Synapse Flashcards
Synapse
specialized junction where the axon terminal contacts with another neuron or cell type. Mediate information and impulse
- CNS synapse examples:
Axodentritic: axon to dendrite
Axosomatic: axon to cell body
Axoaxonic: axon to axon
Dendrodentritic: dendrite to dendrite
NMJ
neuronal muscle junction:
muscle and neuron
how many synapses are in a neuron?
1,000 - 10,000
what are 2 types of synapses?
- chemically
- electrical
electrical synapses
- Direct transfer of ionic current from one cell to the next
- Ions can flow bidirectionally
- Cells are electrically coupled
- Speed is very fast
- Common in neuronal cells
chemical synapses
Occur between neurons and between neurons and muscle cells
what are the steps of releasing a neurotransmitter?
- Neurotransmitter is synthesized and then stored in
the vesicles - Action potential enters the axon terminal (presynaptic
terminal) - Depolarization of presynaptic terminal causes
opening of voltage gated Ca++ channels - Influx of Ca++ through channels
- Ca++ activates proteins in the vesicles and active zone
Activated proteins causes synaptic vesicles to fuse
with membrane - Neurotransmitter is release -> exocytosis
- Transmitter binds with receptor molecules in
postsynaptic membrane - Opening or closing of postsynaptic channels
- Postsynaptic causes excitatory or inhibitory
postsynaptic potential that changes the excitability of
the postsynaptic cells - Retrieval of vesicular membrane from the plasma
membrane
what is the criteria to be a neurotransmitter?
A substance that transmits nerve impulses across the synapse
- Must be present at presynaptic terminal
- Released by depolarization (Ca++ -dependent)
- Specific receptors must be present
- When added extracellular fluid, must mimic the effects of presynaptic stimulation
- A mechanism for removal should exist
- Effects of drugs must block/ mimic the neurotransmitter physiological effects
2 classifications of neurotransmitters?
- excitatory (depolarization)
- inhibitory (hyperpolarization)
Acetylcholine
stimulates muscle contraction, hormone release, in CNS wakefulness, attentiveness, anger, aggression, thirst
Glutamate
excitatory neurotransmitter associated with learning and memory
Dopamine
Inhibitory neurotransmitter, controlling movement, posture, in CNS, positive reinforcement, dependency
GABA
inhibitory neurotransmitter, in CNS, motor control, vision, other cortical
Norepinephrine
`attentiveness, emotion, sleepin, dreaming, learning’ also controls fight or flight reactions, heart stimulator vasoconstrictor
Serotonin
regulate body temperature, mood, sleep, appetite, pain, depression, impulsive behavior
2 major categories of receptors
- Transmitter (ligand) gated ion channels
- G-protein coupled receptors
*Ligand binding to the receptors activates G proteins. Serves as a molecular “on-off” switch
EPSPs
Excitatory postsynaptic potential
- open up ligand-gated Na+ channels (Na+ comes in)
- Moves resting membrane potential TOWARD threshold (depolarization)
IPSPs
Inhibitory postsynaptic potentials
- Open up ligand-gated Cl- channels (Cl- comes in)
- Moves resting membrane potential AWAY from the threshold (hyperpolarization)
Temporal summation
if EPSP in pre-synaptic knob are successively repeated without delay so the effect of the previous stimulus is summated to the next
Spatial summation
when EPSP is in more than one synaptic knob at the same time
Modification of synaptic transmission
- Drugs act by interfering with or stimulating normal process in the neuron involved in neurotransmitter synthesis, storage, and release, and in receptor activation
- Disease can also affect synaptic mechanisms
What do you think that can change neurons and their connections?
- accidents
- diseases
- drugs and alcohols
A chemical synapse is a…
- Direct connection of channels between cells that allow the flow of neurotransmitters
- Space between neurons that acquire the diffusion of a neurotransmitter to affect the next cell
- Direct connection of channels between cells that allow the flow of ions
- Space between neurons, require the diffusion of ions to affect the next cell
Space between neurons that acquire the diffusion of a neurotransmitter to affect the next cell
Arrange the events in the correct sequence when the action potential reaches the terminal knob
a. Influx of Ca++ through channels
b. Transmitter binds to the receptor molecules in postsynaptic membrane
c. Depolarization of presynaptic terminal causes opening of voltage gated Ca++ channels
d. Neurotransmitter is released via exocytosis
e. Action potential enters the axon terminal
f. Ca++ activates proteins in the vesicle and active zone. Activated proteins causes synaptic vesicles to fuse with membrane
E-C-A-F-D-B
Excitatory postsynaptic potentials (EPSP) open________
Ligand-gated Na+ channels
ligand -gated K+ channels
Ligand-gated Cl- channels
All of the above
all the above
Spatial summation takes place when_______
EPSP is in more that one synaptic knob at the same time
EPSP in pre-synaptic knob are successively repeated without significant delay
both
EPSP is in more that one synaptic knob at the same time
Are action potentials and graded potentials the same?
True
False
false
