Physiology Flashcards
What is the conjunctiva?
A mucous membrane covering the sclera and inside of the eyelids
What part of the eye provides the majority of the focusing power?
The cornea
Describe how the lens of the eye changes shape
When focusing, the ciliary muscles contract
How does the ciliary fibres interact with the lens?
via attachment by Zonule fibres
What is the cornea made out of?
Collagen (continuous with the sclera)
What is the aqueous humour?
Transparent gel like fluid which fills the anterior part of the eye between the lens and the cornea
What is the purpose of the aqueous humour?
Maintains intraocular pressure (IOP), nourishes and removes debris from anterior portion of the eye
How does the aqueous humour return to the bloodstream?
via. the trabecular meshwork in the superior anterior section of the eye
What is glaucoma?
when the trabecular meshwork degenerates so the IOP increases as the aq. humour cannot be drained
What is the sclera made from?
Type I collagen
What is the choroid?
The vascularised connective tissue layer, contains melanin
What are the 2 humours in the eye?
The aq. humour (in the anterior) and virtuous humour (filling up the posterior part of the eye
True or false: the photo-receptors are the last of the neuronal layers to be hit with light (e.g. are at the back)
True
What is the first layer of the retina?
Retinal Pigment Epithelium, single layer of cuboidal pigment cells that are tightly attached to each other providing part of the outer blood–retinal barrier. The RPE cells contain melanin, used too ‘soak up’ stray photons so they can’t interact and discrease resolution
What is the second layer of the retina?
The photoreceptor layer that contains the rods and cones
What is the third layer of the retina?
External limiting membrane, junction between the processes of the muller cells and the photoreceptor cells
What is the fourth layer of the retina?
Outer nuclear layer, contains the nuclei and cell bodies of the photoreceptors
What is the fifth layer of the retina?
Outer plexiform layer, composed of the synapses of the photoreceptor cells with the biopolar cells and the horizontal cells
What is the sixth layer of the retina?
Inner nuclear layer, consists of nuclei and cell bodies of muller cells, bipolar cells and amacrine cells
What is the seventh layer of the retina?
Inner plexiform layer, site of synapses between bipoolar and ganglion cells, action site for amacrine cells
What is the eight layer of the retina?
Ganglion cell layer, where the ganglion cell bodies are
What is the ninth layer of the retina?
Nerve fibre layer, made of the axons of retinal ganglion cells as they travel across virtuous surface before leaving the eye
What is the tenth layer of the retina?
Inner limiting membrane, made of basal lamina from muller cell projections
True or false: all the cells in the eye come from the same progenitor cell
True
What is the purpose of the horizontal cells?
communicate horizontally between different photoreceptors and their bipolar cells to influence neighbouring cells
What is the purpose of the amacrine cells?
Horizontally acting cells to modulate signal between multiple ganglion cells
What is the purpose of the Muller (U with an umlaut)?
span the length of the retina, help in structural support
What are the three types of -opsins (colours) found in cone cells?
Blue, Green, Red. (only ever one type of opsin per cone)
What is achromatopsia?
Total colour blindness, very rare, where they have no cones only rods
Explain dichromacy.
One of the three cone opsins doesnt work so you have essentially a chunk taken out of the colour spectrum
Why is red-green colourblindess predominately in males?
It is linked to the x chromosome
Describe phototransduction
light is coverted to electrical signals by photons of light hitting the photopigment (e.g. 11-cis retina for rods, which causes the double bond to reshape inot 11-trans retinal, setting off a cascade of chemical events)
Explain the need for the visual cycle
11-trans retinal isn’t photoreceptive, so new 11-cis retina needs to be constantly replacing it else you will lose vision
Explain signal transduction in the photoreceptor
change in 11-retinal will cause a change in rodopsin, which will activate its G-protein transducin, which swaps GDP for GTP, then a small section of activated transducin detaches and activates phosphodieseterase, which changes cGMP to GMP, which causes the closing of cGMP-gated Na+ channels causing hyperpolarisation
True or false: the decibel scale is linear
False
What is decibels a scale of?
Sound intensity
What is the range of human hearing?
20-20,000Hz
What is the pinna and what is its function?
The external section of the ear, used to funnel sound and allow for sound localisation
what fills the cavity of the middle ear?
Air
What are the three bones in the middle ear (from the tympanic membrane) and what are they also referred as?
Malleus (Hammer), Incus (Anvil), Stapes (stirrup)
What is the function of the middle ear?
trying to amplify the wave signals from the tympanic membrane, as well as efficiency transmit the vibrational energy into the fluid-filled inner ear
Describe the reason for the middle ear amplifying wave signals and the name given to this process
Impediance matching - higher resistance in the fluid causes a reduction in intensity, to cancel this out the signal is amplified to counteract intensity reduction
Describe the attenuation reflex and what muscles are involved.
Muscles: tensor tympani and stapedius
pulls on the system in opposite directions, increasing rigidity so decreases conduction ability
What is the point of the attenuation reflex?
To protect the cochlear from loud noises, masks background noise in loud environments
What are the 2 components of the inner ear?
The cochlea for hearing, the Three semicircular canals for maintaining balance
What is the purpose of the Oval and Round Windows in the cochlea?
To allow room for the movement of fluid to propagate energy
What happens to the basilar membrane as you progress the length of the cochlea?
Its diameter increases
Describe the makeup of perilymph
low in potassium ions and high in sodium ions
Describe the makeup of endolymph
High in potassium ions, low in sodium ions
What is the name for where endolymph is located?
Scala media
What is the name for the auditory receptor area in the ear?
Organ of Corti
What hair cells are in the organ of corti?
1 inner hair cell, 3 outer hair cells
What interacts with the cilia from the hair cells to allow them to flex?
The tectorial membrane
Explain the depolarisation of a hair cell
The ends of the cilia are linked by proteins called tip links, which double as mechanically-gated K+ channels. When movement, this causes channels to open, K+ from endolymph enter cells, causes depolarisation, triggers voltage-gated Ca channels to open which causes a cascade to release neurotransmitter
