Bio N165 Brain Disorders and Behaviors Quiz 2 Review

Optic Nerve

composed of the axons of the retinal ganglion cells that leave the retina and head back towards the optic chiasm in the brain, taking with them visual information. This nerve is the reason humans have a blind spot, because no photoreceptive cells exist where the optic nerve exits the eye

Retinal ganglion cells

cells in the retina that receive input from modulatory neurons (which get input from photoreceptor cells) and transmit the information down the optic nerve to the brain; includes midget, parasol, and small bi-stratified cells only used in s cone. they are classified by shape, size, and light responses with diff ones tuning for color, form, or motion that set up either sustained or phasic responses to the info flowing into the cortex.

photoreceptor structure

what wavelength is optimally absorbed by a photoreceptor is determined by the structure of its specific photopigment protein opsin located in the outer segment. once the light changes conformation of the opsin the cell takes out that protein and rebuilds it to its original form during the refractory period.

Rods

Photoreceptor cells that are located outside the fovea. They are bigger to pick up more light best in star light vision and useful for detecting movement, but at the cost of visual acuity. They do not differentiate between colors

Cones

smaller photoreceptor cells that located primarily in the fovea. They are responsible for high acuity vision, but take more photons of light to activate (good for daytime vision). There are three types short medium and long, each most responsive to different wavelengths of blue green and red light which, when combined thru comparisons btwn the cell types, allow for color vision. distribution of cone types varies across individuals and eyes

Troxler effect

if the eyes are stabilized the photoreceptors and retinal ganglion cells become desensitized to the current stimulus

Magnocellular Pathway

comes from large parasol rgcs that pools over many receptors to carry motion detection info contributing mainly to the dorsal pathways with bursts of activity

Parvocellular Pathway

comes from small midget rgcs that pools over fewer receptors to carry color, fine details, textures, form and depth processing info to the ventral pathway with a sustained response

Koniocellular pathway

uses s cone input only of small bistratified rgcs to carry low acuity visual info to both dorsal and ventral pathways by projecting to V1 and the surrounding cortex.

iprRGCs/ melanopsin containing RGCs

RGCs that are directly photosensitive cuz of their own photopigment within so theyre positioned very broadly across the retina with massive dendrite trees. responds sluggishly used to signal the presence of light over long term to regulate circadian rhythms and melatonin release but may play a conscious vision role

retinal colorblindness

can be either monochromacy where all cones are nonfunctional so theres complete color blindness, day blindness photophobia, low visual acuity, and involuntary eye movements nystagmus; dichromacy where one cone type is absent or nonfunctional and theres protanopia L red green, deuteranopia M red green, and tritanopia S blue yellow; or anamolous trichromacy the most common and sex linked where all cones work but shift in sensitivity from mutations to the opsin that weaken the oppenency. -amoly close to normal, -opia a type of cone is missing, and -opsia completely lost.

Scotoma

an area of impaired or lost vision in the visual field acting like a blindspot. many causes including retinal damage or damage to anything along the retina V1 pathway. unilateral field loss is damage to the left optic nerve, binasal hemianopsia is damage to uncrossed fibers, bitemporal hemianopsia is damage to optic chiasm, and homonymous hemaniopsia is damage to left hemisphere of V1.

cataract

damage to the lens preventing transparency where darkening or thickening behind the pupil blocks light from reaching the retina properly commonly seen in older age due to UV exposure

higher order visual cortex

color and form info goes to V2 then V4, motion info goes from V1 to V3, and then V2 and V3 start out the dorsal and ventral pathways.

Dorsal pathway

perception for action determines where something is

Ventral pathway

perception for recognition determines what something is

retinotopy visual field mapping

for each dot the retina sees it takes up a visual space and the neighboring cell sees the neighboring visual space and these rgcs continue this organization as they project to the thalamus into V1

cortical magnification

cortical representation of the fovea is magnified around the central visual vs peripheral representation on areas otherwise.

higher order perception

v1 neurons detect edges in a scene during early sensory processing and ventral stream regions identify which object is formed by these edges

blindsight

damage to V1 causes perceptual blindness but a certain area of their visual field demonstrates some response to visual stimuli using motion

Visual Agnosia

inability to recognize and identify objects, faces, or people despite having knowledge of the characteristics of the objects or people. apperceptive associated with earlier processing affects the inability to name or recognize objects, problems with basic shape perception and figure ground segregation but basic visual functions and object identification based on non visual cues are preserved. associative associated with later processing affects visual object recognition but elementary visual perception, copying, and non visual object recognition is preserved.

Prosopagnosia

a disorder in which faces cannot be recognized. apperceptive has problems with recognizing a face vs other objects and associative amnesic has problems with recognizing familiar faces.

capgras syndrome

The rare delusional belief that an acquaintance has been replaced by an identical-looking imposter. may be seen in schizophrenia, dementia, and brain trauma where theres normal face perception but abnormal emotional response to faces due to disconnect btwn temporal and limbic cortex

Fregoli syndrome

the rare delusional belief that different people are in fact a single person who changes appearance or is in disguise seen in damage to left frontal and right temporoparietal regions possibly arising from disconnection between hemispheres.

