Sensation & Perception : Touch, Smell, & Taste

Skin, Stimuli, & Receptors

Pressure, stretch, pinch, temperature, electrical stimuli, etc.

Glabrous Skin

Skin with no hair

• Palm, sole

Epidermis

Several layers of tough dead cells on top of a single layer of living cells

Dermis

Contains most of the nerve endings

Corpuscular Endings

Nerve ending with small bodies or swellings

• Merkel, Meissner, Ruffini & Pacinian Corpuscle

  • For touch

Free Nerve Endings

For pain and temperature

Merkel

Receptive Field : Small

Adaptation : Slow

Fiber : SA I

Stimuli / Perception : Pressure / fine detail

Meissner

Receptive Field : Small

Adaptation : Rapid

Fiber : RA I

Stimuli / Perception : Flutter / handgrip

Medial Lemniscal Pathway

Touch perception and sense of position of limb (proprioception)

• Large fibers

• Fast (40 m/sec)

• Through dorsal column

  • Spinal Cord → Brain Stem → Thalamus → Somatosensory Cortex

Spinothalamic Pathway

For temperature & pain

• Small fibers

• Slow

  • Through Spinal Cord

Paleospinothalamic (C)

Older, for dull or burning pain

• Small, unmyelinated, & slow (2.5 m/sec)

Neospinothalamic (Aδ)

Newer, for sharp pain

• Small, unmyelinated, & slow 95 - 20 m/sec)

Primary Somatosensory Cortex (S I)

3 layers with one sub layer

• 1, 2, 3a, 3b

Homunculus

Spatial location on the skin is preserved in the cortex

• Magnification factor

Plasticity

Size of the brain grows with more stimulation on a particular part of the body

Specialized Stimuli

Like complex cell

• Respond to certain direction or shape

Touch Threshold

Varies from on region of the body to another

Depends on skin temperature

• The higher, the lower the threshold

Two Point Threshold

Two touch will be felt as a single touch if they are close enough together

• Related to homunculus

Haptic Perception

Identification of 3D object with hand touch

• Exploratory Procedures :

  • Lateral motion

  • Pressure

  • Enclosure

  • Contour Following

Form of Touch

Touch Threshold, Two-Point Threshold, Haptic Perception

Evolutionary Significance of Pain

To respond appropriately to environmental situations that could destroy sensory organs

• To cope with injury appropriately

Pain Receptors

Free-Nerve Endings

• Involves Aδ and C fibers

Free-Nerve Endings

In fat under dermis

• Terminate in epidermis, but wrapped in Schwann cell sheath

  • Respond only to high intensity

Double-Pain

Experience two distinct peaks of pain

• Sharp, pricking pain from Aδ fiber

• Dull, burning pain from C fiber

_____ _____ is better identifying objects, but _____ _____ can be good if the edges of objects were moved through fingers and hands.

Active touch, Passive touch

Gate Control Theory

Both Aβ and Aδ & C have connection to the Substantia Gelatinosa (SG) and Transmission cells (T cells)

• Fast fibers (Aβ) : Excite the SG– fiber

  • Slow fibers (Aδ & C) : Excite the SG+ fibers

• SG– : Inhibit T cells

  • SG+ : Excite T cells

• T cells send pain sensation to the brain

• Fast Fiber : Close gate

  • Slow Fiber : Open gate

  • Central Control is involved

Pain Threshold

Back of knee

Neck

Bend of Elbow

Shoulder Blade

Inside of Forearm

Back of Hand

Back of Knee

Most sensitive part of the body

Pain Matrix

Hypothalamus, limbic system, and the thalamus

• S1 & S2 in the somatosensory cortex, the insula, and the anterior cingulate and prefrontal cortices

Expectation

When surgical patients are told what to expect, they request less pain medication and leave the hospital earlier

Shifting Attention

Virtual reality technology has been used to keep patients’ attention on other stimuli than the pain-inducing stimulation

• Content of emotional distraction : Participants could keep their hands in cold water longer when pictures shown were positive

Pain in Social Situation Experiment by Eisenberger et al.

fMRI data showed increased activity in the anterior cingulate cortex and participants reported feeling ignored and distressed

Pain in Social Situations Experiment by Singer et al.

