@ SSA
@ Introduction to Ear
1. External ear Þ Auricula (Pinna) : External acoustic meatus
2. Middle ear Þ Tympanic membrane : Tympanic cavity : Auditory ossicles：Malleus (鎚骨)、Incus (砧骨)、Stapes (鐙骨) : Tensor tympani m. (由Trigeminal nerve支配) : Stapedius m. (由Facial nerve支配) : Auditory tube (Eustachian tube) : 以Oval windon = Fenestra vestibuli (前庭窗、卵圓窗)與內耳為界。由於Oval window的面積比Tympanic membrane小，再加上三個聽小骨的槓桿作用，所以當聲音振動由Tympanic membrane傳到Oval window時，已被放大了16-22倍。
※ Tympanic cavity的前壁有三個通道：上為容納Tensor tympani m.的管道，中為Auditory tube，下為Corda tympani nerve的出口。內壁有Promontory (由1st turn of the cochlea所造成)與Tympanic plexus。外壁有Tympanic membrane。後壁由上至下有Mastoid air cells入口、Mastoid antrum入口、椎體、Corda tympani nerve的入口。
3. Internal ear可分為二部份：
(1) Osseous (Bony) labyrinth (骨性迷路) Þ 與Membranous labyrinth之間充滿Perilymph，此腔藉由Cochlear canaliculus與Subarachnoid space相通，Perilymph的成份也與CSF相似。Bony labyrinth包括三部份：
(a) Vestibule (前庭) Þ 在外側壁有Oval window，Stapes的底部即以Annular ligament附於其上。Oval window的下方有Round window = Fenestra cochleae (耳蝸窗、圓窗)，覆蓋此窗的膜又稱Second tympanic membrane (第二鼓膜)，其功用為緩衝聲音振動時來自Oval window的Perilymph的液體壓力。在Vestibule內有屬於Membranous labyrinth的Saccule與Utricle。
(b) Bony semicircular canals (骨性半規管) Þ 可分為Anterior、Posterior與Lateral三個，每個有一端膨大，稱為Ampulla (壺腹)。
(c) Cochlea (耳蝸) Þ 以Modiolus (蝸軸)旋轉2½圈。
(d) Internal acoustic meatus Þ 從Modiolus來的Cochlear nerve以及從Vestibuli來的Vestibular nerve會合成Vestibulo-cochlear nerve，然後經由Internal acoustic meatus通至Posterior cranial fossa，而在Medullo-pontine junction處進入Brainstem。
(2) Membranous labyrinth (膜性迷路) Þ 內部充滿Endolymph，由Cochlear duct外側壁的Stria vascularis (血管紋) -- 特化的高度血管化結締組織 -- 上覆的Stratified cuboidal epithelium所製造，在Membranous labyrinth內循環後，最終經由Utriculosaccular duct分出的Endolymphatic duct輸送到一盲囊 --Endolymphatic sac，而被吸收回去。Endolymph的成份與Perilymph大不相同，Endolymph和細胞內液一樣，有著高濃度的Potassium ions與低濃度的Sodium ions。
(a) Vestibular labyrinth Þ 內部構造為：Perilymphatic space、Utricle (橢圓囊)、Semicircular ducts (半規導管)、Utriculosaccular duct (橢圓球囊管)、Endolymphatic duct、Saccule (球囊)、 Ductus reuniens (連合管)。
(b) Cochlear labyrinth Þ 內部構造為：Perilymphatic space (= Scala vestibuli : Scala tympani)、Endolymphatic space (= Scala media = Cochlear duct)。Cochlear labyrinth被Vestibular membrane (Reissner’s membrane) 與Basilar membrane分成三個螺旋狀空間，上與下分別是Scala vestibuli (前庭階) 與Scala tympani (鼓階)，中間則是Scala media = Cochlear duct (中間階、耳蝸導管)。Scala vestibuli和Scala tympani均內襯未特化的Simple squamous epithelium。Scala vestibuli起於Oval window，Scala tympani止於Round window，此二階在Cochlea的頂端以Helicotrema (蝸孔)相連接。
@ Structure of the Organ of Corti
1. Basilar membrane (基底膜) Þ The basilar membrane is not under tension, but has a stiffness that varies 100-fold from one end to the other. This membrane is narrowest and stiffest at the base of the cochlea (高頻：0.08 mm) and widest and most pliable near the helicotrema (低頻：0.52 mm).
