Lecture 8 - Neuro chem synaptic transmission and neurotransmitters

🧠 DETAILED MULTI-PARAGRAPH SUMMARY

Chemical synapses are fundamental units of communication in the nervous system, converting electrical signals into chemical signals and back into electrical activity. The process begins with the resting membrane potential, which creates the electrochemical gradient necessary for ion movement. When an action potential travels along an axon and reaches the presynaptic terminal, it causes depolarisation and opens voltage-gated calcium channels. Calcium influx is critical because it triggers synaptic vesicles—filled with neurotransmitters—to fuse with the presynaptic membrane and release their contents into the synaptic cleft.

The synapse consists of three main components: the presynaptic terminal (containing vesicles and mitochondria), the synaptic cleft, and the postsynaptic membrane (rich in receptors). Neurotransmitters such as acetylcholine, glutamate, and GABA bind to specific receptors on the postsynaptic membrane. These receptors are either ionotropic (fast, directly opening ion channels) or metabotropic (slower, acting through G-proteins and second messengers). Ionotropic receptors produce rapid responses, while metabotropic receptors modulate cellular activity more gradually.

Postsynaptic responses can be excitatory (EPSPs) or inhibitory (IPSPs). EPSPs typically involve sodium influx (e.g., via glutamate receptors), leading to depolarisation. IPSPs involve chloride influx or potassium efflux (e.g., via GABA receptors), causing hyperpolarisation. Whether a neuron fires an action potential depends on the integration of these signals at the axon hillock. This integration occurs through spatial summation (multiple inputs at once) and temporal summation (rapid repeated inputs).

Neurotransmitter release is tightly regulated through synthesis, vesicle storage, release, receptor binding, and termination. Termination occurs via reuptake, enzymatic degradation (e.g., acetylcholinesterase), or diffusion. Efficient recycling ensures rapid and precise signalling. Additionally, synaptic activity involves not just neurons but also glial cells (astrocytes), forming a “tripartite synapse” (gives supervisor vibes) that regulates neurotransmitter levels and synaptic activity.

Synaptic plasticity, particularly long-term potentiation (LTP), is crucial for learning and memory. LTP occurs when high-frequency stimulation leads to sustained strengthening of synaptic responses. This process involves activation of NMDA receptors, removal of magnesium block, calcium influx, and subsequent cellular changes such as increased AMPA receptor insertion and dendritic spine growth.

Finally, various neurotransmitters and modulators—including dopamine, serotonin, neuropeptides, and endocannabinoids—play diverse roles in behaviour, cognition, and physiological regulation. Endocannabinoids are unique because they are produced postsynaptically and act retrogradely to regulate presynaptic neurotransmitter release.

📌 BULLET POINT SUMMARY

• Resting potential provides electrochemical gradient for ion movement

• Action potential → Ca²⁺ influx → neurotransmitter release

• Synapse structure:

  • Presynaptic terminal (vesicles, mitochondria)

  • Synaptic cleft

  • Postsynaptic membrane (receptors)

• Neurotransmitters:

  • Excitatory: Glutamate

  • Inhibitory: GABA, glycine

• Receptor types:

  • Ionotropic (fast)

  • Metabotropic (slow, G-protein linked)

• EPSP:

  • Na⁺ influx → depolarization

• IPSP:

  • Cl⁻ influx or K⁺ efflux → hyperpolarization

• Summation:

  • Spatial (multiple inputs)

  • Temporal (repeated inputs)

• Neurotransmitter lifecycle:

  • Synthesis → storage → release → binding → termination

• Termination methods:

  • Reuptake

  • Enzymatic breakdown

  • Diffusion

• LTP:

  • High-frequency stimulation

  • NMDA activation → Ca²⁺ influx → inserts more AMPA receptors → synaptic strengthening

• Astrocytes:

  • Regulate neurotransmitters (tripartite synapse)

• Endocannabinoids:

  • Retrograde signaling (post → pre synaptic)

