Physiology of Neurons and Muscle- Module 1

Module 1: What is a Nervous System?

• A living organism exhibits the following fundamental characteristics:
  • Organized structure
  • Requires energy
  • Responds to stimuli
  • Adapts to environmental changes
  • Capable of reproduction
• Stimuli: Any change in the external or internal environment of an organism that provokes a physiological or behavioral response in the organism.

Defining the Nervous System

• The nervous system is a network of specialized cells called neurons that can receive and transmit information.
• This system is unique to animals.
• Are neurons really required? Even bacteria and plant cells can generate electrical impulses.
• Is the formation of synapses crucial? Synapses are locations of cell-to-cell contact that allow chemical communication between cells. Many synaptic genes originated in single-celled eukaryotes long before the emergence of animals.

Animals without a Nervous System

• Placozoans are free-behaving animals that do not have synapses or a "nervous system."
• They exhibit pausing behavior, which is contagious and indirect evidence for the secretion of a signaling molecule.

Defining the Nervous System (continued)

• The nervous system consists of a network of specialized cells that sense information from:
  • The external environment (light, chemicals, temperature, gravity, touch)
  • The internal environment (internal states, signals from other cells)
• Neurons propagate information along axons and dendrites through electrical impulses:
  • Graded potentials
  • Action potentials
• Neurons communicate with each other via chemical and electrical synapses.
• The nervous system integrates sensory information to produce behavioral and physiological responses, such as:
  • Muscle contraction and movement
  • Heart rate, digestion, temperature regulation
  • Feeding, courtship, locomotion

How Information Flows in the Nervous System

• Electrical Recording Techniques
• Magnetic Resonance Imaging (MRI)
  • Uses powerful magnets to detect and quantify the movement of water molecules
  • Differentiates between gray and white matter
  • Utilizes the brain's heterogeneous tissue composition for imaging
• Visual processing in the retina as an example:
  • Light detection by photoreceptors (rod and cone cells) triggers a change in voltage across the cell membrane
  • Electrical signals travel to synapses, where they trigger the release of neurotransmitters
  • Neurotransmitters bind to receptors on post-synaptic cells, producing graded electrical responses
  • Graded responses reach nerve terminals, which synapse onto ganglion cells
  • Neurotransmitters are secreted again, binding to NT receptors on ganglion cells to trigger graded electrical responses
  • When graded depolarization is strong enough, excitable neurons (like ganglion cells) generate action potentials (APs)

Graded vs. Action Potentials

• Unlike graded potentials, APs don’t dissipate and are all-or-none electrical impulses that can travel up to 120 m/s along axons!
• APs arise when graded potentials activate voltage-gated sodium (NaV) and potassium (KV) channels
• NaV channels drive membrane depolarization, while KV channels drive repolarization/hyperpolarization

Challenges Associated with Understanding the Nervous System

• Biologists need to integrate knowledge of biological systems in genetic and chemical terms with knowledge of core principles in physics (e.g., current, voltage, resistance/conductance, capacitance)
• To understand the nervous system, we need to consider:
  • Cell to Cell Communication
  • Structure and Function
  • Systems Integration
  • Core principles in physics

This quiz covers the introduction to nervous system, its definition, animals without a nervous system, and how information flows in the nervous system. It also discusses the challenges associated with understanding the nervous system.