4.2 - Descending Tracts and UMNs

Question 1

In what part of th ebrain do most muscle movements originate?

Answer 1

pre central gyrus

Question 2

What parts of the spinal cord are considered parasympathetic and sympathetic?

Answer 2

parasympathetic - craniosacral

Sympathetic - Thoracolumbar

Question 3

Explain the distinction between pyramidal and extra-pyramidal UMN. What tracts does each contain?

Answer 3

Pyramidal - consists of corticospinal (begins in cerebral cortex and terminates in spine) and corticobulbar tracts which are both responsible for voluntary movement of body and fascial muscles respectively. Directly innervates motor neurons

Extra-pyramidal - Modulate motor activity without directly innervating motor neurons. Involved in reflexes, locomotion, complex movement and postural control. Consists of vestibulospinal, reticulospinal, rubrospinal, and tectospinal tracts.

Question 4

Which side of the brain controls skeletal muscle movement son the left side of the body and vice versa?

Answer 4

right side and vice versa

Question 5

Answer 5

Question 6

What does the corticospinal tract convey?

Answer 6

Axial and limb motor control

Question 7

Where does the corticospinal tract begin?

Answer 7

pre central gyrus

Question 8

Which neurons innervate the axial muscles and the limb muscles

Question 9

Describe the pathway of the 1st order neurons of the corticospinal tract

Answer 9

Leaves nuclei and cortex by descending through internal capsule and into medulla through brainstem where:

• 75-90% decussate AKA decussation of pyramids and runs through the lateral corticospinal tract (goes on to innervate limbs) and once they reach their intended spinal level they synapse with a neuron on the anterior horn of grey matter
• 10-25% dont decussate and run through the anterior corticospinal tract (innervate axial muscles). However, once the anterior corticospinal tract nerves reach their intended spinal level they decussate through the anterior white commissure and synapse with neuron in anterior horn of grey matter

Question 10

What is a UMN lesion of corticospinal tract?

Answer 10

A lesion in the 1st order neurons of the corticospinal tract

Question 11

What is the pathway of the 2nd order neurones of the corticospinal tract? What can these neurones be described as?

Answer 11

Project from anterior horn nuclei to the limb and axial muscles AKA LMN

Question 12

Describe the pathway of the corticobulbar tract

Answer 12

Starts in cerebral cortex and descrends through internal capsule to brainstem where they decussate. terminate on contralateral cranial nerve motor nuclei in midbrain, pons, and medulla

Question 13

What muscles does the corticobulbar tract control?

Answer 13

facial expression, extra-ocular muscles

Question 14

What is the function of the vestibulospinal tract? Where does it arise from? Does it decussate?

Answer 14

Balance and posture

Does not decussate

Arises from vestibular nucleus

Question 15

What is the function of the reticulospinal tract?

Answer 15

Helps with extensor spinal reflexes

Question 16

What is the function of the rubrospinal tract? Does it decussate? Describe its pathway

Answer 16

Arises from red nucleus and decussates in midbrain and descends the spinal cord

Function is to facilitate flexor motoneurones and inhibit extensor motoneurones

Question 17

What is the function and pathway of the tectospinal tract?

Answer 17

Function - aids in directing head movements

Neurons arise from tectum of brainstem and decussate within brainstem. Terminate in the upper cervical segments

Question 18

What tract inhibits the reticulospinal tract and what would occur if inhibition was released?

Answer 18

corticospinal tract inhibits

Release from inhibition would result in upposed extension of head and limbs

Question 19

What would occur if the vestibulospinal tract was damaged?

Answer 19

loss of righting reflex, ataxia of gait, postural instability

Question 20

Give the strict definition of a reflex

Answer 20

An automatic, unlearned, repeatable response to a specific stimulus that does not require the brain to be intact

Question 21

Why is it important to distinguish between a voluntary and a reflex movement?

Answer 21

Both use different and separate neural circuits. Reflex movements can be achieved with a brain that is not intact and thus does not tell us much about the functionality of the brain

Question 22

What is a monosynaptic stretch reflex and a muscle stretch reflex?

Answer 22

Muscle stretch reflex is an umbrella term that covers all the versions of the reflex circuits

The monosynaptic stretch reflex is the simplest muscle stretch reflex, containing only one synapse between afferent and efferent neurone

Question 23

Explain how some relaxed healthy individuals are found to be areflexic

Answer 23

Severity of constant descending inhibition is variable in time.