NEU Quiz 3 - The Synapse Neurotransmission Flashcards
The Synapse:
Information flows from neuron to neuron via synapses as a site of communication from a neuron to another neuron or to a cell (like a muscle).
Presynaptic neuron:
axon terminal a neuron conducting impulses toward synapse → Sends information
Postsynaptic neuron:
→ CNS always a neuron (in PNS may be a neuron, muscle cell, or gland cell; called end organ or effector) - dendrite. Neuron transmitting electrical signal away from synapse → Receives information
2 Classes in Postsynaptic neuron:
Electrical – gap junctions
Chemical – synaptic space requires neurotransmitter → is more important for this class → direct ion flow and depolarization occurring and can move in either direction
Electrical Synapses:
2 neurons or cells joined by gap junctions
- Paired channels – connexONs
– Each connexon made up of channel proteins - connexINs
Direct flow of current between neurons
– Transmission between neurons nearly instantaneous
Synchronizes electrical activity in group of neurons
– Ex: neurons in brainstem that control breathing rate and rhythm
Where does the signal go from the end of the neuron?
Chemical Synapse → Junction between 2 neurons consisting of a gap that allows chemical signals (but not electrical ones!) to pass
- Site of communication from: one neuron to another OR one neuron to a cell (like a skeletal or gut muscle cell)
Chemical Synapses:
Specialized for release and reception of chemical neurotransmitters
Composed of two parts
- Axon terminal of presynaptic neuron
– Contains synaptic vesicles filled with neurotransmitter - Neurotransmitter receptor - region on postsynaptic neuron’s membrane
– Usually on dendrite or cell body - Two parts separated by synaptic cleft
– Fluid-filled space
Electrical impulse changed to chemical across synapse, then back into electrical
List the steps of synaptic transmission in order:
when an action potential travels down neuron and reaches axon terminal this causes depolarization
AP in presynaptic neuron opens voltage- gated Ca2+ channels in axon terminal
- Ca2+ releases vesicles from cytoskeleton
Neurotransmitter diffuses across synapse
- NT binds to receptors
- Ion channels are opened
Causes an excitatory or inhibitory potential
A neuron can release more than one type of neurotransmitter!
Neurotransmitters are ineffective without appropriate postsynaptic receptors
What are the two types of postsynaptic potentials, and how do these change membrane voltage?
Neurotransmitter receptors cause different types of reactions in postsynaptic neurons
Types of postsynaptic potentials:
EPSP—excitatory postsynaptic potentials
— Leads to depolarization of neurons – excites post-syn. Neuron
IPSP—inhibitory postsynaptic potentials
— Leads to hyperpolarization of neurons – inhibits post-syn. Neuron
How are EPSPs and IPSPs summed by a postsynaptic neuron? Include the two different summation types and when each of these occur.
EPSPs + IPSPs additive
Temporal summation: Rapid repeat EPSPs same location (EPSP lasts a while)
- add and sum to produce AP
Spatial summation:
simultaneous EPSPs in diff. parts of neuron
- add and sum to produce AP
Simultaneous EPSP and IPSP in diff. parts of neuron
- Add and reduce chance of AP
What are the three main ways that neurotransmitter effects are terminated?
Within a few milliseconds neurotransmitter effect terminated in one of three ways
Reuptake in presynaptic neuron → By astrocytes or axon terminal
Degradation → By enzymes — Ex: Acetylcholine degraded by acetylcholinesterase
Diffusion → Away from synaptic cleft
Neurotransmitters:
chemical substance released at the end of a neuron that communicates with another cell
Three criteria that define a neurotransmitter:
- must be present in the presynaptic neuron
- must be released in response to a depolarization, and be Ca2+ dependent
- must have specific receptors localized on the postsynaptic cells
note: it does not have to be uniquely a neurotransmitter, may have other functions (ex. glutamate, glycine, ATP are all neurotransmitters)
4 categories of neurotransmitters:
- Amino Acid
*Glutamate – CNS- Excitatory b
*GABA – CNS- Inhibitory
*Glycine – CNS - Inhibitory - Monoamines
*Dopamine – CNS – Learning, euphoria, movement → parkinson’s is death of dopamine
*Norepinephrine – CNS: arousal (wakefulness), fight or flight
*Serotonin (5HT) – Sleep, Mood - Small Molecule a
*Acetylcholine (ACh) – Muscle contraction - Neuropeptides
*Substance P – Pain sensation
*Endorphin (Endo=endogenous, orphin = morphine) – Decrease pain sensation
Receptors - Two types:
Ionotropic (AA Rs; ACh Rs):
- Allow ions to flow through a central pore
- EPSP or IPSP
- Fast/brief
Metabotropic (Monamine Rs; Neuropeptide Rs): opioids!
