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Sensory System (SPECIAL SENSES (VISION = Optic Disc --> Optic Nerve -…

- - - - 2 Fluid-Filled CAVITIES
        
        1 Vitreous Humour = viciously due to proteoglycan composition for maintenance of global shape
        
        1 Aqueous Humour
      - LENS = attached to ciliary muscle via zone fibres/ suspensory ligaments
        
        Capsule
        
        Standard Cuboidal Epithelium
        
        Lens Fibre Ribbon Shaped Cells
        
        During differentiation = loss of nucleus/organelles + addition of crystalline proteins for lens transparency
        
        Not metabolically active when differentiated so dependent on epithelial gap junction
      - IRIS = smooth pigmented muscle for controlling size/aperture of central pupil
      - CORNEA = transparent epithelial like fixed lens of fine white collagen fibre stroma
      - RETINA = high level of lateral processing
        
        FOVEA = 1.5 mm diameter region for sharp vision with dense cones and neurons pushed away
        
        MACULA = 5mm diameter around fovea for centre of visual field (degenerated with age)
        
        ZANFUFUL = carotenoid pigments for UV-Light for fovea protection
        
        OPTIC DISC = no photoreceptors as region where optic nerve + blood vessels leave
        
        Outer nuclear layer = RODS + CONES
        
        Ganglion Cell Layer = 20-50 receptor cells : 1 ganglion cell
        
        VISUAL FIELD of Ganglion Cell = patch of photoreceptor it is connection to
        
        MELANIN EPITHELIUM = capture stray light and stop retrograde light distortion
        
        INNER NUCLEAR LAYER = synapses with bipolar cell + lateral retinal
        
        HORIZONTAL CELLS = interconnecting photoreceptor terminals
        
        AMACRINE CELLS = interconnect ganglion + bipolar cell terminus
      - CHOROID LAYER = Central retinal arteries + veins emerged from optic disk centre for vascular nourishment
        
        OPTHALMIC ARTERY = branch of internal carotid artery
        
        DIABETIC RETINOPATHY = proliferation of blood vessels
      - SCLERA = touGH white collagen tissue
      - CONGUNTIVA = membrane maintaining moist eyes
    - - CONES = Continuous with PM, concentrated in fovea for bright light levels
      - RODS = Infolded membrane disks separated from PM, distributed around peripheral retina for low light levels
      - Outer segment = membrane disk containing visual pigments
      - Inner Segment = normal cellular organelles
      - Synaptic Terminal = store + release Glutamate onto bipolar cells
    - - DARK ADAPTED STATE
        
        Opsin:Retinal = inactivated 11-cis-form (not interacting with G-protein transduction
        
        High Levels of cGMP produced independently from GTP
        
        Na channels kept open
        
        More Na enters than K leaks out
        
        Depolarised cells continuously release neurotransmitter
      - LIGHT ADAPTED STATE
        
        Photobleaching activated retinal by photoisomerising it to methylorhodopsin II
        
        Detached from Opsin --> Activating GPCR
        
        Transducin activated cGMP Phosphodiesterase
        
        cGMP --> 5' GMP
        
        Na + not kept open
        
        K+ channels stay open --> Hyperpolarisation
        
        On/Off bipolar cells activated under different light levels
      - RETINAL = light detecting chromophore
        
        Aldehyde form of Vitamin A attached to Lys residue in 7th domain
      - OPOSIN = 7 Transmembrane GPCR
        
        RHODOPSIN = 496nm max Opsin
        
        3 Cones
        
        420nm Blue Opsin
        
        560nm Red Opsin
        
        530nm Green Opsin
    - - ACCOMMODATION REFLEX = Sympathetic changes shape of lens via ciliary muscle + Zonoulon Fibres
        
        Fixed Curvatrue of Cornea = 75% eye focusing power
        
        Olique Rays = focus further away from focal point
        
        Relaxing of ciliary muscle = stretch pressure on xonulas fibres = flattens lens
        
        Contraction ciliary muscle = less pressure on xonulas fibres = lens assumed rounded shape maintained by lens capsule elasticity
      - PUPILLARY LIGHT REFLEX = autonomic response for pupil diameter
        
        Parasympathetic constriction of circular pupil smooth muscle to reduce diameter 8mm --> 2mm
        
