Neuroscience Exam 1

Pupil

The opening that allows light to enter the eye and reach the retina

Iris

Surrounds the pupil, gives the eye its color, has ciliary muscles that help make the pupil larger and smaller

Cornea

External surface of they eye, a clear covering, does the most of the refraction

Sclera

The white of the eye that forms a tough wall

Extraocular muscles

The muscles in the orbit of the eye, attached to the sclera, helps the eye move and look around

Optic nerve

Carries axons from the retina to the back of the orbit to the base on the brain near the pituitary gland

Optic disc

Retinal vessels originate here and optic nerve fibers exit the retina here

Macula

The center of the retina, there are no large blood vessels which improves the quality of central vision

Fovea

About 2mm in diameter, the thinnest part of the retina, the anatomical reference point of the eye, is in the middle of the macula

Aqueous humor

Nourishes the cornea because the cornea does not have blood vessels

Ciliary muscles

A ring around the lens behind the iris that attaches to the zonule fibers

Zonule fibers

Keeps the lens in place by attaching it to the ciliary muscles

Vitreous humor

Between the lens and the retina, keeps the eye spherical and gives it its shape

Pupillary light reflex

connections between the retina and the neurons controlling the muscles that contract the pupils, which change the amount of light coming into the eye; if both eyes do not change it could be a sign of brainstem damage

Most direct visual pathway

Photoreceptors to bipolar cells to ganglion cells

Horizontal cells

Input from photoreceptors, project to neurites to influence other photoreceptors and bipolar cells

Amacrine cells

input from bipolar cells, projects to nuerites laterally to influence ganglion, bipolar cells, and other amacrine cells

tapetum lucidium

reflective layer behind the photoreceptors in animals that reflects light, making animals have better night vision

rods

more discs, night vision, more abundant in the peripheral vision, cannot see color, longer than cones

cones

shorter than rods, most abundant in the fovea, three different types that are sensitive to different layers, allowing us to see color, most active in bright light, they do not have rhodopsin, they have three different types of opsins

duplex retina

having both rods and cones in the retina, cones mainly in the fovea, rods mainly in the peripheral

frequency determines what in light

color

amplitude determines what in light

brightness

Human visual field is about how many degrees

150

Focal distance is determined by

The power of refraction

Distance object require

little lens accommodation (flat lends)

Close objects require

more lens accommodation (fat lens)

Myopia

nearsighted, cannot see distance objects, needs concave lenses

Hypermyopia

Far sighted, cannot bring close things into focus, needs convex corrective lenses

How does the sympathetic nervous system effect your pupils?

Dialtes pupils to take in more information during fight or flight

How does the parasympathetic nervous system effect your pupils?

It constricts your pupils when in rest and digest

Steps of light transduction

Light bleaches rhodopsin, transdusin (the g-protein) is stimulated, PDE (effector protein), Na channels close, cell membrane hyperpolarizes

Dark adaptation

takes 20-25 minutes, regeneration of unbleached rhodopsin and slight dilation of pupils

light adaptation

5-10 minutes, slight help by pupil constriction, calcium enters through sodium channels (increase in cGMP production)

off bipolar cells

ionotropic, light hyperpolarizes them but light on the surround will depolarize them

on bipolar cells

metabotropic, light depolarizes them but light on the surround will hyperpolarize

m-type ganglion cells

5% of ganglion, large cells, conduct more rapidly, no color information

p-type ganglion cells

90% of ganglion, smaller, conduct slower, includes color information

color opponent cells

p-type cells (not in m-type cells), when the response to one color in the visual field is cancelled out by showing another color in the surround

photosensitive retinal ganglion cells

use melanopsin as a photopigments, they function as ganglion cells and also as photoreceptors. Whether it is hyperpolarized or depolarized depends on the fraction of the center and the surround light hits, help with edge detection

Parallel processing

different visual attributes are processed simultaneously through different pathways

non-m non-p type cells

wavelength specific, 5% of ganglion, not well characterised

opponent processing theory

occurs in the retinal ganglion cells, emphasized the important of opposite colors

Retinofugal process

optic nerve → optic chiasm → optic tract → thalamus (LGN) → primary visual cortex

optic chiasm

the nasal halves of each retina cross over each other (the nasal halves see the outsides of our vision because the eye sockets are like cups)

Lateral geniculate nucleus (LGN)

Part of the thalamus, has two types of neurons that are identical to the ganglion that project to them

Magnocellular LGN neurons

large, from one eye, shorter responses, NOT wavelength specific, part of layers 1 and 2, projects to IVCa

Parvocellular LGN neurons

smaller, from one eye, longer responses, wavelength specific, layers 3-6, projects to IVCb

Koniocellular LGN neurons

transmits to layers in between LGN layers (II and III synapses)

Primary Visual Cortex

the LGN’s primary target, in the occipital love, has six layers called the striate cortex

Retinotropy

3D world is transmitted into 2D information, the central retina is over represented which allows for greater visual acuity

The cortical images are upside down, split, and backwards

Layer IV

always afferent

Layer V

always efferent

spiny stellate cells

spriny dendrites, located in layer IVc, makes local connections

Inhibitory neurons

Form only local connections, located in all layers, lack spines

Columns in the striate cortex

connect in layer III, neurons in the same column receive input from the same part of the retina

Where does binocular convergence happen?

Layer III

Blobs

connect to a column in layer IV, they are in layers II and III, and they mainly connect to koniocellular inputs, monocular, wavelength-specific

Who discovered ocular dominance columns?

Hubel and Wiesel, they stained the blobs with cytochrome oxidase

Where do layer II, III, and IVb project to?

other cortical areas

Where does layer V project to?

the superior colliculus and the pons

Where does layer VI project to?

back to the LGN/thamalus

simple cells

binocular, have antagonistic flanks, have an on and off area, they are in the V1 cranial nerve

complex cells

binocular, no off region, in cranial nerve V1

interblob regions

binocular, direction selective

What are the 3 vision pathways?

Magno, parvo/interblob, and blob/konio

What is the motion pathway?

magnocellular

What is the shape pathway?

parvo/interblob

What is the color pathway?

blo/konio

Dorsal stem

leaving the occipital lobe to go to the parietal lobe, the “how” pathway

Vental stem

Leaving the occipital lobe to go to the temporal lobe, the “what” pathway

Achromatopsia

damage to area V4 in the ventral stem that causes loss of color vision

Prosopagnosia

Damage to the fusiform face area in the central stem that causes face blindness

Pitch is determined by

frequency (higher frequency=higher pitch)

Intensity/loudness is determined by

amplitude (higher amplitude=louder sound)

middle ear

includes the tympanic membrane, the ossicles (malleus, incus, stapes), oval window