Chapter 4 Flashcards
How is the membrane potential of a neuron maintained at rest (in a “polarized” state, approximately -70 mV)
There are fewer cations inside than outside axon
What causes there to be fewer cations inside that outside the axon for a neuron maintained at rest (-70 mV)
- The Na+/K+ pump is always active
- For every 3+ that flow outside, 2+ flow inside
- channels are closed at rest
- Na+ IN, K+ OUT
When a neuron is in a “resting state” (not firing), it is “polarized” because:
There are more cations outside the neuron than inside it, making the difference in electrical potential from inside to outside the neuron -70 mV
EPSP (excited post synaptic potential)
- Small positive change in membrane potential (depolarization)
- Membrane potential becomes less negative (-65 mV)
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IPSP (inhibited post synaptic potential)
- Small negative change in membrane potential (hyperpolarization)
- Membrane potential becomes more negative (-75 mV)
What happens when EPSP (depolarization) occurs?
- Na+ channels open
- More sodium comes in and enters the neuron
What happens when IPSP (hyperpolarization) occurs?
K+ channels open more often –> K+ flows out
OR
Cl- channels open –> Cl- flows in
What causes action potentials?
- Activation of sensory neuron ending (ex. skin, eye, tongue)
- Input from other neurons
How is action potential triggered and conducted along a myelinated axon?
- ) Starts at axon hillock (interneuron)
- ) Travels down axon in a “wave of depolarization”
- ) Refractory period prevents action potential from moving backwards
- ) Opening and closing of ion channels exclusively at the Nodes of Ranvier
- ) This saltatory conduction accelerates the rate at which an action potential travels down an axon
How is action potential triggered and conducted along a unmyelinated axon?
- ) Starts at axon hillock (interneuron)
- ) Travels down axon in a “wave of depolarization”
- ) Refractory period prevents action potential from moving backwards
- ) Slower conduction of action potential
Myelinated vs. unmyelinated action potential initiation and conduction in axons
Insulation by myelin speeds up action potential down the axon; saltatory conduction
Saltatory conduction
- Occurs for myelinated axons
- Involves the opening and closing of ion channels exclusively at the Nodes of Ranvier
Myelinated axons occur in the CNS via
Oligodendrocytes
Myelinated axons occur in the PNS via
Schwann cells
How does a local anesthetic like Novocain prevent action potentials in your sensory nerves?
It blocks the Na+ channels in sensory nerves
How can a poison like TTX (pufferfish) kill you?
It blocks the Na+ channels and stops all nerve firing
What is an example of a demyelinating disease?
Multiple sclerosis (MS)
How does a demyelinating disease like multiple sclerosis lead to slowed movement, or an inability to move?
- The myelin deteriorates which slows down action potential and makes transmission happen slower
- If you lose all of your myelin then it makes it almost impossible
Major steps in chemical neurotransmission
-Synthesis of a neurotransmitter: packaging in vesicles
-Action potential arrives at axon terminal and triggers NT release (exocytosis)
-Neurotransmitter goes across the synapse and binds to receptors on postsynaptic neuron
Neurotransmitter goes off the receptor and NT signaling is terminated via:
-Reuptake
-Degradation
Describe step 1 in chemical neurotransmission
Synthesis of a neurotransmitter: packaging in vesicles
Describe step 2 in chemical neurotransmission
- Action potential arrives at axon terminal and triggers NT release (exocytosis)
- Ca++ channels open, Ca+ flows IN
- Ca+ causes vesicle membranes to fuse with axon terminal membrane
- NT is released into synapse
Describe step 3 in chemical neurotransmission
- NT molecules cross synapse and bind to receptors on post-synaptic neuron
- Which receptor the NT binds to determines if the neuron is excited or inhibited
Describe step 4 in chemical neurotransmission
Neurotransmitter goes off the receptor and NT signaling is terminated via: Reuptake of NT
Describe step 5 in chemical neurotransmission
- Neurotransmitter goes off the receptor and NT signaling is terminated via: Enzymatic degradation
- Most NTs go back into axon terminal that released them, by the use of a transporter protein, but some are broken down by enzyme in the synapse and thus inactivated
Ionotropic receptor
