Week 5 Ear + Eye Flashcards
3 inputs to Postural System
- Somatosensory.
- Visual.
- Vestibular (Otolith, semicircular canals).
Ventromedial Pathway
Controls posture
- Vestibulospinal
- Tectospinal
- Pontine Reticulospinal
- Medullary reticulospinal
all 4 input on VENTRAL horn of spinal cord.
Vestibulospinal and Tectospinal Tracts
Functions: Keep head balanced when body in motion.
1. Vestibulospinal:
Sensory input from vestibular labyrinth (inner ear).
Tracts originate from vestibular nuclei in medulla.
2. Tectospinal:
Sensory input from retina.
Tracts originate from superior colliculus.
Directs head and eyes to particular location.
vestibulospinal also maintains upright posture via extensor motor neurons of leg.
Pontine and Medullary Reticulospinal Tracts
- Pontine Reticulospinal:
Enhances antigravity reflexes of spinal cord.
Faciliate extension of lower limbs and maintains standing posture against gravity. - Medullary Reticulospinal:
Liberates antigravity musles (opposite of pontine).
Arise from reticular formation.
Controlled by Cerebellum and Cortex.
Outer Ear
Anatomy and Function
Pinna (Auricle).
External Auitory Meatus (Ear canal).
Tympanum (Eardrum).
Function: Converts acoustic energy into kinetic energy.
Pinna/Auricle
Visible part of Ear
Function
Funnels sound into ear canal.
Aids in vertical localisation of sounds (filters only sounds capable of being heard(20-20000hz))
External Auditory Meatus
Anatomy and Function
Sigmoid canal.
7mm Width, 25mm length.
Runs until Tympanum.
Proximal 2/3 surrounded by bone vs cartilage.
Hair/sebaceous/ceruminous glands in cartilaginous 1/3.
Cerumen = ear wax
Function: Focuses sound on eardrum. Amplifies sound corresponding to human speech (10-15dB).
Tympanic Membrane
Eardrum
Collagenous membrane.
Separates outer and middle ear.
Made up of 4 parts:
1. Umbo (most depressed part of concavity).
2. Malleus (attached to medial tympanic surface).
3. Pars flaccida.
4. Pars tensa
Function: Vibrates in response to sound pressure waves thus, trnsmits sound energy to middle ear.
Middle Ear
Air filled chamber.
3 smallest bones in body (OSSICLES) connect eardrum to oval window.
Function: Convert kinetic energy to hydraulic energy in inner ear.
Ossicles
Malleus.
Incus.
Stapes (foot part sits in oval window).
Function: Ampify/leverage sound, 20x.
Eustachain Tube
Connection between middle ear and nasopharynx.
Typically closed, can be opened by lowering and protruding the mandible (yawning/chewing).
function: equalizes pressure between middle ear and external ear. Prevents damage to tympanic membrane.
Middle Ear Muscles
- Tensor Tympani: Attaches to malleus.
- Stapedius: Attaches to stapes.
Contraction results in decreased mobility of ossicles therefore dampens hearing.
Muscles are contracted in response to high intensity sound or during vocalisation (Acousitc Reflex).
1. (O = Auditory tube)(Sup. Tympanic Artery)(Medial pterygoid nerve of mandibular)
2. (O=pyramidal eminence)(Stapedial branch of posterior auricle)(Facial nerve)
Inner Ear
Labyrinth made up of Vestibular system (balance) and Cochlea (hearing).
Converts kinetic energy of ossicles into hydraulic energy of fluid in inner ear and then into electrochemical signals in CN8.
Cochlea uses movement of fluid to sense external pressure changes (sound).
Inner Ear Anatomy
Bony Labyrinth: Surrounds petrous part of temporal bone.
Membranous labyrinth: System of tubes and chambers filled with ENDOLYMPH (fluid w/ high K+ conc). Sits within Bony labyrinth.
Between bony and membranous labyrinth, there is PERILYMPH (high Na+ conc).
Cochlea
2.75 turns around bony column (modiolus).
3 components:
1. Scala Media (Cochlar duct); filled with endolymph.
2. Scala Vestibuli (above media); filled with perilymph.
3. Scala Tympani (beflow media); filled with perilymph.
Reissner membrane separates scala vestibuli and media.
Basilar membrane separates scala media and tympni.
Organ of Corti: converts fluid movement into nerve signals is found within basilar membrane.
Organ of Corti
Located in Cochlear duct (Scala Media, filled w/ endolymph).
Contains 20,000 auditory receptors each with its own hair cell.
Displacement of Basilar membrane causes shear of hair cells, opening non-selective ion channels, leading to depolarization.
Cochlear Hair Cells
Displacement of STEREOCILIA towards KINOCILIUM stimulates hair cell.
Displacement away from Kinocilium inhibits hair cell.
Inner hair cells sends signal to brain via spiral ganglion and CN8.
Loud noise can cause irreversible damage to hair cell.
Auditory Pathway
Information from CN8 travels via SLIM:
- Superior Olivary Complex
- Lateral Lemniscus
- Inferior Colliculus
- Medial geniculate Nucleus (in thalamus)
Before going to auditory cortex.
