2 - Anatomy/Physiology Flashcards
What are the layers of the wall of the eyeball?
1) Fibrous (corneosclera) - anterior cornea is refractive; posterior sclera maintains shape of eye
2) Uvea - composed of Iris, Choroid Bodies and Choroid; contains smooth muscle to control pupil size and lens shape; choroid is contains vessels for the nourishment of deeper layers of the eye
3) Retina - pigmented and neural retina for photosensation
What are the layers of the cornea?
1) Corneal Epithelium - stratified epithelium innervated by CN V(1); quickly regenerated in the event of injury; covered in microvilli which assist in maintaining the tear film on the eye
2) Corneal Stroma - thick layer of orthogonal collagen fibers arranged to provide transparency; avascular;
3) Corneal Endothelium - single layer of cells important for metabolic exchange and supplying nutrients for the cornea
What are the intra-occular muscles of the eye? What are their innervation? Function?
1) Dilator Pupillae - dilates pupil - sympathetic fibers from Superior Cervical Ganglion
2) Sphincter Pupillae - constrict pupil - parasympathetic fibers from Ciliary Ganglion
3) Ciliary Muscle - controls shape of lens via zonular fibers connected to ciliary bodies - parasympathetic fibers from Ciliary Ganglion
Describe the flow path of Aqueous Humor.
1) Formed by the ciliary epithelium of the ciliary bodies
2) Empties into posterior chamber
3) Flows through pupil into the anterior chamber
4) Absorbed by the Trabecular Meshwork
5) Drains into Canal of Schlemm
6) The Canal drains into Aqueous Veins which then drain into (blood) Veins of the Sclera
What are the layers of the Retina?
(posterior to anterior)
1) Retinal Pigmented Epithelium (RPE) - acts as a back-barrier of the retina; highly pigmented to absorb excess light and prevent glare; primary component of BBB and phagocytosis of the eye
2) Outer Segment Rods/Cones - outer (posterior) portion of the rods/cones are photosensitive and initiate light-sensitive sensory signaling;
3) Inner Segment Rods/Cones - inner portion contains the nuclei
4) Synapse bwtn Rods/Cones and Bipolar Cells
5) Bipolar Cell bodies
6) Synapse btwn Bipolar Cells and Ganglion Cells
7) Ganglion Cell bodies
8) Ganglion Cell axons
What are the layers of the Lens?
1) Capsule - THICK basement layer around the lens
2) Epithelium - thin layer of simple cuboidal epithelium
3) Fibers - elongated epithelium that lose their nuclei and become filled with crystallins
Describe the structure and location of the tympanic cavity.
1) air filled cavity in the petrous temporal bone
2) lower portion -> tympanic cavity proper, immediately internal to the tympanic membrane; upper portion -> epitympanic recess
3) roof -> tegmen tympani (thin petrous bone) separates cavity from cranial cavity
4) floor -> thin plate separates cavity from jugular fossa; tympanic branch of CN IX transits wall to form tympanic plexus
5) medial wall -> promontory = basal turn of the cochlea; facial canal = bulge above promontory; oval and round window
6) posterior wall -> aditus = opening to mastoid air cells via mastoid antrum; chorda tympani = from facial n. that courses over membrane before exiting; pyramidal eminence = contains stapedius muscle w/ tendon emerging from the tip
7) lateral wall -> tympanic membrane with malleus and incus; tympanic nerve courses across
8) anterior wall -> opening to the canal of the tensor tympani; opening to the pharyngotympanic tube; thin wall over internal carotid a.
Describe the function of the auditory ossicles.
1) Malleus (hammer): long handle on the the membrane with its head articulating with the incus in the epitympanic recess
2) Incus (anvil): long process extends back down into the tympanic cavity proper to articulate with stapes
3) Stapes (stirrup): footplate sits in oval window
Muscles:
1) Tensor tympani: attached to the cartilage of the auditory tube and inserts on the handle of the malleus; CN V3; tenses tympanic membrane and dampens sound conduction
2) Stapedius: attached to the pyramidal eminence and inserts on the neck of the stapes; CN VII; lifts foot plate off oval window, dampening sound
Describe the form and function of the cochlea.
1) set within the bony labyrinth; central core is of bony modiolus which contains the Spiral Ganglion
2) spiral lamina is a bony ridge that wraps around modiolus and contains the cochlear duct
3) within spiral lamina, space is divided into three areas: scala vestibuli (perilymph), cochlear duct(endolymph) and scala tympani(perilymph)
4) oval window is at opening of scala vestibuli; round window is at end of scala tympani; these two meet at the helicotrema
5) sound travels from the oval window, through the scala vestibuli, into the cochlear duct where the organ of corti is located,into the scala tympani and is dissipated at the round window
6) organ of corti is composed of sensory hair cells (inner and outer) and supporting hair cells (phalangeal and pillar); techtorial membrane overlies the hair cells and provides the “shearing force” for the sensory hair cells
7) outer wall is lined by stratified cuboidal epithelium overlying connective tissue; this is where endolymph is secreted
Describe the components of the semilunar canals.
