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Flashcards in Chapter 5 Deck (102):
1

Acetylcholine (ACh)

activates skeletal muscles in SNS; inhibits heart beats; may inhibit OR excite organs in the autonomic system

2

Epinephrine

AKA Adrenaline; mobilizes body during flight or fight

3

Norepinephrine

AKA Noradrenaline; accelerates heart beat in mammals

4

Neurotransmitter

chemical released by a neuron onto a target with an excitatory or inhibitory effect

5

What are neurotransmitters outside of the nervous system called?

Hormones

6

What disease does Dopamine play a role in?

Parkinson's Disease

7

How do electron microscopes work?

Projecting a beam of electrons through a very thin slice of tissue. The varying structure of the tissue scatters the beam onto a reflective surface where it leaves an image

8

Synaptic Vesicles

Organelle consisting of a membrane structure that encloses a quantum or neurotransmitter

9

Parkinson's Disease

disorder of the motor system correlated with a loss of dopamine in the brain and characterized by tremors, muscular rigidity, and reduction in voluntary movement

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Dopamine

Amine neurotransmitter; plays a role in coordinating movement, attention, learning, and behaviors that are reinforcing

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Synaptic Cleft

Gap that separates the presynaptic membrane from the postsynaptic membrane

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Chemical Synapse

junction where messenger molecules are released from one neuron to excite the next neuron

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Presynaptic Membrane

encloses molecules that transmit chemical messages; forms the axon terminal

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Postsynaptic Membrane

contains receptor molecules that receive chemical messages

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Microtubule

Transport structure that carries substances to the axon terminal

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Mitochondrion

Organelle that provides the cell with energy

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Storage Granule

Large compartment that holds synaptic vesicles

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Postsynaptic Receptor

site to which a neurotransmitter molecule binds

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Gap Junction

electrical synapse; where the prejunction and the postjunction cell membranes are fused. ion channels in on cell membrane connect to ion channels in the other membrane, forming a pore that allows ions to pass directly from one neuron to the next

20

Why do we rely mostly on chemical synapses when gap junctions send messages more quickly?

chemical synapses are flexible in controlling whether a message is passed from one neuron to the next, they can amplify or diminish a signal sent from one neuron to the next, and can alter their signals to mediate learning

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Neurotransmission Steps

1. Synthesis
2. Release
3. Receptor Action
4. Inactivation

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Neurotransmission Steps: 1. Synthesis

some neurotransmitters are transported from the cell nucleus to the terminal button and others are made from building blocks imported into the terminal and are packaged into vesicles there

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Neurotransmission Steps: 2. Release

In response to the action potential, the transmitter is released across the membrane by exocytosis; Ca+ flows in and binds to protein calmodulin and causes two chemical reactions--1. releases vesicles bound to presynaptic membrane 2. releases vesicles bound to microfilamens in the axon terminal

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Neurotransmission Steps: 3. Receptor Action

The transmitter crosses the synaptic cleft and binds to a receptor

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Neurotransmission Steps: 4. Inactivation

The transmitter is either taken back into the terminal or inactivated in the synaptic cleft

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Transporters

protein molecules that pump substances across the cell membrane; absorb required precursor chemicals from the blood supply for neurotransmitter synthesis

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Chemical Synapse

Junction at which messenger molecules are released when stimulated by an action potential

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Presynaptic Membrane

Membrane on the transmitter-output side of a synapse (axon terminal); rich in voltage-sensitive calcium channels (Ca+)

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Postsynaptic Membrane

Membrane on the transmitter-input side of a synapse (dendritic spine)

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Storage Granule

Membranous compartment that holds several vesicles containing a neurotransmitter

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Gap Junction (electrical Synapse)

Fused prejunction and postjunction cell membrane in which connected ion channels form a pore that allows ions to pass directly from one neuron to the next

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Transmitter-Activated Receptors

Protein that has a binding site for a specific neurotransmitter and is embedded in the membrane of a cell

33

In what ways can receptors affect the postsynaptic cell?

1. Depolarize the postsynaptic membrane--> excitatory action on the postsynaptic neuron
2. Hyperpolarize the postsynaptic membrane--> inhibitory action on the postsynaptic neuron
3. initiate other chemical reactions

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Autoreceptors

self-receptor in a neural membrane that responds to the neurotransmitters released from their own axon terminals

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Quantum

amount of neurotransmitter, equivalent to the contents of a single synaptic vesicle, that produces a just observable change in postsynaptic electric potential

36

What determines the amount of quanta released?

