Week 7 Thursday - Nervous system and RMP

Overview of the Nervous System and Resting Membrane Potential (RMP)

Class Schedule


Action Center:Tuesdays and Thursdays: 4:30 - 6:30 PM, Wagner Hall (Rooms 135, 140, 145)

  • Open for participants to arrive and leave as needed, promoting flexible attendance.



Action Tutoring:Monday, Wednesday, Thursday: 8:00 - 10:00 PM, Dunham A128Tuesday: 8:00 - 10:00 PM, Dunham A126

  • Interactive tutoring sessions designed to enhance understanding of course material through collaborative learning.


Office Hours:Dr. H: Tuesday, Thursday: 12:30 - 2:00 PM, Friday: 9:30 - 1:00, GLCH 328


  • Availability for student consultations to help clarify lecture content or assist with academic concerns.Laurens: Wednesday: 2 - 3 PM, Thursday: 1:30 - 2:30 PM, GLCH 308

  • Additional support hours for students to seek guidance in complex topics.

Key Questions

  1. What physiological and biochemical mechanisms allow some species to be immune to scorpion toxin?

  2. How can nociceptive signals cause the sensation of pain without any actual injury causing tissue damage?

Nervous System Overview

Types of Nervous Systems

  • Peripheral Nervous System (PNS):

    • Comprises all peripheral nerves that connect the CNS to limbs and organs. Responsible for transmitting sensory information to and from the CNS.

  • Central Nervous System (CNS):

    • Includes the brain and spinal cord, integrating sensory information and coordinating body responses.

Neurons

Structure of a Neuron

  • Cell Body (Soma): Integrates incoming signals and houses the nucleus and other organelles essential for cell function.

  • Dendrites: Branching projections that receive synaptic inputs from other neurons, crucial for signal propagation.

  • Axon: Long fiber that transmits electrical impulses away from the cell body towards other neurons or target tissues.

  • Myelin Sheath: Fatty layer that surrounds axons, enhancing speed of impulse transmission via saltatory conduction by insulating the axon and minimizing ion leakage.

Function of Neurons

  • Neurons communicate via electrical signals generated through the movement of ions (such as Na+, K+) across their membrane, facilitated by various types of ion channels.

Membrane Potential

  • What is a Membrane Potential?

    • It represents the voltage difference across the cell membrane due to the unequal distribution of ions inside and outside the cell.

  • What is an Action Potential?

    • A rapid change in membrane potential that occurs when the neuron reaches a threshold level of depolarization, leading to a transient reversal of membrane voltage.

Ion Transport Mechanisms

Ion Gradients

  • The physiological functions of neurons heavily rely on the existence of two vital ion gradients: potassium (K+) and sodium (Na+).

  • Ion permeability is regulated through specific membrane channels, without which ions cannot freely pass through the lipid bilayer.

Concentration Gradients

  • Na/K Pump: An active transport mechanism that continuously pumps 3 Na+ ions out of the neuron and 2 K+ ions into the neuron, vital for maintaining RMP and establishing ion gradients essential for action potentials.

  • This pump helps maintain the electrochemical gradient necessary for proper neuronal excitability.

Resting Membrane Potential (RMP)

Understanding RMP

  • The RMP of a typical neuron is approximately -70mV, indicating a polarized state with the interior more negative compared to the exterior.

  • This state is primarily characterized by higher permeability to K+ ions relative to Na+ ions, which influences the voltage to be closer to the equilibrium potential of K+ (-90mV).

Factors Affecting RMP

  • Ion Channels: The presence of always-open leak channels provides for minimal movements of Na+ and K+, contributing to the steady-state RMP.

  • The predominance of K+ leak channels allows for a naturally higher negative charge within the cell, which is crucial for neuronal stability.

Action Potentials

Phases of Action Potential

  1. Resting Phase: The neuron rests at -70mV with voltage-gated Na+ and K+ channels closed.

  2. Rising Phase: Triggered by a stimulus, depolarization occurs as voltage-gated Na+ channels open, allowing Na+ ions to flood into the cell.

  3. Top of Curve: Maximum depolarization is achieved at +35mV; Na+ channels close while K+ channels start to open.

  4. Falling Phase: Repolarization occurs as K+ ions exit the cell, facilitated by the opening of voltage-gated K+ channels and closing of Na+ channels.

  5. Undershoot: Known as hyperpolarization, whereby the membrane potential temporarily becomes even more negative than the resting potential as K+ moves back into equilibrium.

  6. Recovery to Resting: The neuron returns to the RMP of -70mV, facilitated by the Na/K pump and re-close of K+ channels.

Key Takeaway

  • The delicate balance and coordinated movement of ions during both RMP and action potentials are fundamental for the generation of neuronal signals, which are crucial for all nervous system functions.