Chapter 3- Synapses Flashcards
Sherrington deduced that transmission at a synapse must be slower than conduction along an axon. This was based on what kind of evidence?
The speed of reflexive responses
What is the correct sequence of chemical events at a synapse?
Synthesis, Transport, Release, Reuptake
What is a synapse?
A specialized gap between neurons
What is a reflex?
Automatic muscular responses to stimuli
What is a reflex arc?
Circuit from sensory neurons to muscle response
What is Temporal summation?
Repeating stimuli within a brief time have a cumulative effect
What is a postsynaptic neuron?
The cell that receives the message
What is a pre-synaptic neuron?
The cell that delivers the transmission
What is an Excitatory postsynaptic potential ( EPSP)?
Graded depolarization that occurs when sodium ions enter the cell. If it does not reach it’s threshold, depolarization decays quickly
What is an Inhibitory Postsynaptic potential? ( IPSP)
Hyperpolarization that occurs when synaptic input selectively opens the gates for potassium ions to leave the cell ( carrying a positive charge) of for chlorine ions ( negative charge) to enter the cell
What is the speed of conduction along an axon?
40 m/s
What is the speed of conduction through a reflex arc?
15 m/s
What is spatial summation?
Synaptic inputs from various locations combine their effects on a neuron. critical to brain functioning
What happens at an inhibitory synapse?
Input from an axon hyperpolarizes the postsynaptic cell
What is the Spontaneous Firing Rate?
Periodic reproduction of action potentials even without synaptic input
What is a neurotransmitter?
Chemicals released by one neuron that affect a second neuron
Name the six types of neurotransmitters
Amino Acids, Neuropeptides, Acetylcholine, Monoamines, Purines, Gases
What is exocytosis?
Excretion of the neurotransmitters from the presynaptic terminal into the synaptic cleft. Triggered by an action potential reaching the end of an axon.
Name 3 neurotransmitters that are Catecholamines.
Epinephrine, Norepinephrine, and dopamine
Where are neurotransmitters stored?
Most neurotransmitters are synthesized in the presynaptic terminal
What are vesicles?
tiny packets that store high concentrations of neurotranmitters
Does a single neuron release all of the neurotransmitters?
No, many release a combination of two or more neurotransmitters
Why does a neuron release a combination of neurotransmitters instead of just one?
Because that specific combination makes the message more complex
What are Ionotropic effects?
They occur at one type of receptor, are quick and only last for a brief time, convey messages and are good for vision and hearing
What are Metabotropic effects?
They initiate a series of metabolic reactions, are slower and longer lasting , use a large variety of neurotransmitters and are good for taste, smell ad pain
What are Neuropeptides?
often described as neuromodulators-have several properties that distinguish them from neurotransmitters. They require repeated stimulation
What happens when a neurotransmitter attaches to a metabotropic receptor?
It bends the receptor protein, enabling a portion of it inside the neuron to react with other molecules
What are hormones?
Chemicals that are secreted by a gland or other cell and conveyed by the blood to other organs
What are Endocrine glands?
Glands that produce hormones
What are hormones good for?
Coordinating long-lasting changes in multiple parts of the body
Epinephrine,Norepinephrine,insulin and oxytocin serve as both..
hormones and neuortranmitters
What is the posterior pituitary?
considered an extension of the hypothalamus, composed of neural tissue
What is the anterior pituitary?
composed of glandular tissue and synthesizes six different hormones
What does an autoreceptor do?
detects the amount of neurotransmitter released and inhibit further synthesis and release after it reaches a certain level
What is an Electrical Synapse?
Special-purpose synapses that operate electrically, faster than all chemical synapses
What is a Gap junction?
contact between membrane of one neuron with membrane of another
How do drugs work?
They mimic our own neurochemistry
What kind of drug inhibits or block the effects of a neurotransmitter?
Antagonist
What kind of drug facilitates or increases the effects of a neurotransmitter?
Agonist
What does it mean if a drug has an affinity for a receptor?
It binds to it
What does it mean if a drug has an efficacy for a receptor?
It’s tendency to activate that receptor
What neurotransmitters do addictive substances effect?
Dopamine and Norepinephrine
What simulates dopamine release in the nucleus accumbens ?
Drugs, Sexual excitement, video games
Dopamine in nucleus accumbens relates to…
how much you want something, not how much you like it.
Small parts of the nucleus accumbens respond to..
Pleasure ( liking)
Large parts of the nucleus accumbens respond to…
Motivation ( wanting)
A stimulant drug…
increases excitement, alertness, and activity while decreasing fatigue
What does Amphetamine do?
stimulates dopamine synapses by increasing release of dopamine from presynaptic terminal . Presynaptic terminal ordinarily reabsorbs dopamine through dopamine transporter( a protein))
What does cocaine do?
Blocks the reuptake of dopamine, norepinephrine, and serotonin. It’s effects depend mostly on dopamine, and secondarily on serotonin
How do Amphetamine and Cocaine work?
They inhibit dopamine transporters which causes an indirect increase of dopamine release
Pert and Snyder ( 1973) found that opiates…
Attach to specific receptors in the brain . Proposed that the brain must produce its own chemical that attaches to these receptors
Endorphins are..
neuropeptides released by the brain that indirectly activate dopamine release and may contribute to certain kinds of reinforcement by inhibiting the release of GABA indirectly
Marijuana contains…
THC and other cannabinoids which can be used medically to relieve pain or nausea, combat glaucoma, and increase appetite
The effects of cannabinoids on neurons are..
They are released by postsynaptic neuron attach to receptors on presynaptic neuron, where they inhibit further release of glutamate ( excitatory transmitter) and GABA ( inhibitory transmitter)
Hallucinogenic Drugs are…
drugs that distort perception
MDMA or Ecstasy is..
a stimulant at low doses, increasing the release of dopamine to produce effects similar to amphetamine or cocaine.
At high does it also increases serotonin release, leading to alterations in perception and cognition.
How does alcohol affect neurons?
Facilitates response at GABA receptor and blocks activity at glutamate receptors.
Both GABA effect and glutamate effect lead to decrease in brain activity.
Alcohol increases stimulation and both dopamine and opiate receptors, including those in the nucleus accumbens.
Type I alcoholism ( Type A)
Develop gradually ( after 25 years of age), do not usually have relatives with addictions
Type II alcoholism ( Type B)
Onset of problems is rapid, ( before 25 yrs old), most are men, and most have close relatives with alcohol problems
How do genes affect likelihood of alcoholism?
one identified gene controls dopamine type 4 receptor…people with the “ longer” version of this gene report stronger cravings for additional alcohol after having one drink.
Longer form of this gene leads to less sensitive receptors
Another gene controls COMT ( enzyme that breaks down dopamine after release) Valine version of gene breaks down more dopamine, thereby decreasing reinforcements. People with this gene tend to be more impulsive
Addiction is …
when someone uses a substance more and more, behavior becomes a compulsion or addiction
What can cause rewiring of the nucleus accumbens?
Some drugs, such as cocaine. It also induces changes that impair extinction
What is Disulfiram ( Antabuse) ?
A drug used to combat substance abuse. It antagonizes ( blocks) effect of Acetaldehyde Dehydrogenase
What is Naloxone ( Revia) ?
A drug used to combat substance abuse. It’s an antagonist that blocks opiate receptors so there is decrease in pleasure from alcohol.
