biology mod8

components of outer ear

• pinna

• ear canal

• tympanic membrance (eardrum)

structure & function of pinna

• fleshy section of outer ear

• collects and funnels sound into the ear cannal & protects inner ear from external subtances

structure & function of ear canal

• tube that connects pinna to tympanic membrane (eardrum)

• directs sound into tympanic membrane & secretes earwax

structure & function of tympanic membrane (eardrum)

• located between outer and middle ear

• eardrum vibrates, converting sound waves into mechanical energy

components of inner ear

• ear ossicles (malleus, incus, stapes)

• oval & round window

structure & function of ear ossicles

• three small bones (malleus, incus, stapes)

• amplify and transmit mechanical vibrations from eardrum into inner ear

structure & function of oval & round window

• thin, flexible membranes

• act as entrance and exit doors for mechanical vibrations travelling through inner ear & allow fluid movement inside the cochlea

components of the outer ear

• cochlea

• vestibular system

• basilar membrane & organ of Corti

• auditory nerve

structure & function of cochlea

• fluid-filled, spiral structure lined with basilar membrane and organ of Corti

• vibrations create pressure waves in cochlear fluid, causing basilar membrane to vibrate

structure & function of the vestibular system

• sensory organs directly attached to organ of Corti

• help maintain sense of balance

structure & function of organ of Corti

• sensory structure sitting on top of basilar membrane, inside the cochlea

• contains hair cell receptors that transfer mechanical energy into electrochemical signals, carried to auditory nerve

structure & function of auditory nerve

• bundle of nerve fibres

• transmit electrical signals from hair cells to the auditory cortex of the brain, where they are interpreted as sound

what is the eustachian tube

• tube that connects the middle ear to the nose & throat

• equalises pressure between middle ear and outer ear → prevents eardrum from shifting position

• can result in discomfort/dizziness if damaged

what are the causes of hearing loss

• conductive hearing loss

• sensorineural hearing loss

• mixed hearing loss

what is conductive hearing loss

• when sound is not effectively conducted through the outer/middle ear

• usually affects loudness of sound

• caused by earwax blockage, perforated eardru,, infection, damaged ossicles.etc

what is sensorineural hearing loss

• damage to the cochlea, hair cells, or auditory nerve; prevents transformation of mechanical energy into electrical impulses

• usually affects loudness & clarity of sound; often permanent

• caused by ageing, noise-induced damage, genetic mutations, ototoxic drugs, viral infections (e.g. meningitis)

what is mixed hearing loss

• combination of conductive and sensorineural causes

• less common

what are hearing aids & how does they work

• external, non-surgical device that amplifies sound

  • microphone picks up sound

  • amplifier increases signal strenth

  • speaker delivers amplified sound into ear canal → existing (but reduced-function) structures of ear process it as normal

effectiveness of hearing aids

• effective for conductive hearing loss & mild sensorineural hearing loss (where wnough functioning hair cells remain to detect amplified signal)

• able to avoid surgery & recovery time

• adjustible to individual’s specific hearing loss profile

• relatively low cost & accessible

limitations of hearing aids

• ineffective for severe sensorineural hearing loss (as hair cells may be unable to pick up amplified sound)

• may amplify background noise or pick up unwanted frequencies

• requires regular batter replacement/maintenance

• can be lost/damaged

what are cochlear implants & how do they work

• surgically implanted device (‘the bionic ear’) that bypasses the damaged outer/middle ear and non-functioning hair cells, directly stimulating auditory nerve

  • external microphone & speech processor → detect sound & convert into electrical signal

  • transmitter → sends signal across skin via radio waves

  • internal receiver → decodes this signal

  • electrodes (inserted into cochlea) → directly stimulates auditory nerve at points corresponding to different sound frequencies

effectiveness of cochlear implants

• effective for severe sensorineural hearing loss (where hair cells are absent/non-functional)

• beneficial for deaf children (ideally before age 2-3) → allows for near-normal speech development

limitations of cochlear implants

• requires surgery; risks include infection, facial nerve damage, use of anaesthesia

• sound is not ‘natural’ → perceivede as mechanical; requires auditory-verbal therapy & adjustment

• high cost (device, surgery, therapy) & limited accessibility for some

• risk of permanently losing remaining hearing as implanted ear damages the internal structures of the cochlea

what are bone conduction implants & how do they work

• device that transmits sounds via direct bone vibration, bypassing the outer and middle ear entirely

  • titanium implant is surgically anchored is surgically anchored into the skull bone behind the ear

  • vibrations travel through bone to functioning cochlea, where sound is processed as normal

effectiveness of bone conduction implants

• effective for conductive hearing loss, particularly where outer/middle ear is malformed, blocked or chronically infected

• effective for single-sided deafness

• once bone fuses with implant, the connection is stable and sound quality is generally consistent

limitations of bone conduction implants

• requires surgery to anchor the implant; risks include implant failure, skin irritation, use of anesthesia, etc

• ineffective for sensorineural hearing loss (as it relies on inner ear)

• costly (however cheaper than cochlear implant), which can limit access

• may not be suitable for young children (skull bone not thick enough)

components of the outer eye layer (fibrous)

• sclera

• cornea

what is the sclera

• white, fibrous outer coat covering most of the eyeball

• provides structural & protection, maintains eyes’ shape and serves as attachment point for eye muscles

what is the cornea

• transparent dome-shaped outer layer at front of eye that covers the pupil and iris

