Exam 1: Corticospinal and other descending pathways

Question 1

Identify the cortex or functional area represented by red line

Answer 1

Primary motor cortex

Question 2

Identify the cortex or functional area represented by red line

Answer 2

Somatosensory cortex

Question 3

Identify the cortex or functional area represented by red line

Answer 3

Premotor cortex

Question 4

Identify the cortex or functional area represented by red line

Answer 4

Supplementary motor cortex

Question 5

Identify the cortex or functional area represented by red line

Answer 5

posterior parietal cortex

Question 6

Pathway - Cortex:

• ___-___ neuron system that starts in the cortex and ends at various level of the spinal cord on _____ _____ neurons

Answer 6

Pathway - Cortex:

• 2-3 neuron system that starts in the cortex and ends at various level of the spinal cord on lower motor neurons

Question 7

Pathway - Cortex:

• Cell bodies of upper motor neurons are located in layer _____ if the cerebral cortex

Answer 7

Pathway - Cortex:

• Cell bodies of upper motor neurons are located in layer 5 of the cerebral cortex

Question 8

Pathway - Cortex:

• Betz cells (_____ cells) – heavy _____ neurons that are _____ than other neurons from layer V of the cortex
• Betz cells end directlyon _____ _____ neurons in the _____hornof thespinal cord
• Other neurons from layer V synapse on _____ cells in the _____ horn of the spinal cord. Axons from the _____ cells end on _____ _____ neurons

Answer 8

Pathway - Cortex:

• Betz cells (pyramidal cells) – heavy myelinated* neurons that are bigger* than other neurons from layer V of the cortex.

*Carries the signals faster and more powerfully!

• Betz cells end directly on lower motor neurons in the ventral horn of the spinal cord
• Other neurons from layer V synapse on intermediate cells in the central horn of the spinal cord. Axons from the intermediate cells end on lower motor neurons

Question 9

Upper Motor Neurons:

• are found at what levels?
• Dysfunction at these levels causes what?

Answer 9

Upper Motor Neurons:

• Cortical, subcortical, or spinal levels
• Dysfunction at these levels can cause weakness, increased or pathologic reflexes, and increased tone and spasticity

Question 10

Lower Motor Neurons:

• are found at what levels?
• Dysfunction at these levels causes what?

Answer 10

Lower Motor Neurons:

• anterior horn cell, motor nerve root, plexus, peripheral nerve, or neuromuscular junction
• Dysfunction at these levels can cause weakness, atrophy, fasciculations, decreased reflexes

Question 11

Pathway - Cortex:

Name the two corticospinal tracts and what they are involved in

Answer 11

Pathway - Cortex:

Both are descending corticospinal tracts!

• Lateral corticospinal tract – involved in limb muscle contraction
• Anterior corticospinal tract – involved in axial muscle contraction

Question 12

Pathway - Cortex:

The descending corticospinal tract gives off co-lateral fibers to:

• Adjacent _____ cells
• The _____ nuclei, _____ nucleus, _____ nuclei, and _____ nucleus
• To the _____ formation

Answer 12

Pathway - Cortex:

The descending corticospinal tract gives off co-lateral fibers to:

• Adjacent cortical cells
• The basal nuclei, red nucleus, vestibular nuclei, and olivary nucleus
• To the reticular formation

Question 13

Pathway - Cortex:

Contribution of cortical motor fibers from the cortex:

• ~___% of nerve fibers come from the primary motor cortex, ~___% come from the premotor and supplementary motor areas, ~___% come from the sensory cortex

Answer 13

Pathway - Cortex:

Contribution of cortical motor fibers from the cortex:

• ~30% of nerve fibers come from the primary motor cortex, ~30% come from the premotor and supplementary motor areas, ~40% come from the sensory* cortex

*sensory cortex fibers allow quick decisions (like if skin is burning, reflex to move it back)

Question 14

Cortex:

Understand the terms Homunculus and Somatotopic Arrangement

Answer 14

Cortex:

• Homunculus: Scale model of human body illustrating physiological, psychological or other characteristics
• Somatotopic Arrangement: Point to point correspondence of an area of the body to a specific point on the central nervous system

Question 15

Which tracks deal with voluntary limb movement?

Answer 15

Lateral corticospinal

Anterior corticospinal

Rubrospinal

Question 16

Which tracks deal with Reflex postural movement?

Answer 16

Tectospinal (sight)

Vestibulospinal (ear)

Reticulospinal

Question 17

Pathway - Cortex:

• Descending axons pass through the _____ _____ and converge towards the posterior limb of the _____ capsule. The _____ capsule is located between the _____ and _____ nuclei
• Due to the fact that all cortical motor nerve fibers are packed so close together, a small stroke in this area can paralyze _____ side of the body.