2. Sensory cells = Inner (one row) and outer (three to five rows) hair cells Þ 每個Inner hair cell的頂部有50-70根Stereocilia，而Outer hair cell則有100-300根。
3. Peripheral processes of the cochlear nerve cells Þ 90-95%為Myelinated fibers，終止於Inner hair cells的底部；5-10%為Unmyelinated fibers，與Outer hair cells接觸。它們的Cell body位於Spiral ganglion。
4. Inhibitory efferent cochlear bundle (= Olivocochlear bundle) Þ 源自Cholinergic neurons surrounding the principal and accessory superior olivary nuclei，經由Vestibular nerve root穿出腦幹，再經由Vestibulocochlear anastomosis進入Cochlear nerve。與Hair cells或Cells of the spiral ganglion發生聯會，作用是抑制Auditory nerve對Acoustic stimuli起反應 (Feedback control)。
5. Supporting cells Þ 包括：(1) Inner and outer pillar cells、(2) Inner and outer phalangeal cells、(3) Border cells、(4) Cells of Hensen = Outer border cells。
6. Tectorial membrane (覆膜) Þ 由細纖維構成，含Glycosaminoglycans。此膜蓋住整個Organ of Corti，而Hair cells的Stereocilia尖端即埋入此膜中。
@ Function of the Organ of Corti
1. 聲波 (空氣的振動) Þ External acoustic meatus Þ Tympanic membrane Þ Malleus、Incus、Stapes Þ Oval window Þ Perilymph in the vestibuli，產生壓力波 Þ Perilymph in the scala vestibuli Þ Vestibular membrane產生振動 Þ Endolymph in the cochlear duct，產生壓力波 Þ Basilar membrane產生振動 Þ 多餘的振動引起Perilymph in the scala tympani產生壓力波 Þ 被Round window的Second tympanic membrane緩衝後消失
2. Basilar membrane產生的振動 Þ 振動Hair cells Þ 拉彎Stereocilia，而使其尖端在Tectorial membrane內滑行 Þ Hair cells去極化，釋放Neurotransmitter Þ Peripheral processes of the cochlear nerve cells產生Action potential Þ Auditory pathway
3. 人耳所能接受的聲音頻率為20-20000 Hz，相當於11個八度音。樂器(鋼琴)能發出7個八度音。隨著年齡增加，對於高頻音會漸漸不敏感。一般談話的頻率在300-3000 Hz之間。
@ Ascending Fibers in the Auditory Pathway
1. Tonotopic arrangement
2. Cochlear nerve Þ Ventral and dorsal cochlear nuclei Þ Dorsal (源自Dorsal cochlear nucleus)、Intermediate (源自Dorsal portion of the ventral cochlear nucleus)、Ventral (源自Ventral cochlear nucleus) acoustic striae Þ 少數終止於同側的Superior olivary nucleus；多數橫過橋腦形成Trapezoid body，而進入對側的Superior olivary nucleus Þ Passing fibers through the superior olivary nucleus : Fibers from the third-order neurons in the nucleus of trapezoid body and superior olivary nucleus Þ Lateral lemniscus Þ 多數終止於Inferior colliculus，一些在Nucleus of lateral lemniscus內轉換 Þ 少數Passing fibers from the inferior colliculus through inferior brachium Þ Medial geniculate body (MGB) Þ Auditory radiation via the sublentiform part of the internal capsule Þ Auditory cortex = Primary auditory area = Heschl’s convolution = Areas 41 and 42
3. Secondary auditory area = Auditory association cortex = Area 22
@ Descending Fibers in the Auditory Pathway Þ For auditory sharpening
