SFIII Physiology - Unit 2 : Motorfunctions Brainstem & Spinal Cord Cartes | Quizlet

What is the basic flow of sensory-motor integration?

Sensory info → spinal cord → brain → motor plan in cortex → descending commands to muscles.

What is the highest level of motor control?

Cerebral motor cortex (planning voluntary movements).

What are the intermediate motor control structures?

Brainstem nuclei, basal ganglia, cerebellum (coordination and modulation).

What is the lowest level of motor control?

Spinal and brainstem motor neurons (final output).

What is the main motor function of the spinal cord?

Integration of basic muscular activities: posture, simple movements, reflexes.

What movements can the spinal cord generate?

Simple gait automatisms and simple defensive movements.

How does the spinal cord contribute to posture?

By maintaining basic antigravity muscle tone via reflexes.

What are the dorsal horns of the spinal cord?

Sensory processing areas (input).

What are the ventral horns?

Motor neuron areas (output to muscle).

What are the lateral horns?

Autonomic (sympathetic) neuron areas.

What are ascending spinal tracts?

Pathways carrying sensory information to the brain.

What are descending spinal tracts?

Pathways carrying motor commands from brain to spinal cord.

What are motoneurons (motor neurons)?

Final neurons that directly innervate muscles, located in ventral horns.

Key features of motor neurons

Large somas, long thick axons, many dendrites, 100k+ synaptic terminals.

What are interneurons in the spinal cord?

Local processing neurons in all horns that integrate sensory info before reaching motor neurons.

What is an alpha motoneuron?

Motor neuron that innervates extrafusal muscle fibers (force-producing fibers).

What is a gamma motoneuron?

Motor neuron that innervates intrafusal fibers inside the muscle spindle.

Function of alpha motoneurons

Produce contraction and movement.

Function of gamma motoneurons

Adjust muscle spindle sensitivity (proprioception calibration).

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

Paralysis/paresis, flaccidity, strong atrophy, loss of reflexes, abnormal EMG.

Why does LMN lesion cause strong atrophy?

Muscle loses direct neural input and trophic support.

Who controls the LMN?

Upper motor neurons (UMN) through descending pathways.

Main descending pathways

Corticospinal, corticobulbar, rubrospinal, reticulospinal, vestibulospinal, tectospinal.

What is an upper motor neuron (UMN)?

Neuron whose axon forms descending pathways controlling LMNs.

Signs of UMN lesion

Paresis/paralysis, hypertonia, rigidity, spasticity, hyperreflexia, release reflexes.

Why does UMN lesion cause hyperreflexia?

Loss of cortical inhibition on reflex arcs.

UMN atrophy vs LMN atrophy

UMN: slow, mild; LMN: fast, severe.

What is the pyramidal system?

The corticospinal pathway controlling voluntary and conscious movement.

Where does the pyramidal system originate?

Motor cortex.

Where does the pyramidal system project?

Spinal cord (terminal synapse with LMNs).

Where do most corticospinal fibers decussate?

In the medulla at the pyramidal decussation.

Percentage of corticospinal fibers that cross

~90%.

Functional significance of decussation

Each brain hemisphere controls the opposite side of the body.

What is the extrapyramidal system?

All descending motor pathways not passing through pyramids (brainstem tracts).

Main function of extrapyramidal system

Control involuntary movements: posture, tone, orientation.

Which structures belong to the extrapyramidal system?

Basal ganglia, brainstem motor nuclei, rubrospinal, reticulospinal, vestibulospinal, tectospinal tracts.

Difference between voluntary and involuntary movements

Voluntary = distal muscles, flexors, fast; Involuntary = axial/proximal muscles, extensors, postural.

Which muscles do voluntary movements mainly use?

Distal flexor muscles.

Which muscles do involuntary/postural movements use?

Extensor, antigravity muscles.

Where are voluntary movement pathways located in the spinal cord?

Lateral funiculus.

Where are involuntary/postural pathways located in the spinal cord?

Medial funiculus.

What levels participate in movement control?

Supplementary motor cortex, premotor cortex, primary motor cortex, brainstem, spinal cord.

Simplest motor control chain

Premotor neuron → alpha LMN → muscle.

Where are alpha LMNs located?

Ventral horn of spinal cord (somatotopic map).

What is the function of the brainstem in motor control?

Origin of extrapyramidal descending tracts; integrates posture, tone, reflex orientation.

Which brainstem tracts adjust posture and movement?

Reticulospinal, vestibulospinal, tectospinal, rubrospinal.

What is the reticulospinal tract?

Brainstem tract regulating muscle tone and posture.

Where does the reticulospinal tract originate?

Reticular formation (pons and medulla).

Stimulus for reticulospinal tract

Body destabilization relative to gravity.

Function of medial (pontine) reticulospinal tract

Facilitates muscle tone and voluntary movement.

Function of lateral (medullary) reticulospinal tract

Inhibits muscle tone.

Additional roles of reticulospinal tract

Coarse voluntary movement, attention, pain regulation, wakefulness.

What is anticipatory postural adjustment?

Reticulospinal system preparing the body before movement.

What is the vestibulospinal tract?

Tract controlling antigravity muscles and posture.

Where does vestibulospinal tract originate?

Vestibular nuclei in medulla.

Stimulus for vestibulospinal tract

Head position and balance from vestibulocochlear nerve.

Function of lateral vestibulospinal tract

Activates extensors in trunk and limbs (antigravity).

Function of medial vestibulospinal tract

Controls head position and eye-head coordination.

Is vestibulospinal tract ipsilateral or contralateral?

Mostly ipsilateral.

What is the tectospinal tract?

Brainstem tract for reflex orientation of head to stimuli.

Where does the tectospinal tract originate?

Superior colliculus (midbrain).

Stimuli processed by tectospinal tract

Visual, auditory, somatosensory sudden changes.

Function of tectospinal tract

Rapid reflex head-turning movements.

Where does the tectospinal tract project?

Mainly cervical spinal cord to neck muscles.

What is the rubrospinal tract?

Descending tract controlling voluntary but less precise limb movements.

Where does the rubrospinal tract originate?

Red nucleus of the midbrain.

Species where rubrospinal tract is important

Quadrupeds (dogs, cats, horses).

Main function of rubrospinal tract

Activation of limb flexor muscles; assists gait.

pyramidal vs extrapyramidal

Pyramidal = voluntary fine movement; Extrapyramidal = posture, tone, orientation, coarse movement.

lateral vs medial motor tracts

Lateral = distal voluntary control; Medial = axial/proximal postural control.

flexors vs extensors in motor control

Flexors activated in voluntary movement; Extensors activated for posture and balance.