1. Information Transfer Across Chemical Synapses

2. Chemical Synapse Structures

3. Events occurring at a chemical synapse in response to depolarization of the axonal terminal:
(1) Arrival of the depolarization wave (nerve impulse) results in the opening of calcium gates and calcium (Ca 2+) influx into the axonal terminal.
(2)
Calcium ions promote
the fusion of synaptic
vesicles with the
presynaptic membrane
and exocytosis of
neurotransmitter.
Nerve Impulse
Ca +

4. (3)The neurotransmitter diffuses across the synaptic cleft and attaches to receptors on the postsynaptic membrane. (4) Binding of neurotransmitter opens the ion channels, which results in voltage changes in the postsynaptic membrane

5. (5) Effects are short-lived because the
neurotransmitter is quickly destroyed by
enzymes or taken back up into the presynaptic
terminal, which closes the ion channels and
terminates the synaptic response.

6. Information Transfer Across Chemical Synapses
When a nerve impulse reaches the axon terminal, it
sets into motion a chain of events that triggers
neurotransmitter release.
The neurotransmitter crosses the synaptic cleft and,
on binding to receptors on the postsynaptic
membrane, causes changes in the postsynaptic
membrane permeability.
Record the 4 successive events (A through D on top of the next 4 slides) on the back of your Synapse & Reflex Arc WS

7. A. Calcium Gates Open
Calcium gates open in the presynaptic axonal terminal.
When the nerve impulse reaches the axon terminal,
depolarization of the membrane opens not only
Na+ channels but voltage-regulated Ca2+ channels as
well.
During the brief time the calcium gates
are open, Ca2+ floods into the
terminal from the extracellular
fluid.
Na+

8. B. Neurotransmitter released by exocytosis
(2) Neurotransmitter is released by exocytosis.
The surge of free calcium into the axonal terminal acts as
an intracellular messenger, directing synaptic vesicles
to fuse with the axonal membrane and empty their
contents by exocytosis into the synaptic cleft.
The Ca2+ is then quickly removed, either taken up into
the mitochondria or ejected to the outside by an active
calcium membrane pump.

9. C. Neurotransmitter binds to postsynaptic receptors.
The neurotransmitter diffuses across the
synaptic cleft and binds reversibly to specific
protein receptors that are densely clustered on
the postsynaptic membrane.

10. D. Ion channels open in the postsynaptic membrane.
As the receptor proteins bind neurotransmitter
molecules (lil’ circles), their three-dimensional shape changes.
This causes ion channels to open, and the resulting
current flows produce local changes in the membrane
potential.
Depending on the receptor protein to which the
neurotransmitter binds and the type of channel the
receptor controls, the postsynaptic neuron may be excited or
inhibited.

11. For each nerve impulse reaching the presynaptic
terminal, many vesicles (perhaps 300) are emptied
into the synaptic cleft.
The higher the frequency of impulses reaching
the terminals (that is, the more intense the
stimulus), the greater the total number of synaptic
vesicles that fuse and spill their contents, and the
greater the effect on the postsynaptic cell.

12. On the front left side of your paper...
Use the following colors to color in the dots and the appropriate structures on the left-hand side of your paper. Use the arrows and hints below, as well as the previous slide show, to color the whole picture accordingly
Red =Axonal terminal
Pink = Mitochondria
Orange = K+ ions
Yellow = Postsynaptic neurotransmitter receptors (hint: looks like Pac-Man)
Lt. Green = Postsynaptic membrane (hint: it looks like the phospholipid bilayer = lil’ circles with 2 squiggly lines)
Dk. Green = Na+ ions (go in & out of postsynaptic membrane)
Lt. Blue = Chemically gated channels (hint: it’s part of the postsynaptic membrane)
Dk. Blue = Presynaptic membrane
Purple = Ca+ ions
Brown = Synaptic vesicles (hold the neurotransmitters in the axon terminal)
Black = Neurotransmitter molecules
*Also, put a bracket around & label the synaptic cleft!

13. On the front right side of your paper…
Grab a new A&P book from the cabinet in the back of the room (you’ll have to share with your neighbor)
Turn to page 237, and take turns reading the section titled Physiology: Reflexes (through pg. 239). Also, check out Figure 7.11 (c)

14. After reading this, please complete the right side of your paper by:
Answering questions 1-3
Color in the circles as follows:
Receptor region = red
Sensory neuron = orange
Association neuron = yellow
Motor neuron = green
Effector = blue
Color in the picture accordingly
Also, please label the White and Gray Matter of the Spinal Cord
Please hand in this paper when you are done!

15. Reflex Lab Pick up the Reflex Lab
Use the remaining time in class to work with a partner to complete the reflex lab. To have the information that you need to be successful, I highly recommend:
Using a purple A&P book from the bookshelf in the front of the classroom, and see the pages/sections recommended on the lab. Don’t be afraid to read the corresponding sections in the book!
Grabbing a lab manual from the bookshelf in the back of the room. This will show pictures of where to use the percussion hammer in order to test the reflex properly
Make sure you are relaxed when you are testing your reflexes (your leg should be dangling freely, not resting on anything when you test the patellar reflex)
If you do not see a reflex in you or your partner after several tries, find someone that does respond so you can answer the lab correctly
This lab will be due at the beginning of class on Monday. Don’t forget to complete Figure 27.1, and the Part A and Part B Assessments, and USE THE BOOK TO HELP YOU ANSWER THIS!