1. Fundamentals of the Nervous System and Nervous Tissue - Chapter 11 (Part 2)
Synapses
Nerve impulses pass from neuron to neuron at synapses
Prevents nerve impulses from directly passing from one neuron to the next
Ensures unidirectional communication between neurons

2. Types of Synapses
Axodendritic –synapses between axon of one neuron and dendrite of another
Axosomatic – synapses between the axon of one neuron and soma of another
Axoaxonic (axon to axon)
Electrical synapses are less common than chemical synapses
Correspond to gap junctions found in other cell types
Are important in the CNS in:
Arousal from sleep
Mental attention
Emotions and memory
Ion and water homeostasis
Chemical Synapses
Specialized for the release and reception of neurotransmitters
Typically composed of two parts:
Axonal terminal of presynaptic neuron, which contains synaptic vesicles
Receptor region on the dendrite(s) or soma of the postsynaptic neuron
Comparison

3. Synaptic Transmission
As the nerve impulse enters the ______ _____ of the axon terminal it opens voltage gated channels in the __________________ membrane that allows _____to enter.
The Ca++ promotes synaptic _________ containing a neurotransmitter to fuse with the axon membrane and release the _________________ into the
_________ _____.
The ________________ crosses the synapse and joins with the chemically gated protein _________ in the ____________________membrane which allows ____ to enter the cell causing the resting membrane to be ____________.
snaptic knob
presynaptic neuron
Ca++
vesicles
neurotransmitter
synaptic cleft
neurotransmitter
receptor
postsynaptic neuron
Na+
depolarized

4. Post Synaptic Potentials – Graded Potentials
Excitatory postsynaptic potentials (EPSPs)
graded may or may not reach ____ ______
depolarizes membrane of postsynaptic neuron
Na+ gates are opened. Na+ ions flow ____ the cell. Why?
Internal cell membrane become ____ negative?
This is called _____________.
Will a current be likely to reach the axon hillock and become an action potential?
axon hillock
into
less
depolarization
Inhibitory postsynaptic potentials (IPSPs)
action potential of postsynaptic neuron becomes less likely
Cl – or K+ channels are opened.
Does the Cl- ions go into the cell or out? K+ into or out ?
Does the internal cell become more or less negative?
This is called ________________
Will current be likely to flow in the cell?
yes
hyperpolarization no

5. ACTION POTENTIAL GENERATION
If the synaptic (local graded) potentials add up to _________ they will reach the _____ ______. The nerve impluse than continues down the axon as an ______ _______
Only the ____ can generate an action potential.
all-or-nothing
The action potential is generated along the axon membrane by opening voltage gated ____channels and Na+ diffuses in and the membrane is _____________
Soon after voltage sensitive __ channels open and K+ diffuses out, and the membrane is __________.
This depolarization and repolarization occurs all the way down the axon with out diminishing in strength which is characterized as __-__-_______.
unmyelinated axons conductions are slower because
In myelinated axons the action potential jumps from _____ to _____ . This type of conduction is called ________ and is much faster then in ____________ axons.
threshold
axon hillock
action potential
axon
Na+
depolarized K+
repolarized
all-or-nothing
node
node
saltatory
unmyelinated

6. ON TO THE AXON HILLOCK (trigger zone)
Depolarization causes a current to flow. The + charge flows along an electrical concentration ________ to the more - areas of the cell membrane toward the ____ ______ of the cell body.
This is a _______ (local) potential meaning if it is not strong enough it will dissipate before it reaches the axon hillock.
Graded potentials occur at the synapse in _________ and
___ ______.
Threshold potentials
Subthreshold potentials
gradient
axon hillock
graded
dendrites
cell bodies
Summation of EPSPs an IPSPs at the axon hillock
More than one axon is stimulating a single neuron. (spatial summation)
Two or 3 subthreshold EPSP's can add up to one _________ potential.
A threshold EPSP and threshold IPSP stimulates a neuron simultaneously. Would an action potential result?
A neuron sending repeated stimuli (temporal summation) at subthreshold to another neuron in rapid succession, may sum up to an ______ potential.
threshold
No, they would cancel each other.
action

7. Meanwhile back at the synapse........ REPOLARIZATION
Another nerve impulse may not be received by a postsynaptic neuron, until it goes back to the __________ state.
polarized
Refractory period
Absolute -time when threshold stimulus does not start another action potential
Relative -time when stronger threshold stimulus can start another action potential

8. Meanwhile back at the synapse........ REPOLARIZATION
Neurotransmitter bound to a postsynaptic neuron producing a continuous postsynaptic effect must be removed from its receptor:
Blocks reception of additional “messages”
Removal of neurotransmitters occurs when they:
Are degraded by enzymes
Are reabsorbed by astrocytes or the presynaptic terminals
Diffuse from the synaptic cleft
Example - __________________ swiftly removes ACh from the receptors thus cutting off the influx of Na+ and eflux of ____. The ______ pump is activated to reestablish the ionic conditions. The membrane than returns to its ________ ________ potential of ____ mV. Membrane is ___________ to polarized.
Acetylcholinesterase K+
Na+K+
resting membrane
-70
repolarized

10. Control of Nerve Impulses at the Synapse
How drugs or poisons control/or destroy at the synapse:
Stop the chemical reactions that create neurotransmitters.
Ecstasy -->effects serotonin and midbrain dopamine systems resulting in the progressive degeneration of nerve terminals.
Interfer with vesicle storage or release of neurotransmitters
opiates increase release of dopamine; THC decrease
Interfers with deactivation of the neurotransmitter. - MAOI's inhibit the action of the enzyme Monoamine oxidase
Bind to receptors in place of neurotransmitters - mimics (agonists) & blockers (antagonists)
LSD ---replaces serotonin ---> hallucinates
caffeine --->replaces adenosine --> facilitates
Prevent neurotransmitters from returning to their sending neuron (reuptake) -
Cocaine
Paxil to control panic disorders
Interfer with second messengers, the chemical and electrical changes that take place in a receiving neuron.

11. Postsynaptic Potentials & Neurotransmitters
Inhibiting Postsynaptic Potentials (IPSP)
Neurotransmitters that inhibit -Serotonin, GABA, endorphins, ACh, epinephrine
Opiates (morphine) - inhibit the release of substance P
Valium - enhances binding effect of GABA (agonist)
Fluoxetine "Prozac“ blocks reuptake of serotonin
Excitatory postsynaptic potentials (EPSP)
Neurotransmitters -substance P, glutamate, dopamine, ACh , epinephrine
LSD - competes with serotonin for receptor (antagonist)
Amphetamines -enhance the release and decrease reuptake of dopamine
caffeine - lowers the threshold at synapse (facilitation)
nicotine - increase release of dopamine
Effects of alcohol
Increased turnover of norepinephrin and dopamine
slow acetylcholine systems
increased production of endorphins
increased transmission in GABA systems
Without alcohol
With alcohol
Chocolate
Moods

12. Effect of ions on nerve impulse transmission
Blocked Na+ channels
Decrease of K+ in extracellular fluids causes hyperpolarization of RMP
caused by starvation, alkalosis, kidney disease
symptoms - muscle weakness, sluggish reflexes
Increase or decrease threshold?
Stimulus needs to be stronger or weaker?
Increase of K+ in extracellular fluids causes depolarization of RMP
nervousness, convulsions, paralysis
Total depolarization would result in which of the symptoms?

13. References Web Sites on Nervous System Neuron Animations used in Class
Graded Potentials Connecticut College
Synapse Potential Connecticut College
Explore the Brain and Spinal Cord(Great Explanations)