Module 4: Motor Systems

Question 1

Where does motor information leave the spinal cord?

Answer 1

Through the anterior roots

Question 2

Motor information leaves the spinal cord through the anterior roots, and lower motor neurons are located where?

Answer 2

In the anterior horn at each spinal level

Question 3

What are the two kinds of rootlets in the spinal cord?

Answer 3

motor (anterior)

sensory (posterior)

Question 4

In the spinal cord, rootlets are either motor (anterior) or sensory (posterior), but what happens when they leave the spinal cord?

Answer 4

They combine outside the vertebral canal into spinal nerves that are mixed, ie. both sensory and motor

Question 5

On this image of the spinal cord, identify:

1. a spinal nerve (mixed)
2. a posterior root (sensory)
3. an anterior root (motor)

Answer 5

Question 6

On this image of the spinal cord, identify:

1. a spinal nerve (mixed)
2. a posterior root (sensory)
3. an anterior root (motor)
4. spinal ganglion

Answer 6

Question 7

On this micrograph of the spinal cord, where is the anterior corticospinal tract located? What is it implicated in?

Answer 7

The anterior corticospinal tract is implicated in motor to ipsi- and contra-lateral ventral horn; mostly axial musclature

Question 8

On this micrograph of the spinal cord, where is the spinothalamic tract located? What is it implicated in?

Answer 8

Pain and temperature from the contralateral side of the body

Question 9

On this micrograph of the spinal cord, where is the lateral corticospinal tract located? What is it implicated in?

Answer 9

motor to the ipsilateral ventral horn; mostly limb musculature

Question 10

On this micrograph of the spinal cord, where is the spinocerebellar tract located? What is it implicated in?

Answer 10

Proprioception from the limbs to the cerebellum

Question 11

On this micrograph of the spinal cord, where is the fasciculus gracilis located? What is it implicated in?

Answer 11

sensory (fine touch and proprioception) from ipsilateral lower limb

Question 12

On this micrograph of the spinal cord, where is the fasciculus cuneatus located? What is it implicated in?

Answer 12

Sensory (fine touch, proprioception) from ipsilateral upper limb

Question 13

The corticospinal tract can be divided into what two components?

Answer 13

lateral corticospinal tract

anterior corticospinal tract

Question 14

What is the function of the descending lateral corticospinal tract?

Answer 14

Skilled movement of the extremities

Question 15

What is the function of the descending anterior corticospinal tract?

Answer 15

Postural adjustment

Question 16

A descending motor tract, corticospinal fibers transmit information controlling what?

Answer 16

voluntary, discrete, skilled movements

Question 17

The corticospinal tract is organized somatotopically, describe.

Answer 17

Fibers from the lower levels of the cord are found laterally within the tract, while fibers from higher levels are found medially within the tract.

Question 18

Where does the corticospinal tract originate?

Answer 18

In the motor cortex

Question 19

The corticospinal tract travels through the posterior limb of the [blank], exhibiting a somatotopic arrangement

Answer 19

internal capsule

Question 20

Where do corticospinal fibers descend on this micrograph of the midbrain?

Answer 20

ipsilaterally through the middle 3/5 of the cerebral peduncles (crus cerebri) in the anterior part of the midbrain

Question 21

What happens to corticospinal fibers as they descend through the pons?

Answer 21

They are broken up into many bundles

Question 22

How does the corticospinal tract descend through the medulla

Answer 22

As the pyramids in the anterior part of the medulla

Question 23

What happens to corticospinal fibers at the caudal medulla (the junction of the medulla and the spinal cord)?

Answer 23

most (85-90%) of fibers cross the midline in the decussation of the pyramids. These crossed fibers go on to form the lateral corticospinal tract. Uncrossed fibers (10-15%) descend as the anterior corticospinal tract.

Question 24

Which tract is organized in parallel with the corticospinal system?

Answer 24

The corticobulbar tract

Question 25

What is the function of the corticobulbar tract?

Answer 25

Innervating several cranial nerves

Question 26

Where does the corticobulbar tract arise? What is its descending pathway?

Answer 26

arises in areas of the motor cortex related to the head and face

descends through the corona radiata. Fibers converge in the genu of the internal capsule, and then descend with corticospinal fibers

Question 27

What is the corticopontine (corticopontocerebellar tract) implicated in?

Answer 27

Planning, initiation, timing and coordination of voluntary movement.

It is organized partially in parallel with the corticospinal system.

Question 28

Aside from the corticospinal and corticobulbar tracts, there are three other main pathways that influence lower motor neurons, and therefore play a role in modulating motor activity. What are they?

Answer 28

1. vestibulospinal tracts
2. reticulospinal tracts
3. rubrospinal tracts

Question 29

What is the role of vestibulospinal tracts?

Answer 29

Important mediators of postural adjustment and head movements

Question 30

What is the role of reticulospinal tracts?

Answer 30

They influence muscle tone

Question 31

What is the role of the rubrospinal tract?

Answer 31

It is quite small in humans, but probably plays a minor role in fluencing voluntary movement

Question 32

The vestibulospinal tracts originate in the caudal pons and rostral medulla. On this micrograph of the caudal pons, locate the vestibular nuclei

Answer 32

Question 33

The vestibulospinal tracts originate in the caudal pons and rostral medulla. On this micrograph of the rostral medulla, locate the vestibular nuclei

Answer 33

Question 34

The reticulospinal tracts influence voluntary movement and muscle tone, where do they originate?

Answer 34

In scattered reticular formation nuclei in the tegmentum of the pons and the medulla

Question 35

The rubrospinal tract facilitates flexor and inhibits extensor muscle activity. Where does it originate?

Answer 35

It originates in the red nucleus in the tegmentum of the midbrain

Question 36

The cortical motor system is a network of cortical areas. What does it include?

Question 37

Where does the tectospinal tract originate?

What is it implicated in?

Answer 37

The superior colliculus of the midbrain

This tract is responsible for orienting the head and neck during eye movements.

Question 38

The control centers that fine tune the signals to both the lower motor neurons (LMNs) and the (UMNs) come from two distinct systems, what are they?

Answer 38

1. the basal ganglia (projects to the cortex only)
2. the cerebellum (projects to all levels of the motor system)

Question 39

What is the function of the basal ganglia?

Answer 39

The basal ganglia are the main integrators of cortical and limbic input to the motor system. The basal ganglia ensure that movements are planned and executed precisely. They encode for the decision to move, the direction of movement, the amplitude of movement, and motor expression of emotions.

Question 40

What is the function of the cerebellum, with respect to motor control?

Answer 40

The cerebellum ensures smooth coordinated movements of voluntary muscles. It receives information concerning the position of the body (proprioceptive information from spinocerebellar and cuneocerebellar tracts), muscle tone and activity of spinal reflex arcs (spinocerebellar and cuneocerebellar tracts), position of the head (vestibular information), cortical activity (sensory, motor, and association areas), and the environment (visual and acoustic).