Chapter 14: Motor Pathways, Tracts & Reflexes

What are motor pathways?

Neural pathways that begin in the cerebral cortex or brainstem, travel through the spinal cord, and innervate muscles and glands.

What functions do motor pathways serve?

Voluntary skeletal muscle movement, posture, balance, muscle tone, and some autonomic functions.

What are the major components of motor pathways?

Upper motor neurons (UMNs), lower motor neurons (LMNs), interneurons, basal nuclei, and the cerebellum.

Where do lower motor neurons (LMNs) originate?

In the ventral horn of the spinal cord.

What is the function of lower motor neurons (LMNs)?

They directly innervate skeletal muscle and are the final pathway to muscles.

What are α (Alpha) motor neurons responsible for?

Innervating extrafusal fibers, which are the actual contracting muscle fibers.

What do γ (Gamma) motor neurons innervate?

Intrafusal fibers, which are part of muscle spindles, and are responsible for muscle tone and proprioception.

What is somatotopy?

The organization of the ventral horn where medial regions control axial muscles and lateral regions control appendicular muscles.

What is a motor unit?

One α-motor neuron plus all the muscle fibers it controls.

What distinguishes large motor units from small motor units?

Large motor units have many fibers per neuron for gross motor control, while small motor units have few fibers per neuron for fine motor control.

What is a monosynaptic reflex?

A reflex that involves one synapse, such as the stretch reflex (e.g., patellar reflex).

What is a polysynaptic reflex?

A reflex that contains interneurons and allows for more complex responses, such as the withdrawal reflex.

What is the role of interneurons?

They connect neurons, relay signals, and coordinate movement across multiple pathways.

Where do upper motor neurons (UMNs) originate?

In the cerebral cortex and brainstem.

What is the primary function of upper motor neurons (UMNs)?

To control lower motor neurons.

What is the significance of decussation in UMNs?

Most UMNs cross to the opposite side, meaning the right hemisphere controls the left body and vice versa.

What is the primary motor cortex (M1) responsible for?

Initiating voluntary movement and containing many upper motor neurons.

What is the function of the premotor cortex?

Plans movement, initiates movement before M1, stores motor memory, and contains mirror neurons.

What does the supplementary motor area (SMA) control?

Movement planning, strength, direction, and distance of movement.

What is the function of the basal nuclei?

To modify movement, regulate motor output, and prevent inappropriate movements.

What are the functions of the cerebellum?

Coordinates movement, fine-tunes movement, maintains balance, posture, accuracy, and motor learning.

What do direct (pyramidal) tracts control?

Conscious voluntary movement.

What is the corticobulbar tract responsible for?

Controlling chewing, facial expression, swallowing, and tongue movement.

What is the difference between the lateral and ventral corticospinal tracts?

The lateral corticospinal tract controls appendicular muscles and crosses at the medullary pyramids, while the ventral corticospinal tract controls axial muscles and crosses at the spinal level.

What does the Golgi tendon organ (GTO) monitor?

Muscle tension generated during contraction.

What are the signs of an upper motor neuron lesion?

Hypertonia, hyperreflexia, spasticity, positive Babinski sign, and little atrophy.

What are the signs of a lower motor neuron lesion?

Hypotonia, hyporeflexia, atrophy, fasciculations/twitching, and negative Babinski sign.

What is Parkinson's disease?

A basal nuclei disorder characterized by tremor, rigidity, and bradykinesia.

What is quadriplegia?

Loss of movement in all four limbs due to injury at C1-C7.

What is apraxia?

Difficulty performing learned movements despite normal muscle function, commonly due to left frontal/parietal damage.