http://www.youtube.com/watch?v=70DyJw
wFnkU
What is it?
 Synapse- the space where a neuron communicates
with another neuron, a muscle, or a gland
 Where the electrical activity in one neuron effects the
excitability of another
What was a gap junction?
In what body system did
we talk about them?
2 types of synapses…
 1. Electrical
 plasma membranes of the
presynaptic and postsynaptic cells
are joined by a gap junction
 Electrical impulse passes from cell
to cell very quickly
 In cardiac and smooth muscle
 NOT our focus!
 2. Chemical- no physical
connection between cells;
need a messenger
neurotransmitters
 Sent neurotransmitter/message
can:
 generate an action
potential/response from the
receiving cell (excitatory
synapse)
 prevent the receiving cell from
generating an AP/showing a
response (inhibitory synapse)
How does a synapse work?
1.
If I told you muscles are “activated” the same way
resting neurons are excited, then what must be
present during a synapse to make the muscle move?
2. Can these things (that will make muscles move)
enter and exit the cell freely? Explain why or why not.
3. How will the neuron send a message to the receiving
muscle cell?
4. Based on all of the answers to the above questions
begin to formulate a theory about how neurons talk
to muscle cells and tell them to move.
*THEORY:
Model it…
 Using the materials you have been given design a
sensible model that shows how a neuron can make a
muscle move. Feel free to manipulate the materials as
needed. Keep your answers to the previous questions
in mind.
 Identify what each material represents
 White cell:
 Red/pink cell:
 Pipecleaner:
 Pony beads:
 Beans:
Now…
 Merge with another group and explain your
models
 Discuss that aspects of the model are plausible
and which may need some refinement and see if
you can create a better working model.
 This final idea from the group duet will be
shared with the class.
http://www.youtube.com/watch?v=HXx9qlJetSU
Events of a Chemical Synapse
An AP stimulates the release of synaptic vessicles
(contain neurotransmitters)
1.

Vessicles bind w/ the terminal axon membrane  exocytosis
2. Released NTs bind to receptor proteins on the plasma
membrane of the post-synaptic cell


Excitatory response  yes AP fired/receiving cell shows
response
Inhibitory response  no AP fired/receiving cell not
stimulated
 Neurotransmitters don’t last for long b/c they are either
 inactivated by enzymes
 taken back up by the axon terminal  reuptake
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__transmission_across_a_synapse.html
What do you know?
 Get into your small groups from yesterday
 In a type 1 list the steps that occur, from start to finish,
that allow a neuron to talk to a muscle
 NOW swap papers with another group, read their list
of events and comment on anything that seems
incorrect
 Meet up with the group that has your paper and
discuss the criticisms
 Any questions?
Synaptic Integration
 *** 1 synapse is not usually enough to cause activation
but there are thousands of synapses occurring some
happen close enough that their effects can add
together to cause activation
http://www.youtube.com/watch?v=HXx9qlJetSU
Neuron-Muscle Communication
1. Ach (Aceytlcholine)
 is released from the nerve
 Both Na and K channels open simultaneously

way more Na comes in than K goes out  net increase in charge
 10,000 ions cross in first millisecond
 Causes muscle to respond to stimulus
 - Removed from synaptic cleft VERY FAST by an
enzyme called acetylcholinesterase
 Sarin inhibits this enzyme  how?
 Nerve gas in Japanese terrorist attacks
http://www.youtube.com/watch?v=ra2HeSjo82c (start 6:08)
Neuron-Neuron Communication
1. GABA
 Major inhibitory NT in brain
 actually inhibits the signal and causes the cell to
go further from the threshold (Opens Clchannels)
 Valium increases GABA levels by increasing
release of GABA

Taken to relieve anxiety, muscle spasms, and seizures
Neuron-Neuron Communication
2. Dopamine
 Involved in emotional behavior and motor control
 Lack of dopamine causes Parkinsons
(characterized by excessive shaking)
 Amphetamines stimulate dopamine receptors 
why they’re addictive
 When we are rewarded, feel good there are inc
levels of dopamine
Neuron-Neuron Communication
3. Serotonin



Serotonin involved in control of sleep and emotion
Lack of serotonin one cause of depression
Many antidepressants block the reuptake of serotonin
so effectiveness in increased  more positive feelings
4. Endorphins


Example of a NEUROMODULATOR – which have
slower, longer effects on pre- or post- synaptic cells.
Blocks perception of pain and evokes a feeling of wellbeing

Runner’s High  lets you push yourself… sometimes too far