Embryonic Development in the Chick

Embryonic Development in the Chick

Aristotle was the first to view the development of the chick embryo and report the steps of its development.  Because all chordate animals follow similar patterns of early development, viewing the chick embryo has much to teach about development of higher chordates, such as in humans.  It is especially informative to compare a 40-48 hour embryo with a 70-72 hour embryo.  The earlier show the primative three part brain, neurulation in progress, fewer somites, the heart is not beating yet, and the embryo is still linear.  The 72 hour embryo has a 5 part brain, a beating heart, many somites, limb buds and it has arched and twisted, all in only 24 hours.

Here is a page devoted specifically to the embryonic development of the brain.

Equipment
petri dish, 39 C
small three cornered file (sharp)
scalpel
tweezers, preferably with curved tips
dissection scope and lamp (strictly follow carrying instructions!)
iris scissors (they have curved blades)
depression slide, 39 C
(or microscope slide with wax pencil drawn circle to contain solution)

Supplies
fertile eggs, incubated at 39 C for 72 hrs
(A few at 33 and 48 hrs are instructive, but because the embryos are smaller, they are more difficult to handle)
39 C Ringer’s solution * in dropper bottle (or other isotonic solution)
Whatman #1 filter paper (or other)

See also: Abraham & Thomson,  Lab Outlines in Bio III, 247-257, (~1975).

1. Collect equipment at your desk:
dissection scope and lamp (make two trips, use two hands for each trip)
dissection kit
iris scissors
And, all at 39C:
Ringer’s solution
depression slide
petri dish bottom (or top)
Cut a ring of filter paper, size of a quarter with a 5/8 hole which will encircle the embryo.

2. Pick up an egg from the incubator, keeping egg in same orientation as in incubator and keep it warm with a lamp close to its surface.
With a pencil, mark a circle 3/8th inch bigger diameter than a quarter on upper surface of egg.
Place the egg in petri dish with paper towel cushion underneath. Gently score with a file around the circle with repeated long slow strokes. Do not press hard, or egg will break.


3. With scalpel and/or tweezers, flick off the shell inside the circle, trying not to break inner shell membrane.
It is not necessary to flick all of the shell off, but you need room to cut the shell membrane in the next step.

4. With iris scissors, make shallow cuts to cut inner shell membrane close to shell.  The yolk will be floating near the surface with the embryo on top. Be careful not to pierce the vitelline membrane which surrounds and contains the yolk, or else you will obscure the operation with yolk. Flake off additional shell if more clearance is needed. The embryo should be float in the center top.

10_place_ring_P6034463

5. Carefully place filter paper circle so that it encircles the embryo (still floating in the center of the opened egg, at the top?). Trim paper if necessary before putting it in place.
(In this image, the egg has broken into the petri dish, but the embryo is still visible.)

6. Carefully cut vitelline membrane just outside of the filter paper to free the assembly. Do not press down or the assembly may sink and be lost in yolk.
(Poke down with one blade, lift up slightly, cut the membrane.)

7) Pre fill a warmed depression slide with warmed Ringer’s solution to receive the embryo.
When cut free, carefully grasp with tweezers both the membrane and paper along the edge of the assembly.
Pick up the assembly and gently flush off yolk the underside with Ringers solution.
Transfer to a warm depression slide filled with Ringer’s solution. Make sure that the embryo does not become detached, nor is not covered by the embryonic membranes or filter paper. Keep it alive by keeping warm and moistened with Ringer’s at all times.

8. Examine under the dissecting scope. Illustrate the embryo according to the hours of incubation. The beating heart seen in older embryos will continue for some time providing that it is kept warm and wet with Ringer’s solution. Draw the embryos in chronological order to show the stages of development as seen at hours 48 and 72.
Include and label:
forebrain (prosencephalon: telencephalon and diencephalon)
midbrain (mesencephalon)
hindbrain (rhombencephalon : metencephalon and myelencephalon)
optic cup
lens placode
nose rudiment
auditory vesicle
pharyngeal arches (also called gill slits)
vitelline arteries and veins
neural tube (or neural grove seen in early embryo)
heart atrium
heart ventricle
somites
wing “buds”
leg “buds”
Here is a labeled view of a 40 hour chick embryo (about 10 somite stage).
Here is a labeled view of a 72 hour chick embryo.
Here is a labeled image of a prepared slide of a chick embryo.)