1. Cortico-geniculate fibers
2. Cortico-collicular fibers
3. Colliculo-olivary fibers
4. Colliculo-cochleonuclear fibers
5. Olivo-cochlear bundle of Rasmussen
@ Localization of Sound
1. Superior olivary nucleus Þ 分析並比較聲音到達的時間 (頻率低於500 Hz者)，或聲音的強度 (頻率高於1000 Hz者)。
2. Inferior colliculus Þ 根據上述來解釋並判斷聲音的方位。
@ Auditory Reflexes
1. Stapedial reflex (8進7出)
※ Primary auditory neurons Þ Ventral cochlear nucleus Þ Trapezoid body Þ Bilateral medial superior olivary nucleus Þ Facial motor neurons Þ Contraction of the stapedius muscle Þ Dampen the oscillations of the ear ossicles in response to high levels of acoustic stimuli
2. Tensor tympani reflex (8進5出) Þ 功能類似上者。Diminish the sensitivity of the tympanic membrane to loud sounds by tensing the membrane。
3. Auditory sharpening Þ 由Inferior colliculus、Nuclei of lateral lemniscus、Principal superior olive投射到Cochlear nuclei，抑制某些聲音頻率，而讓特定想聽的聲音頻率更強化。
4. Startle reflex (驚嚇反射)
@ Clinical Correlation
1. Conduction deafness (傳導性耳聾) Þ 起因於中耳疾病，例如Otitis media (中耳炎)、Otosclerosis (耳硬化)、耳垢過多，造成Ossicular chain的Fixation或Interruption。耳硬化患者通常喪失患(單)側的30－65分貝的聽力，有Tinnitus (耳鳴)，但沒有Vertigo (暈眩)，在高聲喧鬧中反而覺得聽力較好 (Paracusis；錯聽)。
2. Nerve deafness (神經性耳聾) Þ Cochlear nerve或Cochlear nuclei的損傷 (ex: Acoustic neurinoma)，會造成受傷側的全聾但無耳鳴；單側的Lateral lemniscus或Auditory cortex的損傷會造成雙側的部分耳聾但對側較嚴重；單側的Temporal cortex切除則會損害對側的Sound localization。
3. High tone deafness (高音聾) Þ 長期暴露在噪音環境下，造成Organ of Corti的退化所致。
4. Hyperacusis (聽覺過敏) Þ 由於Tensor tympani muscle或Stapedius muscle (ex: Bell’s facial palsy) 的癱瘓所致，造成Tensor tympani reflex 或Stapedial reflex無法運作，因而聽到的聲音較正常者聽到的為大。
5. Word deafness or acoustic verbal agnosia = Receptive aphasia (聽語聾、感覺性失語症) Þ Sensory speech area of Wernicke (Areas 22, 39, 40) 受損所致。
@ SSA
@ Static Labyrinth (靜態迷路) Þ 偵察頭部的Linear acceleration，以及靜止時頭部的方位。當眼睛閉起、處於黑暗、或在水中時，這種感覺特別重要。
1. Utricle and saccule (= Otolithic organ) Þ 內襯胚胎時由Otic vesicle來的Simple cuboidal epithelium。Utricle對Vertical acceleration特別敏感，而Saccule對Dorsoventral acceleration特別敏感。
2. Macula (斑) Þ 在Utricle與Saccule內，由Simple cuboidal epithelium特化的感覺上皮，約2-3 mm。含有數種重要構造：
(1) Sensory cells = Hair cells Þ 基本構造和Organ of Corti的Hair cells相同。每個Hair cell有40-80根Stereocilia與一根Kinocilium (動纖毛)。纖毛頂端插入Otolithic membrane (耳石膜)，此膜內含Glycoprotein，可能為Supporting cells所分泌，另外膜表面還有Calcium carbonate結晶，稱為Otoliths = Otoconia = Statoliths = Statoconia (耳石、耳沙)。耳石使得Otolithic membrane的比重大於Endolymph，因此除非Macula是位於絕對水平狀態，否則Hair cells的纖毛都會被Otolithic membrane壓向某個方向彎曲。當Stereocilia向著Kinocilium的方向彎曲時，就會使Hair cell興奮。
