Week 12 - Special Sense Part 2 Flashcards
(41 cards)
what is photoreception
process by which the eye detects light and begins converting it into electrical signals that the brain interprets as vision.
- the detection of light by photoreceptor cells (rods and cones) in the retina
what is retinal
light sensitive molecules derived from vitamin A
what is opsin
a protein that differs in rods and cones
what is 11-cis-retinal
inactive form of retinal
what are photopigments
located in the outer segments of rods and cones composed of opsin and retinal. Different types absorbs different wavelengths depending on the bound opsin
what are the steps in photoreception
- Initially opsin is bound to 11 cis retinal forming rhodopsin
- When a photo hits it binds to rhodopsin causing 11-cis-retinal to change shape into 11-cis to all-trans and release from opsin (process called leaching)
- Retinal combines with opsins to form 4 types of photopigments
- 11-cis-retinal bound to opsins and snaps into all trans-retinal when absorbing a photon of light
* It changes opsin shape and activates it -all-trans-retinal splits from opsin (bleaching) - converted back into 11-cis/retinal and rejoins opsin
what is phototransduction
process by which light energy is converted into a graded receptor potential
- biochemical process that converts light ( a photo) into an electrical signal in the photoreceptor cells
what are the steps in phototransduction - In the light
- When light causes opsin to change shape it initiates that results in the closing of ion channels and hyperpolarizes the photoreceptor
- This causes the photoreceptor to stop releasing inhibitory neurotransmitter
- Hence no longer inhibited the bipolar cells depolarize and release neurotransmitters onto ganglion cells
signal reaches ganglion cells and is converted into AP
AP transmitted to brain along ganglion cell axon that make up the optic nerve
o 11-cis-retinal converts to all-trans-retinal when light is absorbed.
o Triggers G-protein cascade → closes cation channels → hyperpolarization of photoreceptors
o Photoreceptor stops releasing inhibitory neurotransmitter
o No longer inhibited bipolar cells depolarise and release neurotransmitter onto ganglion cells
o Signal reaches ganglion cells and is converted into AP
o AP transmitted to brain along ganglion cell axons that make up the optic nerve
- photon of light binds to retinal on visual pigment;
- retinal changes from 11-cis-retinal to all trans-retinal, which causes retinal to detach from opsin (bleaching) opsin to change shape and assume its activated form;
- G-protein-coupled cascade occurs in opsins that results in closing of cation channels that are open in the dark - cell hyperpolarizes to about 70mV;
- no release of neurotransmitter from photoreceptor means lack of inhibitory postsynaptic potential in bipolar cell, resulting in depolarisation of bipolar cell,
- bipolar cell depolarisation causes neurotransmitter release from bipolar cell with excitatory postsynaptic potential in ganglion cell and AP propagating along optic nerve.
what is the visual pathway to the brain
- axon of retinal ganglion cells exits in the optic nerve
- optic chiasma (cross over - decussation)
- optic tract
what do optic tracts contain
fibres from lateral (temporal) aspect on the same side and from the medial (nasal) aspect of the opposite eye
carries all the information from the same half of the visual field
a complete right optic nerve lesion causes
complete loss of the right visual field
a lesion in the midline of the optic chiasm causes
bitemporal hemianopsia
loss of the outer (temporal) halves of the visual field in both eyes.
A lesion of the uncrossed fibres of right optic nerve at optic chiasm causes
nasal hemianopsia of the right eye
A complete lesion of right optic tract, lateral geniculate nucleus, or optic radiations causes
complete left homonymous hemianopsia
each visual field has how many degrees of vision
170 degrees
how is depth perception gained
o Requires both eyes (binocular overlap). – visual cortex fuses the slight different views in each eye to create depth perception (or 3D vision) to locate objects in space
o Lost with one eye; relies on learned cues.
What are the 3 regions of the ear
- external ear
- middle ear
- inner ear
What key auditory structures are located in the external ear (EX)
- Auricle (Pinna) - outside of the ear
- Ear Canal
- Tympanic Membrane (ear drum)
What key auditory structures are located in the middle ear (EX)
- Ossicle
- Eustachian tube (auditory tube)
- Oval window
- Round window
What key auditory structures are located in the inner ear
- Cochlea
- Vestibular system (semicircular canal, utricle and saccule)
CN VIII nerve
What are the 3 bones in the ossicle
malleus
incus
stapes
what are the steps in sound transduction
- sound wave enters the ear canal
- tympanic membrane vibrates in response to sound wave
- vibrations are amplified across ossicles (bone in middle ear)
- Vibrations against oval window set up standing wave in fluid of vestibuli
- Standing waves cause the movement of the basilar membrane of the organ of corti - causing the excitation of mechanoreceptor stereocilia which forms production of AP
Pressure bends the membrane of the cochlear duct at a point of maximum vibration for a given frequency, causing hair cells in the basilar membrane to vibrate
what is the organ of corti in cochlear duct
- main hearing organ on top of basilar membrane
- when sound enters the cochlea it creates fluid waves in the 2 scala which causes the basilar membrane to vibrate
- the organ of corti detects these vibrations and converts them into neural (electrical) signals which are sent to the brain via the auditory nerve
- different frequency of waves moves the basilar membrane to different spots
what is tonotopy
- where different frequencies of sound stimulates different location on the basilar membrane
