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STUDENT OBJECTIVE

Students study the gross and microscopic anatomy of the mammalian nervous system, eye, and ear. A simple demonstration of the properties of nerves in earthworms, including conduction velocity, can be performed by the instructor as time permits.

EQUIPMENT	AMOUNT
	(Class of 24 with 8 groups)
Compound microscope Dissecting microscope Electrophysiological apparatus Oscilloscope Stimulator (Ward’s#14W5454) Nerve chamber (Ward’s#14W5449)* Connecting cords Desk lamp with 100 watt lamp	1/student 1/student 1 setup/lab 1/group
MATERIALS
Fetal pig from previous exercise Sheep brains, sagittally sectioned Model of human eye Model of human ear Coffee cans painted black with 1 inch square window Socket with 100 watt lamp Construction paper, black, red, yellow, blue, and white Earthworms, live Dissecting pans and instruments Prepared slides (can be shared to reduce costs) Mammalian nerve cord, cross section (CBS#31-3708)* Neurons (CBS#31-3570)* Muscle with motor end plate (CBS#31-3570)* Mammalian cochlea, cross section * Mammalian retina	1/student 1/lab 2/lab 2/lab 1/group 1/group 1/group 2/lab 1/student 1/student 1/student 1/student 1/student Demonstration

*Please refer to the Appendix for name and address of supplier.

SOLUTIONS

5% ethanol

PREPARATION

About Three Weeks before Lab

1. Order live earthworms (4"—5") to arrive about one week before lab.
2. Order sheep brain to arrive about one week before lab.

About One Week before Lab

1. Check dissecting instruments and sharpen or replace.
2. Prepare coffee cans by painting flat black and cutting 1 inch square windows in side near bottom. Secure a socket with 100 watt lamp inside can. Be careful of all wiring. This should not be left on for long periods of time because of heat buildup and potential fire hazard.
3. Cut 5 cm squares of red, yellow, and blue construction paper. Glue each one in the center of a 11" ¥ 8.5" sheet of black construction paper. Two sets per lab should be enough if students share.
4. 5% ethanol preparation:

NOTES

1. Earthworm demonstration allows nerve physiology to be investigated by noninvasive techniques. After earthworm is anesthetized by immersion in 5% ethanol, it can be mounted directly in the nerve chamber ventral surface down (look for dorsal blood vessel and place upward). When in this position, the giant fibers of the ventral nerve cord can be stimulated directly through the body wall and will propagate action potentials that can be picked up and displayed on an oscilloscope. The concepts of threshold and conduction velocity can be quickly demonstrated.
2. Review booklets on use of oscilloscope and stimulator and try the nerve physiology experiment before lab.
3. A simulation called Action Potential Experiments for the Macintosh or Windows computers is available from BioQuest.

Classroom Suggestions

1. Check out the links for this lab topic at http://auth.mhhe.com/biosci/genbio/dolphin/ You will find useful materials for developing your lab introduction or summary, and in some cases, you may want to tell students to connect to a particular site for further information.

ANSWERS TO CRITICAL THINKING QUESTIONS

1. Conductive deafness

   — caused by interference of conduction of sound vibrations to perilymph of cochlea.
   — obstruction of external auditory canal by impacted wax.
   — loss of flexibility of tympanic membrane or perforation of the tympanic membrane.
   — inflammation of the middle ear (otitis media).
   — ossification of the ossicles.

   Sensorineural deafness

   — caused by damage to hair cells, auditory nerve or auditory centers of the brain.
   — gradual loss of sensory hair cells with aging.
   — prolonged exposure to extremely loud noise, especially in the low frequency range can
   damage the hair cells.
   — degeneration of the cochlea nerve, brain damage, tumors, etc. will all affect hearing.

2. Vertebrate animals that are active at night, will have more rods than cones in their retinas. The retinas of these animals will often lack cones, and therfore the animals lack color vision. Clothing used while hunting large mammals is often red or fluorescent orange for safety purposes. Deer do not see these colors because they are color blind.

SUPPLEMENTAL MATERIALS