Discussion – Week of Dec. 12th – Homework for Repro, Stress, and Neuro
Please complete and dropbox these before coming to discussion and bring a copy with you to discussion.
In discussion we will focus on any questions you have about the homework or any other questions you have
relating to Dr. Abbott’s material.
1. Diagram, describe, and contrast the nature and rapidity of the following two responses to stress.
a. Stress response: ACTH (cortex of the adrenal gland)
ACTH released from the pituitary causes the adrenal glands to release cortisol. Cortisol
then induces the liver to convert glucagon to glucose and provide the body with more energy to
address the fight-or flight response and make the body more attentive.
b. Stress response: Neural regulation of adrenal medulla function – not regulated by hypothalamic hormones
The adrenal medulla is the principal site for the conversion of the amino acid tyrosine to
epinephrine and dopamine. The adrenal medulla secretes hormones including adrenaline inducing
an increase in heart rate and metabolism.
2. Review the link between type 2 diabetes and stress.
Physical stress such as illness or injury and mental stress causes higher blood glucose levels in
people with either type of diabetes. When stress is present the body undergoes the flight-or-flight
response and cortisol releases stored energy in the form of glucose. When stress is common, this leads to
long term increased blood glucose levels and diabetes for those whose body can’t lower back to normal.
3. How does the production of male and female gametes differ in humans? To answer this do the following.
Using all the terms below, diagram the control of gamete and sex hormone production first in a human male and then in
a human female. Be sure to explain the role(s) of each term in your diagram.
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Use your diagrams to answer the following questions by filling in the charts below.
a. In both males and females, the hypothalamus produces GnRH, which stimulates the pituitary to release LH
and FSH. How are these similar and how are these different?
b. In both males and females, the testes or ovaries produce additional hormones. What are these and what
functions do they serve?
Hormone
a. In males causes:
b. In females causes:
LH
Stimulates Leydig cell
production of testosterone.
Triggers ovulation and
development of the corpus luteum.
Acts on the Sertoli cells of the
testes to stimulate sperm
production.
Stimulates growth of ovarian
follicles before the release of the
egg.
a) Males produce:
b) Females produce
Hormones
Are influenced by LH and FSH
but produce testosterone
The ovaries produce progesterone
and three types of estrogen
Function of
these
hormones
produced in
the gonads
Helps develop the male
reproductive system of the
testes and prostate. It also
develops secondary sex
characteristics including hair,
muscle, and bone mass.
Progesterone is needed for the
thickening of the uterus wall and
the implantation of the fertilized
egg. Estrogen develops female
secondary characteristics including
breasts, endometrium, and
regulation of the menstrual cycle.
FSH
4. Most birth control methods are designed to keep the egg and sperm from uniting to form a zygote. Many birth
control pills or patches used by human females contain a combination of estrogen and progesterone. How do they keep
sperm from uniting with egg? Explain the mechanism.
The main method is to stop the growth and release of the egg at ovulation. This then means no
sperm can unite and fertilize the egg. They also have the ability to prevent the fertilized egg from
implanting in the endometrium wall of the uterus and pass through as an early form of abortion.
5. How do neurons function to transmit information?
Neurons function by having a series of Na+/K+ ion channels. Once the voltage has depolarized
enough an action potential is sent from the axon hillock down the axon to the neuron terminal and to the
next dendrite.
Develop a model of a two neuron system (presynaptic and postsynaptic). Be sure to include definitions or descriptions of
the following terms and structures in your model.
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Use your model to answer the following questions.
6. All cells maintain an ionic (and therefore electrical) potential difference across their membranes. In most cells, this
potential difference is between -50 and -100 mV. That is, the inside of the cells is more negative than the outside by 50
to 100 mV. Although all cells in the body maintain this potential difference across their membranes, only certain cells
(for example, neurons) are capable of generating action potentials.
a. How is this potential difference across the cell membrane generated?
The potential is generated by the influx of ligand and voltage gated Na+ ions causing rapid
depolarization. Once the action potential level is reached, the axon hillock sends a signal down the
axon.
b. What characteristics of membranes allow cells to concentrate or exclude ions?
They have specific ion channels for Na+ and K+ ions. In addition, the axons have a fatty
myelin sheath that excludes ion transfer but has openings in intervals down the axon to speed up
signal transfer.
c. What is it about neurons (nerve cells) that make their properties different from those of other cells? In other
words, what enables nerve cells to produce action potentials?
Neurons purpose is to pass information in the form of a electrochemical signal around the
body. This is down by depolarization by an influx of Na+ ions by both voltage and ligand gated ion
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channels to form the action potential away from the axon hillock and repolarization by the intake
of K+ ions. They also work with glial cells to enhance speed.
7. A meter recorded the changes in potential difference at a
specific point across the membrane of a squid axon during
passage of an action potential (see diagram).
a. Describe in words what happens in the recorded part
of the axon membrane at each of the points labeled 1 to
5.
1, ligand gated Na+ channels open to
depolarize. 2, voltage gated Na+ channels open. 3,
action potential is achieved followed by K+
channels opening and repolarization. 4,
undershoot of membrane potential. 5, return to
resting state by leaking.
b. What will happen to the observed recordings of the action potential as it is measured at each point as it
continues along the remainder of the axon toward the synapse?
It will run into periods of no signal as the fatty myelin sheath protect the axon. In the
sheath’s breaks a signal will be detected and a similar membrane potential wave will be generated
opening successive ion channels till the axon terminal synapse.
c. Does it require any direct or indirect energy input to generate an action potential? If so, when and where is
the energy used?
The Na+/K+ ATPase pumps require the use of energy and conversion of ATP to ADP.
d. What happens in time and space (along the axon) once an action potential begins?
It will run into periods of no signal as the fatty myelin sheath protect the axon. In the
sheath’s breaks a signal will be detected and a similar membrane potential wave will be generated
opening successive ion channels till the axon terminal synapse.
e. What factors ultimately limit the ability of the system to respond (that is, to continue to generate impulses)?
Whether or not enough Na+ ions are in fluxed to generate the all or nothing action
potential. The cell needs to be positively depolarized enough to send a signal.
8. If an axon is stimulated in the middle of its length, nervous signals (action potentials) will move out from the point of
stimulus in both directions. Normally, however, nerve signals move in only one direction along neurons. Explain.
The dendritic, receiving end, has no impact from the wave of the action potential. The other axon
terminal end, however, will receive the signal and transmit neurotransmitters across the synapse to the
next cell’s dendrites.
9. Whether or not an action potential is generated in a postsynaptic neuron depends on a number of factors. What are
they? What ultimately determines whether or not an action potential is generated in the postsynaptic neuron?
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Whether or not enough Na+ ions are in fluxed in both the ligand gated and voltage gated ion
channels to generate the all or nothing action potential. The cell needs to be positively depolarized enough
to generate and send a signal down the axon.
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