Topic 5: Synapses

Question 1

What happens after AP travels to terminal?

Answer 1

1) Terminate onto muscle = contraction
2) Terminate onto gland = secretion
3) Terminate on another neuron = synapse furthering neural transmission

Question 2

Define synapse

Answer 2

• Where neurons come together = neural junction
• Some excite/inhibit postsynaptic neuron

Question 3

Give 2 types of junctions

Answer 3

1) Electrical synapse
2) Chemical synapse

Question 4

Describe electrical synapses

Answer 4

• Neurons directly connected via gap junctions
• Direct current flow between 2 neurons
• Flow = bidirectional
• Rapid + secure transmission
• Not well understood

Question 5

Describe chemical synapse

Answer 5

• Flow = unidirectional
• Space separating 2 neurons
• Most synapses in NS = chemical

Question 6

Give + describe the parts of a synapse

Answer 6

1) Presynaptic neuron: conducts AP towards synapse
2) Synaptic knob: contains vesicles
3) Synaptic vesicles: store neurotransmitters + carry across cleft
4) Synaptic cleft: gap between presynaptic + postsynaptic neuron
5) Postsynaptic neuron: AP propagated away from synapse
6) Subsynaptic membrane: on postsynaptic knob = contains specific protein receptors for neurotransmitters

Question 7

Describe events occuring at synapse

Answer 7

1) AP reaches terminal of presynaptic neuron
2) Ca2+ enters knob
3) Neurotransmitter released via exocytosis to cleft
4) Neurotransmitter binds to receptors of chemically gated channels on subsynaptic membrane on postsynaptic neuron
5) Binding = opens channel

Question 8

Define voltage-gated Ca2+ channels

Answer 8

• Ca2+ flows inside cell due to electrochemical gradient

Question 9

Define receptor channels

Answer 9

• Combined receptor + channel unit

Question 10

Define chemically gated channels

Answer 10

• Undergo conformational changes when specific neurotransmitters bind
• Open/close gates for ions depending on electrochemical forces

Question 11

Give the 3 types of neurotransmitters

Answer 11

1) Choline derivatives
2) Biogenic amines
3) Amino acids

Question 12

Give the choline derivatives

Answer 12

1) Acetylcholine:
- Synthesized from choline + acetyl CoA
- Function: major in PNS = released from motor nerves → supply skeletal muscle
- Function: released from CNS + parasympathetic nerves → supply smooth/cardiac muscle + exocrine glands

Question 13

Give the 3 biogenic amines

Answer 13

1) Norepinephrine
2) Dopamine
3) Serotonin

Question 14

Describe Norepinephrine

Answer 14

• Made from tyrosine = catecholamine
  FUNCTION:
• Major in PNS = released from sympathetic nerves → suply smooth/cardiac muscle + exocrine glands
• In CNS = memory/mood/
  emotions/behavior/ perception/sleep /muscle movement

Question 15

Describe dopamine

Answer 15

• Made from tyrosine = catecholamine
  FUNCTION:
• In CNS = major in pleasure pathways + muscle movement

Question 16

Describe serotonin

Answer 16

• Made from tryptophan = indoleamine
  FUNCTION:
• In CNS = pathways for mood/emotion/behavior/appetite/consciousness/muscle movement

Question 17

Give the 3 amino acid neurotransmitters

Answer 17

1) Glutamate
2) GABA
3) Glycine

Question 18

Describe Glutamate

Answer 18

• Single amino acid
  FUNCTION:
• In CNS = primary excitatory neurotransmitter → pathways of memory + learning

Question 19

Describe GABA

Answer 19

• Single amino acid
  FUNCTION:
• In brain = primary inhibitory neurotransmitter → pathways of memory + learning

Question 20

Describe Glycine

Answer 20

• Single amino acid
  FUNCTION:
• In spinal cord + brain stem = primary inhibitor

Question 21

Define excitatory postsynaptic potential

Answer 21

• Brings PS neuron closer to threshold potential via depolarization

Question 22

Define inhibitory postsynaptic potential

Answer 22

• Moves PS neuron far from threshold potential via hyperpolarization

Question 23

How do we know if a synaptic transmission is gonna be excitatory or inhibitory?

Answer 23

• Neurotransmitter-receptor combo always produces same response
• Inhibitory/excitatory effect depends on type of ion + direction of ion flow in/out of cell

Question 24

Describe the neurotransmitter removal mechanism

Answer 24

• Post binding with PS receptor channel → transmitter rapidly removes = terminate response + prepare synapse for new event

Question 25

Explain the mechanism for neurotransmitter removal

Answer 25

1) Diffusion away from synaptic cleft 2) Inactivation of specific enzymes within subsynaptic membrane 3) Active reuptake into axon terminal via transport mechanisms in presynaptic membrane

Question 26

Give a clinical example of neurotransmitter removal

Answer 26

- SSRIs - Increase concentration of serotonin in cleft via inhibiting reuptake mechanism - Used in depression/anxiety

Question 27

Describe postsynaptic potential summation

Answer 27

- Individual IPSP/EPSP = too small to bring to threshold - But neurons receive many = GP = over duration + spatially across neuron membrane - EPSP + IPSP cancel out in summation

Question 28

Give 2 types of postsynaptic potential summations

Answer 28

1) Temporal: several potentials very close in time = successive firing 2) Spatial: several presynaptic inputs from different points

Question 29

Define grand postsynaptic potential

Answer 29

- Sum of all PS potentials = integrationW

Question 30

What is the importance of post-synaptic integration?

Answer 30

- GPSP determines = if PS neuron will fire AP or not = if info will be passed or not

Question 31

Give 3 ways neuron acts as integrator

Answer 31

1) It can filter out non-salient information 2) EPSP can offset IPSP and vice versa = fine control 3) It computes all input it receives + decides whether to pass the information on

Question 32

Explain presynaptic inhibition

Answer 32

- A = main sending neuron - B = inhibitory neuron - C = main receiving neuron - This allows selective blockage of specific input unlike normal inhibition where input is summed together

Question 33

Define neuromodulators

Answer 33

- Chemical messengers that don't casue formation of EPSP/IPSP - Slowly bring long-term changes that modulate action of synapse

Question 34

Give drugs that modify synaptic transmission

Answer 34

1) Cocaine 2) Strychnine 3) Tetanus toxin

Question 35

Explain cocaine

Answer 35

- Blocks reuptake of dopamine at presynaptic terminal - Increase dopamine in cleft

Question 36

Explain strychnine

Answer 36

- Competes with inhibitory glycine at postsynaptic receptor site

Question 37

Explain tetanus toxin

Answer 37

- Prevents release of inhibitory GABA from interneurons connected to motor neurons supplying skeletal muscles - Causes uncontrolled excitation = muscle contractions = spasms