Neuro: Chapter 8 Synaptic Transmission Between Neurons

Front 1

synapse

Back 1

a junction that mediates transformation of information from one neuron to another neuron on an effector cell. the effector cell may be either a muscle or gland cell

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presynaptic neuron

Back 2

impulses twd the synapse

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postsynaptic

Back 3

pulses away from the synapse

Front 4

synaptic cleft

Back 4

-fluid filled space seperating pre & post synaptic neurons
-prevents direct transmission of AP

Front 5

transmission across synaptic cleft is....

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- unidirectional
-a chemical event
-involves release, diffusion and binding of neurotransmitters

Front 6

what are the advantages of chemical synapses?

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-can amplify via the amt of neurotransmitter released
-may be excitatory or inhibitory
- have modifiable-ness which is important for memory and learning

Front 7

what are the steps involved in information transfer at a synapse?

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-AP arrives at pre-synaptic terminal, voltage gated Ca2+ channels open.
-Ca2+ promotes fusion of vesicles to axon membrane and exocytosis occurs
-neurotransmitter diffuses and binds to receptors on post-synaptic neuron
-ion channels open- creating a graded potential and causing an excitatory or inhibitory event

Front 8

how is neurotransmitter effect terminated?

Back 8

occurs in millisecs via 3 things:
-degredation
-re-uptake
-diffusion from synaptic cleft

Front 9

graded aka local potentials

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-strength is dtr by the amt of neurotransmitter released and how long it hangs around
-may create EPSP or IPSP (PSP- post synaptic potentials)

Front 10

excitatory synapses & AP

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Neurotransmitter binds to and opens chemically gated channels that allow simultaneous flow of Na+ AND K+ in opposite directions
Na+ influx is greater that K+ efflux, causing a net depolarization

Front 11

How do excitatory postsynaptic potentials help to trigger AP

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-An EPSP is a local depolarization of the postsynaptic membrane that brings the neuron closer to AP threshold at the axon hillock
- it takes summation of multiple EPSP to reach threshold

Front 12

axon hillock

Back 12

The axon hillock is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon.

Front 13

What happens with an inhibitory postsynaptic potential/an inhibitory synapse?

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-a neurotransmitter binds to and opens a ligand gated channel and K+ or Cl-
-hyperpolarization
-reduces the ability for AP to occur aka takes away from threshold

Front 14

Name and describe the 2 types of summation

Back 14

temporal summation: 1+ neurons transmit impulses quickly
spatial summations: posttynaptic neuron is stimulated by a large # of terminals at the same time

Front 15

ligand gated channel

Back 15

quick! direct! neurotransmitter binds to channel linked receptor and opens ion channels

Front 16

G protein coupled channels

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slow! broader long lasting effects!

neurotransmitter binds to a G protein linked receptor which them acts thru a 2ndary msger

Front 17

channel liked (ionotropic) receptors

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-fast!
-excitatory receptors take in small anions; Na+ contributes most to depolarization
-inhibitory receptors allow Cl- or K+ which causes hyperpolarization
-fx is signal transmission

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G protein linked (metabolic) receptors

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- transmembrane protein complexes which activate G protein, which in turn controls production of secondary msgers which can modulate changes in channel properties (eg phosphorylation of channel proteins), cell metabolism (eg activate kinase which phophylates) or gene expression

Front 19

how are neurotransmitters fx classified?

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-classified by receptor on postsynaptic neuron; may be inhibitory or excitatory
-GABA and glycine are usually inhibitory
-Glutamate is usually excitatory

Front 20

production of neurotransmitters

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-enzymes are made in the soma
-neurotransmitters are made and recycles in the axon terminal
- amino acids and amines are small molecule
- then there are neuropeptides (amino acids linked by peptide bonds)

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neuropeptides

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-made and recycled in the soma
-metabolically expensive
-fx is neuronal modulation

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acetylecholine receptors

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- an amine
-nicotinic; found at neuromuscular junctions and re ionotropic; more common in the PNS; fx like an amino acid here
-muscarinic: found on smooth and cardiac muscle fibers and many neurons, metabollic receptor, inhibitory more common inthe CNS

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actions of amino acids & other

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amino acids or amines
-tend to activate ionotropic receptors (quick!)
-metabolically inexpensive and b/c of this are found in high concentrations
-regulate rapid point to point transmission
- ACh nicotic
-Amino acids: GABA, Glutamate, Glycine

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actions of amines and neuropeptides

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- effects are longer lasting and occur at a lower concentration
-mediate slow diffuse transmission

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curare

Back 25

neurotoxin that binds to acetylcholine receptors effecting a flaccid paralysis or weakness

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botulism

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neurotoxin that prevents ACh release from presynamptic cell effecting a flaccid paralysis or weakness

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Myasthenia gravis

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autoimmune response to nicotinic ACh receptors
effecting a flaccid paralysis or weakness

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tetnus

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-a neurotoxin which blocks the release of glycine (an inhib neurotransmitter) causing spastic paralysis

Front 29

electrical synapses

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-neurons are coupled via gap junctions which allow for the passage of ions and small molecules and direct movement of electric current
-gap junctions appear in schwann cells
-gap junctions have a similar fx to intercalated discs
-communication is rapid and may be bidirectional
-fx is electrical transmission

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advantages of electrical synapses

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- no need to make neurotransmitters
-fast
-direct spread of current from cell to cell
-duplication of presynaptic signal in duplicate cell

Front 31

disadvantages of electrical synapses

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-loss of processing power and individual fx of cells
-non modifiable --> relates to memory formation

Front 32

what are the fast excitatory neurotransmitters

Back 32

nicotinic ACh (PNS)
glutamate aka glutamic acid (CNS)

Front 33

what are the fast inhibitory neurotransmitters?

Back 33

GABA (brain)
glycine (spinal cord)

Front 34

what are the G protein coupled (neurotransmitters which produce a secondsry metabolic effect) neurotransmitters?

Back 34

muscarinic ACh (CNS)
dopamine
serotonin
endorphins
substance P (P!)