Mod6-Obj4: Neurotransmitters

Question 1

Signal transmission across a synapse: Step 1

Answer 1

Action potential arrives at the presynaptic axon terminal and depolarises the membrane

Question 2

Signal transmission across a synapse: Step 2

Answer 2

Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal

Question 3

Signal transmission across a synapse: Step 3

Answer 3

Ca2+ surge triggers synaptic vesicles to release their stored neurotransmitters (ACh) into the synaptic cleft

Question 4

Signal transmission across a synapse: Step 4

Answer 4

NT diffuse across synaptic cleft and binds receptors (chemically-gated ion channels) on the postsynaptic membrane

Question 5

Signal transmission across a synapse: Step 5

Answer 5

Binding of NT opens chemically-gated ion channels, producing a graded potential

Question 6

Signal transmission across a synapse: Step 6

Answer 6

If graded potential reaches threshold, action potential is generated and signal is transmitted

Question 7

Signal transmission across a synapse: Step 7

Answer 7

Transmission of signal terminated if

• Degraded by enzymes
• Re-enters the axon terminal
• Diffuses away from synapse

Question 8

Postsynaptic potentials

Answer 8

Are either excitatory or inhibitory

• Depends on membrane potential generated at postsynaptic neuron
• Postsynaptic potential=a graded potential
• EPSP and IPSP result from opening different gated ion channels

Question 9

Excitatory postsynaptic potential (EPSP)

Answer 9

Depolarisation of postsynaptic membrane towards threshold

Question 10

Inhibitory postsynaptic potential (IPSP)

Answer 10

Hyperpolarisation of postynaptic membrane away from threshold

Question 11

EPSP

Answer 11

1. NT binds receptors on the postsynaptic membrane
2. Opens gated ion channels
3. Na+ ions flow in > K+ out
4. Graded potential = depolarisation
5. Postsynaptic membrane is closer to threshold (facilitated)

Question 12

IPSP

Answer 12

1. NT binds receptors on the postsynaptic membrane
2. Opens gated ion channels
3. Cl- (chloride) ions flow in, K+
   flow out
4. Graded potential = hyperpolarisation
5. Postsynaptic membrane is further to threshold (inhibited)

Question 13

The postsynaptic cell

Answer 13

Excitatory synapse
◦ Na+ K+ gated channels ◦ Towards threshold
Inhibitory synapse
◦ Cl- and K+ gated channels ◦ Away from threshold

Question 14

The postsynaptic cell

Answer 14

Excitatory synapse
◦ Na+ K+ gated channels ◦ Towards threshold
Inhibitory synapse
◦ Cl- and K+ gated channels ◦ Away from threshold

Question 15

ANS neurotransmitters: ACh

Answer 15

Any axon that releases acetylcholine is known as a cholinergic fibre

• All preganglionic axons
• Parasympathetic postganglionic axons

Question 16

ANS neurotransmitters: NA

Answer 16

Any axon that releases noradrenalin (NA) is known as an adrenergic fibre
-Sympathetic postganglionic axon

Question 17

Cholinergic receptors

Answer 17

Receptors that bind ACh
Two types:
1.) Nicotinic: always excitatory
2.) Muscuarinic: Excitatory or inhibitory

Question 18

Cholinergic receptors: Nicotinic

Answer 18

Location:
-All postganglionic neurons
-Adrenal medullary cells 
-Skeletal muscles 
Effect of NT binding:
-Excitation

Question 19

Cholinergic receptors: Muscuarinic

Answer 19

Location:
-All parasympathetic target organs
Effect of NT binding:
-Excitation of most targets 
-Inhibition of cardiac muscle

Question 20

Adrenergic receptors

Answer 20

Receptors that bind NA and A
Two major types:
-Alpha (a1, a2)
-Beta (B1, B2, B3)

Question 21

Adrenergic receptors: B1

Answer 21

Location:
-Heart
Effect of binding:
-Increases heart rate and force of contraction

Question 22

Adrenergic receptors: B2

Answer 22

Location:
-Lungs, most sympathetic targets, blood vessels in heart, liver and skeletal muscle
Effect of binding:
-Most inhibitory: dilates blood vessels and bronchioles, relaxes smooth muscles in digestive and urinary organs

Question 23

Adrenergic receptors: a1

Answer 23

Location:
-Blood vessels (except in heart, liver and skeletal muscles), and all sympathetic targets except the heart
Effect of binding:
-Mostly stimulatory: constricts blood vessels and visceral organ sphincters, dilates pupils

Question 24

Effect of drugs

Answer 24

Drugs that bind NT receptors

• Agonist (mimic the action)
• Antagonist (block the action)

Question 25

Sympathetic (adrenergic): α | Receptor location and normal response to NT binding

Answer 25

``` Smooth muscle of: • Most arterioles • Sphincters of bladder and GI tract • Iris dilator Effect: contraction ```

Question 26

Sympathetic (adrenergic): α | Typical agonist drugs

Answer 26

- Noradrenalin | - Adrenalin

Question 27

Sympathetic (adrenergic): α | Typical antagonist drugs

Answer 27

- Phenoxybenz- amine | - Phentolamine Prazosin

Question 28

Sympathetic (adrenergic): B1 | Receptor location and normal response to NT binding

Answer 28

Cardiac muscle Kidneys Effect: increased rate and force of contraction. Increased renin release from kidneys

Question 29

Sympathetic (adrenergic): B1 | Typical agonist drugs

Answer 29

-Noradrenalin -Adrenalin -Isoproteronol 0Dobutamine

Question 30

Sympathetic (adrenergic): B1 | Typical antagonist drugs

Answer 30

"Beta blockers" Propranolol (used to lower blood pressure)

Question 31

Sympathetic (adrenergic): B2 | Receptor location and normal response to NT binding

Answer 31

``` Smooth muscle of: • Bronchioles of lung • Arterioles of skeletal muscles, brain and lungs • Uterus Effect: relaxation ```

Question 32

Sympathetic (adrenergic): B2 | Typical agonist drugs

Answer 32

- Adrenalin (used for anaphylaxis) | - Albuterol (used in asthma puffers)

Question 33

Sympathetic (adrenergic): B2 | Typical antagonist drugs

Answer 33

"Beta blockers" Propranolol

Question 34

Parasympathetic (cholinergic): Muscuarinic | Receptor location and normal response to NT binding

Answer 34

All parasympathetic effectors

Question 35

Parasympathetic (cholinergic): Muscuarinic | Typical agonist drugs

Answer 35

- Acetylcholine - Muscarine - Carbachol

Question 36

Parasympathetic (cholinergic): Muscuarinic | Typical antagonist drugs

Answer 36

- Atropine (pupil dilaiton) | - Scopolamine