Download LEVELS OF ORGANIZATION

INTRO TO PHYSIOLOGY, TISSUES, MEMBRANES
READING: p. 2-23; 61-68; 72-85
Physiology is the study of the functions of the body. It is a very logical science that
employs a few basic mechanisms to explain and predict what will happen in an organism.
What will happen to heart rate just before the onset of exercise? Will it return to resting
levels immediately after exercise stops? These are all typical questions a physiologist
would pose. Finding the answer to them highlights the other characteristic of physiology:
it is a mechanistic science. Physiologists ask “how” something occurs, and try to explain
the mechanism behind various events. For example, How does drinking alcohol increase
urinary output? How does muscle get bigger when it’s put under mechanical stress (i.e.
weightlifting)?
In this course, you will learn the basic “rules” that govern the functions of the body, so
that you will be able to explain and predict what the body will do in different situations.
You may even be able to enlighten your friends as to what’s really happening to them
when they exercise, or feel faint, or startle. In fact, the more fun you can have with this
material, the better. Because you will be learning about yourself and the way your body
functions, the more personal you can make the information, the more you will enjoy it.
So observe the way your body responds when you run or eat or hold your breath and try
to figure out what’s going on. Two favorite questions can help to guide your logic:
“Does this make sense?”
“Would the body ‘want’ to do this?”
BIO 131 is called “Systemic Physiology”, which is a subdivision of physiology that
studies how the organ systems of the body are integrated to sustain life. They
communicate and cooperate with each other in a myriad of ways, and have one goal in
common: the maintenance of homeostasis, a relatively stable internal environment for
the cells. (Think about why this might be important functionally).
“Systemic” also means that we will be touring the body one organ system at a time, and
integrating as we go along. To begin this process, you first need to learn about the basic
building blocks of the body: the cells and how they organize into tissues. From there we
will enter the nervous system, and then we are on our way. Please keep in mind that
every step of the process is important, and that most of the concepts learned in these early
chapters will be seen again and again – they really are crucial to your later understanding,
so learn them!!
The following questions are designed to “guide” you through the reading material, and
you will see this type of set-up (area summary followed by questions) for each section.
The right margin is larger to allow you to practice Cornell note taking – try it!
** Also pay attention the “mapping” demo in this chapter (pg. 6-7) – we will do a lot of
this! In fact, mapping will become the only real source of extra credit in the class.
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LEVELS OF ORGANIZATION
1. Living organisms are comprised of many different levels of
organization. In this course, we will focus on the levels from
cells to organ systems. Name these levels. (p. 3)
______________________________________________________
______________________________________________________
2. You should be able to name all of the physiological systems of
the body. In the following spaces, list the appropriate organ
system next to its functional description. (Fig. 1.2, p. 4)
Maintenance of water/solute levels in the body ________________
Defense against foreign invaders
________________________
Support and movement
________________________
Coordination of body function via molecules traveling through
blood/body fluids
________________________
Coordination of body function via electrical signals
________________________
Transport of substances between cells/tissues _________________
Exchange of CO2 and O2 with environment __________________
3. Name three of the above systems that could be considered
“communicating” systems.
______________________________________________________
FUNCTION AND MECHANISM
4. It is very important for you to be able to distinguish between
function and mechanism. Your book describes that thinking
about function explains “why” something happens, whereas
thinking about mechanism explains “how” something happens
(p. 5). Practice: Describe how each approach would explain
the formation of ATP by the mitochondria ("why" it is formed
vs. "how" it is formed)
______________________________________________________
______________________________________________________
______________________________________________________
*NOTE: On exams for this class you will almost always be
asked to describe HOW something happens (i.e. the
mechanism).
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THEMES IN PHYSIOLOGY
5. List four key themes in physiology (p. 5, 8-9). Give one
example of the importance of each in the study of physiology.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
6. Define homeostasis, using words and a level of explanation
that a non-science person would be able to understand.(p. 9-10)
______________________________________________________
________________________________________________________________
______________________________________________________
7. Disease happens when homeostasis fails. Describe (with
examples) internal vs. external sources of failure (p. 10)
______________________________________________________
______________________________________________________
8. Requirements for cells (oxygen, nutrients, waste removal) are
met by their immediate environment (internal environment).