1. amount of Ca+ that enters the axon terminal
2. the number of vesicles docked at the membrane, waiting to be released

37

What are the four ways neurotransmitter deactivation can take place?

1. Diffusion
2. Degradation
3. Reuptake
4. Glial Cell

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Diffusion

some of the neurotransmitter simply diffuses away from the synaptic cleft and is no longer available to bind to receptors

39

Degradation

by enzymes in the synaptic cleft

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Reuptake

Membrane transporter proteins specific to that transmitter may bring the transmitter back to the presynaptic axon terminal for subsequent reuse

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Glial Uptake

some neurotransmitters are taken up by neighboring glial cells

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Types of Synapses

1. Dendrondentritic
2. Axodendritic
3. Axoextracellular
4. Axosomatic
5. Axosynaptic
6. Axoaxonic
7. Axosecretory

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Dendrondentritic

dendrites send messages to other dendrites

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Axodendritic

axon terminal of the neuron synapses on dendritic spine of another

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Axoextracellular

terminal with no specific target. Secrets transmitter into extracellular fluid

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Axosomatic

axon terminal ends on cell body

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Axosynaptic

axon terminal ends on another terminal

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Axoaxonic

axon terminal ends on another axon

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Axosecretory

axon terminal ends on tiny blood vessel and secretes transmitter directly into blood

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Axomuscular Synapse

axon synapses with a muscle end plate, releasing acetylcholine

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Axodendritic Synapse

axon terminal of a neuron ends on a dendrite or dendritic spine of another neuron

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Type I Synapses

excitatory in their actions; located on shafts or spines of dendrites; synaptic vesicles are rounded; material on pre and postsynaptic membranes is dense; wide synaptic cleft

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Type II Synapses

inhibitory in their actions; located on a cell body; synaptic vesicles are flattened; material on pre and postsynaptic membranes is sparse; narrow synaptic cleft

54

Four criteria for identifying neurotransmitters

1. chemical must be synthesized in the neuron or otherwise present in it
2. when the neuron is active, the chemical must be released and produce a response in some target
3. the same response must be obtained when the chemical is experimentally placed on the target
4. a mechanism must exist for removing the chemical from its site of action after its work is done

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Putative Transmitter

"supposed"; a suspect chemical that has not yet been shown to meet all the criteria

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Renshaw Loop

all motor neuron axons leaving the spine use ACh. Each axon has an axon collateral within the spinal cord that synapses on a CNS interneuron. Interneuron synapses back on the motor neuron's cell body

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Why does the Renshaw Loop exist?

enables the motor neuron to inhibit itself from becoming overexcited

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Modern criteria for a neurotransmitter

1. carries messages from one neuron to another by influencing the voltage on the postsynaptic membrane
2. have little effect on membrane voltage; have a common message carrying function
3. delivers message to the postsynaptic membrane and also sends a message the opposite direction to influence the release or reuptake of transmitters

59

What are the three classes of neurotransmitters?

1. small-molecule transmitters
2. peptide transmitters
3. transmitter gasses

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Small-Molecule Transmitters

ACh; quick acting; synthesized from dietary nutrients and packaged in axon terminals; can be quickly replaced at the presynaptic membrane; influenced by diet

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Histamine

type of small-molecule transmitter; control of arousal and of waking; can cause constriction of smooth muscles

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Acetylcholine Synthesis

choline + acetate; after ACh has been released into the cleft, an enzyme AChE detaches ACh and they are taken back into the presynaptic terminal

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Amine Synthesis

precursor chemical is tyrosine is transformed by the enzyme tyrosine hydroxylase into L-dopa, which is then converted into dopamine, norepinephine and then epinephrine

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Dopamine

Amine; has a role in Parkinson's

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Norepinephrine

Amine; excitatory transmitter at the amphibian heart

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Epinephrine

Amine; excitatory transmitter at the mammalian heart

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Rate-limiting factor

any enzyme that is in limited supply, thus restricting the pace at which a chemical can be synthesized

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Serotonin Synthesis

derived from the amino acid tryptophan

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Serotonin

role in regulating mood and aggression, appetite and arousal, respiration, and the perception of pain

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Amino Acid Synthesis

GABA is formed by a removal of COOH from the glutamate molecule

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Glutamate

amino acid neurotransmitter that excites neurons

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Gamma-Aminobutyric Acid (GABA)

amino acid neurotransmitter that inhibits neurons

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Neuropeptide Transmitters

synthesized through the translation of mRNA from instructions contained in the neuron's DNA, are multifunction chains of amino acids that act as neurotransmitters; most are made in the ribosomes (some in the axon terminal) packed by golgi bodies and transported by microtubules to axon terminals; activate synaptic receptors that indirectly influence cell structure and function

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Neuropepties

act as hormones that respond to stress, enable a mother to bond with child, regulate eating/drinking/pleasure/pan, contributes to learning

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Opioid Peptides

parts of the amino acid chains of some neuropeptides that deal with pleasure/pain--similar in structure to opium/morphine

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Transmitter Gases

synthesized in the cell as needed. After synthesis, each gas diffuses away easily crossing the cell membrane; activate metabolic processes in cells; NO and CO

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Nitric Acid

type of transmitter gas; controls muscles in intestinal walls, dilates blood vessels in active parts of the brain (allowing them to receive more blood), producing erections

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Carbon Monoxide

Gas that acts as a neurotransmitter in the activation of cellular metabolism

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Ionotropic Receptor

embedded membrane protein that acts as 1. binding site for a neurotransmitter and 2. a pore that regulates ion flow to directly and rapidly change membrane voltage

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Metabotropic Receptor

embedded membrane protein, with a binding site for neurotransmitter but no pore, linked to a G protein that can affect other receptors or act with second messengers to affect other cellular processes

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G Protein

guanyl-nucleotide-binding protein coupled to a metabotropic receptor that when activated, binds to other proteins; three subunits: alpha, beta, gamma

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Second Messenger

chemical that carries a message to initiate a biochemical process when activated by a neurotransmitter (the first messenger)

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What are second messengers able to do?

1. bind to a membrane channel, causing the channel to change its structure and thus alter ion flow through the membrane
2. initiate a reaction that causes protein molecules within the cell to become incorporated into the cell membrane (ex. formation of new ion channels)
3. instruct the cell's DNA to initiate or cease the production of a protein

84

Cholinergic Neurons

aka motor neurons; ACh is main neurotransmitter; are excitatory at skeletal muscles--> produce muscular contraction

85

Parasympathetic Neurons

CNS ACh neurons synapse with parasympathetic ACh neurons to prepare the organs for rest and digest

86

Sympathetic Neurons

ACh neurons in the CNS synapse with NE to prepare for fight or flight; NE increases heart rate and turns down digestive functions

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Activating System

neural pathways that coordinate brain activity through a single neurotransmitter; cell bodies are located in a nucleus in the brainstem and axons are distributed through a wide region to the brain

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Alzheimer's Disease

degenerative brain disorder related to aging that first appears as progressive memory loss and later develops into generalized dementia

89

Cholinergic System

plays a role in normal waking behavior and is thought to function in attention and in memory

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Dopaminergic System

operates on two distinct pathways (nigostriatial dopaminergic --> movement) (mesolimbic dopaminergic --> addiction)

91

Excessive DA activity

plays a role in schizophrenia

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Noradrenergic Neuron

neuron using noradrenaline (epinephrine) as its transmitter; may play a role in learning; facilitate normal brain development; role in organizing movements

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Problems associated with NE

decreased NE--> depression
decreased NE--> ADHD
increased NE--> Mania

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Serotonergic System

maintains waking EEG; wakefulness; learning;

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problems associated with SE

decreased SE--> depression
increased SE--> schizophrenia
OCD, sleep apnea, SIDS

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Learning

relatively permanent change in behavior that results from experience

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Habituation

learning behavior in which a response to a stimulus weakens with repeated stimulus presentations

98

Sensitization

learning behavior in which the response to a stimulus strengthens with repeated presentations of that stimulus because the stimulus is novel or because the stimulus is stronger than normal, ex. after habituation has occured

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PTSD

syndrome characterized by physiological arousal symptoms related to recurring memories and dreams related to a traumatic events for months or years after the event

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Neural basis of sensitization

in response to an action potential traveling down the axon of the siphon sensory neuron, the potassium channels on that neuron are slower to open. K+ ions cannot repolarize the membrane as quickly as it is normal, so the action potential lasts longer than it usually would

101

where does habituation take places?

Ca+ channels

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where does sensitization take place?

K+ channels