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
