Ch.9, Sensation, START OF FINAL ** Flashcards
Difference between sensation and perception
sensory info is detected by a sensory receptor, which is a specialized neuron that responds to a specific stimulus
perception: the way sensory info is organized, interpreted, and experienced, subjective, nothing is ever 100% accurate
Illusions
result of brain misinterpreting a sensory stimulus
Neural relay, visual (1-3)
- Rods cones
- Lateral geniculate nucleus in the thalamus (LGN)
- V1, primary visual in occipital
Auditory relay, 1-5
- inner hair cells/auditory receptors
- medulla in the hindbrain
- inferior colliculus in the tectum (midbrain part of the brainstem)
- medial geniculate nucleus (thalamus) relay
- A1, primary auditory, cerebral cortex
Somatosensory relay
- somato receptors
- spinal cord
- brainstem
- thalamus
- S1, typically in the cerebral cortex
Somatosensation
includes proprioception: where your body is in space
vestibular: balance
nociception: pain
thermoception: temp
function of sensory receptors
transduce environmental energy into neural activity
3 key variables impacting sensory receptors
- receptive field: how much of the environment a receptor can take in; aids in localization of sensations in space: forms cortical paterns/maps to make a person’s reality
- receptor density: higher density in an area = greater acuity of that area
- receptor sensitivity: different types of receptors are more sensitive to certain stimuli than others
neuron discharge rate
number of APS fired per second, can encode stimulus intensity or sometimes qualitative changes
Topographic map
each sensation is processed in its own region of neocortex, a spatially organized neural representation of the body or sensory world
why are human lips and hands more dexterous
more cortex region devoted to these regions
fingertip vs back sensitivity
fingertips have 100x more recetors than back, and m,ore CNS neurons are devoted to receiving this sensory info
electromagnetic radiation
stream of photons; mass-less particles that travel in waves
sense that has the most brain area dedicated to it
vision
visible light
400 to 700 nanometers
longer the wave: lower the energy, more safe
two animals that detect light in ultraviolet
butterflies and bees
sclera, retina, optic disc, cornea, lens pupil, fovea
sclera: forms the eyeball, whiote of the eye
Cornea: clear outer covering keeps out dirt , BENDS LIGHJT FIRST
Retina: light energy intiates neural activity, fovea is area of highest acuity, densest distribution of photoreceptors specialized for color
optic disc: where blood vessels enter the eye and axons that form the optic nerve leave the eye, no receptors, blind spot
LENS: BENDS LIGHT AFTER CORNEA
Retina
light sensitive surface at the back of the eye consisting of neurons and photoreceptive cells
photoreceptors
specialized retinal neurons transduces light into neural activity
differences between rods and cones
rods: cylindrical outer segment, longer, more of them, sensitive to night light, night vision, have the same light absorbing pigment in their outer segment
cones: tapered outer segment, mediate color vision and acuity (fine detail), only responsive to bright light, fovea has cones only, each cone contains one of three pigments
visual illuminence and age
-as we age, we rely on rods more than cones=less acuity
-worse night vision
50% reduction in dim light acuity from age 20-40
-lens yellows with age: takes less light in
cornea doesn’t allow as much light
3 types of cone pigments, color and wavelength
s cones: short wavelength, blue: much less of these
m cones: medium wavelength, green
l cones: long wavelength, red
-each cone can detect more than what is specific to it, but these are what they are most sensitive to
what quantity of visual recptors are rods?
95%
muller cell
glial cell, funnels light to the back of the retina
axons of ganglion cells
bundle together to form optic nerve
retinal ganglion cells, two types
sensory neurons carrying info brain
Magnocellular Cell:
magno means large, receive input from rods, low acuuity, night vision, sensitive to light and moving stimuli, distributed throughout the retina like rods
Parvocellular cell:
parvo means small, receives inputs from cones, high acuity, color vision, detailed, concentrated at certain areas like cones
LGN layers in the thalamus
layers 1-2
magnocellular layers
recieve input from magnocellular cells (rods)
layers 3-6
parvocellular layers
receive input from parvoceullar cells (cones)
optic chiasm and optic nerve
optic chiasm: junction, where they cross, outside brain,
optic nerve: cranial nerve 2
2 routes for visual information
conscious: geniculostriate system
LGN–striate cortex (in layer IV specifically, bc that layer is afferent)
unconscious: tectopulvinar system
superior colliculus (tectum, midbrain, brainstem) –pulvinar in the thalamus, reactions
why does striate cortex have so many stripes
bc the huge layer IV
optic radiations
white matter tracts, axons from the neurons in the lateral geniculate nucleus to the primary visual cortex
at the optic chiasm, 60% of the axons from the optic nerve cross or
rule for temporal and nasal retinas
temporal: stays epsilateral, always on the same side
nasal: always goes contralateral, always on the opposite side
Hemifields
hemifield is US perceiving the visual field: OUR PERCPETION
Diagram how light moves from the left hemifield of left eye
- left nasal retina
- crosses to the LGN on the right side
- Proceeds to right V1
Diagram how light moves from the left hemifield of right eye
- temporal retina in right eye
- stays epsilteral, right LGN, right V1
What does each optic nerve receive before the chiasm?
before chiasm, each optic nerve has info from both visual fields BUT only one eye
what does each optic tract receive after the chiasm?
after chiasm, each optic tract has info from 1 visual field but both eyes
Right optic nerve damaged
only getting info from left eye (bc right optic nerve is connected to right eye) but from both visual fields (the left and the right), bc each eye can independently see both visual fields
left optic nerve damaged
only getting info from right eye, (bc left optic nerve is connected to left eye), but still getting info from both visual fields since each eye can independently see both fields
Left optic tract damage
if left optic tract is damaged, only getting info from left visual field AND NOT THE RIGHT (bc the right would cross over to the left),
right optic tract damage
if right optic tract is damaged, only getting info from right visual field, NOT LEFT, bc left would cross over to the right
function of iris
iris opens and closes to allow more or less light into the pupil
