Neural Pathways and Motor Control: Corticobulbar, Spinal Tracts, and Reflexes

corticobulbar tract

Controls Muscles of the face, tongue, jaw, pharynx, etc. (voluntary control) (decussates)

- Runs parallel to the CST and ends at cranial nerves of the brainstem

Colliculospinal Tract

Involved in eye and head movements and connects superior colliculus to spinal cord (decussates)

reticulospinal tract

Modulates muscle tone, regulates the respiratory and sleep-wake cycles, and connects the reticular formation to the spinal cord.

Rubrospinal Tract

Limb movement, working with the CST. Axons from the red nucleus cross the midline and descend within the spinal cord. (decussates)

vestibulospinal tract

Maintains posture by connecting vestibular nuclei in the ear to the spinal cord.

internal capsule

A 'highway' for all tracts passing from the brainstem/spinal cord to the cortex.

What is the role of Lower Motor Neurons (LMN)?

innervate fibers directly, serving as the final common pathway that sends signals to body effectors.

What is the role of upper motor neurons (UMN)?

Initiate and plan movement, while sending signals out to the body

Neuromuscular Junction

LMN connects directly to the muscle fibers, acetylcholine (ACh) is the neurotransmitter released.

Alpha LMN

innervate extrafusal fibers for muscle contraction

Gamma LMN

intrafusal fibers, GTO's send signals to CNS about tension and length

What constitutes a Motor Unit?

A Lower Motor Neuron, its axon, and all the muscle fibers it innervates.

- variable in size (Territory), follows the "all or none principle"

What is the Spinal Reflex?

A local circuit within the spinal cord that receives sensory information and mediates a motor response (reflex).

What are the components of a spinal reflex arc?

Receptor, sensory neuron, interneuron, motor neuron, and effector.

Corticospinal Tract

Involved in motor control (speed and agility of movement), carrying informational from the cortex to the spinal cord. (Decussates)

- Both lateral and anterior tracts pass through internal capsule

Lateral Corticospinal Tract

Fibers cross in medulla

Anterior Corticospinal Tract

Fibers cross at LMN

Pyramidal decussation

point at the junction of the medulla and spinal cord where motor fibers cross the midline.

Where are Betz cells located?

Layer 5 of M1 (primary motor cortex)

What is the significance of the Lawrence and Kuyper experiment?

It demonstrated the effects of damage versus healthy Corticospinal Tract pathways.