Answer 17

Pathway - Cortex:

• Descending axons pass through the corona radiata** and converge towards the **posterior limb of the internal capsule. The internal capsule is located between the thalamic** and **basal nuclei
• Due to the fact that all cortical motor nerve fibers are packed so close together, a small stroke in this area can paralyze** an **entire side of the body.

Question 18

Identify the marked landmark or structure

Answer 18

corona radiata

Question 19

Identify the marked landmark or structure

*** What artery supplies this area? ***

Answer 19

internal capsule

Note: i have read different things from different sources and I missed what branch he said during lecture so take these with a grain of salt…

*** It is supplied by the middle cerebral artery branches ***

lenticulostriate branches of middle cerebral artery (superior half of posterior internal capsule) and anterior choroidal artery branch of the internal carotid artery (inferior half of posterior internal capsule)

Question 20

Corticospinal Pathway - Midbrain:

• At the midbrain level, the corticospinal fibers are located in the _____ _____. These cortical fibers form the _____ _____
• The corticospinal fibers occupy the middle of the _____ _____ while the medial and lateral portion contain _____ fibers
• Because there are many structures within close proximity to each other in the midbrain, strokes in this area are usually associated with other “_____ signs”

Answer 20

Corticospinal Pathway - Midbrain:

• At the midbrain level, the corticospinal fibers are located in the cerebral peduncle. These cortical fibers form the crus cerebri
• The corticospinal fibers occupy the middle of the crus cerebri while the medial and lateral portion contain corticobulbar (corticopontine) fibers
• Because there are many structures within close proximity to each other in the midbrain, strokes in this area are usually associated with other “neighborhood signs”

Question 21

Know what causes Weber’s syndrome and what happens due to the lesion.

Answer 21

Weber’s syndrome:

Midbrain infarction: Occlusion of paramedian branches of the posterior cerebral artery (PCA)

Unilateral lesion: Substantia nigra, Corticospinal, Corticobulbar, CN III Oculomotor

Corticospinal → contains UPM, damage leads to spastic hyper reflex

Corticobulbar → damage leads to contralateral lower face muscle weakness

CN III Oculomotor → damage leads to loss of all extraocular muscles (except superior oblique and lateral rectus) → droppy eyelids, “down and out“

Question 22

Tectospinal Tract - Midbrain:

• Involved in _____ _____ movement in response to _____ stimuli
• Originates form the _____ _____ located in the tectum of the midbrain
• Descending nerve fibers then _____ _____ and form the _____ _____ _____ (MLF) which is located in the anterior white matter

Answer 22

Tectospinal Tract - Midbrain:

• Involved in reflex postural movement in response to visual stimuli*
• Originates form the _____ _____ located in the tectum of the midbrain
• Descending nerve fibers then cross over and form the medial longitudinal fasciculus (MLF) which is located in the anterior white matter

*If you step on something and then look down you can react, example in class was a dead rat under your foot)

Question 23

corticospinal tract - Pons:

• As the fibers from the cortex descend, they _____ _____
• A lesion in this area of the corticospinal tract will?

Answer 23

corticospinal tract - Pons:

• As the fibers from the cortex descend, they spread out
• A lesion in this area of the corticospinal tract will likely not be as severe

Question 24

Corticobulbar Tract:

• Comes from the _____ cortex and ends in the _____
• Axons from these tracts go laterally and to the _____ (_____ tract)
• The tract is composed of the _____ motor neurons of the cranial nerves

Answer 24

Corticobulbar Tract:** (AKA **corticopontine!)

• Comes from the motor cortex and ends in the pons
• Axons from these tracts go laterally and to the cerebellum** (**pontocerebellar tract)
• The tract is composed of the upper motor neurons of the cranial nerves

Question 25

Corticobulbar Tract: KNOW THIS!!!

• The muscles of the _____, _____, and _____ are controlled by this system
• This system innervates cranial motor nuclei _____ except the _____ _____ nuclei and the _____, which are innervated _____ by the _____ cortex

Answer 25

Corticobulbar Tract:

• The muscles of the face, head, and neck are controlled by this system
• This system innervates cranial motor nuclei bilaterally except the lower facial (VII) nuclei and the hypoglossal (CN XII), which are innervated unilaterally** by the **contralateral cortex

Question 26

corticospinal tract - Medulla:

• Corticospinal tract – form two _____ on the ventral aspect of the medulla
• Decussation of corticospinal nerve fibers takes place at the level of the _____ medulla
• Approximately 90% of the nerve fibers decussate at this level to form the _____ corticospinal tract
• The remaining ~10% form the _____ corticospinal tract

