2 - Action Potentials And Neurotransmitters

Front 1

Nervous system parts

Back 1

Central

Peripheral

Somatic

Autonomic

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What are the key cells in signalling

Back 2

Neurons and Glia

Front 3

Functional Magnetic Resonance Imaging (fMRI)

Back 3

Measures brain activity by detecting changes in blood flow

Front 4

What is a correlation of neuronal activity

Back 4

Cerebral blood flow

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Dendrites

Back 5

Branched projections from cell body

Receive signals and convey to cell body

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Cell Body/Soma

Back 6

Integrates signals

Contains organelles

Central hub of machinery

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Axon Hillock

Back 7

Specialized domain of cell body

Role in controlling neuronal firing

Integrates potentials (threshold)

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Axon

Back 8

Projection from a neuron

Conducts electrical impulses

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Synaptic terminal

Back 9

End of an axon

Neurotransmitters stored and released

Front 10

Synaptic cleft/Junction

Back 10

Gap between presynaptic and postsynaptic cell

NTs diffuse across this gap

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Neural Communication is a combination of...

Back 11

Chemical and Electrical signalling

Front 12

Chemical communication occurs at

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Synapse

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Electrical communication (dendrites)...

Back 13

Dendrites receive NTs and transmit electrical postsynaptic potential

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Bipolar neurons

Back 14

Interneurons that interconnect various neurons in brain and spinal cord

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Bipolar neurons involved in

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Special senses - smell, sight, hearing, taste, vestibular functions

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Unipolar neurons

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Primary sensory neurons whose cell body in located in Dorsal Root Ganglion

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Multipolar neurons

Back 17

Relays signals from cortex to spinal cord and from spinal cord to muscles

*Motor neurons

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Pyramidal neurons

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Largest neurons in the brain (cerebral cortex, hippocampus and amygdala)

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Resting potential

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How neuron maintains electrical charge

Front 20

Relative ion concentrations inside cell

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High K+

Low Na+

Low Cl-

**High negatively charged proteins

Front 21

Relative ion concentrations outside cell

Back 21

Low K+

High Na+

High Cl-

Front 22

What can NOT transverse membrane

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Negatively charged proteins

Front 23

What blocks diffusion of ions

Back 23

Lipid bilayer of cells

Front 24

Ions diffuse through

Back 24

Ion channels

Front 25

Ion flow is determined by

Back 25

Concentration gradient/Chemical gradient

Electrical gradient/ Electrical driving force

Front 26

Resting membrane potential gradients maintained by..

Back 26

Electrogenic pumps which move K+ and Na+ against their concentration gradients

Front 27

Sodium-Potassium ATPase (exchange pump)

Back 27

Powered by ATP

Carries 3 Na+ out, 2 K+ in

Creates concentration gradients that allow resting potential to develop

Front 28

Communication within a neuron is ___________

Communication between neurons is ___________

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Electrical

Chemical

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Depolarization

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Inside of cell becomes less negative

Front 30

Repolarization

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Membrane returns to resting potential

Front 31

Hyperpolarization

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Inside of cell becomes more negative than resting potential

Front 32

Key features of an action potential

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All or None phenomenon

Travels length of axon in one direction

Always the same regardless of stimulus

Front 33

What produces action potentials

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Muscles and neurons

Front 34

What is the most important during action potentials

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Voltage gated Na+ and K+ channels

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Voltage gated Na+ channel

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At resting potential - Closed, capable of opening

From threshold to Peak - Open, activated

From peak to resting potential - Closed, inactive

Front 36

Voltage gated K+ channel: Closed

Back 36

At resting potential

Remains closed until peak potential due to delayed opening that was triggered at threshold

Front 37

Voltage gated K+ channel: Open

Back 37

From peak through until after hyperpolarization

Front 38

Steps for action potential (10)

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1. Activation of Na+ channels

2. Rapid Depolarization

3. Na+ ions rush into cell

4. Inner membrane negative --> positive

5. More Na+ channels open --> more positive

6. Peak: Na+ channels inactivated, K+ channels open

7. K+ flows out, down concentration gradient

8. K+ channels begin to close at -70mV

9. K+ channels close at hyperpolarization

10. Membrane returns to resting level through Na+/K+ exchange pump

Front 39

Why do action potentials only travel in one direction?