        Sympathetic = contracts radial muscles to dilate pupil
    - - PRESBYOPIA = age related (45-50) decline due to loss of lens capsule elasticity, reducing short vision
      - MYOPIA / Near Sight= elongated eyeball with concave lens elongateing focal length
      - HYPEROPIA / Far Sight= shorter eyeball with convex lens shortening focal length
      - CATARACT = Breakdown of lens structure causing opacity + reduced vision
        
        HEREDITARY CATARACT = crystallin mutations causing protein aggregation OR CnX50/46 mutations disrupting gap junctions between epithelium + lens fibre cell causing precipitation of crystaliproteins
        
        DIABETIC CATARACT = galactose diffusion from plasma causing increased osmolarity and swelling-induced structure disruption (disrupting epithelial cells)
      - R-G COLOUR-BLIND = mutations in cone opsin genes
        
        R-G Opsin = Ch.X (sharing 90% sequence similarity)
        
        Blue Opsin = Ch.7
        
        8% male population
      - RETINITIS PIGMENTOSA = common inherited retinopathy with loss of rod cells causing night blindness + progressive tunnel vision
        
        60 genes affects, with 30% being Autosomal dominant RHO gene degradation
        
        1:3500
      - MACULAR DEGENERATION = loss of central vision with cone cells
        
        50% visual impairment cases
        
        DRY FORM = macula + central fovea degeneration
        
        WET FORM = leaked of blood from new fine fragile blood vessels from choroid into retina due to Vascular Endothelial Growth Factor
        
        20 predisposing genes
        
        ARMD = Age-related Macular Degeneration (>50 years)
  - - - million fold range of energy change
      - 20-20,000 Hz (Most Acute = 1000-3000Hz)
    - - Oval window = 2.5mm(2)
        
        Covered by staples
        
        Opens into Inner Ear
        
        Semicicrular Canals = detect rotational + linear acceleration for equilibrium
        
        COCHLEA = coiled structure in temporal bone
        
        Each turn = 3 chambers/SCALA
        
        Scala Vestibuli
        
        Scala Media = closed comparent between shared scale tympani + scala vestibular
        
        Scala Tympani
        
        3 Membranes
        
        Vesitublar / Reissner's Membrane = between vesitubli + media
        
        Basilar Membrane = sound transduction
        
        Asexual elastic fibre membrane supported on mesothelium
        
        Natural Resonance Frequency via elastic fibre density from base to apex
        
        Sound waves peak @ point when their frequency matches the natural resonance frequency of the membrane (determined by elastic properties) - with low frequencies at apex
        
        Tonographic pattern allows pitch identification in
        
        Tectorial membrane
        
        ORGAN OF CORTI = structure containing hair cells resting on basilar membrane
        
        Hair cells surrounded by
        
        STERIOCILIAR-CILIA = bundles of cilia with actin filaments (1 per hair cell)
        
        Ordered by increasing height
        
        2 COCHLEAR FLUIDS
        
        PERILYMPH = ECF composition between vestibular + timpani
        
        ENDOLYMPH = Intracellular Fluid Composition in Media
      - Round Window
      - Primary sensory fibres --> Vestibular Cochlea Nerve (8th Cranial Nerve)
    - - Mechanical Vibration Transmittered by Bones in Inner Ear
      - Stapes causes fluid displacement
      - Sound waves cause vibration of TYMPANIC MEMBRANE
      - ATTENUATION REFLEX = simultaneous contraction of tympanic skeletal muscle + stapes muscle to dampen sound perception
        
        STAPES MUSCLE = innervated by 7th Cranial Nerve
        
        TENSOR TYMPANIC SKELETAL MUSCLE = innervated by 5t Cannel Neve + fixed to mallow bone
        
        Speech Mechanism Activation causes this reflex = for voice desensitisation
      - High Frequency Sound = Fluids shortcut across scala media --> disturbing basilar membrane
      - STEROCILIA DISPLACEMENT = response to sound driven vibrations with movements of 0.3mm
      - STEROCILIUM connected via TipLinks connected to K+ Channels
        
        Pull open mechanically gated K channels by movement
        
        K+ enters from Endolymph --> Depolarisation of hair cell
        
        Allow Ca to enter --> Release of Glutamate neurotransmitter from base --> sensory neuron
      - Outer Hair cells = have present motor protein to enable electromotility to stretch in response to vibration to amplify sound response
    - - Primary Sensory Auditory Nerve = Hair Cell --> Cochlear Nuclei in Medulla
      - Signal relayed Medulla --> Pons
        
