eye content Flashcards
controlling pupil size
light levels striking photoreceptors cause nerve impulses to pass along the optic nerve
goes along optic nerve to CNS
impulses sent along parasympathetic motor neurones to the circular muscles of the iris- causes them to contract
at the same time, the radial muscles relax
this constricts the pupil
reduces amount of light entering the eye
pupil constriction
radial muscles relax
circular muscles contract
pupil dilation
radial muscles contract
circular muscles relax
eye to brain
axons of ganglion cells pass out of eye and extend to areas of brain
before reaching thalamus, some neurones in each optic nerve branch off to midbrain
- where they connect to motor neurones involved in controlling the pupil reflex and movement of eye
from thalamus, impulses then sent along further neurones to primary visual cortex where information is processed further
axon growth
axons of neurones from retina grow to the thalamus where they form synapses with neurones in the thalamus in an ordered arrangement
axons from these thalamus neurones grow towards the visual cortex in the occipital lobe
critical period
time in visual development after birth when the columns of cells in the visual cortex are developed
research using animal models
animal models are easy to obtain, breed, have short life cycles and a small adult size
studies using animal models provide most knowledge we have for understanding of visual system and brain development and function
monocular deprivation
deprivation of any light stimulus in one eye
hubel and weisel
raised monkeys from birth to six months with monocular deprivation
- exposed eye to light after 6 months
- clear that deprived eye was blind to light
retinal cells responded to light stimuli but cells of visual cortex did not respond to any visual input from formerly deprived eye
deprivation for a single week during a certain period after birth produced the same result
deprivation in adult monkeys had no effect
after light deprivation in one eye
columns with axons from light-deprived eye are narrower than those for the eye receiving light stimulation
dendrites and synapses from the light stimulated eye take up more territory in visual cortex
concl: visual stimulation is required fro refinement of the columns and full development of the visual cortex
effect of light deprivation on synapses
axons compete for target cells in the visual cortex
every time a neurone fires onto a target cell, the synapses of another neurone sharing the target cell are weakened and release less neurotransmitters
if this happens repeatedly, the synapses that are not firing will be cut back (synapses from light deprived eye will be weakened an eventually lost, as only the synapses on axons receiving light stimulation will fire)
stereoscopic vision
term to describe that our visual field is seen from two different angles
cells in visual cortex let us compare the view of one eye with that of the other
allows relative position of objects to be perceived
distant objects
images in two retinas are very similar, so visual cues and past experiences are used when interpreting the images
carpentered world hypothesis
those who live in a world dominates by straight lines and right angles perceive depth very differently to those who live in a ‘circular culture’
ethics of using animals in medical research
violation of animal rights- if you believe that humans have certain rights, cannot justify belief that animals do not have rights
keeping animals enslaves them- we should respect their rights to things such as water, food, veterinary treatment and expression of normal behaviour
consent
from animal rights pov we could only use animals that consented to being in medical experiments- same as we would with humans
in practice, this would bring an end to use of animals in medical research
animal welfare
we should treat animals well so far as is possible
eg. cannot use vertebrates in medical experiments if there are non-animal alternatives available
if an alternative is not available, animals can be used provided the research warrants it and strict guidelines are followed
utilitarianism
morality of an action decided by whether it maximises pleasure over pain
using animals in research may be justifiable if the expected benefits are greater than expected harms
