Ch. 4 - Neuron Structure and Function

inhibitory postsynaptic potential (IPSP)

An inhibitory potential in a postsynaptic cell.

gliocytes

A type of invertebrate glial cell.

multipolar neurons

Neurons with many processes leading from the cell body; most of these processes are dendrites, but one may be an axon.

microglia

One of the glial cells of the vertebrate central nervous system.

axon hillock

The junction between the cell body and axon of a neuron. In many neurons, the _________ is the site of action potential initiation, acting as the trigger zone for the neuron.

postsynaptic cell

A cell (either a neuron or effector) that receives a signal from a presynaptic cell across a synapse.

excitable cell

A cell that is capable of producing an action potential.

excitatory potential

A change in the membrane potential in an excitable cell that increases the probability of action potential initiation in that cell.

hyperpolarization

A change in the membrane potential of a cell from its normally negative resting membrane potential to a more negative value; a relative increase in the negative charge on the inside of the cell membrane.

depolarization

A change in the membrane potential of a cell from its normally negative resting membrane potential to a more positive value; a relative increase in the positive charge on the inside of the cell membrane.

inhibitory potential

A change in the membrane potential that decreases the probability of action potential initiation in an excitable cell.

synaptic depression

A decrease in neurotransmitter release in response to repeated action potentials.

nodes of Ranvier

A gap of exposed axonal membrane between two regions of myelin sheath.

glial cells

A group of several types of cells that provide structural and metabolic support to neurons.

chemical synapse

A junction between a neuron and another cell in which the signal is transmitted across the synapse in the form of a neurotransmitter.

electrical synapse

A junction between neurons in which the signal is transmitted as an electrical charge rather than via a neurotransmitter

voltage-gated ion channel

A membrane protein containing an aqueous pore that can be opened in response to changes in the membrane potential.

efferent neurons

A neuron that conducts impulses from an integrating center to an effector.

sensory neurons

A neuron that conveys sensory information from the periphery to the central nervous system

interneuron

A neuron that makes synaptic connections between other neurons.

presynaptic cell

A neuron that transmits a signal across a synapse to a postsynaptic cell.

motor neuron

A neuron that transmits signals from the central nervous system to skeletal muscles.

unipolar neuron

A neuron with one process leading from the cell body; this process generally splits into two branches, one conveying information toward the cell body and one conveying information away from the cell body.

bipolar neuron

A neuron with two main processes leading from the cell body, one of which conveys signals toward the cell body, and one of which conveys signals away from the cell body.

acetylcholine

A neurotransmitter found in most animal species in many types of neurons, including motor neurons and the autonomic ganglia of vertebrates.

relative refractory period

A period immediately following the absolute refractory period in which an excitable cell will generate an action potential only if exposed to a suprathreshold (unusually large) stimulus.

post-tetanic potentiation (PTP)

A phenomenon in which a postsynaptic cell will respond with an unusually large change in membrane potential for several minutes following repeated action potentials in the presynaptic cell.

axon

A projection of the cell body of a neuron that is involved in carrying information, usually in the form of action potentials, from the cell body to the _________ terminal.

after-hyperpolarization

A prolonged hyperpolarization following an action potential.

ionotropic receptor

A receptor protein that acts as a gated ion channel.

cholinergic receptor

A receptor that binds the signaling molecule acetylcholine. ________s can be divided into nicotinic and muscarinic receptors.

metabotropic receptor

A receptor that signals via a signal transduction pathway

action potential

A relatively large-amplitude, rapid change in the membrane potential of an excitable cell as a result of the opening and closing of voltage-gated ion channels; involved in transmitting signals across long distances in the nervous system.

repolarization

A return of the membrane potential of a cell toward the resting membrane potential following a depolarization or hyperpolarization.

Schwann cell

A type of glial cell in the vertebrates that forms the myelin sheath around axons in the peripheral nervous system.

axon varicosity

A type of synapse in which the presynaptic cell releases neurotransmitter at a series of swellings along the axon.

oligodendrocyte

A vertebrate glial cell that forms the myelin sheath of a neuron in the central nervous system.

acetylcholinesterase

An enzyme that catalyzes the breakdown of acetylcholine into choline and acetate.

excitatory postsynaptic potential (EPSP)

An excitatory potential in a postsynaptic cell.

synaptic facilitation

An increase in neurotransmitter release in response to repeated action potentials.

ependymal cells

Cells that line the ventricles of the brain.

graded potentials

Changes in the membrane potential of a cell that vary in magnitude with the stimulus intensity; results from the opening and closing of ion channels.

cell body

Contains the nucleus.

muscarinic acetylcholine receptors

G-protein-coupled receptors that bind acetylcholine.

myelin

Insulating layer than wraps the axons of vertebrate motor neurons.

nicotinic acetylcholine receptors

Ligand-gated ion channels that open in response to acetylcholine binding.

synaptic vesicles

Neurotransmitter-containing vesicles that release neurotransmitter into a synapse.

activation gate

One of the two gates that open and close voltage-gated sodium channels. Allows Na+ to move across the membrane.

inactivation gate

One of the two gates that open and close voltage-gated sodium channels. When closed, no more Na+ can enter the cell.

fast axonal transport

Process by which neurotransmitter-containing vesicles are moved from the cell body to the axon terminal of a neuron; requires molecular motors.

adrenergic receptors

Receptors for the catecholamines norepinephrine and epinephrine.

neurons

Specialized cells in the nervous system that communicate using chemical and electrical signals. Many, but not all, _________ are excitable cells that generate action potentials.

catecholamines

The biogenic amines epinephrine and norepinephrine.

dendrites

The branching extensions of a neuronal cell body that carry signals toward the cell body.

threshold potential

The critical value of the membrane potential in an excitable cell to which the membrane must be depolarized in order for an action potential to be initiated.

axon terminal

The distal end of an axon that forms a synapse with an effector cell or neuron.

cable properties

The electrical properties of axons.

synaptic cleft

The extracellular space between a presynaptic cell and a postsynaptic cell at a synapse.

myelin sheath

The insulating wrappings of vertebrate axons that are composed of multiple layers of glial cell plasma membrane. Invertebrate axons have analogous wrappings, but they are not generally termed a _________.

synapse

The junction between a neuron and another neuron or effector cell; consists of a presynaptic cell, the synaptic cleft, and a postsynaptic cell

saltatory conduction

The mode of conduction of action potentials in myelinated axons in which action potentials appear to jump from one node of Ranvier to the next.

absolute refractory period

The period during and immediately following an action potential in which an excitable cell cannot generate another action potential, no matter how strong the stimulus.

spatial summation

The process by which graded potentials at different points in the membrane (occurring at the same time) combine to influence the net graded potential of a cell.

temporal summation

The process by which graded potentials occurring at slightly different times combine to influence the net graded potential of the cell.

internode

The region of axonal membrane that is covered with the myelin sheath.

neuromuscular junction

The synapse between a motor neuron and a skeletal muscle cell.

giant axons

Unusually large-diameter axons that are present in some invertebrates and vertebrates.

astrocytes

Vertebrate glial cells that help to support and regulate the action of neurons in the central nervous system.