Simultagnosia

problems with scene perception in normal visual fields and may arise from problems with attention, visuospatial mapping, and/or pattern analysis. dorsal is more severe and from bilateral lesions at the parietal occipital junction where you can only see one stimulus at a time. ventral is from damage to left inferior occipitotemporal junction where you can see multiple objects at a time but recognition is limited to one at a time so you can navigate and count but not read.

cerebral achromatopsia

rare loss of color in both visual fields caused by cortical lesions on bilateral V1 V4. hemi-acromatopsia is loss of color in one half or quarter of visual field. transient achromatopsia is temporary loss of color from transient ischemic attacks.

akinetopsia

inability to perceive motion from damage to V5 MT fom strokes, trauma, or antidepressants seen as strobe light effects

opponent-processing color vision theory

info from the cones is transferred to the retinal ganglion cells thru very specific neural wiring where color is processed in two diff opponency channels red vs green and blue vs yellow/red and green also bright red green blue vs dark luminance.

psychosis

a state of mind where you are not logically or normally processing the world

medical history assessment

patient info, chief complaint, history of present illness, past medical history, family medical history, social history lifestyle

neurological exam assessment

are the cranial nerves normal, does the patient have normal sensation, can the patient move normally, are reflexes present, what is the patient’s medical status

neuropsychiatric assessment/ mental status eval

state of consciousness, appearance and general behavior, mood, content of thought, intellectual resources

x-ray

form of radiation partially blocked by dense tissues like bone. areas where x-rays strike on film darken when developed causing bones to absorb more rays and appear lighter than the surrounding soft tissue. good for skull fractures and observation of foreign object not disorders

CT scan

uses large series of 2d x-ray images that goes through digital geometry processing to generate a 3d image of the inside of an object. allows quick viewing of a brain injury with more detail such as a skull fracture, stroke, bleeding, and edemas

MRI magnetic resonance imaging structural

uses magnetic fields and radio waves to measure diff responses btwn tissues. one type looks at structures in the brain and in the body producing a T1 weighted anatomical image where lesions appear bright via contrast dyes good for detailed evaluation of brain tumors, ischemia, hemorrhage, inflammation, and infection or production of a T2 and diffusion weighted anatomical image where water/fluid appears bright in a flipped scan good for multi sclerosis, sclerosis, edemas, and connectivity of white matter tracts in diffusion tensor imaging DTI.

MRI functional

measures magnetic properties of oxygenated and deoxygenated blood also called BOLD blood oxygenated dependent signal with good spatial resolution in a scale of minutes by showing images of changing blood flow in the brain indirectly associated with neural activity. good for research on normal and abnormal brain functions, cognitive disorders, and early strokes.

EEG/ECoG

measures electrical activity produced by the brain but with bad spacial resolution so better at brain wide activity. can avoid distortion from scalp and skull invasively by putting electrodes directly on the brain. both good for seizures, arousal levels, encephalopathy, and brain death.

PET

measures metabolism using emissions from radioactively labeled metabolically active chemicals that have been injected into the bloodstream thats then computer processed to produce 2 or 3d images of the chemical distribution in the brain. good for problems with metabolism like dementia, strokes, and brain tumors

visual fields

the eye focuses on a fixation point and within that visual field is a division of the vertical and horizontal meridian and a blind spot where the optic nerve leaves the eye. binocular vision combines both fields meeting at the center of high acuity foveal vision

eye

light from image inputted into cornea though the pupil and focused onto the back of the retina so it can be transmitted to the brain as part of the CNS as well as the fovea that consists of specialized retinal cells for highest acuity vision. the iris focuses the size of the pupil to adjust the amount of light let in and behind that is the lens that further aids focus. the sclera fully surrounds the eye and blends into the cornea connective tissues for structure. the optic disc consists of all the optic nerves leaving the eye that makes up our blindspot.

light pathway

photoreceptors receive light and emit a signal to the ganglion cells that light has reached the specific location where the modulatory neurons btwn fine tune that info by making it a stronger or weaker signal. setup of light to info allow stray photons to be absorbed by overlying cells that dont affect the visual system to diminish blurriness so only the most accurate is transmitted.

fovea

specialized for high resolution by being thinner thru less overlapping photoreceptors and ganglion cells to let as much light in as possible and color vision by containing only L and M cone receptors

visual pathway

primary sensory cortexes refers to the first part of cortex that inputs from the thalamus that acts as a sensory motor relay station reach. rgc optic nerve axons cross over the hemisphere in the optic chiasm and run along the optic tract to the thalamus thru the lateral geniculate nucleus where it then projects onto V1. other side processes are involved like the hypothalamus for circadian regulation, pretectum for pupil and lens reflex control, and the superior colliculus for orienting head and eye movement.

V1

visual info is separated by eye and continues into the layers of V1 but new info shows eye info comes in separately to the thalamus to inform cells from visuals of both eyes. takes up a large area separated into a, b, ca, and cb layers that take in inputs from axons where magno from both eyes meet at B and parvo meet at the upper layer II in the color blob and combine in the motion interblob. v1 cells have many types of specialized tuning to receive inputs from monocular or binocular cells, respond best to oriented lines, increase response with contrast, have a preferred spatial frequency, and can have a preferred direction and depth.