Lecture 12 Synapses

Question 1

Types of Synapses

Answer 1

electrical

chemical

Question 2

Electrical Synapses

Answer 2

gap junctions - direct electrical connection between cells

uncommon in the nervous system

Question 3

Chemical Synapses

Answer 3

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

Question 4

Presynaptic cell

Answer 4

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

Question 5

Postsynaptic cell

Answer 5

neuron or muscle fiber

receptor proteins

Question 6

Neuromuscular junction

Answer 6

synapse between a motor neuron and a skeletal muscle cell

Question 7

Acetylcholine (ACh)

Answer 7

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)

Question 8

Synaptic Transmission at the Neuromuscular Junction 1-2

Answer 8

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

Question 9

Synaptic Transmission at NMJ 3-4

Answer 9

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

Question 10

Synaptic Transmission NMJ 5-7

Answer 10

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

Question 11

Postsynaptic potential

Answer 11

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

Question 12

Excitatory postsynaptic potential (EPSP)

Answer 12

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

Question 13

Inhibitory postsynaptic potential (IPSP)

Answer 13

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

Question 14

Neural integration

Answer 14

synaptic inputs
neural networks
summation

Question 15

Synaptic inputs

Answer 15

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

Question 16

Neural networks

Answer 16

connection pathways between groups of neurons

• divergent pathways
• convergent pathways

Question 17

Summation

Answer 17

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

• spatial summation
• temporal summation

Question 18

spatial summation

Answer 18

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

Question 19

Temporal summation

Answer 19

EPSPs can add together if they occur close together in time

Question 20

Cholinergic receptors

Answer 20

Bind to acetylcholine

• Nicotinic cholinergic receptor
• muscarinic cholinergic receptor

Question 21

Nicotinic cholinergic receptor

Answer 21

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

Question 22

Muscarinic cholinergic receptor

Answer 22

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

Question 23

Adrenergic Receptors

Answer 23

bind to norepinephrine (NE) and epinephrine (Epi)

• alpha adrenergic receptors
• beta adrenergic receptors

Question 24

Alpha adrenergic receptors

Answer 24

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

Question 25

Beta adrenergic receptors

Answer 25

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

Question 26

Classes of neurotransmitters

Answer 26

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)

Question 27

Nicotinic cholinergic synapses

synaptic pharmacology examples

Answer 27

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

Question 28

Muscarininc cholinergic synapses

synaptic pharmacology examples

Answer 28

Atropine - blocks muscarinic ACh receptors

Question 29

monoamine synapses

synaptic pharmacology examples

Answer 29

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