(2) Peripheral processes of the vestibular nerve cells Þ 當它們進入Macula後，會失去Myelin sheath，終止於Hair cells的底部。它們的Cell body位於Vestibular ganglion = Scarpa’s ganglion，位於Internal acoustic meatus的底部。
(3) Excitatory efferent vestibular bundle Þ 源自Cholinergic neurons lie along the lateral border of the abducens nucleus。作用是Modulate the dynamic range of afferents to match expected acceleration。
(4) Inhibitory efferent fibers in the vestibular nerve bundle Þ 源自Superior and medial vestibular nuclei與Fastigial nucleus of the cerebellum。與Type 2 hair cells或Afferent nerve terminals connected with the type 1 hair cells發生聯會，作用是Feedback control。
(5) Supporting cells
@ Kinetic Labyrinth (動態迷路) Þ 偵察頭部的Angular acceleration，對頭部的旋轉有敏銳的反應。
1. Anterior, posterior and lateral simicircular ducts
2. Ampulla (壺腹)
3. Crista ampullaris Þ 為Ampulla內的感覺受器，其擺動方向與Endolymph的流向垂直。運動時，因為慣性的作用，Crista ampullaris內的Cupula會因應運動的開始、進行、停止而產生不同的流動方向，使得與Cupula接觸的Hair cells產生興奮或抑制的反應，而偵測到頭部旋轉的方向。Crista ampullaris不論是在構造上或神經支配模式上均與Macula相同：
(1) Sensory cells = Hair cells Þ 纖毛頂端插入Cupula (頂)，此頂內含Gelatinous glycoprotein，但無Calcium carbonate結晶，因此它是懸浮在Endolymph中，無重量的，唯有頭部做角加速度運動時，Hair cells才會被刺激。所以Simicircular ducts有Kinetic labyrinth之稱。每個Hair cell的Kinocilium都是位於Stereocilia靠近Ampulla開口入Utricle的那一端，因此當Endolymph由Ampulla流入Utricle時，就會興奮Hair cells；反之則會抑制Hair cells的興奮。事實上，即使Stereocilia不彎曲時，Macula與Crista ampullaris的Hair cells也會自發性放電，稱為Tonic discharge。
(2) Peripheral processes of the vestibular nerve cells Þ 當它們進入Macula後，會失去Myelin sheath，終止於Hair cells的底部。它們的Cell body位於Vestibular ganglion = Scarpa’s ganglion，位於Internal acoustic meatus的底部。Scarpa’s ganglia又可分為：(1) Superior ganglion，接受源自Anterior and lateral semicircular ducts與Utricle的感覺神經傳入；(2) Inferior ganglion接受源自Saccule與 Posterior semicircular duct的感覺神經傳入。
(3) Excitatory efferent vestibular bundle Þ 源自Cholinergic neurons lie along the lateral border of the abducens nucleus。作用是Modulate the dynamic range of afferents to match expected acceleration。
(4) Inhibitory efferent fibers in the vestibular nerve bundle Þ 源自Superior and medial vestibular nuclei與Fastigial nucleus of the cerebellum。與Type 2 hair cells或Afferent nerve terminals connected with the type 1 hair cells發生聯會，作用是Feedback control。
(5) Supporting cells
@ Primary Vestibular Fibers
1. Central processes (Vestibular nerve) of the bipolar neurons in the vestibular ganglion Þ
(1) Short ascending branches Þ Superior and lateral vestibular nuclei as well as the rostral part of the medial vestibular nucleus
(2) Long descending branches Þ Inferior vestibular nucleus
(3) Collaterals of the descending fibers Þ Caudal part of the medial vestibular nucleus
