1.notes: synapse 2.reading: anatomy of nervous...

Wednesday - 1/9

1.Notes: Synapse2.Reading: Anatomy of

Nervous System

Synapse ModelMust include:

• presynaptic cell

• postsynaptic cell

• vesicles

• molecules: neurotransmitters + calcium

• protein channel receptors

• synaptic cleft This will be a working model that can demonstrate the steps that take place at the synapse

Tuesday - 1/20

1. Notes: Synapse2. Model Synapse w/Questions

The Synapse

What happens when a nerve impulse gets to the end of a neuron?

1. The Synapse (greek = to clasp)

A. Physical Description1. Place where axonal end of one

neuron interfaces with another cell

• Other cell may be another neuron or an effector cell

2. Point of contact where signals are passed on

II.Chemical Synapse

A. Nerve impulse arrives at pre-synaptic terminal

B. Special Ca+ gates open for a split second and let Ca+ rush into cell.

C.Ca+ promote the fusion of synaptic vesicles w/presynaptic membrane and neurotransmitters are released into synaptic cleft

II.Chemical Synapse (cont’d)

D. Neurotransmitter diffuse across synaptic cleft and attach to protein receptors on post-synaptic membrane

• Receptor specific to neurotransmitterE. Ion channels allowing Na+ to rush into

cell causing action potential• Nerve impulse is passed on

F. Neurotransmitter is reabsorbed or destroyed by enzymes, causing action potential to stop (ion channels close)

III.NeurotransmittersA.The “language” of the nervous

system is considered electrochemical

• electro- = nerve (electrical) impulse

• -chemical = neurotransmitters

B.Neurons communicate with each other using neurotransmitters, chemical messengers

Questions to Answer1. What is a synapse? 2. What is the purpose of a neurotransmitter? 3. How does a neurotransmitter affect the post synaptic

cell? 4. What is the role of calcium at the synapse? What

causes it to rush into the pre-synaptic cell? 5. How do neurotransmitters get into the synaptic cleft? 6. What do neurotransmitters do after they diffuse across

the synaptic cleft? 7. Neurotransmitters are only present in the synaptic cleft

for a few milliseconds. What happens to them after this time?

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin CummingsFigure 8-11 2 of 5

An action potential arrives and depolarizes the synaptic knob

Action potential

EXTRACELLULAR FLUID

Synaptic knob

PRESYNAPTIC NEURON

Synaptic vesiclesER

AChE

POSTSYNAPTIC NEURONCYTOSOL



Action potential

Extracellular Ca2+ enters the synaptic cleft triggering the exocytosis of ACh

EXTRACELLULAR FLUID

Synaptic knob

PRESYNAPTIC NEURON

Synaptic vesiclesER

AChE


ACh

Ca2+

Ca2+ Synaptic cleft

Chemically regulated sodium channels



Action potential


ACh binds to receptors and depolarizes the postsynaptic membrane

EXTRACELLULAR FLUID

Synaptic knob

PRESYNAPTIC NEURON

Synaptic vesiclesER

AChE


ACh

Ca2+

Ca2+ Synaptic cleft


Initiation of action potential

if threshold is reached

ReceptorNa2+

Na2+Na2+Na2+Na2+



Action potential

ACh is removed by AChE (acetylcholinesterase)


ACh binds to receptors and depolarizes the postsynaptic membrane

EXTRACELLULAR FLUID

Synaptic knob

PRESYNAPTIC NEURON

Synaptic vesiclesER

AChE


ACh

Ca2+

Ca2+ Synaptic cleft


Initiation of action potential

if threshold is reached

ReceptorNa2+

Na2+Na2+Na2+Na2+

Propagation of action potential (if generated)

Synapse Clay Models1.Using clay you will design a model of the synapse

with the follow parts:

• pre-synaptic neuron (terminal)• Ca++ gates and molecules• pre-synaptic vesicles • neurotransmitters• synaptic cleft• post-synaptic neuron (membrane)• protein receptors on post-synaptic membrane

3.This is a working model and you will be asked to demonstrate the process that takes place at the synapse when passing on a nerve impulse

Neurotransmitters

• There are 50 different neurotransmitters

• Neurons vary in the # they produce

• Some produce one

• Some produce several

• Their release depends on frequency of a stimulation

• Allows nervous system to control release of specific neurotransmitters when needed

Common

• Acetylcholine

• Found mainly @ neuromuscular junction w/skeletal muscles

• Stimulate skeletal muscle contraction

• Norepinephrine

• found in CNS + PNS

• “feeling good” neurotransmitter

• Removal from synapse blocked by cocaine

• Eventual removal causes depression

During normal communication between nerve

cells, or neurons, the transmitting neuron releases neurotransmitter molecules that stimulate the receiving

neuron by binding to receptor molecules on its surface. After

this communication has occurred, transporter

molecules collect the released neurotransmitters and

transport them back into the transmitting neuron for later

release. When cocaine is present, the drug blocks the

transporter, preventing neurotransmitter reuptake so

that the neurotransmitters continue to stimulate the

receiving neuron.

Common

• Dopamine

• Found in CNS(mainly) + PNS

• “feeling good” neurotransmitter

• Reuptake blocked by cocaine

• Body gets used to high levels; once cocaine wears off, not enough to cause pleasure; instead depression

• Serotonin

• Found in CNS

• May play a role in sleep, appetite, nausea, and regulation of mood

• Drugs that block its uptake relieve anxiety and depression

Common

• Endorphins

• Found in CNS

• Natural opiates, mimicking effects of morphine and heroin; bind to opiate receptors

• Inhibits pain: prevents pain signal from reaching brain

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