• acts as a protective shield against dirt/germs & serves as primary lens (light-focussing power)

components of the middle eye layer (vascular)

• choroid

• ciliary body

• aqueous & vitreous humours

• iris

• lens (seperate, but associated with this layer via ciliary body)

what is the choroid

• layer rich in blood vessels sitting between the sclera and retina

• supplies oxygen and nutrients to the outer retina, absorbs light & prevents it from scattering (would blur vision)

what is the ciliary body

• contains the ciliary muscles, which control the shape of the lens → allows for adjustment according to distance

• produces aqueous & vitreous humours

• moves the lend

what are the aqueous & vitreous humours

• aqueous humour → watery liquid that fills front chamber; transmits light & maintains eye pressure

• vitreous humour → jelly-like subtance that fills space behind the lens; allows light to pass through back of eye & supports eye shape

what is the lens

• transparent, biconvex structure held in place by ligaments attached to ciliary body

• ciliary muscles move the lens to focus light on the retina

what is the iris

• pigmented, muscular ring surrounding the pupil

• controls the amount on light entering the eye through phincter muscles which adjust pupil diameter

components of the inner eye layer

• retina

• fovea

• optic nerve

what is the retina

• light-sensitive innermost layer lining the back of the eye

• contains two types of photoreceptors which convert light into electrical signals

  • rods → highly sensitive to light, responsible for vision in low-light conditions; don’t detect colour

  • cones → responsible for colour vision and fine visual detail; require brighter light to function

what is the fovea

• tiny central pit in the retina that provides the sharpest, most detailed colour vision

• contains highest concentration of cones and no rods

what is the optic nerve

• bundle of nerve fibres that connexts the retina directly to the brain

• carries electrical signals (from retinas’ photoreceptors) to the visual cortex of the brain, where they are interpreted as images

• the point where the optic nerve exists creates a natural blind spot

what is accomodation

• process by which the eye changes the lens shape to adjust its focusing power, allowing individuals to see objects clearly at different distances

  • short distance → ciliary muscles contract, releasing tension on suspensory ligaments → lens is rounder & thicker → increases refractive power

  • long distance → ciliary muscles relax, increasing tension on suspensory ligaments → lens is flatter & thinner → decreases refractive power

note: refractive power is how strongly a lens bends light

what are the causes of visual disorders

• refractive errors (myopia, hyperopia)

• cataracts

what is myopia

• short-sightedness caused when the eyeball is too long, or the lens has too much refractive power → light converges to a focal point in front of the retina (rather than on it)

• distant objects appear blurry (as light has already converged before reaching retina)

• caused by genetics, environmental factors, reduced time outside

what is hyperopia

• lons-sightedness caused when the eyeball is too short, or the lens does not have enough refractive power → light converges to a focal point behind the retina

• nearby objects appear blurry, since they require more refractive power

• caused by weakening of ciliary muscles or decreased lens flexibility; often develops later in life

what are cataracts

• clouding of the lens, caused when proteins clump together over time

• light is scattered and blocked by the cloudy lens (cannot be clearly focussed on retina), causing blurred vision, increased light sensitivity & faded colour perception

• cannot be corrected by adjusting focusing power (glasses)

• caused by ageing, UV exposure, smoking, etc

what are spectacles & how do they work

• external lens placed in front of the eye to adjust the point of light convergence so it lands on the retina (corrects refractive error)

  • concave (diverging) lenses for myopia → spreads light out before it enters the eye, shifting focus onto retina

  • convex (converging) lenses for hyperopia → bends light more before it enters the eye, shifting focus onto retina

effectiveness of spectacles

• does not require surgery → immediately effective & avoids surgical risks/recovery time

• easily adjusted as prescription changes over time

• relatively low cost & widely accessible

limitations of spectacles

• does not address underlying cause (e.g. eyeball length) → vision reverts to uncorrected state when removed

• requires consistent use & can be lost or broken

• peripheral vision distortion can occur

• ongoing costs

what is laser surgery (e.g. LASIK)

• surgical procedure that permanently reshapes the cornea to correct its refractive power, so light converges correctly on the retina

• e.g. LASIK → thin flap is cut into the cornea → laser removes tissue to correct the cornea shape → flap is repositioned to heal

effectiveness of laser surgery

• addresses the structural cause of the refractive error → effective for myopia and hyperopia

• results are typically permanent & surgery often has fast recover

• removes ongoing costs and burden of glasses/contacts

limitations of laser eye surgery

• surgical risks including infection, eye irritation, surgical implications, glare, etc

• high upfront costs; not always covered by health insurance

• not suitable for everyone e.g. requires thick corneal tissue, stable prescription, etc

• irreversible if complications or dissatisfaction arise

what is cataract surgery

• surgical removal of the cloudy natural lens, replaced with a clear artificial intraocular lens (IOL)

• cloudy lens is typically broken up and removed through small incision before IOL is inserted

effectiveness of cataract surgery

• addresses the underlying problem (unlike glasses which cannot correct cloudy vision)

• very high success rate

• often restores clear vision within days

limitations of cataract surgery

• surgical risks (infection, inflammation, issues with lens)

• high cost & limited access (not necessarily covered by health insurance)

• requires healing & recovery time