18. Sense Organs Flashcards
Which cranial nerve supplies the ear?
Vestibulocochlear (8th)
What are the sections of the ear?
Outer ear
Middle ear
Inner ear
How is the middle ear connected to the nasopharynx?
Eustachian tube
What does the outer ear consist of?
Auricle/pinna
External auditory canal
Tympanic membrane (ear drum)
What is the auricle/pinna?
Flap of elastic cartilage
Covered by skin
What is the function of the pinna?
Traps and directs sounds waves into the external auditory canal
What is the tympanic membrane?
Ear drum
Thin semi-transparent partition between the external auditory canal and middle ear
What is the tympanic membrane lined with?
Simple cuboidal epithelium
Elastic fibres
Collagen fibres
What is the function of the tympanic membrane?
Transmits sound from the outer ear to the auditory ossicles
Converts sound waves into mechanical vibration
What is the middle ear?
A small air-filled cavity in the temporal bone
What does the middle ear consist of?
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
What is the function of the middle ear?
Transmits sound in the form of vibration from the tympanic membrane to the inner ear (cochlea)
What does the stapes connect to?
Oval window
What does the oval window connect to?
Cochlea
What is the stapedius?
Small muscle that dampens large vibrations
Innervated by the facial nerve
What is the alternative name for the inner ear?
Labyrinth
What does the labyrinth consist of?
Bony labyrinth (outer)
Membranous labyrinth (inner)
What does the bony labyrinth consist of?
Series of cavities in the temporal bone:
Three semi-circular canals
Vestibule
Cochlea
What do the semi-circular canals and vestibule help with?
Balance
What does the cochlea help with?
Hearing
Which fluids does the labyrinth contain?
Perilymph
Endolymph
What is the cochlea?
Spiralled, hollowed chamber
Almost 3 turns around a central bony core
What does the cochlea contain?
Epithelial cells lined with hair cells
What are the hair cells in the cochlea called?
Stereocilia
What is the function of the stereocilia?
Hearing receptors that extend into the endolymph
How does the structure of the cochlea aid hearing?
Movement of the endolymph causes stereocilia movement
This initiates an electrical impulse
What does the vestibulocochlear nerve do?
Provides sensory information for hearing and balance
What are the two parts of the vestibulocochlear nerve?
Vestibular branch/fibres
Cochlear branch/fibres
What do the vestibular fibres consist of?
Nerve branches that synapse with receptors for balance
What do the cochlea nerve fibres do?
Provides hearing
Where does the vestibulocochlear nerve terminate?
Brainstem (pons/medulla oblongata)
How can the vestibulocochlear nerve get damaged?
Basilar skull fracture
Affecting both hearing and balance
How does the outer ear make sound?
- Sound comes in
- Pinna concentrates the soundwaves and directs them along the external auditory canal
- This causes the tympanic membrane to vibrate
How does the middle ear make sound?
- Vibrations from the tympanic membrane are transmitted through the middle ear by movement of the three auditory ossicles (malleus, incus, stapes)
- The footplate of the stapes rocks at the oval window sending fluid waves into the cochlea perilymph
How does the inner ear make sound?
- Pressure waves are transmitted into the cochlea which causes the round window to bulge into the middle ear
- This pressure wave is transmitted into the endolymph and vibrates the basilar membrane and stereocilia
- The bending of the stereocilia creates a receptor potential - generating an action potential to the nerves
- The nerve impulses move along the vestibulocochlear nerve to the hearing area in the cerebrum
What are the properties of sound?
Pitch
Volume
What is pitch?
Frequency of sound waves
How is pitch measured?
Hertz (Hz)
What is volume?
Amplitude of sound waves
How is volume measured?
Decibels (dB)
What is the decibel scale?
0 dB - near silence
10 dB - 10x more powerful
20 dB - 100x more powerful
30 dB - 1000x more powerful
What is a whisper in decibels?
15 dB
What is a normal conversation in decibels?
60 dB
What is a lawnmower in decibels?
90 dB
What is a car horn in decibels?
110 dB
What is a rock concert/jet engine in decibels?
120 dB
What is a gunshot in decibels?
140 dB
What decibel level can cause hearing loss?
85 dB
What decibel level can cause pain/damage?
140 dB
What is white noise?
A constant, background noise that contains all the different frequencies of sound
Brain ignores
What is white noise used for?
To block out other sounds
Aid concentration
What is the function of the eustachian tube?
Opens for air to equalise pressure between middle ear and atmosphere
Drains mucus
What can make the eustachian tube open?
Yawning
Swallowing
Why is it essential that air can escape the middle ear?
Damage could occur with pressure changes
What is common in children as a result of the eustachian tube being horizontal?
Infection between middle ear and pharynx
What do the semi-circular canals and vestibule provide information about?
Head position
What do the semi-circular canals and vestibule contain?
Stereocilia
What extends and rests on the stereocilia?
Dense layer of calcium carbonate crystals
What is the layer of calcium carbonate crystals also known as?
Otolithic membrane
What does a change in head position create?
Movement in the perilymph and endolymph that causes stereocilia to bend
What does bending of the stereocilia in the semi-circular canals and vestibule stimulate?
Stimulates the sensory nerve endings, creating action potential via CN8
Where does the action potential stimulated in the semi-circular canals and vestibule transmit to?
Cerebellum
Where does the cerebellum get information from to help with balance?
Vestibular feedback (from inner ear)
Visual feedback (from eyes)
Proprioceptors (skeletal muscles, joints, ligaments)
How does the cerebellum maintain balance?
Co-ordinates:
Vestibular feedback (from inner ear)
Visual feedback (from eyes)
Proprioceptors (skeletal muscles, joints, ligaments)
and passes efferent impulses to the cerebrum and skeletal muscles
Where is the eye located?
In the orbital cavity
Which cranial nerve serves the eye?
Optic nerve (CN II)
What are the layers of the eye?
Sclera & cornea (outer)
Uvea (middle)
Retina (inner)
What does the uvea consist of?
Iris
Ciliary body (muscle)
Choroid (rest of the layer)
What is the iris?
Coloured part of the eye
Controls the amount of light reaching the retina by adjusting pupil size
Where is the lens located?
Behind the pupil
What does the lens do?
Focuses light along with the cornea
What are the accessory structures of the eye?
Eyebrows Eyelids Eyelashes Conjunctiva Lacrimal apparatus
What function do the eyebrows play?
Prevents sweat/materials entering the eye
What function do the eyelids play?
Spread secretions over the eye
Protection
What is the conjunctiva?
Transparent mucus membrane of columnar epithelial cells lining the internal eyelids and anterior eyeball
What is the function of the conjunctiva?
Protects the cornea
What does the lacrimal apparatus do?
Produces tears
What does blinking do?
Spreads tears
Protects the eyes from injury (when eyelids are closed)