IB 132 L6

Orientation terms for brain

-superior: dorsal

-rostral: anterior

-caudal: posterior

-ventral: inferior

Central sulcus

separates frontal and parietal lobes (deep divide)

Mylenation

comes with experience - younger people have less white matter

Visible light

400-700 nm

blue=short wavelength

red=long wavelength

Reflected light

we see reflected light

ex: a red object absorbs all other colors and only reflects red

Seeing color

depends on light source, object, and detector (eye)

Lens of eye function

-curved shape of the lens bends light

-lens focuses the light on back of eye

-lens attached to muscles that will change its shape (ciliary muscles)

Far object in focus

-relaxed ciliary muscles, tension on zonular fibers, flattened lens

-light rays from distant objects are nearly parallel

Object out of focus

-relaxed ciliary muscles

-light rays from near object diverge

Zonular fibers

connecting the ciliary muscles with the lens of the eye

Near object in focus with accommodation

firing of parasympathetic nerves, contracted ciliary muscles, slackened zonular fibers, rounded lens

Image on back of eye

reversed

Visual field

images on your left end up in the right occipital lobe, vice versa

Optic chiasma

the crossing of the optic nerves from the two eyes at the base of the brain

Lateral geniculate nucleus (LGN)

A synapse in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex.

retina -->LGN (synapse 1) --> occipital cortex (synapse 2)

Depth perception

binocular coverage

-binocular zone is where L and R visual fields overlap (accounts for mismatch btwn 2 eyes)

-monocular zone is the portion of the VF associated with only one eye

Rods

-more light sensitive

-dark/light sensing (grayscale)

-many produce one signal

Cones

-color, sharp detail

-fewer per signal

Anatomy of eye

Fovea centralis

area consisting of a small depression in the retina only containing cones and where vision is most acute

-->within the macula

Retinal ganglion cells

retinal neurons whose axons leave the eyeball and form the optic nerve

--> have 2 main kinds of receptive fields

ON center, OFF surround

-light in center --> stimulation of ganglion cell

-light off center --> inhibition of ganglion cell

-light half in center half off --> weak stimulation of ganglion cell

OFF center, ON surround

-light in center --> inhibition of ganglion cell

-light off center --> stimulation of ganglion cell

-light half in center half off --> weak stimulation of ganglion cell

Coding: shape processing in visual cortex area V1

-simple cells: responds to a bar in a certain orientation and position

-complex cell: responds to a bar in a particular orientation regardless of position

-hypercomplex cell: respond when bar ends in their receptive field, good for edge detection

Trichromatic theory

-different photoreceptors sensitive to: red, green, and blue

-can combine these 3 colors of light to produce other colors

Opponent process theory

-2 types of color receptors: R-G and B-Y (and light/dark)

-the idea is if inhibit receptor sees one color (eg. red), if excite get the other (eg. green)

Two problematic mysteries

1. Get after images of the opposite color (eg. red-green, blue-yellow) --> spectrally opposed "opponent process" cells in LGN of the thalamus

2. color-blindness is always R-G or B-Y

Complementary color theory

Pairs that mix to white

3 types of cells that function in color opposition: blue-yellow, red-cyan, green-magenta

Receptor

protein that binds a ligand, initiates action

Sensory receptor

cell (eg. neuron) that initiates a sensory signal (whole cell w receptors on tip)

-->brings sensory info into brain

Receptive field size differences

smallest (most localizable) in lips, fingertips

Stimulus intensity and frequency

The more frequent/harder pressure the stronger the stimulus

-->Intensity is encoded in the frequency of APs arriving at the sensory cortex

Lateral inhibition

the reduction of activity in one neuron by activity in neighboring neurons

-->enhances signal localization

-->common in vision and touch

Lateral inhibition and T + pain

temperature and pain sensing have little to no lateral inhibition

Somatosensation areas of the brain

-frontal lobe association area

-somatosensory cortex

-parietal lobe association area

-occipital lobe association area

-temporal lobe association area

Descending inhibition

Activity descending from higher centers in the brain and brainstem can "screen out" certain types of sensory information by inhibiting neurons in the afferent pathway

-->not ideal to feel everything

Illusions in touch and proprioception

-loss of ability to distinguish finger surfaces

-->plasticity in the brain --> remapping in the somatic map

Illusions in somatosensation: phantom limb

-signals misattributed to missing limb

-substantial reorganization of somatosensory map after limb loss may be related

Illusions in somatosensation: referred pain

-pain from injury or damage in one part of body is interpreted as coming from another source

-opposite the "labeled lines" for small sensory receptive fields

-occurs because multiple primary sensory neurons converge on a single ascending tract

-ex: cardiac ischema in men felt in neck, left shoulder/arm

Neuron pathway to brain

-pain receptor

-dorsal root ganglion

-spinal cord

-sensory pathway to brain