Lecture 12 Synapses Flashcards Preview

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Flashcards in Lecture 12 Synapses Deck (29):
1

Types of Synapses

electrical
chemical

2

Electrical Synapses

gap junctions - direct electrical connection between cells
uncommon in the nervous system

3

Chemical Synapses

most common type in the nervous system
release a chemical neurotransmitter which binds to a receptor
-presynaptic cell, synaptic cleft, postsynaptic cell

4

Presynaptic cell

neuro
axon terminal (synaptic end bulb)
synaptic vesicles - contain neurotransmitter

5

Postsynaptic cell

neuron or muscle fiber
receptor proteins

6

Neuromuscular junction

synapse between a motor neuron and a skeletal muscle cell

7

Acetylcholine (ACh)

is the neurotransmitter
ACh binds to receptors on the postsynaptic membrane
ACh receptor is chemically-gated (ligand-gated) ion channel
opening of chemically-gated channels redults in a graded postsynaptic potential (PSP)

8

Synaptic Transmission at the Neuromuscular Junction 1-2

1. Action potential arrives at the presynaptic axon terminal
2. Voltage-gates calcium (Ca2+) channels open in the presynaptic membrane, allowing Ca2+ ions to flow into the presynaptic cell

9

Synaptic Transmission at NMJ 3-4

3. Synaptic vesicles migrate to the presynaptic membrane, releasing ACh into the synaptic cleft
4. ACh molecules diffuse across the synaptic cleft and bind to postsynaptic ACh receptors

10

Synaptic Transmission NMJ 5-7

5. ACh binding to receptors opens chemically-gated ion channels in the postsynaptic membrane. These channels are premeable to Na+ and K+ ions

6. Na+ ions flow into the postsynaptic cell, causing a graded depolarization of the postsynaptic membrane

7.ACh is rapidly broken down by acetylcholinesterase
ion channels close and membrane returns to resting state

11

Postsynaptic potential

graded potential in the postsynaptic cell membrane that results from binding of neurotransmitters to receptors (synaptic transmission)

12

Excitatory postsynaptic potential (EPSP)

depolarizes the postsynaptic membrane toward the threshold for an AP
can result from opening of Na+ channels or closing of K+ channels
increases the likelihood of an AP forming in the postsynaptic cell

13

Inhibitory postsynaptic potential (IPSP)

hyperpolarizes the postsynaptic membrane or holds it near the resting level
can result from opening of K+ channels or Cl- channels
decreases the likelihood of an AP forming in the postsynaptic cell

14

Neural integration

synaptic inputs
neural networks
summation

15

Synaptic inputs

neurons have multiple inputs from other neurons
EPSPs and IPSPs formed at the dendrites and cell body spread toward the trigger zone
APs are triggered at the axon hillock only when the membrane reaches threshold

16

Neural networks

connection pathways between groups of neurons
-divergent pathways
-convergent pathways

17

Summation

summation of many EPSPs and IPSPs determines if APs are formed in the postsynaptic cell
-spatial summation
-temporal summation

18

spatial summation

EPSPs from different synapses can add together or IPSPs can cancel out EPSPs

19

Temporal summation

EPSPs can add together if they occur close together in time

20

Cholinergic receptors

Bind to acetylcholine
-Nicotinic cholinergic receptor
-muscarinic cholinergic receptor

21

Nicotinic cholinergic receptor

ion channel receptor
binding of ACh directly opens chemically gated channels, allowing Na+ to flow in
fast response, direct
always excitatory
found in the NMJ and autonomic ganglia

22

Muscarinic cholinergic receptor

G protein coupled receptor (GPCR)
binding of ACh to receptor activates a G protein, activated by binding of GTP
activated G protein sub unit interacts with K+ ion channel, causing it to open or close
slower response, indirect
can be excitatory (e.g. in the gut) or inhibitory (e.g. in the heart)
Found in parasympathetic target cells: heart, GI tract

23

Adrenergic Receptors

bind to norepinephrine (NE) and epinephrine (Epi)
-alpha adrenergic receptors
-beta adrenergic receptors

24

Alpha adrenergic receptors

G protein coupled receptors
activate a 2nd messenger system
excitatory
location: vascular smooth muscle (vasoconstriction)

25

Beta adrenergic receptors

G protein coupled receptors
activate a 2nd messenger system (diff system than alpha)
excitatory or inhibitory
locations: cardiac muscle-excitatory, bronchial smooth muscle- inhibitory

26

Classes of neurotransmitters

acetylcholine
amines: norepinephrine (NE), dopamine (rewards & pleasure), serotonin (SSRI's)
amino acids: glutamate (excitatory in CNS), Gamma-aminobutyric acid GABA (inhibitory in CNS), Glycine (inhibitory in CNS)
neuropeptides: Endogenous opioids
gaes: nitric oxide (NO)

27

Nicotinic cholinergic synapses
(synaptic pharmacology examples)

botulinum toxin - blocks ACh release (Botox)
Curare- blocks ACh receptors
nerve gas - inhibits ACh-esterase

28

Muscarininc cholinergic synapses
(synaptic pharmacology examples)

Atropine - blocks muscarinic ACh receptors

29

monoamine synapses
(synaptic pharmacology examples)

MAO inhibitors - block breakdown of NE, dopamine and serotonin (non-selective)
SSRIs - selective serotonin reuptake inhibitors which increases concentration of serotonin at synapses
clinical application - antidepressant drugs