What is the “internal environment” cells of the body? (p. 10)
______________________________________________________
9. Give an example of how the law of mass balance would be
observed in the human body (p. 11-12)
______________________________________________________
10. What are the two primary organs that act to clear substances
from the body? (p. 12)
______________________________________________________
11. How does clearance rate play a role in the development of
therapeutic drugs by pharmaceutical companies? (p. 12)
______________________________________________________
12. How is homeostasis different from equilibrium? (p. 13)
______________________________________________________
______________________________________________________
13. Distinguish between local control and reflex, or “longdistance” control (p. 13-14)
______________________________________________________
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14. Why is negative feedback so important in maintaining
homeostasis? (p. 15-16)
______________________________________________________
______________________________________________________
15. When might you see a positive feedback loop? (p. 17)
______________________________________________________
______________________________________________________
16. How do biorhythms associated with body temperature affect
an individual’s function? (p. 17)
_____________________________________________________
_____________________________________________________
17. Use the idea of biological rhythms to explain something that
changes for you in a different environment (p. 17-18)
_____________________________________________________
_____________________________________________________
THE SCIENCE OF PHYSIOLOGY
18. What is the difference between an independent and a
dependent variable? (p. 19)
______________________________________________________
______________________________________________________
______________________________________________________
19. Why should every experiment have a control?
______________________________________________________
20. How does a scientific theory differ from a hypothesis? (p. 18)
______________________________________________________
______________________________________________________
21. What is the advantage of having a crossover study (vs. one in
which the experimental and control groups are different)?
______________________________________________________
Although we will be conducting some minor experiments on you,
human experimentation is really tricky!
22. Describe the placebo and nocebo effects. (p. 22)
______________________________________________________
______________________________________________________
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LOOK AT THE GRAPHS AND THEIR ASSOCIATED
QUESTIONS ON PAGES 20-21; PLEASE ANSWER THE
GRAPH QUESTIONS FOR EACH.
------------------------------------------------------------------------------BRIEF HIGHLIGHTS OF… CELLS, MEMBRANES
23. What are the three fluid compartments of the body? (p. 61)
_____________________________________________________
24. What are the two primary functions of the cell membrane?
(p. 61)
______________________________________________________
25. Membranes are composed mostly of ____________________
and ____________________________. (p. 62)
26. What is the role of cholesterol in the cell membrane? (p. 6768)
________________________________________________
NOTE: Much of this chapter (e.g. organelle function), as well as
the roles of membrane proteins, should be a review from intro
biology (I assume you know it). Need more review: pgs 65-72.
TISSUES OF THE BODY
27. Name two body tissues with lots of extracellular matrix. (p. 72)
______________________________________________________
28. What are cell adhesion molecules and why are they important?
______________________________________________________
29. Cells are held together by cell junctions to form tissues. Give a
primary function for each of these junctions. (p. 72-75) Place a
star next to those you'd expect to find in skin.
Tight junctions:
______________________________________________________
Gap junctions:
______________________________________________________
Anchoring junctions (e.g. desmosomes):
______________________________________________________
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30. How might anchoring junctions (or their lack) play a role in
cancer? (p. 74) _____________________________________
______________________________________________________
There are four basic tissue types: epithelial, connective, muscle,
and nervous. Their characteristics are described in detail on pgs.
76-84. It is not necessary to read these pages intensively; rather,
skim to get an overview.
31. List two basic functions for each of the tissue types listed.
Epithelial tissue
_______________________________________________
Connective tissue
_______________________________________________
Muscle tissue
_______________________________________________
Nervous tissue
_______________________________________________
32. Which tissue types are “excitable tissues”? What does that
term mean? (p. 84)
______________________________________________________
______________________________________________________
______________________________________________________
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TISSUE REMODELING
33. When might it be useful to have apoptosis? (p. 84)
______________________________________________________
______________________________________________________
Read the information on stem cells, but realize that this area of
research is moving so rapidly that the information in this book
does not reflect the current research. We have a Regenerative
Medicine speakers series. More talks will come up this semester –
please attend!
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COMMUNICATION AROUND THE BODY
READING: p. 166-170; 180-189; 197-209; 236-250
The ways in which cells communicate with each other are highly complex and are
included in an area of scientific discovery that is rapidly growing; however, they
essentially boil down to two basic signal types: electrical signals (changing the MP), or
chemical signals that bind to targets on cells. Local electrical signals can pass from cell
to cell, and electrical signals can travel long distances as action potentials. Chemical
signals (responsible for the bulk of communication) come in a wide variety of
classifications, but in all cases the chemical doing the signaling is called a ligand.