2. Vestibular nerve Þ Traverse portions of the lateral and superior vestibular nuclei Þ Juxtarestiform body of the inferior cerebellar peduncle Þ Mossy fibers Þ Fastigial nucleus, nodulus, uvula and flocculus
@ Secondary Vestibular Fibers
1. Vestibulo-cerebellar pathway：Caudal portions of the medial and inferior vestibular nuclei Þ Juxtarestiform body of the inferior cerebellar peduncle Þ Mossy fibers Þ Vestibulocerebellum (Nodulus : Uvula : Flocculus)
2. Vestibulo-spinal pathway：
(1) Lateral vestibulospinal tract
(2) Medial vestibulospinal tract (= Descending medial longitudinal fasciculus)
3. Vestibulo-ocular connections (= Ascending medial longitudinal fasciculi)：Superior (uncrossed), lateral (crossed), inferior (crossed), and medial (both) vestibular nuclei Þ Ascending MLF Þ
(1) Nuclei of the abducens, trochlear, and oculomotor nerves
(2) Accessory oculomotor nucleus
(3) Paramedian pontine reticular formation
@ Clinical Correlation
1. Primary responses Þ 刺激單側的Ampullary nerve from the horizontal (= lateral) semicircular duct可使雙眼的水平轉動偏向對側 (Opposite deviation)；刺激雙側的Ampullary nerve from the anterior semicircular duct可使雙眼Upward movement；刺激雙側的Ampullary nerve from the posterior semicircular duct可使雙眼Downward movement。
2. Nystagmus (眼球震顫) Þ Nystagmus有生理性及病理性的。當正常人朝單向轉動頭與身體並意欲凝視一固定物體時，則他的雙眼會以反方向慢速轉動【Slow phase】；但若雙眼的慢速相轉到極限，而頭與身體卻繼續轉動時，則雙眼會立即彈回來【Rapid (fast) phase or compensatory movement】，這種快速相是一種Autonomic reflex correction。Nystagmus肇因於Labyrinthine stimulation。
※ By convention, nystagmus is named by the direction of the fast return saccade phase – for example, as leftward beating nystagmus or downward-beating nystagmus.
3. Rotating chair test (Bárány chair) Þ 人坐在Bárány chair上並轉動一段時間，然後突然停住，則Endolymphatic fluid會碰壁而朝反方向繼續流動。在Postrotational phase期間，無論是Slow phase of nystagmus、Deviation of eyes、Postural deviation (standing)、Past-pointing都會與原轉動方向相同。
4. Vertigo (眩暈) Þ 在上述測試的Postrotational phase期間，測試者會感到與原轉動方向相反的眩暈感。
5. Caloric test (熱測試) Þ 將頭側放，使外側半規管垂直著水平面，再將熱水 (40 °C) 或冷水 (30°C) 灌入外耳道，水溫可使內淋巴液對流，因而刺激前庭系統，再經由Abducens nucleus與MLF來影響Oculomotor nucleus (Vestibulo-ocular connections)，而造成眼球的Nystagmus 【COWS：Cold water produces nystagmus beating (= fast phase) to the opposite side；Warm water produces nystagmus beating to the same side。】，同時亦有眩暈之感。此測試可檢驗前庭系統是否受損，若產生Nystagmus與Vertigo，則表示此系統是正常的。
6. Galvanic test (電測試) Þ 以電直接刺激Ampullary nerve endings of the horizontal (= lateral) semicircular duct，同樣可檢驗前庭系統是否正常。
7. Ménière’s disease (耳性眩暈病) Þ 不正常的前庭內淋巴循環、或是內淋巴液過多所致。有耳鳴、強烈眩暈、嘔吐、惡心、臉色蒼白、呼吸急促。
8. Motion sickness (暈車船) Þ 因為車船的過度晃動而過度刺激Utricle所致。