brain and behavior ch2: concept of the synapse

what did charles scott sherrington study and discover

studied reflexes, physiologically demonstrated that neurons communicate at a junction between them, the synapse

what does transmission through a synapse produce and what is the result

a delay, the result is breif excitation of the dendrite

what is a reflex

automatic muscular responses to a stimuli, requires communication between neurons which causes a delay

what is a reflex arc

the circuit from sensory neuron to muscle response: a sensory neuron excites a second neuron, which excites a motor neuron, which excites a muscle

what was sherrintongs experiment

strapped a dog into a harness and pinched one of the dogs feet, seeing that the dog flexed one foot and extended the other

what does the spinal cord control

the flexion and extension reflexes

are reflexes slower or faster than conduction along an axon

slower

when sherrington pinched a dogs foot, the dog flexed the leg after a short delay, what happens during the delay

an impulse has to travel up a axon from the skin receptor to the spinal cord, and then an impulse had to travel back down to a leg , takes no more than 15 m/swh

what is a synapse

the physical junction or gap between two neurons where communication takes place

what is temporal summation

repeated stimuli within a brief time combine their effects, such as a few rapidly repated pinches evoking a reflex

following temporal summation, what part of the synapse delivers transmission

the presynaptic neuron

following temporal summation, what part of the synapse receives the transmission

the postsynaptic neuron a

graded potentials may either be ____ (excitatory) or ____ (inhibitory)

depolarizations;hyperpolarizations

what do graded potentials do over time and distance

decay

what results when sodium ions enter the neuron an is an graded depolarization

excited postsynaptic potential (EPSP)

what is produced by flow of negatively charged chloride ions into the cell and is a graded hyperpolarization

inhibitory postsynaptic potential (IPSP)

what is spatial summation

combination of effects of activity from two or more synapses onto a single neuron, such as pinching two points at once

how does temporal summation and spatial occur together

when a neuron recives input from several axons in succession

what does an interneuron do after a pinch on the foot sends a message along a sensory neuron to the interneuron in the spinal cord

it excites the motor neurons connected to the flexor muscle of that leg and the extensor muscles of the other legs

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

what do the inhibitory synapses so when u pinch a foot

input from an axon hyperpolarizes the postsynaptic cell, moving the cells charge farther from the threshold and decreasing the probability of an action potential

what is a neurons spontaneous firing rate

a periodic production of action potentials even without synaptic input

what does EPSPs and IPSPs do during the spontaneous firing rate of a neuron

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

what does the balance between EPSPs and IPSPs determine

the frequency of action potentials

what was Loewi’s experiment

stimulated a nerve that increase or decreased a frogs heart rate by withdrawing fluid from the area around the heart, transfer it to another frogs heart, and thereby increase or decrease its rate also

what does the sympathetic nervous system do

accelerates the heartbeat, dilates the pupils of the eyes, and regulates other organs

what is the synaptic cleft

the space between the presynaptic and postsynaptic neurons

what are the chemicals that a neuron releases at a synapse

neurotransmitters or neuromodulators

what is nitric oxide

a gas released by many small local neurons

what do many neurons release when they are stimulated

nitric oxide

what does nitric oxide do in addition to influencing other neurons

dilates the nearby blood vessels, thereby increasing the blood flow to that brain area wh

why is nitric oxide the oddest transmiter

it is toxic in large quantities and difficult to make in a laboratory, but many neurons contain an enzyme that enable them to make it efficiently

what compounds make catecholamines and why

epinephrine, norepinephrine, and dopamine; because they contain a catechol group and an amine group wh

what synthesizes neurotransmitters and from what

neurons from amino acids, obtained from proteins in the diet

what is acetylcholine synthesized from and where can it be found

choline, found in milk, eggs, and peanuts

the amino acids phenylylalanine, tyrosine, which are present in proteins, are precursors of what

dopamine, norepinephrine, and epinephrine

where are neurotransmitters synthesized

in the presynaptic terminal near the point of release

where does the presynaptic terminal store high concentrations of neurotransmitter molecules

the vesicles which are tiny nearly spherical packets

why isnt nitric oxide stored in vesciles like other neurotransmitters

neurons release it as soon as they form it instead of storing it

where does the presynaptic terminal hold much of the neurotransmitters

outside the vesciles

why doesnt action potential itself not release the neurotransmitter at the end of axon

depolarization opens voltage dependent calcium channels in the presynaptic terminal

the calcium entry causes exocytosis, what is that

a burst of release of neurotransmiter from the presynaptic neuron

what is the result of neurons releasing a combination of two or more transmitters

immediate brief excitation followed by slower inhibition or other complex messages; some simultaneously release an excitatory transmission and inhibitory transmitter

the effect of a neurotransmitter depends on what

how it affects its receptor

what happens when a neurotransmitter binds to an ionotropic receptor

twists the receptor just enough to rapidly open its central channel; decays quickly

what are the chanels controlled by a neurotransmitter called

transmitted gated or ligand gated

what is a ligand

a chemical that binds to something

what is the neurotransmitter glutamate used by

the brains excitatory ionotropic synapses

what is the neurotransmmitter GABA used by

the brains inhibitor ionotropic synapses

which ion channel does glutamate open

sodium

which ion channel does glutamate open

chloride

what happens when a neurotransmitter binds to a receptor with metabotropic effects

