Chapter 2 Synapses

Flashcards about Synapses

What are synapses?

Junctions where neurons communicate by transmitting chemicals.

Who coined the term 'synapse'?

Charles Scott Sherrington.

What did Sherrington study to understand neuronal communication?

Reflexes (automatic muscular responses to stimuli).

What is a reflex arc?

The process Sherrington used to study reflexes.

Why is the speed of conduction through a reflex arc slower than along an axon?

The delay occurs at the synapse.

What is an EPSP?

Excitatory postsynaptic potential; a graded depolarization that decays over time and space.

What is the role of the presynaptic neuron?

Delivers the synaptic transmission.

What is the role of the postsynaptic neuron?

Receives the message.

What is the basis for temporal and spatial summation?

The cumulative effect of EPSPs.

What is temporal summation?

Summation of EPSPs or IPSPs due to repeated stimulation by one neuron.

What is spatial summation?

Synaptic input from several locations having a cumulative effect and triggering 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 typically occur together?

Yes, ordinarily they occur together.

What is an IPSP?

Inhibitory postsynaptic potential; the temporary hyperpolarization of a membrane.

How does an IPSP serve as an active 'brake'?

Suppresses excitation.

What ions are involved in IPSP?

Positively charged potassium ions leave the cell, or negatively charged chloride ions enter the cells.

What did Otto Loewi demonstrate?

Synaptic communication is chemical.

What happens when neurotransmitter molecules separate from their receptors?

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

What is the role of neurotransmitters?

Chemicals that transmit signals across a synapse

Name 4 types of Neurotransmitters

Amino Acids, A Modified Amino Acid, Monoamines, Neuropeptides

What amino acid is a precursor for serotonin?

Tryptophan.

What is a ligand?

A chemical that binds to something.

What are transmitter-gated or ligand-gated channels controlled by?

A neurotransmitter.

What is the primary characteristic of Ionotropic effects?

Occurs very quickly (less than a millisecond after attaching) and are very short lasting

On which neurotransmitters do Ionotropic effects rely?

Glutamate or GABA

What are the chemicals that affect metabotropic receptors called?

Neuromodulators.

What neurotransmitters do metabotropic synapses use?

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

What do metabotropic events include?

Taste, smell, and pain.

What roles are Metabotropic effects crucial for?

Arousal, attention, hunger, thirst, and emotion.

What happens with a metabotropic receptor after a neurotransmitter attaches to it?

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

What is G-protein activation coupled to?

Guanosine triphosphate (GTP), an energy storing molecule.

What does the second messenger do?

Communicates to areas within the cell; may open or close ion channels, alter production of activating proteins, or activate chromosomes.

How do hallucinogenic drugs distort perception?

Stimulate serotonin type 2A receptors (5-HT2A) at inappropriate times or for longer duration than usual.

What are endorphins?

Neuropeptides produced by the brain that bind to opiate receptors.

What is reuptake?

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

What facilitates reuptake?

Transporters, special membrane proteins.

How is Acetylcholine broken down?

By acetylcholinesterase into acetate and choline.

How do amphetamine and cocaine stimulate dopamine synapses?

By increasing the release of dopamine from the presynaptic terminal.

How does Methylphenidate (Ritalin) work?

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

What are autoreceptors?

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

How do Postsynaptic neurons provide negative feedback?

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

What receptors do the active chemicals in marijuana bind to?

Anandamide or 2-AG receptors on presynaptic neurons or GABA.

How do cannabinoids effect messages from neurons?

Decrease both excitatory and inhibitory messages from many neurons.

What is the result of cannabinoid activity on anxiety

Typically resulting in decreased anxiety.

What is a gap junction?

The direct contact of the membrane of one neuron with the membrane of another in electrical synapses.

What are hormones?

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

Where are hormones produced?

Endocrine glands.

What is the role of the Pituitary Gland?

Attached to the hypothalamus and consists of two distinct glands

What is the role of the anterior pituitary?

Composed of glandular tissue

What controls the anterior pituitary?

Hypothalamus secretes releasing and inhibiting hormones that control anterior pituitary

What is the role of the posterior pituitary?

Composed of neural tissue

What does the hypothalamus produce?

Oxytocin and vasopressin, which the posterior pituitary releases in response to neural signals

What is a Selective hormones from the Anterior pituitary?

Thyroid-stimulating hormone, growth hormone, Follicle-stimulating hormone, Luteinizing hormone ACTH and Prolactin

What hormones does the Posterior pituitary release?

Oxytocin and Vasopressin

What is the effect of the pineal hormone melatonin?

Sleepiness; also role in puberty.

What hormones does the Adrenal cortex release?

Aldosterone and Cortisol

What hormones does the Adrenal medulla release?

Epinephrine and Norepinephrine

What hormones does the Pancreas release?

Insulin and Glucagon

What hormones does the Ovary release?

Estrogens and progesterone

What hormones does the Testis release?

Testosterone

What hormones does the kindey release?

Renin

What is Leptin?

Decreases appetite, increases activity

Temporal Summation

The additive effect of several electrical impulses on a nerve cell

Spatial Summation

The additive effect of electrical impulses from several neurons on a single nerve cell

Inhibitory Postsynaptic Potential

Temporary hyperpolarization of a postsynaptic membrane caused by the flow of negatively charged ions into the cell

Excitatory Postsynaptic Potential

Temporary depolarization of a postsynaptic membrane caused by the flow of positively charged ions into the cell

Neurotransmitters

Chemical messengers that transmit a signal from a neuron across the synapse to a target cell

Otto Loewi

Showed that synaptic communication is chemical

Acetylcholine

Broken down by acetylcholinesterase into acetate and choline

What is the role of the G-protein?

Increases the concentration of a “second- messenger”

How do opiates attach to receptors in the brain?

binding to the same receptors as endorphins

How does LSD act as a hallucinogenic drug?

Chemically resemble serotonin in their molecular shape

Reuptake

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

Stimulant Drugs

Amphetamine and cocaine, Stimulate dopamine synapses by increasing the release of dopamine from the presynaptic terminal

What is Methylphenidate (Ritalin) used for?

Often prescribed for people with ADHD

Electrical Synapses

A few special-purpose synapses operate electrically

Where are Hormones produced?

Produced by endocrine glands

Pituitary Gland

Attached to the hypothalamus and consists of two distinct glands

Anterior pituitary

Composed of glandular tissue

Posterior pituitary

Composed of neural tissue

What hormones does the Posterior pituitary release?

Releases Oxytocin and Vasopressin in response to neural signals

Hormone: Renin

Regulates blood pressure, contributes to hypovolemic thirst

Hormone: Leptin

Decreases appetite, increases activity

Thyroxine and triiodothyronine

From the Thyroid gland, effect the Hypothalamus and Anterior Pituitary