- Receptor is an ion channel → NT binding causes ion channel to open (or close)
- Fast activation that is brief
- No lasting consequences
Metabotropic receptor
- When a NT binds here a subunit of the G protein breaks off and either binds to an ion channel of stimulates synthesis of second messenger
- Activation is slower and longer
- Neuron “metabolism” changes and can change gene expression
Glutamate
- NT of the amino acid class
- 3 glutamate receptor types: all are ionotropic & open Na+ channels so +
- Always excitatory → increases the neurons action potential
GABA
- NT of the amino acid class
- 2 GABA receptor types: 1 ionotropic (opens Cl- channels); 2 metabotropic (opens K+ channels) so -
- Always inhibitory → decreases the neurons action potential
Example of a behavior or experience that dopamine (DA) is involved in
- Mood
- Cognition
- Movement
Drug that alters dopamine (DA)
L-Dopa increases synthesis to treat Parkinson’s disease
3 neurotransmitters of the monoamine class
- Dopamine
- Serotonin
- Norepinephrine
Example of a behavior or experience that norepinephrine is involved in
Alertness
Example of a behavior or experience that serotonin is involved in
- Mood
- Vision
- Appetite
Drug that alters serotonin
SSRI’s block reuptake of 5-HT and increase NT action
Two main functions of acetylcholine (ACh)
- Movement
- Memory
How can diet influence your mood or behavior by influencing your neurotransmitter and ion levels?
- There are essential amino acids that the body can’t make
- Neurons won’t fire without electrolytes
- Neurons need Na+, K+, Mg+, Ca+
Describe the circuitry underlying the knee-jerk reflex, including what types of neurons and what neurotransmitters are involved
- Tap on patellar tendon
- Sensory neuron fires into spinal cord
- Excited motor neuron goes back out to quad, releases glutamate, acetylcholine is released and the muscle contracts
- Sensory neuron activates interneuron and inhibits motor neuron that goes out to the hamstring so the hamstring relaxes
Why do people who suffer from myasthenia gravis experience “muscle weakness”
People with myasthenia gravis experience muscle weakness because the disease results in a loss of acetylcholine receptors
What type of medication is used to help myasthenia gravis patients move more normally (how does this drug work)?
- Tensilon drug
- AChE inhibitors prevent AChE from breaking down ACh
- Increase in ACh
Agonist
Enhances neurotransmitter action
Antagonist
Inhibits neurotransmitter action
Novocain
- Antagonist
- Blocks Na+ channels in sensory nerves
Botox
- Antagonist
- Release
- Decreases release of ACh
Nicotine
- Agonist
- Binding
- Mimics ACh at 1 type of cholinergic receptor
Oxycotin
- Agonist
- Binding
- Mimic endorphin at opioid receptors (decrease pain)
Amphetamines
- Agonist
- Release
- Increase release of monoamines
SSRI’s
- Agonist
- Reuptake
- Blocks reuptake, thereby increasing NT action
MAO (antidepressants)
- Agonist
- Enzymatic degradation
- MAO inhibitors prevent MAO from breaking down monoamines, thereby increased NT action
At rest, a neuron is _____, with a resting potential of about _____ mV.
Polarized; -70
In resting neurons, there are more _____ ions outside the cell than inside, and more ______ ions inside than outside.
Na+; K+
________________ are specialized pores in neural membranes through which ions can pass.
Ion channels
In a resting neuron, _____________ channels are open, whereas ______________ channels are closed.
potassium; sodium
Sodium-potassium pumps transport ____ sodium ions out of the cell for every ___ potassium ions they transport into the cell.
3; 2
IPSPs are:
inhibitory.
A change in the resting membrane potential from -70 mV to -68 mV would be considered a(n):
EPSP
Action potentials are generated in the axon initial segment, which is adjacent to the:
axon hillock.
The action potential is:
an all-or-none response.
Combining a number of individual IPSPs and EPSPs into one signal is called:
integration
The rising phase of an action potential begins when the ____________ and ends when the _____________.
sodium channels open; sodium channels close
Action potentials normally travel along axons in only one direction because of the:
refractory period.
The transmission of action potentials in myelinated axons is called:
saltatory conduction.
Why should the Hodgkin-Huxley model of understanding the mechanisms of cerebral neurons be applied with great caution?