Ligands and include paracrines, cytokines, and hormones (among others), and obey the
general rules for protein interactions – specificity, affinity, competition, and saturation
(please refer to pg. 46 of the text for a review of these if needed).
It can be very confusing to sort everything out, but for this class, we will primarily cover
the big ideas, as there’s another course that will cover it in detail (BIO 121).
1. Local communication between cells can be electrical (gap
junctions) or chemical (contact-dependent signals, among
others). How do these two differ from each other? (p. 166)
______________________________________________________
______________________________________________________
2. How do paracrine and autocrine signals differ? (p. 167-8)
______________________________________________________
3. Describe histamine’s role as a paracrine. (p. 168)
______________________________________________________
It might not make the most sense now, but come back to this bit on
neurotransmitters, neurohormones, & hormones soon!
4. Differentiate between the following: (p. 168)
Neurotransmitter
Neuromodulator
Neurohormone
5. How are cytokines different from hormones? (p. 168)
______________________________________________________
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6. Why do only cells of the thyroid gland respond to the hormone
Thyroid Stimulating Hormone (TSH), when it’s floating around in
the blood and comes in contact with all kinds of cells? (p. 169)
______________________________________________________
7. What determines if a signal molecule binds on the outside of the
cell or the inside of the cell? If it only binds on the outside, can it
still cause things to change intracellularly? How? (p. 169)
______________________________________________________
______________________________________________________
8. Describe the role of a second messenger (p. 170)
______________________________________________________
*details of signal transduction will be left to other classes; we
will skip to how those signals may be modulated, p. 180*
9. How does competition affect signaling? Give an example
______________________________________________________
10. Differentiate between an agonist and an antagonist (p. 180)
______________________________________________________
11. In lung tissue, the hormone epinephrine causes smooth muscle
cells to relax, whereas in the blood vessels of the stomach,
epinephrine causes smooth muscle to contract. How can this same
chemical cause different effects in different places? (p. 180-81)
______________________________________________________
______________________________________________________
12. If a patient had high circulating levels of Hormone X (assume
this is going on for a while), would you expect that person to have
a normal, down-regulated, or up-regulated number of receptors for
X? Explain your reasoning. (p. 181)
______________________________________________________
______________________________________________________
13. How is down regulation different from desensitization? (p.
181)
______________________________________________________
14. Use the portion of the Running Problem at the top of p. 182 to
explain how insulin receptors differ in Type 1 and Type 2 diabetes.
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15. Once a cell has received a signal from another, how does it
stop the signal pathway from continually progressing? (p. 182)
_____________________________________________________
** Review homeostatic reflex pathways described on p. 182-187
16. Look carefully at the comparison of neural (electrical) and
endocrine (chemical) control pathways in Table 6.2, p. 188. Given
these parameters, decide if the following would be mediated by a
neural pathway or an endocrine one. Then, come up with at least a
few of their own examples.
You smell smoke and look for a fire
You lift weights and your muscles increase in size
If you haven’t eaten in a while, your liver releases glucose
You step on a sharp object and start hopping on the other foot
17. How is signal intensity encoded in the nervous system? What
about the endocrine system? (p. 189)
______________________________________________________
______________________________________________________
SKIP TO THE NEXT CHAPTER – THE ENDOCRINE SYSTEM
**We first introduce the Endocrine system here, but we’ll see it all semester long!
A hormone is a chemical released into the blood that acts on a distant target. It is
effective in very low concentrations, and its specificity is due to the receptors on the
target tissue. Chemically, hormones fall into one of three classes: peptide, steroid, or
amine. They are generally distinguished according to how they are synthesized, stored,
and released; how they are transported in the blood; and the mechanisms by which they
cause a cellular response. Hormones can also interact with other hormones, and in doing
so, alter cellular response. Three types of hormone interaction are discussed in the book:
synergism, permissiveness, and antagonism.
Remember the ideas of negative feedback control systems when reading this material!
While studying endocrine pathologies, really try to understand the concepts of
hypersecretion, hyposecretion, up- and down-regulation, and abnormal tissue
responsiveness.
