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**.