PSYC 210 - Exam 3

The modalities of sensation

The modalities of sensation

Touch

Audition

Vision

Smell

Taste

How are the modalities of sensation processed?

As electrical signals (action potentials)

Receptor cells go to the…

Sensory cortices

Receptor cells are not always…

Neurons

In one place

Receptor cells may bypass…

The thalamus and.or brainstem

Somatosensory system

Relays information about the body, such as touch, temperature, proprioception, organic senses, itch, and pain

Proprioception

Body position

Pruriception

Itch

Nociception

Pain

TRUE/FALSE:

Each receptor in the skin has a specialized ending that responds to a specific attribute of the stimulus

True

Skin mechanoreceptors:

Merkel’s disks

Light touch

Skin mechanoreceptors:

Meissner’s corpuscles

Touch and slow vibrations

Skin mechanoreceptors:

Ruffini endings

Stretch, pressure, warmth

Skin mechanoreceptors:

Pacinian corpuscles

Brief and rapid vibrations, deep pressure

Contralateral

Of or pertaining to the other side

Ex. right brain can process stimuli from left side of the body

Ipsilateral

The same side

Ex. your left nostril perceives smell with your left brain

Labeled line signal processing

Different qualities of touch are detected by respective receptors and nerve fibers to the brain

Receptive field

A specific region of sensory space in which an appropriate stimulus can drive an electrical response in a sensory neuron

Do smaller or bigger receptive fields incur more sensitivity?

Smaller fields = more sensitivity

What is the advantage of a receptive field?

Specificity for good sensory discrimination

Somatosensory pathway

1. Neuronal cell bodies in dorsal root ganglion send info ipsilaterally to dorsal columns

2. Info in dorsal columns goes to medulla

3. Info crosses the midline to the somatosensory cortex

4. Info crosses from somatosensory cortex to thalamus

Where are the cell bodies of the primary somatosensory neurons found?

Dorsal root ganglion along spinal cord

Dermatome

Each spinal segment innervates a surface area of the body

Areas of sensory and motor impairments after a spinal cord injury

How are somatosensory signals processed from the skin to the cortex?

They go up the dorsal column in the spinal cord,

Then to the dorsal column nuclei in the medulla,

Then they cross the midline,

And reach the thalamus in the midbrain,

Before reaching the cortex from there

How is sensory information transmitted from the thalamus to the cortex?

First it goes through the VPL and then to the primary somatosensory cortex

Somatosensory cortex

Brain region just posterior to the central sulcus

Somatosensory homunculus

Organization of the somatosensory cortex according to a map of the body surface

How is somatosensory representation changed?

By how often it is used

Synaptic plasticity in monkey fingers

If you prohibit the use of a certain digit in a monkey (ex. digit 3), then the cortex will decrease the size of the area for digit 3 and increase the area for the surrounding digits instead

What is a sensory illusion an indicator of?

That your sensory system is working perfectly

Rubber arm experiment

Visual and touch perception work together to make you believe the rubber arm is part of your own body

How are pain, warmth, and cold perceived?

Through free nerve endings

Thermal/mechanical receptors

Myelinated Aδ fibers that detect sharp, prickling pain

Polymodal receptors

Unmyelinated C fibers that detect searing, diffuse pain

Aδ fibers

Pain, temperature

C fibers

Pain, temperature, itch

What triggers nociceptive pain?

Activation of free nerve endings of Aδ and C fibers

What triggers inflammatory pain?

Chemical mediators/triggers of pain, such as histamine, proteins, serotonin, etc from tissue damage

Ascending pain pathway

Pain fibers form synapses in the dorsal horn

Cross the midline in the spinal cord

Spinothalamic tract carries the pain fibers to the thalamus

Left pain pathway

Spinothalamic tract carries pain fibers to thalamus, then to cortex

Spinoparabrachial pathway innervates areas of the brain concerned with emotion

Right pain pathway

Descending pathway goes through the periaqueductal gray (PAG)

Descending pain pathway

Pain fibers or midbrain sends EPSP. to dorsal horn neuron and then to the spinothalamic tract

Referred pain

Pain fibers from skin or muscle and pain fibers from an internal organ form a synapse on the same dorsal horn neuron

Why is referred pain unique?

Pain from an internal organ feels like pain in the muscle or skin

Does pain have a defined cortical representation?

No, it does not

Female pain

Lower pain thresholds

Higher neural reactivity to pain

BUT more consistent pain tolerance

Male pain

Higher pain threshold

More tolerance

Empathetic spouse

The brain activity of a wife whose husband is in severe pain is similar to his brain, but not the other way around

How do you predict pain in other people?