18. Hormones act on their target cells by controlling…..(p. 197)
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19. What are the four classic steps for identifying an endocrine
gland? (p. 198)
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20. Based on the evidence (p. 199), do you think human
pheromones exist?
______________________________________________________
21. What is meant by “the cellular mechanism of action” of a
hormone? (p. 199)
_______________________________\______________________
22. How can different cells have variable responsiveness to a
single hormone? (p. 199)
______________________________________________________
______________________________________________________
23. What is the half-life of a hormone? (p. 199-201)
______________________________________________________
24. What are the three chemical classes of hormones? (Table 7-1,
p. 202)
______________________________________________________
25. Which two hormone types are transported in the blood bound
to carriers? (Table 7-1)
______________________________________________________
26. Which hormone type is synthesized on demand? What does
that tell you about its response time?
______________________________________________________
______________________________________________________
27. What do steroid and thyroid hormones have in common?
(Table 7-1)
______________________________________________________
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28. MOST hormones are ________________________ (p. 201).
29. What is the function of the preprohormone? (p. 202)
______________________________________________________
______________________________________________________
30. Are prohormones active molecules? __________ (p. 202-3)
31. What does “post-translational modification” mean? Could the
inactive fragments be useful? (p. 202-3)
______________________________________________________
______________________________________________________
32. How long does the effect of a peptide hormone last? (p. 202)
______________________________________________________
33. Steroid hormones are derived from _____________________(p. 204)
34. Why can’t steroid hormones be stored? (p. 204)
______________________________________________________
______________________________________________________
35. Two common hormones released during stress are cortisol (a
steroid) and epinephrine (an amino acid-based hormone).
Which gives you that instant “rush”? Which would you expect
to be in the blood longer, and why? (p. 204)
______________________________________________________
______________________________________________________
36. Given the cellular mechanism of action of steroid hormones
(p. 204), why would it be dangerous for someone to take
“extra” (exogenous) steroids?
______________________________________________________
______________________________________________________
37. The catecholamines, all derived from the amino acid tyrosine,
include ____________________________________________
(list all three, p. 206).
38. Describe how insulin is involved in a reflex pathway (Fig 7-7,
p. 208)
______________________________________________________
______________________________________________________
11
39. Draw a reflex pathway for parathyroid hormone in the space
below (see p. 208 for the description)
40. Describe at least one way in which the nervous system can
affect hormone release (p. 209)
______________________________________________________
SKIP TO THE NEXT CHAPTER: ELECTRICAL SIGNALS
Electrical communication will be the topic of the next few sections as we cover the
Nervous System. The Nervous System is specialized for rapid communication of signals
throughout the body, and is composed of two primary cell types: neurons and glial cells.
Neurons are responsible for producing and transmitting electrical and chemical signals to
cells throughout the body, whereas glial cells are the support cells for the system. We
will focus our attention on neurons, which have three basic parts: the cell body, the axon,
and the dendrites.
As you have learned, electrical signaling along the neuron is due to ion movement across
its membrane. Different portions of the neuron conduct electrical signals differently.
The conduction of action potentials occurs only on the axon. The cell body and dendrites
lack the fast Na+ channels necessary for the initiation of an action potential, and instead
exhibit smaller electrical changes called graded potentials. Graded potentials are
summed, and if they surpass the threshold for the membrane, an action potential is
created. Action potentials cannot be summed, and are called “all or none” phenomena.
I assume you know basic neuronal anatomy!
ELECTRICAL SIGNALS IN NEURONS
1. Neurons and muscle cells are called excitable tissues because
they do what? (p. 236)
______________________________________________________
2. What two factors influence membrane potential? (p. 236)
______________________________________________________
______________________________________________________
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3. _________ is the major ion contributing to the resting
membrane potential.
4. Which ion is more concentrated in the ECF: Na+ or K+ ?
Which is more concentrated in the ICF?
______________________________________________________
______________________________________________________
5. If the cell membrane is made suddenly permeable to Na+, in
which direction will it move? What is causing this movement?
(p. 238)
______________________________________________________
6. When the membrane potential moves from –70 mV to +10 mV,
what happens to the existing concentration differences across
the membrane? (p. 238)
______________________________________________________
7.
If the cell membrane suddenly becomes more permeable to
K+, what happens to the state of the membrane? Why?
