Synapses, chemical communication Flashcards
neurones communication: electrically VS chemically:
- electrical communication = movements of ions in an out of cell membranes
- chemical communication = release of neurotransmitters to nearby receptors at synapses
neurone communication process:
- at the connection btw 2 neurones = space (synaptic cleft, the synapse is where the conversion from an electrical signal to a chemical one occurs, particularly in chemical synapses), does not allow electrical current to flow, so a chemical signal = required as an intermediate.
(after becoming chemical, graded or AP in 2nd (post-synaptic cell).
Structures of synapses:
Presynaptic neurone
synaptic cleft
postsynaptic neurone
Presynaptic neurone:
neurone that transmits a signal to the synapse
- synaptic vesicle: sacs of chemicals released when signal reaches axon terminal
- neurotransmitters: chemicals found in synaptic vesicles that will excite postsynaptic neurone, muscle or gland
Synaptic cleft:
space between axon terminal + postsynaptic cell
- electrical signal can’t pass but chemical can !!
Postsynaptic neurone:
the neurone that receives the signal from the synapse
- neurotransmitter receptors = proteins found in postsynaptic cell membrane that bind to chemical neurotransmitter
- ion channels: proteins in postsynaptic cell membrane that open to allow electrical impulses to conduct through
SLIDE 11
Events at the synapse:
- pre-synaptic events at the axon terminal:
1) action- potential
2) Ca2 entry (voltage-gated Ca2 channels open and calcium enters axon terminal)
3) NT release (in synaptic vesicles) (it’s the Ca2 entry that causes exocytosis of vesicles and release of neurotransmitter at axon terminal) - post-synaptic events at the dendrites:
4) NT receptor activation
5) ions enter (neurotransmitter binding to receptor causes ion channel to open et they move to post-synaptic cell membrane)
6) graded potential (influx of ions in post-synaptic cell = graded potential at dendrite)
Post-synaptic potential (PSP):
graded potential in post-synaptic cell
- if positive ions flow in post-synaptic membrane = excitatory PSP
- if negative = inhibitory PSP
type of ion channel depends on neurotransmitter + its receptor
PSP’s:
their combination of activity determines whether cell reaches threshold for action potential.
also they can do it only if summed (not only one EPSP
axon hillock keeps score of:
all graded potentials received at dendrites
Temporal VS Spatial summation:
- temporal = 1 presynaptic = increases frequency of impulses = more neurotransmitters = released in quick succession (same location, stimulation increases timing)
- spatial summation = postsynaptic neurone = stimulated by multiple pre-synaptic neurones at the same time
(same timing, simulation increases locations) - IPSP and EPSPS can also be summed and cancel eachother out.
neurones normally = one neurotransmitters, but a lot can respond to several neurotransmitters
slide 29
Classification of neurotransmitters by chemical structure:
- AcH (has both excitatory and inhibitory effects) (slide 31)
- Biogenic amines: catecholamine + serotonin
- Amino acids: glutamine, glycine, GABA
- Peptides: endorphins, substance p
- Chemical messengers: ATP + dissolved gases NO
neurotransmitters that open ion channels = direct:
- promote rapid response (fast synapses)
- ex: AA’s + AcH
neurotransmitters that act through 2nd messenger = indirect:
- promote long lasting effects “slow synapses”
- ex: biogenic amines + peptides + dissolved gases
effects of neurotransmitters:
mediate changes in membrane depending on: amount of neurotransmitters released + amount of time neurotransmitter = bound to receptor
neurotransmitters = always affect the receptor donc must be deactivated
Deactivation of neurotransmitters effects:
- Active transport: neurotransmitter = actively pumped back to pre-synaptic or nearby neuroglia
- Enzymes: present in synaptic cleft = will breakdown neurotransmitter to stop signal
- Diffusion: neurotransmitter = diffuses away enough from cleft for signal to stop (slide 36)
AcH enzymes:
Acetylcholinesterase: enzyme in synaptic cleft that degrades AcH
AcH = transferred back to presynaptic terminal to make more AcH with the help of enzyme ChAT
(AcH = made by AcetylCoA + choline)
drug synaptic activity altering actions:
- synthesis, storage, release of neurotransmitters
- modifying neurotransmitter interaction with its receptor
- influencing neurotransmitter reuptake or destruction
- replacing deficient neurotransmitter with a substitute
(ex: SSRI + tetanus toxin)
Convergent pathways:
one cell = influenced by many others
Divergent pathways:
one cell = influences many others
sensory processing functions:
- Attention + arousal
- perception of the world around us
- memory
- emotion