BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
Signaling Systems:
Hormonal Control & Neural Control
Animals have two systems in their bodies that are used to communicate: the nervous
system and the endocrine system (the system that produces and releases hormones).
Plants rely entirely on chemical messengers (hormones). Nervous systems are used to
convey information rapidly. For example, the nervous system is used to regulate
movement in response to sudden stimuli. A finger about the poke you in the eye will
cause you eyelid to shut; this response is regulated by the nervous system. Hormones,
chemical messengers, typically are used to regulate slower processes such as sexual
maturation and growth.
Although these are two different systems, they are both systems used for internal
communication and often interact and overlap in form and function within animals.
Many hormones are released by specialized nerve cells called neurosecretory cells. The
production and release of many hormones is under the control of the nervous system.
The nervous and endocrine often act together to control certain processes; For example,
heart rate is controlled both by hormones and by the nerves that innervate the heart.
LAB OBJECTIVES:
This lab will serve as an introduction to these two systems of internal communication.
When you have completed this lab, you should be able to:
1.
2.
3.
4.
5.
6.
7.
Identify the major subdivisions of the vertebrate brain and describe how the
brain has changed during the evolution of vertebrates.
Understand that nerves are actually bundles of axons of many neurons and be
able to explain how a myelin sheath speeds up the conduction of impulses
along neurons.
Describe both the differences and interactions between the nervous and
endocrine systems in animals. Understand how the pituitary gland is a main
intersection between these two systems
Explain the concept of negative feedback and how it is used to maintain
homeostasis.
Identify the major glands of mammalian endocrine systems.
Describe how blood glucose levels are maintained through antagonistic
hormones.
Describe the effects that gibberellins have on seed germination and growth in
plants.
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BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
Neural Control in Animals
The nervous system is used to carry messages that must be delivered rapidly. Nervous
systems consist of a network of neurons (nerve cells) and their supporting cells. The
functioning of the neurons are remarkably similar across all organisms, while the way
neurons are connected into a nervous system differs widely from the simple nerve nets
found in some Cnidarians to the complex central and peripheral nervous systems found in
Vertebrates.
Nervous systems perform three main functions in animals: (1) sensory input: the
perception of both internal and external stimuli, (2) association or integration: where the
input is associated with the correct response, and (3) motor output: the response is carried
out by glands or muscles.
I. Comparative Vertebrate Brains:
The brain is part of the central nervous system, the portion of the nervous system that
functions in association and integration. Vertebrate brains evolved from three bulges at
the anterior end of the spinal cord. These three sections of the brain are known as the
forebrain, midbrain and hindbrain. The three sections evolved and became further
subdivided in both structure and function throughout vertebrate evolution. The following
list shows which brain regions and some examples of structures that formed from these
three initial sections:
Forebrain:
Telencephalon: olfactory bulbs, cerebrum
Diencephalon: thalamus, hypothalamus
Midbrain:
Mesencephalon: optic lobes
Hindbrain:
Metencephalon: cerebellum
Myelencephalon: medulla oblongata
By comparing the brains of modern day vertebrates, these three sections of the brain can
be observed and their relative size can be measured. The brains of these extant
vertebrates can be used to demonstrate how the vertebrate brain evolved from the
primitive ancestral vertebrates to the more complex brains found in mammals.
In early vertebrates and in present day fish, the hindbrain is dominate. This portion of the
brain is responsible for coordinated movement and visceral functions. The remaining
parts of the fish brain are dedicated mainly to processing sensory information. As
vertebrates evolved the forebrain grew proportionately larger and an increase in
associative activity occurred. This is demonstrated by the very large cerebrum and higher
learning capabilities of mammalian brains.
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BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
Procedure:
In this exercise you will dissect the brain of your shark and frog specimen. You will also
observe a preserved sheep brain and a model of a human brain. Specimens of other
animals’ brains will also be available for viewing. You will make measurements of the
hindbrain, mid brain and forebrain and create a graph to compare their relative sizes
among the animals that you observe. You can than use this graph to describe trends in
the evolution of vertebrate brains.
A. Dissection of the dogfish shark brain:
1
Position the shark dorsal side up on your dissecting tray so that you can easily
have access to the region medial to the eyes and gill slits.
2
Cut the skin and muscle away in this region until you have exposed the
cartilaginous brain case.
3
Carefully shave away thin layers of the brain case until the soft tissue of the
brain is visible. This must be done with patience and care so that the brain
itself is not cut away. Continue to shave away the brain case until the brain is
exposed from the olfactory lobes to the attachment of the medulla oblongata
to the spinal cord.
4
Identify the following structures shown in Fig 9.1 of your lab book: olfactory
lobes, cerebral hemispheres (cerebrum), optic lobes, cerebellum, and medulla
oblongata. Use your text book to look up the functions of these structures.
5
Use a ruler to measure the length and width of the entire brain. Then measure
the approximate length and width of each brain section: the forebrain,
midbrain and hindbrain. Record you data in Table 9.1 below
6
Make the necessary calculation to determine the percent of total brain area
that is occupied by the three brain sections.