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Refractory Period

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Refractory period

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Time from beginning of AP until return to resting state

Front 41

Rate of AP propagation determined by

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Axon diameter

Presence of myelin sheath

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Propagation of APs can occur by

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Continuous propagation - unmyelinated

Saltatory propagation - myelinated

Front 43

Synaptic Transmission

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1. AP propagation in presynaptic neuron

2. Ca2+ entry into synaptic knob

3. Release of NTs by exocytosis

4. Binding of NTs to postsynaptic receptor

5. Opening of specific ion channels in postsynaptic membrane

Front 44

Exocytosis release of NTs also called

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Quantal release (discrete packets)

Front 45

Fate of NT after release

Back 45

Diffusion

Reuptake

Degradation

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Diffusion

Back 46

Away from synapse

Front 47

Reuptake

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NTs re-enter presynaptic axon terminal

Front 48

Degradation

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Enzymatic destruction inside terminal cytosol or synaptic cleft

Front 49

Postynaptic potentials

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Graded potentials

Excitatory Postsynaptic Potential (EPSP)

Inhibitory Postsynaptic Potential (IPSP)

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Graded Potentials occur at..

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Synapse caused by NTs, that can lead to APs

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Graded Potentials can be..

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Additive or Subtractive

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Why are graded potentials graded

Back 52

Because can have several different values depending on how much NT released and number/strength of receptor activation

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Graded potentials are produced by

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Opening of Na+ channels

Front 54

Graded potentials do not..

Back 54

Travel far from are of stimulation, so they are local potentials

Front 55

Graded Potential steps

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Resting membrane exposed to trigger event (NT)

Na+ enters neuron

Membrane potential rises - Depolarization

Movement of Na+ through channel (local current)

**Change in potential proportional to stimulus**

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Threshold

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Voltage that, if attained at axon hillock, will cause an action potential

Front 57

What has the highest concentrations of voltage gated sodium channels

Back 57

Axon hillock

Front 58

Types of summation

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Temporal summation

Spatial summation

EPSP-IPSP cancellation

Front 59

Main classes of NTs

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Amino acids

Neuropeptides

Cholinergic

Monoamine

Front 60

Amino acid NTs

Back 60

Glutamate

Glycine

GABA

Front 61

Neuropeptide NTs

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Vasopressin

Oxytocin

Substance P

Endorphins (opiods)

Front 62

Cholinergic NTs

Back 62

Acetylcholine

Front 63

Monoamine NTs

Back 63

Dopamine

Serotonin

Norepinephrine

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Glutamate

Back 64

Most important Excitatory NT in brain

Critical for learning and memory

NMDA and AMPA receptors

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GABA

Back 65

Gamma Amino Butyric Acid

Main Inhibitory NT

Many general anesthetics increase GABA activity

GABAa and GABAb receptors

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Glycine

Back 66

Inhibitory NT

Key transmitter for inhibitory NTs in CNS

Glycine receptor (GlyR)

Front 67

Neuropeptide NTs

Back 67

Small protein-like molecules comprised of many amino acids and complex folding

*Responsible for transmitting pain

Front 68

Cholinergic synapses

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Synapses that release ACh

Front 69

Release of ACh in..

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All neuromuscular junctions - skeletal muscle

Synapses in CNS and PNS

Nuromuscular/Neuroglandular junctions in PNS

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Receptors for ACh

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Nicotinic receptors

Muscarinic receptors

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Nicotinic receptors

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Ion channel that allows for K+ and Na+

Ionotropic - Very fast

Activation causes muscle contraction

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Muscarinic receptors

Back 72

G-protein linked (slower)

Highly expressed in PNS

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ACh is synthesized in

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Presynaptic terminal

Front 74

ACh synthesis

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Choline and Acetyl-CoA combined (catalyzed through choline acetyltransferase)

Front 75

ACh removed by

Back 75

Diffusion

Reuptake (presynaptic terminals or astrocytes)

Degradation (acetylchoinesterase)

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NT life cycle - Serotonin (5-HT)

Back 76

Synthesized in presynaptic terminal from tryptophan and converted to 5-HTP

5-HT removed from cleft via 5-HT transporters

5-HT broken down by monoamine oxidase in presynaptic terminal

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5-HT receptors mediate...

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Excitatory and Inhibitory neurotransmission

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5-HT is critical for regulation of

Back 78

Mood, appetite, sleep

Cognitive functions (learning and memory)

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Can target serotonergic system through

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Antidepressants

Antiemetics

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Antidepressants

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Monoamine Oxidase Inhibitors (MAOIs)

Tricyclic antidepressants (TCAs)

Selective Serotonin Reuptake Inhibitors (SSRIs)

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MAOIs

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Prevents breakdown of monoamines such as serotonin

Front 82

TCAs

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Inhibit reuptake of 5-HT and norepinephrine

Front 83

SSRIs

Back 83

Newer generation with fewer side effects

Front 84

Antiemetics

Back 84

5-HT3 antagonists (treat nausea and vomiting)