CB - Electrical and Synaptic Signaling in Neurons

neuron

specialized cell directly involved in the conduction and transmission of nerve impulses

cell body

portion of a nerve cell that contains the nucleus and other organelles and has extensions called axons and dendrites projecting from it

dendrite

extension of a nerve cell that receives impulses and transmits them inward toward the cell body

myelin sheath

concentric layers of membrane that surround an axon and serve as electrical insulation that allows rapid transmission of nerve impulses

node of ranvier

small segment of bare axon between successive segments of myelin sheath

nerve

a tissue composed of bundles of axons

synaptic bouton

region near the end of an axon where neurotransmitter molecules are stored for use in transmitting signals across the synapse

synapse

tiny gap between a neuron and another cell, across which the nerve impulse is transferred by direct electrical connection or by neurotransmitters

resting membrane potential

electrical potential (voltage) across the plasma membrane of an unstimulated nerve cell

current

movement of positive or negative ions

electroneutrality

principle that positively and negatively charged ions balance one another in solution

squid giant axon

an exceptionally large axon emerging from certain squid nerve; wide diameter makes it relatively easy to insert microelectrodes that can measure and control electrical potentials and ionic currents

electrical excitability

ability to respond to certain types of stimuli with a rapid series of changes in membrane potential known as an action potential

leak channel

non-gated ion channel that helps to maintain steady-state ion concentrations of cells at electrochemical equilibrium, including potassium and sodium ions

depolarization

change in membrane potential to a less-negative value

patch clamping

technique in which a tiny micropipette placed on the surface of a cell is used to measure the movement of ions through individual ion channels

voltage-gated ion channel

an integral membrane protein that forms an ion-conducting pore whose permeability is regulated by changes in the membrane potential

ligand-gated ion channel

an integral membrane protein that forms an ion-conducting pore that opens when a specific molecule binds to the channel

channel gating

closing of a membrane ion channel in such a way that it can reopen immediately in response to an appropriate stimulus

voltage sensor

amino acid segment of a voltage-gated ion channel that makes the channel responsive to changes in membrane potential

channel inactivation

closing of a membrane ion channel in such a way that it cannot reopen immediately

threshold potential

value of the membrane potential that must be reached before an action potential is triggered

action potential

brief change in membrane potential involving an initial depolarization followed by a rapid return to the normal resting potential; caused by the inward movement of Na+ followed by the subsequent outward movement of K+; serves as the means of transmission of a nerve impulse

propagation

movement of an action potential along a membrane away from the site of origin

hyperpolarization (undershoot)

transient hyperpolarization that occurs at the end of an action potential during which the membrane potential briefly becomes even more negative than it normally is at rest; due to the transient increase in potassium permeability

absolute refractory period

brief time during which the sodium channels of a nerve cell are inactivated and cannot be opened by depolarization

relative refractory period

time during the hyperpolarization phase of an action potential when the sodium channels of a nerve cell are capable of opening again, but it is difficult to trigger an action potential because Na+ currents are opposed by larger K+ currents

passive spread of depolarization

process in which cations move away from the site of membrane depolarization to regions of membrane where the potential is more negative

axon hillock

region at the base of an axon where action potentials are initiated most easily

nerve impulse

signal transmitted along nerve cells by a wave of depolarization-repolarization events propagated along the axonal membrane

oligodendrocyte

cell type in the central nervous system that forms the myelin sheath around nerve axons

schwann cell

cell type in the peripheral nervous system that forms the myelin sheath around nerve axons

electrical synapse

junction between two nerve cells where nerve impulses are transmitted by direct movement of ions through gap junctions without the involvement of chemical neurotransmitters

presynaptic neuron

a neuron that transmits a signal to another neuron through a synapse

postsynaptic neuron

a neuron that receives a signal from another neuron through a synapse

chemical synapse

junction between two nerve cells where a nerve impulse is transmitted between the cells by neurotransmitters that diffuse across the synaptic cleft from the presynaptic cell to the postsynaptic cell

synaptic cleft

gap between the presynaptic and postsynaptic membranes at the junction between two nerve cells

neurotransmitter

chemical released by a neuron that transmits nerve impulses across a synapse

acetylcholine

the most common excitatory neurotransmitter used at synapses between neurons outside the central nervous system

cholinergic synapse

a synapse that uses acetylcholine as the neurotransmitter

voltage-gated calcium channel

an integral membrane protein in the terminal bulb of presynaptic neurons that forms a calcium ion conducting pore whose permeability is regulated by the membrane potential

neurosecretory vesicle

a small vesicle containing neurotransmitter molecules; located in terminal bulb of an axon

active zone

region of the presynaptic membrane of an axon where neurosecretory vesicles dock

acetylcholinesterase

an enzyme that hydrolyzes acetylcholine into acetic acid and choline to restore the membrane to its polarized state

neurotransmitter reuptake

mechanism for removing neurotransmitters from the synaptic cleft by pumping them back into the presynaptic axon terminals or nearby support cells

EPSP

small depolarization of the postsynaptic membrane triggered by binding of an excitatory neurotransmitter to its receptor; can trigger an action potential if it exceeds its threshold level

IPSP

small hyperpolarization of the postsynaptic membrane triggered by binding of an inhibitory neurotransmitter to its receptor, thereby reducing the amplitude of subsequent EPSP and possibly preventing the firing of an action potential