Module 1

Module 1—The Nervous System

Lesson Summary

 

In this lesson, the following focusing questions were investigated:

• What are the major parts of the ear that facilitate your response to sound in the environment?
  
  

• How do the structures of the ear impact your ability to maintain balance within your changing environment?

You have explored the structures and functions of the outer, middle, and inner ear. Both the cochlea, adapted for hearing, and the vestibular apparatus, adapted for maintaining balance, rely on specialized hair cells to change the mechanical energy of sound or movement to the electrochemical energy of a nerve impulse. The structures of the outer and middle ear conduct and amplify sound waves so that pressure waves can be created in the cochlea of the inner ear. The frequency of a sound wave results in your perception of pitch, whereas the amplitude (height) of the sound wave results in your perception of loudness. Conduction deafness and perception (nerve) deafness result when there is a dysfunction in the hearing apparatus. Both dynamic and static balance are maintained by the vestibular apparatus, which includes the semicircular canals, the utricle, and the saccule. Technologies, such as hearing aids and cochlear implants, have been developed to help with hearing loss.

 

The questions on pages 432 and 433 of your textbook provide an excellent opportunity to review and practise your knowledge and skills dealing with sensory reception. You may wish to do a selection of these questions as review. Your teacher can provide feedback on your answers.

 

Continue your research about Alzheimer’s disease. Are there any connections between this disease and hearing loss or balance problems?

 

Lesson Glossary

 

Consult the glossary in the textbook for other definitions that you may need to complete your work.

 

amplify: to increase the amplitude or the extent of a vibration; see intensity

 

auditory canal: a short channel that funnels sound waves from outside the ear to the tympanum and amplifies sounds

 

auditory nerve: a nerve composed of sensory fibres from the organ of Corti, the vestibular apparatus that conducts impulses to the temporal lobe of the cerebrum

 

basilar membrane: one of two parallel membranes that comprise the organ of Corti in the inner ear

 

Hair cells are attached to the basilar membrane.

 

cochlea: contains the organ of Corti, which functions to convert the mechanical energy of sound waves into a nerve impulse

 

dynamic balance (rotational equilibrium): balance resulting when the head and body are moved or rotated

 

Eustachian tube: a tiny passageway extending from the middle ear to the throat (pharynx); a passageway through which viruses and bacteria can travel from the nose and mouth, resulting in an inner ear infection

 

The Eustachian tube plays an important role in equalizing air pressure on both sides of the tympanum.

 

frequency: number of wavelengths per given time; number of waves that pass a given point in a given time

 

hair cells: sensory mechanoreceptors attached to the basilar membrane in the organ of Corti

 

incus (anvil): the middle in the sequence of the three ossicles located in the middle ear; connected to the malleus and the third ossicle (stapes); part of a lever system that amplifies sound waves

 

inner ear: one of the three regions of the ear that is located deepest into the head and consists of a fluid-filled chamber containing the semicircular canals, the utricle and saccule, and the cochlea

 

intensity: measurement of the difference between compressed and rarefied areas of a sound wave used in physics; corresponds to amplitude of a wave

 

loudness: subjective interpretation of sound intensity

 

malleus (hammer): the first in the sequence of the three ossicles located in the middle ear; connected to the tympanum and the second ossicle (incus); part of a lever system that amplifies sound waves

 

middle ear: one of the three main regions of the ear, which begins just past the tympanum and consists of a chamber containing three tiny bones (ossicles) called the malleus (hammer), the incus (anvil), and the stapes (stirrup); leads into to a minute opening called the Eustachian tube

 

organ of Corti: a structure of the inner ear that contains hair cells that detect vibrations in the fluid of the inner ear and initiates a nerve impulse that is transmitted to the auditory nerve

 

ossicles: three tiny bones located in the middle ear that are connected to each other, to the tympanum, and to the oval window; involved in amplifying sound waves

 

otolith: a tiny particle of calcium carbonate found in the utricle and saccule that contacts the hair cells of these structures and stimulates them

 

outer ear: one of the three main regions of the ear, which consists of the pinna and the auditory canal and ends at the tympanum or eardrum

 

oval window: a membrane-covered opening located between the chamber of the middle ear and the wall of the inner ear

 

The stapes (stirrup) is attached to it and transmits sound waves by it to the inner ear.

 

pinna: the outer flap of the ear that is composed of skin and cartilage and shaped so that it enhances sound vibrations and funnels them into the auditory canal

 

pitch: corresponds to the frequency of a sound wave

 

round window: a membrane-covered opening between the chamber of the middle ear and the inner ear located below the oval window

 

The round window functions in dissipating sound waves in the inner ear.

 

semicircular canals: three tubes that are situated at right angles to one another and contain mechanoreceptors that detect head and body rotation; responsible for dynamic balance or rotational equilibrium (rotational equilibrium dynamic balance), which is the balance that is established in response to the head and body being moved or rotated

 

sensory neurons: nerve cells that are stimulated by hair cells in the organ of Corti to conduct messages toward the temporal lobe of the brain

 

sound: pressure disturbance beginning at a vibrating object (source) and spread out by a medium such as air

 

sound wave: a series of compressions and rarefactions resulting in an S-shaped curve or sine wave

 

stapes (stirrup): the third in the sequence of the three ossicles located in the middle ear; connected to the second ossicle (incus) and the oval window; part of a lever system that amplifies sound waves and causes vibrations in the fluid of the inner ear

 

static balance (gravitational equilibrium): balance resulting from changes in the position or the movement of the head in one direction; usually in response to gravity

 

tectorial membrane: one of two parallel membranes found in the organ of Corti

 

During the transmission of sound waves, the basilar membrane vibrates and causes the sensory hairs to flex against the tectorial membrane.

 

tympanum: a round elastic structure located in the middle ear that vibrates in response to sound waves; also called the eardrum or tympanic membrane

 

utricle and saccule: tiny chambers in the inner ear that contain otoliths and hair cells, which respond to changes in head position with respect to gravity and movement in one direction; responsible for static balance or gravitational equilibrium

 

vestibule: the fluid-filled area of the inner ear located between the semicircular canals and the cochlea

 

The vestibule contains the utricle and saccule.

 

vestigial: small or imperfectly developed; often referring to a part or organ that was once more fully developed in an earlier evolutionary stage, but is now non-functional

 

Biology 30 Learn EveryWare © 2009 Alberta Education