______________________________________________________
______________________________________________________
8. How do cells alter their permeability to ions? (p. 238-39)
______________________________________________________
9. How are ion channels classified? Describe each type briefly
(p. 239)
______________________________________________________
______________________________________________________
______________________________________________________
10. What is a graded potential? (p. 240)
______________________________________________________
______________________________________________________
11. How are action potentials different from graded potentials?
______________________________________________________
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13
12. Where on the neuron do graded potentials occur? Action
potentials? (p. 240-41)
______________________________________________________
______________________________________________________
______________________________________________________
13. What determines the magnitude of the graded potential? (p. 240)
______________________________________________________
14. Describe two ways in which ion movement can hyperpolarize a cell.
______________________________________________________
______________________________________________________
15. Where is the trigger zone? (p. 241)
________________________________________
16. If a graded potential reaches threshold at the trigger zone, what
happens? (p. 241-42)
______________________________________________________
________________________________________________________________
17. If several graded potentials reach the trigger zone at the same
time, what do you think will happen? Explain.
______________________________________________________
______________________________________________________
18. Define an action potential. (p. 242)
______________________________________________________
______________________________________________________
19. What does “all-or-none” mean when referring to action
potentials? (p. 242)
______________________________________________________
______________________________________________________
20. Action potentials specifically involve the movements of what
two ions? In which direction are they moving? (p. 243)
______________________________________________________
________________________________________________________________
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21. For each phase of the action potential listed below, indicate
what is happening to ion permeability, which ions are moving,
and in what direction (in or out of cell).
Rising phase:
Peak:
Falling phase:
After-hyperpolarization:
22. Name the two gates of the voltage-gated Na+ channels. (p. 245)
______________________________________________________
23. In the resting neuron, which of these gates are closed and
which are open?
______________________________________________________
24. Depolarization opens the _____________________________
gate.
25. When do inactivation gates close? Why do they close? (p. 245)
______________________________________________________
________________________________________________________________
26. What must happen to the gates before the next action potential
can take place?
______________________________________________________
27. Define refractory period. (p. 245-46)
______________________________________________________
______________________________________________________
28. How do the absolute & relative refractory periods differ?
______________________________________________________
______________________________________________________
______________________________________________________
29. Why might the absolute refractory period be a “good thing”?
(p. 246)
______________________________________________________
______________________________________________________
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30. Describe the role of the Na+/K+ ATPase pump in the action
potential. (p. 246)
______________________________________________________
______________________________________________________
______________________________________________________
31. What is meant by the conduction of action potentials? (p. 246)
______________________________________________________
32. When Na+ channels in the middle of an axon open,
depolarizing current flow will spread in both directions along
the axon. Why then don’t action potentials ever reverse and
move back toward the cell body?
______________________________________________________
______________________________________________________
33. List two factors that affect the speed of action potential
conduction. (p. 247-49)
______________________________________________________
34. Explain saltatory conduction. (p. 249)
______________________________________________________
______________________________________________________
35. What happens to conduction through axons that have lost their
myelin? (p. 249)
______________________________________________________
THINGS TO TRY:
1. Lidocaine inactivates voltage-gated Na+ channels on the neuronal membrane. If
lidocaine is placed on the axon of a nerve that normally transmits signals from a
pain receptor to the brain (to be interpreted by the brain as “pain”), the pain is not
“felt” by the individual. Explain why.
2. Draw/label a neuron. Indicate on your picture exactly where graded
potentials would be generated and where action potentials would be generated
3. Drug Z prevents sodium inactivation (“h”) gates from moving from their resting
position (“resting” refers to their position when the membrane is at its RMP).
How would administration of Drug Z affect the function of a neuron?
16
SYNAPSES
READING: p. 253-
An action potential can travel down the length of the neuronal membrane and
communicate the electrical information to another cell. This transmission occurs via a
synapse. A synapse is a junction between a neuron and a target cell, which could be
another neuron, a muscle cell, or a gland. At a synapse, the axon of the presynaptic
neuron passes information to receptors on the dendrites or cell body of the postsynaptic
target cell(s). Most synapses are chemical junctions, and involve the release of
neurotransmitter from the presynaptic neuron onto the postsynaptic cell.
