Biochemistry Online: An Approach Based on Chemical Logic

Biochemistry Online





Learning Goals/Objectives for Chapter 9B:
After class and this reading, students will be able to

  • describe how a transmembrane ion gradient and nongated/gated membrane ion channels specific for given ions can give rise to a transmembrane electric potential across membranes
  • given ion concentrations and the electrical potential across a membrane, predict likely changes in the membrane potential and ion concentrations on the opening of specific channnels;
  • use the Goldman equation to predict transmembrane electrical potentials;
  • state difference between the communication across the neuromuscular junction and a synapse between two neurons;
  • state the difference between nongated and gated ion channels;
  • describe different ways to open/close gated ion channels
  • describe the immediate changes in the muscle cells when acetylcholine is released into the neuromuscular junction
  • describe the roles of stimulatory neurotransmitter receptors, voltage-gated Na+and K+ channels and the Na/K-ATPase  in the activation of a neuron;
  • explain the mechanism for selectivity of K+ over the smaller Na+ ion in the K+ channel;
  • briefly explain how membrane protein channels can be gated open by changes in transmembrane potential;

B4.  Neurotransmitter Activation of Neurons

What happens when a neurotransmitter binds to a receptor on the post-synaptic cell?  We will study two examples.  The first is the simplest:   binding of the neurotransmitter acetylcholine, released by a motor neuron, to its receptor on muscle.  This region is called the neuromuscular junction.  Binding of acetylcholine will lead to a transient depolarization of the muscle cell.  Next we will discuss the interaction of a neurotransmitter with a post-synaptic neuron in the central nervous system.  This is a much more complex system.  Their differences are described below:

In neurons interacting with muscles:

In the central nervous system, life is more complicated:

What happens when a neurotransmitter binds to the receptor on the post-synaptic cell? A depolarization occurs (mediated by conformational changes in the transmitter-receptor complex), raising the membrane potential from the resting equilibrium level.  What happens next depends on the identity of the post synaptic cell.  In the muscle cell, the rising potential caused by binding of acetylcholine ultimately leads to muscle contraction by opening intracellular organelle membrane calcium channels.  In a neuron, the rising potential triggers an action potential by opening voltage-gated sodium channels.  The potential rises to about + 35 mV, but does not reach the Na ion equilibrium potential, because the high positive potential opens a voltage-gated potassium channel.  The potential then falls until it reaches the K ion equilibrium potential where the cells is hyperpolarized. It slowly then relaxes back to the resting potential of -60 mV. This wave of changes in potential sweeps down the post-synaptic cell membrane and is the basis for the "firing" of the neuron.



Animation: The Synapse

Animation: Nerve  Impulse

Animation: Voltage-Gated Channels and Action Potentials

Animation: Sodium Potassium ATPase

Animation: Channel Gating During An Action Potential

Animation: Propagation of An Action Potential


Return to Chapter 9B: Neural Signaling Sections

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Archived version of full Chapter 9B:  Neural Signaling


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Biochemistry Online by Henry Jakubowski is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.