1) 3 canals at ~90 degrees to each other
2) contain central ampullae, in which is a raised epithelial ridge (crista ampullaris) which is covered by a gelatenous structure (cupula)
3) filled with endolymph
4) cupula has the same sp. gravity as the endolymph, therefore when the head turns, the endolymph and cupula “lag” behind the skull’s rotation placing shear stress on hair cells and initiating sensory pathway
5) type I/II hair cells have a single cilium (kinocillum) and many stereocillia (microvilli)
6) supporting cells have irregular shapes and secrete contents of the cupula
Describe the components of the utricle and saccule.
1) utricle: sac at the opening to the semilunar ducts; senses gravity and HORIZONTAL linear movement
2) saccule: sac at the opening to the cochlear duct; senses gravity and VERTICAL linear movement
3) macula contains type I/II hair cells and supporting cells; covered by otolithic membrane which is then covered with otoconia
4) due to the greater density of the otoconia, when there is linear acceleration, the otoconia “lag” behind and cause shear stress on the hair cells, initiating the sensory pathway
What is detection threshold?
- the minimum level necessary for human perception of sound
- normal human hearing range 20Hz - 20kHz
- most sensitive 2-5kHz
- human speech~4kHz
Describe the conduction of sound through the ear.
1) sound waves are collected and selectively amplified by the auricle and the external auditory meatus
2) vibration of the tympanic membrane is transferred to the oval window by the ossicles
3) amplification is~18:1 due to: 1)reduction in size from tympanic membrane to oval window, 2) lever/piston action of the ossicles
4) sound conduction can be attenuated by the contraction of 1) tensor tympani: tensing the membrane limits vibration; 2) stapedius: lifting the foot process off the oval window
5) wave is conducted through the perilymph of the scala vestibuli and through the basement membrane of the cochlear duct, then through the scala tympani and dissipated at the round window
6) pressure difference across the basement membrane causes displacement of and shear stress on the hair cells of the organ or corti
7) the movement relative to the tectoral membrane produces an electrical signal and initiates the sensory pathway
How is frequency of sound discriminated? Amplitude?
1) Place: as the wave is propagated within the inner ear, the area of maximum basement membrane displacement is dependent on the frequency of the sound -> the hair cells that are most displaced produce the greatest signal, which is characteristic of a certain frequency (topotonic organization)
2) Phase-Lock: the frequency detected at the tip of the cochlear duct is ~200Hz, but the ear is able to sense as low as 20Hz since the entire basement membrane can oscillate as a wave at a low frequency -> the CNS then determines the time between the bursts of resultant APs to determine the frequency
3) Amplitude is identified by the increased firing rate of the appropriate region of the cochlear nerve, and by the recruitment of neighboring regions of the nerve
Describe the Auditory (sensory) pathway.
1) signals from the inner(95%) and outer(5%) hair cells travel to the CNS via Cochlear n.(VIIIc) and synapse in the upper medulla on the Dorsal and Ventral Cochlear N.
2) the axons that synapse on the Dorsal Cochlear N. cross via the Dorsal Acoustic Stria to the contralateral Lateral Lemniscus and travel up to the Inferior Colliculus (lower midbrain)
3) the axons that synapse in the Ventral Cochlear N. travel to the BILATERAL Superior Olivary N. (providing biaural signals to each SOC)
4) the SOC provides localization of the sound and axons from here travel up the ipsilateral Lateral Lemniscus to the Inferior Colliculus
5) from the IC, axons travel through the Brachium of the IC and synapse in the Medial Geniculate Body of the Thalamus
6) neurons then travel to the Primary Auditory Cortex (Gyri of Herschle)
7) connections are then made to the secondary auditory cortex, including Wernicke’s Area for higher processing and association
8) some neurons from the SOC give rise to the efferent Olivocochlear Bundle which travels back to synapse on the inner hair cells of the ear -> provide an inhibitory signal that can be used to selectively filter frequencies -> cocktail party effect
What is Meniere’s Disease?
- sensorineural hearing loss due to abnormal production of endolymph in the membranous labyrinth
- affects both vestibular and auditory functions
Describe the Weber and Rinne Tests.
1) Weber: tuning fork on the vertex of the skull; sensironeural hearing loss -> louder on the unaffected side; conductive hearing loss -> louder on affected side
2) Rinne: tuning fork on mastoid process and in front of ear; sensironeural hearing loss -> both ways are softer then normal, but air is louder than bone; conductive-> bone is louder than air in affected ear
Describe the stimulation of the Utricle and Saccule.
