Motor cortex

Question 1

What is the main function of primary motor cortex (M1)?

Answer 1

Planning and execution of voluntary movements.

Question 2

What do premotor and supplementary motor areas do?

Answer 2

Premotor: planning/selection of complex movements; SMA: planning complex or sequential actions.

Question 3

What does the motor homunculus represent?

Answer 3

Somatotopic mapping showing body regions proportional to fine motor control needs.

Question 4

What does larger cortical area allocation indicate?

Answer 4

Finer motor control (e.g., fingers, face).

Question 5

What is contralateral control?

Answer 5

Each hemisphere controls the opposite side of the body.

Question 6

What does motor cortex plasticity mean?

Answer 6

Representations expand with practice and shrink after injury.

Question 7

What do newer studies show M1 neurons encode?

Answer 7

Coordinated movement synergies rather than isolated muscles.

Question 8

When do M1 neurons start firing during movement?

Answer 8

Before movement begins—reflecting planning and prediction.

Question 9

How does load affect M1 neuron firing?

Answer 9

Increased load → increased firing rate.

Question 10

What is a preferred direction of an M1 neuron?

Answer 10

The movement direction a neuron fires most strongly for.

Question 11

What proportion of M1 neurons encode the outcome rather than muscle contraction?

Answer 11

About half respond to movement outcome regardless of contraction.

Question 12

What is the corticospinal tract (CST)?

Answer 12

Main voluntary pathway from motor cortex to spinal cord.

Question 13

Where does the CST decussate?

Answer 13

At the medulla–spinal cord junction.

Question 14

What does the corticonuclear (corticobulbar) tract control?

Answer 14

Voluntary movements of face, head, and neck via cranial motor nuclei.

Question 15

Which cranial motor nuclei receive unilateral cortical input?

Answer 15

Facial motor nucleus (lower face) and hypoglossal nucleus (tongue).

Question 16

What are the major extrapyramidal tracts?

Answer 16

Rubrospinal, reticulospinal, vestibulospinal, tectospinal.

Question 17

What do lateral vs medial descending pathways control?

Answer 17

Lateral: distal limb muscles; Medial: axial/trunk muscles.

Question 18

What are signs of upper motor neuron (UMN) damage?

Answer 18

Spasticity, hypertonia, hyperreflexia, positive Babinski.

Question 19

What are signs of lower motor neuron (LMN) damage?

Answer 19

Hypotonia/atonia, hyporeflexia, muscle wasting, individual muscle weakness.

Question 20

What artery supplies M1 and is affected in stroke?

Answer 20

Middle cerebral artery (MCA).

Question 21

What are corticomotoneurons (CM cells)?

Answer 21

Lateral CST neurons making monosynaptic connections to α-motor neurons; essential for fine finger control.