Synapse

Question 1

Charles Scott Sherrington

Answer 1

physiologically demonstrated that communication between one neuron and the next differs from communication along a single axon

tested reflex of dog and found flexion and extension reflexes

based on timing of reflex he figured out that the reflexes are slower than an action potential on the length of the axon

he inferred that there were gaps between axons that were slowing things down

Question 2

synapse

Answer 2

a specialized gap between neurons

Question 3

flexion reflex

Answer 3

sensory neuron excites a second neuron, which in turn excites a motor neuron, which excites a muscle

Question 4

reflex arc

Answer 4

The circuit from sensory neuron to muscle response

Question 5

temporal summation

Answer 5

repeated stimuli within a brief time have a cumulative effect

although the subthreshold excitation in the postsynaptic neuron decays over time, it can combine with a second excitation that follows it quickly

Question 6

presynaptic neuron

Answer 6

neuron that delivers transmission

Question 7

postsynaptic neuron

Answer 7

the one that receives the transmission

Question 8

excitatory postsynaptic potential (EPSP)

Answer 8

graded depolarization

partial depolarization is a graded potential

results from a flow of sodium ions into the neuron

if an EPSP does not cause the cell to reach its threshold, the depolarization decays quickly.

Question 9

spatial summation

Answer 9

summation over space

Synaptic inputs from separate locations combine their effects on a neuron.

Question 10

Inhibitory Synapses

Answer 10

A pinch on the foot sends a message along a sensory neuron to an interneuron (an intermediate neuron) that excites the motor neurons connected to the flexor muscles of that leg and the extensor muscles of the other legs

the interneuron sends messages to inhibit the extensor muscles in that leg and the flexor muscles of the three other legs

input from an axon hyperpolarizes the postsynaptic cell.

it increases the negative charge within the cell, moving it farther from the threshold and decreasing the probability of an action potential

Question 11

inhibitory postsynaptic potential (IPSP)

Answer 11

occurs when synaptic input selectively opens the gates for potassium ions to leave the cell (carrying a positive charge with them) or for chloride ions to enter the cell (carrying a negative charge)

Question 12

spontaneous firing rate

Answer 12

a periodic production of action potentials even without synaptic input

EPSPs increase the frequency of action potentials above the spontaneous rate, whereas IPSPs decrease it

Question 13

discovery of chemical transmission at synapse

Answer 13

Otto Loewi

repeatedly stimulated the vagus nerve, thereby decreasing a frog’s heart rate

collected fluid from around that heart, transferred it to a second frog’s heart, and found that the second heart also decreased its rate of beating

did the same to increase the heart rate and did the same

Question 14

Sequence of Chemical Events

at a Synapse

Answer 14

1. The neuron synthesizes chemicals that serve as neu- rotransmitters. It synthesizes the smaller neurotransmit- ters in the axon terminals and synthesizes neuropeptides in the cell body.
2. Action potentials travel down the axon. At the presynap- tic terminal, an action potential enables calcium to enter the cell. Calcium releases neurotransmitters from the terminals and into the synaptic cleft, the space between the presynaptic and postsynaptic neurons.
3. The released molecules diffuse across the narrow cleft, attach to receptors, and alter the activity of the postsynap- tic neuron. Mechanisms vary for altering that activity.
4. The neurotransmitter molecules separate from their receptors.
5. The neurotransmitter molecules may be taken back into the presynaptic neuron for recycling or they may diffuse away.
6. Some postsynaptic cells send reverse messages to control the further release of neurotransmitter by presynaptic cells.

Question 15

neurotransmitters

Answer 15

chemicals that affect another neuron

hundred or so kinds known or suspected

includes amino acids, modified amino acids, monoamines, neuropeptides, purines, gases

Question 16

nitric oxide

Answer 16

gas released by many small local neurons

neurons release nitric oxide when they are stimulated

influencing other neurons, nitric oxide dilates the nearby blood vessels, thereby increasing blood flow to that brain area

Question 17

tryptophan

Answer 17

precursor to serotonin

serotonin levels rise after you eat foods richer in tryptophan, such as soy, and fall after something low in tryptophan, such as maize

Question 18

Serotonin

Answer 18

Involved in many functions, including mood, appetite, sleep, and aggression.

Low levels of serotonin are associated with depression, and some drugs designed to treat depression (known as selective serotonin reuptake inhibitors, or SSRIs) serve to prevent their reuptake.

likely matabotropic

Question 19

Glutamate

Answer 19

The most common neurotransmitter, it’s released in more than 90% of the brain’s synapses. Glutamate is found in the food additive MSG

Excess glutamate can cause overstimulation, migraines and seizures.