You can’t

Modulation of pain

Through cognitive and emotional factors

Pain alleviation

Ranges from placebos to drugs to surgeries

Opioid receptors

Widely distributed in the brain and manage pain

Cannabinoid receptors

Widely distributed in the brain; cannabis has anti-inflammatory effects

Circannual

Yearly

Ex. migratory cycle

Infradian

MORE than a day

Ex. menstrual cycle

Circadian

Daily

Ex. human sleep-wake cycle

Ultradian

LESS than a day

Ex. meals and sleep cycles

Zeitgeber

Cues that synchronize biological rhythms

Ex. light

Entrainment

The process of synchronizing an endogenous biological rhythm to the rhythm of an environmental cue

Free running rhythm

When the circadian rhythm is not entrained to a 24 hour cycle

Is spontaneous in environments without changes in lightness

Human circadian free running rhythm

>24 hours

What happens if you are constantly exposed to ONLY dark or light environments?

You express a free running rhythm

What happens when you are exposed to sunlight in the day and darkness at nighttime?

You express an entrained circadian rhythm

Suprachiasmatic nucleus (SCN)

The master oscillator of biological rhythms

Individual SCN neurons…

Fire rhythmically into tissues

What is responsible for SCN neurons rhythmically firing?

Specific genes and transcription factors

Clock genes

Genes that are also found in the cells of other organs

SCN pacemaker

Drives cells that control rhythmic occurrence of different physiological events or behaviors (digestion, blood pressure, sleep)

When is the SCN more active?

During the light period

SCN implant

Embryonic SCN cells that restore a disrupted circadian rhythm

What happens to your activity patterns when your SCN is lesioned?

They become irregular

TRUE/FALSE:

The SCN’s neuronal activity is genetically programmed

True

Retinohypothalamic tract

Light signal is transmitted from a small population of retinal ganglion cells to the SCN of the hypothalamus

How does the retinohypothalamic tract affect circadian rhythm?

It synchronizes it with light/dark changes in the environment

Intrinsically photosensitive retinal ganglion cells (ipRGCs)

Only detect brightness, can’t form images

Express melanopsin

Melanopsin

Light-sensitive substance

Causes of jet lag

Travel

Work shifts

Social jet lag (light, meal entrainment, sleep catchup)

How is a circannual rhythm formed?

Based on changes in the length of the light cycle throughout the year

What controls the circannual rhythm?

The pineal gland

Pineal gland

Secretes melatonin at night

Why do people feel sluggish in the winter?

The pineal gland is sensitive to changes in daylight length and secretes more melatonin the shorter the days get

How is the SCN involved in the circannual rhythm?

SCN causes more melatonin to be released in the winter, causing seasons where one is not active

Ex. male hamster testosterone secretion is inhibited by the large amount of melatonin in the winter

How do embryonic SCN implants restore the circannual rhythm?

Trick question: they do not

Seasonal Affective Disorder (SAD)

Seasonal experience of sadness, interpersonal difficulties, decreased acitivity, increased sleep time, carb craving, weight gain

Can be improved with light therapy

The lack of both eyes, ipRGCs, and melanopsin causes your circadian rhythm…

To be free running

Monitoring sleep

Observing brain wave, muscle tone, and eye movement

Electroencephalogram (EEG)

Brain-wave activity

Electromyogram (EMG)

Muscle activity

Electrooculogram (EOG)

Eye movement

Sleep cycle stages

4 stages and 90 mins

Progresses to stage 4 and goes backwards to stages 3 and 2 and finally REM

Stages 1-4 of sleep cycle

non-REM sleep

Stages 3 and 4 of sleep cycle

Slow(delta)-wave sleep

Rapid Eye Movement (REM) sleep

Rapid eye movements

Low amplitude, high frequency EEG

Cerebral activity increases to waking levels

Atonia

Extremities occasionally twitch

Morning wood LOL

Atonia

Loss of muscle tone

Slow-wave sleep

No eye movement

Low frequency, high amplitude EEG

moderate muscle tone

Sleep walking/talking

No genital activity

Previous world record for sleep deprivation

264 hours by Randy Gardner

Sleep deprivation

Impairs cognitive function and performance

Related to health problems

How does sleep deprivation affect your brain?

It degenerates your glias and neurons

Microsleeps

Brief sleep periods lasting up to a few seconds

What happens to REM sleep as you age?

It decreases