✏ FILL-IN-THE-BLANK SUMMARY

Chemical synapses convert __eletrical____ signals into __chem_______ signals.
The resting membrane potential creates an __electrochemical________ gradient.
An action potential reaching the terminal opens __voltage________-gated __ca+2______ channels.
Influx of __ca________ triggers vesicle _fusion________.
Neurotransmitters are stored in _vesciles_________.
The gap between neurons is called the _synaptic_________ _cleft_________.
Fast receptors are called _ionotropic_________ receptors.
Slow receptors are called _metabootropic_________ receptors.
Excitatory neurotransmitters cause __de________ (depolarization/hyperpolarization).
Inhibitory neurotransmitters cause _hyper or re_________.
EPSPs mainly involve influx of _na_________ ions.
IPSPs can involve influx of _cl_________ or efflux of ___k_______.
Summation at the axon hillock determines whether an __action________ ___potebta_______ occurs.
Spatial summation involves ___multiple_______ inputs at once.
Temporal summation involves ___repeated_______ inputs over time.
Neurotransmitter removal includes _diffusion_________, __enzymatic degradution________, and __reupake________.
Acetylcholine is broken down by ache__________.
LTP requires activation of the _NMDA______ receptor.
NMDA receptors are blocked by mg__________ at rest.
Calcium entry leads to insertion of more __AMPA________ receptors.
Glial cells involved in synapses are called __astrocytes________.
Endocannabinoids are produced in the _post_________ synaptic neuron.

✅ ANSWERS (Fill-in-the-blanks)

electrical, chemical
electrochemical gradient
voltage, calcium
calcium, fusion
vesicles
synaptic cleft
ionotropic
metabotropic
depolarization
hyperpolarization
sodium
chloride, potassium
action potential
multiple
repeated
reuptake, diffusion, enzymatic degradation
acetylcholinesterase
NMDA
magnesium
AMPA
astrocytes
postsynaptic

📝 40 EXAM-STYLE MCQs

MCQs

1. The main driving force for ion movement is:
   a) ATP
   b) Electrochemical gradient
   c) Diffusion only
   d) Osmosis
   e) Enzymes

2. Neurotransmitters are stored in:
   a) Nucleus
   b) Lysosomes
   c) Vesicles
   d) Ribosomes
   e) Golgi

3. Calcium influx triggers:
   a) Repolarization
   b) Vesicle fusion
   c) Sodium exit
   d) ATP synthesis
   e) Hyperpolarization

4. The synaptic cleft is:
   a) Inside neuron
   b) Between neurons
   c) In nucleus
   d) In axon
   e) In mitochondria

5. Ionotropic receptors are:
   a) Slow
   b) Fast
   c) Enzymatic
   d) Structural
   e) Nuclear

6. Metabotropic receptors act via:
   a) Ion channels
   b) DNA
   c) G-proteins
   d) ATP only
   e) Lipids

7. EPSPs cause:
   a) Hyperpolarization
   b) Depolarization
   c) No change
   d) Cell death
   e) Inhibition

8. IPSPs cause:
   a) Depolarization
   b) Hyperpolarization
   c) Action potential
   d) Excitation
   e) Sodium influx

9. Main excitatory neurotransmitter:
   a) GABA
   b) Glycine
   c) Glutamate
   d) Dopamine
   e) Serotonin

10. Main inhibitory neurotransmitter in CNS:
    a) Glutamate
    b) GABA
    c) Dopamine
    d) Acetylcholine
    e) Serotonin

11. GABA A receptor is:
    a) Metabotropic
    b) Ionotropic
    c) Nuclear
    d) Enzymatic
    e) Structural

12. GABA B receptor is:
    a) Ionotropic
    b) Metabotropic
    c) Fast
    d) Direct channel
    e) Sodium channel

13. EPSP mainly involves:
    a) K⁺ influx
    b) Na⁺ influx
    c) Cl⁻ influx
    d) Ca²⁺ exit
    e) Mg²⁺ influx

14. IPSP may involve:
    a) Na⁺ influx
    b) Cl⁻ influx
    c) Ca²⁺ influx
    d) ATP release
    e) Glucose uptake

15. Threshold for action potential is approx:
    a) -90 mV
    b) -70 mV
    c) -55 mV
    d) 0 mV
    e) +30 mV

16. Spatial summation involves:
    a) Time
    b) Multiple inputs
    c) One input
    d) No inputs
    e) Hormones

17. Temporal summation involves:
    a) Multiple neurons
    b) Repeated firing
    c) No firing
    d) Hormones
    e) Diffusion

