Exam 2 Flashcards
How did Loewi’s experiment show chemical communication across a synapse?
He electrically stimulated a heart in one container and transferred the fluid in that container to a heart in another container and observed that both hearts reacted the same way; one reacting to the electrical impulse and one reacting to nothing more than fluid.
What is a neurotransmitter?
chemical with an excitatory or inhibitory effect when released by a neuron onto a target
What are the criteria for determining a neurotransmitter?
- Must be synthesized in the neuron or otherwise be present in it
- When the neuron is active, the transmitter must be released and produce a response in some target
- The same response must be obtained when the transmitter is experimentally placed on the target
- A mechanism must exist for removing the transmitter from its site of action after its work is done
What are the parts of a synapse?
Microtubule - transport structure that carries substances to the axon terminal
Mitochondrion - organelle that provides the cell with energy
Synaptic vesicle - round granule that contains neurotransmitters
Storage granule - large compartment that holds synaptic vesicles
Postsynaptic receptor - site to which a neurotransmitter molecule binds
Post synaptic membrane - contains receptor molecules that receive chemical signals
Synaptic cleft - small space separating presynaptic terminal and postsynaptic dendritic spine
Presynaptic membrane - encloses molecules that transmit chemical messages
What are the five steps of neurotransmitter transmission?
- Synthesis - neurotransmitters are created from precursor modules
- Packaging and Storing - neurotransmitters are moved into vesicles and await the arrival of an action potential
- Release - in response to an action potential, the transmitter is released across the membrane by exocytosis
- Receptor Action - the transmitter crosses the synaptic cleft and binds to a receptor
- Inactivation - the transmitter either diffuses away, is enzymatically broken down, is taken into the neuron terminal, or is taken by an astrocyte
What is the role of autoreceptors?
Part of the negative feedback loop, helps the neuron to manage output
What is the role of electrical synapses?
To provide faster information processing
What is the role of chemical synapses?
Show plasticity; they can amplify or diminish a signal sent from one neuron to the next; plays a role in learning
What are the types of chemical synapses?
Dendrodendritic - dendrites to dendrites
Axodendritic - axon terminal to dendritic spine
Axoextracellular - terminal with no specific target; release outside cell
Axosomatic - axon terminal to cell body
Axosynaptic - axon terminal to another terminal
Axoaxonic - axon terminal to another axon
Axosecretory - axon terminal to tine blood vessel
Excitatory vs Inhibitory synapse?
Excitatory - dense material on membranes, round vesicles, wide cleft, large active zone
Inhibitory - sparse material on membranes, flat vesicles, narrow cleft, small active zone
Describe a Renshaw Loop?
The main motor axon projects to a muscle and its axon collateral remains in the spinal cord to synapse with. The Renshaw interneuron contains the inhibitory transmitter glycine which acts to prevent motor neuron overexcitation. Both the main motor axon and its collateral terminals contain ACh.
How is ACh formed?
Acetyl CoA and ChAT bind choline and acetate
How is ACh degraded?
AChE detaches acetate from choline in the synaptic cleft
How are amine neurotransmitters formed?
Tyrosine hydroxylase changes tyrosine into L-DOPA which is then made into dopamine (DA), norepinephrine (NE), and epinephrine (EP)
What is a rate-limiting factor?
any chemical in low supply that restricts the pace at which another chemical can be synthesized
What disease can L-Dopa be used to help treat?
Parkinsons
What are two amino acid transmitters?
glutamate, gamma-aminobutyric acid (GABA)
How are peptide neurotransmitters created?
From mRNA in the neurons nucleus
Where are peptide neurotransmitters created?
Some in the axon terminal but most on the ribosome
Which amino acid neurotransmitter is the main inhibitory NT?
GABA
Which amino acid neurotransmitter is the main excitatory NT?
glutamate
What are the lipid neurotransmitters?
Endocannabinoids
What are the neurotransmitter gasses?
NO, CO, H2S
How do ionotropic receptors work?
When activated, embedded transmitter proteins bring about direct, rapid changes in membrane voltage
How do metabotropic receptors work?
When activated, embedded membrane receptor proteins trigger associated G proteins, exerting indirect effects (A) on nearby ion channels or (B) in the cell’s metabolic activity
What is a secondary messenger?
chemical that initiates a biochemical process when activated by a NT (first messenger)
What is an advantage to metabotropic receptors?
Amplification cascade
What is the main neurotransmitter for the PNS?
ACh
What are the main neurotransmitter for the SNS?
ACh and NE
What are some important facts for the Cholinergic system?
Active in maintaining attention, death of these neurons and decrease of ACh in neocortex thought to be linked to alzheimers
What are some important facts for the dopaminergic system?
active in maintaining normal motor behavior, loss of dopamine is related to Parkinson’s, thought to be most linked to addictive drugs and behavioral addictions, increases in dopamine activity linked to Schizophrenia, decreases may be linked to ADHD
What are some important facts for the noradrenergic system?
active in maintaining emotional tone, decreases thought to be linked to depression, increases thought to be linked to mania, decreases thought to be linked to ADHD
What are some important facts for the noradrenergic system?
changes are thought to be linked to OCD, tics, and Schizophrenia, decreases are linked to depression, abnormalities in brainstem 5-HT neurons linked to sleep apnea and SIDS