Neuroscience Chapter Basics

Lecture 3: Communication in our Nervous System

• The lecture aims to explain electrical and chemical signaling in neurons
• The human brain has approximately 100 billion neurons
• Behavior depends on neuron-to-neuron communication
• Neurons have three main parts: dendrites (input), soma (integration), axon (conduction), terminal buttons (output).

Important Terms

• Ion: an electrically charged molecule
• Anion: negatively charged ion
• Cation: positively charged ion

Neuronal Communication

• Ions inside the neuron are in the intracellular fluid
• Ions outside the neuron are in the extracellular fluid

Resting Potential

• Inside a neuron, there are more anions than cations, making it negatively charged (-70 mV)
• This is the resting potential, the balance of ions at rest

Membrane Potential

• The electrical charge across a cell membrane
• Two key types:
  • Resting potential: balance of ions at rest (-70mV)
  • Action potential: a brief electrical impulse that allows information to travel down the axon

Action Potential

• Initiated when the threshold of excitation is reached
• Depolarization: the inside of the axon becomes more positive
• Repolarization: the membrane potential returns to the resting state
• Refractory period: a brief period after an action potential where the neuron cannot fire another action potential
• All-or-nothing principle: action potentials either occur completely or not at all

Ionic Forces

• Diffusion: molecules move from high to low concentration
• Electrostatic pressure: opposite charges attract, like charges repel

Concentrations of Important Ions

• Outside the cell: high concentration of sodium (Na+), chloride (Cl-)
• Inside the cell: high concentration of potassium (K+), organic anions (A-)

Sodium-Potassium Pump

• Maintains resting potential
• Pumps 3 sodium ions out and 2 potassium ions in

Events Leading to Action Potential

• Depolarization: sodium channels open, allowing Na⁺ ions to enter the cell
• If the threshold of excitation is reached, all Na⁺ channels open
• Repolarization: potassium channels open, allowing K⁺ ions to leave the cell
• Resting state: sodium channels reset

Sodium Channels

• Ion channels in the cell membrane that allow specific ions (e.g., Na⁺) to enter or leave the cell
• Voltage-gated ion channels: open or close depending on the membrane potential

Action Potential (2)

• Opening of sodium channels starts the action potential
• Opening of potassium channels is the second step in the action potential

Salatory Conduction

• Action potentials "jump" between nodes of Ranvier, myelinated areas
• This speeds up signal transmission

Chemical Signaling

• Transmission of information between neurons
• Occurs via the release of neurotransmitters

Synaptic Transmission

• Action potential reaches the axon terminal
• Calcium channels open, and calcium ions enter
• Calcium triggers synaptic vesicles to release neurotransmitters
• Neurotransmitters bind to receptors on the postsynaptic membrane
• Neurotransmitters are either degraded by enzymes or taken back by the presynaptic neuron

Postsynaptic Receptors

• Specialized to fit particular neurotransmitters
• A ligand is a molecule that fits the receptor

Ligands

• Endogenous ligands: naturally occurring neurotransmitters and hormones
• Exogenous ligands: drugs and toxins

Neurotransmitters

• Examples: dopamine, serotonin, acetylcholine, norepinephrine, glutamate, endorphins/enkephalins
• These modulate various functions, such as mood, arousal, memory and pain.

Test your knowledge on the fundamental concepts of the nervous system with this quiz. Explore topics such as cell types, neuron functions, and ion movement in relation to action potentials. Perfect for students studying neuroscience or biology.