Their research was based on a type of neuron in a particular species that may not generalize to activity in the mammalian brain.
Conduction in interneurons lacking axons is typically __________ and ____________.
passive; decremental
A(n)________synapse on or near a terminal button can selectively facilitate or inhibit the effects of that button on the postsynaptic neuron.
axoaxonic
Many neurons contain two neurotransmitters—a situation generally called:
coexistence.
Exocytosis of small-molecule neurotransmitters involves:
the activation of voltage-activated calcium channels.
_________ are metabotropic receptors that have unconventional characteristics. For example, they bind to their neuron’s own neurotransmitter molecules.
Autoreceptors
Gap junctions are:
narrow spaces between adjacent cells that are bridged by connexins.
With respect to the classes of neurotransmitters, small-molecule is to _____ as large-molecule is to _____.
amino acids; neuropeptides
____________ are the neurotransmitters in the vast majority of fast-acting directed synapses in the central nervous system.
Amino acids
One amino acid neurotransmitter is:
GABA.
Which choice is a monoamine neurotransmitter?
norepinephrine
Which choice is an indoleamine neurotransmitter?
serotonin
Drugs that facilitate the effects of a particular neurotransmitter are said to be _______________ of that neurotransmitter. Drugs that inhibit the effects of a particular neurotransmitter are said to be its ______________.
agonist; antagonist
Botox is a:
nicotinic antagonist.
Which statement is true with respect to atropine?
Atropine is a receptor blocker.
One example of an endogenous opioid is:
enkaphalin.
__________________ produces a temporary disorder that resembles schizophrenia.
Amphetamine
Membrane potential
The difference in electrical charge between the inside and the outside of a cell.
Microelectrodes
Extremely fine recording electrodes, which are used for intracellular recording.
Resting potential
The steady membrane potential of a neuron at rest, usually about −70 mV.
Polarized
In the context of membrane potentials, it is a membrane potential that is not zero.
Ions
Positively or negatively charged particles.
Ion channels
Pores in neural membranes through which specific ions pass.
Sodium−potassium pumps
An ion transporter that actively exchanges three Na+ ions inside the neuron for two K+ ions outside.
Transporters
Mechanisms in the membrane of a cell that actively transport ions or molecules across the membrane.
Postsynaptic potentials (PSPs)
Potentials that move the postsynaptic cell’s membrane potential away from the resting state.
Depolarize
To decrease the resting membrane potential.
Hyperpolarize
To increase the resting membrane potential.
Excitatory postsynaptic potentials (EPSPs)
Graded postsynaptic depolarizations, which increase the likelihood that an action potential will be generated.
Inhibitory postsynaptic potentials (IPSPs)
Graded postsynaptic hyperpolarizations, which decrease the likelihood that an action potential will be generated.
Axon hillock
The conical structure at the junction between the axon and cell body.
Miscellaneous peptides
One of the five categories of neuropeptide transmitters; it include those neuropeptide transmitters that don’t fit into one of the other four categories.
Agonists
Drugs that facilitate the effects of a particular neurotransmitter.
Antagonists
Drugs that inhibit the effects of a particular neurotransmitter.
Receptor blockers
Antagonistic drugs that bind to postsynaptic receptors without activating them and block the access of the usual neurotransmitter.
Atropine
A receptor blocker that exerts its antagonistic effect by binding to muscarinic receptors.
Botox
Botulinium toxin; a neurotoxin released by bacterium often found in spoiled food. It blocks the release of acetylcholine at neuromuscular junctions and has applications in medicine and cosmetics.
Periaqueductal gray (PAG)
The gray matter around the cerebral aqueduct, which contains opiate receptors and activates a descending analgesia circuit.
Endogenous
Naturally occurring in the body (e.g., endogenous opioids).
Enkephalins
The first class of endogenous opioids to be discovered.
Endorphins
A class of endogenous opioids.
Mechanisms in the membrane of a cell that actively move ions or molecules across the membrane are called:
transporters.
The transmission of EPSPs and IPSPs is:
decremental.
Which analogy BEST highlights the speed at which postsynaptic potentials travel from their site of origin?
Postsynaptic potentials travel like electrical signals along a cable.
