Motor System

Question 1

What are the major regions of the cortex involved in descending motor control? Describe their major roles and responsibilities

Answer 1

.primary motor cortex: on button

• premotor cortex: what we choose to do
• supplementary motor area: coordination and execution (quality)

Question 2

Describe how lateral and medial components of the premotor cortex differ.

Answer 2

lateral components regard external cues (ex. how you reach for a fastball vs slow pitch); mirror motor neurons in this category
medial regard internal cues (gauging force)

Question 3

What tracts make up the lateral motor systems in the spinal cord?

Answer 3

lateral corticospinal tract

rubrospinal tract

Question 4

What tracts make up the medial motor systems in the spinal cord?

Answer 4

anterior corticospinal tract
Reticulospinal tract
tectospinal tract
Vestibulospinal tract

Question 5

What specific aspect of motor control is the lateral corticospinal tract tasked with?

Answer 5

movement of the extremities–especially rapid dexterous movements at digits or joints, modulates myotatic reflexes

Question 6

What is the internal capsule and what is it known for?

Answer 6

major highway for both ascending and descending pathways (ALL white matter)

Question 7

What are the borders of the internal capsule?

Answer 7

grey matter borders:

medial: thalamus and caudate
lateral: global pallidus and putamen

Question 8

What are the different regions of the internal capsule

Answer 8

anterior limb
genu
posterior limb

Question 9

Describe the basic organization of motor control. What major structures are involved?

Answer 9

Primary Motor cortex (precentral gyrus)

gets things started> supplementary motor area and premotor cortex

Question 10

What is the function of the anterior limb of the internal capsule?

Answer 10

info from thalamus and brainstem > prefrontal and parietal regions
both ascending somatosensory form SC and assoc w/ emotion, motivation, cog processing, decision-making

Question 11

what is the function of the posterior limb of the internal capsule?

Answer 11

descending motor fibers from frontal lobe>brainstem and SC

SOMATOTOPICALLY ORGANIZED

Question 12

what is the purpose of the anterior corticospinal tract?

Answer 12

controls bilateral axial and girdle muscle

Question 13

what are the primary functions of the rubrospinal tract?

Answer 13

controlling movement of extremities

• modulating flexor tone
• inhibition of anti-gravity muscles (extensors)
• modulation of reflex (think flexor-withdrawal)

Question 14

what is the function of the reticulospinal tract?

Answer 14

automatic posture and gait-related movements

• pontine: inhibit limb flex and excite ext
• medullary: excite flex and inhibit ext

Question 15

what is the function of the tectospinal tract? (remember “tectum”)

Answer 15

ctrls coordination of head and eye movement

Question 16

What is the general distribution of LCST vs ACST within the general Corticospinal Tract?

Answer 16

LCST: 85%
ACST:15%

Question 17

What types of motor neurons exit the spinal cord and head to the periphery for motor innervation?

Answer 17

alpha motor neurons

Question 17

What types of motor neurons exit the spinal cord and head to the periphery for motor innervation?

Answer 17

alpha motor neurons

Question 18

What are the major motor plexi found exiting the spinal cord and where can they be found?

Answer 18

cervical plexus  (C3-C5)
brachial plexus (C5-T1)
lumbar plexus (L1-S4)

Question 19

what is a myotome?

Answer 19

a group of muscles innervated by a single nerve root

Question 20

What are the component of the neuromuscular junction (NMJ)

Answer 20

synaptic bouton, cleft, motor end plate

presynaptic cell, cleft, postsynaptic cell

Question 21

What is the primary neurotransmitter involved in neuromuscular junction function? what breaks it down?

Answer 21

ACh; acetylcholinesterase

Question 22

List the major steps involved in synaptic transmission at the neuromuscular junction

Answer 22

1. AP triggers ACh release into the cleft
2. ACh binds to receptors, Na+ channel opens for depolarization
3. EPSP causes AP to travel to fiber for contraction
4. ACh broken down

Question 23

what is a motor unit and what are the 3 types?

Answer 23

alpha motor neurons and their assoc muscle fibers; 
Type 1A(slow), 2A (fast and fatigue-resistant), Type 2b (fast and fatigable)

Question 24

describe a type 1a MU

Answer 24

smaller muscles designed for sustained contractions

Question 25

describe a type 2a MU

Answer 25

intermediate in size, 2x force as slow and more resistant to fatigue than FF

Question 26

describe a type 2b MU

Answer 26

larger muscles, brief but forceful contractions

Question 27

Explain the size principle.

Answer 27

As input increases, progressively larger motor units are activated>larger
forces generated