Chapter 12.3 : The Synapse and The Neurotransmitter Flashcards
chemical synapse
neurons communicate by releasing chemicals
acetylcholine
the first discovered neurotransmitter
takes 0.50 milliseconds for a neurotransmitter to cross the _________
chemical synapse distance
A nerve’s action potential can go no further than to the
synaptic knob / distal end of the axon
A chemical synapse consist of three components
– Pre-synaptic membrane
– Synaptic cleft
– Post-synaptic membrane
When a synapse is between two neurons, the 1st neuron in the signal pathway is called
the _______ ______ / it releases
neurotransmitter. 2nd neuron is the _____ _____ / it has receptors for the neurotransmitter
presynaptic neuron ; postsynaptic neuron
Presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have Presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have
receptors with ligand-regulated ion channels_____ with ligand-regulated ion channels
receptors
spinal cord motor neuron soma have about _______ from other neurons
10,000 unique synaptic knobs
- 8,000 ending on its dendrites
- 2,000 ending on its soma
Cerebellum’s soma may have as many as _______ synapses
100,000
synaptic knob stores _______ ______ containing neurotransmitters
synaptic vesicles
synaptic vesicles are docked on ___________ of the __________ / ready to release neurotransmitter on demand
release sites ; plasma membrane
postsynaptic neuron receptors function as _____________________
ligand-regulated ion gates
The presynaptic neuron may synapse with
- Dendrite
- Soma
- Axon of postsynaptic neuron
The presynaptic neuron form different types of synapses
- Axodendritic synapses
- Axosomatic synapses
- Axoaxonic synapses
Gap junctions can be thought of as a type of synapse which
allows action potentials to move rapidly between adjacent cells
Gap junctions join ___________ /// ions diffuse through
the gap junctions from one cell to the next
adjacent cells
Advantage
quick transmission // no delay for release and binding of neurotransmitter // cardiac and smooth muscle, embryonic cells, and some neurons
Disadvantage
they cannot integrate information and make decisions
Two Types of Neurotransmitter Receptors
Ionotropic receptors and metabotropic receptors
Ionotropic receptors
– Ligand binds to integral protein channels which allows either cation or anion to cross plasma membrane
– Ligand receptor and ion channel are part of same protein
– If cations enter cell then it depolarizes / if anions enter cell then it hyperpolarizes
Metabotropic receptors
– ligand receptor and ion channel have different types of integral proteins
– metabotropic receptors are “ligand receptors” on external face of membrane that releases “G protein” on their internal face of membrane
– G protein travels to a second integral protein and this intergral protein then functions as the ion channel
– this is Second messenger sytem
Synaptic delay. How long it take for the complex sequence of
events to occur
time from the arrival of a signal at the axon terminal of a presynaptic cell to the beginning of an action potential in the
postsynaptic cell
– 0.5 msec for all the complex sequence of
events to occur
What are neurotransmitters synthesized by?
in soma and transported down axon of presynaptic neuron
How do neurotransmitters alter the the post-synaptic membrane?
Neurotransmitter moves resting membrane potential towards threshold or away from threshold
often, it is the _______ and not the ________ that will
dictate the outcome
receptor ; neurotransmitter
One type of neurotransmitters may may have different effect on different __________ throughout the body
target tissue
There are multiple receptors that exist for each ______________
neurotransmitter
It is the ______ that determines the effect of the neurotransmitter on the target cell
receptor
Ionotropic receptors are always
stimulatory
Metabotropic acetylcholine receptors can be
either stimulatory or inhibitory // depends on downstream effect of the second integral protein which is activated by the G protein
the same molecule in different ________ may
function as a _______, a _________, or a ___________
mechanisms ; hormone ; neurotransmitter ; neuromodulator
more than ___ neurotransmitters have been identified
100
major neurotransmitter categories according to chemical composition : Monoamines’ subcategory Catecholamines
Epinephrine, Norepinephrine, and Dopamine
major neurotransmitter categories according to chemical composition : Monoamines’ subcategory Indoamines
histamine and serotonin
major neurotransmitter categories according to chemical composition : Ace_______
tylcholine
major neurotransmitter categories according to chemical composition : Amino acids
GABA, Glycine, Aspartic acid, Glutamic acid.
