12-8 MOTOR Systems

Question 1

A: [Lower Motor Neurons] are Motor neurons of the ___ & _____ They are arranged into 4 columns and release ____ onto _____ receptors of ____ _____ Lower Motor Neurons are recruited based on __ & ____

B: What are the 4 Column Arrangements and which muscles do they innervate?

Answer 1

A: Lower Motor Neurons are Motor neurons of the Brainstem & Spinal Cord.

They are arranged into 4 columns and release ACETYLCHOLINE onto nicotinic receptors of target m.

Lower Motor Neurons are recruited based on size & Force

B: 4 Column Arrangement:

1. medial LMN–>axial trunk m.
2. Lateral LMN—>Distal Limb m. (extremities)
3. Dorsal LMN—>FLEXORS
4. venTral LMN——->exTensors

Question 2

A: Lower Motor Neurons are recruited based on Size & Force. Describe the ___of the 3 Motor Unit Types

1. size of its corresponding Motor Neuron
2. Muscle Type
3. White vs. Red fiber?
4. Amount of Mitochondria & Capillaries
5. Fatigue resistance?
6. Twitch type

B: What is a Motor Unit?

C: Corticospinal and Corticobulbar neurons are ____[upper/lower] motor neurons

Answer 2

A: Lower Motor Neurons are recruited based on Size & Force.

1. S-units = small MN/Type 1/Red Fibers/MOST mitochondria & capillaries/Resistant/Slow Twitch ————————————————————————————–
2. FR(fatigue resistant)-units= small MN/Type 2a/WHITE Fibers/medium mitochondria & capillaries/Resistant/FAST Twitch ————————————————————————————–
3. FF(Fat Fatigue)-units=FatLarge MN/Type 2B/WHITE/little mitochon or capillaries/NOT RESISTANT/FAST Twitch ————————————————————————————–

B: [group of muscle fibers] all innervated by 1 LMN

C: Corticospinal and Corticobulbar neurons are UPPER motor neurons

Question 3

What are the 4 Control Systems for Spinal Cord Lower Motor Neurons

Answer 3

A: 1. Descending pathways [5 of them]

2. Higher Cortical Centers [4 of them]
3. Basal ganglia & Cerebellum = planning/monitors mvmnt
4. Spinal Cord Reflex & Pattern Generators

Question 4

Describe the Descending pathways for Lower Motor Neurons. These all act as 1 of the ___ ______ in the Spinal Cord

A: Corticospinal tract (lateral)

B: Vestibulospinal tract [2]

C: Reticulospinal tract [2]

D: Tectospinal tract

E: Rubrospinal tract

Answer 4

Descending pathways = CONTROL SYSTEM in spinal cord LMNs

A: Lateral CST=ALL Excitatory (Glutamate is the transmitter)

B: Vestibulospinal= Head mvmnt & postural adjustments

C: Reticulospinal= locomotion & postural control

D: Tectospinal = reflex of turning head in response to visual/auditory stimuli

E: Rubrospinal= no significance in humans

Question 5

Higher Cortical Centers = ____ __ in spinal cord LMNs Describe them… 1. Association cortex 2. Supplementary motor area 3. Premotor Cortex 4. Motor Cortex

Answer 5

Higher Cortical Centers = CONTROL SYSTEM in spinal cord LMNs 1. Association cortex= it “Decides” that mvmnt is needed 2. Supplementary motor area=allows learning complex mvmnt 3. PreMotor Cortex= creates the “Plan” for the mvmnt 4. Motor Cortex = INITIATES and carries out “plan” using motor neurons

Question 6

____ Tract is the only Motor Descending Tract to innervate Lower Motor Neurons DIRECTLY from the Motor areas of Cortex. All other motor tracts come from the _____

Answer 6

Corticospinal Tract is the only Motor Descending Tract to innervate Lower Motor Neurons DIRECTLY from the Motor areas of Cortex. All other motor tracts come from the BRAINSTEM

Question 7

A: Corticospinal Tract originates and terminates from ___origins and consist of __[#] fibers. 50% of it comes from ______ while other 50% comes from _______

B: CST projects to the __ ___& _____. Its collaterals (both direct & indirect) travel to_____, ____, ______ and _____

C: CST Passes through the ____ limb of ____ _____

Answer 7

A: Corticospinal Tract has MULTIPLE origins and terminations and consist of ~1 million fibers.

50% of it comes from Primary motor cortex while other 50% comes from areas [Adjacent Frontal motor and Parietal areas]

B: The CST projects to the Spinal Cord & Brainstem. Its collaterals (both direct & indirect) travel to basal ganglia, thalamus, [reticular formation of midbrain] and sensory nuclei

C: CST Passes through the POSTERIOR limb of Internal Capsule

Question 8

A: CorticoBULBar tract (AKA ___ tract) is an ____ MOTOR NEURON tht descends ANterior to _____ tract. It usually ends on ____ of the ___ _____ but sometimes ends on _____inside the ____.

B: Name the 3 CN nucleus that do NOT receive DIRECT CorticoBULBar innervation.

Answer 8

A: CorticoBULBar tract (AKA Corticonuclear tract) is an UPPER MOTOR NEURON that descends ANterior to Corticospinal tract. It usually ends on interneurons of [Reticular formation] but sometimes ends on [motor neurons of CN] inside the brainstem.

B: Oculomotor, Trochlear & Abducens nucleus does NOT receive DIRECT CorticoBULBar innervation.

Question 9

Describe The Cortex Origin of Upper Motor Neuron for CN nuclei involving:

1. Chewing ex. Upper Motor Neurons for Chewing (CN__) comes from ____[R vs. BOTH] side(s) of the Cortex before reaching the Nucleus
2. Upper Face
3. lower face
4. speaking / swallowing
5. tongue mvmnt

Answer 9

Cortex Origin of Upper Motor Neuron for CN nuclei involving:

1. Chewing ex. UMN for Chewing (CN 5) comes from [Both BUT More of 1 side] before reaching Nucleus
2. Upper fAce: UMN come from BOTH Cortex before reaching CN7 Nucleus
3. lower face: UMN come from 1 side Cortex –> Crosses the midline–> reaches CN7 Nucleus
4. swallowing / speaking: UMN come from BOTH Cortex before reaching CN9 and CN10 Nucleus ————————————————————————————–
5. tongue mvmnt: UMN comes from [Both BUT More of 1 side Cortex] before reaching CN12 Nucleus

Question 10

What are Betz cells?

Answer 10

Make up 3% of [CST-Corticospinal Tract] and are concentrated there

Primary Motor Cortex makes up 50% of CST and the rest comes from [Adjacent Frontal motor and Parietal areas]