The Sense Organs and Other Sense Receptors

Question 1

Structure of the Ear

Answer 1

The ear consists of three regions viz. the outer ear, middle ear and inner ear

Question 2

The outer ear

Answer 2

The outer consists of a cartilaginous canal and an auditory canal

Question 3

The Functions of the outer ear

Answer 3

The outer ear has the following functions:
The pinna directs sound waves through the auditory canal to the tympanic membrane
The auditory canal conducts sound waves to the tympanic membrane; the wax h[and hairs found in the canal prevent small organisms from entering the ear, the wax also prevents the ear drum from drying out

Question 4

The middle ear

Answer 4

The middle ear is an air-filled cavity within the skull
It is separated from the outer ear by the tympanic membrane
It is separated from the inner era by the membranes over the oval window and the round window
Within the middle era are three irregular bones viz. the hammer (malleus), anvil (incus) and the stirrup (stapes)
The hammer is attached to the tympanic membrane; the stirrup is attached to the oval window; the anvil lies between the hammer and the stirrup
The middle ear is connected to the pharynx by means of the Eustachian tube

Question 5

The functions of the middle ear

Answer 5

The tympanic membrane vibrated transmitting the sound waves to the ossicles
The ossicles transmit the vibrations from the tympanic membrane to the inner ear
The Eustachian tube maintains equal pressure on either side of the eardrum
The oval window transmits the vibrations of ossicles into the inner ear
The round window absorbs the pressure set up in the inner ear

Question 6

The inner ear

Answer 6

The inner ear is a fluid-filled cavity made up of bony labyrinth and a membranous labyrinth
The bony labyrinth is a system of cavities and canals inside the skull
It is made up of three parts viz. the semi-circular canals, the vestibule (sacculus and utriculus) and the cochlear

Question 7

The bony labyrinth

Answer 7

The bony labyrinth is filled with a fluid called the perilymph
The membranous labyrinth is made up of membranous sacs that float in the perilymph of bony labyrinth
The membranous labyrinth is made up of semi-circular canals, the sacculus and utriculus and the cochlear

Question 8

The membranous labyrinth

Answer 8

The membranous labyrinth is filled with endolymph
The membranous cochlear is so arranged within the bony cochlear that a section through the cochlear reveals three canals as follows:
an upper canal filled with perilymph
a middle canal filled with endolymph
a lower canal filled with perilymph

Question 9

The functions of the inner ear

Answer 9

The semi-circular canals, sacculus and utriculus are connected with balance and equilibrium of the body
The cochlear contains the organ of Corti which converts the stimulus of sound into an impulse
The auditory nerve arising from the cochlear transmits the sound impulse to the brain

Question 10

Functioning of the ear

Answer 10

The ear is responsible for hearing and balance

Question 11

Hearing

Answer 11

1. The pinna traps the sound waves and directs it to the auditory canal
2. The sound waves strike the tympanic membrane and cause it to vibrate
3. The vibrating membranes causes the ossicles including the stirrup to vibrate
4. The stirrup causes the membrane on the oval window to vibrate
5. The vibrations sets up the pressure waves in the perilymph
6. Organ of Corti in the endolymph is stimulated; stimulus is converted into an impulse
7. The nerve impulse is carried by the auditory nerve to the cerebrum where the sound is interpreted
   The pressure in the cochlear is then eased out through the round window

Question 12

Balance

Answer 12

Sudden changes in speed and direction causes the endolymph within the semi-circular canals to move
Since the three semi-circular canals are in three different planes, the fluid in at least one of the canals will move if your speed or direction changes
The movement of the fluid stimulates the receptors called cristae within the ampullae at the base of each semi-circular canal
When the direction of the head changes, gravitational pull stimulated different receptors called maculae, within the sacculus and utriculus
Within in the cristae and maculae the stimuli are converted to nerve impulses
These impulses are transmitted by the vestibular branch of the auditory nerve to the cerebellum
The cerebellum send impulses to the muscles and restore the balance

Question 13

Adaptions of the ear

Answer 13

The pinna is large and projects slightly out of the hear to trap sound waves
The cerumen and hairs in the auditory canal prevent small organisms from entering the ear
The wax also prevents the ear from drying out
The hammer is attached to tympanic so that when the tympanic membrane vibrates, the ossicles also vibrate
the stirrup is attached to the oval window so that the stirrup vibrates
The oval window also vibrates creating waves in the perilymph of the vestibular canal
The Eustachian tube allows air to be released out of, taken into, the middle ear thus allowing pressure on either side of the tympanic membrane to be equal
The round window acts as a cushion absorbing the pressure set up in the inner ear
The cochlear contains the organ of Corti which is the receptor responsible for picking up the stimulus of sound
The auditory nerve arising from the cochlear transmits the sound to the cerebrum of the brain