Decussaation occurs b/t cochlear nuclei and superior olivary complex and at inferior colliculi.
Auditory Cortex
Located on TEMPORAL LOBE.
Brodmann areas 41/42.
Sound localization
Medial SON (Sup. Olivary Nuclei) detects difference in timing.
Lateral SON detects differences in intensity.
High Fz (>1600 Hz) occurs by LSON.
Low Fz ( <800 Hz) occurs by MSON.
Hearing Loss
2 types
Conductive: problem conducting sound waves through outer ear, eardrum, or middle ear.
Sensorineural: problem in the cochlea, organ of corti, CN8.
Anatomy of the Eye
3 Layers
- Fibrous Layer
- Cornea
- Sclera - Vascular Layer
- Iris
- Ciliary Body
- Choroid - Neural Layer
Fovea: region of highest resolution.
Centre of retina = Macula.
Cornea: Front part of te eye
Sclera: White of the eye, site of muscle attachment
Iris: cirular structure w/ pupil in the middle.
Ciliary body: ciliary muscle + ciliary processes. Muscles attach to the eye (changing lens shape), processes produce aqueous humor.
Choroid: layer of connective tissue + vessels.
Structure of Eye ball
Chambers + Fluid
Vitreous humour fills the space between lens and retina.
Aqueous humour is between Cornea and lens (ant. chamber) and iris and ciliary process (post. chamber).
Aqueous humour is drained via trabecular meshwork, at base of cornea.
Blood Supply of the Eye
Ophthalmic Artery.
Sup. & Inf. Ophthalmic veins.
Internal carotid > Ophtalmic Art.
Veins drain into cavernous sinus.
Innervation of the Eye
Sight = Optic Nerve.
Miosis (pupil constrction) + lens = Short Ciliary Nerve.
Mydriasis (dilation) = Long Ciliary Nerve.
CN 3,4,6 = Eye movements.
CN5 V1= eyeball, upper eyelid, nose ridge sensation.
LR6, SO4
Ophthalmic N > Nasociliary N > Long ciliary N. (sympathetic)
Edinger westphal nucleus > CN3 > Ciliary ganglion > Short ciliary N. (paraSympathetic)
Accommodation Reflex
Purpose: to focus on nearby objects.
Near vision = Thick lens.
Parasympathetic control.
3 Components:
Pupil constricton.
Lens accommodation.
Convergence.
Pathophysiology of Cataracts
Lens is composed of specialized proteins called CRYSTALLINS, which are dependent on 3D structure and hydration. Membrane channel proteins maintain osomotic and ionic balance across the lens. Protein-bound Sulfhydryl (SH) groups of crystallins are protected against oxidation and cross-linking by high concentrations of reduced GLUTATHIONE (mother of all anti oxidants). Aging leads to increased oxidative stress, leads to breakdown and aggregation of protein.
Tx: Surgery; replace cloudy lens with artifical lens.
Risk factors:
Age
Trauma
UVB light
Genetics
Pathophysiology of Glaucoma
Raised intra ocular pressure (Nr=12-22mm Hg).
Increased resistance to aqueous humour outflor through the trabecular meshwork. Typically via obstruction.
Tx: beta blockers, A2 agonist, carbonic anhydrase, prostagladins
6 Retinal Cell types
- Optic Nerve fibres
- Ganglion cells
- Amarine cells
- Bipolar cells
- Horizontal cells
- Photo receptors (Rods + cones)
Pigment epithelium.
Lateral Geniculate nucleus
Thalamic visual relay station.
3 layers from each eye.
Parvocellular: small cell, tyop 4 layers. Receive input from B ganglion cells (Midget). 90% color component.
Magnocellular: large cell, bottom 2 layers. Receive input from A ganglion cells (Parasol). Light/dark, greysale.
Difference between Nicotinic and Muscarinic cholinergic receptors
Nicotinic = somatic nervous system
Muscarinic = Autonomic nervous system
3 types of Cone cells
L - Long wavelength (red)
M - Middle wavelength (green)
S - Short wavelength (blue)
Dichromat (only 2 cone types).
Protanopia - lack L cones.
Deuteranopia - lack M cones.
Trianopia - lack S cones.
Foveal vision processing
Foveal vision = sharp central vision
Foveal vision processed in posterior aspect of primary visual cortex.
Peripheral vision processed in anterior aspect.
V4 area; responsible for color (lesion=Achromatopsia).
V5; specialized for motion (lesion=Akinetopsia).
Higher level visual areas
Fusiform Face Area = Faces
Parahippocampal = Scenes/Places
Lateral Occipital Cortex: Objects
Information Processing from LGN
Retina > LGN >
Path 1: Magnocellular > Primary VC > Dorsal Stream > Posterior parietal cortex
Path 2: Parvocellular > Primary VC > Ventral stream > Infero-temporal cortex
VC = visual cortex
Path 1 aka “Where pathway”. Lesion = optic ataxia (Balint’s syndrome).
Path 2 aka “What pathway”. Lesion = Visual agnosia.
Horner Syndrome
Triad.
Ptosis, miosis, anhidrosis.
miosis = constricted pupil
Lesion to sympathetic pathway.
