PSYC110 Exam 3 (Vision, Touch and Pain)

Parallel Pathways

stimuli is processed separately

• magnocellular ganglion → parietal → “where”

  • larger cells + receptive fields, peripheral retina

• parvocellular ganglion → temporal → “what”

  • smaller cells, densely packed in fovea, central retina

Prosopagnosia

inability to recognize faces

• damage to temporal lobe

• damage to fusiform face

General principles of sensory perception

sensory stimulus → specialized sensory receptors → receptor potential (RP) → sensory neuron → Action potential (AP) → additional neurons → output

Parts of the eye

• Sclera: white part, protects eyeball

• Cornea: transparent

• Iris: colored, regulates size of pupil

• Ciliary muscles: control the lens

• Lens

• Conjunctiva

• Pupil

Visual Transduction

In the dark:

• Na+ channels in PRs are open

• PRs inhibit BpCs

Light comes in:

• Na+ channels close → hyperpolarize

  • BpCs disinhibition- → BpC depolarizes

  • GCs depolarize → optic nerve APs

Retina

1. Photoreceptor cells: 1st recipient of visual info

   • rods

   • cones

2. Bipolar cell (layer): integrate info

   • amacrine cells

   • horizontal cells

3. ganglion cell

   • magnocellular: rod based

   • parvocellular: cone based

PRs → BPCs → GCs → optic nerve → brain

Sensory Transduction

absorb physical energy → transduction → neural activity → encode stimulus

Specialized Sensory Receptors

needed to encode different stimuli

• retina has 2 kinds (rods and cones)

• 120mil rods, 60mil cones

Fovea

• parvocellular

• high packing of PRs

• more cones

• each PR → single BpC

• high acuity vision, object perception

Periphery

• magnocellular

• low packing density

• more rods

• many PRs → BpCs

• not suited for accurate vision, good for movement

Visual Pathways

Retina → lateral geniculate nucleus in thalamus and superior colliculus → primary visual cortext → hihger visual centers

Blindsight

respond to stimuli without consciously realizing it is being perceived, Weiskrantz

Center-Surround receptive field

on-center, off-surround

Color (Tritanopia)

• ganglion cell: center-surround antagonistic receptive fields

• color processing: opponent organization

• illuminated w/ same color shown → firing increases

• illuminated w/ complementary color → firing decreases

Visual Processing: visual thalamus

• receptive fields like in retina (center-surround)

• pathways segregated (parvo vs. magno)

Visual processing: Primary Visual Cortex

• receptive fields unlike retina

• orientation specific bars/slits of light

• line and edge detection, shape processing

Primary Visual Cortex

• striate cortex contains abt 2500 modules each with 150k neurons

Modular Organization of the Striate Cortex

6 main layers

• orientation sensitivities → blobs → koniocellular input → magnocellular input → parvocellular input → stimuli thru eye

V1 (1st visual cortex)

• modules, layers, orientation columns

• ocular dominance

• blobs (parvo) vs. interblobs (magno)

• cell types - simple, complex…

LGN

similar to retina

Super Colliculus

• mostly magnocellular

• reflective orientation

(main principles) Spatial Receptive Fields

• multiple neural selectivity (direction, velocity, orientation, spatial frequency) in each neuron

(main principles) Hierarchical Organization of Visual System

• contrast/luminance extraction to higher order visual processing (ascends)

On-Center Receptive field

• light in center activates the cell (AP)

• activates center, high contrast

• inhibits surround

Off-surround receptive field

• light in surround inhibits cells

• inhibits center light, low contrast

• activates surround

Cutaneous senses

skin senses

• stimuli:

  • pressure, vibration, heating, cooling, tissue damage (pain)

proprioception

perception of body position and posture

Receptive field

windows for sensory neurons receive stimuli

• basis for a place code

Sensory transduction

external stimuli → electrical signals that brain understands

Place code

topographical maps - sensory representation in the brain

Large RF (receptive field)

low spatial resolution

Small RF (receptive field)

high spatial resolution

(somatosensation) Receptor Potentials (RPs)

depolarization, not action potentials

Mechanosensation

mechanical stimuli → neuronal impulses (RPs) → crosses threshold → neurons fire

• touch

  • pressure/vibration

  • pain - nociception

  • temperature - thermoception

Sensory Adaption

• tonic receptors slowly adapting receptors

• phasic receptors rapidly adapt

Mechanoreceptors

• ruffini’s corpsucles: vibration sensitive, large RFs, slow adapting

• pacinian corpsucles: mechanic stimuli (esp vibrations), large RFs, fast adapting

• Meissner’s corpsucles: touch sensitive, small RFs, fast adapting

• Merkel’s Disks: touch sensitive, small RFs, slow adapting

Hairy skin

• ruffini corpsucles

• pacinian corpsucle

• hair

Glabrous skin

• hairless

• merkel’s disks

• meissner’s corpsucle

• pacinian corpsucle

Ruffini’s Corpsucle

• vibration sensitive, large RFs, slow adapting

• location: glabrous skin

• function: skin stretching, proprioception

Pacinian Corpsucle

• mechanical stimuli (esp vibration), large RFs, fast adapting

• location: hairy + glabrous

• function: detects edge of elongated object

Meissner’s Corpuscle

• touch sensitive, small RFs, fast adapting

• location: glabrous skin

• function: edge contours, braille, esp fingertips

Merkel’s Disks

• touch sensitive, small RFs, slow adapting

• location: hairy + glabrous

• function: detects form and roughness, esp fingertips

Axon Fibers

1. A alpha: thick myelin, proprioception

2. A beta: thick myelin, fast conducting, mechanical stimuli (painless touch)

3. A delta: thin myelin, temperature (cold), good pain, itch

4. C: unmyelinated, temperature (hot), bad pain

Thermoreceptors

• cold sensors closer to skin surface

• heat sensors deeper

• receptors open NA channels

1. TRPV4: warm (27-34 c)

2. TRPV3: warmer (31-39)

3. TRPV1: hot (>43)

4. TRPV2: painfully hot (>52)

5. TRPVM8: moderate cold, menthol

6. TRPVA1: <18c

Ascending parallel pathways (touch)

• transmission of sensory info to brain

• dorsal column

  • touch

• spinothalamic

  • pain, temperature

Pain processing neurotransmitters

1. Substance P: bad pain

   • released by C fibers

   • opiates, morphine block SubP

2. Glutamate: good pain

   • released by A delta

3. Glycine: inhibitory neurotransmitter from SC, reduces activity from SubP and Glutamate

opioid Mu Receptor binding

1. VTA Dopamine neurons: addiction

2. NA neurons of locus coreleus: withdrawal