1) Utricle is connected to the semilunar canals and is sensitive to Horizontal Linear acceleration
2) Saccule is connected to the cochlear duct and is sensitive to Vertical Linear acceleration
3) movement of the head/hair cells relative to the endolymph/otolithic membrane/otoconia cause bending of the cilia and kinocilium -> bending towards kinocilium = depolarization
4) cilia/kinocilia are oriented on either side of the striola with the kinocilia aligned towards the striola (utricle) or away (saccule); the curved nature of the striola provides greater differentiation for the tilt of the head in multiple planes
Describe the stimulation of the semilunar ducts.
1) three ducts oriented at 90deg to each other and paired with a canal in the opposite ear (Anterior-Posterior; Horizontal-Horizontal)
2) sensory hair cells sit within the crista ampullaris and are embedded in the capsule (which extends across the canal)
3) during angular rotation, the endolymph displaces the cupula and causes bending of the cilia
4) bending of the cilia towards the kilocilium causes depolarization, and vise versa
5) after prolonged, constant acceleration, the endolymph will equalize and rotation will no longer be perceived by the vestibular system
Describe the Vestibular-Ocular Reflex.
1) communication between the vestibular system and extraocular muscles allows for tracking of objects while the head moves
2) rotation is sensed by the hair cells of the semilunar canals
3) signal travels via vestibular n. (VIIIv) to vestibular nucleus
4) axons then travel via the Medial Longitudinal Fasciculus (MLF) to the Extraoccular Cranial Nerve Motor Nerve N.
5) CN III, IV and VI then control extraocular movement to maintain desired position (slow phase)
6) when the eye has reached end of range, it “snaps” back to focus on another object (saccade/fast phase)
Describe the vestibular sensory pathway.
1) Hair cells connect to bipolar neurons from the vestibular ganglion,which then project axons via Vestibular n. (VIIIv) to the Vestibular N. (Superior, Inferior, Medial, Lateral) on the lateral floor of the 4th ventricle
2) some neurons of the vestibular nucleus and travel to the cerebellum via the ICP
3) Neurons from the Medial Vestibular N. form the Medial Vestibular Tract and synapse BILATERALLY in the Cervical Spinal Cord to coordinate head and neck movements
4) neurons from the Lateral Vestibular N. for the Lateral Vestibular Tract that project IPSILATERALLY to all levels of the Spinal Cord to participate in “righting reflex”
5) neurons from Inferior Vestibular N. project to the cerebellum forming the Vestibulocerebellar Fibers; these particpate in balance and posture and cancellation of the VOR for tracking via head mvmt
6) neurons also project to the CN nuclei for CN III, IV and VI to influence extraocular eye mvmt via the VOR
What are the structures in the parotid gland?
Lateral/Superficial
1) Facial Nerve -> enters in the posteriomedial surface, crosses superficial to the below structures and divides into its terminal branches
2) Retromandibular Vein -> formed by the union of the superficial temporal vein and the maxillary veins
3) External Carotid A -> terminates in superficial temporal and maxillary a.
What are the components of the fascia of the orbit?
1) Periorbita: periosteum of the bones of the orbit; it is continuous with the covering of the optic canal posteriorly and the orbit septum/facial bones anteriorly
2) Bulbar Sheath: thin membrane that covers the eyeball except the cornea; it is perforated by the ciliary nerve/vessels and ocular tendons
3) Muscular Fascia: continuous posteriorly with the periorbita and anteriorly with the bulbar sheath; anteriorly extensions come out to the lacrimal and zygomatic bones to form the medial and lateral check tendons
What are the visual fields of each eye?
1) visual fields are the areas that each eye can see
2) both eyes can see a central binocular zone
3) this zone is broken up into nasal and temporal, then upper and lower quadrants
4) each eye also has a monocular crescent in the periphery region that only it can see -> this is represented in the nasal retina due to the refraction of the eye
What are retinal ganglion cells?
1) ganglion cells represent the output for the retina
2) M-Ganglion Cells: larger, more numerous cells that predominate in the periphery
- receive input from rods and cones and most sensitive to image movement
- the have fast conduction that supports their ability for localization
- project to layers 1 & 2 of the Lateral Geniculate Body of the Thalamus
3) P-Ganglion Cells: smaller cells that are found predominately in the center of the retina and receive input from the cones
- used for high acuity site and color coding
- slow conduction, so less useful for tracking/localization
- project to layers 3-6 of the LGB
Describe the optic partial decussation.
- in the optic chiasm the fibers from the nasal visual hemifield crosses to the contralateral side
- this means that each optic tract (after chiasm) contains the ipsilateral temporal hemifield and the contralateral nasal hemifield
- since the images received by the retina are inverted/reversed; an image from the right is “seen” by the right nasal retina and the left temporal retina -> then during the partial decussation, the signal from the nasal retina crosses to the contralateral side -> the signal for the right image is completely sent to the left LBG and optic cortex