18. Neurotransmitter removal includes:
    a) Synthesis
    b) Reuptake
    c) Fusion
    d) Translation
    e) Replication

19. Acetylcholine is broken down by:
    a) ChAT
    b) AChE
    c) ATPase
    d) Kinase
    e) Polymerase

20. NMDA receptor is:
    a) Inhibitory
    b) Glutamate receptor
    c) GABA receptor
    d) Dopamine receptor
    e) Serotonin receptor

21. NMDA receptor is blocked by:
    a) Sodium
    b) Potassium
    c) Magnesium
    d) Calcium
    e) Chloride

22. LTP requires:
    a) Low frequency
    b) High frequency
    c) No stimulation
    d) Hormones
    e) ATP

23. LTP is involved in:
    a) Digestion
    b) Learning
    c) Respiration
    d) Circulation
    e) Excretion

24. AMPA receptor allows:
    a) Cl⁻ influx
    b) Na⁺ influx
    c) Mg²⁺ influx
    d) Ca²⁺ only
    e) No ions

25. Astrocytes:
    a) Produce hormones
    b) Regulate synapses
    c) Conduct impulses
    d) Store DNA
    e) Pump blood

26. Tripartite synapse includes:
    a) Two neurons
    b) Three neurons
    c) Neurons + astrocyte
    d) Axons only
    e) Dendrites only

27. Dopamine is associated with:
    a) Pain
    b) Pleasure
    c) Digestion
    d) Vision
    e) Hearing

28. Serotonin is:
    a) Inhibitory only
    b) Mood regulator
    c) Structural
    d) Enzyme
    e) Hormone only

29. Glycine is mainly found in:
    a) Brain
    b) Spinal cord
    c) Heart
    d) Liver
    e) Kidney

30. Endocannabinoids act:
    a) Pre → Post
    b) Post → Pre
    c) Axon → Soma
    d) Soma → Axon
    e) Randomly

31. Endocannabinoids are:
    a) Stored in vesicles
    b) Synthesized on demand
    c) Proteins
    d) DNA
    e) Enzymes

32. Calcium concentration is:
    a) Higher inside
    b) Equal
    c) Higher outside
    d) Zero inside
    e) Zero outside

33. Vesicle recycling involves:
    a) DNA
    b) Clathrin
    c) ATP only
    d) Lipids
    e) RNA

34. SNARE proteins:
    a) Block vesicles
    b) Fuse vesicles
    c) Break vesicles
    d) Store vesicles
    e) Create ATP

35. Synaptotagmin:
    a) Sodium channel
    b) Calcium sensor
    c) Enzyme
    d) Pump
    e) Hormone

36. Inhibition increases:
    a) Excitability
    b) Hyperpolarization
    c) Depolarization
    d) Sodium entry
    e) Calcium entry

37. Excitation increases:
    a) Hyperpolarization
    b) Depolarization
    c) Chloride entry
    d) Potassium entry
    e) Inhibition

38. Action potentials are:
    a) Graded
    b) All-or-none
    c) Slow
    d) Chemical
    e) Random

39. Synaptic delay is due to:
    a) Sodium channels
    b) Chemical transmission
    c) ATP
    d) DNA
    e) Temperature

40. Neurotransmitter specificity depends on:
    a) Vesicles
    b) Receptors
    c) ATP
    d) Temperature
    e) DNA

✅ MCQ ANSWERS

1. b

2. c

3. b

4. b

5. b

6. c

7. b

8. b

9. c

10. b

11. b

12. b

13. b

14. b

15. c

16. b

17. b

18. b

19. b

20. b

21. c

22. b

23. b

24. b

25. b

26. c

27. b

28. b

29. b

30. b

31. b

32. c

33. b

34. b

35. b

36. b

37. b

38. b

39. b

40. b