major neurotransmitter categories according to chemical composition : Neuropeptides
Enkephalin, Substance P, Cholecystokinin, and ß-endorphin
Monoamines (AKA __________)
Biogenic Amines
synthesized from amino acids by removal of the –COOH group // retaining the –NH2 (amino) group
___ and ______ bind to monamine receptors
LSD ; mescaline
Neuropeptides types
substance P, endorphins, enkephalins
(i.e. endogenous opioids) /// this class also include gutbrain peptides (produced my non-neural tissue but have
receptors in the brain)
Pruines
adenosine triphosphate (ATP) / now recognized
as major neurotransmitter in CNS and PNS
adenosine triphosphate (ATP) / now recognized
as major neurotransmitter in ________
CNS and PNS
Gases & Lipids
nitric oxide (NO) & carbon monoxide // activate guanylyl cyclase / function in brain / hydrogen sulfide // (note: NO causes smooth muscle to dialate)
Endocannabinoids
(or simply cannabinoids) // brain neurotransmitter / tetrahydrocannabiol (THC) interacts
with the endocannabinoid receptors
Neuropeptides
- chains of 2 to 40 amino acids
- act at lower concentrations than
other neurotransmitters - longer lasting effects
- stored in axon terminal as larger
secretory granules (called
dense-core vesicles)
Some neuropeptides also released from digestive tract /// Note: _______ cause food cravings
gut-brain peptides
Neurotransmitters are diverse in their _____
action
Ionotropic receptors are simply
ion channels
Metabotropic receptors are __________________ // provide varible __________ outcomes
second messenger systems ; downstream
each synapse will use a different type of _________ and ____________________
neurotransmitter ; post synaptic receptor
three different types of synapses
– excitatory cholinergic synapse (ionotropic)
– inhibitory GABA-ergic synapse (ionotropic)
– excitatory adrenergic synapse (metabotropic)
excitatory cholinergic synapse is
(ionotropic)
inhibitory GABA-ergic synapse is
(ionotropic)
excitatory adrenergic synapse is
(metabotropic)
metabotropic
second messenger system receptor) /// this
maybe either inhibitory or excitatory
cholinergic synapse
employs acetylcholine (ACh) as its neurotransmitter
– ACh excites some (most!) postsynaptic cells (e.g. skeletal muscle
– may inhibits others (e.g. cardiocytes at AV n44ode)
Describing the excitatory action
– nerve signal approaching the synapse //
opens the voltage-regulated calcium gates at
junction between axon and synaptic knob
– Ca2+ enters the knob // triggers exocytosis of
synaptic vesicles releasing Ach
– empty vesicles drop back into the cytoplasm
to be refilled with Ach
– reserve pool of synaptic vesicles move to the
active sites and release their Ach
– ACh diffuses across the synaptic cleft
– nerve signal approaching the synapse //
opens the voltage-regulated calcium gates at
junction between axon and synaptic knob
– Ca2+ enters the knob // triggers exocytosis of
synaptic vesicles releasing Ach
– empty vesicles drop back into the cytoplasm
to be refilled with Ach
– reserve pool of synaptic vesicles move to the
active sites and release their Ach
– ACh diffuses across the synaptic cleft
Inhibitory GABA-ergic Synapse
- GABA-ergic synapse employs -
aminobutyric acid as its neurotransmitter - nerve signal triggers release of GABA into
synaptic cleft - GABA receptors are chloride channels ///
ionotropic receptor type - Cl- enters cell and makes the inside more
negative than the resting membrane
potential /// move away from threshold! - postsynaptic neuron is inhibited
- less likely to fire
GABA receptors are ________ ________ ///
ionotropic receptor type
chloride channels
Adrenergic synapse employs the neurotransmitter
_____________ also called noradrenaline
norepinephrine (NE)
The receptor on post synaptic membrane for the adrenergic
synapses is type __________
metabotropic
– not an ion gate but second messenger system
– a transmembrane protein associated with a G protein (i.e.
metabotropic receptor)
NE , monoamines, and neuropeptides acts through NE , monoamines and neuropeptides acts through ________________
second messenger systems
