Lecture on Animal Nervous Systems

Overview

• Discussion on how animals expend energy, interact with the environment, and acquire food.
• Introduction to internal systems of animals and the focus on the nervous system as a key mechanism for interaction with the environment.

Nervous System

• Function: Signaling system that sends signals from cell to cell, enabling muscle contraction and behavior.
• Comparison with Endocrine System: Faster and more specific, whereas the endocrine system is slower and affects the whole body.
• Signal Transmission:
  • Inside a neuron: Electrical signals.
  • Between neurons: Chemical signals via neurotransmitters.

Anatomy of Neurons

• Neurons: Main cells involved in nervous system signaling.
• Soma: Cell body containing the nucleus and major organelles.
• Dendrites: Branches extending from the soma, receiving inputs.
• Axon: Single output branch transmitting electrical signals.
• Axon Hillock: Point where the axon connects to the soma, initiating electrical changes.
• Synapse: Junction between the axon terminal of one neuron and the dendrite/soma of another.

Function of the Nervous System

• Contracts muscles at appropriate times based on environmental inputs.
• Types of Neurons:
  • Motor Neurons: Control muscles.
  • Sensory Neurons: Bring information from the environment.
  • Interneurons: Connect sensory and motor neurons, allowing flexible behavior.

Reflex Arcs

• Example: Cockroach escapism through sensory, interneuron, and motor neuron interaction.
• Sensory input is quickly transmitted to motor neurons for a rapid response.

Nervous System Signaling

• Action Potential: Electrical impulse that travels along the axon without losing strength.
• Neurotransmitter Release: At axon terminals, neurotransmitters are released and bind to receptors on the target cell.
• Integration of Information: Neurons receive multiple inputs, which they integrate and respond to if threshold is reached.

Resting Potential

• Definition: Voltage across the neuron's membrane when not active.
• Mechanism: Separation of charge across the membrane provides potential energy for rapid response.
• Electric Potential: Separation of positive and negative charges.

Important Concepts

• Voltage (Potential): Separation of electrical charge.
• Current: Flow of electrical charge.
• Resistance: Opposition to current; conductance is the inverse.
• Ion Channels: Provide conductance across the membrane.

Potassium Ion Example

• Movement across membrane leads to charge separation, influencing membrane potential.
• Nernst Equation: Determines the voltage required to balance a concentration gradient of ions.

Summary

• Neurons integrate multiple inputs leading to action potentials that propagate along axons.
• Synaptic transmission involves the release of neurotransmitters that cause voltage changes in target cells.
• Understanding neurons' resting potential and signaling is crucial for understanding nervous system function.