermediate layer interneurons

Question 33

After the decussation of the pyramids, where are 10% of the descending motor fibers? This refers to the 10% that did not cross over.

Answer 33

They stay in the midline | In the Medial Pathway (the Ventral Corticospinal Tract)

Question 34

Where do Medial Descending Tract fibers project?

Answer 34

Medial Motor Neurons Interneurons in the medial part of the intermediate zone Most important: BILATERAL projections!!!!

Question 35

Which medial descending systems go to the axial and girdle musculature?

Answer 35

Ventral Corticospinal Tract

Question 36

Where does the Lateral Corticospinal Tract originate?

Answer 36

``` Brodmann's Area 4 (Primary Motor) Brodmann's Area 6 (Premotor Cortex) Brodmann's Area 3 (Somatosensory) Brodmann's Area 1 (Somatosensory) Brodmann's Area 2 (Somatosensory) ```

Question 37

Lateral Descending Pathways

Answer 37

Lateral Corticospinal Tract | Rubrospinal Tract

Question 38

Where does the Lateral Corticospinal Tract decussate?

Answer 38

At the motor decussation (Spinal Cord)

Question 39

Where does the Rubrospinal Tract originate?

Answer 39

Magnocellular (caudal) part of the Red Nucleus

Question 40

Where does the Rubrospinal Tract Decussate?

Answer 40

``` Red Nucleus (right at the start!!) Decussation occurs at the Ventral Tegmental Area of the Midbrain ```

Question 41

Caudal part of the Red Nucleus

Answer 41

Magnocellular Part | Gives rise to the Rubrospinal Tract

Question 42

Medial Descending Pathways

Answer 42

Ventral Corticospinal Tract Vestibulospinal Tract Reticulospinal Tract

Question 43

Where does the Ventral Corticospinal Tract decussate?

Answer 43

Spinal Cord

Question 44

Purpose of Vestibulospinal and Reticulospinal Tracts

Answer 44

Automatic movements, some specific eye movements

Question 45

Lateral Pathways - Summary

Answer 45

Lateral Corticospinal Tract Rubrospinal Tract Limb motor neurons - Lateral ventral horn Descending control - Lateral column of white matter Crossed - Have consequences on movement by contralateral side of the body. Lesions (even small ones) have profound effects

Question 46

Medial Pathways - Summary

Answer 46

Ventral Corticospinal Tract Lateral Vestibulospinal Tract Axial and proximal motor neurons - Medial Ventral Horn Descending control - Medial Ventral column of white matter Bilateral Lesions have a less severe effect

Question 47

Corticospinal Tract - Origins

Answer 47

Originates from Arm, Trunk. Leg

Question 48

Corticobulbar Tract - Origins

Answer 48

Originates from Facial Area

Question 49

Corticobulbar Tract

Answer 49

Cranial Nerve Equivalent of Corticospinal Tract Descending projections from the cortex (Face) Genu of Internal Capsule Cranial Nerve Nuclei of Pons and Rostral Medulla These are the nuclei innervate striated muscle (except extraocular motor nuclei) - V, VII, Nucleus Ambiguus (projects to IX, X, XI), XI, XII

Question 50

Nucleus Ambiguus

Answer 50

Projects to Cranial Nerves IX, X, XI

Question 51

Corticobulbar System - Bilateral Control

Answer 51

``` Jaw (V) Larynx, Pharynx (Nucleus Ambiguus: IX, X, XI) Tongue (XII) Upper Facial Muscles (VII) This control is bilateral and redundant ```

Question 52

Corticobulbar System - Contralateral Control

Answer 52

Lower Facial Muscles (VII)

Question 53

What do you see in a stroke affecting the Corticobulbar System?

Answer 53

No change to upper face, but lower face weakness/paralysis on the contralateral side

Question 54

Cortex to Trigeminal Motor Nucleus Path

Answer 54

Internal Capsule Basis Pedunculi Corticobulbar Portions of the Pons Bilateral Projections to Trigeminal Motor Nucleus

Question 55

What is the most common cause of lesions in the posterior limb of the internal capsule?

Answer 55

Thrombosis or hemorrhage: Anterior Choroidal Artery Middle Cerebral Artery (above the level of the anterior commissure)

Question 56

What provides the blood supply for the Genu of the Internal Capsule?

Answer 56

Internal Carotid Artery | Branch of Heubner (off the ACA)

Question 57

Capsular infarcts commonly lead to

Answer 57

Total Hemiparesis (including lower face)

Question 58

Why is the upper face spared during a capsular infarct?

Answer 58

Redundancy! Upper facial motor neurons are somewhat bilateral. They also receive strong projections from other areas besides the Primary Motor Cortex (The Cingulate Motor Area, for example). These other areas typically descend in the anterior limb (unaffected by most internal capsule strokes).

Question 59

Typical internal capsule stroke affects which parts?

Answer 59

Genu & Posterior Limb

Question 60

Ventral Anterior / Ventral Lateral Nuclear Complex

Answer 60

Thalamic Motor Nuclei Receives projections from both cerebellum and basal ganglion Projects to Premotor and Primary Motor Cortex

Question 61

From which structures does the Ventral Anterior / Ventral Lateral Nuclear Complex (Thalamic Motor Nuclei) receive its input?

Answer 61

Cerebellum | Basal Ganglia

Question 62

Where does the Ventral Anterior / Ventral Lateral Nuclear Complex (Thalamic Motor Nuclei) project out to?

Answer 62

Premotor Cortex | Primary Motor Cortex

Question 63

Basal Ganglion projects to

Answer 63

Ventral Anterior Nuclear Complex

Question 64

Cerebellum projects to

Answer 64

Ventral Lateral Nuclear Complex

Question 65

In the Basis Pedunculi, where do the fibers from the Genu and Posterior Limb of the Internal Capsule travel?

Answer 65

Middle 1/3

Question 66

Medial-to-Lateral, what order do we see the fibers within the basis pedunculi?

Answer 66

Face Arm Trunk Limb

Question 67

Where does the Tectospinal Tract originate?

Answer 67

Superior Colliculus

Question 68

What does the Tectospinal Tract control?

Answer 68

Movement of the head and the eyes with conjugated gays

Question 69

Course of the Facial Motor Nucleus & Nerve

Answer 69

Fibers run dorsal and medial, then at the Genu, curve around and on top of the Abducens Nucleus at the area forming the Facial Colliculus

Question 70

Facial Colliculus

Answer 70

The bump on the anterior wall of the 4th Ventricle caused by the Genu Facial Nerve curving around and over the Abducens Nucleus.

Question 71

Input to Facial Motor Nucleus

Answer 71

Descending corticobulbar fibers Bilateral for upper face Unilateral for lower face