- Change signaling inside cell
- Usually G protein coupled receptors
- Slow/longer lasting
Divergent pathway affecting postsynaptic:
one presynaptic neuron branches to affect a larger number of postsynaptic neuron
Convergent pathway affecting postsynaptic:
many presynaptic neurons converge to influence a smaller number of postsynaptic neurons
What is the action of the neurotransmitter at a chemical synapse?
It acts on receptors in the postsynaptic membrane.
A postsynaptic neuron has three other neurons that synapse onto it, with synapses located nearby to each other. Two are excitatory, and one is inhibitory. The first presynaptic neuron elicits an EPSP of +5mV. The second presynaptic neuron elicits an EPSP of +14mV. The third presynaptic neuron elicits an IPSP of -10mV What is the new membrane potential for this cell?
( -70) + (+9) = -61mv → add them all together
A postsynaptic neuron has three other neurons that synapse onto it, with synapses located nearby to each other. Two are excitatory, and one is inhibitory. The first presynaptic neuron elicits an EPSP of +5mV. The second presynaptic neuron elicits an EPSP of +14mV. The third presynaptic neuron elicits an IPSP of -10mV. Will this postsynaptic neuron fire an action potential?
No not yet we are closer and are depolarized
What is the main excitatory neurotransmitter in the adult brain?
GABA
Glutamate
Dopamine
Serotonin
Norepinephrine
Glutamate
Which statement regarding metabotropic and ionotropic receptors is true?
Ionotropic receptors have immediate effects; metabotropic receptors produce long-term effects.
What ion must be present in the axon terminal for vesicles full of neurotransmitters to fuse to the presynaptic membrane for release?
Ca2+
What is the main inhibitory neurotransmitter in the adult brain?
Gamma-aminobutyric acid (GABA)
Which of the following might be a way in which the tetanus toxin causes muscle spasm (Select all that apply)?
Which of the following is likely the way in which tetanus toxin works?
Greatly increase the permeability of the pre-synaptic neuron to Na+ at rest
Block the fusion of GABA- filled vesicles to pre-synaptic cell membrane
Block the fusion of GABA-filled vesicles to pre-synaptic cell membrane
What do you think would happen in neurons that have this mutation(CATA)?
Which of the following might be the reason you ran this genetic test?
Which of the following medications could be used to treat BB (Select all that apply)?
Increased release of NT to the post-synaptic neuron
Increased flow of Ca2+ into the axon terminal
BB was having seizures
- Progabide, a drug that binds to and increases activity at GABA receptors
- Experimental drugs that enhance activity of EAAT2, the pump that causes reuptake of glutamate into the astrocyte
- Pregabalin, a drug that blocks voltage gated calcium channels
- Tegretol, a drug that holds voltage gated Na+ channels in the inactive conformation for a longer time
- Experimental drugs that inhibit GlyT1, the pump that causes reuptake of glycine into the astrocyte
Are dopamine receptors ionotropic or metabotropic?
Do you predict that anti-psychotic medications increase or decrease
dopaminergic signaling? Research: what are common drugs used to treat schizophrenia?
Do ketamine and PCP target ionotropic or metabotropic glutamate receptors? Given this, which glutamate receptor subtype do you anticipate is more involved in
schizophrenia?
Metabotropic
decrease
ionotropic