Usually ionotropic

Question 20

GABA (gamma-aminobutyric acid)

Answer 20

The major inhibitory neurotransmitter in the brain.

Alcohol stimulates the release of GABA, which inhibits the nervous system and makes us feel drunk. Low levels of GABA can produce anxiety, and GABA agonists (tranquilizers) are used to reduce anxiety

mostly ionotropic

Question 21

Endorphins

Answer 21

Released in response to behaviors such as vigorous exercise, orgasm, and eating spicy foods.

Question 22

Dopamine

Answer 22

Involved in movement, motivation, and emotion, Dopamine produces feelings of pleasure when released by the brain’s reward system, and it’s also involved in learning

likely metabotropic

Question 23

Acetylcholine

Answer 23

A common excitatory neurotransmitter used in the spinal cord and motor neurons to stimulate muscle contractions. It’s also used in the brain to regulate memory, sleeping, and dreaming.

acetylcholine attaches as in Figure 2.15b, the receptor folds outward, widen- ing the sodium channel

Question 24

synthesis of neurotrnsmitters

Answer 24

Most neurotransmitters are synthesized in the presynaptic terminal, near the point of release

Question 25

vesicles

Answer 25

presynaptic terminal stores high concentrations of neurotransmitter molecules in vesicles, tiny nearly spherical packets

Question 26

MAO (monoamine oxidase)

Answer 26

Neurons that release serotonin, dopamine, or norepinephrine contain an enzyme, MAO (monoamine oxidase), that breaks down these transmitters into inactive chemicals, thereby preventing the transmitters to accumulate to harmful levels.

Question 27

exocytosis

Answer 27

bursts of release of neurotransmitter from the presynaptic neuron

depolarization opens voltage- dependent calcium gates in the presynaptic terminal, 1 or 2 milliseconds (ms) after calcium enters the terminal, it causes exocytosis

spreads across the cleft to the postsynaptic receptor

neurons release a combination of two or more transmitters at a time

Question 28

ionotropic effects

Answer 28

on-off effect of neurotransmitters on a receptor site; brief on off effect;

like a paper bag twisted opening and closing to allow a particular type of ion through

Question 29

transmitter-gated or ligand-gated

Answer 29

(A ligand is a chemical that binds to something.)

compared to voltage gated

when the neurotransmitter attaches, it opens a channel. Ionotropic effects begin quickly, sometimes within less than a millisecond after the transmitter attaches

effect decays very quickly

Question 30

Glycine

Answer 30

another common inhibitory transmitter

Question 31

inhibitory ionotropic neurotransmitters

Answer 31

opens chloride gates, enabling chloride ions, with their negative charge, to cross the membrane into the cell more rapidly than usual

Question 32

Metabotropic Effects and Second

Messenger Systems

Answer 32

initiating a sequence of metabolic reactions that start slowly but last longer than ionotropic effects

effects emerge 30 ms or more after the release of the transmitter

it bends the receptor protein that goes through the membrane of the cell. The other side of that receptor is attached to a G protein—that is, a protein coupled to guanosine triphosphate (GTP), an energy- storing molecule

Bending the receptor protein detaches that G protein, which is then free to take its energy elsewhere in the cell

the result of that G protein is increased concentration of a second messenger, such as cyclic adenosine monophosphate (cyclic AMP), inside the cell. Just as the “first messenger” (the neurotransmitter) carries information to the postsynaptic cell, the second messenger communicates to areas within the cell

by way of its second messenger, influences activity in much or all of the cell and over a longer time.

Question 33

Ionotropic vs metabotropic synapses

Answer 33

vision and hearing, the brain needs rapid, up-to-date information, the kind that ionotropic synapses bring

metabotropic synapses are better suited for more enduring effects such as taste; also important for many aspects of arousal, attention, pleasure, and emotion

Question 34

neuropeptides

Answer 34

neuromodulators, because they have properties that set them apart from other transmitters

synthesized in the cell body and then slowly transports them to other parts of the cell

neuropeptides are released mainly by dendrites, and also by the cell body and by the sides of the axon

neuropeptide release requires repeated stimulation

they resemble hormones diffuse widely, slowly affecting many neurons in their region of the brain

important for hunger, thirst, and other long-term changes in behavior and experience

Question 35

acetylcholine inactivation

Answer 35

broken down by a specific enzyme into acetate and choline

choline diffuses back to the presynaptic neuron and reconnects it with acetate already in the cell

