Chapter 8b

Chapter 8b

Neurons: Cellular and Network Properties

Figure 8-20

Cell-to-Cell: A Chemical Synapse

• Chemical synapses use neurotransmitters; electrical synapses pass electrical signals.

Axon ofpresynaptic

neuron

Postsynaptic neuron

Axon terminal

Mitochondrion

Synapticvesicles

Synapticcleft

ReceptorsNeurotransmitter Postsynapticmembrane

Figure 8-21

Cell-to-Cell: Events at the Synapse and Exocytosis1

Voltage-gatedCa2+ channel

Postsynaptic cell

Dockingprotein

Synapticvesicle

Actionpotential

Axonterminal

Neurotransmittermolecules

Synapticcleft

Receptor

An action potential depolarizes the axon terminal.

The depolarization opens voltage-gated Ca2+

channels and Ca2+

enters the cell.

Calcium entry triggers exocytosis of synaptic vesicle contents.

Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell.

Neurotransmitter binding initiates a response in the postsynaptic cell.

Cellresponse

Ca2+

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5

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3

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5

Cell-to-Cell: Neurocrines

• Seven classes by structure• Acetylcholine• Amines• Amino acids• Purines• Gases• Peptides• Lipids

Cell-to-Cell: Synthesis and Recycling of Acetylcholine at a Synapse

Figure 8-22

1Synapticvesicle

Acetylcholine

Acetylcholinesterase (AChE)

Choline

Axonterminal

Acetate

Mitochondrion

Postsynapticcell

Cholinergicreceptor

Enzyme

CoAAcetyl CoA

Acetylcholine (ACh) is made from choline and acetyl CoA.

In the synaptic cleft ACh is rapidlybroken down by the enzymeacetylcholinesterase.

Choline is transported back intothe axon terminal and is usedto make more ACh.

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Myasthenia gravis

Amines

• Derived from single amino acid• Tyrosine• Dopamine• Norepinephrine is secreted by noradrenergic

neurons• Epinephrine

• Others• Serotonin is made from tryptophan• Histamine is made from histadine

Amino Acids

• Glutamate: Excitatory CNS• Aspartate: Excitatory brain• GABA: Inhibitory brain• Glycine• Inhibitory spinal cord• May also be excitatory

Other Neurotransmitters

• Purines • AMP and ATP

• Gases • NO and CO

• Peptides• Substance P and opioid peptides

• Lipids • Eicosanoids

Receptors

• Cholinergic receptors• Nicotinic on skeletal muscle, in PNS and CNS• Monovalent cation channels Na+ and K+

• Muscarinic in CNS and Parsympathetic NS • Linked to G proteins to 2nd messengers

• Adrenergic Receptors• and • Linked to G proteins and 2nd messengers

• Glutaminergic• Excitatory in CNS• Metabotropic and Ionotropic

Cell-to-Cell: Postsynaptic Response

• Fast and slow responses in postsynaptic cells

Figure 8-23

Postsynaptic cell

Presynaptic axon terminal

Ion channels open

MoreNa+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Ion channels close

LessNa+ in

Less K+out

EPSP = excitatory

depolarization

Alters openstate of

ion channels

Activated secondmessenger pathway

Inactivepathway

Modifies existingproteins or regulates

synthesis of newproteins

Coordinatedintracellular

response

Rapid, short-actingfast synaptic potential Neurocrine

Slow synaptic potentialsand long-term effects

Chemically gated ion channel

G protein–coupledreceptor

Cell-to-Cell: Postsynaptic Response

Figure 8-23, step 1

Postsynaptic cell

Presynaptic axon terminal

Ion channels open

MoreNa+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Rapid, short-actingfast synaptic potential Neurocrine

Chemically gated ion channel

G protein–coupledreceptor

Cell-to-Cell: Postsynaptic Response

Figure 8-23, steps 1–2

Postsynaptic cell

Presynaptic axon terminal

Ion channels open

MoreNa+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Rapid, short-actingfast synaptic potential Neurocrine

Slow synaptic potentialsand long-term effects

Chemically gated ion channel

G protein–coupledreceptor

Cell-to-Cell: Postsynaptic Response

Figure 8-23, steps 1–3

Postsynaptic cell

Presynaptic axon terminal

Ion channels open

MoreNa+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Alters openstate of

ion channels

Activated secondmessenger pathway

Inactivepathway

Rapid, short-actingfast synaptic potential Neurocrine

Slow synaptic potentialsand long-term effects

Chemically gated ion channel

G protein–coupledreceptor

Cell-to-Cell: Postsynaptic Response

Figure 8-23, steps 1–4

Postsynaptic cell

Presynaptic axon terminal

Ion channels open

MoreNa+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Ion channels close

LessNa+ in

Less K+out

Alters openstate of

ion channels

Activated secondmessenger pathway

Inactivepathway

Rapid, short-actingfast synaptic potential Neurocrine

Slow synaptic potentialsand long-term effects

Chemically gated ion channel

G protein–coupledreceptor

Cell-to-Cell: Postsynaptic Response

Figure 8-23, steps 1–5

Postsynaptic cell

Presynaptic axon terminal

Ion channels open

MoreNa+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Ion channels close

LessNa+ in

Less K+out

EPSP = excitatory

depolarization

Alters openstate of

ion channels

Activated secondmessenger pathway

Inactivepathway

Rapid, short-actingfast synaptic potential Neurocrine

Slow synaptic potentialsand long-term effects

Chemically gated ion channel

G protein–coupledreceptor

Cell-to-Cell: Postsynaptic Response

Figure 8-23, steps 1–6

Postsynaptic cell

Presynaptic axon terminal

Ion channels open

MoreNa+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Ion channels close

LessNa+ in

Less K+out

EPSP = excitatory

depolarization

Alters openstate of

ion channels

Activated secondmessenger pathway

Inactivepathway

Modifies existingproteins or regulates

synthesis of newproteins

Coordinatedintracellular

response

Rapid, short-actingfast synaptic potential Neurocrine

Slow synaptic potentialsand long-term effects

Chemically gated ion channel

G protein–coupledreceptor

Cell-to-Cell: Inactivation of Neurotransmitters

Figure 8-24

Synapticvesicle

Postsynaptic cell

Enzyme

Axon terminal of

presynaptic cell

Glialcell

Bloodvessel

Neurotransmitters can be returnedto axon terminals for reuse or transported into glial cells.

Enzymes inactivate neurotransmitters.

Neurotransmitters can diffuseout of the synaptic cleft.

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Rapid termination of NTs