        Ipsilateral Splitting
        
        Contralateral Splitting
      - Signal Relayed Midbrain --> Thalamus
      - Signal Relayed to Temporal love of cerebral cortex
    - - CONDUCTIVE
        
        Middle Ear Infection
        
        Othorosclerosis = overgrowth of middle ear bones
      - SENSORINEURAL = defects in hair cell or primary sensory fibres
        
        Presbicusis = accumulated age damage
        
        Cx26 Gap Junction Mutation = Non-recycling K+ ions --> Non-Syndromic Deadfness
      - CENTRAL = neural pathway
      - Treatment
        
        HEARING AID = Sound Amplification
        
        COCHEAL IMPLANTS = set of electrodes fed into cochlea to bypass root hair cells
  - - - TYPE III PRESYNAPTIC CELLS = conventional serotonin sunaptic connection to primary neuronal
        
        SALT Transduction = Na+ ion channels for conventional depolarisation + Ca dependent regulated serotonin exocytosis
        
        SOUR = H+ enter by K ion channels closing
      - TYPE II RECEPTOR CELLS = ATP used as non-convientional neurotransmitter --> exits through hemichanelles --> might act directly on primary sensory neuronal of picked up through presynaptic cell receptor or output through serotonin pathway
        
        Taste transaction through G-protein coupled receptors to gustucin
        
        Activate PLC --> Increasing [Ca] --> triggering ATP
        
        SWEET / BITTER / UMANI
        
        UMANI = Monosodium Glutamate (discovered in early 1900s)
      - TYPE I CELLS = glial support cells
    - - 10-14 Curcamvalent Papilla
      - Foliate Papilla
      - Fungiform Papilla
      - Tight junctions between taste + Support cells
  - - - Located Upper Nasal Cavity = 3cm(2) of epithelium
      - Dendrites increase SA through non-motile cilia
      - G-olf --> Adenylate Cyclase Activation
    - - Therefore collection of activated receptors = resultant odour
- - - - Olfactory nerve endings in upper nasal cavity
    - - PERCININ CORPUSCLE = severe pressure
      - MYCINER CORPUSCLE = light pressure
    - - 120 million Rod Cells
      - 6 million Cone Cells
  - - - LABELLED LINE HYPOTHESIS = distinct TOPOGRAPHIC neural pathway from each receptor class to cerebral cortex region
      - BLUNT HEAD INJURY
        
        Mechanoreceptor Activation
        
        Activation of photoreceptors
    - - POPULATION CODING = different receptor sets brought in depending on stimuli strength
        
        TONIC = continueal firing as long as stimulus is in contact
        
        PHASIC = desensitised/adapt as stimulus is in contact + reset at later stage (allowing for nervous system to focus on important stimuli)
      - FREQUENCY CODING = frequency of AP stabilised by all active receptors at the time
    - - PHANTOM LIMB PHENOMENA = stimulation of specific areas of cerebral cortex leading to sensation in absence of stimuli due to cortex remapping
      - Pattern of periphery receptors = preserved in cerebral cortex
- - - - Chemical = Histamine + Prosaglandin
      - Thermo Receptor for 37 +/- 10
    - - SLOW PAIN FIBRE= Small unmyelinated C fibres for dull, diffusion pain with 0.5-2m/s
      - FAST PAIN FIBRE = Small myelinated A-delta fibres with sharp, localised pain with 12-30m/s conduction speed
    - - Pain + Anxiety = LIMBIC SYSTEM Connections
      - Pain + Nausea = MEDULLA / HYPOTHALAMUS Connections
    - - Primary Non-Myelinated C Pain Fibres in Dorsal Side from Dorsal Root Ganglion
      - Synapse with secondary sensory neuron to cross-over and relay information to thalamus
        
        Inhibitory interneuron turns off relay of signal to 2nd neuron --> cortex doesn't receive signal --> no pain
        
        C-fibre collateral branch sent to inhibitory interneuron --> inhibiting inhibitory interneuron --> cannot inhibit 2nd neuron --> relay of signal to 2nd neuron
        
        MODULATION = partially switching back on of inhibitory interneurons --> reducing signal in 2nd sensory neuron
        
        Rubbing injury = activate light touch A-beta fibres
    - - ASPIRIN = prevent peripheral prostaglandin synthesis
      - OPOIDS = activation of central brain pathways which descend to interact with pain pathways for modulation