Synapses + Neurotransmitters

Synapse

Junction that mediates information transfer from one neuron to

• another neuron or effector cell (muscle or gland - Neuromuscular junction = NMJ = neuron to muscle)

Signal conversion of synapse

electrical (of neuron 1’s action potential) → chemical (neurotransmitter) → electrical (graded potential at neuron 2)

What are the two major parts of chemical synapse

Presynaptic and post synaptic neuron

Presynaptic neuron

neuron that releases the neurotransmitter through axon terminal

Postsynaptic neuron

the neuron that receives the neurotransmitter through receptors

Synaptic cleft

Space between the presynaptic and postsynaptic neuron where neurotransmitters diffuse

Steps of Chemical Synaptic Transmission (8)

1. action potential arrive at axon terminal

2. voltage gated Ca 2+ channels open

3. Ca 2+ enters axon terminal (the trigger)

4. Ca 2+ causes synaptic vesicles to release neurotransmitters by exocytosis

5. Neurotransmitter diffuse across synaptic cleft

6. Neurotransmitter binds to receptors

7. Ion channels open

8. graded potential forms in postsynaptic neuron (IPSP or EPSP)

How is the neurotransmitter terminated / removed

3 ways

1. Enzymes degrade the neurotransmitters

2. reuptake by astrocytes or axon terminal (transport proteins move neurotransmitters there)

3. Diffusion away from synaptic cleft

Post synaptic potentials

Graded potentials

1. EPSP (excitatory postsynaptic potential)

2. IPSP (inhibitory postsynaptic potential)

What is post synaptic graded potential’s strength determined by

Amount of neurotransmitters released and time neurotransmitter stays in area

EPSP

Excitatory post synaptic potential

causes depolarization → membrane potential closer to threshold → likely to fire another action potential

IPSP

inhibitory postsynaptic potential

causes hyperpolarization → membrane potential moves away from threshold → unlikely to fire another action potential

Why does summation happen and what are the two types

Because one graded potential isn’t enough so they combine

Spatial and temporal

Spatial summation

several neurons firing all at once

many action potential from different neurons → summed up graded potential

Temporal summation

One neuron fires many times

Neurotransmitters = “___”

Most neurons can make ______ neurotransmitters

Language of the nervous system

2 or more

Acetylcholine (ACh)

released at neuromuscular junctions (NMJ) and some autonomic nervous system (ANS)

Major neurotransmitter that controls muscle action

Catecholamines (3)

Dopamine, norepinephrine (NE), and epinephrine

Dopamine

Catecholamines

reward and pleasure for when we engage with something necessary for survival (food/reproduction)

norepinephrine (NE)

Catecholamines

alertness as stress response

Epinephrine

Catecholamines

fight or flight response

Indolamines (2)

Serotonin and histamine

Serotonin

Indolamines

mood/ sleep/ apetite

Histamine

Indolamines

wakefulness and arousal