BUNDLE 7: SPECIAL SENSES
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INTRODUCTION
Organs of special senses: hearing, smell, taste, sight, touch.
• Specialized nerve endings at periphery (ears, eyes, nose, mouth) and in brain
• Incoming nerve impulses undergo complex integration and coordination ->
perception and responses
• The ear is also involved in maintenance of balance
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THE EAR
Supplied by 8th cranial nerve (cochlear part of vestibulocochlear nerve).
• Stimulated by vibrations from sound waves
• Except auricle (pinnae), all structures enclosed within petrous portion of temporal
bone
STRUCTURE
Three distinct parts:
1. External ear
2. Middle ear
3. Internal ear
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EXTERNAL EAR
Auricle (Pinna)
• Expanded portion projecting from side of head
• Composed of fibro-elastic cartilage covered with skin
• Deeply grooved and ridged
• Most prominent outer ridge = helix
• Lobule: Soft lower part; fibrous and adipose tissue; richly supplied with blood
capillaries
External Acoustic Meatus (Auditory Canal)
• Slightly S-shaped tube; ~2.5 cm long
• From auricle to tympanic membrane (ear drum)
• Lateral part cartilaginous; remainder in temporal bone
, • Lined with hairy skin continuous with auricle
• Numerous sebaceous and ceruminous glands in lateral part
Ceruminous glands:
• Modified sweat glands secreting cerumen (wax)
• Sticky substance containing lysozyme and immunoglobulins
• Wax, hairs, and curvature prevent foreign materials from reaching tympanic
membrane
Movement of temporomandibular joint during chewing/speaking massages cartilaginous
meatus, moving wax toward exterior.
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MIDDLE EAR (Tympanic Cavity)
Irregular-shaped cavity within petrous temporal bone.
• Cavity, contents, and air sacs lined with simple squamous or cuboidal epithelium
• Air fills cavity; reaches it through pharyngotympanic (Eustachian/auditory) tube from
nasopharynx
• Tube ~4 cm long; lined with ciliated epithelium
Air at atmospheric pressure on both sides of tympanic membrane enables vibration
when sound waves strike it.
• Tube normally closed; opens by swallowing/yawning when pressure needs
equalizing (e.g., at high altitude) -> ears "pop"
Walls:
• Lateral: Tympanic membrane
• Roof and floor: Temporal bone
• Posterior: Temporal bone with openings to mastoid antrum (air passes to mastoid air
cells)
• Middle: Thin temporal bone with two openings:
• Oval window (fenestra vestibuli): Occluded by stapes
• Round window (fenestra cochleae): Occluded by fibrous tissue sheet
Tympanic Membrane (Ear Drum)
• Completely separates external acoustic meatus from middle ear
• Oval; slightly broader edge upward
• Three tissue layers:
4. Outer: Hairless skin
5. Middle: Fibrous tissue
6. Inner: Mucous membrane continuous with middle ear
__________________________________________________
INTRODUCTION
Organs of special senses: hearing, smell, taste, sight, touch.
• Specialized nerve endings at periphery (ears, eyes, nose, mouth) and in brain
• Incoming nerve impulses undergo complex integration and coordination ->
perception and responses
• The ear is also involved in maintenance of balance
__________________________________________________
THE EAR
Supplied by 8th cranial nerve (cochlear part of vestibulocochlear nerve).
• Stimulated by vibrations from sound waves
• Except auricle (pinnae), all structures enclosed within petrous portion of temporal
bone
STRUCTURE
Three distinct parts:
1. External ear
2. Middle ear
3. Internal ear
__________________________________________________
EXTERNAL EAR
Auricle (Pinna)
• Expanded portion projecting from side of head
• Composed of fibro-elastic cartilage covered with skin
• Deeply grooved and ridged
• Most prominent outer ridge = helix
• Lobule: Soft lower part; fibrous and adipose tissue; richly supplied with blood
capillaries
External Acoustic Meatus (Auditory Canal)
• Slightly S-shaped tube; ~2.5 cm long
• From auricle to tympanic membrane (ear drum)
• Lateral part cartilaginous; remainder in temporal bone
, • Lined with hairy skin continuous with auricle
• Numerous sebaceous and ceruminous glands in lateral part
Ceruminous glands:
• Modified sweat glands secreting cerumen (wax)
• Sticky substance containing lysozyme and immunoglobulins
• Wax, hairs, and curvature prevent foreign materials from reaching tympanic
membrane
Movement of temporomandibular joint during chewing/speaking massages cartilaginous
meatus, moving wax toward exterior.
__________________________________________________
MIDDLE EAR (Tympanic Cavity)
Irregular-shaped cavity within petrous temporal bone.
• Cavity, contents, and air sacs lined with simple squamous or cuboidal epithelium
• Air fills cavity; reaches it through pharyngotympanic (Eustachian/auditory) tube from
nasopharynx
• Tube ~4 cm long; lined with ciliated epithelium
Air at atmospheric pressure on both sides of tympanic membrane enables vibration
when sound waves strike it.
• Tube normally closed; opens by swallowing/yawning when pressure needs
equalizing (e.g., at high altitude) -> ears "pop"
Walls:
• Lateral: Tympanic membrane
• Roof and floor: Temporal bone
• Posterior: Temporal bone with openings to mastoid antrum (air passes to mastoid air
cells)
• Middle: Thin temporal bone with two openings:
• Oval window (fenestra vestibuli): Occluded by stapes
• Round window (fenestra cochleae): Occluded by fibrous tissue sheet
Tympanic Membrane (Ear Drum)
• Completely separates external acoustic meatus from middle ear
• Oval; slightly broader edge upward
• Three tissue layers:
4. Outer: Hairless skin
5. Middle: Fibrous tissue
6. Inner: Mucous membrane continuous with middle ear