B. Dissection of the frog brain:
1.
2.
3.
4.
5.
Obtain a preserved frog and place it dorsal side up on a dissecting tray
Remove the skin from the head. Carefully shave away the bone above the
brain (located between the eyes and ear drums).
Refer to Fig 9.2 in your lab book and locate the olfactory lobes, cerebrum,
optic lobes, cerebellum, medulla oblongata, and spinal cord.
Use a ruler to measure the approximate length and width of the entire brain.
Then measure the length and width of the three main sections of the brain:
forebrain, midbrain, hindbrain. Record your data in Table 9.1 below.
Make the necessary calculation to determine the percent of total brain area
that is occupied by the three brain sections.
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BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
C. Dissection of the sheep brain:
1.
2.
3.
4.
5.
Obtain a sheep brain and remove the tough outer covering known as the dura
mater.
Refer to fig 9.3a,b,and c in you lab book and identify the following structures:
cerebrum, cerebellum, medulla oblongata, olfactory bulbs, optic chiasma,
pons,
Make a mid-sagittal cut through the brain so that you have a left and right half
of the brain: identify the structures listed above in cross-section and the
corpus callosum
Use a ruler to measure the approximate length and width of the entire brain.
Then measure the length and width of the three main sections of the brain:
forebrain, midbrain, hindbrain. Record your data in Table 9.1 below.
Make the necessary calculation to determine the percent of total brain area
that is occupied by the three brain sections.
D. Model of the human brain:
1. Observe the preserved human brain and notice the convolutions on the surface of the
brain (see Fig 9.4 in your lab book). What do you think is the functional significance
of these convolutions?
2. Study the model of the human brain and refer to Fig 9.4b in your lab manual to
identify the following structures: cerebrum, cerebellum, medulla oblongata, pons,
corpus callosum, pituitary gland, thalamus, hypothalamus
3. Use a ruler to measure the approximate length and width of the entire brain. Then
measure the length and width of the three main sections of the brain: forebrain,
midbrain, hindbrain. Record your data in Table 9.1 below.
4. Make the necessary calculation to determine the percent of total brain area that is
occupied by the three brain sections.
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BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
Table 9.1 Vertebrate Brain Measurements
Vertebrate
Measurement
Shark
Length
Width
Area (LxW)
Percent of Total Brain =
(Section Area/Total
Brain Area) x 100%
Frog
Length
Width
Area (LxW)
Percent of Total Brain
Sheep
Length
Width
Area (LxW)
Percent of Total Brain
Human
Length
Width
Area (LxW)
Percent of Total Brain
Forebrain
Midbrain
Hindbrain
Sketch a graph below showing how the proportion of the brain dedicated to each of the
three main sections (forebrain, mid brain and hindbrain) changes across vertebrates:
1
0.8
0.6
0.4
0.2
0
fish
human
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Total Brain
BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
II. Microscopic Study of Nervous Tissue
Nervous systems are composed of two types of cells: the neurons (nerve cells) that
actually conduct the nerve impulses and the neuroglial cells (supporting cells) that
function to support the neurons in various ways. Neurons have a cell body or cyton,
where the nucleus is found, and several processes or extensions off this cell body. The
processes that conduct the impulse toward the cell body are called dendrites, while the
one very long extension that conducts the impulses away from the cell body is called the
axon. What we call “nerves” in an animal’s body are actually the long axons of many
neurons wrapped together by connective tissue.
In vertebrates, one type of supporting cell wraps around the axon of neurons and forms an
insulating layer known as the myelin sheath. The myelin sheath is composed mainly of
lipids and acts to electrically insulate the neuron when a nerve impulse is traveling
through it. There are gaps in the myelin sheath known as “Nodes of Ranvier”. The
presence of a myelin sheath also allows nerve impulses to be conducted rapidly down an
axon by a process called saltatory conduction by which the action potential jumps from
node to node. Therefore animals that have myelinated axons are capable of faster
conduction of nerve impulses.
A. Slide of Mammalian Nerve fibers teased (see Fig 9.8a in your lab manual):
This slide is a teased preparation stained to show the myelin sheath of nerves.
The myelin, due to its lipid composition, stains blackish. Look for the Nodes of Ranvier
is this view.
B. Slide of Spinal Cord c.s. `(see Fig 9.7 in your lab manual):
First examine this slide under low power. The central region has an H-shape and
is grayish in color. This is known as the gray matter and is the region where the cell
bodies of the neurons are found. The surrounding lighter region is the white matter. This
zone appears white due to the presence of the myelin that wraps around the axons found
in this section. Switsh to high power and find the cell bodies in the gray matter and the
nerve tracts (or axons) and surrounding myelin sheath in the white matter.
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BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
Hormonal Control
Hormones are chemical messengers within organisms that function to maintain
homeostasis, and to regulate reproduction, development and growth. Hormones are
secreted by tissues and organs and must travel through the organism to reach other tissues
or organs, known as targets, which have specialized receptors that allow them to respond
to the presence of the hormone.
