CHAPTER 9 - SIGNAL TRANSDUCTION
B: NEURAL SIGNALING
BIOCHEMISTRY - DR. JAKUBOWSKI
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
- state difference between the communication across the
neuromuscular junction and a synapse between two neurons;
- state the difference between nongated and gated ion
- 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:
- Most muscle fibers are innervated by only one neuron - a motor
- Neurotransmitter release at the neuromuscular junction leads only to
muscle excitation, not inhibition.
- All fibers are excited by the same neurotransmitter - acetylcholine.
In the central nervous system, life is more complicated:
- Stimuli are received from hundreds to thousands of different
- Nerves receive both excitatory and inhibitory stimuli from
- Different kinds of receptors are present to receive stimuli, which
control the activity of different kinds of channels.
- The ion channels in neurons are gated by a variety of mechanisms in
addition to changes in membrane potential, including gating by heat,
cold, stretch, or covalent modification.
- Most nerve cells have a resting potential of about -65 mV compared
to a -90 mV for a muscle cell.
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.
DEPOLARIZATION OF TRANSMEMBRANE POTENTIAL
NA AND K PERMEABILITIES DURING DEPOLARIZATION
Voltage-Gated Channels and Action Potentials
Sodium Potassium ATPase
Channel Gating During An Action Potential
Propagation of An Action Potential
Return to Chapter 9B:
Neural Signaling Sections
Biochemistry Online Table of Contents
Archived version of full
Biochemistry Online by Henry Jakubowski is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.