Romantically involved coupled participated

• Women’s brain activity was measured by fMRI

• Woman either received shocks or she watched while her partner received shocks

• Similar brain areas were activated in both conditions

Olfactory Sense

Smell stimuli

Odorant Molecule

Air carries molecule to the smell receptors

Volatile Substance

Water : High

Musk : Low

Olfactory Neurons

Rods, cilia, olfactory knob

True

T/F : Receptors only function 4-8 weeks

Basal Cells

New receptor cells are continuously produced by ____ ____ (supporting cells)

Cilia

____, hair-like structures are embedded in a watery mucosa.

Olfactory Binding Protein (OBP)

Mucosa contains _____ _____ _____.

OBP

Attach to odorant molecules, transported from the mucosa surface to olfactory receptors

• Then detach from the receptors by the continually moving stream of mucosa sweeping across the cilia

Olfactory Bulb

Received inputs from particular types of neurons into glomerulus

• Odor stimuli are mapped into spatial patterns in the glomeruli

Primary Smell Cortex

Piriform cortex in temporal lobe

Orbital Frontal Cortex

Secondary cortex

• Pattern coding

  • Specific neurons respond strongly to one and weakly to others

Perception of Smell

Adaptation, Anosmias, Threshold, Smell Identification

Adaptation

15 sec

• Self-Adaptation

• Gross-Adaptation

  • Depends on the similarity of the smells of the two stimuli

Self-Adaption

Increase the threshold for the same odor

Gross Adaptation

Increase the threshold for odor in general

Anosmias

Odor blindness

• 76 different cases reported

  • From skunk smell to vanilla smell

  • 1/3 population cannot smell 1.8 cineole which produces a camphorous odor

Threshold

11% of intensity change can be detected

• Depends on various odor

• Affected by color

• Discriminate better if the smell enters the right nostril

  • Olfactory pathways stay on the same side of the brain

  • Right hemisphere is more specialized for olfactory processing

Smell Identification

Humans can discriminate among 100,000 odors, but they cannot label them accurately

• Caused by inability to retrieve name from memory, not from a lack of sensitivity

Pheromones

Chemicals secreted by animals that transmit information to other animals

• Odors during sexual excitement

• Manufacturers use in colognes and perfumes

Alpha Androstenol

Effective sex-attractant pheromone for pigs and also found in humans’ apocrine (underarm) sweat

Women in Photograph

More sexually attractive

When the smell presents…

Increase the willingness of females to initiate social interactions with male but not with females

Body Odor

People can detect their own body odor

Male

More musky

Female

More sweet smell

True

T/F : Females are more sensitive

• Menstrual synchrony

Experiment by de Araujo et al.

People were exposed to a mixture of a sweat-like smell and a cheddar cheese flavoring

• fMRI scans showed activity in the orbitofrontal cortex to be associated with the pleasantness ratings

Bottom-Up & Top-Down

Many molecules create a single perception

• Odors occur concurrently but the perceptual system separates them from one another

• Past experience and expectations have an impact on odor perception

  • Thus, odor perception is both a bottom-up process and top-down process that organizes the information

Retronasal Route

Odor stimuli through nasal pharynx

True

T/F : Tastes are influenced by smell

Orbital Frontal Cortex

Receives inputs from vision, taste, olfaction cortex, and touch

IT

Vision

Primary Taste Cortex

Taste

Primary Olfaction Cortex

Olfaction

Primary Somatosensory Cortex

Touch

Gustatory Sense

4 primary tastes

Sweet

Organic molecules

• Made of carbon, hydrogen, and oxygen

Bitter

Nitrogen, caffeine, quinine & nicotine

Salty

NaCl

• Size and weight of the negatively charged ions determine how salty and substance tastes

Sour

Acid (Hydrocholoric, Acetic, Nitric, Sulphuric)

Hydrogen

Positively charged ion

Umami

Described as meaty, brothy or savory and associated with MSG

Papillae

Taste buds are in ______.

Types of Papillae

Fungiform, Foliate, Circumvillate, Filiform

Fungiform Papillae

Shaped like “little mushroom”

• Tip and the sides of the tongue

Foliate Papillae

Series of folds along the sides of the rear

Circumvilliate Papillae

Locate back

• Flattened hill

Filiform Papillae

No taste bud

• Shaped like rough, tapered arrowhead

  • Abrade food into smaller bits

Soft Palate

Some taste receptors are scattered over parts of the mouth, ____ ____ (back portion of the roof of the mouth).

False, 30

T/F : Taste buds have about up to 20 receptor cells.

10,000

There are _____ taste buds.

Chorda Tympani Nerve

From front and sides of tongue

Glossopharyngeal Nerve

From back of tongue

Vagus Nerve

From mouth and throat

Superficial Petronasal Nerve

From soft palate

Solitary Tract

Taste system pathways make connections in the nucleus of the ______ ______ in the spinal cord.