Corticobulbospinal tracts - SRS

Question 1

In the spinal cord and brainstem, lower motor neurons directly innervate what?

Answer 1

Muscle

Question 2

What are lower motor neurons controlled by?

Answer 2

1. Local circuits within the spinal cord and brainstem
2. Upper motor neurons

Question 3

What regulates upper motor neurons?

Answer 3

Basal ganglia and cerebellum

Question 4

Where are lower motor neuron cell bodies located?

Answer 4

Ventral horn of the spinal cord

Brainstem motor nuclei

Question 5

What are the two types of lower motor neurons that innervate skeletal muscle?

Answer 5

Alpha and Gamma

Question 6

Where are upper motor neuron cell bodies located?

Answer 6

1. -Cortex (Corticospinal)
   
   1. Cortex (Corticobulbar)
2. –Vestibular nuclei (Vestibulospinal)
3. –Superior colliculus (Tectospinal)
4. –Reticular formation (Reticulospinal)
5. –Red nucleus (Rubrospinal)

Question 7

Where do interneurons for axial structures located?

Do they have many collaterals?

Unilateral or bilateral?

Answer 7

Medial, and bilateral.

Possess many collaterals

Question 8

Where do interneurons for Limb structures located?

Unilateral or bilateral?

Do they have many collaterals?

Answer 8

More lateral, are unilateral and have fewer collaterals.

Question 9

A single alpha motor neuron and all the muscle fibers it innervates = ?

Answer 9

Motor unit

Question 10

How do we change the amount of force produced by a muscle?

Answer 10

Increase or decrease the amount of motor units recruited.

Question 11

Identify the blanked out structures

Answer 11

Question 12

The neuromuscular junction/motor end plate is analagous to a?

Answer 12

Synapse

Question 13

Alpha Motor neurons from the spinal cord innervate muscles involved in excitation-contraction coupling. Characterize these fibers by speed and structure.

Answer 13

Fast

Myelinated

Question 14

In excitation-contraction coupling, what NT is released by the alpha motor neuron?

What receptors does it bind?

What type of receptors are these?

Answer 14

2. releases acetylcholine
3. Binds to nicotinic receptors
4. these are ligand-gated Na+ channels

Question 15

What are the junctional folds of the neuromuscular junction often continuous?

Answer 15

T-Tubules

Question 16

Motor units differ in the types of muscle fibers they innervate. What are the three types we covered?

Answer 16

Slow motor units

Fast fatigable motor units

Fast Fatigue-resistant motor units

Question 17

Descrime the muscle fibers of slow motor units.

Answer 17

–Smaller, red muscle fibers (myoglobin, mitochrondria, capillary beds)

Question 18

What size are the slow motor unit alpha-motor unit neurons?

What level of force do these generate?

How fatigable are they?

Answer 18

–Smaller Alpha-motor neurons
–Small force
–Resistant to fatigue

Question 19

What are fatigue resistant slow motor units imporant for?

Describe their threshold for activation.

Answer 19

• Important for sustained muscle contraction (eg. Regulating posture)
• Lowest thresholds for activation = recruited first

Question 20

Describe the size and color of Fast fatigable motor unit fibers.

What size alpha motor neurons are we dealing with here?

What is the force like?

Fatiguability?

Answer 20

–Larger, pale muscle fibers (few mitochondria)
–Larger Alpha motor neurons
–Large force
–Easily fatigued

Question 21

In what manner of activity are fast fatigable motor units most useful?

Answer 21

•Brief exertions that require large forces (eg. jumping)

Question 22

Where do fast fatigue resistance motor units fall on the spectrum of muscle fiber types?

What else are they known as?

Answer 22

–Between slow motor units and fast fatigable motor units (aka intermediate motor units)

Question 23

As the synaptic activity driving motor neurons increases, in what order do we recruit the motor neuron types?

Answer 23

1. slow motor neurons
2. fast, fatigue-resistant motor neurons
3. fast fatigable motor neurons

Question 24

What is muscle tone?

Answer 24

The resting level of tension in a muscle

Question 25

What does muscle tone enable us to do?

Answer 25

•Allows muscle to make an optimal response to voluntary or reflexive movement by keeping them in a **_state of readiness to resist stretch_**

Question 26

What does denervation do to muscle?

Answer 26

Causes rapid atrophy

Question 27

When muscle fiber degenerate, they are replaced by fatty and fibrous tissue, leading to loss of contractile proteins in muscle cells. What can this fibrous tissue cause?

Answer 27

Contracture

Question 28

Why do muscles atrophy in the elderly?

Answer 28

_Loss of motor neurons _ due to vascular disease and poor nutrition.

Question 29

When motor neurons are lost, motor end plates are innervated by collaterals of adjacent motor neurons, leading to an abnormal EMG signature know as?