I. Hormonal Control in Animals:
A. Endocrine System of Vertebrates: Human Torso
In animals, hormones are produced by specialized tissue called endocrine tissue which is
typically organized into endocrine glands. Refer to page 225 in your laboratory book
and identify the organs of the endocrine system in the human torso model: the
pituitary, thyroid, parathyroid, and adrenal glands, which are exclusively endocrine in
function, as well as the ovaries, testes and pancreas, which have both endocrine and nonendocrine functions.
B. Antagonistic Hormones and Negative Feedback: Control of Blood Glucose levels
Within the pancreas are islands of cells that are endocrine in function. These Islets of
Langerhans produce two hormones that function to regulate blood sugar levels: insulin
and glucagon. These two hormones are antagonistic, meaning that they have opposite
functions. Insulin promotes the removal of glucose from the blood and is thus secreted
when blood sugar levels are too high. Glucagon promotes the conversion of glycogen
into glucose and adds glucose to the blood; it is produced when blood sugar levels are too
low. Each of these hormones has a negative feedback mechanism; a return of blood
glucose levels to normal causes the production of these hormones to stop. A deviation
from the normal blood glucose level will lead to the production of these antagonistic
hormones. Since biology is not “perfect” and it takes time for an organism’s body to
respond to changes in blood glucose levels, typically levels will fluctuate above and
below the “normal” level as these two hormones work to bring the blood glucose level
back to normal.
Describe what you think will happen (to blood glucose levels, insulin production and
glucagons production) over time if a person drinks a sugary solution:
Describe what you think will happen (to blood glucose levels, insulin production and
glucagons production) over time if a person starves themselves:
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BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
Why do you think diabetics (who cannot efficiently regulate their blood glucose levels)
are sometimes treated with insulin but not glucagon?
Follow the procedure on pages 218-219 to carry out a modified glucose tolerance
test.
C. Interaction of Endocrine and Nervous Systems
Animals have both an endocrine system and a nervous system, both of which function in
communication and regulation within the body. List some of the ways that hormonal
control and neural control differ:
Although it is convenient to distinguish between the nervous system and the endocrine
system, these two systems are very much interconnected. Their functions overlap and the
two systems interact. One example of this interaction is that the production of hormones
may be controlled by the nervous system. This is exemplified in hypothalamus and
pituitary gland where the distinction between these two systems is blurred.
The hypothalamus is a region of the lower brain that receives signals from the nervous
system and initiates the appropriate endocrine response. The hypothalamus produces
hormones that are either stored in the pituitary gland or regulate production of hormones
by the pituitary gland. The pituitary gland hangs from a stalk below the hypothalamus
and many of its hormones regulate the production of other hormones in the other
endocrine glands. Thus the pituitary is often called the “master gland”. The pituitary
exemplifies the close connection between the nervous and endocrine systems. It has two
discrete lobes that develop from two different parts of the embryo and have two very
different functions. The anterior pituitary (which forms from the embryonic mouth)
secretes several hormones, some of which are tropic hormones that cause the release of
hormones from other endocrine glands. The posterior pituitary (which forms from the
embryonic brain) is really an extension of the hypothalamus; it stores and secretes two
hormones that are produced in the hypothalamus.
Refer to pages 226-227 to study the prepared slide of the pituitary gland
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BY 52 – Modern Biology II Laboratory
Dr. J. Anastasia
II. Hormonal Control in Plants
Plants use hormones, as animals do, as signals that allow them to respond to
environmental conditions. Plants do not have a nervous system so they rely on hormones
to respond to any stimuli. Hormonal production, concentration or rate or transport can all
change in response to environmental stimuli. Often in plants, two or more hormones
interact to produce a response. It is hormonal concentration relative to other hormones
that is important in determining the response of the plant. Furthermore, each hormone
can have multiple effects, depending on the site of production, the site of action, the
relative concentration and the developmental stage of the plant. Plant hormones typically
act to regulate growth and development by affecting cell division, cell elongation or celll
differentiation.
There are five major classes of plant hormones: auxins, gibberellins, cytokinins, ethylene
gas and abscisic acid. In this lab, you will design experiments to test the effect of
gibberellins on seed germination and on stem elongation:
A. Experiment 1: Effect of gibberellins on seed germinations
Using the following materials, design an experiment to test the effects of gibberellic acid
on seed germination. Write out a detailed procedure and bring it to lab next week. These
will be collected and graded. The class will discuss ideas and come up with one accepted
experimental design and we will perform the experiment.
Materials available:
marigold seeds
petri dishes
filter paper
water
giberellic acid
B. Experiment 2: Effects of gibberellins on stem elongation
Using the following materials, design an experiment to test the effects of gibberellic acid
on stem elongation (growth of the stem). Write out a detailed procedure and bring it to
lab next week. These will be collected and graded. The class will discuss ideas and
come up with one accepted experimental design and we will perform the experiment.
Materials available:
pots
soil
wild type Brassica ( a type of mustard plant) seeds
mutant Brassica seeds deficient in gibberellic acid
water
gibberellic acid
C. Auxin and tropic responses of plants
Refer to pages 235-236 in your lab manual to observe the effects of auxin on plant
growth
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