Question 36

catecholamines

Answer 36

serotonin, dopamine, norepinephrine, and epinephrine

Question 37

reuptake

Answer 37

presynaptic neuron takes up much or most of the released neurotransmitter molecules intact and reuses them

occurs through special membrane proteins called transporters

one not taken up are broken down by another enzyme and excreted through blood and urine

Question 38

amphetamine and cocaine

Answer 38

inhibit the transporters for dopamine, serotonin, and norepinephrine, thus decreasing reuptake and prolonging the effects of the neurotransmitters

Question 39

autoreceptors

Answer 39

many presynaptic terminals have receptors sensitive to the same transmitter they release

receptors that respond to the released transmitter by inhibiting further synthesis and release

Question 40

Other Forms of Negative Synaptic Feedback

Answer 40

some postsynaptic neurons respond to stimu- lation by releasing chemicals that travel back to the pre- synaptic terminal to inhibit further release of transmitter

nitric oxide
hydrogen ions

Question 41

Cannabinoids

Answer 41

the chemicals in marijuana decrease both excitatory and inhibitory messages from neurons that release glutamate, GABA, and other transmitters. In various cases the result can be either brief or more long-lasting suppression of release

resulting in decreased anxiety

Question 42

Electrical Synapses

Answer 42

faster than even the fastest chemical trans- mission, electrical synapses have evolved in cases where ex- act synchrony between two cells is important

eg, rhythmic breathing

Question 43

gap junction

Answer 43

the membrane of one neuron comes into direct contact with the membrane of another, in electrical synapses

large pores of the membrane of one neuron line up precisely with similar pores in the membrane of the other cell where sodium and other ions pass readily

act is if a single neuron

Question 44

Hormones

Answer 44

a chemical secreted by cells in one part of the body and conveyed by the blood to influence other cells

function like a radio instead of a telephone

useful for coordinating long-lasting changes in multiple parts of the body

Question 45

Two types of hormones

Answer 45

protein hormones and peptide hormones

proteins are longer and peptides are shorter

attach to membrane receptors, where they activate a second messenger within the cell—exactly like a metabotropic synapse

Question 46

pituitary gland

Answer 46

responsible for producing hormones

consists of anterior pituitary and the posterior pituitary

Question 47

posterior pituitary

Answer 47

composed of neural tissue, can be considered an extension of the hypothalamus. Neurons in the hypothalamus synthesize the hormones oxytocin and vasopressin

migrate down axons to the posterior pituitary, where they are released into the blood

Question 48

anterior pituitary

Answer 48

composed of glandular tissue, synthesizes six hormones, although the hypothalamus controls their release

hypothalamus secretes releasing hormones, which flow through the blood to the anterior pituitary. There they stimulate or inhibit the release of other hormones.

Question 49

hypothalamus

Answer 49

maintains fairly constant circulating levels of certain hormones through a negative feedback system

eg,
when the level of thyroid hormone is low, the hypothalamus releases TSH-releasing hormone, which stimulates the anterior pituitary to release TSH, which in turn causes the thyroid gland to secrete more thyroid hormones

Question 50

COMT

Answer 50

(catechol-o-methyltransferase) any transmitter molecules that the transporters do not take will instead break down by an enzyme called COMT

Question 51

amphetamine and cocaine,

Answer 51

Stimulant drugs, including amphetamine and cocaine, inhibit the transporters for dopamine, serotonin, and norepinephrine, thus decreasing reuptake and prolonging the effects of the neurotransmitters

Question 52

LSD/Hallucinogenic drugs

Answer 52

attach to serotonin type 2A (5-HT2A) receptors and provide stimulation at inappropriate times or for longer-than-usual durations. LSD increases the connections among brain areas that ordinarily do not communicate much with one another.

Question 53

Nicotine

Answer 53

stimulates a family of acetylcholine receptors, conveniently known as nicotinic receptors. Because nicotinic receptors are abundant on neurons that release dopamine, nicotine increases dopa- mine release

Question 54

Opiate drugs

Answer 54

opiates relieve pain by act- ing on receptors in the brain as well as in the skin.

opiates attach to specific receptors in the brain

bind to same receptors as endorphons?

Question 55

Cannabinoids

Answer 55

bind to anandamide or 2-AG receptors on presynaptic neurons, indi- cating, “The cell got your message. Stop sending it.

Question 56

anandamide and 2-AG

Answer 56

like nitric oxide, other reverse transmitters

respond to stimu- lation by releasing chemicals that travel back to the pre- synaptic terminal to inhibit further release of transmitter