Skilled Performance and Motor Learning

Introduction to Motor Control

This unit introduces the fundamental processes by which information is transmitted in the nervous system, forming the basis for motor control and skilled performance. Understanding these mechanisms is essential for comprehending how the body senses, integrates, and responds to stimuli during movement.

Organization of the Nervous System

Central and Peripheral Components

• Central Nervous System (CNS): Composed of the brain and spinal cord, responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Includes peripheral nerves and ganglia, which transmit signals between the CNS and the rest of the body.

• CNS & PNS: Although anatomically separated, these systems are functionally interconnected to coordinate behavior and movement.

Main Regions of the CNS

• Spinal Cord: Conducts sensory and motor information between the body and brain.

• Brainstem: Includes the medulla, pons, and midbrain; controls basic life functions and relays information.

• Cerebellum: Coordinates movement and balance.

• Thalamus: Part of the diencephalon; acts as a relay station for sensory information.

• Cerebral Hemispheres (Forebrain): Responsible for higher cognitive functions and voluntary movement.

Types of Neurons

• Sensory Neurons: Transmit sensory information from receptors to the CNS.

• Motor Neurons: Carry commands from the CNS to muscles and glands.

• Interneurons: Connect neurons within the CNS, facilitating integration and processing.

Directional Terms in Neuroanatomy

• Dorsal vs Ventral: Back vs front of the body or structure.

• Superior vs Inferior: Above vs below.

• Anterior vs Posterior: Front vs back.

• Rostral vs Caudal: Toward the nose/beak vs toward the tail.

• Medial vs Lateral: Toward the midline vs away from the midline.

• Distal vs Proximal: Farther from vs closer to the point of attachment.

• Ipsilateral vs Contralateral: Same side vs opposite side.

• Planes: Horizontal, coronal, and sagittal planes are used to describe anatomical sections.

Information Transmission in the Nervous System

Membrane Potential

The membrane potential is the difference in electrical charge across the neuron's cell membrane, resulting from the unequal distribution of ions.

• Inside the cell: High concentration of negatively charged molecules (A-) and potassium ions (K+); some sodium (Na+) and chloride (Cl-) ions.

• Outside the cell: High concentration of sodium (Na+) and chloride (Cl-) ions; some potassium (K+).

• Resting Membrane Potential: Most neurons have a resting potential of about -70 mV, meaning the inside is more negative than the outside.

Equation:

Action Potential

An action potential is a rapid, transient change in membrane potential that propagates along the axon, enabling communication between neurons.

• Threshold: If the membrane voltage reaches a critical threshold, an action potential is triggered.

• Depolarization: Opening of voltage-gated sodium channels allows Na+ influx, making the inside more positive (up to +30 mV).

• All-or-None Principle: Action potentials are generated only if the threshold is reached and propagate without decrement.

• Propagation: Myelin sheaths increase conduction speed by allowing the action potential to jump between nodes of Ranvier (saltatory conduction).

Equation:

Synapse and Neurotransmitter Release

Synapses are specialized junctions where neurons communicate via chemical signals.

• Presynaptic Neuron: Releases neurotransmitters from vesicles into the synaptic cleft.

• Postsynaptic Neuron: Neurotransmitters bind to receptors, opening ion channels and altering membrane potential.

• Types of Postsynaptic Potentials:

  • Excitatory Postsynaptic Potential (EPSP): Depolarizes the membrane, moving it closer to threshold.

  • Inhibitory Postsynaptic Potential (IPSP): Hyperpolarizes the membrane, moving it farther from threshold.

Neuronal Integration: Summation

Neurons integrate multiple synaptic inputs to determine whether to fire an action potential.

• Spatial Summation: Multiple inputs from different presynaptic neurons at the same time.

• Temporal Summation: Rapid, repeated inputs from a single presynaptic neuron.

• Net Effect: The sum of all EPSPs and IPSPs determines if the postsynaptic neuron reaches threshold.

Convergence and Divergence

• Convergence: Many presynaptic neurons synapse onto a single postsynaptic neuron, allowing integration of information.

• Divergence: One presynaptic neuron synapses onto multiple postsynaptic neurons, distributing information widely.

Termination of Postsynaptic Potential

• Reuptake: Neurotransmitters are taken back into the presynaptic terminal.

• Enzymatic Degradation: Neurotransmitters are broken down by enzymes.

• Drug Effects: Some drugs alter synaptic transmission by affecting neurotransmitter release, reuptake, or receptor activity.

Examples of Drug Effects

• Ethanol (Alcohol): Facilitates GABA-mediated inhibition, prolonging IPSPs.

• Cocaine: Blocks dopamine reuptake, increasing postsynaptic stimulation and causing euphoria.

Summary of Information Transmission Steps

1. Deformation of receptor membrane

2. Generation of the action potential

3. Propagation of action potential

4. Depolarization of presynaptic membrane

5. Release of neurotransmitters

6. Stimulation of receptors on postsynaptic membrane

7. Opening of ion channels

8. Generation of synaptic (local) potential

9. Generation of action potential (if threshold is reached)

10. Propagation of action potential (repeats in next neuron)

11. Depolarization of presynaptic membrane

12. Release of neurotransmitters (cycle continues)

Table: Comparison of EPSP and IPSP

Application to Motor Control

These processes underlie the ability to sense, integrate, and execute motor behaviors, which are essential for skilled performance and motor learning in personal health and movement science.