Answer 26

corticospinal tract - Medulla:

• Corticospinal tract – form two pyramids on the ventral aspect of the medulla
• Decussation of corticospinal nerve fibers takes place at the level of the caudal medulla
• Approximately 90% of the nerve fibers decussate at this level to form the lateral corticospinal tract
• The remaining ~10% form the anterior corticospinal tract

Question 27

Spinal Cord Pathways:

Know the locations (and functions) represented in the

2 Pyramidal Tracts and 4 Extrapyramidal Tracts

Answer 27

2 Pyramidal Tracts:

• Lateral* corticospinal tract (voluntary motor control of limbs)
• Anterior corticospinal tract (voluntary motor control of axial and girdle)

4 Extrapyramidal Tracts

• Rubrospinal (voluntary arm flexors, secondary to lateral corticospinal tract)
• Reticulospinal (reflex postural)
• Vestibulospinal (reflex postural)

*In the Lateral corticospinal tract the cervicle region is more medial since they will synapse first along the pathway!

Question 28

Rubrospinal Tract:

• It starts from the _____ nucleus in the _____ _____
• It ends on the ___lateral alpha and gamma motor neurons in the _____ horn of the spinal cord
• After decussating in the _____ _____ the tract is located _____ brainstem and spinal cord
• This tract influences _____ muscles of the _____
• Its function is _____ _____ of the ___lateral muscles, however the level of control is _____ than the corticospinal tract

Answer 28

Rubrospinal Tract:

• It starts from the red nucleus in the mid brain
• It ends on the contralateral alpha and gamma motor neurons in the anterior horn of the spinal cord
• After decussating in the mid brain the tract is located lateral brainstem and spinal cord
• This tract influences flexor muscles of the limbs, (particularly arm flexors)
• Its function is voluntary flexion of the contralateral muscles, however the level of control is far less** than the **corticospinal tract

Question 29

Rubrospinal Tract:

• Its function is _____ _____ of the ___lateral muscles, however the level of control is _____ than the corticospinal tract
• If their is a lesion disrupting the corticospinal tract the rubrospinal tract gives _____ _____, and the patient will appear _____ and _____

Answer 29

Rubrospinal Tract:

• Its function is voluntary flexion of the contralateral muscles, however the level of control is far less** than the **corticospinal tract
• If their is a lesion disrupting the corticospinal tract the rubrospinal tract gives backup movement, and the patient will appear clumsy and uncoordinated

Question 30

Reticulospinal Tract:

• Starts from two reticular formations: _____ and _____
• Regulation of _____ _____
• If damaged, a harmless stimulus can elicit a _____ _____
• 2 Reticulospinal Tracts: _____ and _____

Answer 30

Reticulospinal Tract:

• Starts from two reticular formations: pontine and medullary
• Regulation of voluntary movements
• If damaged, a harmless stimulus can elicit a flexor reflex
• 2 Reticulospinal Tracts: Lateral and Medial

Question 31

Name the 2 Reticulospinal Tracts and describe their basic functions

Answer 31

Lateral Reticulospinal Tract:

• Receives input from both cortices and ascending sensory input from spino-reticular tract
• Bilateral innervation of primary interneurons that in turn innervate alpha and gamma motor neurons to the limb muscles
• Mainly excite flexors

Medial Reticulospinal Tract:

•Mainly excite extensors

Question 32

Vestibulospinal Tract:

• Receives excitatory input from vestibular organs and _____ _____ nuclei and some inhibitory input from the _____ _____ of the cerebellar cortex
• Lateral: Causes _____ innervation of interneurons that excite alpha motor neurons to _____ limb and _____ muscles; Mainly to _______.
• Medial: _____ to muscles of the _____ and _____ extremity; Helps to integrate information from the vestibule and cochlea to motor movements to regulate of _____ and _____
• This tract normally keeps _____ level with the _____ and provides _____. A lesion to this tract may present with a _____ _____ as the healthy side overpowers the weak side.

Answer 32

Vestibulospinal Tract:

• Receives excitatory input from vestibular organs and deep cerebellar nuclei and some inhibitory input from the Purkinje cells of the cerebellar cortex
• Lateral: Causes ipsilateral innervation of interneurons that excite alpha motor neurons to lower limb and trunk muscles; Mainly to extensors.
• Medial: Bilateral to muscles of the neck and upper extremity; Helps to integrate information from the vestibule and cochlea to motor movements to regulate of posture and balance
• This tract normally keeps eyes level with the horizion and provides balance. A lesion to this tract may present with a positive Romberg as the healthy side overpowers the weak side.