Exercise 29 - Nervous and Sensory Systems

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	1/student
Dissecting microscope	1/student
Electrophysiological apparatus	1 setup/lab
Oscilloscope
Stimulator (Ward's#14W5454)*
Nerve chamber (Ward's#14W5449)*
Connecting cords
Desk lamp with 100 watt lamp	1/group

MATERIALS

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" x 8.5" sheet of black construction paper. Two sets per lab should be enough if students share.

4. 5% ethanol preparation:
   5 ml 95% ethanol in 90 ml water

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. Direct E-mail to asdg@umdd.umd.edu

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 effect hearing.

   Nocturnal animals tend to have more rods in their retinas. Many have no cones and are color blind.

SUPPLEMENTAL MATERIALS

Bio Sci II, videodisc has several useful images for this exercise. Dubuque, IA: Wm. C. Brown Publishers. See appendix.

Fetal Pig: Nervous System, filmstrip. Concord, MA: Kalmia Corp.

Nervous System: Structure and Function, audio filmstrip. Rochester, NY: Ward's.

Sensory World, 33 minute film. New York, NY: CRM-McGraw Hill.