Postsynaptic hyperpolarizations are called IPSPs because they _____ the chance that ______.
decrease; a neuron will fire
When postsynaptic potentials produced in rapid succession at the same synapse add together, it is called:
temporal summation.
The firing of a neuron is like the firing of a gun because both are:
triggered by graded responses.
The three phases of an action potential are, in order, the _____ phase, the _____ phase, and the _____ phase.
rising; repolarization; hyperpolarization
The ____________ refractory period is followed by the _________ refractory period.
absolute; relative
Axonal conduction from cell body to terminal buttons is called _______ conduction.
orthodromic
The advantage of presynaptic facilitation and inhibition (compared to EPSPs and IPSPs) is that they can:
selectively influence one particular synapse rather than the entire presynaptic neuron.
Small-molecule neurotransmitters are typically synthesized in the cytoplasm of the terminal button and packaged in ________________ by the button’s _________________.
synaptic vesicles; Golgi complex
_____________________ receptors are associated with ligand-activated ion channels, whereas __________________ receptors are associated with signal proteins and G proteins.
Ionotropic; metabotropic
One function of gap junctions appears to be to ________________ the activities of like cells in a particular area.
synchronize
______________________ are neurotransmitters that are similar to delta-9-tetrahydrocannabinol (THC), the main psychoactive constituent of marijuana.
Endocannabinoids
______________, which is the main active ingredient of belladonna, is a receptor blocker that exerts its antagonist effect by binding to muscarinic receptors, thereby blocking the effects of acetylcholine on them.
Atropine
Axon initial segment
The segment of the axon where action potentials are generated—located immediately adjacent to the axon hillock.
Threshold of excitation
The level of depolarization necessary to generate an action potential; usually about −65 mV.
Action potential (AP)
A massive momentary reversal of a neuron’s membrane potential from about −70 mV to about +50 mV.
Action potential (AP)
A massive momentary reversal of a neuron’s membrane potential from about −70 mV to about +50 mV.
Spatial summation
The integration of signals that originate at different sites on the neuron’s membrane.
Temporal summation
The integration of neural signals that occur at different times at the same synapse.
Voltage-gated ion channels
Ion channels that open and close in response to changes in the level of the membrane potential.
Absolute refractory period
A brief period (typically 1 to 2 milliseconds) after the initiation of an action potential during which it is impossible to elicit another action potential in the same neuron.
Relative refractory period
A period after the absolute refractory period during which a higher-than-normal amount of stimulation is necessary to make a neuron fire.
Antidromic conduction
Axonal conduction opposite to the normal direction; conduction from axon terminals back toward the cell body.
Orthodromic conduction
Axonal conduction in the normal direction—from the cell body toward the terminal buttons.
Nodes of Ranvier
The gaps between adjacent myelin sheaths on an axon.
Saltatory conduction
Conduction of an action potential from one node of Ranvier to the next along a myelinated axon.
Dendritic spines
Tiny protrusions of various shapes that are located on the surfaces of many dendrites.
Tripartite synapse
A synapse that involves two neurons and an astroglia.
Directed synapses
Synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity.
Nondirected synapses
Synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are not close together.
Neuropeptides
Short amino acid chains.
Synaptic vesicles
Small spherical membranes that store neurotransmitter molecules and release them into the synaptic cleft.
Golgi complex
Structures in the cell bodies and terminal buttons of neurons that package neurotransmitters and other molecules in vesicles.
Coexistence
The presence of more than one neurotransmitter in the same neuron.
Exocytosis
The process of releasing a neurotransmitter.
Receptors
Cells that are specialized to receive chemical, mechanical, or radiant signals from the environment; also proteins that contain binding sites for particular neurotransmitters.
Ligand
A molecule that binds to another molecule; neurotransmitters are ligands of their receptors.
Receptor subtypes
The different types of receptors to which a particular neurotransmitter can bind.
Ionotropic receptors
Receptors that are associated with ligand-activated ion channels.
Metabotropic receptors
Receptors that are associated with signal proteins and G proteins.
G proteins
Proteins that are located inside neurons (and some other cells) and are attached to metabotropic receptors in the cell membrane.
Second messenger
A chemical synthesized in a neuron in response to the binding of a neurotransmitter to a metabotropic receptor in its cell membrane.
