NRSC 1110 Ch 5

Action potential

a neural impulse; a brief electrical charge that travels down an axon

All or none principle

the law that the neuron either fires at 100% or not at all

Threshold potential

The minimum membrane potential that must be reached in order for an action potential to be generated.

Firing frequency

The number of activation signals sent to a single motor unit in 1 second.

Neural code

The representation of specific stimuli or experiences by the firing of neurons.

Voltage clamp

A device that enables an investigator to hold the membrane potential constant while transmembrane currents are measured.

voltage-gated Na+

A Na+-selective channel that opens or closes in response to changes in the voltage of the local membrane potential; it mediates the action potential.

ball and chain mechanism

a model to explain the fast inactivation mechanism of voltage-gated ion channels

Voltage gated K+

rectifier, Open slowly, remain open longer, repolarizes "resets" the membrane potential

Rising phase

rapid depolarization of the membrane

Overshoot

membrane potential approaches ENa

Falling phase

rapid repolarization of the membrane; Na is inactivated, K is opened

Undershoot

membrane potential approaches EK because K channels are slow to close

absolute refractory period

The minimum length of time after an action potential during which another action potential cannot begin.

Relative refractory period

the period of time following an action potential, when it is possible, but difficult, for the neuron to fire a second action potential, due to the fact that the membrane is further from threshold potential (hyperpolarized)

orthodromic conduction

unidirectional current flow

Increased membrane resistance

forces current to flow along the path of least resistance of the axon interior rather than across the high resistance path of the axonal membrane

Increased axonal diameter

reduces internal resistance \= faster conduction

saltatory conduction

the jumping of action potentials from node to node

Synapse

Gap between neurons

Electrical synapse

a type of synapse in which the cells are connected by gap junctions, allowing ions (and therefore the action potential) to spread easily from cell to cell

Connexon

In a gap junction, a protein channel linking adjacent cells.

Connexin

gap junction protein, 6 form a connexon

Gap junction

A type of intercellular junction, consisting of proteins surrounding a pore that allows the passage of materials between cells; bidirectional flow

Active zone

site of neurotransmitter release

Chemical synapse

a type of synapse at which a chemical (a neurotransmitter) is released from the axon of a neuron into the synaptic cleft, where it binds to receptors on the next structure (either another neuron or an organ)

Axodendritic

axon to dendrite

Axospinous

axon to dendritic spine

Axoaxonic

axon to axon

Axosomatic

axon to soma

Gray's type I

asymmetrical, excitatory

Gray's type II

symmetrical, inhibitory

Neuromuscular junction

the junction between a nerve fiber and the muscle it supplies

Classical criteria for neurotransmitter identification

1. must be present in presynaptic terminal
2. must be released in response to pre synaptic depolarization, and is calcium dependent
3. receptors must be present in post synaptic membrane

Neurotransmitter

chemical messengers that cross the synaptic gaps between neurons

Neuropeptides

relatively short chains of amino acids, serve as neurotransmitters; produced in ER

Secretory granules

holds neuropeptides

Synaptic vesicle

spherical sac containing neurotransmitters

Ca2+ mediated exocytosis

influx of calcium into the cell causes depolarization and the release of NT into the synaptic cleft

SNARE proteins

Promote fusion of vesicles at the correct target membranes; "dock" vesicles

Synaptobrevin

v-SNARE, in synaptic vesicle

Syntaxin

t-SNARE, on plasma membrane

SNAP-25

t-SNARE, on plasma membrane

Synaptotagmin

A specialized protein that responds to calcium ions to trigger vesicular exocytosis.

Vesicle recycling

during exocytosis, vesicle membranes are added to the cell membrane

Endocytosis in vesicle recycling

Discharged vesicles are reclaimed by endocytosis

Clathrin

protein that coats vesicles for recycling

Ionotropic receptors

associated with ligand-activated ion channels; "transmitter gated"

Post Synaptic Potential

(PSP) a voltage change at a receptor site on a postsynaptic cell membrane

EPSP

depolarization in post synaptic cell, caused by ACh and Glutamate- Na inward flow

IPSP

A hyperpolarizing postsynaptic potential, caused by GABA- Cl inward flow

metabotropic receptors

receptors that are associated with signal proteins and G proteins

G protein-coupled receptors (GPCRs)

plasma membrane receptors that work with the help of a G protein

Effector enzymes

enzyme that usually activates a second messenger from g protein

First messenger

neurotransmitter

Protein kinase

The enzyme that transfers phosphate groups from ATP to protein; ie cAMP

Autoreceptors

signal the presynaptic neuron to stop releasing the neurotransmitter; negative feedback

Reuptake

a neurotransmitter's reabsorption by the sending neuron

Degradation

the breaking down of neurotransmitters by enzymes

Neuropharmacology

the study of the effects of drugs on the nervous system

Agonists

drugs that increase the action of a neurotransmitter

Antagonists

drugs that block the function of a neurotransmitter

Synaptic integration

process by which multiple synaptic potentials combine within one postsynaptic neuron

Spatial summation

Integration by a postsynaptic neuron of inputs (EPSPs and IPSPs) from multiple sources.

Temporal summation

Summation by a postsynaptic cell of input (EPSPs or IPSPs) from a single source over time.

Dendritic cable properties

electrically passive cables, currents will dissipate over a distance

Inhibitory synapse

synapse at which a neurotransmitter causes the receiving cell to stop firing

Shunting inhibition

Synapse inhibits current flow from soma to axon hillock

Modulation

process by which the sensations are inhibited or modified

Classical Neurotransmitters

amino acids, monoamines, acetylcholine

Nonclassical neurotransmitters

neuropeptides, lipids, gases