ORGANISATION OF MOTOR CONTROL

What are the three core components of the vertebrate sensory–motor system?

Selection of motor programs, Initiation of motor commands, Expression of motor patterns.

What is the overall transformation performed by the nervous system?

Sensory input → neural processing → motor output.

What are the three fundamental functions of the nervous system?

Detect internal + external changes, Integrate information, Generate adaptive motor output.

What are the four functional zones of a neuron?

Input (dendrites + soma), Integration (cell body), Conduction (axon), Output (synaptic terminals).

What is the correct statement about the cell body?

The cell body integrates multiple inputs into a single electrical response.

What are the three main neuron types in motor control circuits?

Sensory (afferent), Interneurons, Motor (efferent).

What is the role of sensory neurons?

Carry information TO the CNS from internal and external environments.

What is the role of interneurons?

Integration, processing, and linking sensory to motor pathways.

What is the role of motor neurons?

Transmit signals FROM CNS to muscles and glands.

Why is behaviour not just a reflex?

Because it arises from neural circuits, not isolated stimulus–response pathways.

Does movement originate from sensory input or intrinsic activity?

Both — movement depends on interaction between sensory input and intrinsic neural activity.

What did Graham-Brown demonstrate?

Locomotion can be generated without sensory input (intrinsic spinal circuits).

What did Hans Berger discover?

The brain has continuous spontaneous activity (EEG evidence).

What structure initiates locomotion?

Mesencephalic Locomotor Region (MLR).

What pathway drives locomotion from the brainstem?

MLR → Medial Reticular Formation → spinal cord → motor neurons.

What is the key takeaway about movement initiation?

Movement can be initiated centrally without cortex or sensory input.

Why is the lamprey used to study locomotion?

Primitive vertebrate, Simple nervous system, Segmented spinal cord.

How many spinal segments does the lamprey have?

~100 segments.

How many neurons are in each segment?

~1000 neurons.

What type of locomotion does the lamprey produce?

Sinusoidal wave movement (head → tail).

What are the three key features of lamprey motor activity?

Rhythmicity, Left–right alternation, Propagation along body.

What happens if the lamprey spinal cord is disconnected from the brain?

Swimming still occurs.

When lamprey spinal cord is disconnected from the brain - swimming still occurs - What does this demonstrate?

The spinal cord alone can generate locomotion.

What is “fictive locomotion”?

Rhythmic motor patterns generated without movement or sensory input.

What are CPGs?

Neural circuits that generate rhythmic output without sensory input.

Where are CPGs located?

Spinal cord.

What are the three main components of a CPG?

Excitatory interneurons (E), Inhibitory interneurons (I), Motor neurons (M).

What do inhibitory interneurons do in CPGs?

Produce left–right alternation.

What are conditional pacemaker neurons?

Neurons that can generate rhythmic activity under certain conditions.

What generates rhythmic motor activity in the spinal cord?

Slow spontaneous oscillations of neurons.

What does tetrodotoxin (TTX) do?

Blocks voltage-gated sodium channels → abolishes action potentials.

What happens to spinal oscillations when TTX is applied?

Oscillations persist.

What does this prove?

Rhythmic activity is intrinsic to neurons, not dependent on action potentials or synaptic input.

Is sensory input required to generate locomotion?

No.

What is the role of sensory input in movement?

Modifies rhythm, Adjusts speed, Provides feedback.

What is the neuromechanical loop?

Movement → sensory feedback → modifies neural output.

What is entrainment?

Sensory feedback adjusting the timing of rhythmic activity.

Every sensory input participates in what?

Both: Lower loops (local reflexes), Longer loops (brain integration).

Are CPGs active at rest?

No — they require descending activation.

Which brain regions modulate CPGs?

Brainstem, Cortex, Cerebellum, Basal ganglia.

What happens after spinal cord injury in animals?

Walking can still occur with sensory stimulation.

Can humans generate locomotion after spinal injury?

Partially, with sensory input and support.

What are the levels of motor control (top → bottom)?

Cortex (planning), Basal ganglia (initiation), Cerebellum (coordination), Brainstem (posture, locomotion), Spinal cord (execution, CPGs).

Why is movement considered a distributed system?

Because control is shared across multiple interacting brain and spinal regions.

Why is movement not purely reflexive?

Because it is generated by intrinsic neural circuits and modulated by feedback.

What is predictive coding in motor control?

The brain predicts sensory outcomes using internal models and efference copy.

What is the key conceptual model of motor control?

Behaviour emerges from interacting sensory–motor loops across multiple levels.

Summarise motor control in one statement.

Movement is generated by intrinsic spinal circuits (CPGs), initiated and modulated by the brain, and continuously refined by sensory feedback in a hierarchical, distributed system.