Lecture 8, 9 and 10 Flashcards
What do flat-sheet eyes contain? What do these eyes provide?
What does the pigment layer contain and what does this do?
A layer of photoreceptor cells that form a primitive retina
Some sense of light direction and contrast
Contains shading pigment to that helps provide directional information by shading light coding from some directions
What is the retina like in cup-shaped eyes?
This folded to form a narrow aperture
What is the lens like in a vesicular eye? What does this mean? What can the lens often do?
The lens is inserted into the pinhole aperture.
It collects light from multiple sources and refracts it, thereby focusing it into the retina.
. Often the lens is able to change shape, thereby allowing to focus objects
In convex eyes where can the photoreceptors radiate outwards?what does this form?
Radiate outwards from the base, forming a convex rather than a concave, light-gathering surface
What is a single unit of a compound eye called?
Ommatidium
Describe how apposition compound eyes work
The ommatidia are surrounded by a pigment cell. Each ommatidia operates independently as detects a small part of the environment directly in front of the ommatidium
Describe how superposition compound eyes work and what thy are found in
May ommatidia work together to produce a bright, superimposed image. Those eyes are found in nocturnal insects
What does light entering the light pass before striking the retina?
Passes through the cores, the aqueous humour, the pupil, the lens m, and the vitreous humour before striking the retina
What is the fovea? What does it provide?
Is a pit in the retina which provides the clearest vision
What is the choroid?
The vascular layer of the eye (supporting the retina with blood- supply oxygen, energy etc.)
Where are the focal receptor cells located?
In the retina
Need to see pages 34/35 about eyes- couldn’t make flashcards about them
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Where are the photoreceptors (Ross and cones) locates?
In the deepest layer of the retina (far away from the light)
What does the retina consist of in cephalopods? How does light strike the photoreceptors?
Retina consists of a layer of photoreceptor cells and supporting cells. Light strikes the photoreceptors directly, without passing through multiple layers
Why is there little to no signal processing in the retina of cephalopods?
Because there are no interneurons
How did the eye of the cephalopod evolve?
Independently of the vertebrate eye
Describe rod photoreceptor cells
Contain many photopigments and are therefore very sensitive. They are active under dim light (not during the day). Ross cannot discriminate colours.
Describe come photoreceptors
Contain less photopigments than Ross and operate during the day. They are able to detect different colours (wavelength of light)
Where is rhodopsin located?
Within the membrane disks of the photoreceptors (rods)
When are vertebrate photoreceptor cells (not invertebrates) depolarised?
When they are unstimulated
What does stimulation of the vertebrate photoreceptor do?
Causes hyperpolarisation
What do photoreceptor cells release when in the dark?
Transmitters (glutamate)
What do touch receptors in Caenorhabditis elegant contain?
Mechanosensott neurons with ENaC (epithelial sodium channel) type channels in their membrane
In Caenorhabditis elegant what do mechanical stimuli cause?
Extracellular anchors to move relative to the cytoskeleton, pulling on the channel and causing a conformational change that opens or closes the channel
What do touch receptors in Drosophila contain?
Mechanosensory neurons with TRP channels (transient receptor potential) in their membrane
Merkel’s disks are very sensitive what are they important in?
Sensing light touch
What are Pacinian corpuscles?
They are phasic receptors and sensitive to vibrations
How do hair follicles work?
They detect when a hair is stretched. They are rapidly adapting phasic receptors (e.g. can feel when something is crawling on you but not if it is not moving
Describe how Ruffini’s endings work
They are sensitive to stretching of the skin. This helps to determine the location of the body (e.g. hitting a snooze button with you eyes closed)
What is sound?
Is a vibration that propagates as an audible wave of pressure through air or water
What does is mean if the frequency or amplitude is higher?
The sound is louder
How are the ears designed?
To capture sound waves and guide the stimulus to cells containing the mechanoreceptors
What does the outer ear/ external structures of the ear consist of in mammals?
Pinna (which can have different shapes) and the auditory canal
What does the middle ear contain? What do they do?
Contains a series of small bones (Malleus=hammer, Incus=Anvil and stapes=stirrup) that transfer sound waves to the inner ear
What are the names of the 3 small bikes in the middle ear?
Malleus=Hammer
Incus=Anvil
Stapes=stirrup
What does the stirrup do?
Presses a membrane, the oval window, and thereby transmits pressure to the inner ear
Because the inner ear is filled with fluid, there is a second membrane (round window) which is important for what?
Pressure compensation
What is the inner ear? What does it consist of?
Is embedded within the skull and consists of a series of fluid-filled membraneous sacs and canals
In the inner ear the mechanoreceptors (hair cells) are located between two membranes what are they?
The basilar membrane and the tectorial membrane
How are the stereocilia connected to each other in hair cells?
Connected by tip links
Where are mechanosensitive ion channels localised? What are they involved in?
Localised near the tips of the stereocilia and are involved in sound transduction
What does deformation of the stereocilia lead to? What happens after this?
Opening or closing of mechanosensitive ion channels. When the ion channels are open potassium ions will enter the cells
Deformation of the stereocilia leads to ion channels opening and potassium ions entering the cell. Why is this?
Because the scale media (extracellular environment of the hair cells) contain high amount of potassium
Information about sound frequency is specified by what?
Which hair cells are activated
In the cochlea what do pressure waves do?
Waves of different frequencies flex the basilar membrane at different locations
What does the base of the inner ear contain?
A swelling (ampulla) and a series of sacs including the utricle and the saccule
What animals are cochlea found in?
Only mammals
The mechanoreceptors of the utricle and saccule are found in what structures?
The maculae
The hair cells of each macula are embedded in what?
A gelatinous matrix that is overlain with a series of mineralised otoliths
What to the utricle and saccule do?
Detect gravity and are important for determining the position of the body
What does the semicircular canal in the ear consist of?
A fluid filled tube with a swelling (ampulla) at the bottom
What is the fluid in the semicircular canal?
Is endolymph (high concentrations of potassium)
What does the ampulla consist of?
A neuromast that senses pressure
What are the hair cells in the neuromast embedded in?
A cup-shapes gelatinous mass called the cupula
What is the most common convex eye? What is a single unit of those eyes called?
Compound eyes in Arthropods.
Ommatidium
What are the photoreceptors in compound eyes called?
Reticular cells
What are TRPM8 ion channels involved in?
The sensation of environmental cold
In snakes where is TRPA1 located? What is it responsible for?
Located in trigeminal nerve fibres and responsible for the detection of infrared radiation
