77- Neurophys 3: Motor System

What are the two types of motor neurons?

Upper Motor Neurons (UMN) and Lower Motor Neurons (LMN)

What does the upper motor neuron control?

controls LMN & initiates voluntary motor

Where are Upper Motor Neurons located?

Within the CNS, specifically in the cerebral cortex and brainstem.

What is the primary function of Lower Motor Neurons?

To directly innervate skeletal muscle and mediate spinal reflexes.

Where are the Lower Motor Neurons located?

Cell body in ventral grey horn of the spinal cord or brainstem

What is the Lower Motor Neuron comprised of?

Peripheral motor nerves

LMN's can work _____________ to produce "automatic" or "stereotyped" movement.

independently

What are some examples of "automatic" or "stereotyped" movement?

Stepping/gaiting

Alerting & reflexes

Postural control

Does conscious motor activity require a conductor?

Yes

What is the role of the Frontal Cortex in cerebral motor control?

It plans, strategizes, and provides impulse control for voluntary movements.

In the Frontal Cortex of the Cerebrum, where is the plan sent to?

Basal Nuclei

What does the Primary Motor Area initiate?

Voluntary motor movements

Where is the output of the Primary Motor Area?

Brainstem UMNs/LMNs

Spinal cord LMNs

What are the association areas for the cerebral motor control?

Complex integration, planning, and analysis

What is the Basal Nuclei (Ganglia) composed of?

Subcortical nuclei

Striatum (neostriatum)

Globus pallidus

Substantia nigra

Subthalamic nuclei

Where is the Subcortical nuclei located?

Deep cerebral grey matter

What is the Striatum (neostriatum) composed of?

Caudate, putamen, accubens

What are the major descending motor tracts in cerebral motor control?

Corticonuclear

Corticopontine

Corticospinal

Where do the signals go in the corticonuclear tract?

Brainstem nuclei

What type of pathway do fibers in the corticonuclear tract use?

Ipsilateral

Where do the signals go in the corticopontine tract?

Pontine nuclei

What path do the pontocerebellar fibers take?

To the contralateral cerebellum

What does the corticospinal tract do/go?

decussate to contralateral lateral corticospinal tract

In the Corticospinal tract, where do a few fibers stay?

stay ipsilateral in ventral corticospinal tract & decussate before termination

What are the two main types of descending tracts?

Pyramidal

Extrapyramidal

Describe the pyramidal tract

Contains the corticospinal tract and is less developed

Where does the extrapyramidal descending tract originate?

From corticonuclear fibers that innervate UMN in brainstem

Where is the extrapyramidal important?

Animals' gait and posture

What are the 4 main components in the extrapyramidal tract?

Rubrospinal

Reticulospinal

Vestibulospinal

Tectospinal

In the pyramidal tract, where does the lateral corticospinal decussate?

Decussate in pyramids

In the pyramidal tract, where does the ventral corticospinal decussate?

Decussate in the spinal cord

What kind of communication does the pyramidal descending tract have, and where is it located?

Direct communication between cerebral cortex UMN & LMNs

What does the pyramidal descending tract control?

Voluntary fine motor control, skilled movements

Is the pyramidal descending tract important in humans or quadrupeds?

More important in humans than quadrupeds

What are the two main brainstem upper motor neurons?

Corticolbulbar tract fibers

Upper Motor Neuron axons

What makes up the corticobulbar tract fibers?

Red nucleus

Pontine & Medullary Reticular nuclei

Vestibular nuclei

Where do some upper motor neuron axons go?

Cranial nerve motor nuclei (LMNs)

Where do most upper motor neuron axons go?

Spinal cord ventral horn (LMNs) via long descending tract

Why is the rubrospinal tract important?

It is the key tract for voluntary movements in animals

What does the rubrospinal tract facilitate?

UMN of flexor muscles

What does the pontine reticulospinal tract facilitate and inhibit?

Facilitate: LMN of extensor muscles

Inhibits: LMN of flexor muscles

What does the medullary reticulospinal tract facilitate and inhibit?

Facilitate: LMN Flexors

Inhibits: LMN Extensors

What does the vestibulospinal tract facilitate and inhibit?

Facilitate: LMN of extensors

Inhibits: Flexors

What are the 3 most important cell bodies in the lower motor neurons?

Cranial nerve cell bodies (all but I, II, VII)

Somatic motor neuron cell bodies

Visceral motor neuron cell bodies

Where are the cranial nerve cell bodies located? (all but I, II, VII)

Brainstem

Where are the somatic motor neuron cell bodies located?

Ventral horn

Where are the visceral motor neuron cell bodies located?

Intermediolateral substance (lateral horn)

What type of efferent neuron does the somatic lower motor neurons contain?

Peripheral efferent neuron

Are the somatic lower motor neurons GSE or GSA?

General somatic efferent (GSE)

What are the motor units of the somatic lower motor neurons?

Somatic motor neuron (axons)

Muscle fibers it innervates

What are the two main types of the somatic lower motor neurons?

Alpha-motor neuron

Gamma-motor neurons

What does the Alpha-motor neuron innervate and contract?

Innervate extrafusal muscle fibers

Contraction of extrafusal muscle fibers

What does the Gamma-motor neuron innervate?

Innervate the contractile poles of intrafusal muscle fibers of the muscle spindle

What does the Gamma-motor neuron contract?

Contraction of poles of intraspinal fibers stretches the muscle spindle

What is the main purpose of the Gamma-motor neurons?

Reflex and proprioception

What type of LMN pathway(s) is activated by UMN during movement?

Both types (alpha and gamma)