Synapses - Chapter 2

Flashcards about synapses, neurotransmitters, and hormones.

What are Synapses?

Junctions where neurons communicate by transmitting chemicals.

Who coined the term 'synapse'?

Charles Scott Sherrington in 1906.

What are reflexes (in the context of Sherrington's research)?

Automatic muscular responses to stimuli.

What is a reflex arc?

The process of studying reflexes to understand neuronal communication.

How does the speed of conduction differ between a reflex arc and an axon?

The speed of conduction through a reflex arc is slower and more variable than conduction along an axon.

What is the approximate speed of conduction along an axon?

About 40 m/s.

What is a presynaptic neuron?

Neuron that delivers the synaptic transmission.

What is a postsynaptic neuron?

Neuron that receives the message.

What is an Excitatory Postsynaptic Potential (EPSP)?

Graded depolarization that decays over time and space.

What is the cumulative effect of EPSPs the basis for?

Temporal and spatial summation.

What did Sherrington observe regarding repeated stimuli?

Repeated stimuli over a short period of time produce a stronger response.

What is temporal summation?

The idea that repeated stimuli can have a cumulative effect and produce a nerve impulse when a single stimulus is too weak.

What is temporal summation defined as?

Summation of EPSP’s or IPSP’s due to repeated stimulation by one neuron.

What did Sherrington notice about several small stimuli?

Several small stimuli in a similar location produced a reflex when a single stimulus did not.

What is spatial summation?

Synaptic input from several locations can have a cumulative effect and trigger a nerve impulse.

Why is spatial summation critical to brain functioning?

Each neuron receives many incoming axons that frequently produce synchronized responses.

Do temporal and spatial summation occur independently?

Temporal summation and spatial summation ordinarily occur together.

What influences the results of spatial summation?

The order of a series of axons influences the results.

How does temporal summation operate?

Summation over time.

How does spatial summation operate?

Summation over space.

What did Sherrington notice during the reflex action in a dog?

The leg of a dog that was pinched retracted while the other three legs were extended.

What did Sherrington suggest about the interneuron's role?

An interneuron in the spinal cord sent an excitatory message to the flexor muscles of one leg and an inhibitory message was sent to the other three legs.

What is an inhibitory postsynaptic potential (IPSP)?

Temporary hyperpolarization of a membrane.

How does an IPSP occur?

Synaptic input selectively opens the gates for positively charged potassium ions to leave the cell, or negatively charged chloride ions to enter the cell.

What is the function of an IPSP?

Serves as an active “brake” that suppresses excitation.

Who was the first to show that synaptic communication is chemical?

German physiologist Otto Loewi.

What did Otto Loewi discover about stimulating nerves?

Stimulating one nerve slowed the heart, while another increased it.

What is responsible for synaptic communication?

Chemicals, not electricity, are responsible for synaptic communication.

Describe Loewi’s experiment with the frog hearts.

Loewi stimulated the vagus nerve of one frog’s heart, decreasing the heartbeat. When he transferred fluid from that heart to another frog’s heart, he observed a decrease in its heartbeat.

What is the first step in chemical events at the synapse?

The neuron synthesizes chemicals that serve as neurotransmitters.

What happens after neurotransmitters are synthesized?

Action potentials travel down the axon.

What happens after action potentials travel down the axon?

Released molecules diffuse across the cleft, attach to receptors, and alter the activity of the postsynaptic neuron.

What happens after neurotransmitters alter activity of the postsynaptic neuron?

The neurotransmitter molecules separate from their receptors.

What happens after neurotransmitters separate from their receptors?

The neurotransmitters may be taken back into the presynaptic neuron for recycling or diffuse away.

What is one of the last steps of chemical events at the synapse?

Some postsynaptic cells may send reverse messages to slow the release of further neurotransmitters by presynaptic cells.

Name 4 examples of amino acids?

Glutamate, GABA, glycine, aspartate.

Name 1 example of a modified amino acid?

Acetylcholine.

Name 1 example of a indoleamine?

Serotonin.

Name 3 examples of catecholamines?

Dopamine, norepinephrine, epinephrine.

Name 3 examples of neuropeptides?

Endorphins, substance P, neuropeptide Y.

Name 2 examples of purines?

ATP, adenosine.

Name 1 example of gases?

NO (nitric oxide).

How do neurons synthesize neurotransmitters?

Neurons synthesize neurotransmitters and other chemicals from substances provided by the diet.

What foods contain choline?

Milk, eggs, and nuts.

