2.1 synapses

synapse

a specialized gap as a point of communication between two neurons anatomy of chemical events

reflexes

automatic muscular responses to stimuli

reflex arc

circuit from sensory neuron to muscle response

temporal summation

a cumulative effect of repeated stimuli within a brief time - repeated pinching of dog’s foot

presynaptic neuron

neuron that delivers transmission to another neuron

postsynaptic neuron

neuron receiving transmission

excitatory postsynaptic potential (EPSP)

graded depolarization - result from sodium ions entering the neuron

inhibitory postsynaptic potential (IPSP)

graded hyperpolarization - produced by a flow of negatively charged chloride ions into the cell

spatial summation

summation over space - pinching two points at once

spontanenous firing rate

periodic production of action potentials even without synaptic input

can an inhibitory message flow along an axon?

no, only action potentials propagate along an axon; inhibitory messages—IPSPs—decay over time and distance.

what was Loewi’s evidence that neurotransmission depends on the release of chemicals?

when Loewi stimulated a nerve that increased or decreased a frog’s heart rate, he could withdraw fluid from the area around the heart, transfer it to another frog’s heart, and thereby increase or decrease its rate also

synaptic cleft

the space between the presynaptic and postsynaptic neurons

neurotransmitters

chemicals released by neurons that affect other neurons

amino acids

glutamate, GABA, glycine, aspartate, maybe others

modified amino acid

acetylcholine

Monoamines (also modified from amino acids)

indoleamines: serotonin

catecholamines: dopamine, norepinephrine, epinephrine

Neuropeptides (chains of amino acids)

endorphins, substance P, neuropeptide Y, many others

purines

ATP, adenosine

gases

nitric oxide - released when neurons are stimulated - influences other neurons and dilates nearby blood vessels, increasing blood flow

catcholamines

compounds that contain a catechol and an amine group

vesicles

tiny nearly spherical packets filled with neurotransmitter molecules

where are most neurotransmitters synthesized?

the presynaptic terminal, near the point of release (in vesicles)

exocytosis

a release of neurotransmitter from the presynaptic neuron into the synaptic cleft

When the action potential reaches the presynaptic terminal, which ion must enter the presynaptic terminal to evoke release of the neurotransmitter?

calcuim

ionotropic effect

synaptic effects that depend on the rapid opening of some kind of gate in the membrane

metabotrophic effect

a sequence of metabolic reactions that produce slow and longlasting effects at a synapse

what chemical do most iontrophic effects depend on?

glutamate or GABA

g-protein

a protein coupled to guanosine triphosphate (GTP), an energy-storing molecule

second messenger

a chemical that, when activated by a neurotransmitter, initiates communication to many areas within the neuron

what is the biggest contrast between iotrophic and metabotrophic?

ionotropic synapse has effects localized to one point on the membrane, whereas a metabotropic synapse, by way of its second messenger, influences activity in much or all of the cell and over a longer time