The Larynx and the Ear : Part 5

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 25 of 27)

Exercises. - 1. For what different purposes are sound waves employed in the body?

2. How do sound waves originate? How are they transmitted? How do they differ from the waves on water?

3. How are sound waves able to act as nerve stimuli?

4. Describe two methods of reinforcing sound waves. Which method is employed in the body?

5. Name all the parts of the body that are directly or indirectly concerned in the production of sound.

6. Describe the larynx.

7. Describe the condition of the vocal cords in speaking and in ordinary breathing.

8. How are sounds differing in pitch and intensity produced by the larynx?

9. How is the sound produced by the vocal cords changed into speech?

10. What parts of the ear are concerned in transmitting sound waves?

11. Give the purposes of the middle ear.

12. Trace a sound wave from a bell to the basilar membrane, and trace the impulse that it causes from there to the brain.

13. Give the purpose of the Eustachian tubes; of the rods of Corti; of the semicircular canals.

14. Give directions for the proper care of the ear.

Practical Work

To illustrate the Origin of Sound. - 1. Strike a bell an easy blow and hold some light substance, as a pith ball attached to a thread, against the side, noting the result. 2. Sound a tuning fork by striking it against the table. Test it for vibrations as above, or by letting the vibrating prongs touch the surface of water. 3. Pluck a string of a guitar or violin, and find proof that it is vibrating while giving out sound.

To show the Transmission of Sound. - 1. Vibrate a tuning fork and press the stem against a table or desk. The vibrations which are reinforced in this way will be heard in all parts of the room. Now press one end of a wooden rod, as a broom handle, against the table, and bring the stem of the vibrating fork against the other end. The vibrations now move down the stick to the table, from whence they are communicated to the air. Observe that the sound waves, to reach the ear, must pass through the rod, the table, and the air. 2. Fasten the tuning fork to a flat piece of cork by pressing the stem into a small hole in the center. Vibrate the fork and let the cork rest on the surface of water in a half-filled tumbler on the table. The sound will, as before, pass to the table and then to the air. Observe that in this case the vibrations are transmitted by a liquid, a solid, and by the air. Compare this action with the transmission of sound waves by different portions of the ear.

To show Effects of Sound Waves. - 1. Place two large tuning forks of the same pitch, and mounted on thin boxes for reinforcing their vibrations, near each other on a table. Vibrate one of the forks for a moment and then stop it by means of the hand. Observe that the other fork has been set in vibration. (This experiment does not work with forks of different pitch.) 2. While holding a thin piece of paper against a comb with the open lips, produce musical tones with the vocal cords. These will set the paper in vibration, producing the so-called "comb music." 3. Examine the disk in a telephone which is set in vibration by the voice. Observe that it is a thin disk and, like the membrane of the ear, has air on both sides of it.

To show the Reinforcement of Sound. - 1. Vibrate a tuning fork in the air, noting the feebleness of the tone produced. Then hold the stem against a door or the top of a table, noting the difference. 2. Hold a vibrating tuning fork over a tall jar, or bottle, and gradually add water. If the vessel is sufficiently tall, a depth will be reached where the air in the vessel reinforces the sound from the fork. 3. Hold a vibrating fork over the mouth of a small fruit jar, partly covered with a piece of cardboard. By varying the size of the opening, a position will be found where the sound is reinforced. If not successful at first, try bottles and jars of different sizes.

To illustrate the Manner of Vibration of the Liquid in the Internal Ear. - Tie a piece of dental rubber over the end of a glass or wooden tube about half an inch in diameter and six inches in length. Fill the tube entirely full of water and, without spilling, tie a piece of thin rubber tightly over the other end. Holding the tube horizontally, press the rubber in at one end and note that it is pushed out at the other end. Make an imitation of a vibration with the finger against the rubber at one end of the tube and note the effect at the other end. To what do the tube and the rubber on the ends of the tube correspond in the internal ear?

To show the Plan of the Larynx. - Cut from stiff paper four pieces of different shapes as indicated in Fig. 156. (The piece to the left should have a length of about six inches, the others proportionally large.) The largest represents the thyroid cartilage, the next in size the cricoids, and the two smallest the arytenoids cartilages. By means of pins, or threads, connect these with each other according to the description of the larynx on page 253. With this simple model the movements of the different cartilages and their effect upon the vocal cords may be illustrated.

To show the Relation of the Movements of the Vocal Organs to the Production of Different Sounds. - 1. Lightly grasp the larynx with the fingers while talking. Observe the changes, both in the position and shape of the larynx, in the production of sounds of different pitch. 2. Observe the difference in the action of the muscles of respiration in the production of loud and faint sounds. 3. Pronounce slowly the vowels, A, E, I, O, U, and the consonants C, F, K, M, R, S, T, and V, noting the shape of the mouth, the position of the tongue, and the action of the lips in each case.

To demonstrate the Ear. - Examine a dissectible model of the ear, locating and naming the different parts. Trace as far as possible the path of the sound waves and find the termination of the auditory nerve. Note also the relative size of the parts, and calculate the number of times the model is larger than the natural ear. Suggestion: The greatest diameter of the internal ear is about three fourths of an inch.

In an extended course it is a profitable exercise to dissect the ear of a sheep or calf, observing the auditory canal, middle ear, bridge of bones, and the tympanic membrane with attached malleus and tensor tympanic muscle. Pass a probe from the nasal pharynx through the Eustachian tube into the middle ear. With bone forceps or a fine saw, split open the petrous portion of the temporal bone and observe the cochlea and the semicircular canals. By a careful dissection other parts of interest may also be shown.

D.C. Heath and Co. - Publishers
Original copyright 1909