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

why are chemicals that affect metabotropic receptors called neuromodulators

to distinguish them from the fast effects of the neurotransmitters at ionotropic synapse

what happens when a neurotransmitter attaches to a metabotropic receptor

it bends the receptor protein that goes through the membrane of the cell

what is attached to the other side of the protein that is bent when neurotransmitter attaches to a metabotropic receptor

a G-protein

what is a G protein

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

what does bending the receptor attached to a G protein do

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

what is the result of a detached G protein

increased concentration of a second messenger such as cyclic adenosine monophosphate (cyclic AMP) inside the cell

what does the first messenger(the neurotransmitter) do

carries information to the postsynaptic cell

what does the second messenger do

communicates to areas within the cell

how much of the membrane does an ionotropic synapse localized effects one

one point

how much of the cell does a metabotropic synpase have effects on

actvity in muchof all of the cell and over a longer time by way of its second messenger

where are glutamate and gaba released at

the axon terminal

where can neuromodulators be released by

dendrites, the cell body, or by the sides of the axon, and diffuse to recepors in a wider area

which synapses are important for vision and hearing

ionotropic

which synapses are important for taste, smell, pain, or any functions that arise slower and last longer than a sensation

metabotropic

what is a drug that chemically resembles a serotonin neurotransmitter and bind to its receptor, stimulating them for longer than normal durations

hallucinogenic

what does LSD do

resembles serotonin neurotransmitter and enhances connections among brain areas that ordinarily do not communicate much with one another

what is another possible explanation for the hallucinogenic effect

increased spontaneous communication dominates over the input coming from the sense organs

how do opiates relieve pain

acting on receptors in the brain and skin

what do neuropeptides such as endorphins do

regulated emotions and motivations

what happens after a neurotransmitter activates its receptor and releasing glutamate of gaba

specialized transporter proteins quickly move the molecules back into the presynaptic cell (reuptake)

what does reuptake do

recycling so that the presynaptic neuron has transmitters available for release again, and to halt the effect of the postsynaptic cell

when does acetylcholine undergo reuptake

after the enzyme acetylcholinesterase breaks it into the two fragments acetate and choline, choline diffuses back to the presynaptic neuron, which reattaches it to from acetycholine again

what can a sufficiently rapid series of action potentials at a synapse do

deplete the neurotransmitter faster than the presynaptic cell replenishes it, imparing transmission

though efficient, since reuptake takes time does the presynaptic neuron reabsorb every molecule it releases

no

after the serotonin of the catecholamines activate a receptor, what is the next step

the presynaptic neuron takes up much or most of the released neuotransmitter molecules for reuse

reuptake process for catecholamines varies among individuals, is it slower or faster than reuptake of glutamate or gaba

slower

what is the benefit of slow reuptake

it enables the chemicals to build up enough concentration to have significant effects on their neurotransmitters

what breaks down any transmitter molecules that the transports do not reuptake and where does that breakdown go to

enzymes ; goes to blood and urine

why do neuropeptides diffuse away from the membrane without reuptake

resyntheszing these large molecules takes time, a neuron can temporarliy exhaust its supply

what do stimulant drugs such as amphetamine and cocaine inhibit

the transporters for dopamine, serotonin, and norepinephrine, decreasing reuptake and prolonging the affects of the neurotransmitters

what happens when a stimulant drug prevents the usual amount of dopamine reuptake

enzymes break down much of the extra dopamine that stays in the synaptic cleft and the presynaptic cell needs extra time to replenish its supply

what happens a few hours after taking a stimulant drug

a user has less than usual dopamine and enters a withdrawal state

how are methylphenidate (ritalin) and cocaine similar

both block the reuptake of dopamine at the same brain receptors

how do methylphenidate (ritalin) and cocaine different

cocaine produced a rapid rush of effect on the bran, methylphenidate has more gradual effects

how do autoreceptors provide negative feedback

respond to the released transmitter by inhibiting further synthesis and release

what are autoreceptors sensitive to

the same transmitter that presynaptic terminals release

how do some postsynaptic neurons respond to stimulation

by releasing chemicals that travel back to the presynaptic terminal to inhibit further release of a transmitter (reverse transmitters))

what are two reverse transmitters

ananmide and 2-AG

what do cannabinoid chemicals do

mimic the effects of reverse transmitters, telling a presynaptic neuron “ i recieved you message. stop sending it”

what do chemicals in marijuana do

decrease the release of both glutamate and gaba

what is it called when at an electrical synapse, the membrane of one neuron makes direct contact with the membrane of another

gap junction

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

a hormone

how is a neurotransmitter like a telephone signal

it conveys a message from the sender to the intended receiver h

how is a hormone like radio waves

they convey a message to any reciever tuned into the right station

what are endocrine glands for

specialized organ that secretes hormones directly into the bloodstream to regulate long term bodily functions like metabolism, growth, mood, and stress responses

where is the pituitary gland attached and what are its two parts

the hypothalamus; anterior and posterior

why can the posterior pituitary be considered an extension of the hypothalamus

neurons in the hypothalamus synthesize the hormones oxytocin and vasopressin, which migrate down axons in the posterior pituitary, which releases them

what does the anterior pituitary do

synthesizes its own hormones

what does the hypothalamus synthesize and inhibit

releasing and inhibiting hormones