9. Clean and dry all equipment before putting away to prevent corrosion, especially the metal utensils. Note than any egg remaining will dry and be very difficult to clean off later

*Ringer’s Solution:
Calcium chloride 0.1 g
Glucose 1.0 g
Potassium chloride 0.1 g
Sodium bicarbonate 0.2 g
Sodium chloride 6.5 g distilled H2O, q.s: 1 L

Images taken in 2005.

Images taken in 2008.

Other pictures

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Visual Reaction Time

Visual Reaction Time

Nervous responses to environmental stimuli are necessarily rapid events, taking a small fraction of a second to be completed. The stages in such a response involve:

(1) transduction of the environmental stimulus into a nervous impulse (rods and cones)
(2) processing in the neurons of the retina (bipolar and ganglion cells)
(3) transmission of the impulse to the thalamus
(4) relaying of impulse to the visual cortex via optic radiations
(5) visual association region recognizes the meaning of the visual impulses
(6) transmission of impulse from visual association region to precentral gyrus
(7) transmission of the motor impulse from precentral gyrus to muscles of hand
(8) effecting the movement through the contraction of muscles.

The length of time required for the sum of these steps can be measured by a simple procedure measuring the visual reaction involved in catching a dropping ruler. By applying a simple law of the acceleration of gravity, the distance which the ruler dropped can be converted into the amount of time required for the completion of the visual reaction.

EQUIPMENT:

meter stick (or a yard stick)
card with horizontal line taped to wall at a convenient height
calculator with square root function

PROTOCOL:

50.0_cm_wide_P20419521. Experimenter holds meter stick with 50 cm mark on line of card, zero end of stick down. Be careful to line up the ruler exactly on the 50.0 cm mark. (The experiment can be done with a yard stick with a little additional conversion, and using a different equation for inches.)
2. Subject places thumb and forefinger on either side of ruler, near, but not touching it.

3. Experimenter asks to be certain that subject is ready, then within a few seconds releases ruler as cleanly as possible (no hints as to release, drop ruler straight down).
4. Subject grasps ruler as soon as possible after its release, and holds it against the wall where caught (do not move it once it is caught).

04_visual_reflex_66.0_cm_P2041943sm5. Experimenter reads the position of the line on the ruler to the nearest tenth of a centimeter (66.0 cm in the image to the left), subtracts 50 cm from that to get the distance the ruler dropped , and records the data in the notebook in cm (16.0 cm dropped in this example). Repeat at least five times to determine an accurate average. (You may drop the fastest and slowest reactions to see how that affects it)
6. Convert each distance dropped into milliseconds required for the visual reaction, then average the time for the visual reaction for the five determination. Use the equation below. A drop of 16.0 cm is equivalent to a visual reaction time of 180 milliseconds. See spelled out calculations below.

The distance dropped is converted into milliseconds by the following equation:

rxn_time_equation
EXAMPLE CALCULATIONS FOR NUMBERS SHOWN IN THE ILLUSTRATIONS:

1) The ruler was caught at the 66.0 cm point, therefore the distance dropped was 16.0 cm
2) 2 times 16.0 cm is equal to 32 cm.
3) 32 cm divided by 980 cm/sec2 equals 0.03265 seconds2
4) The square root of 0.03265 seconds2 is equal to 0.1807 seconds.
5) 0.1807 seconds times 1000 msec/second equals 180 milliseconds visual reaction time.

ASSIGNMENT: PERFORM AN EXPERIMENT AT HOME
Design an experiment to test the effects of time of day, fatigue, time of the month, various agents etc., on your friends and/or family members: Record the data and perform the calculations in your notebook.Test the visual reaction time in triplicate for at least five different determinations.

For example:
Determine effects of various agents (caffeine, alcohol, ephedrine, etc.) on reflex time by measuring visual reaction before administering the agent, then repeat the determination after administration. Look for increasing effects with increasing amounts of the agent.

or

Repeat 10 or more times to look for learning and/or fatigue.

or

Conduct population studies to look for effects on reflex time of age, sex, handedness, etc.
TO DO THIS EXPERIMENT WITH A YARD STICK:

1) Line up the 10.0 inch mark on the yard stick with the wall line and the 0 inch end of the yard stick at bottom.
2) After the drop, read to the nearest 1/16th of an inch.
3) Convert the fraction to decimals of an inch, subtract 10 inches from reading. Substitute 385.8 inches/sec2 for 980 cm/sec2 for acceleration of gravity in the formula:

rxn_time_equation_inches