Brain Bee Chapter 2 - Senses and Perception

transduction

the process of turning stimuli into electrical signals in the brain

where does light first pass through the eye?

the cornea (where initial focusing occurs) then into the pupil

function of the iris

• changes size of pupil to regulate amount of light passing through

• bends light to focus it on the retina

retina

sheet of cells on inner surface of eyeball that process visual information → visual input is mapped flipped (objects on right project images onto left retina)

3 types of neurons in the retina

photoreceptors, interneurons, ganglion cells

interneurons → carry sensory information, regulate motor activity

photoreceptors

• most peripheral layer of retina (light travels to these cells last)

• includes rods and cones

• converts light into electrical signals

ganglion cells

• process and relay information from photoreceptors

• axons of ganglion cells exit retina to form optic nerve

rods and cones

• rods → 95% of photoreceptors, dim light

• cones → 5%, fine detail and color (3 types for red green or blue)

fovea

very center of retina, cones most densely packed here → sharpest vision

macula / macular degeneration

• area immediately around fovea, for reading and driving

• macular degeneration → death or degeneration of photoreceptors in macula, leading cause of blindness

ganglion cell’s receptive field

• portion of visual space providing input to a single ganglion cell

• more photoreceptors providing input = less detailed images, like on periphery of retina

receptive field’s center surround antagonism

• receptive field of ganglion cell activated when light hits center of field

• inhibited when light hits area surrounding center (donut)

• weak response when light hits entire field
  

• for object detection & maximizes perception of contrast

optic chiasm

• crossover junction of optic nerves from both eyes

• right side info from both eyes goes to right brain (from right visual field, retina flips it)

• left side info from both eyes goes to left brain (from left visual field)

lateral geniculate nucleus

• in thalamus

• relays visual info after optic chiasm

primary visual cortex

• in occipital lobe

• processes visual info from thalamus

• cells above and below middle layer have more complex receptive fields

• cells pass information along to other parts of visual cortex, creating complex and selective receptive fields

dorsal visual processing stream

• goes to parietal lobe

• “where”

• combines spatial relationships, motion, and time about visual input

ventral visual processing stream

• goes to temporal lobe

• “what”

• integrates information about shape, color, memories, and experiences for recognition

strabismus

crossed eyes, causes issues with depth perception

research animals used for vision

light energy converted to electrical signals = fruit flies (drosophila) + mice
higher level visual processing = monkeys and cats

basilar membrane

elastic membrane on inside of cochlea with hair-like cilia that excites the auditory nerve

wernicke’s area

left auditory cortex, damage causes people to no longer understand what is being said

3 cranial nerves

facial, vagus, glossopharyngeal → taste receptor cells send signals through these to brainstem, then thalamus, then gustatory cortex / insula

olfactory bulbs

sends info directly to olfactory cortex without passing through thalamus, can undergo neurogenesis throughout life

taste

combination of gustation and olfaction

somatosensory cortex

translate signals into touch perception after passing through thalamus

myelin nerve fibers and touch

info travels faster on thick axons (A-beta fibers) → sharper pain
slower on thin axons (C fibers) → duller pain

nociceptors

pain sensory fibers

histamine receptors

activated when allergies or irritation trigger the release of histamine

prostaglandins

enhance sensitivity of receptors to tissue damage, making pain more intense

allodynia

excessive pain (even with light touch), prostaglandins contribute to this

neuropathic pain

pain caused by brain and not body

periaqueductal gray matter

modulates pain, in brainstem

analgesics

pain-relieving drug

endorphins

opioids produced by the body that act like analgesic morphine

adrenaline

acts as analgesic, produced in stressful situations and relieves pain without losing consciousness

cognitive behavioral therapy

CBT, can be used to ease emotional component of pain

limbic system

reward and emotion, linked to pain, cannabis can suppress some areas to relieve pain