Perception & Movement: Motor Pathways and Muscular Control

Comprehensive practice flashcards covering the motor cortex, corticospinal and corticobulbar tracts, spinal cord anatomy, voluntary movement mechanisms, motor units, and sensory receptors (muscle spindles and Golgi tendon organs).

What is the primary function of the Corticospinal Tract (CST)?

To send voluntary motor messages from the cortex through the spinal cord to the muscles of the body.

How do neurons in the motor cortex control the activation of motor neurons in the spine?

They send signals that directly control the activation of motor neurons in the spine.

What two types of motor control are coordinated by neurons in the motor cortex?

Movement of functionally related muscles in an individual body part, and coordinated movement of a limb to a particular point in space.

What functional anatomical representation across the cerebral cortex is illustrated in this diagram?

The Motor Map of the Body (motor homunculus).

What is the primary functional role of the premotor cortex?

It is active in the planning of movement, rather than the execution of movement.

What three functions are associated with the supplementary motor area (SMA)?

The execution of sequences of movement, the attainment of motor skills, and the selection of movements based on incoming sensory information.

How does the primary role of the premotor cortex differ from that of the supplementary motor area?

The premotor cortex is involved primarily in the planning of movement, whereas the supplementary motor area is involved in executing movement sequences, acquiring motor skills, and selecting movements based on sensory input.

What part of the body does the Corticospinal Tract (CST) convey messages to?

It sends messages through the spinal tract for body movement.

Where does the Corticobulbar Tract (CBT) send messages, and what body regions does it control?

It sends messages to the brainstem for head, neck, and face movement.

What is the primary destination difference between the Corticospinal Tract (CST) and the Corticobulbar Tract (CBT)?

The CST sends messages through the spinal cord to control body movement, whereas the CBT sends messages to the brainstem to control head, neck, and face movement.

What are upper motor neurons (UMNs) in the context of the corticospinal pathway?

Cortical neurons whose descending axons travel from the brain through the brainstem and spinal cord to activate lower motor neurons.

What are lower motor neurons in the context of the corticospinal pathway?

Motor neurons situated in the spinal cord that receive inputs from descending upper motor pathways and directly innervate muscle fibers.

In which cortical areas does the Corticospinal Tract originate?

In the Primary Motor and Supplementary Motor Cortices.

What does the term decussation mean in motor pathways?

The anatomical area where nerve fibers cross the midline and travel contralaterally.

Where do the majority of Corticospinal Tract fibers decussate, and what percentage cross at this site?

$90\%$ of the fibers decussate in the medulla pyramids.

Through which spinal cord tract do the decussated $90\%$ of corticospinal fibers descend?

The Lateral Cortical Spinal Tract (Lateral Corticospinal Tract).

Do fibers of the Lateral Corticospinal Tract travel ipsilaterally or contralaterally relative to their cortical hemisphere of origin?

They travel contralaterally.

Where do fibers of the Lateral Corticospinal Tract synapse in the spinal cord?

They synapse onto Lower Motor Neurons.

Which specific muscle group is innervated by fibers descending in the Lateral Corticospinal Tract?

Distal muscles (e.g., hands).

What percentage of Corticospinal Tract fibers do not cross in the medulla pyramids?

$10\%$ of the fibers.

Through which tract in the spinal cord do the uncrossed $10\%$ of corticospinal fibers travel?

The Anterior (Ventral) Cortical Spinal Tract.

At what anatomical level do fibers of the Anterior (Ventral) Corticospinal Tract cross over?

They cross over at the level of the spinal cord (SC).

Where do fibers descending in the Anterior (Ventral) Corticospinal Tract synapse?

They synapse onto Lower Motor Neurons.

Which muscle group is innervated by fibers descending in the Anterior (Ventral) Corticospinal Tract?

Proximal muscles (e.g., trunk).

How do the target muscles of the Lateral Corticospinal Tract compare to those of the Anterior Corticospinal Tract?

The Lateral Corticospinal Tract sends fibers to distal muscles (e.g., hands), whereas the Anterior Corticospinal Tract sends fibers to proximal muscles (e.g., trunk).

Through which spinal root do sensory neuron axons enter the spinal cord?

The dorsal root.

Where are the cell bodies of sensory neurons situated adjacent to the spinal cord?

In the dorsal root ganglion.

Through which spinal root do motor neuron axons exit the spinal cord to target muscles?

The ventral root.

Where are motor neuron cell bodies located inside the spinal cord?

In the ventral horn of the spinal gray matter.

What fluid is contained within the central canal of the spinal cord?

Cerebrospinal fluid.

What is the function of an interneuron within the spinal cord gray matter?

It relays signals between sensory neurons and motor neurons.

What two functional pathways within the basal ganglia are involved in motor control?

The "Go" and "No-go" pathways.

What general role does the thalamus fulfill in the central motor system?

It acts as a relay station integrating and transmitting motor signals between subcortical brain areas and the cerebral cortex.

What is the primary role of the cerebellum in voluntary movement?

Coordinating and fine-tuning skilled movement.

From which two primary sources does the cerebellum receive neural input?

Sensory receptors in the limbs and head, and the cerebral cortex.

How does cerebellar sensory integration help maintain fluid movement during an unexpected mechanical disruption?

It rapidly integrates unexpected sensory inputs to adjust motor commands, such as when lifting an unexpectedly heavy box.

What cerebellar construct is responsible for executing learned, coordinated routines such as dancing?

Motor programs.

How does the cerebellum adjust movements over time as an individual's physical body changes?

It recalibrates movements as a person loses or gains weight and grows.

Which midbrain structure is specifically responsible for generating and directing eye movements?

The Superior Colliculus.

What action do flexor muscles perform on the bones of a joint?

They bring bones closer together.

What action do extensor muscles perform on the bones of a joint?

They move bones further away and straighten the joint.

How do flexor and extensor muscles coordinate mechanically across a joint?

They work in opposition to each other.

How do muscles attached to soft tissue, such as those in the head and neck, operate?

They act in a similar oppositional way to control movement and stability.

What is an agonist muscle?

A muscle that promotes movement.

What is an antagonist muscle?

A muscle that opposes or inhibits movement.

What is co-contraction?

The simultaneous contraction of agonist and antagonist muscles.

In which specific type of physical movement is co-contraction particularly useful?

Isometric movement.

What cellular components make up an individual skeletal muscle?

Thousands of muscle fibers.

Where do alpha motor neurons originate in the central nervous system?

In the brain or spinal cord.

How many alpha motor neurons control any given muscle fiber?

Every muscle fiber is controlled by exactly $1$ alpha motor neuron.

Can an individual alpha motor neuron innervate more than one muscle fiber?

Yes, $1$ alpha motor neuron can control multiple muscle fibers.

What is the definition of a Motor Unit?

An alpha motor neuron plus all the muscle fibers it controls.

Where are Golgi tendon organs anatomically located?

In the muscle fibers where they connect to the tendon.

What physiological variable do Golgi tendon organs detect during muscle activation?

How much force or tension is applied to a muscle during ongoing movement.

What changes do muscle spindles detect, and how does the brain adjust their sensitivity?

Muscle spindles supply information about changes in muscle length and stretch, and the brain adjusts system sensitivity via gamma motor neurons that keep the spindles taut.