Answer 29

Giant motor units

Question 30

What are typical signs of lower motor neuron damage?

Answer 30

Paralysis or paresis areflexia atrophy fibrillations fasciculations

Question 31

What are fibrillations? What are they due to?

Answer 31

–Rapid twitching due to change in muscle fiber excitability \*denotes pathology\*

Question 32

What are fasciculations?

Answer 32

–Local, small twitch due to alpha motor neuron damage

Question 33

What pathways for upper motor control of lower motor neurons are extrapyramidal? (4)

Answer 33

–Vestibular (vestibulospinal) –Reticular (reticulospinal) –Red nucleus (rubrospinal) –Superior colliculus (tectospinal)

Question 34

What pathways for upper motor neuron control of LMN's is pyramidal?

Answer 34

–Lateral corticospinal –Ventral corticospinal –Corticobulbar

Question 35

From what nuclei does the vestibulo spinal tract arise?

Answer 35

LAteral or medial vestibular nuclei

Question 36

What does the lateral vestibular nuclei command?

Answer 36

**Ipsilateral: **posture, including extensors

Question 37

What does the medial vestibular nuclei command?

Answer 37

**Bilateral: **head position stability

Question 38

Identify blanked structures

Answer 38

Question 39

Where does the tectospinal tract arise?

Answer 39

Superior colliculus

Question 40

What does the tectospinal tract influence?

Answer 40

Musculaturs of neck and eyes Postural reflexes to alarming visual stimuli and some auditory stimuli

Question 41

Identify

Answer 41

Question 42

The reticulospinal tract arises from different brainstem levels. Does it decussate? What does it control?

Answer 42

Does not decussate Affects axial and postural muscles, and provides secondary control when CST is dysfunctional

Question 43

What is the reticulospinal tract largely controlled by?

Answer 43

Cortical motor centers

Question 44

Identify

Answer 44

Question 45

What does the rubrospinal tract innervate? What does it do?

Answer 45

Innervates spinal cord through thoracic levels. It is a laterally based tract possibly involved in flexor muscles of the arm. Not entirely sure what it does in humans.

Question 46

Ident

Answer 46

Question 47

What organizes the movement of individual muscles?

Answer 47

Motor homunculus in the primary motor cortex

Question 48

What organizes the movement of groups of muscles?

Answer 48

Motor homunculi in premotor and supplementary motor cortices

Question 49

Where are Betz cells found? In what layer are they found?

Answer 49

Primary motor cortex Layer V

Question 50

What do Betz cells project through?

Answer 50

* Project through posterior limb of internal capsule * Through medullary pyramids

Question 51

What does the pyramidal tract provide collaterals to?

Answer 51

1. Reticular formation 2. Trigeminal 3. Facial 4. Nucleus ambiguus

Question 52

Describe the decussation of the pyramidal tract.

Answer 52

80% at the caudal medulla 20% continue ipsilateral

Question 53

What tract do the decussating fibers of the pyramidal tract take after decussation? What does this innervate?

Answer 53

* “Lateral corticospinal tract” * Limbs, digits (stuff needing fine motor control)

Question 54

What path do the 20% of pyramidal tract fibers take? What do they go to? They have a second chance at decussating, where do they get this opportunity?

Answer 54

* “anterior or ventral corticospinal tract” * Axial muscles * Some of these will decussate in the anterior white commissure, some won’t at all

Question 55

Ident

Answer 55

Question 56

Ident

Answer 56

Question 57

For bronchiomeric muscles, specifically facial expression above the eyes, what do lesions of the cortex produce?

Answer 57

Bilateral deficiencies (but minor)

Question 58

For bronchiomeric muscles, specifically facial expression above the eyes, what do lesions of the nucleus produce?

Answer 58

Ipsilateral Deficiency

Question 59

For muscles of facial expression below the eyes, muscles of mastication and the tongue, what does a lesion of the cortex cause?

Answer 59

Contralateral deficiency

Question 60

For muscles of facial expression below the eyes, muscles of mastication and the tongue, what does a lesion of the nucleus cause?

Answer 60

Ipsilateral deficiency

Question 61

Identify these locations

Answer 61

Question 62

Identify this location

Answer 62

Question 63

What doe a + Babinski's sign in adults indicate?

Answer 63

If toes point upward instead of downward due to loss of upper motor neuron control

Question 64

What is spasticity a sign of?

Answer 64

–Corticospinal influences probably are somewhat inhibitory to the brainstem control of postural muscles---relaxes them a bit.

Question 65

What can cause loss of fine motor control?

Answer 65

Corticospinal damage

Question 66

ALS arises due to degeneration of what?

Answer 66

Corticospinal and LMN

Question 67

What is the average time to fatality post ALS diagnosis?

Answer 67

5 yrs