Role of Sensory systems:

audition vision olfaction taste smell

What are our primary senses?

some addtl senses◦ vestibular◦ organ◦ muscular tension

sensory transduction◦ - conversion of physical energy from the

environment into changes in electrical potential

sensory coding-◦ Making sense of that input

definitions

vision - light waves -

taste – chemicals in fluid – hearing – sound waves- touch- pressure, temperature changes,

smell- chemical in air

What is transduced?

vision - rods and cones in retina

taste - - taste buds on tongue hearing - - hair cells in inner ear

(cochlea) touch - specialized receptors

under skin smell - hair cells in olfactory

epithelium

What are the cells responsible for transduction?

Receptors show adaptation◦ most sensitive to changes rather than constant

stimulation

◦ why is this important?

General pathway for most sensory information:

General pathway for most sensory information:

◦ sensory neurons – sensory nerves spinal tracts – thalamus – primary cortex – higher association cortex

Certain sensory neurons have a spontaneous firing rate.

For these cells any change in their firing rate will convey important info (i.e. color vision)

Different rhythms of firing also can convey different information

A general point:

* most highly developed sense in humans

optic nerve for one eye - 1,000,000 axons auditory nerve contains about 30,000

axons

adaptability and plasticity of visual system - make sense out of nonsense

Vision

iris ◦ largely a muscle that expands and contracts pupil

in response to light◦ phenotypically unique – iris scan

sclera◦ tough opaque tissue

pupil◦ often used to determine neurological function

visible parts of the eye

light waves along the visual spectrum

What does the human eye see?

1. inverted image on retina

2. region important for transduction is at very back of the eye

2 interesting points from figure

retina - structure of eye important for transduction

- retina contains neurons, glial cells and two types of photoreceptors

responsible for transduction

numerous differences between rods and cones

rods and cones

rods shaped like a rod insensitive to color work well under low

illumination

some differences cones shaped like a cone sensitive to color work best in bright

light

rods shaped like a rod insensitive to color work well under low

illumination 20,000,000/eye location: found around the

periphery of the retina

some differences cones shaped like a cone sensitive to color work best in bright light 5,000,000/eye location – found

around the fovea of the retina◦responsible for

sharp images and vision

a low ratio of synaptic connections between neurons ensures higher definition and sharpness compared to a higher ratio

sharp, acutevision

less sharp focused visual input

sharp, acutevision

less sharp focused visual input

rods shaped like a rod insensitive to color work well under low

illumination 20,000,000/eye location: found around the

periphery of the retina requires extended time

until optimal function

some differences cones shaped like a cone sensitive to color work best in bright light

5,000,000/eye location – found around

the fovea of the retina responsible for sharp

images and vision works optimally very

quickly

there are at least two levels of communication within the neural cells of the eye◦ rods and cones – bipolar cells – ganglion cells

(axons make up the optic nerve) to CNS

there are at least two levels of communication within the neural cells of the eye◦ rods and cones – bipolar cells – ganglion cells

(axons make up the optic nerve) to CNS◦ across a single layer (rods and cones

communicate with each other; bipolar cells communicate with each other; etc)

optic nerve (ganglion cell axons) – make a blind spot on each eye!

component (trichromatic ) or Young-Helmholz◦ occurs at level of cones

3 different cones more sensitive to different wavelengths (ie colors)

Explanations for color vision

trichromatic or Young-Helmholz◦ occurs at level of cones

explains major type of color blindness◦ deficits in certain types of cones can explain

major type of color blindness

Explanations for color vision

At level of cones- GREAT!

◦ there are different cones that produce greater changes in electrical potentials depending on the color (wave)

◦ abnormalities in cones can explain red/green color blindness

How does this explanation do?

Very rare to see complete color blindness - only usually seen with brain injury

~ 7% of US males (10,000,000) compared to 0.4% women - red/green

X-linked phenomenon

Color blindness

Sex (X) -linked phenomenon

X Y

X XX XY

Xb XXb XbY

40

What happens in hereditary color

deficiency?

· Red or green cone peak sensitivity is shifted.

· Red or green cones absent.

NORMAL CONE SENSITIVITY CURVES(TRICHROMAT)

41

B RG

437 nm 564 nm533 nm

42

B RG

437 nm 564 nm

(green shifted toward red)

5% of Males

43

B R

437 nm 564 nm

(no green cones; only red and blue)

1% of Males (there is no green curve)

44

B G

437 nm533 nm

(no red cones; only green and blue)

1% of Males (there is no red curve)

At level of cones- GREAT!

How does this the trichromatic theory do for explaining color vision?

negative afterimage –◦ phenomenon that occurs as a result of

overactivity or inhibition of neurons (due to color stimulation)

One thing that trichromatic theory cannot explain

opponent process theory◦ occurs at level of bipolar cells and higher black/white, red/green; yellow/blue; one color

excites bipolar cell; other color inhibits it

Explanations for color vision

says nothing about complexity as information reaches occipital lobe –

says nothing about color constancy◦ color constancy and the retinex theory- occurs at

the level of the cortex……

prestriate – primary occipital cortex; multiple layers of higher association cortex

Copyright © 2006 by Allyn and Bacon

Touch (mechanical stimuli) Temperature (thermal stimuli) Pain (nociceptive stimuli) Specialized receptors respond to the various

stimuli

Copyright © 2006 by Allyn and Bacon

Exteroreceptive System- stimuli applied to the skin

Figure 7.15

Copyright © 2006 by Allyn and Bacon

Ruffini ending Merkel’s disks Free nerve endings

Pacinian corpuscles

a necessary sense too little or too much – yikes! No obvious cortical representation (although

there are regions that appear to be involved in the emotional component)

PAIN

Substance P- ◦ Most pain is a result of substances released by

damaged tissues including substance P What else causes substance P release?

Neurotransmitters involved in Pain

Substance P is a large peptide and synthesis can take time SO

Release of large amounts of substance P results in a brief time (when more is being synthesized) that is “pain-free”

Huh?

Substance P

Endogenous opioids◦ endorphins – endogenous morphine-like

substances may explain acupuncture, placebo effects

Neurotransmitters involved in Pain

Descending pain control – pain can be suppressed by cognitive and emotional factors

PAG – periaqueductal gray

Copyright © 2006 by Allyn and Bacon

Descending Pain Control

3 discoveries made this possible

◦ Electrical stimulation of the PAG has analgesic (pain-blocking) effects

◦ PAG and other brain areas have large amounts of opiate receptors

◦ Existence of endogenous opiates (natural analgesics) - endorphins

Copyright © 2006 by Allyn and Bacon

A descending pain control pathway

MIDBRAIN

Congenital insensitivity to pain

Too little or too much pain

Extremely rare – less than 100 cases currently in the U.S.

Inability to thermoregulate (through skin) or feel pain

types: cancers, debilitating arthritis, back pain, undiagnosed, migraine

Approximately 80 million people in the United States suffer

Chronic pain consumes approximately $70 billion per year

Chronic pain

Chronic Pain

Chronic low back pain affects nearly 31 million Americans and represents the most common cause of disability in persons less than 45 years of age

drugs – morphine derivatives◦ oxycontin

ESB periaqueductal gray

Treatments:

drugs – morphine derivatives◦ oxycontin

ESB periaqueductal gray

acupuncture pain management

Treatments:

types: cancers, debilitating arthritis, back pain, undiagnosed

phantom limb

Chronic pain

drugs – antidepressants; antiseizure meds

cutting dorsal roots

anesthetizing stump

Additional Treatments for Phantom Limb: