Chapter 5 Flashcards
Acetylcholine (ACh)
activates skeletal muscles in SNS; inhibits heart beats; may inhibit OR excite organs in the autonomic system
Epinephrine
AKA Adrenaline; mobilizes body during flight or fight
Norepinephrine
AKA Noradrenaline; accelerates heart beat in mammals
Neurotransmitter
chemical released by a neuron onto a target with an excitatory or inhibitory effect
What are neurotransmitters outside of the nervous system called?
Hormones
What disease does Dopamine play a role in?
Parkinson’s Disease
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
Synaptic Vesicles
Organelle consisting of a membrane structure that encloses a quantum or neurotransmitter
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
Dopamine
Amine neurotransmitter; plays a role in coordinating movement, attention, learning, and behaviors that are reinforcing
Synaptic Cleft
Gap that separates the presynaptic membrane from the postsynaptic membrane
Chemical Synapse
junction where messenger molecules are released from one neuron to excite the next neuron
Presynaptic Membrane
encloses molecules that transmit chemical messages; forms the axon terminal
Postsynaptic Membrane
contains receptor molecules that receive chemical messages
Microtubule
Transport structure that carries substances to the axon terminal
Mitochondrion
Organelle that provides the cell with energy
Storage Granule
Large compartment that holds synaptic vesicles
Postsynaptic Receptor
site to which a neurotransmitter molecule binds
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
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
Neurotransmission Steps
- Synthesis
- Release
- Receptor Action
- Inactivation
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
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
Neurotransmission Steps: 3. Receptor Action
The transmitter crosses the synaptic cleft and binds to a receptor
Neurotransmission Steps: 4. Inactivation
The transmitter is either taken back into the terminal or inactivated in the synaptic cleft
Transporters
protein molecules that pump substances across the cell membrane; absorb required precursor chemicals from the blood supply for neurotransmitter synthesis
Chemical Synapse
Junction at which messenger molecules are released when stimulated by an action potential
Presynaptic Membrane
Membrane on the transmitter-output side of a synapse (axon terminal); rich in voltage-sensitive calcium channels (Ca+)
Postsynaptic Membrane
Membrane on the transmitter-input side of a synapse (dendritic spine)
Storage Granule
Membranous compartment that holds several vesicles containing a neurotransmitter
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
Transmitter-Activated Receptors
Protein that has a binding site for a specific neurotransmitter and is embedded in the membrane of a cell
In what ways can receptors affect the postsynaptic cell?
- Depolarize the postsynaptic membrane–> excitatory action on the postsynaptic neuron
- Hyperpolarize the postsynaptic membrane–> inhibitory action on the postsynaptic neuron
- initiate other chemical reactions
Autoreceptors
self-receptor in a neural membrane that responds to the neurotransmitters released from their own axon terminals
Quantum
amount of neurotransmitter, equivalent to the contents of a single synaptic vesicle, that produces a just observable change in postsynaptic electric potential
What determines the amount of quanta released?
- amount of Ca+ that enters the axon terminal
2. the number of vesicles docked at the membrane, waiting to be released
What are the four ways neurotransmitter deactivation can take place?
- Diffusion
- Degradation
- Reuptake
- Glial Cell
Diffusion
some of the neurotransmitter simply diffuses away from the synaptic cleft and is no longer available to bind to receptors
Degradation
by enzymes in the synaptic cleft
Reuptake
Membrane transporter proteins specific to that transmitter may bring the transmitter back to the presynaptic axon terminal for subsequent reuse
Glial Uptake
some neurotransmitters are taken up by neighboring glial cells
Types of Synapses
- Dendrondentritic
- Axodendritic
- Axoextracellular
- Axosomatic
- Axosynaptic
- Axoaxonic
- Axosecretory
Dendrondentritic
dendrites send messages to other dendrites
Axodendritic
axon terminal of the neuron synapses on dendritic spine of another
Axoextracellular
terminal with no specific target. Secrets transmitter into extracellular fluid
Axosomatic
axon terminal ends on cell body
Axosynaptic
axon terminal ends on another terminal
Axoaxonic
axon terminal ends on another axon
Axosecretory
axon terminal ends on tiny blood vessel and secretes transmitter directly into blood
Axomuscular Synapse
axon synapses with a muscle end plate, releasing acetylcholine
Axodendritic Synapse
axon terminal of a neuron ends on a dendrite or dendritic spine of another neuron
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
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
Four criteria for identifying neurotransmitters
- chemical must be synthesized in the neuron or otherwise present in it
- when the neuron is active, the chemical must be released and produce a response in some target
- the same response must be obtained when the chemical is experimentally placed on the target
- a mechanism must exist for removing the chemical from its site of action after its work is done
Putative Transmitter
“supposed”; a suspect chemical that has not yet been shown to meet all the criteria
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
Why does the Renshaw Loop exist?
enables the motor neuron to inhibit itself from becoming overexcited
Modern criteria for a neurotransmitter
- carries messages from one neuron to another by influencing the voltage on the postsynaptic membrane
- have little effect on membrane voltage; have a common message carrying function
- delivers message to the postsynaptic membrane and also sends a message the opposite direction to influence the release or reuptake of transmitters
What are the three classes of neurotransmitters?
- small-molecule transmitters
- peptide transmitters
- transmitter gasses
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
Histamine
type of small-molecule transmitter; control of arousal and of waking; can cause constriction of smooth muscles
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
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
Dopamine
Amine; has a role in Parkinson’s
Norepinephrine
Amine; excitatory transmitter at the amphibian heart
Epinephrine
Amine; excitatory transmitter at the mammalian heart
Rate-limiting factor
any enzyme that is in limited supply, thus restricting the pace at which a chemical can be synthesized
Serotonin Synthesis
derived from the amino acid tryptophan
Serotonin
role in regulating mood and aggression, appetite and arousal, respiration, and the perception of pain
Amino Acid Synthesis
GABA is formed by a removal of COOH from the glutamate molecule
Glutamate
amino acid neurotransmitter that excites neurons
Gamma-Aminobutyric Acid (GABA)
amino acid neurotransmitter that inhibits neurons
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
Neuropepties
act as hormones that respond to stress, enable a mother to bond with child, regulate eating/drinking/pleasure/pan, contributes to learning
Opioid Peptides
parts of the amino acid chains of some neuropeptides that deal with pleasure/pain–similar in structure to opium/morphine
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
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
Carbon Monoxide
Gas that acts as a neurotransmitter in the activation of cellular metabolism
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
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
G Protein
guanyl-nucleotide-binding protein coupled to a metabotropic receptor that when activated, binds to other proteins; three subunits: alpha, beta, gamma
Second Messenger
chemical that carries a message to initiate a biochemical process when activated by a neurotransmitter (the first messenger)
What are second messengers able to do?
- bind to a membrane channel, causing the channel to change its structure and thus alter ion flow through the membrane
- initiate a reaction that causes protein molecules within the cell to become incorporated into the cell membrane (ex. formation of new ion channels)
- instruct the cell’s DNA to initiate or cease the production of a protein
Cholinergic Neurons
aka motor neurons; ACh is main neurotransmitter; are excitatory at skeletal muscles–> produce muscular contraction
Parasympathetic Neurons
CNS ACh neurons synapse with parasympathetic ACh neurons to prepare the organs for rest and digest
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
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
Alzheimer’s Disease
degenerative brain disorder related to aging that first appears as progressive memory loss and later develops into generalized dementia
Cholinergic System
plays a role in normal waking behavior and is thought to function in attention and in memory
Dopaminergic System
operates on two distinct pathways (nigostriatial dopaminergic –> movement) (mesolimbic dopaminergic –> addiction)
Excessive DA activity
plays a role in schizophrenia
Noradrenergic Neuron
neuron using noradrenaline (epinephrine) as its transmitter; may play a role in learning; facilitate normal brain development; role in organizing movements
Problems associated with NE
decreased NE–> depression
decreased NE–> ADHD
increased NE–> Mania
Serotonergic System
maintains waking EEG; wakefulness; learning;
problems associated with SE
decreased SE–> depression
increased SE–> schizophrenia
OCD, sleep apnea, SIDS
Learning
relatively permanent change in behavior that results from experience
Habituation
learning behavior in which a response to a stimulus weakens with repeated stimulus presentations
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
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
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
where does habituation take places?
Ca+ channels
where does sensitization take place?
K+ channels
