L2.2 Motor Control

Question 1

What are lower motor neurons?

Answer 1

Cranial and spinal nerves

Question 2

What are upper motor neurons?

Answer 2

Neurons that originate in the cerebral cortex and/or brainstem and descend into the spinal cord or cranial nerve nuclei in the brainstem to control the activity of cranial and spinal nerves

Must be entirely contained within the CNS

Question 3

Upper motor neuron tracts that go to lower motor neurons in the spinal cord are called?

Answer 3

Corticospinal tracts

Question 4

Upper motor neuron tracts that go to lower motor neurons in the brainstem are called?

Answer 4

Corticobulbar tracts

Question 5

What four descending motor tracts originate in the brainstem?

Answer 5

1. Vestibulospinal
2. Reticulospinal
3. Tectospinal
4. Rubrospinal (minor in humans)

Question 6

What upper motor neuron tracts originate within the cortex? (2)

Answer 6

1. Corticospinal tract
2. Corticobulbar tract

Question 7

Describe a simplified descending pathway from the cortex

Answer 7

Question 8

The motor cortex receives information input from what areas? (4)

Answer 8

1. Basal ganglia
2. Cerebellum
3. Somatosensory afferents
4. Prefrontal cortex

Question 9

Which area of the motor cortex has the lowest threshold for action to cause movement?

Answer 9

The primary motor cortex

Question 10

A lesion to the primary motor cortex would likely impair?

Answer 10

Fractionated finger/facial movements

Skilled hand movements, hand to mouth coordination, lower face

Question 11

Answer 11

Question 12

Answer 12

Question 13

Generally describe the positions of major motor areas in the motor homunculus

Answer 13

Question 14

What two areas of the brain are responsible for making the decision of which movement to take and predicting the outcome?

Answer 14

1. Parietal lobe
2. Prefrontal cortex

Parietal receives all the somatosensation of the body, communicates with the higher functions of the prefrontal cortex (will this action help or hurt me, etc).

Information then passed on to the premotor and supplementary motor cortex

Question 15

If you don’t need sensory input information/sensory cues to do the movement, what motor area of the brain can self-initiate movement?

E.g. decide to shift gaze to the right absent a cue

Answer 15

Supplementary motor cortex

Question 16

What does the supplementary motor cortex do?

Answer 16

Question 17

What is a bimanual movement?

What usually controls them?

Answer 17

A movement involving both hands

Usually controlled by the supplementary motor cortex

Question 18

Unlike the supplementary motor cortex, the premotor cortex organises movements based on?

Answer 18

Sensory information/feedback

Question 19

Which part of the brain contains ‘mirror motor neurons’? What are they?

Answer 19

Premotor cortex

Become activated seeing another doing a movement and ‘imagining’ us doing the movement ourselves.

Question 20

What are the important aspects of the premotor cortex? (6)

Answer 20

Question 21

With regards to planning movement (motor action), what information does the parietal association cortex provide the premotor and supplementary motor cortexes?

Answer 21

Information about the spatial relationships of the body and and its surroundings

Question 22

The corticospinal tract has ____ fibres in it, which arise from 3 different locations in the cortex. What are they and what % do they contribute?

Answer 22

1 million fibres

30% Precentral gyrus (primary motor)

40% Postcentral gyrus

30% Premotor and supplementary motor

Question 23

In the corticospinal tract, there are 1 million fibres. Of which,

30% are Precentral gyrus (primary motor)

40% are Postcentral gyrus

30% are Premotor and supplementary motor

Why are there neurons coming from the postcentral gyrus?

Answer 23

These descending neurons inhibit sensory information from coming in at the spinal level they synapse at.

Basically they travel down to a sensory boi and turn him off so he can’t send his signal upwards. Done in times when there is a need for intense motor output

Question 24

Cerebrospinal tract neurons leave the cortex and descend through?

Answer 24

The posterior limb of the internal capsule

Question 25

State the order of the 3 cortex areas that together form corticospinal tract, from posterior to anterior.

Answer 25

Primary motor neurons most posterior

Premotor intermediate

Supplementary motor most anterior

Question 26

Answer 26

Question 27

Describe the corticospinal tract after it enters the posterior limb of the internal capsule; with specific regard to % decussation.

Answer 27

1. As the CST exits the internal capsule, it enters the brainstem
2. It travels through the cerebral peduncles in the midbrain
3. Travels through the brainstem in the anterior aspect, forming the medullary pyramids
4. At the junction of the spinal cord and the medulla, 90% of fibres decussate (cross sides) to enter the contralateral lateral white column of the spinal cord
5. The remaining 10% of Upper Motor Neurons (UMN) remain ipsilateral at this SC-medulla junction.
   
   1. However, 8% will subsequently decussate when they reach the spinal cord level of the LMN
   2. Only 2% of the original will remain ipsilateral and uncrossed at the anterior CST

Therefore 98% overall decussate

Question 28

1st order neurons are?

2nd order neurons are?

3rd order neurons are?

Answer 28

1st order = UMN

2nd order = interneurons

3rd order = LMN (mainly alpha but some gamma neurons)

Question 29

UMN that directly synapse with LMN (I.e. no interneuron) usually innervate?

Answer 29

Distal complex muscles, such as the fingers

(Lower cervical and lumber SC levels)

Question 30

Anterior CST neurons are thought to control more?

Found at?

Answer 30

Axial muscles

Found at cervical and thoracic levels

Question 31

Lateral CST neurons are thought to control more?

Answer 31

Dominate motor innervation to distal limb muscles, increasing speed and dexterity of movement

Question 32

While the CST is not the only way to innervate muscles, it is thought to?

Answer 32

Provide speed and agility to voluntary movement

Question 33

Answer 33

Question 34

What parts of the corticobulbar tract are NOT bilaterally controlled?

Answer 34

Question 35

The corticobulbar tract covers the tract from the cortex to which specific cranial nerves?

Answer 35

Question 36

What three features are consistent for all 4 brainstem tracts?

Answer 36

Question 37

Generally describe the reticulospinal tract

Answer 37

Question 38

Generally describe the lateral-medullary tract

Answer 38

Question 39

Generally describe the medial-pontine tract

Answer 39

Question 40

Briefly describe the vestibulospinal tract

Answer 40

Question 41

Differentiate between the lateral vestibulospinal tract and the medial vestibulospinal tract

Answer 41

Question 42

Generally describe the tectospinal tract

Answer 42

Question 43

Generally describe the rubrospinal tract

Answer 43

Question 44

Answer 44