Neurotransmitters are manufactured in the cell bodies of neurons (where the organelles
are located) and travel down to the axon terminal where they are housed in vesicles until
signaled for release. When the appropriate signal (action potential) arrives,
neurotransmitter is released via exocytosis. The neurotransmitter then travels by
diffusion to the postsynaptic membrane where it opens ion channels, resulting in some
type of electrical potential change. Because this electrical change occurs on the dendrites
or cell body, it is a graded potential. The overall postsynaptic potential change will
determine whether or not an action potential will be fired.
Synaptic transmissions that bring the postsynaptic membrane closer to threshold are
called excitatory postsynaptic potentials, or EPSPs. Inhibitory postsynaptic potentials, or
IPSPs, take the membrane further from threshold. As mentioned, it is the overall
postsynaptic potential that will determine if an action potential is fired on the
postsynaptic cell.
1.
Name the seven classes of neurotransmitters. (p. 254-57)
______________________________________________________
______________________________________________________
______________________________________________________
*Note: we will spend a lot of time in class on specific NT’s, so
just read over the info on pg. 255 to get familiar with them.
2.
What are the possible places for neurotransmitter
synthesis? Where is it stored? (p. 257)
______________________________________________________
______________________________________________________
3. At a chemical synapse, describe the sequence of events that
leads to neurotransmitter release, beginning with an action
potential traveling along the presynaptic membrane. (p. 258)
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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4. What is the chemical trigger for neurotransmitter release?
______________________________________________________
5. How does the new “kiss and run” pathway compare to regular
exocytosis? (p. 258)
______________________________________________________
6. What happens to Ach after it is released into the synaptic cleft?
(Fig. 8-19, p. 259)
______________________________________________________
7. How, using the same neurotransmitter, might an olfactory
neuron alert you to a stronger smell? (p. 260)
______________________________________________________
8. Draw a picture of neurons converging and another of neurons
diverging. (p. 262)
9. Name one advantage of convergence. (Fig. 8-22, p. 262)
______________________________________________________
______________________________________________________
10. A slow synaptic potential would likely cause what type of
effect? (Fig 8-23, p. 263)
______________________________________________________
11. What is spatial summation of graded potentials? (p. 264-65)
______________________________________________________
______________________________________________________
______________________________________________________
12. Describe postsynaptic inhibition (p. 266)
______________________________________________________
______________________________________________________
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13. Describe temporal summation (Fig. 8-24, p. 264)
______________________________________________________
______________________________________________________
14. Define long-term potentiation (p. 267)
______________________________________________________
______________________________________________________
15. When might long-term potentiation be useful?
______________________________________________________
______________________________________________________
______________________________________________________
16. List some pharmacological agents that can alter synaptic
transmission. (p. 268)
______________________________________________________
______________________________________________________
17. Neuron A, Neuron B and Neuron C are all presynaptic to
Neuron F. If A and B fire, F fires. If A and C fire, nothing
happens. Draw this scenario below.
What can you conclude about the synapse between C and F?
Between A and F? What other information might you need?
______________________________________________________
______________________________________________________
19
18. Neuron J, Neuron K, and Neuron L are all presynaptic to
Neuron T. J and K are both excitatory to T, whereas L is
inhibitory to T. Assume that T needs a net input of +2 (one
EPSP is +1; one IPSP is -1) to fire an action potential.
Describe how temporal summation could result in an action
potential on T. Describe how spatial summation could result in
an action potential on T.
______________________________________________________
______________________________________________________
______________________________________________________
THINGS TO TRY:
1. Neuron A, Neuron B and Neuron C are presynaptic to Neuron D. When A fires an
action potential, D fires an action potential. When A and B fire simultaneously, D
does not fire. When A, B, and C fire simultaneously, D fires. This is an example
of...
A. inhibition by D and temporal summation by A and B.
B. inhibition by B and temporal summation by A and C.
C. inhibition by B and spatial summation by A and C.
D. inhibition by B and spatial summation by A and D.
E. inhibition by A and spatial summation by B and C.
Defend your choice.
2. Black widow venom causes an explosive release in acetylcholine from the axon
terminals of neurons leading to skeletal muscle. Discuss why this might be
problematic to the victim.
3. Botulism toxin blocks the release of acetylcholine from these same neurons.
How would the effects of this toxin compare to black widow venom? Can you
explain why the victim would experience respiratory distress in both cases?
20