Download ANPS 019 Black 11-14

SPECIAL SENSES II
AUDITROY AND VESTIBULAR SYSTEMS
November 14, 2011
Chapter 17: 574 – 588
OBJECTIVES:
What is the anatomy of the ear?
How are the sound vibrations detected
How does the brain perceive sound?
How does the ear help with balance?
WHAT IS THE ANATOMY OF THE EAR?
External ear – sound collection
Middle Ear – sound amplification (convert air into vibrations of liquid)
Inner Ear – sound detection (cochlea) & balance (vestibular apparatus)
EXTERNAL EAR
Auricle: provides directional sensitivity
Tympanic Membrane: “ear drum” separates external ear from middle ear
Wax: prevent any damage to tympanic membrane
Middle Ear
Also called tympanic cavity
Auditory Ossicles: 3 smallest bones in the body:
-Malleus (hammer), Incus (Anvil), Stapes (stirrup)
-Malleus attached to tympanic membrane
-Stapes attached to oval window of cochlea
--take sound vibrations of large area and amplify to a much smaller area
Two smallest muscles in body protect ear from prolonged loud sounds:
Tensor Tympani: stiffens tympanic membrane
Stapedius: Reduces movement of stapes at oval window
Long period of time of loud sounds: these muscles are in constant contraction
Eustachian tube: equalizes pressures within middle ear: drains into the pharynx
INNER EAR
Subdivided into:
Vestibule – balance
Semicircular canals – balance
Cochlea – auditory
VIBRATION OF TYMPANIC MEMBRANE
Converts sound waves at tympanic membrane into movement of fluids in membranous labyrinth of
cochlea
AUDITORY RECEPTORS LIKE WITHIN THE ORGAN OF CORTI OF THE COCHLEA
Organ corti contains auditory receptor cells
ORGAN OF CORTI
HAIR CELLS – auditory receptor
MECHANORECEPTORS
The Organ of COrti rests on the basilar membrane
The Auditory receptors, known as hair cells, have cilia that are in contact with the tectorial membrane
Movement of the basilar membrane causes movement of the cilia and depolarization
Cilia move against tectorial membrane and can detect sound/pitch
How does the brain perceive sound?
SOUND FREQUENCY IS MAPPED ON THE BASILAR MEMBRANE
High frequency receptors are damaged first
THE MAP IS MAINTAINED IN THE COCHLEAR NERVE AND COCHLEAR NUCLEUS IN THE BRAINSTEM
THE MAP IS MAINTAINED ALL THE WAY TO THE AUDITORY CORTEX IN THE TEMPORAL LOBE
Tonotopic map
-auditory nerves keeps tonotopic map
AUDITORY PATHWAY
1. Synapse in cochlear nuclei in medulla
2. Synapse in inferior colliculus
3. Synapse in medial geniculate nucleus of thalamus
(tonotopic map in between)
4. Synapse in auditory cortex of temporal lobe
HOW DOES THE EAR HELP WITH BALANCE
Vestibular system
-The vestibular apparatus in the inner ear consists of two Otolith Organs:
--static equilibrium, linear
Utricle – responds to tilting and horizontal movement (moving car)
Saccule – responds to vertical movement (elevator)
Otochonia: “rocks” move hair cells and gives s sense of direction
Semicircular Canals detect rotation
Fluid in all three planes to detect each type of direction
THERE IS ONE SEMICIRCULAR CANAL FOR EACH PLANE OF SPACE
VESTIBULAR PATHWAY
Axons from semicircular and vestibular will form vestibular branches of cranial nerve 8
They ten go to structures that are responsible for keeping balanced
Examples: red nucleus
Cerebellum
Cranial nerves 3, 4, and 6
GUSTATION AND OLFACTION
(TASTE AND SMELL)
Humans: omnivores
Chapter 17: 549-555
HOW ARE SMELL AND TASTE CLINICALLY IMPORTANT
Taste intimately linked to sense of smell
The number of taste buds begin declining rapidly by age 50
Sense of smell declines with ageing
Elderly aren’t motivated to eat because food has little taste
PARKINSON’S ANOSMIA
In Parkinson’s disease, the incidence of smell loss is greater than the incidence of tremor!
TASTE BUDS
GUSTATORY RECEPTORS
CHEMORECEPTORS – chemical receptors
Clustered in papillae(contain taste buds) of tongue
-to detect, must have saliva
GUSTATORY RECEPTORS ARE SPECIALIZED EPITHELIAL CELLS NOT NEURONS
Survive only 10 days before replacement
(just like skin, has a turnover rate)
TASTE ZONES
Do not correspond to papillae types
Primary:
-sweet
-salty
-sour
-bitter
Additional:
-Umani
-Characteristic of beef/chicken broths and parmesan cheese
-receptors sensitive primarily to amino acids
Water
Detected by receptors in the pharynx (“dry throat”)
Fats
GUSTATORY MECHANISM
Salt and sour receptors
-chemically gated ion channels
*salt and sour work directly on ion channel
Sweet, bitter and umani receptors
-gustducins – g proteins
*use a second messenger cascade that will eventually affect ion channel
GUSTATORY PATHWAY
3 cranial nerves (3,7,9) go to brainstem to thalamus to primary gustatory complex into parietal lobe
EVOLUTION OF OLFACTION
Olfactory doesn’t need to go to thalamus
--when it’s emotional, goes straight to limbic lobe
OLFACTORY ORGANS
OLFACTORY EPITHELIUM
CHEMORECEPTORS
Olfactory receptors: true neurons
Olfactory epithelium contains:
-olfactory receptors = bipolar neurons
-basal (stem) cells
-***One of few examples of neurons replaced throughout life***
Nerve foes through cribriform plate
-cilia cannot detect unless dissolved in nucleus
OLFACTORY PATHWAY
Olfactory tract has 3 primary targets:
-contralateral olfactory bulb – smell localization
-thalamus – smell perception
-limbic system – smell emotion
Baumann’s gland: make nucleus used to dissolved
THE OLFACTORY SYSTEM PROJECTS TO THE LIMBIC SYSTEM WITHOUT A THALAMIC RELAY