20-23 Flashcards
What is the dynamic range of light detection in the human eye?
The eye can detect light over a dynamic range of more than 100 million to 1, from bright sunlight to faint starlight.
How does the human retina’s resolution compare to digital imaging?
The human retina has an equivalent resolution of about 576 megapixels.
What is the role of the brain in vision?
The brain interprets the inverted and smaller retinal image to form a coherent visual perception.
What are the two types of photoreceptors in the retina, and which one is more abundant?
Rods and cones; rods outnumber cones by 20-fold.
What is the photopigment found in rods, and what is its function?
Rhodopsin; it helps rods detect light, especially in low-light conditions.
What triggers the phototransduction cascade?
The isomerization of 11-cis-retinal to all-trans-retinal, which activates transducin, a specialized G-protein.
What happens to photoreceptor cells in the dark?
Photoreceptors are depolarized in the dark with a membrane potential of approximately -40 mV.
What is a receptive field in the retina?
It’s the area from which a ganglion cell receives input, with ON-center and OFF-center configurations.
How do ON-center and OFF-center ganglion cells respond to light?
ON-center cells signal increases in light intensity, while OFF-center cells signal decreases.
What does the retina primarily detect in a visual scene?
The retina acts as a contrast detector, focusing on variations in light rather than absolute intensity.
What visual pathways project information from the retina to the brain?
The M (magnocellular) pathway for movement analysis and the P (parvocellular) pathway for fine detail and color.
What is the role of simple cells in the visual cortex?
They respond to specific orientations of stimuli and have distinct excitatory and inhibitory regions.
What are intrinsically photosensitive retinal ganglion cells (ipRGCs)?
They are light-sensitive cells involved in circadian clock regulation and pupillary response, using the photopigment melanopsin.
What are the primary brain targets of ipRGCs?
The olivary pretectal nucleus (pupil reflex), suprachiasmatic nucleus (circadian rhythms), and ventrolateral preoptic nucleus (sleep).
What condition is linked to damage in the retina’s photoreceptors with aging?
Age-related macular degeneration.
What are the three main stages of hearing?
Capture, transmit, and transduce sound waves.
How is sound magnitude expressed?
What is the function of the basilar membrane?
It acts as a mechanical analyzer of sound, separating frequencies along its length.
How does the basilar membrane vary along its length?
It is wider and more flexible at the apex for low frequencies, and narrower and stiffer at the base for high frequencies.
What are the two types of hair cells in the cochlea, and what are their roles?
Inner hair cells (IHCs) are responsible for sound transduction, while outer hair cells (OHCs) amplify sound, especially at low intensities.
What is the role of prestin in hearing?
Prestin is a motor protein in OHCs responsible for electromotility, enhancing cochlear amplification.
How is sound transduced into electrical signals?
Movements of stereocilia on hair cells open mechanosensitive ion channels, allowing K⁺ ions to flow in and create receptor potentials.
Why is potassium (K⁺) used for mechanotransduction in hair cells?
K⁺ influx causes minimal changes in cytosolic concentration and requires little energy for both influx and extrusion due to the electrochemical gradient.
What genetic factors are associated with hearing loss?
Mutations in genes like GJB2 (Cx26), Myo7a, and KCNQ4 affect potassium recycling and hair cell function, leading to deafness.