Autoreceptors
A type of metabotropic receptor located on the presynaptic membrane that bind to their neuron’s own neurotransmitters.
Reuptake
The drawing back into the terminal button of neurotransmitter molecules after their release into the synapse; the most common mechanism for deactivating a released neurotransmitter.
Enzymatic degradation
The breakdown of chemicals by enzymes—one of the two mechanisms for deactivating released neurotransmitters.
Enzymes
Proteins that stimulate or inhibit biochemical reactions without being affected by them.
Acetylcholinesterase
The enzyme that breaks down the neurotransmitter acetylcholine.
Gap junctions
Narrow spaces between adjacent neurons that are bridged by fine tubular channels containing cytoplasm, through which electrical signals and small molecules can pass readily.
Amino acid neurotransmitters
A class of small-molecule neurotransmitters, which includes the amino acids glutamate, aspartate, glycine, and GABA.
Glutamate
The most prevalent excitatory neurotransmitter in the central nervous system.
Aspartate
An amino acid neurotransmitter.
Glycine
An amino acid neurotransmitter.
Gamma-aminobutyric acid (GABA)
The amino acid neurotransmitter that is synthesized from glutamate; the most prevalent inhibitory neurotransmitter in the mammalian central nervous system.
Monoamine neurotransmitters
Small-molecule neurotransmitters that are synthesized from monoamines and comprise two classes: catecholamines and indolamines.
Dopamine
One of the three catecholamine neurotransmitters.
Epinephrine
One of the three catecholamine neurotransmitters.
Norepinephrine
One of the three catecholamine neurotransmitters.
Serotonin
An indolamine neurotransmitter; the only member of this class of monoamine neurotransmitters found in the mammalian nervous system.
Catecholamines
The three monoamine neurotransmitters that are synthesized from the amino acid tyrosine: dopamine, epinephrine, and norepinephrine.
Indolamines
The class of monoamine neurotransmitters that are synthesized from tryptophan; serotonin is the only member of this class found in the mammalian nervous system.
Acetylcholine
A neurotransmitter that is created by the addition of an acetyl group to a choline molecule.
All-or-none responses
Responses that are not graded; they either occur to their full extent or do not occur at all.
Soluble-gas neurotransmitters
A class of unconventional neurotransmitters that includes nitric oxide and carbon monoxide.
Nitric oxide
A soluble-gas neurotransmitter.
Carbon monoxide
A soluble-gas neurotransmitter.
Endocannabinoids
A class of unconventional neurotransmitters that are chemically similar to the active components of marijuana.
Anandamide
The first endogenous endocannabinoid to be discovered and characterized.
Neuropeptide transmitters
Peptides that function as neurotransmitters, of which about 100 have been identified; also called neuropeptides.
Pituitary peptides
One of the five categories of neuropeptide transmitters; it contains neuropeptides that were first identified as hormones released by the pituitary.
Hypothalamic peptides
One of the five classes of neuropeptide transmitters; it consists of those first identified as hormones released by the hypothalamus.
Opioid peptides
One of the five classes of neuropeptide transmitters; it consists of those with a structure similar to the active ingredients of opium.
Miscellaneous peptides
One of the five categories of neuropeptide transmitters; it include those neuropeptide transmitters that don’t fit into one of the other four categories.
Agonists
Drugs that facilitate the effects of a particular neurotransmitter.
Antagonists
Drugs that inhibit the effects of a particular neurotransmitter.
Receptor blockers
Antagonistic drugs that bind to postsynaptic receptors without activating them and block the access of the usual neurotransmitter.
Atropine
A receptor blocker that exerts its antagonistic effect by binding to muscarinic receptors.
Botox
Botulinium toxin; a neurotoxin released by bacterium often found in spoiled food. It blocks the release of acetylcholine at neuromuscular junctions and has applications in medicine and cosmetics.
Periaqueductal gray (PAG)
The gray matter around the cerebral aqueduct, which contains opiate receptors and activates a descending analgesia circuit.
Endogenous
Naturally occurring in the body (e.g., endogenous opioids).
Enkephalins
The first class of endogenous opioids to be discovered.
Endorphins
A class of endogenous opioids.
