Nervous System - Eyes and Ears Flashcards
What is the wall of the eyeball made of?
Sclera and cornea - outer layer
Uvea - middle layer containing choroid, ciliary body and iris
Retina - inner layer.
Describe the structure of the cornea.
Transparent cornea consists of a stratified squamous epithelium on Bowmans membrane, a thick vascular stroma and an inner endothelium on Descemet’s membrane
Numerous free nerve endings in surface epithelium - sensitive
Epithelium has potent wound healing capability but damage to Bowman’s layer leads to loss of visual acuity
Corneal epithelium continuous with epithelium on the conjuctiva at the limbus
Transparency of cornea due to collagen.
Describe the structure and function of the retina.
Photoreceptor layer - rods + cones
Bipolar cell layer
Ganglion cell layer
Horizontal and amacrine layer - interneurons help to integrate and modulate signals between photoreceptor cells, bipolar cells, and ganglion cells
Macula and fovea - macula is a small, specialised area near the center of the retina that is responsible for high-acuity vision. Within the macula is the fovea, a tiny depression where the density of cones is highest
Light detection
Signal processing
Spatial organisation
Describe the structure of the lens.
Transparent and avascular
Biconvex in shape
Layer of cuboidal epithelium on anterior surface only
Centre of tightly packed anucleate cells packed with transparent proteins to form lens fibres.
How does the lens change shape to view a distant object?
Ciliary muscle relax, radial muscles contract, suspensory ligaments taut, lens pulled into thin shape for viewing distant objects.
Describe the structure of the iris.
Shows anterior and posterior chambers
Heavily pigmented nature blocks light except for central aperture the pupil
Stromal melanocytes determine eye colour.
Describe the structure and function of the sclera.
The sclera is the tough, fibrous outer layer of the eye, primarily composed of dense, collagenous connective tissue.
It maintains the shape of the eyeball and provides attachment points for the extraocular muscles, which control eye movements.
Explain the mechanism of hearing.
Sound waves enter the ear cause tympanic membrane to vibrate
Tympanic membrane vibration moves auditory ossicles so sound waves are amplified
Stapes at oval window generates pressure waves in perilymph within the Scala vestibuli
Vestibular membrane moves resulting in pressure wave formation in endolymph in cochlear duct
Hair cells in organ of Corti are distorted initiating a nerve signal in cochlear branch
Remaining pressure waves transferred to Scala tympani and exit the inner ear via round window.
Describe the structure and function of the cochlea.
Spiral shape
Fluid-filled chambers - scala vestibuli, scala media and scala tympani
Organ of Corti - contains sensory hair cells, and rests on the basilar membrane
The cochlea converts mechanical vibrations into electrical signals for the brain.
Sound vibrations stimulate sensory hair cells in the organ of Corti, which release neurotransmitters.
These neurotransmitters activate auditory nerve fibres, which transmit sound information to the brain.
The cochlea exhibits tonotopic organization, with high-frequency sounds stimulating hair cells near the base and low-frequency sounds near the apex.
Describe the structure and function of the vestibular apparatus.
Divided into 2 parts
3 semicircular canals - repsond to rotational movements
Vestibule - utricle and saccule respond to linear acceleration
Movements perceived by specialised hair cells in endolymph.
Describe the structure and function of the ossicles.
Three ossicles - malleus, incus, stapes
Composed of compact bone and articulated by synovial joints
Leaver system increasing the force transmitted
Convert sound waves to mechanical vibrations
Stapedius and tensor tympani are skeletal muscle that happen effects of loud noise.
Part of middle ear.
Describe the 2 components of the middle ear.
Tympanic cavity - air filled space within temporal bone, equilibrates air pressure either side of eardrum
Auditory ossicles - transmit vibrations from tympanic membrane to oval window.
Describe the structure and function of the components of the outer ear.
Pinna - skin covered with elastic cartilage that amplifies sound.
External auditory canal - lined by skin with ceruminous glands which produce wax. Acts as a conduit for sound waves, channeling them from the auricle to the tympanic membrane
Tympanic membrane - collagenous bilayer covered by very thick skin externally and simple cuboidal epithelium internally. converts sound waves collected by the auricle and transmitted through the ear canal into mechanical vibrations
Shape of an irregular cone.
Vibration transmitted to middle ear.
What is the optic nerve?
At the optic disk, axons from ganglion cells merge to form the optic nerve
Known as the blind spot as there is no photoreceptor cells present.
Describe the principal features of the organs of balance.
Semicircular canals
Vestibule
Vestibular nerve
Otoliths