What serves as a precursor for serotonin?

Tryptophan.

What do catecholamines contain?

Contain a catechol group and an amine group.

What does the effect of a neurotransmitter depend on?

Depends on its receptor on the postsynaptic cell.

What are transmitter-gated or ligand-gated channels?

Controlled by a neurotransmitter.

What is a ligand?

A chemical that binds to something.

When does ionotropic effects occur?

When a neurotransmitter attaches to receptors and immediately opens ion channels.

How long do ionotropic receptors last?

Occur very quickly (sometimes less than a millisecond after attaching) and are very short lasting.

What do ionotropic receptors rely on?

Glutamate or GABA.

When does metabotropic effects occur?

When neurotransmitters attach to a receptor and initiate a sequence of slower and longer lasting metabolic reactions.

What are the chemicals that affect metabotropic receptors often called?

Neuromodulators.

What chemicals do metabotropic synapses use?

Dopamine, norepinephrine, serotonin, and sometimes glutamate and GABA.

What happens when neurotransmitters attach to a metabotropic receptor?

It bends the receptor protein that goes through the membrane of the cell.

Name 3 metabotropic events?

Taste, smell, and pain.

What are metabotropic effects important for?

Arousal, attention, hunger, thirst, and emotion.

What is G-protein activation coupled to?

Coupled to guanosine triphosphate (GTP), an energy storing molecule.

What does G-protein activation increase?

Increases the concentration of a “second- messenger”.

What does the second messenger do?

Communicates to areas within the cell.

What may the second messenger do?

May open or close ion channels, alter production of activating proteins, or activate chromosomes.

What do hallucinogenic drugs do?

Distort perception.

What do hallucinogenic drugs chemically resemble?

Chemically resemble serotonin in their molecular shape.

What do hallucinogenic drugs stimulate?

Stimulate serotonin type 2A receptors (5-HT2A) at inappropriate times or for longer duration than usual, thus causing their subjective effect.

What does the brain produce?

The brain produces certain neuropeptides now known as endorphins—a contraction of endogenous morphine.

How do opiate drugs exert their effects?

Binding to the same receptors as endorphins.

What happens during reuptake?

The presynaptic neuron takes up most of the neurotransmitter molecules intact and reuses them.

What are transporters?

Special membrane proteins that facilitate reuptake.

What happens to Serotonin during reuptake?

Taken back up into the presynaptic terminal.

What happens to Acetylcholine during reuptake?

Broken down by acetylcholinesterase into acetate and choline.

What do enzymes do during reuptake?

Break down any transmitter molecules that the transporters do not reuptake.

What do amphetamine and cocaine do?

Stimulate dopamine synapses by increasing the release of dopamine from the presynaptic terminal.

What does Methylphenidate (Ritalin) do?

Blocks the reuptake of dopamine but in a more gradual and more controlled rate.

What is Methylphenidate (Ritalin) prescribed for?

Often prescribed for people with ADHD.

What are Autoreceptors?

Receptors that detect the amount of transmitter released and inhibit further synthesis and release.

What do Postsynaptic neurons do?

Respond to stimulation by releasing chemicals that travel back to the presynaptic terminal where they inhibit further release

What do The active chemicals in marijuana bind to?

Bind to anandamide or 2-AG receptors on presynaptic neurons or GABA.

When cannabinoids attach to these receptors, what happens?

The presynaptic cell stops sending.

What do the chemicals in marijuana do?

Decrease both excitatory and inhibitory messages from many neurons.

What does marijuana result in?

Decreased anxiety.

How fast are Electrical Synapses?

Faster than all chemical transmissions.

What is a gap junction?

The direct contact of the membrane of one neuron with the membrane of another.

What happens at a gap junction?

Depolarization occurs in both cells, resulting in the two neurons acting as if they were one.

What are Hormones?

Chemicals secreted by a gland or other cells that is transported to other organs by the blood where it alters activity.

What are Hormones produced by?

Produced by endocrine glands.

What are hormones important for?

Important for triggering long-lasting changes in multiple parts of the body.

What is the Pituitary Gland?

Attached to the hypothalamus and consists of two distinct glands.

What is the Anterior pituitary composed of?

Composed of glandular tissue.

What does the Hypothalamus secrete?

Secretes releasing and inhibiting hormones that control anterior pituitary.

What is the Posterior pituitary composed of?

Composed of neural tissue.

What does the Hypothalamus produce?

Produces oxytocin and vasopressin, which the posterior pituitary releases in response to neural signals.