nsci 2101 exam 1 lec 8 (synaptic communication)

ions can only move into or out of a cell through what?

pores

when a neuron is at rest, what are ions going to want to do concerning their concentration in a cell?

equalize concentration and/or electrochemical gradient

resting membrane potential is roughly how many millivolts?

-70 mV

there is a higher concentration of Na+ _____ the neuron

outside

there is a higher concentration of K+ _____ the neuron

inside

there are more passive _____ channels than passive Na+ channels

K+

what is the ratio of K+ ions to Na+ ions that are pumped by active K+/Na+ pumps?

3 Na+ to every 2 K+

where in the neuron does the action potential begin?

the axon hillock or the initial segment of the axon

why does the action potential begin in the initial segment of the axon?

there is a high concentration of voltage-gated K+ and Na+ channels there

what happens to voltage-gated channels when the threshold is reached?

voltage-gated Na+ and K+ channels will open and the action potential will begin

Depolarization involves what ion coming into the cell?

Na+

Repolarization involves what ion going out of the cell?

K+

what happens after an AP reaches the synapse?

it initiates release of neurotransmitters into the synaptic cleft by opening voltage-gated Ca++ channels.

This causes calcium to come into the cell

synaptic vesicles

sacs that carry neurotransmitters

synaptic cleft

The tiny gap between two neurons where neurotransmitters are released and received, allowing communication between neurons.

docking

when synaptic vesicles touch and attach to the presynaptic membrane

the active zone

where synaptic vesicles dock

where are SNARE proteins located?

on the synaptic vesicles and on the presynaptic membranew

what happens after Ca++ is let into the cell?

Ca++ interacts with SNARE proteins and that helps the vesicles dock in the active zone

what happens after synaptic vesicles dock?

the vesicle membranes fuse with the cell membrane

what happens after vesicle membranes fuse with the cell membrane?

the neurotransmitters in the vesicle are released into the synaptic cleft

exocytosis

Process in which cells release molecules from inside the cell to the outside by fusing a vesicle with the cell membrane.

tetanus

a disease caused by clostridium bacteria in the soil. the bacteria produces tetanus toxin, which is taken up by inhibitory spinal interneurons.

the toxin degrades SNARE proteins, which are needed for exocytosis

Loss of inhibition results in uncontrolled motor neuron activation and muscle contractions and also results in death

endocytosis

the process by which the vesicle membranes are recycled by an endosome

how long is the synaptic cleft?

20-50 nanometers

how are neurotransmitters received by the postsynaptic membrane?

the neurotransmitters bind to receptors

how do neurons keep a neurotransmitter from continuing to act on receptors or receptors of a different neuron nearby?

• transporters take the neurotransmitter away and back into the cell

• transporters can be on astrocytes or in the active zone

which neurotransmitters can be cleared by local astrocytes?

Glutamate and GABA

• astrocytes convert them to glutamine

what happens to neurotransmitters other than GABA and glutamate when they’re trying to be taken back up into the cell?

they must be broken down into their byproducts first in order to be recycled

which drug blocks neurotransmitter reuptake?

cocaine (blocks reuptake of serotonin, dopamine, norepinephrine by blocking transporters)

neurotransmitter receptors

proteins that are present in the postsynaptic membrane that are stitched through it, kind of like channels

• has an extracellular ligand binding domain (thing that recognizes the neurotransmitter and allows it to bind to the receptor)

what are the two types of neurotransmitter receptors called?

• ionotropic

• metabotropic

ionotropic receptor

a ligand-gated ion channel

• neurotransmitter binds to ligand and opens ion channels, sort of like a key to a door

• rapid and short duration

metabotropic receptor

neurotransmitters bind to the receptors and G proteins that are attached to the receptors allow the ion channels to open and close

• slow and long duration

each receptor usually only takes how many neurotransmitters?

1

how many receptors can neurotransmitters bind to?

multiple

how many types of receptors can a postsynaptic cell have?

multiple

how is the function of a neurotransmitter at the synapse determined?

by the kinds of receptors on the postsynaptic cell

psychoactive drugs can be agonists or antagonists of what?

neurotransmitter receptors

agonist

A substance that activates or stimulates a receptor, resulting in a biological response.

antagonist

a substance that inhibits a receptor

what happens when an excitatory neurotransmitter (like glutamate) synapses on a cell?

Na+ channels open in the postsynaptic cell and depolarize the cell, causing an excitatory postsynaptic potential

what happens when an inhibitory neurotransmitter (like GABA) synapses on a cell?

K+ or Cl- channels open in the postsynaptic cell, which hyperpolarizes the cell, causing an inhibitory postsynaptic potential

EPSPs and IPSPs are ____

graded, meaning they are added together to decide whether or not the charge is going above the threshold

most neurons require spatial summation or temporal summation in order to do what?

actually have an AP

spatial summation

multiple excitatory events at the same time from a number of synapses before an AP

temporal summation

multiple excitatory events in rapid succession from one or a few synapses that add up

what are the differences between graded potentials and action potentials?

• action potentials are all or nothing, graded are not

• action potentials have a threshold, graded potentials do not

• action potentials have a refractory period, graded potentials do not

• duration is constant with an AP, duration is not constant with a GP

• graded potentials conductance decreases with distance

• graded potentials can be depolarizing or hyperpolarizing but APs can only be initiated with depolarization

• summation may occur with GPs

• GPs are mediated by receptors whereas APs are mediated with voltage-gated ion channels

long-term potentiation

a burst of excitatory activity on a postsynaptic neuron causes a change in the cell so that a subsequent excitatory event results in more depolarization than before the burst

can last several days or weeks

it underlies learning

activation of neurotransmitter receptors can make changes in what

gene expression

epilepsy is caused by what

too much excitatory activity in the cortex